The Project Gutenberg EBook of Acetylene, The Principles Of Its Generation
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Title: Acetylene, The Principles Of Its Generation And Use
Author: F. H. Leeds
W. J. Atkinson Butterfield
Release Date: May, 2005 [EBook #8144]
This file was first posted on June 19, 2003
Last Updated: May 17, 2013
Language: English
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Charles Franks, and the Online Distributed Proofreading Team
ACETYLENE
THE PRINCIPLES OF ITS GENERATION AND USE
A PRACTICAL HANDBOOK ON THE PRODUCTION, PURIFICATION, AND SUBSEQUENT
TREATMENT OF ACETYLENE FOR THE DEVELOPMENT OF LIGHT, HEAT, AND POWER
Second Edition
REVISED AND ENLARGED
BY
F. H. LEEDS, F.I.C.
FOR SOME YEARS TECHNICAL EDITOR OF THE JOURNAL "ACETYLENE"
AND
W. J. ATKINSON BUTTERFIELD, M.A.
AUTHOR OF "THE CHEMISTRY OF GAS MANUFACTURE"
PREFATORY NOTE TO THE FIRST EDITION
In compiling this work on the uses and application of acetylene, the
special aim of the authors has been to explain the various physical and
chemical phenomena:
(1) Accompanying the generation of acetylene from calcium carbide and
water.
(2) Accompanying the combustion of the gas in luminous or incandescent
burners, and
(3) Its employment for any purpose--(a) neat, (b) compressed into
cylinders, (c) diluted, and (d) as an enriching material.
They have essayed a comparison between the value of acetylene and other
illuminants on the basis of "illuminating effect" instead of on the
misleading basis of pure "illuminating power," a distinction which they
hope and believe will do much to clear up the misconceptions existing on
the subject. Tables are included, for the first time (it is believed) in
English publications, of the proper sizes of mains and service-pipes for
delivering acetylene at different effective pressures, which, it is
hoped, will prove of use to those concerned in the installation of
acetylene lighting systems.
_June_ 1903
NOTE TO THE SECOND EDITION
The revision of this work for a new edition was already far advanced when
it was interrupted by the sudden death on April 30, 1908, of Mr. F. H.
Leeds. The revision was thereafter continued single-handed, with the help
of very full notes which Mr. Leeds had prepared, by the undersigned. It
had been agreed prior to Mr. Leeds' death that it would add to the
utility of the work if descriptions of a number of representative
acetylene generators were given in an Appendix, such as that which now
appears at the conclusion of this volume. Thanks are due to the numerous
firms and individuals who have assisted by supplying information for use
in this Appendix.
W. J. ATKINSON BUTTERFIELD
WESTMINSTER
_August 1909_
CONTENTS
CHAPTER I
INTRODUCTORY--THE COST AND ADVANTAGES OF ACETYLENE LIGHTING
Intrinsic advantages
Hygienic advantages
Acetylene and paraffin oil
Blackened ceilings
Cost of acetylene lighting
Cost of acetylene and coal-gas
Cost of acetylene and electric lighting
Cost of acetylene and paraffin oil
Cost of acetylene and air-gas
Cost of acetylene and candles
Tabular statement of costs (_to face_)
Illuminating power and effect
CHAPTER II
THE PHYSICS AND CHEMISTRY OF THE REACTION BETWEEN CARBIDE AND WATER
Nature of calcium carbide
Storage of calcium carbide
Fire risks of acetylene lighting
Purchase of carbide
Quality and sizes of carbide
Treated and scented carbide
Reaction between carbide and water
chemical nature
heat evolved
difference between heat and temperature
amount of heat evolved
effect of heat on process of generation
Reaction:
effects of heat
effect of heat on the chemical reaction
effects of heat on the acetylene
effects of heat on the carbide
Colour of spent carbide
Maximum attainable temperatures
Soft solder in generators
Reactions at low temperatures
Reactions at high temperatures
Pressure in generators
CHAPTER III
THE GENERAL PRINCIPLES OF ACETYLENE GENERATION ACETYLENE GENERATING
APPARATUS
Automatic and non-automatic generators
Control of the chemical reaction
Non-automatic carbide-to-water generators
Non-automatic water-to-carbide generators
Automatic devices
Displacement gasholders
Action of water-to-carbide generators
Action of carbide-to-water generators
Use of oil in generator
Rising gasholder
Deterioration of acetylene on storage
Freezing and its avoidance
Corrosion in apparatus
Isolation of holder from generator
Water-seals
Vent pipes and safety valve
Frothing in generator
Dry process of generation
Artificial lighting of generator sheds
CHAPTER IV
THE SELECTION OF AN ACETYLENE GENERATOR
Points to be observed
Recommendations of Home Office Committee
British and Foreign regulations for the construction and installation of
acetylene generating plant
CHAPTER V
THE TREATMENT OF ACETYLENE AFTER GENERATION
Impurities in calcium carbide
Impurities of acetylene
Removal of moisture
Generator impurities in acetylene
Filters
Carbide impurities in acetylene
Washers
Reasons for purification
Necessary extent of purification
Quantity of impurities in acetylene
Purifying materials
Bleaching powder
Heratol, frankoline, acagine, and puratylene
Efficiency of purifying material
Minor reagent
Method of a gas purifier
Methods of determining exhaustion of purifying material
Regulations for purification
Drying
Position of purifier
Filtration
General arrangement of plans
Generator residues
Disposal of residue
CHAPTER VI
THE CHEMICAL AND PHYSICAL PROPERTIES OF ACETYLENE
Physical properties
Leakage
Heat of combustion
Explosive limits
Range of explosibility
Solubility in liquids
Toxicity
Endothermic nature
Polymerisation
Heats of formation and combustion
Colour of flame
Radiant efficiency
Chemical properties
Reactions with copper
CHAPTER VII
MAINS AND SERVICE-PIPES--SUBSIDIARY APPARATUS
Meters
Governors
Gasholder pressure
Pressure-gauges
Dimensions of mains and pipes
Velocity of flow in pipes
Service-pipes and mains
Leakage
Pipes and fittings
Laying mains
Expelling air from pipes
Tables of pipes and mains
CHAPTER VIII
COMBUSTION OF ACETYLENE IN LUMINOUS BURNERS--THEIR DISPOSITION
Nature of luminous flames
Illuminating power
Early burners
Injector and twin-flame burners
Illuminating power of self-luminous burners
Glassware for burners
CHAPTER IX
INCANDESCENT BURNERS--HEATING APPARATUS--MOTORS--AUTOGENOUS SOLDERING
Merits of incandescent lighting
Conditions for incandescent lighting
Illuminating power of incandescent burners
Durability of mantles
Typical incandescent burners
Acetylene for heating and cooking
Acetylene motors
Blowpipes
Autogenous soldering and welding
CHAPTER X
CARBURETTED ACETYLENE
Carburetted acetylene
Illuminating power of carburetted acetylene
Carburetted acetylene for "power"
CHAPTER XI
COMPRESSED AND DISSOLVED ACETYLENE--MIXTURES WITH OTHER GASES
Compression
Dissolved acetylene
Solution in acetone
Liquefied acetylene
Dilution with carbon dioxide
Dilution with air
Mixed carbides
Dilution with, methane and hydrogen
Self-inflammable acetylene
Enrichment with acetylene
Partial pressure
Acetylene-oil-gas
CHAPTER XII
SUNDRY USES
Destruction of noxious moths
Destruction of phylloxera and mildew
Manufacture of lampblack
Production of tetrachlorethane
Utilisation of residues
Sundry uses for the gas
CHAPTER XIII
PORTABLE ACETYLENE LAMPS AND PLANT
Table and vehicular lamps
Flare lamps
Cartridges of carbide
Cycle-lamp burners
Railway lighting
CHAPTER XIV
VALUATION AND ANALYSIS OF CARBIDE
Regulations of British Acetylene Association
Regulations o£ German Acetylene Association
Regulations of Austrian Acetylene Association
Sampling carbide
Yield of gas from small carbide
Correction of volumes for temperature and pressure
Estimation of impurities
Tabular numbers
APPENDIX
DESCRIPTIONS OP GENERATORS
America: Canada
America: United States
Austria-Hungary
Belgium
France
Germany
Great Britain and Ireland
INDEX
INDEX TO APPENDIX
ACETYLENE
CHAPTER I
INTRODUCTORY--THE COST AND ADVANTAGES OF ACETYLENE LIGHTING
Acetylene is a gas [Footnote: For this reason the expression, "acetylene
gas," which is frequently met with, would be objectionable on the ground
of tautology, even if it were not grammatically and technically
incorrect. "Acetylene-gas" is perhaps somewhat more permissible, but it
is equally redundant and unnecessary.] of which the most important
application at the present time is for illuminating purposes, for which
its properties render it specially well adapted. No other gas which can
be produced on a commercial scale is capable of giving, volume for
volume, so great a yield of light as acetylene. Hence, apart from the
advantages accruing to it from its mode of production and the nature of
the raw material from which it is produced, it possesses an inherent
advantage over other illuminating gases in the smaller storage
accommodation and smaller mains and service-pipes requisite for the
maintenance of a given supply of artificial light. For instance, if a
gasholder is required to contain sufficient gas for the lighting of an
establishment or district for twenty-four hours, its capacity need not be
nearly so great if acetylene is employed as if oil-gas, coal-gas, or
other illuminating gas is used. Consequently, for an acetylene supply the
gasholder can be erected on a smaller area and for considerably less
outlay than for other gas supplies. In this respect acetylene has an
unquestionable economical advantage as a competitor with other varieties
of illuminating gas for supplies which have generally been regarded as
lying peculiarly within their preserves. The extent of this advantage
will be referred to later.
The advantages that accrue to acetylene from its mode of production, and
the nature of the raw material from which it is obtained, are in reality
of more importance. Acetylene is readily and quickly produced from a raw
material--calcium carbide--which, relatively to the yield of light of the
gaseous product, is less bulky than the raw materials of other gases. In
comparison also with oils and candles, calcium carbide is capable of
yielding, through the acetylene obtainable from it, more light per unit
of space occupied by it. This higher light-yielding capacity of calcium
carbide, ready to be developed through acetylene, gives the latter gas a
great advantage over all other illuminants in respect of compactness for
transport or storage. Hence, where facilities for transport or storage
are bad or costly, acetylene may be the most convenient or cheapest
illuminant, notwithstanding its relatively high cost in many other cases.
For example, in a district to which coal and oil must be brought great
distances, the freight on them may be so heavy that--regarding the
question as simply one of obtaining light in the cheapest manner--it may
be more economical to bring calcium carbide an equal or even greater
distance and generate acetylene from it on the spot, than to use oil or
make coal-gas for lighting purposes, notwithstanding that acetylene may
not be able to compete on equal terms with oil--or coal-gas at the place
from which the carbide is brought. Likewise where storage accommodation
is limited, as in vehicles or in ships or lighthouses, calcium carbide
may be preferable to oil or other illuminants as a source of light.
Disregarding for the moment intrinsic advantages which the light
obtainable from acetylene has over other lights, there are many cases
where, owing to saving in cost of carriage, acetylene is the most
economical illuminant; and many other cases where, owing to limited space
for storage, acetylene far surpasses other illuminants in convenience,
and is practically indispensable.
The light of the acetylene flame has, however, some intrinsic advantages
over the light of other artificial illuminants. In the first place, the
light more closely resembles sunlight in composition or "colour." It is
more nearly a pure "white" light than is any other flame or incandescent
body in general use for illuminating purposes. The nature or composition
of the light of the acetylene flame will be dealt with more exhaustively
later, and compared with that afforded by other illuminants; but,
speaking generally, it may be said that the self-luminous acetylene light
is superior in tint, to all other artificial lights, for which reason it
is invaluable for colour-judging and shade-matching. In the second
place, when the gas issues from a suitable self-luminous burner under
proper pressure, the acetylene flame is perfectly steady; and in this
respect it in preferable to most types of electric light, to all self-
luminous coal-gas flames and candles, and to many varieties of oil-lamp.
In steadiness and freedom from flicker it is fully equal to incandescent
coal-gas light, but it in distinctly superior to the latter by virtue of
its complete freedom from noise. The incandescent acetylene flame emits a
slight roaring, but usually not more than that coming from an
atmospheric coal-gas burner. With the exception of the electric arc,
self-luminous acetylene yields a flame of unsurpassed intensity, and yet
its light is agreeably soft. In the third place, where electricity is
absent, a brilliancy of illumination which can readily be obtained from
self-luminous acetylene can otherwise only be procured by the employment
of the incandescent system applied either to coal-gas or to oil; and
there are numerous situations, such as factories, workshops, and the
like, where the vibration of the machinery or the prevalence of dust
renders the use of mantles troublesome if not impossible. Anticipating
what will be said later, in cases like these, the cost of lighting by
self-luminous acetylene may fairly be compared with self-luminous coal-
gas or oil only; although in other positions the economy of the Welsbach
mantle must be borne in mind.
Acetylene lighting presents also certain important hygienic advantages
over other forms of flame lighting, in that it exhausts, vitiates, and
heats the air of a room to a less degree, for a given yield of light,
than do either coal-gas, oils, or candles. This point in favour of
acetylene is referred to here only in general terms; the evidence on
which the foregoing statement is based will be recorded in a tabular
comparison of the cost and qualities of different illuminants. Exhaustion
of the air means, in this connexion, depletion of the oxygen normally
present in it. One volume of acetylene requires 2-1/2 volumes of oxygen
for its complete combustion, and since 21 volumes of oxygen are
associated in atmospheric air with 79 volumes of inert gases--chiefly
nitrogen--which do not actively participate in combustion, it follows
that about 11.90 volumes of air are wholly exhausted, or deprived of
oxygen, in the course of the combustion of one volume of acetylene. If
the light which may be developed by the acetylene is brought into
consideration, it will be found that, relatively to other illuminants,
acetylene causes less exhaustion of the air than any other illuminating
agent except electricity. For instance, coal-gas exhausts only about 6-
1/2 times its volume of air when it is burnt; but since, volume for
volume, acetylene ordinarily yields from three to fifteen times as much
light as coal-gas, it follows that the same illuminative value is
obtainable from acetylene by considerably less exhaustion of the air than
from coal-gas. The exact ratio depends on the degree of efficiency of the
burners, or of the methods by which light is obtained from the gases, as
will be realised by reference to the table which follows. Broadly
speaking, however, no illuminant which evolves light by combustion
(oxidation), and which therefore requires a supply of oxygen or air for
its maintenance, affords light with so little exhaustion of the air as
acetylene. Hence in confined, ill-ventilated, or crowded rooms, the air
will suffer less exhaustion, and accordingly be better for breathing, if
acetylene is chosen rather than any other illuminant, except electricity.
Next, in regard to vitiation of the air, by which is meant the alteration
in its composition resulting from the admixture of products of combustion
with it. Electric lighting is as superior to other modes of lighting in
respect of direct vitiation as of exhaustion of the air, because it does
not depend on combustion. Putting it aside, however, light is obtainable
by means of acetylene with less attendant vitiation of the air than by
means of any other gas or of oil or candles. The principal vitiating
factor in all cases is the carbonic acid produced by the combustion. Now
one volume of acetylene on combustion yields two volumes of carbonic
acid, whereas one volume of coal-gas yields about 0.6 volume of carbonic
acid. But even assuming that the incandescent system of lighting is
applied in the case of coal-gas and not of acetylene, the ratio of the
consumption of the two gases for the development of a given illuminative
effect will be such that no more carbonic acid will be produced by the
acetylene; and if the incandescent system is applied either in both cases
or in neither, the ratio will be greatly in favour of acetylene. The
other factors which determine the vitiation of the air of a room in which
the gas is burning are likewise under ordinary conditions more in favour
of acetylene. They are not, however, constant, since the so-called
"impurities," which on combustion cause vitiation of the air, vary
greatly in amount according to the extent to which the gases have been
purified. London coal-gas, which was formerly purified to the highest
degree practically attainable, used to contain on the average only 10 to
12 grains of sulphur per 100 cubic feet, and virtually no other impurity.
But now coal-gas, in London and most provincial towns, contains 40 to 50
grains of sulphur per 100 cubic foot. At least 5 grains of ammonia per
100 cubic foot in also present in coal-gas in some towns. Crude acetylene
also contains sulphur and ammonia, that coming from good quality calcium
carbide at the present day including about 31 grains of the former and
25 grains of the latter per 100 cubic feet. But crude acetylene is also
accompanied by a third impurity, viz., phosphoretted hydrogen or
phosphine, which in unknown in coal-gas, and which is considerably more
objectionable than either ammonia or sulphur. The formation, behaviour,
and removal of those various impurities will be discussed in Chapter V.;
but here it may be said that there is no reason why, if calcium carbide
of a fair degree of purity has been used, and if the gas has been
generated from it in a properly designed and smoothly working apparatus--
this being quite as important as, or even more important than, the purity
of the original carbide--the gas should not be freed from phosphorus,
sulphur, and ammonia to the utmost necessary or desirable extent, by
processes which are neither complicated nor expensive. And if this is
done, as it always should be whenever the acetylene is required for
domestic lighting, the vitiation of the air of a room due to the
"impurities" in the gas will become much less in the case of acetylene
than in that of even well-purified coal-gas; taking equal illuminating
effect as the basis for comparison.
Acetylene is similarly superior, speaking generally, to petroleum in
respect of impurities, though the sulphur present in petroleum oils, such
as are sold in this country for household use, though very variable, is
often quite small in amount, and seldom is responsible for serious
vitiation of the atmosphere.
Regarding somewhat more closely the relative convenience and safety of
acetylene and paraffin for the illumination of country residences, it may
be remarked that an extraordinarily great amount of care must be bestowed
upon each separate lamp if the whole house is to be kept free from an
odour which is very offensive to the nostrils; and the time occupied in
this process, which of itself is a disagreeable one, reaches several
hours every day. Habit has taught the country dweller to accept as
inevitable this waste of time, and largely to ignore the odour of
petroleum in his abode; but the use of acetylene entirely does away with
the daily cleaning of lamps, and, if the pipe-fitting work has been done
properly, yields light absolutely unaccompanied by smell. Again, unless
most carefully managed, the lamp-room of a large house, with its store of
combustible oil, and its collection of greasy rags, must unavoidably
prove a sensible addition to the risk of fire. The analogue of the lamp-
room when acetylene is employed is the generator-house, and this is a
separate building at some distance from the residence proper. There need
be no appreciable odour in the generator-house, except during the times
of charging the apparatus; but if there is, it passes into the open air
instead of percolating into the occupied apartments.
The amount of heat developed by the combustion of acetylene also is less
for a given yield of light than that developed by most other illuminants.
The gas, indeed, is a powerful heating gas, but owing to the amount
consumed being so small in proportion to the light developed, the heat
arising from acetylene lighting in a room is less than that from most
other illuminating agents, if the latter are employed to the extent
required to afford equally good illumination. The ratio of the heat
developed in acetylene lighting to that developed in, _e.g._,
lighting by ordinary coal-gas, varies considerably according to the
degree of efficiency of the burners, or, in other words, of the methods
by which light is obtained from the gases. Volume for volume, acetylene
yields on combustion about three and a half times as much heat as coal-
gas, yet, owing to its superior efficiency as an illuminant, any required
light may be obtained through it with no greater evolution of heat than
the best practicable (incandescent) burners for coal-gas produce. The
heat evolved by acetylene burners adequate to yield a certain light is
very much less than that evolved by ordinary flat-flame coal-gas burners
or by oil-lamps giving the same light, and is not more than about three
times as much as that from ordinary electric lamps used in numbers
sufficient to give the same light. More exact figures for the ratio
between the heat developed in acetylene lighting and that in other modes
of lighting are given in the table already referred to.
In connexion with the smaller amount of heat developed per unit of light
when acetylene is the illuminant, the frequently exaggerated claim that
acetylene does not blacken ceilings at all may be studied. Except it be a
carelessly manipulated petroleum-lamp, no form of artificial illuminant
employed nowadays ever emits black smoke, soot, or carbon, in spite of
the fact that all luminous flames commercially capable of utilisation do
contain free carbon in the elemental state. The black mark on a ceiling
over a source of light is caused by a rising current of hot air and
combustion products set up by the heat accompanying the light, which
current of hot gas carries with it the dust and dirt always present in
the atmosphere of an inhabited room. As this current of air and burnt gas
travels in a fairly concentrated vertical stream, and as the ceiling is
comparatively cool and exhibits a rough surface, that dust and dirt are
deposited on the ceiling above the flame, but the stain is seldom or
never composed of soot from the illuminant itself. Proof of this
statement may be found in the circumstance that a black mark is
eventually produced over an electric glow-lamp and above a pipe
delivering hot water. Clearly, therefore, the depth and extent of the
mark will depend on the volume and temperature of the hot gaseous
current; and since per unit of light acetylene emits a far smaller
quantity of combustion products and a far smaller amount of heat than any
other flame illuminant except incandescent coal-gas, the inevitable black
mark over its flame takes very much longer to appear. Quite roughly
speaking, as may be deduced from what has already been said on this
subject, the luminous flame of acetylene "blackens" a ceiling at about
the same rate as a coal-gas burner of the best Welsbach type.
There is one respect in which acetylene and other flame illuminants are
superior to electric lighting, viz., that they sterilise a larger volume
of air. All the air which is needed to support combustion, as well as the
excess of air which actually passes through the burner tube and flame in
incandescent burners, is obviously sterilised; but so also is the much
larger volume of air which, by virtue of the up-current due to the heat
of the flame, is brought into anything like close proximity with the
light. The electric glow-lamp, and the most popular and economical modern
enclosed electric arc-lamp, sterilise only the much smaller volume of air
which is brought into direct contact with their glass bulbs. Moreover,
when large numbers of persons are congregated in insufficiently
ventilated buildings--and many public rooms are insufficiently
ventilated--the air becomes nauseous to inspire and positively
detrimental to the health of delicate people, by reason of the human
effluvia which arise from soiled raiment and uncleansed or unhealthy
bodies, long before the proportion of carbonic acid by itself is high
enough to be objectionable. Thus a certain proportion of carbonic acid
coming from human lungs and skin is more harmful than the same proportion
of carbonic acid derived from the combustion of gas or oil. Hence
acetylene and flame illuminants generally have the valuable hygienic
advantages over electric lighting, not only of killing a far larger
number of the micro-organisms that may be present in the air, but, by
virtue of their naked flames, of burning up and destroying a considerable
quantity of the aforesaid odoriferous matter, thus relieving the nose and
materially assisting in the prevention of that lassitude and anæmia
occasionally follow the constant inspiration of air rendered foul by
human exhalations.
The more important advantages of acetylene as an illuminant have now been
indicated, and it remains to discuss the cost of acetylene lighting in
comparison with other modes of procuring artificial light. At the outset
it may be stated that a very much greater reduction in the price of
calcium carbide--from which acetylene is produced--than is likely to
ensue under the present methods and conditions of manufacture will be
required to make acetylene lighting as cheap as ordinary gas lighting in
towns in this country, provided incandescent burners are used for the
gas. On the score of cheapness (and of convenience, unless the acetylene
were delivered to the premises from some central generating station)
acetylene cannot compete as an illuminant with coal-gas where the latter
costs, say, not more than 5s. per 1000 cubic feet, if only
reasonable attention is given to the gas-burners, and at least a quarter
of them are on the incandescent system. If, on the other hand, coal-gas
is misused and wasted through the employment only of interior or worn-out
flat-flame burners, while the best types of burner are used for
acetylene, the latter gas may prove as cheap for lighting as coal-gas at,
say, 2s. 6d. per 1000 cubic feet (and be far better hygienically);
whereas, contrariwise, if coal-gas is used only with good and properly
maintained incandescent burners, it may cost over 10s. per 1000 cubic
feet, and be cheaper than acetylene burned in good burners (and as good
from the hygienic standpoint). More precise figures on the relative costs
of coal-gas lighting and acetylene lighting are given in the tabular
statement at the close of this chapter.
With regard to electric lighting it is somewhat difficult to lay down a
fair basis of comparison, owing to the wide variations in the cost of
current, and in the efficiency of lamps, and to the undoubted hygienic
and aesthetic claims of electric lighting to precedence. But in towns in
this country where there is a public electricity supply, electric
lighting will be used rather than acetylene for the same reasons that it
is preferred to coal-gas. Cost is only a secondary consideration in such
cases, and where coal-gas is reasonably cheap, and nevertheless gives
place to electric lighting, acetylene clearly cannot hope to supplant the
latter. [Footnote: Where, however, as is frequently the case with small
public electricity-supply works, the voltage of the supply varies
greatly, the fluctuations in the light of the lamps, and the frequent
destruction of fuses and lamps, are such manifest inconveniences that
acetylene is in fact now being generally preferred to electric lighting
in such circumstances.] But where current cannot be had from an
electricity-supply undertaking, and it is a question, in the event of
electric lighting being adopted, of generating current by driving a
dynamo, either by means of a gas-engine supplied from public gas-mains,
by means of a special boiler installation, or by means of an oil-engine
or of a power gas-plant and gas-engine, the claims of acetylene to
preference are very strong. An important factor in the estimation of the
relative advantages of electricity and acetylene in such cases is the
cost of labour in looking after the generating plant. Where a gas-engine
supplied from public gas-mains is used for driving the dynamo, electric
lighting can be had at a relatively small expenditure for attendance on
the generating plant. But the cost of the gas consumed will be high, and
actually light could be obtained directly from the gas by means of
incandescent mantles at far loss cost than by consuming the gas in a
motor for the indirect production of light by means of electric current.
Therefore electric lighting, if adopted under these conditions, must be
preferred to gas lighting from considerations which are deemed to
outweigh those of a much higher cost, and acetylene does not present so
great advantages over coal-gas as to affect the choice of electric
lighting. But in the cases where there is no public gas-supply, and
current must be generated from coal or coke or oil consumed on the spot,
the cost of the skilled labour required to look after either a boiler,
steam-engine and dynamo, or a power gas-plant and gas-engine or oil-
engine and dynamo, will be so heavy that unless the capacity of the
installation is very great, acetylene will almost certainly prove a
cheaper and more convenient method of obtaining light. The attention
required by an acetylene installation, such as a country house of upwards
of thirty rooms would want, is limited to one or two hours' labour per
diem at any convenient time during daylight. Moreover, the attendant need
not be highly paid, as he will not have required an engineman's training,
as will the attendant on an electric lighting plant. The latter, too,
must be present throughout the hours when light is wanted unless a heavy
expenditure has been incurred on accumulators. Furthermore, the capital
outlay on generating plant will be very much less for acetylene than for
electric lighting. General considerations such as these lead to the
conclusion that in almost all country districts in this country a house
or institution could be lighted more cheaply by means of acetylene than
by electricity. In the tabular statement of comparative costs of
different modes of lighting, electric lighting has been included only on
the basis of a fixed cost per unit, as owing to the very varied cost of
generating current by small installations in different parts of the
country it would be futile to attempt to give the cost of electric
lighting on any other basis, such as the prime cost of coal or coke in a
particular district. Where current is supplied by a public electricity-
supply undertaking, the cost per unit is known, and the comparative costs
of electric light and acetylene can be arrived at with tolerable
precision. It has not been thought necessary to include in the tabular
statement electric arc-lamps, as they are only suitable for the lighting
of large spaces, where the steadiness and uniformity of the illumination
are of secondary importance. Under such conditions, it may be stated
parenthetically, the electric arc-light is much less costly than
acetylene lighting would be, but it is now in many places being
superseded by high-pressure gas or oil incandescent lights, which are
steady and generally more economical than the arc light.
The illuminant which acetylene is best fitted to supersede on the score
of convenience, cleanliness, and hygienic advantages is oil. By oil is
meant, in this connection, the ordinary burning petroleum, kerosene, or
paraffin oil, obtained by distilling and refining various natural oils
and shales, found in many countries, of which the United States
(principally Pennsylvania), Russia (the Caucasus chiefly), and Scotland
are practically the only ones which supply considerable quantities for
use in Great Britain. Attempts are often made to claim superiority for
particular grades of these oils, but it may be at once stated that so for
as actual yield of light is concerned, the same weight of any of the
commercial oils will give practically the same result. Hence in the
comparative statement of the cost of different methods of lighting, oil
will be taken at the cheapest rate at which it could ordinarily be
obtained, including delivery charges, at a country house, when bought by
the barrel. This rate at the present time is about ninepence per gallon.
A higher price may be paid for grades of mineral oil reputed to be safer
or to give a "brighter" or "clearer" light; but as the quantity of light
depends mainly upon the care and attention bestowed on the burner and
glass fittings of the lamp, and partly upon the employment of a suitable
wick, while the safety of each lamp depends at least as much upon the
design of that lamp, and the accuracy with which the wick fits the burner
tube, as upon the temperature at which the oil "flashes," the extra
expense involved in burning fancy-priced oils will not be considered
here.
The efficiency (_i.e._, the light yielded per pint or other unit
volume consumed) of oil-lamps varies greatly, and, speaking broadly,
increases with the power of the lamp. But as large or high-power lamps
are not needed throughout a house, it is fairer to assume that the light
obtainable from oil in ordinary household use is the mean of that
afforded by large and that afforded by small lamps. A large oil-lamp as
commonly used in country houses will give a light of about 20 candle-
power, while a convenient small lamp will give a light of not more than
about 5 candle-power. The large lamp will burn about 55 hours for every
gallon of oil consumed, or give an illuminating duty of about 1100
candle-hours (_i.e._, the product of candle-power by burning-hours)
per gallon. The small lamp, on the other hand, will burn about 140 hours
for every gallon of oil consumed, or give an illuminating duty of about
700 candle-hours per gallon. Actually large lamps would in most country
houses be used only in the entrance hall, living-rooms, and kitchen,
while passages and minor rooms on the lower floors would be lighted by
small lamps. Hence, making due allowance for the lower rate of
consumption of the small lamps, it will be seen that, given equal numbers
of large and small lamps in use, the mean illuminating duty of a gallon
of oil as burnt in country houses will be 987, or, in round figures, 990
candle-hours. Usually candles are used in the bedrooms of country houses
where the lower floors are lighted by means of petroleum lamps; but when
acetylene is installed in such a house it will frequently be adopted in
the principal bed- and dressing-rooms as well as in the living-rooms, as,
unless candles are employed very lavishly, they are really totally
inadequate to meet the reasonable demands for light of, _e.g._, a
lady dressing for dinner. Where acetylene displaces candles as well as
lamps in a country house, it is necessary, in comparing the cost of the
new illuminant with that of the candles and oil, to bear in mind the
superior degree of illumination which is secured in all rooms, at least
where candles were formerly used.
In regard to exhaustion and vitiation of the air, and to heat evolved,
self-luminous petroleum lamps stand on much the same footing as coal-gas
when the latter is burned in flat-flame burners, if the comparison is
based on a given yield of light. A large lamp, owing to its higher
illuminating efficiency, is better in this respect than a small one--
light for light, it is more hygienic than ordinary flat-flame coal-gas
burners, while a small lamp is less hygienic. It will therefore be
understood at once, from what has already been said about the superiority
on hygienic grounds of acetylene to flat-flame coal-gas lighting, that
acetylene is in this respect far superior to petroleum lamps. The degree
of its superiority is indicated more precisely by the figures quoted in
the tabular statement which concludes this chapter.
Before giving the tabular statement, however, it is necessary to say a
few words in regard to one method of lighting which, may possibly develop
into a more serious competitor with acetylene for the lighting of the
better class of country house than any of the illuminating agents and
modes of lighting so far referred to. The method in question is lighting
by so-called air-gas used for raising mantles to incandescence in
upturned or inverted burners of the Welsbach-Kern type. "Air-gas" is
ordinary atmospheric air, more or less completely saturated with the
vapour of some highly volatile hydrocarbon. The hydrocarbons practically
applied have so far been only "petroleum spirit" or "carburine," and
"benzol." "Petroleum spirit" or "carburine" consists of the more highly
volatile portion of petroleum, which is removed by distillation before
the kerosene or burning oil is recovered from the crude oil. Several
grades of this highly volatile petroleum distillate are distinguished in
commerce; they differ in the temperature at which they begin to distil
and the range of temperature covered by their distillation, and, speaking
more generally, in their degree of volatility, uniformity, and density.
If the petroleum distillate is sufficiently volatile and fairly uniform
in character, good air-gas may be produced merely by allowing air to pass
over an extended surface of the liquid. The vapour of the petroleum
spirit is of greater density than air, and hence, if the course of the
air-gas is downward from the apparatus at which it is produced, the flow
of air into the apparatus and over the surface of the spirit will be
automatically maintained by the "pull" of the descending air-gas when
once the flow has been started until the outlet for the air-gas is
stopped or the spirit in the apparatus is exhausted. Hence, if the
apparatus for saturating air with the vapour of the light petroleum is
placed well above all the points at which the air-gas is to be burnt--
_e.g._, on the roof of the house--the production of the air-gas may
by simple devices become automatic, and the only attention the apparatus
will require will be the replenishing of its reservoir from time to time
with light petroleum. But a number of precautions are required to make
this simple process operate without interruption or difficulty. For
instance, the evaporation of the spirit must not be so rapid relatively
to its total bulk as to lower its temperature, and thereby that of the
overflowing air, too much; the reservoir must be protected from extreme
cold and extreme heat; and the risk of fire from the presence of a highly
volatile and highly inflammable liquid on or near the roof of the house
must be met. This risk is one to which fire insurance companies take
exception.
More commonly, however, air-gas is made non-automatically, or more or
less automatically by the employment of some mechanical means. The light
petroleum, benzol, or other suitable volatile hydrocarbon is volatilised,
where necessary, by the application of gentle heat, while air is driven
over or through it by means of a small motor, which in some cases is a
hot-air engine operated by heat supplied by a flame of the air-gas
produced. These air-gas producers, or at least the reservoir of volatile
hydrocarbon, may be placed in an outbuilding, so that the risk of fire in
the house itself is minimised. They require, however, as much attention
as an acetylene generator, usually more. It is difficult to give reliable
data as to the cost of air-gas, inclusive of the expenses of production.
It varies considerably with the description of hydrocarbon employed, and
its market price. Air-gas is only slightly inferior hygienically to
acetylene, and the colour of its light is that of the incandescent light
as produced by coal-gas or acetylene. Air-gas of a certain grade may be
used for lighting by flat-flame burners, but it has been available thus
for very many years, and has failed to achieve even moderate success. But
the advent of the incandescent burner has completely changed its position
relatively to most other illuminants, and under certain conditions it
seems likely to be the most formidable competitor with acetylene. Since
air-gas, and the numerous chemically identical products offered under
different proprietary names, is simply atmospheric air more or less
loaded with the vapour of a volatile hydrocarbon which is normally
liquid, it possesses no definite chemical constitution, but varies in
composition according to the design of the generating plant, the
atmospheric temperature at the time of preparation, the original degree
of volatility of the hydrocarbon, the remaining degree of volatility
after the more volatile portions have been vaporised, and the speed at
which the air is passed through the carburettor. The illuminating power
and the calorific value of air-gas, unless the manufacture is very
precisely controlled, are apt to be variable, and the amount of light,
emitted, either in self-luminous or in incandescent burners, is somewhat
indeterminate. The generating plant must be so constructed that the air
cannot at any time be mixed with as much hydrocarbon vapour as
constitutes an explosive mixture with it, otherwise the pipes and
apparatus will contain a gas which will forthwith explode if it is
ignited, _i.e._, if an attempt is made to consume it otherwise than
in burners with specially small orifices. The safely permissible mixtures
are (1) air with less hydrocarbon vapour than constitutes an explosive
mixture, and (2) air with more hydrocarbon vapour than constitutes an
explosive mixture. The first of these two mixtures is available for
illuminating purposes only with incandescent mantles, and to ensure a
reasonable margin of safety the mixing apparatus must be so devised that
the proportion of hydrocarbon vapour in the air-gas can never exceed 2
per cent. From Chapter VI. it will be evident that a little more than 2
per cent. of benzene, pentane or benzoline vapour in air forms an
explosive mixture. What is the lowest proportion of such vapours in
admixture with air which will serve on combustion to maintain a mantle in
a state of incandescence, or even to afford a flame at all, does not
appear to have been precisely determined, but it cannot be much below 1-
1/2 per cent. Hence the apparatus for producing air-gas of this first
class must be provided with controlling or governing devices of such
nicety that the proportion of hydrocarbon vapour in the air-gas is
maintained between about 1-1/2 and 2 per cent. It is fair to say that in
normal working conditions a number of devices appear to fulfil this
requirement satisfactorily. The second of the two mixtures referred to
above, viz., air with more hydrocarbon vapour than constitutes an
explosive mixture, is primarily suitable for combustion in self-luminous
burners, but may also be consumed in properly designed incandescent
burners. But the generating apparatus for such air-gas must be equipped
with some governing or controlling device which will ensure the
proportion of hydrocarbon vapour in the mixture never falling below, say,
7 per cent. On the other hand, if saturation of the air with the vapour
is practically attained, should the temperature of the gas fall before it
arrives at the point of combustion, part of the spirit will condense out,
and the product will thus lose part of its illuminating or calorific
intensity, besides partially filling the pipes with liquid products of
condensation. The loss of intensity in the gas during cold weather may or
may not be inconvenient according to circumstances; but the removal of
part of the combustible material brings the residual air-gas nearer to
its limit of explosibility--for it is simply a mixture of combustible
vapour with air, which, normally, is not explosive because the proportion
of spirit is too high--and thus, when led into an atmospheric burner, the
extra amount of air introduced at the injector jets may cause the mixture
to be an explosive mixture of air and spirit, so that it will take fire
within the burner tube instead of burning quietly at the proper orifice.
This matter will be made clearer on studying what is said about explosive
limits in Chapter VI., and what is stated about incandescent acetylene
(carburetted or not) in Chapters IX. and X. Clearly, however, high-grade
air-gas is only suitable for preparation at the immediate spot where it
is to be consumed; it cannot be supplied to a complete district unless it
is intentionally made of such lower intensity that the proportion of
spirit is too small ever to allow of partial deposition in the mains
during the winter.
It is perhaps necessary to refer to the more extended use of candles for
lighting in some few houses in which lamps are disliked on aesthetic, or,
in some cases, ostensibly on hygienic grounds. Candle lighting, speaking
broadly, is either very inadequate so far as ordinary living-rooms are
concerned, or, if adequate, is very costly. Tests specially carried out
by one of the authors to determine some of the figures required in the
ensuing table show that ordinary paraffin or "wax" candles usually emit
about 20 per cent. more light than that given by the standard spermaceti
candle, whose luminosity is the unit by which the intensity of other
lights is reckoned in Great Britain; and also that the light so emitted
by domestic candles is practically unaffected by the sizes--"sixes,"
"eights," or "twelves"--burnt. In the sizes examined the light evolved
has varied between 1.145 and 1.298 "candles," perhaps tending to increase
slightly with the diameter of the candle tested. Hence, to obtain
illumination in a room equal on the average to that afforded by 100
standard candles, or some other light or lights aggregating 100 candle-
power, would require the use of only 80 to 85 ordinary paraffin,
ozokerite, or wax candles. But actually the essential objects in a room
could be equally well illuminated by, say, 30 candles well distributed,
as by two or three incandescent gas-burners, or four or five large oil-
lamps. Lights of high intensity, such as powerful gas-burners or oil-
lamps, must give a higher degree of illumination in their immediate
vicinity than is really necessary, if they are to illuminate adequately
the more distant objects. The dissemination and diffusion of their light
can be greatly aided by suitable colouring of ceilings, walls and
drapings; but unless the illumination by means of lights of relatively
high intensity is made almost wholly indirect, candles or other lights of
low intensity, such as small electric glow-lamps, can, by proper
distribution, be made to give more uniform or more suitably apportioned
illumination. In this respect candles have an economical and, in some
measure, a material advantage over acetylene also. (But when the method
of lighting is by flames--candle or other--the multiplication of the
number of units which is involved when they are of low intensity,
seriously increases the risk of fire through accidental contact of
inflammable material with any one of the flames. This risk is much
greater with naked flames, such as candles, than with, say, inverted
incandescent gas flames, which are to all intents and purposes fully
protected by a closed glass globe.) Hence, in the tabular statement which
follows of the comparative cost, &c., of different illuminants, it will
be assumed that 30 good candles would in practice be equally efficient in
regard to the illumination of a room as large oil-lamps, acetylene
flames, or incandescent gas-burners aggregating 100 candle-power.
For the same reason it will be assumed that electric glow-lamps of low
intensity (nominally of 8 candle-power or less), aggregating 70-80
candle-power, will practically serve, if suitably distributed, equally as
well as 100 candle-power obtained from more powerful sources of light.
Electric glow-lamps of a nominal intensity of 16 candles or thereabouts,
and good flat-flame gas-burners, aggregating 90-95 candle-power, will
similarly be taken as equivalent, if suitably distributed, to 100 candle-
power from more powerful sources of light. Of the latter it will be
assumed that each source has an intensity between 20 and 30 candle-power,
such as is afforded by a large oil-lamp, a No. 1 Welsbach-Kern upturned,
or a "Bijou" inverted incandescent gas-burner, or a 0.70-cubic-foot-per-
hour acetylene burner. Either of these sources of light, when used in
sufficient numbers, so that with proper distribution they light a room
adequately, will be taken in the tabular statement which follows as
affording, per candle-power evolved, the standard illuminating effect
required in that room. The same illuminating effect will be regarded as
attainable by means of candles aggregating only 35 per cent., or small
electric glow-lamps aggregating 77 per cent., or large electric glow-
lamps and flat-flame gas-burners aggregating 90 to 95 per cent. of this
candle-power; while if sources of light of higher intensity are used,
such as Osram or Tantalum electric lamps, or the larger incandescent gas-
burners (the Welsbach "C" or "York," or the Nos. 3 or 4 Welsbach-Kern
upturned, or the No. 1 or larger size inverted burners) or incandescent
acetylene burners, it will be assumed that their aggregate candle-power
must be in excess by about 15 per cent., in order to compensate for the
impossibility of obtaining equally well distributed illumination. These
assumptions are based on general considerations and data as to the effect
of sources of light of different intensities in giving practically the
same degree of illumination in a room; it would occupy too much space
here to discuss more fully the grounds on which they have been made. It
must suffice to say that they have been adopted with the object of being
perfectly fair to each means of illumination.
COST PER HOUR AND HYGIENIC EFFECT OF LIGHTING BY DIFFERENT MEANS
The data (except in the column headed "cost per 100 candle-hours") refer
to the illumination afforded by medium-sized (0.5 to 0.7 cubic foot per
hour) acetylene burners yielding together a light of about 100 candle-
power, and to the approximately equivalent illumination as afforded by
other means of illumination, when the lighting-units or sources of light
are rationally distributed.
Interest and depreciation charges on the outlay on piping or wiring a
house, on brackets, fittings, lamps, candelabra, and storage
accommodation (for carbide and oil) have been taken as equivalent for all
modes of lighting, and omitted in computing the total cost. The cost of
labour for attendance on acetylene plant, oil lamps, and candles is an
uncertain and variable item--approximately equal for all these modes of
lighting, but saved in coal-gas and electric lighting from public supply
mains.
______________________________________________________________________
| | | | | | |
| | |Candle- | Number |Aggregate| Cost |
| | |Power of| of | Candle- | per |
| | Description of | each |Lighting | Power | 100 |
|Illuminant. | Burner or Lamp. |Lighting| Units |Afforded.|Candle-|
| | | Unit. |Required.|(About.) |Hours. |
| | |(About.)| | |Pence. |
|____________|____________________|________|_________|_________|_______|
| | | | | | |
| |Self-luminous; 0.5 | | | | |
| | cubic foot per hour| 18 | 5 | 90 | 1.11 |
| |Self-luminous; 0.7 | | | | |
| Acetylene | cubic foot per hour| 27 | 4 | 108 | 1.02 |
| |Self-luminous; 1.0 | | | | |
| | cubic foot per hour| 45.5 | 3 | 136 | 0.85 |
| |Incandescent; 0.5 | | | | |
| | cubic foot per hour| 50 | 3 | 150 | 0.49 |
|____________|____________________|________|_________|_________|_______|
| | | | | | |
| Petroleum | Large lamp . . . . | 20 | 5 | 100 | 0.84 |
| (paraffin | | | | | |
| oil) | Small lamp . . . . | 5 | 14 | 70 | 1.31 |
|____________|____________________|________|_________|_________|_______|
| | | | | | |
| |Flat flame (bad) 5 | | | | |
| | cubic feet per hour| 8 | 10 | 80 | 3.75 |
| |Flat flame (good) 6 | | | | |
| Coal Gas | cubic feet per hour| 16 | 6 | 96 | 2.25 |
| |Incandescent (No. 1 | | | | |
| | Kern or Bijou In- | 25 | 4 | 100 | 0.38 |
| | verted); 1-1/2 | | | | |
| | cubic feet per hour| | | | |
|____________|____________________|________|_________|_________|_______|
| | | | | | |
| Candles |"Wax" (so-called) . | 1.2 | 30 | 35 | 6.14 |
|____________|____________________|________|_________|_________|_______|
| | | | | | |
| | Small glow . . . . | 7 | 11 | 77 | 2.81 |
| | Large glow . . . . | 13 | 7 | 91 | 2.90 |
| Electricity| | | | | |
| | Tantalum . . . . . | 19 | 5 | 95 | 1.52 |
| | Osram . . . . . . | 14 | 7 | 98 | 1.00 |
|____________|____________________|________|_________|_________|_______|
___________________________________________________________________
| | | | |
| | | | |
| | | | Equivalent |
| | Description of | Assumed Cost | Illumin- |
|Illuminant. | Burner or Lamp. | of Illuminant. | ation. |
| | | | Pence. |
| | | | |
|____________|____________________|____________________|____________|
| | | | |
| |Self-luminous; 0.5 | Calcium carbide | |
| | cubic foot per hour| (yielding 5 | 1.00 |
| |Self-luminous; 0.7 | cubic feet of | |
| Acetylene | cubic foot per hour| acetylene per | 1.10 |
| |Self-luminous; 1.0 | lb.) at 15s. | |
| | cubic foot per hour| per cwt., inclu- | 1.16 |
| |Incandescent; 0.5 | ding delivery | |
| | cubic foot per hour| charges. | 0.74 |
|____________|____________________|____________________|____________|
| | | | |
| Petroleum | Large lamp . . . . | Oil, 9d. per gal- | 0.84 |
| (paraffin | | lon, including | |
| oil) | Small lamp . . . . | delivery charges. | 0.92 |
|____________|____________________|____________________|____________|
| | | | |
| |Flat flame (bad) 5 | | |
| | cubic feet per hour| Public supply | 3.00 |
| |Flat flame (good) 6 | from small | |
| Coal Gas | cubic feet per hour| country works, | 2.16 |
| |Incandescent (No. 1 | at 5s. per 1000 | |
| | Kern or Bijou In- | cubic feet. | 0.38 |
| | verted); 1-1/2 | | |
| | cubic feet per hour| | |
|____________|____________________|____________________|____________|
| | | | |
| Candles |"Wax" (so-called) . | 5d. per lb. | 2.60 |
|____________|____________________|____________________|____________|
| | | | |
| | Small glow . . . . | Public supply | 2.16 |
| | Large glow . . . . | from small | 2.64 |
| Electricity| | town works | |
| | Tantalum . . . . . | at 6d. per | 1.45 |
| | Osram . . . . . . | B.O.T. unit. | 0.98 |
|____________|____________________|____________________|____________|
_______________________________________________________________________
| | | | | | |
| | |Inci- | Exhaus- |Vitiation | Heat |
| | | den- | tion of | of Air. |Produced.|
| | Description of | tal |Air.Cubic|Cubic Feet|Number of|
|Illuminant. | Burner or Lamp. |Expen-|Feet Dep-| of Car- |Units of |
| | | ces. |rived of |bonic Acid| Heat. |
| | | | Oxygen. | Formed. |Calories.|
|____________|____________________|______|_________|__________|_________|
| | | | | | |
| |Self-luminous; 0.5 | | | | |
| | cubic foot per hour| [1] | 29.8 | 5.0 | 900 |
| |Self-luminous; 0.7 | | | | |
| Acetylene | cubic foot per hour| | 33.3 | 5.6 | 1010 |
| |Self-luminous; 1.0 | | | | |
| | cubic foot per hour| | 35.7 | 6.0 | 1000 |
| |Incandescent; 0.5 | | | | |
| | cubic foot per hour| [2] | 17.9 | 3.0 | 545 |
|____________|____________________|______|_________|__________|_________|
| | | | | | |
| Petroleum | Large lamp . . . . | | 140.0 | 19.6 | 3630 |
| (paraffin | | [3] | | | |
| oil) | Small lamp . . . . | | 154.0 | 21.6 | 4000 |
|____________|____________________|______|_________|__________|_________|
| | | | | | |
| |Flat flame (bad) 5 | | | | |
| | cubic feet per hour| Nil | 270.0 | 27.0 | 7750 |
| |Flat flame (good) 6 | | | | |
| Coal Gas | cubic feet per hour| Nil | 195.0 | 19.5 | 5580 |
| |Incandescent (No. 1 | | | | |
| | Kern or Bijou In- | [4] | 27.0 | 2.7 | 775 |
| | verted); 1-1/2 | | | | |
| | cubic feet per hour| | | | |
|____________|____________________|______|_________|__________|_________|
| | | | | | |
| Candles |"Wax" (so-called) . | Nil | 100.5 | 13.7 | 2700 |
|____________|____________________|______|_________|__________|_________|
| | | | | | |
| | Small glow . . . . |2s.6d.| Nil | Nil | 285 |
| | Large glow . . . . |2s.6d.| " | " | 360 |
| Electricity| | [5] | | | |
| | Tantalum . . . . . |7s.6d.| " | " | 172 |
| | Osram . . . . . . | 6s. | " | " | 96 |
|____________|____________________|______|_________|__________|_________|
[Footnote 1: Interest and depreciation charges on generating and
purifying plant = 0.15 penny. Purifying material and burner renewals =
0.05 penny.]
[Footnote 2: Mantle renewals as for coal-gas.]
[Footnote 3: Renewals of wicks and chimneys = 0.02 penny.]
[Footnote 4: Renewals and mantles (and chimneys) at contract rate of 3s.
per burner per annum.]
[Footnote 5: Renewals of lamps and fuses, at price indicated per lamp per
annum.]
The conventional method of making pecuniary comparisons between different
sources of artificial light consists in simply calculating the cost of
developing a certain number of candle-hours of light--_i.e._, a
certain amount of standard candle-power for a given number of hours--on
the assumption that as many separate sources of light are employed as may
be required to bring the combined illuminating power up to the total
amount wanted. In view of the facts as to dissemination and diffusion, or
the difference between sheer illuminating power and useful illuminating
effect, which have just been elaborated, and in view of the different
intensities of the different unit sources of light (which range from the
single candle to a powerful large incandescent gas-burner or a metallic
filament electric lamp), such a method of calculation is wholly illusory.
The plan adopted in the following table may also appear unnecessarily
complicated; but it is not so to the reader if he remembers that the
apparently various amount of illumination is corrected by the different
numbers of illuminating units until the amount of simple candle-power
developed, whatever illuminant be employed, suffices to light a room
having an area of about 300 square feet (_i.e._, a room, 17-1/2 feet
square, or one 20 feet long by 15 feet wide), so that ordinary print may
be read comfortably in any part of the room, and the titles of books,
engravings, &c., in any position on the walls up to a height of 8 feet
from the ground may be distinguished with ease. The difference in cost,
&c., of a greater or less degree of illumination, or of lighting a larger
or smaller room by acetylene or any other of the illuminants named, will
be almost directly proportional to the cost given for the stated
conditions. Nevertheless, it should be recollected that when the
conventional system is retained--useful illuminating effect being
sacrificed to absolute illuminating power--acetylene is made to appear
cheaper in comparison with all weaker unit sources of light, and dearer
in comparison with all stronger unit sources of light than the
accompanying table indicates it to be. In using the comparative figures
given in the table, it should be borne in mind that they refer to more
general and more brilliant illumination of a room than is commonly in
vogue where the lighting is by means of electric light, candles, or oil-
lamps. The standard of illumination adopted for the table is one which is
only gaining general recognition where incandescent gas or acetylene
lighting is available, though in exceptional cases it has doubtless been
attained by means of oil-lamps or flat-flame gas-burners, but very rarely
if ever by means of carbon-filament electric glow-lamps, or candles. It
assumes that the occupants of a room do not wish to be troubled to bring
work or book "to the light," but wish to be able to work or read
wheresoever in the room they will, without consideration of the
whereabouts of the light or lights.
It should, perhaps, be added that so high a price as 5s. per 1000
cubic feet for coal-gas rarely prevails in Great Britain, except in small
outlying towns, whereas the price of 6d. per Board of Trade unit
for electricity is not uncommonly exceeded in the few similar country
places in which there is a public electricity supply.
CHAPTER II
THE PHYSICS AND CHEMISTRY OF THE REACTION BETWEEN CARBIDE AND WATER
THE NATURE OF CALCIUM CARBIDE.--The raw material from which, by
interaction with water, acetylene is obtained, is a solid body called
calcium carbide or carbide of calcium. Inasmuch as this substance can at
present only be made on a commercial scale in the electric furnace--and
so far as may be foreseen will never be made on a large scale except by
means of electricity--inasmuch as an electric furnace can only be worked
remuneratively in large factories supplied with cheap coal or water
power; and inasmuch as there is no possibility of the ordinary consumer
of acetylene ever being able to prepare his own carbide, all descriptions
of this latter substance, all methods of winning it, and all its
properties except those which concern the acetylene-generator builder or
the gas consumer have been omitted from the present book. Hitherto
calcium carbide has found but few applications beyond that of evolving
acetylene on treatment with water or some aqueous liquid, hygroscopic
solid, or salt containing water of crystallisation; but it has
possibilities of further employment, should its price become suitable,
and a few words will be devoted to this branch of the subject in Chapter
XII. Setting these minor uses aside, calcium carbide has no intrinsic
value except as a producer of acetylene, and therefore all its
characteristics which interest the consumer of acetylene are developed
incidentally throughout this volume as the necessity for dealing with
them arises.
It is desirable, however, now to discuss one point connected with solid
carbide about which some misconception prevails. Calcium carbide is a
body which evolves an inflammable, or on occasion an explosive, gas when
treated with water; and therefore its presence in a building has been
said to cause a sensible increase in the fire risk because attempts to
extinguish a fire in the ordinary manner with water may cause evolution
of acetylene which should determine a further production of flame and
heat. In the absence of water, calcium carbide is absolutely inert as
regards fire; and on several occasions drums of it have been recovered
uninjured from the basement of a house which has been totally destroyed
by fire. With the exception of small 1-lb. tins of carbide, used only by
cyclists, &c., the material is always put into drums of stout sheet-iron
with riveted or folded seams. Provided the original lid has not been
removed, the drums are air- and water-tight, so that the fireman's hose
may be directed upon them with impunity. When a drum has once been
opened, and not all of its contents have been put into the generator,
ordinary caution--not merely as regards fire, but as regards the
deterioration of carbide when exposed to the atmosphere--suggests either
that the lid must be made air-tight again (not by soldering it),
[Footnote: Carbide drums are not uncommonly fitted with self-sealing or
lever-top lids, which are readily replaced hermetically tight after
opening and partial removal of the contents of the drum.] or preferably
that the rest of the carbide shall be transferred to some convenient
receptacle which can be perfectly closed. [Footnote: It would be a
refinement of caution, though hardly necessary in practice, to fit such a
receptacle with a safety-valve. If then the vessel were subjected to
sudden or severe heating, the expansion of the air and acetylene in it
could not possibly exert a disruptive effect upon the walls of the
receptacle, which, in the absence of the safety-valve, is imaginable.]
Now, assuming this done, the drums are not dependent upon soft solder to
keep them sound, and so they cannot open with heat. Fire and water,
accordingly, cannot affect them, and only two risks remain: if stored in
the basement of a tall building, falling girders, beams or brickwork may
burst them; or if stored on an upper floor, they may fall into the
basement and be burst with the shock--in either event water then having
free access to the contents. But drums of carbide would never be stored
in such positions: a single one would be kept in the generator-house;
several would be stored in a separate room therein, or in some similar
isolated shed. The generator-house or shed would be of one story only;
the drums could neither fall nor have heavy weights fall on them during a
fire; and therefore there is no reason why, if a fire should occur, the
firemen should not be permitted to use their hose in the ordinary
fashion. Very similar remarks apply to an active acetylene generator.
Well built, such plant will stand much heat and fire without failure; if
it is non-automatic, and of combustible materials contains nothing but
gas in the holder, the worst that could happen in times of fire would be
the unsealing of the bell or its fracture, and this would be followed,
not at all by any explosion, but by a fairly quiet burning of the
escaping gas, which would be over in a very short time, and would not add
to the severity of the conflagration unless the generator-house were so
close to the residence that the large flame of burning gas could ignite
part of the main building. Even if the heat were so great near the holder
that the gas dissociated, it is scarcely conceivable that a dangerous
explosion should arise. But it is well to remember, that if the
generator-house is properly isolated from the residence, if it is
constructed of non-inflammable materials, if the attendant obeys
instructions and refrains from taking a naked light into the
neighbourhood of the plant, and if the plant itself is properly designed
and constructed, a fire at or near an acetylene generator is extremely
unlikely to occur. At the same time, before the erection of plant to
supply any insured premises is undertaken, the policy or the company
should be consulted to ascertain whether the adoption of acetylene
lighting is possibly still regarded by the insurers as adding an extra
risk or even as vitiating the whole insurance.
REGULATIONS FOR THE STORAGE OF CARBIDE: BRITISH.--There are also certain
regulations imposed by many local authorities respecting the storage of
carbide, and usually a licence for storage has to be obtained if more
than 5 lb. is kept at a time. The idea of the rule is perfectly
justifiable, and it is generally enforced in a sensible spirit. As the
rules may vary in different localities, the intending consumer of
acetylene must make the necessary inquiries, for failure to comply with
the regulations may obviously be followed by unpleasantness.
Having regard to the fact that, in virtue of an Order in Council dated
July 7, 1897, carbide may be stored without a licence only in separate
substantial hermetically closed metal vessels containing not more than 1
lb. apiece and in quantities not exceeding 5 lb. in the aggregate, and
having regard also to the fact that regulations are issued by local
authorities, the Fire Offices' Committee of the United Kingdom has not up
to the present deemed it necessary to issue special rules with reference
to the storage of carbide of calcium.
The following is a copy of the rules issued by the National Board of Fire
Underwriters of the UNITED STATES OF AMERICA for the storage of calcium
carbide on insured premises:
RULES FOR THE STORAGE OF CALCIUM CARBIDE.
(_a_) Calcium carbide in quantities not to exceed six hundred (600)
pounds may be stored, when contained in approved metal packages not to
exceed one hundred (100) pounds each, inside insured property, provided
that the place of storage be dry, waterproof and well ventilated, and
also provided that all but one of the packages in any one building shall
be sealed and the seals shall not be broken so long as there is carbide
in excess of one (1) pound in any other unsealed package in the building.
(_b_) Calcium carbide in quantities in excess of six hundred (600)
pounds must be stored above ground in detached buildings, used
exclusively for the storage of calcium carbide, in approved metal
packages, and such buildings shall be constructed to be dry, waterproof
and well ventilated.
(_c_) Packages to be approved must be made of metal of sufficient
strength to insure handling the package without rupture, and be provided
with a screwed top or its equivalent.
They must be constructed so as to be water- and air-tight without the use
of solder, and conspicuously marked "CALCIUM CARBIDE--DANGEROUS IF NOT
KEPT DRY."
The following is a summary of the AUSTRIAN GOVERNMENT rules relating to
the storage and handling of carbide:
(1) It must be sold and stored only in closed water-tight vessels, which,
if the contents exceed 10 kilos., must be marked in plain letters
"CALCIUM CARBIDE--TO BE KEPT CLOSED AND DRY." They must not be of copper
and if soldered must be opened by mechanical means and not by
unsoldering. They must be stored out of the reach of water.
(2) Quantities not exceeding 300 kilos. may be stored in occupied houses,
provided the single drums do not exceed 100 kilos. nominal capacity. The
storage-place must be dry and not underground.
(3) The limits specified in Rule 2 apply also to generator-rooms, with
the proviso also that in general the amount stored shall not exceed five
days' consumption.
(4) Quantities ranging from 300 to 1000 kilos. must be stored in special
well-ventilated uninhabited non-basement rooms in which lights and
smoking are not allowed.
(5) Quantities exceeding 1000 kilos. must be stored in isolated fireproof
magazines with light water-tight roofs. The floors must be at least 8
inches above ground-level.
(6) Carbide in water-tight drums may be stored in the open in a fenced
enclosure at least 30 feet from buildings, adjoining property, or
inflammable materials. The drums must be protected from wet by a light
roof.
(7) The breaking of carbide must be done by men provided with respirators
and goggles, and care taken to avoid the formation of dust.
(8) Local or other authorities will issue from time to time special
regulations in regard to carbide trade premises.
The ITALIAN GOVERNMENT rules relating to the storage and transport of
carbide follow in the main those of the Austrian Government, but for
quantities between 300 and 2000 kilos sanction is required from the local
authorities, and for larger quantities from superior authorities. The
storage of quantities ranging from 300 to 2000 kilos is forbidden in
dwelling-houses and above the latter quantity the storage-place must be
isolated and specially selected. No special permit is required for the
storage of quantities not exceeding 300 kilos. Workmen exposed to carbide
dust arising from the breaking of carbide or otherwise must have their
eyes and respiratory organs suitably protected.
THE PURCHASE OF CARBIDE.--Since calcium carbide is only useful as a means
of preparing acetylene, it should be bought under a guarantee (1) that it
contains less impurities than suffice to render the crude gas dangerous
in respect of spontaneous inflammability, or objectionable in a manner to
be explained later on, when consumed; and (2) that it is capable of
evolving a fixed minimum quantity of acetylene when decomposed by water.
Such determination, however, cannot be carried out by the ordinary
consumer for himself. A generator which is perfectly satisfactory in
general behaviour, and which evolves a sufficient proportion of the
possible total make of gas to be economical, does not of necessity
decompose the carbide quantitatively; nor is it constructed in a fashion
to render an exact measurement of the gas liberated at standard
temperature and pressure easy to obtain. For obvious reasons the careful
consumer of acetylene will keep a record of the carbide decomposed and of
the acetylene generated--the latter perhaps only in terms of burner-
hours, or the like; but in the event of serious dispute as to the gas-
making capacity of his raw material, he must have a proper analysis made
by a qualified chemist.
Calcium carbide is crushed by the makers into several different sizes, in
each of which all the lumps exceed a certain size and are smaller than
another size. It is necessary to find out by experiment, or from the
maker, what particular size suits the generator best, for different types
of apparatus require different sizes of carbide. Carbide cannot well be
crushed by the consumer of acetylene. It is a difficult operation, and
fraught with the production of dust which is harmful to the eyes and
throat, and if done in open vessels the carbide deteriorates in gas-
making power by its exposure to the moisture of the atmosphere. True dust
in carbide is objectionable, and practically useless for the generation
of acetylene in any form of apparatus, but carbide exceeding 1 inch in
mesh is usually sold to satisfy the suggestions of the British Acetylene
Association, which prescribes 5 per cent, of dust as the maximum. Some
grades of carbide are softer than others, and therefore tend to yield
more dust if exposed to a long journey with frequent unloadings.
There are certain varieties of ordinary carbide known as "treated
carbide," the value of which is more particularly discussed in Chapter
III. The treatment is of two kinds, or of a combination of both. In one
process the lumps are coated with a strong solution of glucose, with the
object of assisting in the removal of spent lime from their surface when
the carbide is immersed in water. Lime is comparatively much more soluble
in solutions of sugar (to which class of substances glucose belongs) than
in plain water; so that carbide treated with glucose is not so likely to
be covered with a closely adherent skin of spent lime when decomposed by
the addition of water to it. In the other process, the carbide is coated
with or immersed in some oil or grease to protect it from premature
decomposition. The latter idea, at least, fulfils its promises, and does
keep the carbide to a large extent unchanged if the lumps are exposed to
damp air, while solving certain troubles otherwise met with in some
generators (cf. Chapter III.); but both operations involve additional
expense, and since ordinary carbide can be used satisfactorily in a good
fixed generator, and can be preserved without serious deterioration by
the exercise of reasonable care, treated carbide is only to be
recommended for employment in holderless generators, of which table-lamps
are the most conspicuous forms. A third variant of plain carbide is
occasionally heard of, which is termed "scented" carbide. It is difficult
to regard this material seriously. In all probability calcium carbide is
odourless, but as it begins to evolve traces of gas immediately
atmospheric moisture reaches it, a lump of carbide has always the
unpleasant smell of crude acetylene. As the material is not to be stored
in occupied rooms, and as all odour is lost to the senses directly the
carbide is put into the generator, scented carbide may be said to be
devoid of all utility.
THE REACTION BETWEEN CARBIDE AND WATER.--The reaction which occurs when
calcium carbide and water are brought into contact belongs to the class
that chemists usually term double decompositions. Calcium carbide is a
chemical compound of the metal calcium with carbon, containing one
chemical "part," or atomic weight, of the former united to two chemical
parts, or atomic weights, of the latter; its composition expressed in
symbols being CaC_2. Similarly, water is a compound of two chemical parts
of hydrogen with one of oxygen, its formula being H_2O. When those two
substances are mixed together the hydrogen of the water leaves its
original partner, oxygen, and the carbon of the calcium carbide leaves
the calcium, uniting together to form that particular compound of
hydrogen and carbon, or hydrocarbon, which is known as acetylene, whose
formula is C_2H_2; while the residual calcium and oxygen join together to
produce calcium oxide or lime, CaO. Put into the usual form of an
equation, the reaction proceeds thus--
(1) CaC_2 + H_2O = C_2H_2 + CaO.
This equation not only means that calcium carbide and water combine to
yield acetylene and lime, it also means that one chemical part of carbide
reacts with one chemical part of water to produce one chemical part of
acetylene and one of lime. But these four chemical parts, or molecules,
which are all equal chemically, are not equal in weight; although,
according to a common law of chemistry, they each bear a fixed proportion
to one another. Reference to the table of "Atomic Weights" contained in
any text-book of chemistry will show that while the symbol Ca is used,
for convenience, as a contraction or sign for the element calcium simply,
it bears a more important quantitative significance, for to it will be
found assigned the number 40. Against carbon will be seen the number 12;
against oxygen, 16; and against hydrogen, 1. These numbers indicate that
if the smallest weight of hydrogen ever found in a chemical compound is
called 1 as a unit of comparison, the smallest weights of calcium,
carbon, and oxygen, similarly taking part in chemical reactions are 40,
12, and 16 respectively. Thus the symbol CaC_2, comes to convoy three
separate ideas: (_a_) that the substance referred to is a compound
of calcium and carbon only, and that it is therefore a carbide of
calcium; (_b_) that it is composed of one chemical part or atom of
calcium and two atoms of carbon; and (_c_) that it contains 40 parts
by weight of calcium combined with twice twelve, or 24, parts of carbon.
It follows from (_c_) that the weight of one chemical part, now
termed a molecule as the substance is a compound, of calcium carbide is
(40 + 2 x 12) = 64. By identical methods of calculation it will be found
that the weight of one molecule of water is 18; that of acetylene, 26;
and that of lime, 56. The general equation (1) given above, therefore,
states in chemical shorthand that 64 parts by weight of calcium carbide
react with 18 parts of water to give 26 parts by weight of acetylene and
56 parts of lime; and it is very important to observe that just as there
are the same number of chemical parts, viz., 2, on each side, so there
are the same number of parts by weight, for 64 + 18 = 56 + 26 = 82. Put
into other words equation (1) shows that if 64 grammes, lb., or cwts. of
calcium carbide are treated with 18 grammes, lb., or cwts. of water, the
whole mass will be converted into acetylene and lime, and the residue
will not contain any unaltered calcium carbide or any water; whence it
may be inferred, as is the fact, that if the weights of carbide and water
originally taken do not stand to one another in the ratio 64 : 18, both
substances cannot be entirely decomposed, but a certain quantity of the
one which was in excess will be left unattacked, and that quantity will
be in exact accordance with the amount of the said excess--indifferently
whether the superabundant substance be carbide or water.
Hitherto, for the sake of simplicity, the by-product in the preparation
of acetylene has been described as calcium oxide or quicklime. It is,
however, one of the leading characteristics of this body to be
hygroscopic, or greedy of moisture; so that if it is brought into the
presence of water, either in the form of liquid or as vapour, it
immediately combines therewith to yield calcium hydroxide, or slaked
lime, whose chemical formula is Ca(OH)_2. Accordingly, in actual
practice, when calcium carbide is mixed with an excess of water, a
secondary reaction takes place over and above that indicated by equation
(1), the quicklime produced combining with one chemical part or molecule
of water, thus--
CaO + H_2O = Ca(OH)_2.
As these two actions occur simultaneously, it is more usual, and more in
agreement with the phenomena of an acetylene generator, to represent the
decomposition of calcium carbide by the combined equation--
(2) CaC_2 + 2H_2O = C_2H_2 + Ca(OH)_2.
By the aid of calculations analogous to those employed in the preceding
paragraph, it will be noticed that equation (2) states that 1 molecule of
calcium carbide, or 64 parts by weight, combines with 2 molecules of
water, or 36 parts by weight, to yield 1 molecule, or 26 parts by weight
of acetylene, and 1 molecule, or 74 parts by weight of calcium hydroxide
(slaked lime). Here again, if more than 36 parts of water are taken for
every 64 parts of calcium carbide, the excess of water over those 36
parts is left undecomposed; and in the same fashion, if less than 36
parts of water are taken for every 64 parts of calcium carbide, some of
the latter must remain unattacked, whilst, obviously, the amount of
acetylene liberated cannot exceed that which corresponds with the
quantity of substance suffering complete decomposition. If, for example,
the quantity of water present in a generator is more than chemically
sufficient to attack all the carbide added, however largo or small that
excess may be, no more, and, theoretically speaking, no less, acetylene
can ever be evolved than 26 parts by weight of gas for every 64 parts by
weight of calcium carbide consumed. It is, however, not correct to invert
the proposition, and to say that if the carbide is in excess of the water
added, no more, and, theoretically speaking, no less, acetylene can ever
be evolved than 26 parts by weight of gas for every 36 parts of water
consumed, as might be gathered from equation (2); because equation (1)
shows that 26 parts of acetylene may, on occasion, be produced by the
decomposition of 18 parts by weight of water. From the purely chemical
point of view this apparent anomaly is explained by the circumstance that
of the 36 parts of water present on the left-hand aide of equation (2),
only one-half, _i.e._, 18 parts by weight, are actually decomposed
into hydrogen and oxygen, the other 18 parts remaining unattacked, and
merely attaching themselves as "water of hydration" to the 56 parts of
calcium oxide in equation (1) so as to produce the 74 parts of calcium
hydroxide appearing on the right-hand side of equation (2). The matter is
perhaps rendered more intelligible by employing the old name for calcium
hydroxide or slaked lime, viz., hydrated oxide of calcium, and by writing
its formula in the corresponding form, when equation (2) becomes
CaC_2 + 2H_2O = C_2H_2 + CaO.H_2O.
It is, therefore, absolutely correct to state that if the amount of
calcium carbide present in an acetylene generator is more than chemically
sufficient to decompose all the water introduced, no more, and
theoretically speaking no less, acetylene can ever be liberated than 26
parts by weight of gas for every 18 parts by weight of water attacked.
This, it must be distinctly understood, is the condition of affairs
obtaining in the ideal acetylene generator only; since, for reasons which
will be immediately explained, when the output of gas is measured in
terms of the water decomposed, in no commercial apparatus, and indeed in
no generator which can be imagined fit for actual employment, does that
output of gas ever approach the quantitative amount; but the volume of
water used, if not actually disappearing, is always vastly in excess of
the requirements of equation (2). On the contrary, when the make of gas
is measured in terms of the calcium carbide consumed, the said make may,
and frequently does, reach 80, 90, or even 99 per cent. of what is
theoretically possible. Inasmuch as calcium carbide is the one costly
ingredient in the manufacture of acetylene, so long as it is not wasted--
so long, that is to say, as nearly the theoretical yield of gas is
obtained from it--an acetylene generator is satisfactory or efficient in
this particular; and except for the matter of solubility discussed in the
following chapter, the quantity of water consumed is of no importance
whatever.
HEAT EVOLVED IN THE REACTION.--The chemical reaction between calcium
carbide and water is accompanied by a large evolution of heat, which,
unless due precautions are taken to prevent it, raises the temperature of
the substances employed, and of the apparatus containing them, to a
serious and often inconvenient extent. This phenomenon is the most
important of all in connexion with acetylene manufacture; for upon a
proper recognition of it, and upon the character of the precautions taken
to avoid its numerous evil effects, depend the actual value and capacity
for smooth working of any acetylene generator. Just as, by an immutable
law of chemistry, a given weight of calcium carbide yields a given weight
of acetylene, and by no amount of ingenuity can be made to produce either
more or less; so, by an equally immutable law of physics, the
decomposition of a given weight of calcium carbide by water, or the
decomposition of a given weight of water by calcium carbide, yields a
perfectly definite quantity of heat--a quantity of heat which cannot be
reduced or increased by any artifice whatever. The result of a production
of heat is usually to raise the temperature of the material in which it
is produced; but this is not always the case, and indeed there is no
necessary connexion or ratio between the quantity of heat liberated in
any form of chemical reaction--of which ordinary combustion is the
commonest type--and the temperature attained by the substances concerned.
This matter has so weighty a bearing upon acetylene generation, and
appears to be so frequently misunderstood, that a couple of illustrations
may with advantage be studied. If a vessel full of cold water, and
containing also a thermometer, is placed over a lighted gas-burner, at
first the temperature of the liquid rises steadily, and there is clearly
a ratio between the size of the flame and the speed at which the mercury
mounts up the scale. Finally, however, the thermometer indicates a
certain point, viz., 100° C, and the water begins to boil; yet although
the burner is untouched, and consequently, although heat must be passing
into the vessel at the same rate as before, the mercury refuses to move
as long as any liquid water is left. By the use of a gas meter it might
be shown that the same volume of gas is always consumed (_a_) in
raising the temperature of a given quantity of cold water to the boiling-
point, and another equally constant volume of gas is always consumed
(_b_) in causing the boiling water to disappear as steam. Hence, as
coal-gas is assumed for the present purpose to possess invariably the
same heating power, it appears that the same quantity of heat is always
needed to convert a given amount of cold water at a certain temperature
into steam; but inasmuch as reference to the meter would show that about
5 times the volume of gas is consumed in changing the boiling water into
steam as is used in heating the cold water to the boiling-point, it will
be evident that the temperature of the mass is raised as high by the heat
evolved during the combustion of one part of gas as it is by that
liberated on the combustion of 6 times that amount.
A further example of the difference between quantity of heat and sensible
temperature may be seen in the combustion of coal, for (say) one
hundredweight of that fuel might be consumed in a very few minutes in a
furnace fitted with a powerful blast of air, the operation might be
spread over a considerable number of hours in a domestic grate, or the
coal might be allowed to oxidise by exposure to warm air for a year or
more. In the last case the temperature might not attain that of boiling
water, in the second it would be about that of dull redness, and in the
first it would be that of dazzling whiteness; but in all three cases the
total quantity of heat produced by the time the coal was entirely
consumed would be absolutely identical. The former experiment with water
and a gas-burner, too, might easily be modified to throw light upon
another problem in acetylene generation, for it would be found that if
almost any other liquid than water were taken, less gas (_i.e._, a
smaller quantity of heat) would be required to raise a given weight of it
from a certain low to a certain high temperature than in the case of
water itself; while if it were possible similarly to treat the same
weight of iron (of which acetylene generators are constructed), or of
calcium carbide, the quantity of heat used to raise it through a given
number of thermometric degrees would hardly exceed one-tenth or one-
quarter of that needed by water itself. In technical language this
difference is due to the different specific heats of the substances
mentioned; the specific heat of a body being the relative quantity of
heat consumed in raising a certain weight of it a certain number of
degrees when the quantity of heat needed to produce the same effect on
the same weight of water is called unity. Thus, the specific heat of
water being termed 1.0, that of iron or steel is 0.1138, and that of
calcium carbide 0.247, [Footnote: This is Carlson's figure. Morel has
taken the value 0.103 in certain calculations.] both measured at
temperatures where water is a liquid. Putting the foregoing facts in
another shape, for a given rise in temperature that substance will absorb
the most heat which has the highest specific heat, and therefore, in this
respect, 1 part by weight of water will do the work of roughly 9 parts by
weight of iron, and of about 4 parts by weight of calcium carbide.
From the practical aspect what has been said amounts to this: During the
operation of an acetylene generator a large amount of heat is produced,
the quantity of which is beyond human control. It is desirable, for
various reasons, that the temperature shall be kept as low as possible.
There are three substances present to which the heat may be compelled to
transfer itself until it has opportunity to pass into the surrounding
atmosphere: the material of which the apparatus is constructed, the gas
which is in process of evolution, and whichever of the two bodies--
calcium carbide or water--is in excess in the generator. Of these, the
specific heat at constant pressure of acetylene has unfortunately not yet
been determined, but its relative capacity for absorbing heat is
undoubtedly small; moreover the gas could not be permitted to become
sufficiently hot to carry off the heat without grave disadvantages. The
specific heat of calcium carbide is also comparatively small, and there
are similar disadvantages in allowing it to become hot; moreover it is
deficient in heat-conducting power, so that heat communicated to one
portion of the mass does not extend rapidly throughout, but remains
concentrated in one spot, causing the temperature to rise objectionably.
Steel has a sufficient amount of heat-conducting power to prevent undue
concentration in one place; but, as has been stated, its specific heat is
only one-ninth that of water. Water is clearly, therefore, the proper
substance to employ for the dissipation of the heat generated, although
it is strictly speaking almost devoid of heat-conducting power; for not
only is the specific heat of water much greater than that of any other
material present, but it possesses in a high degree the faculty of
absorbing heat throughout its mass, by virtue of the action known as
convection, provided that heat is communicated to it at or near the
bottom, and not too near its upper surface. Moreover, water is a much
more valuable substance for dissipating heat than appears from the
foregoing explanation; for reference to the experiment with the gas-
burner will show that six and a quarter times as much heat can be
absorbed by a given weight of water if it is permitted to change into
steam, as if it is merely raised to the boiling-point; and since by no
urging of the gas-burner can the temperature be raised above 100° C. as
long as any liquid water remains unevaporated, if an excess of water is
employed in an acetylene generator, the temperature inside can never--
except quite locally--exceed 100° C., however fast the carbide be
decomposed. An indefinitely large consumption of water by evaporation in
a generator matters nothing, for the liquid may be considered of no
pecuniary value, and it can all be recovered by condensation in a
subsequent portion of the plant.
It has been said that the quantity of heat liberated when a certain
amount of carbide suffers decomposition is fixed; it remains now to
consider what that quantity is. Quantities of heat are always measured in
terms of the amount needed to raise a certain weight of water a certain
number of degrees on the thermometric scale. There are several units in
use, but the one which will be employed throughout this book is the
"Large Calorie"; a large calorie being the amount of heat absorbed in
raising 1 kilogramme of water 1° C. Referring for a moment to what has
been said about specific heats, it will be apparent that if 1 large
calorie is sufficient to heat 1 kilo, of water through 1° C. the same
quantity will heat 1 kilo. of steel, whose specific heat is roughly 0.11,
through (10/011) = 9° C., or, which comes to the same thing, will heat 9
kilos, of steel through 1° C.; and similarly, 1 large calorie will raise
4 kilos. of calcium carbide 1° C. in temperature, or 1 kilo. 4° C. The
fact that a definite quantity of heat is manifested when a known weight
of calcium carbide is decomposed by water is only typical; for in every
chemical process some disturbance of heat, though not necessarily of
sensible (or thermometric) character, occurs, heat being either absorbed
or set free. Moreover, if when given weights of two or more substances
unite to form a given weight of another substance, a certain quantity of
heat is set free, precisely the same amount of heat is absorbed, or
disappears, when the latter substance is decomposed to form the same
quantities of the original substances; and, _per contra_, if the
combination is attended by a disappearance of heat, exactly the same
amount is liberated when the compound is broken up into its first
constituents. Compounds are therefore of two kinds: those which absorb
heat during their preparation, and consequently liberate heat when they
are decomposed--such being termed endothermic; and those which evolve
heat during their preparation, and consequently absorb heat when they are
decomposed--such being called exothermic. If a substance absorbs heat
during its formation, it cannot be produced unless that heat is supplied
to it; and since heat, being a form of motion, is equally a form of
energy, energy must be supplied, or work must be done, before that
substance can be obtained. Conversely, if a substance evolves heat during
its formation, its component parts evolve energy when the said substance
is being produced; and therefore the mere act of combination is
accompanied by a facility for doing work, which work may be applied in
assisting some other reaction that requires heat, or may be usefully
employed in any other fashion, or wasted if necessary. Seeing that there
is a tendency in nature for the steady dissipation of energy, it follows
that an exothermic substance is stable, for it tends to remain as it is
unless heat is supplied to it, or work is done upon it; whereas,
according to its degree of endothermicity, an endothermic substance is
more or less unstable, for it is always ready to emit heat, or to do
work, as soon as an opportunity is given to it to decompose. The
theoretical and practical results of this circumstance will be elaborated
in Chapter VI., when the endothermic nature of acetylene is more fully
discussed.
A very simple experiment will show that a notable quantity of heat is set
free when calcium carbide is brought into contact with water, and by
arranging the details of the apparatus in a suitable manner, the quantity
of heat manifested may be measured with considerable accuracy. A lengthy
description of the method of performing this operation, however, scarcely
comes within the province of the present book, and it must be sufficient
to say that the heat is estimated by decomposing a known weight of
carbide by means of water in a small vessel surrounded on all sides by a
carefully jacketed receptacle full of water and provided with a sensitive
thermometer. The quantity of water contained in the outer vessel being
known, and its temperature having been noted before the reaction
commences, an observation of the thermometer after the decomposition is
finished, and when the mercury has reached its highest point, gives data
which show that the reaction between water and a known weight of calcium
carbide produces heat sufficient in amount to raise a known weight of
water through a known thermometric distance; and from these figures the
corresponding number of large calories may easily be calculated. A
determination of this quantity of heat has been made experimentally by
several investigators, including Lewes, who has found that the heat
evolved on decomposing 1 gramme of ordinary commercial carbide with water
is 0.406 large calorie. [Footnote: Lewes returns his result as 406
calories, because he employs the "small calorie." The small calorie is
the quantity of heat needed to raise 1 gramme of water 1° C.; but as
there are 1000 grammes in 1 kilogramme, the large calorie is equal to
1000 small calories. In many respects the former unit is to be
preferred.] As the material operated upon contained only 91.3 per cent.
of true calcium carbide, he estimates the heat corresponding with the
decomposition of 1 gramme of pure carbide to be 0.4446 large calorie. As,
however, it is better, and more in accordance with modern practice, to
quote such data in terms of the atomic or molecular weight of the
substance concerned, and as the molecular weight of calcium carbide is
64, it is preferable to multiply these figures by 64, stating that,
according to Lewes' researches, the heat of decomposition of "1 gramme-
molecule" (_i.e._, 64 grammes) of a calcium carbide having a purity
of 91.3 per cent. is just under 26 calories, or that of 1 gramme-molecule
of pure carbide 28.454 calories. It is customary now to omit the phrase
"one gramme-molecule" in giving similar figures, physicists saying simply
that the heat of decomposition of calcium carbide by water when calcium
hydroxide is the by-product, is 28.454 large calories.
Assuming all the necessary data known, as happens to be the case in the
present instance, it is also possible to calculate theoretically the heat
which should be evolved on decomposing calcium carbide by means of water.
Equation (2), given on page 24, shows that of the substances taking part
in the reaction 1 molecular weight of calcium carbide is decomposed, and
1 molecular weight of acetylene is formed. Of the two molecules of water,
only one is decomposed, the other passing to the calcium hydroxide
unchanged; and the 1 molecule of calcium hydroxide is formed by the
combination of 1 atom of free calcium, 1 atom of free oxygen, and 1
molecule of water already existing as such. Calcium hydroxide and water
are both exothermic substances, absorbing heat when they are decomposed,
liberating it when they are formed. Acetylene is endothermic, liberating
heat when it is decomposed, absorbing it when it is produced.
Unfortunately there is still some doubt about the heat of formation of
calcium carbide, De Forcrand returning it as -0.65 calorie, and Gin as
+3.9 calories. De Forcrand's figure means, as before explained, that 64
grammes of carbide should absorb 0.65 large calorie when they are
produced by the combination of 40 grammes of calcium with 24 grammes of
carbon; the minus sign calling attention to the belief that calcium
carbide is endothermic, heat being liberated when it suffers
decomposition. On the contrary, Gin's figure expresses the idea that
calcium carbide is exothermic, liberating 3.9 calories when it is
produced, and absorbing them when it is decomposed. In the absence of
corroborative evidence one way or the other, Gin's determination will be
accepted for the ensuing calculation. In equation (2), therefore, calcium
carbide is decomposed and absorbs heat; water is decomposed and absorbs
heat; acetylene is produced and absorbs heat; and calcium hydroxide is
produced liberating heat. On consulting the tables of thermo-chemical
data given in the various text-books on physical chemistry, all the other
constants needed for the present purpose will be found; and it will
appear that the heat of formation of water is +69 calories, that of
acetylene -58.1 calories, and that of calcium hydroxide, when 1 atom of
calcium, 1 atom of oxygen, and 1 molecule of water unite together, is
+160.1 calories. [Footnote: When 1 atom of calcium, 2 atoms of oxygen,
and 2 atoms of hydrogen unite to form solid calcium hydroxide, the heat
of formation of the latter is 229.1 (cf. _infra_). This value is
simply 160.1 + 69.0 = 229.1; 69.0 being the heat of formation of water.]
Collecting the results into the form of a balance-sheet, the effect of
decomposing calcium carbide with water is this:
_Heat liberated._ | _Heat absorbed._
|
Formation of Ca(OH)_2 16O.1 | Formation of acetylene 58.1
| Decomposition of water 69.0
| Decomposition of carbide 3.9
| Balance 29.1
_____ | _____
|
Total 160.1 | Total 160.1
Therefore when 64 grammes of calcium carbide are decomposed by water, or
when 18 grammes of water are decomposed by calcium carbide (the by-
product in each case being calcium hydroxide or slaked lime, for the
formation of which a further 18 grammes of water must be present in the
second instance), 29.1 large calories are set free. It is not possible
yet to determine thermo-chemical data with extreme accuracy, especially
on such a material as calcium carbide, which is hardly to be procured in
a state of chemical purity; and so the value 28.454 calories
experimentally found by Lewes agrees very satisfactorily, considering all
things, with the calculated value 29.1 calories. It is to be noticed,
however, that the above calculated value has been deduced on the
assumption that the calcium hydroxide is obtained as a dry powder; but as
slaked lime is somewhat soluble in water, and as it evolves 3 calories in
so dissolving, if sufficient water is present to take up the calcium
hydroxide entirely into the liquid form (_i.e._, that of a
solution), the amount of heat set free will be greater by those 3
calories, _i.e._, 32.1 large calories altogether.
THE PROCESS OF GENERATION.--Taking 28 as the number of large calories
developed when 64 grammes of ordinary commercial calcium carbide are
decomposed with sufficient water to leave dry solid calcium hydroxide as
the by-product in acetylene generation, this quantity of heat is capable
of exerting any of the following effects. It is sufficient (1) to raise
1000 grammes of water through 28° C., say from 10° C. (50° F., which is
roughly the temperature of ordinary cold water) to 38° C. It is
sufficient (2) to raise 64 grammes of water (a weight equal to that of
the carbide decomposed) through 438° C., if that were possible. It would
raise (3) 311 grammes of water through 90° C., _i.e._, from 10° C.
to the boiling-point. If, however, instead of remaining in the liquid
state, the water were converted into vapour, the same quantity of heat
would suffice (4) to change 44.7 grammes of water at 10° C. into steam at
100° C.; or (5) to change 46.7 grammes of water at 10° C. into vapour at
the same temperature. It is an action of the last character which takes
place in acetylene generators of the most modern and usual pattern, some
of the surplus water being evaporated and carried away as vapour at a
comparatively low temperature with the escaping gas; for it must be
remembered that although steam, as such, condenses into liquid water
immediately the surrounding temperature falls below 100° C., the vapour
of water remains uncondensed, even at temperatures below the freezing-
point, when that vapour is distributed among some permanent gas--the
precise quantity of vapour so remaining being a function of the
temperature and barometric height. Thus it appears that if the heat
evolved during the decomposition of calcium carbide is not otherwise
consumed, it is sufficient in amount to vaporise almost exactly 3 parts
by weight of water for every 4 parts of carbide attacked; but if it were
expended upon some substance such as acetylene, calcium carbide, or
steel, which, unlike water, could not absorb an extra amount by changing
its physical state (from solid to liquid, or from liquid to gas), the
heat generated during the decomposition of a given weight of carbide
would suffice to raise an equal weight of the particular substance under
consideration to a temperature vastly exceeding 438° C. The temperature
attained, indeed, measured in Centigrade degrees, would be 438 multiplied
by the quotient obtained on dividing the specific heat of water by the
specific heat of the substance considered: which quotient, obviously, is
the "reciprocal" of the specific heat of the said substance.
The analogy to the combustion of coal mentioned on a previous page shows
that although the quantity of heat evolved during a certain chemical
reaction is strictly fixed, the temperature attained is dependent on the
time over which the reaction is spread, being higher as the process is
more rapid. This is due to the fact that throughout the whole period of
reaction heat is escaping from the mass, and passing into the atmosphere
at a fairly constant speed; so that, clearly, the more slowly heat is
produced, the better opportunity has it to pass away, and the less of it
is left to collect in the material under consideration. During the action
of an acetylene generator, there is a current of gas constantly
travelling away from the carbide, there is vapour of water constantly
escaping with the gas, there are the walls of the generator itself
constantly exposed to the cooling action of the atmosphere, and there is
either a mass of calcium carbide or of water within the generator. It is
essential for good working that the temperature of both the acetylene and
the carbide shall be prevented from rising to any noteworthy extent;
while the amount of heat capable of being dissipated into the air through
the walls of the apparatus in a given time is narrowly limited, depending
upon the size and shape of the generator, and the temperature of the
surrounding air. If, then, a small, suitably designed generator is
working quite slowly, the loss of heat through the external walls of the
apparatus may easily be rapid enough to prevent the internal temperature
from rising objectionably high; but the larger the generator, and the
more rapidly it is evolving gas, the less does this become possible.
Since of the substances in or about a generator water is the one which
has by far the largest capacity for absorbing heat, and since it is the
only substance to which any necessary quantity of heat can be safely or
conveniently transmitted, it follows that the larger in size an acetylene
generator is, or the more rapidly that generator is made to deliver gas,
the more desirable is it to use water as the means for dissipating the
surplus heat, and the more necessary is it to employ an apparatus in
which water is in large chemical excess at the actual place of
decomposition.
The argument is sometimes advanced that an acetylene generator containing
carbide in excess will work satisfactorily without exhibiting an
undesirable rise in internal temperature, if the vessel holding the
carbide is merely surrounded by a large quantity of cold water. The idea
is that the heat evolved in that particular portion of the charge which
is suffering decomposition will be communicated with sufficient speed
throughout the whole mass of calcium carbide present, whence it will pass
through the walls of the containing vessel into the water all round.
Provided the generator is quite small, provided the carbide container is
so constructed as to possess the maximum of superficial area with the
minimum of cubical capacity (a geometrical form to which the sphere, and
in one direction the cylinder, are diametrically opposed), and provided
the walls of the container do not become coated internally or externally
with a coating of lime or water scale so as to diminish in heat-
transmitting power, an apparatus designed in the manner indicated is
undoubtedly free from grave objection; but immediately any of those
provisions is neglected, trouble is likely to ensue, for the heat will
not disappear from the place of actual reaction at the necessary speed.
Apparent proof that heat is not accumulating unduly in a water-jacketed
carbide container even when the generator is evolving gas at a fair speed
is easy to obtain; for if, as usually happens, the end of the container
through which the carbide is inserted is exposed to the air, the hand may
be placed upon it, and it will be found to be only slightly warm to the
touch. Such a test, however, is inconclusive, and frequently misleading,
because if more than a pound or two of carbide is present as an undivided
mass, and if water is allowed to attack one portion of it, that
particular portion may attain a high temperature while the rest is
comparatively cool: and if the bulk of the carbide is comparatively cool,
naturally the walls of the containing vessel themselves remain
practically unheated. Three causes work together to prevent this heat
being dissipated through the walls of the carbide vessel with sufficient
rapidity. In the first place, calcium carbide itself is a very bad
conductor of heat. So deficient in heat-conducting power is it that a
lump a few inches in diameter may be raised to redness in a gas flame at
one spot, and kept hot for some minutes, while the rest of the mass
remains sufficiently cool to be held comfortably in the fingers. In the
second place, commercial carbide exists in masses of highly irregular
shape, so that when they are packed into any vessel they only touch at
their angles and edges; and accordingly, even if the material were a
fairly good heat conductor of itself, the air or gas present between each
lump would act as an insulator, protecting the second piece from the heat
generated in the first. In the third place, the calcium hydroxide
produced as the by-product when calcium carbide is decomposed by water
occupies considerably more space than the original carbide--usually two
or three times as much space, the exact figures depending upon the
conditions in which it is formed--and therefore a carbide container
cannot advisedly be charged with more than one-third the quantity of
solid which it is apparently capable of holding. The remaining two-thirds
of the space is naturally full of air when the container is first put
into the generator, but the air is displaced by acetylene as soon as gas
production begins. Whether that space, however, is occupied by air, by
acetylene, or by a gradually growing loose mass of slaked lime, each
separate lump of hot carbide is isolated from its neighbours by a
material which is also a very bad heat conductor; and the heat has but
little opportunity of distributing itself evenly. Moreover, although iron
or steel is a notably better conductor of heat than any of the other
substances present in the carbide vessel, it is, as a metal, only a poor
conductor, being considerably inferior in this respect to copper. If heat
dissipation were the only point to be studied in the construction of an
acetylene apparatus, far better results might be obtained by the
employment of copper for the walls of the carbide container; and possibly
in that case a generator of considerable size, fitted with a water-
jacketed decomposing vessel, might be free from the trouble of
overheating. Nevertheless it will be seen in Chapter VI. that the use of
copper is not permissible for such purposes, its advantages as a good
conductor of heat being neutralised by its more important defects.
When suitable precautions are not taken to remove the heat liberated in
an acetylene apparatus, the temperature of the calcium carbide
occasionally rises to a remarkable degree. Investigating this point, Caro
has studied the phenomena of heat production in a "dipping" generator--
_i.e._, an apparatus in which a cage of carbide is alternately
immersed in and lifted out of a vessel containing water. Using a
generator designed to supply five burners, he has found a maximum
recording thermometer placed in the gas space of the apparatus to give
readings generally between 60° and 100° C.; but in two tests out of ten
he obtained temperatures of about 160° C. To determine the actual
temperature of the calcium carbide itself, he scattered amongst the
carbide charge fragments of different fusible metallic alloys which were
known to melt or soften at certain different temperatures. In all his ten
tests the alloys melting at 120° C. were fused completely; in two tests
other alloys melting at 216° and 240° C. showed signs of fusion; and in
one test an alloy melting at 280° C. began to soften. Working with an
experimental apparatus constructed on the "dripping" principle--
_i.e._, a generator in which water is allowed to fall in single
drops or as a fine stream upon a mass of carbide--with the deliberate
object of ascertaining the highest temperatures capable of production
when calcium carbide is decomposed in this particular fashion, and
employing for the measurement of the heat a Le Chatelier thermo-couple,
with its sensitive wires lying among the carbide lumps, Lewes has
observed a maximum temperature of 674° C. to be reached in 19 minutes
when water was dripped upon 227 grammes of carbide at a speed of about 8
grammes per minute. In other experiments he used a laboratory apparatus
designed upon the "dipping" principle, and found maximum temperatures, in
four different trials, of 703°, 734°, 754°, and 807° C., which were
reached in periods of time ranging from 12 to 17 minutes. Even allowing
for the greater delicacy of the instrument adopted by Lewes for measuring
the temperature in comparison with the device employed by Caro, there
still remains an astonishing difference between Caro's maximum of 280°
and Lewes' maximum of 807° C. The explanation of this discrepancy is to
be inferred from what has just been said. The generator used by Caro was
properly made of metal, was quite small in size, was properly designed
with some skill to prevent overheating as much as possible, and was
worked at the speed for which it was intended--in a word, it was as good
an apparatus as could be made of this particular type. Lewes' generator
was simply a piece of glass and metal, in which provisions to avoid
overheating were absent; and therefore the wide difference between the
temperatures noted does not suggest any inaccuracy of observation or
experiment, but shows what can be done to assist in the dissipation of
heat by careful arrangement of parts. The difference in temperature
between the acetylene and the carbide in Caro's test accentuates the
difficulty of gauging the heat in a carbide vessel by mere external
touch, and supplies experimental proof of the previous assertions as to
the low heat-conducting power of calcium carbide and of the gases of the
decomposing vessel. It must not be supposed that temperatures such as
Lewes has found ever occur in any commercial generator of reasonably good
design and careful construction; they must be regarded rather as
indications of what may happen in an acetylene apparatus when the
phenomena accompanying the evolution of gas are not understood by the
maker, and when all the precautions which can easily be taken to avoid
excessive heating have been omitted, either by building a generator with
carbide in excess too large in size, or by working it too rapidly, or
more generally by adopting a system of construction unsuited to the ends
in view. The fact, however, that Lewes has noted the production of a
temperature of 807° C. is important; because this figure is appreciably
above the point 780° C., at which acetylene decomposes into its elements
in the absence of air.
Nevertheless the production of a temperature somewhat exceeding 100° C.
among the lumps of carbide actually undergoing decomposition can hardly
be avoided in any practical generator. Based on a suggestion in the
"Report of the Committee on Acetylene Generators" which was issued by the
British Home Office in 1902, Fouché has proposed that 130° C., as
measured with the aid of fusible metallic rods, [Footnote: An alloy made
by melting together 55 parts by weight of commercial bismuth and 45 parts
of lead fuses at 127° C., and should be useful in performing the tests.]
should be considered the maximum permissible temperature in any part of a
generator working at full speed for a prolonged period of time. Fouché
adopts this figure on the ground that 130° C. sensibly corresponds with
the temperature at which a yellow substance is formed in a generator by a
process of polymerisation; and, referring to French conditions, states
that few actual apparatus permit the development of so high a
temperature. As a matter of fact, however, a fairly high temperature
among the carbide is less important than in the gas, and perhaps it would
be better to say that the temperature in any part of a generator occupied
by acetylene should not exceed 100° C. Fraenkel has carried out some
experiments upon the temperature of the acetylene immediately after
evolution in a water-to-carbide apparatus containing the carbide in a
subdivided receptacle, using an apparatus now frequently described as
belonging to the "drawer" system of construction. When a quantity of
about 7 lb. of carbide was distributed between 7 different cells of the
receptacle, each cell of which had a capacity of 25 fluid oz., and the
apparatus was caused to develop acetylene at the rate of 7 cubic feet per
hour, maximum thermometers placed immediately over the carbide in the
different cells gave readings of from 70° to 90° C., the average maximum
temperature being about 80° C. Hence the Austrian code of rules issued in
1905 governing the construction of acetylene apparatus contains a clause
to the effect that the temperature in the gas space of a generator must
never exceed 80° C.; whereas the corresponding Italian code contains a
similar stipulation, but quotes the maximum temperature as 100° C.
(_vide_ Chapter IV.).
It is now necessary to see why the production of an excessively high
temperature in an acetylene generator has to be avoided. It must be
avoided, because whenever the temperature in the immediate neighbourhood
of a mass of calcium carbide which is evolving acetylene under the attack
of water rises materially above the boiling-point of water, one or more
of three several objectionable effects is produced--(_a_) upon the
gas generated, (_b_) upon the carbide decomposed, and (_c_)
upon the general chemical reaction taking place.
It has been stated above that in moat generators when the action between
the carbide and the water is proceeding smoothly, it occurs according to
equation (2)--
(2) CaC_2 + 2H_2O = C_2H_2 + Ca(OH)_2
rather than in accordance with equation (1)--
(1) CaC_2 + H_2O = C_2H_2 + CaO.
This is because calcium oxide, or quicklime, the by-product in (1), has
considerable affinity for water, evolving a noteworthy quantity of heat
when it combines with one molecule of water to form one molecule of
calcium hydroxide, or slaked lime, the by-product in (2). If, then, a
small amount of water is added to a large amount of calcium carbide, the
corresponding quantity of acetylene may be liberated on the lines of
equation (1), and there will remain behind a mixture of unaltered calcium
carbide, together with a certain amount of calcium oxide. Inasmuch as
both these substances possess an affinity for water (setting heat free
when they combine with it), when a further limited amount of water is
introduced into the mixture some of it will probably be attracted to the
oxide instead of to the carbide present. It is well known that at
ordinary temperatures quicklime absorbs moisture, or combines with water,
to produce slaked lime; but it is equally well known that in a furnace,
at about a red heat, slaked lime gives up water and changes into
quicklime. The reaction, in fact, between calcium oxide and water is
reversible, and whether those substances combine or dissociate is simply
a question of temperature. In other words, as the temperature rises, the
heat of hydration of calcium oxide diminishes, and calcium hydroxide
becomes constantly a less stable material. If now it should happen that
the affinity between calcium carbide and water should not diminish, or
should diminish in a lower ratio than the affinity between calcium oxide
and water as the temperature of the mass rises from one cause or other,
it is conceivable that at a certain temperature calcium carbide might be
capable of withdrawing the water of hydration from the molecule of slaked
lime, converting the latter into quicklime, and liberating one molecule
of acetylene, thus--
(3) CaC_2 + Ca_2(OH) = C_2H_2 + 2CaO.
It has been proved that a reaction of this character does occur, the
temperature necessary to determine it being given by Lewes as from 420°
to 430° C., which is not much more than half that which he found in a
generator having carbide in excess, albeit one of extremely bad design.
Treating this reaction in the manner previously adopted, the thermo-
chemical phenomena of equation (3) are:
_Heat liberated._ | _Heat liberated._
|
Formation of 2CaO 290.0 | Formation of acetylene 58.1
| Decomposition of Ca(OH)_2 [1] 229.1
| Decomposition of carbide 3.9
Balance 1.1 |
______ | _____
|
291.1 | 291.1
[1 Footnote: Into its elements, Ca, O_2, and H_2; _cf._ footnote,
p: 31.]
Or, since the calcium hydroxide is only dehydrated without being
entirely decomposed, and only one molecule of water is broken up, it may
be written:
Formation of CaO 145.0 | Formation of acetylene 58.1
| Decomposition of Ca(OH)_2 15.1
| Decomposition of water 69.0
Balance 1.1 | Decomposition of carbide 3.9
_____ | _____
|
146.1 | 146.1
which comes to the same thing. Putting the matter in another shape, it
may be said that the reaction between calcium carbide and water is
exothermic, evolving either 14.0 or 29.1 calories according as the
byproduct is calcium oxide or solid calcium hydroxide; and therefore
either reaction proceeds without external assistance in the cold. The
reaction between carbide and slaked lime, however, is endothermic,
absorbing 1.1 calories; and therefore it requires external assistance
(presence of an elevated temperature) to start it, or continuous
introduction of heat (as from the reaction between the rest of the
carbide present and the water) to cause it to proceed. Of itself, and
were it not for the disadvantages attending the production of a
temperature remotely approaching 400° C. in an acetylene generator, which
disadvantages will be explained in the following paragraphs, there is no
particular reason why reaction (3) should not be permitted to occur, for
it involves (theoretically) no loss of acetylene, and no waste of calcium
carbide. Only one specific feature of the reaction has to be remembered,
and due practical allowance made for it. The reaction represented by
equation (2) proceeds almost instantaneously when the calcium carbide is
of ordinarily good quality, and the acetylene resulting therefrom is
wholly generated within a very few minutes. Equation (3), on the
contrary, consumes much time for its completion, and the gas
corresponding with it is evolved at a gradually diminishing speed which
may cause the reaction to continue for hours--a circumstance that may be
highly inconvenient or quite immaterial according to the design of the
apparatus. When, however, it is desired to construct an automatic
acetylene generator, _i.e._, an apparatus in which the quantity of
gas liberated has to be controlled to suit the requirements of any
indefinite number of burners in use on different occasions, equation (3)
becomes a very important factor in the case. To determine the normal
reaction (No. 2) of an acetylene generator, 64 parts by weight of calcium
carbide must react with 36 parts of water to yield 26 parts by weight of
acetylene, and apparently both carbide and water are entirely consumed;
but if opportunity is given for the occurrence of reaction (3), another
64 parts by weight of carbide may be attacked, without the addition of
any more water, producing, inevitably, another 26 parts of acetylene. If,
then, water is in chemical excess in the generator, all the calcium
carbide present will be decomposed according to equation (2), and the
action will take place without delay; after a few minutes' interval the
whole of the acetylene capable of liberation will have been evolved, and
nothing further can possibly happen until another charge of carbide is
inserted in the apparatus. If, on the other hand, calcium carbide is in
chemical excess in the generator, all the water run in will be consumed
according to equation (2), and this action will again take place without
delay; but unless the temperature of the residual carbide has been kept
well below 400° C., a further evolution of gas will occur which will not
cease for an indeterminate period of time, and which, by strict theory,
given the necessary conditions, might continue until a second volume of
acetylene equal to that liberated at first had been set free. In practice
this phenomenon of a secondary production of gas, which is known as
"after-generation," is regularly met with in all generators where the
carbide is in excess of the water added; but the amount of acetylene so
evolved rarely exceeds one-quarter or one-third of the main make. The
actual amount evolved and the rate of evolution depend, not merely upon
the quantity of undecomposed carbide still remaining in contact with the
damp lime, but also upon the rapidity with which carbide naturally
decomposes in presence of liquid water, and the size of the lumps. Where
"after-generation" is caused by the ascent of water vapour round lumps of
carbide, the volume of gas produced in a given interval of time is
largely governed by the temperature prevailing and the shape of the
apparatus. It is evident that even copious "after-generation" is a matter
of no consequence in any generator provided with a holder to store the
gas, assuming that by some trustworthy device the addition of water is
stopped by the time that the holder is two-thirds or three-quarters full.
In the absence of a holder, or if the holder fitted is too small to serve
its proper purpose, "aftergeneration" is extremely troublesome and
sometimes dangerous, but a full discussion of this subject must be
postponed to the next chapter.
EFFECT OF HEAT ON ACETYLENE.--The effect of excessive retention of heat
in an acetylene generator upon the gas itself is very marked, as
acetylene begins spontaneously to suffer change, and to be converted into
other compounds at elevated temperatures. Being a purely chemical
phenomenon, the behaviour of acetylene when exposed to heat will be fully
discussed in Chapter VI. when the properties of the gas are being
systematically dealt with. Here it will be sufficient to assume that the
character of the changes taking place is understood, and only the
practical results of those changes as affecting the various components of
an acetylene installation have to be studied. According to Lewes,
acetylene commences to "polymerise" at a temperature of about 600° C.,
when it is converted into other hydrocarbons having the same percentage
composition, but containing more atoms of carbon and hydrogen in their
molecules. The formula of acetylene is C_2H_2 which means that 2 atoms of
carbon and 2 atoms of hydrogen unite to form 1 molecule of acetylene, a
body evidently containing roughly 92.3 per cent. by weight of carbon and
7.7 per cent. by weight of hydrogen. One of the most noteworthy
substances produced by the polymerisation of acetylene is benzene, the
formula of which is C_6H_6, and this is formed in the manner indicated by
the equation--
(4) 3C_2H_2 = C_6H_6.
Now benzene also contains 92.3 per cent. of carbon and 7.7 per cent. by
weight of hydrogen in its composition, but its molecule contains 6 atoms
of each element. When the chemical formula representing a compound body
indicates a substance which is, or can be obtained as, a gas or vapour,
it convoys another idea over and above those mentioned on a previous
page. The formula "C_2H_2," for example, means 1 molecule, or 26 parts by
weight of acetylene, just as "H_2" means 1 molecule, or 2 parts by weight
of hydrogen; but both formulæ also mean equal parts by volume of the
respective substances, and since H_2 must mean 2 volumes, being twice H,
which is manifestly 1, C_2H_2 must mean 2 volumes of acetylene as well.
Thus equation (4) states that 6 volumes of acetylene, or 3 x 26 parts by
weight, unite to form 2 volumes of benzene, or 78 parts by weight. If
these hydrocarbons are burnt in air, both are indifferently converted
into carbon dioxide (carbonic acid gas) and water vapour; and, neglecting
for the sake of simplicity the nitrogen of the atmosphere, the processes
may be shown thus:
(5) 2C_2H_2 + 5O_2 = 4CO_2 + 2H_2O.
(6) 2C_6H_6 + 15O_2 = 12CO_2 + 6H_2O.
Equation (5) shows that 4 volumes of acetylene combine with 10 volumes of
oxygen to produce 8 volumes of carbon dioxide and 4 of water vapour;
while equation (6) indicates that 4 volumes of benzene combine with 30
volumes of oxygen to yield 24 volumes of carbon dioxide and 12 of water
vapour. Two parts by volume of acetylene therefore require 5 parts by
volume of oxygen for perfect combustion, whereas two parts by volume of
benzene need 15--_i.e._, exactly three times as much. In order to
work satisfactorily, and to develop the maximum of illuminating power
from any kind of gas consumed, a gas-burner has to be designed with
considerable skill so as to attract to the base of the flame precisely
that volume of air which contains the quantity of oxygen necessary to
insure complete combustion, for an excess of air in a flame is only less
objectionable than a deficiency thereof. If, then, an acetylene burner is
properly constructed, as most modern ones are, it draws into the flame
air corresponding with two and a half volumes of oxygen for every one
volume of acetylene passing from the jets; whereas if it were intended
for the combustion of benzene vapour it would have to attract three times
that quantity. Since any flame supplied with too little air tends to emit
free carbon or soot, it follows that any well-made acetylene burner
delivering a gas containing benzene vapour will yield a more or lens
smoky flame according to the proportion of benzene in the acetylene.
Moreover, at ordinary temperatures benzene is a liquid, for it boils at
81° C., and although, as was explained above in the case of water, it is
capable of remaining in the state of vapour far below its boiling-point
so long as it is suspended in a sufficiency of some permanent gas like
acetylene, if the proportion of vapour in the gas at any given
temperature exceeds a certain amount the excess will be precipitated in
the liquid form; while as the temperature falls the proportion of vapour
which can be retained in a given volume of gas also diminishes to a
noteworthy extent. Should any liquid, be it water or benzene, or any
other substance, separate from the acetylene under the influence of cold
while the gas is passing through pipes, the liquid will run downwards to
the lowest points in those pipes; and unless due precautions are taken,
by the insertion of draw-off cocks, collecting wells, or the like, to
withdraw the deposited water or other liquid, it will accumulate in all
bends, angles, and dips till the pipes are partly or completely sealed
against the passage of gas, and the lights will either "jump" or be
extinguished altogether. In the specific case of an acetylene generator
this trouble is very likely to arise, even when the gas is not heated
sufficiently during evolution for polymerisation to occur and benzene or
other liquid hydrocarbons to be formed, because any excess of water
present in the decomposing vessel is liable to be vaporised by the heat
of the reaction--as already stated it is desirable that water shall be so
vaporised--and will remain safely vaporised as long as the pipes are kept
warm inside or near the generator; but directly the pipes pass away from
the hot generator the cooling action of the air begins, and some liquid
water will be immediately produced. Like the phenomenon of after-
generation, this equally inevitable phenomenon of water condensation will
be either an inconvenience or source of positive danger, or will be a
matter of no consequence whatever, simply as the whole acetylene
installation, including the service-pipes, is ignorantly or intelligently
built.
As long as nothing but pure polymerisation happens to the acetylene, as
long, that is to say, as it is merely converted into other hydrocarbons
also having the general formula C_(2n)H_(2n), no harm will be done to the
gas as regards illuminating power, for benzene burns with a still more
luminous flame than acetylene itself; nor will any injury result to the
gas if it is required for combustion in heating or cooking stoves beyond
the fact that the burners, luminous or atmospheric, will be delivering a
material for the consumption of which they are not properly designed. But
if the temperature should rise much above the point at which benzene is
the most conspicuous product of polymerisation, other far more
complicated changes occur, and harmful effects may be produced in two
separate ways. Some of the new hydrocarbons formed may interact to yield
a mixture of one or more other hydrocarbons containing a higher
proportion of carbon than that which is present in acetylene and benzene,
together with a corresponding proportion of free hydrogen; the former
will probably be either liquids or solids, while the latter burns with a
perfectly non-luminous flame. Thus the quantity of gas evolved from the
carbide and passed into the holder is less than it should be, owing to
the condensation of its non-gaseous constituents. To quote an instance of
this, Haber has found 15 litres of acetylene to be reduced in volume to
10 litres when the gas was heated to 638° C. By other changes, some
"saturated hydrocarbons," _i.e._, bodies having the general formula
C_nH_(2n+2), of which methane or marsh-gas, CH_4 is the best known, may
be produced; and those all possess lower illuminating powers than
acetylene. In two of those experiments already described, where Lewes
observed maximum temperatures ranging from 703° to 807° C., samples of
the gas which issued when the heat was greatest were submitted to
chemical analysis, and their illuminating powers were determined. The
figures he gives are as follows:
I. II.
Per Cent. Per Cent.
Acetylene 70.0 69.7
Saturated hydrocarbons 11.3 11.4
Hydrogen 18.7 18.9
_____ _____
100.0 100.0
The average illuminating power of these mixed gases is about 126 candles
per 5 cubic feet, whereas that of pure acetylene burnt under good
laboratory conditions is 240 candles per 5 cubic feet. The product, it
will be seen, had lost almost exactly 50 per cent. of its value as an
illuminant, owing to the excessive heating to which it had been, exposed.
Some of the liquid hydrocarbons formed at the same time are not limpid
fluids like benzene, which is less viscous than water, but are thick oily
substances, or even tars. They therefore tend to block the tubes of the
apparatus with great persistence, while the tar adheres to the calcium
carbide and causes its further attack by water to be very irregular, or
even altogether impossible. In some of the very badly designed generators
of a few years back this tarry matter was distinctly visible when the
apparatus was disconnected for recharging, for the spent carbide was
exceptionally yellow, brown, or blackish in colour, [Footnote: As will be
pointed out later, the colour of the spent lime cannot always be employed
as a means for judging whether overheating has occurred in a generator.]
and the odour of tar was as noticeable as that of crude acetylene.
There is another effect of heat upon acetylene, more calculated to be
dangerous than any of those just mentioned, which must not be lost sight
of. Being an endothermic substance, acetylene is prone to decompose into
its elements--
(7) C_2H_2 -> C_2 + H_2
whenever it has the opportunity; and the opportunity arrives if the
temperature of the gas risen to 780° C., or if the pressure under which
the gas is stored exceeds two atmospheres absolute (roughly 30 lb. per
square inch). It decomposes, be it carefully understood, in the complete
absence of air, directly the smallest spark of red-hot material or of
electricity, or directly a gentle shock, such as that of a fall or blow
on the vessel holding it, is applied to any volume of acetylene existing
at a temperature exceeding 780° or at a gross pressure of 30 lb. per
square inch; and however large that volume may be, unless it is contained
in tubes of very small diameter, as will appear hereafter, the
decomposition or dissociation into its elements will extend throughout
the whole of the gas. Equation (7) states that 2 volumes of acetylene
yield 2 volumes of hydrogen and a quantity of carbon which would measure
2 volumes were it obtained in the state of gas, but which, being a solid,
occupies a space that may be neglected. Apparently, therefore, the
dissociation of acetylene involves no alteration in volume, and should
not exhibit explosive effects. This is erroneous, because 2 volumes of
acetylene only yield exactly 2 volumes of hydrogen when both gases are
measured at the same temperature, and all gases increase in volume as
their temperature rises. As acetylene is endothermic and evolves much
heat on decomposition, and as that heat must primarily be communicated to
the hydrogen, it follows that the latter must be much hotter than the
original acetylene; the hydrogen accordingly strives to fill a much
larger space than that occupied by the undecomposed gas, and if that gas
is contained in a closed vessel, considerable internal pressure will be
set up, which may or may not cause the vessel to burst.
What has been said in the preceding paragraph about the temperature at
which acetylene decomposes is only true when the gas is free from any
notable quantity of air. In presence of air, acetylene inflames at a much
lower temperature, viz., 480° C. In a manner precisely similar to that of
all other combustible gases, if a stream of acetylene issues into the
atmosphere, as from the orifices of a burner, the gas catches fire and
burns quietly directly any substance having a temperature of 480° C. or
upwards is brought near it; but if acetylene in bulk is mixed with the
necessary quantity of air to support combustion, and any object exceeding
480° C. in temperature comes in contact with it, the oxidation of the
hydrocarbon proceeds at such a high rate of speed as to be termed an
explosion. The proportion of air needed to support combustion varies with
every combustible material within known limits (_cf._ Chapter VI.),
and according to Eitner the smallest quantity of air required to make
acetylene burn or explode, as the case may be, is 25 per cent. If, by
ignorant design or by careless manipulation, the first batches of
acetylene evolved from a freshly charged generator should contain more
than 25 per cent. of air; or if in the inauguration of a new installation
the air should not be swept out of the pipes, and the first makes of gas
should become diluted with 25 to 50 per cent. of air, any glowing body
whose temperature exceeds 480° C. will fire the gas; and, as in the
former instance, the flame will extend all through the mass of acetylene
with disastrous violence and at enormous speed unless the gas is stored
in narrow pipes of extremely small diameter. Three practical lessons are
to be learnt from this circumstance: first, tobacco-smoking must never be
permitted in any building where an escape of raw acetylene is possible,
because the temperature of a lighted cigar, &c., exceeds 480° C.;
secondly, a light must never be applied to a pipe delivering acetylene
until a proper acetylene burner has been screwed into the aperture;
thirdly, if any appreciable amount of acetylene is present in the air, no
operation should be performed upon any portion of an acetylene plant
which involves such processes as scraping or chipping with the aid of a
steel tool or shovel. If, for example, the iron or stoneware sludge-pipe
is choked, or the interior of the dismantled generator is blocked, and
attempts are made to remove the obstruction with a hard steel tool, a
spark is very likely to be formed which, granting the existence of
sufficient acetylene in the air, is perfectly able to fire the gas. For
all such purposes wooden implements only are best employed; but the
remark does not apply to the hand-charging of a carbide-to-water
generator through its proper shoot. Before passing to another subject, it
may be remarked that a quantity of air far less than that which causes
acetylene to become dangerous is objectionable, as its presence is apt to
reduce the illuminating power of the gas unduly.
EFFECT OF HEAT ON CARBIDE.--Chemically speaking, no amount of heat
possible of attainment in the worst acetylene generator can affect
calcium carbide in the slightest degree, because that substance may be
raised to almost any temperature short of those distinguishing the
electric furnace, without suffering any change or deterioration. In the
absence of water, calcium carbide is as inert a substance as can well be
imagined: it cannot be made to catch fire, for it is absolutely
incombustible, and it can be heated in any ordinary flame for reasonable
periods of time, or thrown into any non-electrical furnace without
suffering in the least. But in presence of water, or of any liquid
containing water, matters are different. If the temperature of an
acetylene generator rises to such an extent that part of the gas is
polymerised into tar, that tar naturally tends to coat the residual
carbide lumps, and, being greasy in character, more or less completely
protects the interior from further attack. Action of this nature not only
means that the acetylene is diminished in quantity and quality by partial
decomposition, but it also means that the make is smaller owing to
imperfect decomposition of the carbide: while over and above this is the
liability to nuisance or danger when a mass of solid residue containing
some unaltered calcium carbide is removed from the apparatus and thrown
away. In fact, whenever the residue of a generator is not so saturated
with excess of water as to be of a creamy consistency, it should be put
into an uncovered vessel in the open air, and treated with some ten times
its volume of water before being run into any drain or closed pipe where
an accumulation of acetylene may occur. Even at temperatures far below
those needed to determine a production of tar or an oily coating on the
carbide, if water attacks an excess of calcium carbide somewhat rapidly,
there is a marked tendency for the carbide to be "baked" by the heat
produced; the slaked lime adhering to the lumps as a hard skin which
greatly retards the penetration of more water to the interior.
COLOUR OF SPENT CARBIDE.--In the early days of the industry, it was
frequently taken for granted that any degradation in the colour of the
spent lime left in an acetylene generator was proof that overheating had
taken place during the decomposition of the carbide. Since both calcium
oxide and hydroxide are white substances, it was thought that a brownish,
greyish, or blackish residue must necessarily point to incipient
polymerisation of the gas. This view would be correct if calcium carbide
were prepared in a state of chemical purity, for it also is a white body.
Commercial carbide, however, is not pure; it usually contains some
foreign matter which tints the residue remaining after gasification. When
a manufacturer strives to give his carbide the highest gas-making power
possible he frequently increases the proportion of carbon in the charge
submitted to electric smelting, until a small excess is reached, which
remains in the free state amongst the finished carbide. After
decomposition the fine particles of carbon stain the moist lime a bluish
grey tint, the depth of shade manifestly depending upon the amount
present. If such a sludge is copiously diluted with water, particles of
carbon having the appearance and gritty or flaky nature of coke often
rise to the surface or fall to the bottom of the liquid; whence they can
easily be picked out and identified as pure or impure carbon by simple
tests. Similarly the lime or carbon put into the electric furnace may
contain small quantities of compounds which are naturally coloured; and
which, reappearing in the sludge either in their original or in a
different state of combination, confer upon the sludge their
characteristic tinge. Spent lime of a yellowish brown colour is
frequently to be met with in circumstances that are clearly no reproach
to the generator. Doubtless the tint is due to the presence of some
coloured metallic oxide or other compound which has escaped reduction in
the electric furnace. The colour which the residual lime afterwards
assumes may not be noticeable in the dry carbide before decomposition,
either because some change in the colour-giving impurity takes place
during the chemical reactions in the generator or because the tint is
simply masked by the greyish white of the carbide and its free carbon.
Hence it follows that a bad colour in the waste lime removed from a
generator only points to overheating and polymerisation of the acetylene
when corroborative evidence is obtained--such as a distinct tarry smell,
the actual discovery of oily or tarry matters elsewhere, or a grave
reduction in the illuminating power of the gas.
MAXIMUM ATTAINABLE TEMPERATURES.--In order to discover the maximum
temperature which can be reached in or about an acetylene generator when
an apparatus belonging to one of the best types is fed at a proper rate
with calcium carbide in lumps of the most suitable size, the following
calculation may be made. In the first place, it will be assumed that no
loss of heat by radiation occurs from the walls of the generator;
secondly, the small quantity of heat taken up by the calcium hydroxide
produced will be ignored; and, thirdly, the specific heat of acetylene
will be assumed to be 0.25, which is about its most probable value. Now,
a hand-fed carbide-to-water generator will work with half a gallon of
water for every 1 lb. of carbide decomposed, quantities which correspond
with 320 grammes of water per 64 grammes (1 molecular weight) of carbide.
Of those 320 grammes of water, 18 are chemically destroyed, leaving 302.
The decomposition of 64 grammes of commercial carbide evolves 28 large
calories of heat. Assuming all the heat to be absorbed by the water, 28
calories would raise 302 grammes through (28 X 1000 / 302) = 93° C.,
_i.e._, from 44.6° F. to the boiling-point. Assuming all the heat to
be communicated to the acetylene, those 28 calories would raise the 26
grammes of gas liberated through (28 X 1000 / 26 / 0.25) = 4308° C., if
that were possible. But if, as would actually be the case, the heat were
distributed uniformly amongst the 302 grammes of water and the 20 grammes
of acetylene, both gas and water would be raised through the same number
of degrees, viz., 90.8° C. [Footnote: Let x = the number of large
calories absorbed by the water; then 28 - x = those taken up by the gas.
Then--
1000x / 302 = 1000 (28 - x) / (26 X 0.25)
whence x = 27.41; and 28 - x = 0.59.
Therefore, for water, the rise in temperature is--
27.41 X 1000 / 302 = 90.8° C.;
and for acetylene the rise is--
0.59 X 1000 / 26 / 0.25 = 90.8° C.]
If the generator were designed on lines to satisfy the United States Fire
Underwriters, it would contain 8.33 lb. of water to every 1 lb. of
carbide attacked; identical calculations then showing that the original
temperature of the water and gas would be raised through 53.7° C.
Provided the carbide is not charged into such an apparatus in lumps of
too large a size, nor at too high a rate, there will be no appreciable
amount of local overheating developed; and nowhere, therefore, will the
rise in temperature exceed 91° in the first instance, or 54° C. in the
second. Indeed it will be considerably smaller than this, because a large
proportion of the heat evolved will be lost by radiation through the
generator walls, while another portion will be converted from sensible
into latent heat by causing part of the water to pass off as vapour with
the acetylene.
EFFECT OF HIGH TEMPERATURES ON GENERATORS.--As the temperature amongst
the carbide in any generator in which water is not present in large
excess may easily reach 200° C. or upwards, no material ought to be
employed in the construction of such generators which is not competent to
withstand a considerable amount of heat in perfect safety. The ordinary
varieties of soft solder applied with the bitt in all kinds of light
metal-work usually melt, according to their composition, at about 180°
C.; and therefore this method of making joints is only suitable for
objects that are never raised appreciably in temperature above the
boiling-point of water. No joint in an acetylene generator, the partial
or complete failure of which would radically affect the behaviour of the
apparatus, by permitting the charges of carbide and of water to come into
contact at an abnormal rate of speed, by allowing the acetylene to escape
directly through the crack into the atmosphere, or by enabling the water
to run out of the seal of any vessel containing gas so as to set up a
free communication between that vessel and the air, ought ever to be made
of soft solder--every joint of this character should be constructed
either by riveting, by bolting, or by doubly folding the metal sheets.
Apparently, a joint constantly immersed in water on one side cannot rise
in temperature above the boiling-point of the liquid, even when its other
side is heated strongly; but since, even if a generator is not charged
with naturally hard water, its fluid contents soon become "hard" by
dissolution of lime, there is always a liability to the deposition of
water scale over the joint. Such water scale is a very bad heat
conductor, as is seen in steam boilers, so that a seam coated with an
exceedingly thin layer of scale, and heated sharply on one side, will
rise above the boiling-point of water even if the liquid on its opposite
side is ice-cold. For a while the film of scale may be quite water-tight,
but after it has been heated by contact with the hot metal several times
it becomes brittle and cracks without warning. But there is a more
important reason for avoiding the use of plumbers' solder. It might seem
that as the natural hard, protective skin of the metal is liable to be
injured or removed by the bending or by the drilling or punching which
precedes the insertion of the rivets or studs, an application of soft
solder to such a joint should be advantageous. This is not true because
of the influence of galvanic action. As all soft solders consist largely
of lead, if a joint is soldered, a "galvanic couple" of lead and iron, or
of lead and zinc (when the apparatus is built of galvanised steel), is
exposed to the liquid bathing it; and since in both cases the lead is
highly electro-negative to the iron or zinc, it is the iron or zinc which
suffers attack, assuming the liquid to possess any corrosive properties
whatever. Galvanised iron which has been injured during the joint-making
presents a zinc-iron couple to the water, but the zinc protects the iron;
if a lead solder is present, the iron will begin to corrode immediately
the zinc has disappeared. In the absence of lead it is the less important
metal, but in the presence of lead it is the more important (the
foundation) metal which is the soluble element of the couple. Where
practicable, joints in an acetylene generator may safely be made by
welding or by autogenous soldering ("burning"), because no other metal is
introduced into the system; any other process, except that of riveting or
folding, only hastens destruction of the plant. The ideal method of
making joints about an acetylene generator is manifestly that of
autogenous soldering, because, as will appear in Chapter IX. of this
book, the most convenient and efficient apparatus for performing the
operation is the oxy-acetylene blow-pipe, which can be employed so as to
convert two separate pieces of similar metal into one homogeneous whole.
In less critical situations in an acetylene plant, such as the partitions
of a carbide container, &c., where the collapse of the seam or joint
would not be followed by any of the effects previously suggested, there
is less cause for prohibiting the use of unfortified solder; but even
here, two or three rivets, just sufficient to hold the metal in position
if the solder should give way, are advisedly put into all apparatus. In
other portions of an acetylene installation where a merely soldered joint
is exposed to warm damp gas which is in process of cooling, instead of
being bathed in hard water, an equal, though totally dissimilar, danger
is courted. The main constituent of such solders that are capable of
being applied with the bitt is lead; lead is distinctly soluble in soft
or pure water; and the water which separates by condensation out of a
warm damp gas is absolutely soft, for it has been distilled. If
condensation takes place at or near a soldered joint in such a way that
water trickles over the solder, by slow degrees the metallic lead will be
dissolved and removed, and eventually a time will come when the joint is
no longer tight to gas. In fact, if an acetylene installation is of more
than very small dimensions, _e.g._, when it is intended to supply
any building as large as, or larger than, the average country residence,
if it is to give satisfaction to both constructor and purchaser by being
quite trustworthy and, possessed of a due lease of life, say ten or
fifteen years, it must be built of stouter materials than the light
sheets which alone are suitable for manipulation with the soldering-iron
or for bending in the ordinary type of metal press. Sound cast-iron,
heavy sheet-metal, or light boiler-plate is the proper substance of which
to construct all the important parts of a generator, and the joints in
wrought metal must be riveted and caulked or soldered autogeneously as
mentioned above. So built, the installation becomes much more costly to
lay down than an apparatus composed of tinplate, zinc, or thin galvanised
iron, but it will prove more economical in the long run. It is not too
much to say that if ignorant and short-sighted makers in the earliest
days of the acetylene industry had not recommended and supplied to their
customers lightly built apparatus which has in many instances already
begun to give trouble, to need repairs, and to fail by thorough
corrosion--apparatus which frequently had nothing but cheapness in its
favour--the use of the gas would have spread more rapidly than it has
done, and the public would not now be hearing of partial or complete
failures of acetylene installations. Each of these failures, whether
accompanied by explosions and injury to persons or not, acts more
powerfully to restrain a possible new customer from adopting the
acetylene light, than several wholly successful plants urge him to take
it up; for the average member of the public is not in a position to
distinguish properly between the collapse of a certain generator owing to
defective design or construction (which reflects no discredit upon the
gas itself), and the failure of acetylene to show in practice those
advantages that have been ascribed to it. One peculiar and noteworthy
feature of acetylene, often overlooked, is that the apparatus is
constructed by men who may have been accustomed to gas-making plant all
their lives, and who may understand by mere habit how to superintend a
chemical operation; but the same apparatus is used by persons who
generally have no special acquaintance with such subjects, and who, very
possibly, have not even burnt coal-gas at any period of their lives.
Hence it happens that when some thoughtless action on the part of the
country attendant of an acetylene apparatus is followed by an escape of
gas from the generator, and by an accumulation of that gas in the house
where the plant is situated, or when, in disregard of rules, he takes a
naked light into the house and an explosion follows, the builder
dismisses the episode as a piece of stupidity or wilful misbehaviour for
which he can in nowise be held morally responsible; whereas the builder
himself is to blame for designing an apparatus from which an escape of
gas can be accompanied by sensible risks to property or life. However
unpalatable this assertion may be, its truth cannot be controverted;
because, short of criminal intention or insanity on the part of the
attendant, it is in the first place a mere matter of knowledge and skill
so to construct an acetylene plant that an escape of gas is extremely
unlikely, even when the apparatus is opened for recharging, or when it is
manipulated wrongly; and in the second place, it is easy so to arrange
the plant that any disturbance of its functions which may occur shall be
followed by an immediate removal of the surplus gas into a place of
complete safety outside and above the generator-house.
GENERATION AT LOW TEMPERATURES.--In all that has been said hitherto about
the reaction between calcium carbide and water being instantaneous, it
has been assumed that the two substances are brought together at or about
the usual temperature of an occupied room, _i.e._, 15 degrees C. If,
however, the temperature is materially lower than this, the speed of the
reaction falls off, until at -5 degrees C., supposing the water still to
remain liquid, evolution of acetylene practically ceases. Even at the
freezing-point of pure water gas is produced but slowly; and if a lump of
carbide is thrown on to a block of ice, decomposition proceeds so gently
that the liberated acetylene may be ignited to form a kind of torch,
while heat is generated with insufficient rapidity to cause the carbide
to sink into the block. This fact has very important bearings upon the
manipulation of an acetylene generator in winter time. It is evident that
unless precautions are taken those portions of an apparatus which contain
water are liable to freeze on a cold night; because, even if the
generator has been at work producing gas (and consequently evolving heat)
till late in the evening, the surplus heat stored in the plant may escape
into the atmosphere long before more acetylene has to be made, and
obviously while frost is still reigning in the neighbourhood. If the
water freezes in the water store, in the pipes leading therefrom, in the
holder seal, or in the actual decomposing chamber, a fresh batch of gas
is either totally incapable of production, because the water cannot be
brought into contact with the calcium carbide in the apparatus, or it can
only be generated with excessive slowness because the carbide introduced
falls on to solid ice. Theoretically, too, there is a possibility that
some portion of the apparatus--a pipe in particular--may be burst by the
freezing, owing to the irresistible force with which water expands when
it changes into the solid condition. Probably this last contingency,
clearly accompanied as it would be by grave risk, is somewhat remote, all
the plant being constructed of elastic material; but in practice even a
simple interference with the functions of a generator by freezing,
ideally of no special moment, is highly dangerous, because of the great
likelihood that hurried and wholly improper attempts to thaw it will be
made by the attendant. As it has been well known for many years that the
solidifying point of water can be lowered to almost any degree below
normal freezing by dissolving in it certain salts in definite
proportions, one of the first methods suggested for preventing the
formation of ice in an acetylene generator was to employ such a salt,
using, in fact, for the decomposition of the carbide some saline solution
which remains liquid below the minimum night temperature of the winter
season. Such a process, however, has proved unsuitable for the purpose in
view; and the explanation of that fact is found in what has just been
stated: the "water" of the generator may admittedly be safely maintained
in the fluid state, but from so cold a liquid acetylene will not be
generated smoothly, if at all. Moreover, were it not so, a process of
this character is unnecessarily expensive, although suitable salts are
very cheap, for the water of the generator is constantly being consumed,
[Footnote: It has already been said that most generators "consume" a much
larger volume of water than the amount corresponding with the chemical
reaction involved: the excess of water passing into the sludge or by-
product. Thus a considerable quantity of any anti-freezing agent must be
thrown aside each time the apparatus is cleaned out or its fluid contents
are run off.] and as constantly needs renewal; which means that a fresh
batch of salt would be required every time the apparatus was recharged,
so long as frost existed or might be expected. A somewhat different
condition obtains in the holder of an acetylene installation. Here,
whenever the holder is a separate item in the plant, not constituting a
portion of the generating apparatus, the water which forms the seal of a
rising holder, or which fills half the space of a displacement holder,
lasts indefinitely; and it behaves equally well, whatever its temperature
may be, so long as it retains a fluid state. This matter will be
discussed with greater detail at the end of Chapter III. At present the
point to be insisted on is that the temperature in any constituent of an
acetylene installation which contains water must not be permitted to fall
to the freezing-point; while the water actually used for decomposition
must be kept well above that temperature.
GENERATION AT HIGH TEMPERATURES.--At temperatures largely exceeding those
of the atmosphere, the reaction between calcium carbide and water tends
to become irregular; while at a red heat steam acts very slowly upon
carbide, evolving a mixture of acetylene and hydrogen in place of pure
acetylene. But since at pressures which do not materially exceed that of
the atmosphere, water changes into vapour at 100° C., above that
temperature there can be no question of a reaction between carbide and
liquid water. Moreover, as has been pointed out, steam or water vapour
will continue to exist as such at temperatures even as low as the
freezing-point so long as the vapour is suspended among the particles of
a permanent gas. Between calcium carbide and water vapour a double
decomposition occurs chemically identical with that between carbide and
liquid water; but the physical effect of the reaction and its practical
bearings are considerably modified. The quantity of heat liberated when
30 parts by weight of steam react with 64 parts of calcium carbide should
be essentially unaltered from that evolved when the reagent is in the
liquid state; but the temperature likely to be attained when the speed of
reaction remains the same as before will be considerably higher for two
conspicuous reasons. In the first place, the specific heat of steam in is
only 0.48, while that of liquid water is 1.0. Hence, the quantity of heat
which is sufficient to raise the temperature of a given weight of liquid
water through _n_ thermometric degrees, will raise the temperature
of the same weight of water vapour through rather more than 2 _n_
degrees. In the second place, that relatively large quantity of heat
which in the case of liquid water merely changes the liquid into a
vapour, becoming "latent" or otherwise unrecognisable, and which, as
already shown, forms roughly five-sixths of the total heat needed to
convert cold water into steam, has no analogue if the water has
previously been vaporised by other means; and therefore the whole of the
heat supplied to water vapour raises its sensible temperature, as
indicated by the thermometer. Thus it appears that, except for the
sufficient amount of cooling that can be applied to a large vessel
containing carbide by surrounding it with a water jacket, there is no way
of governing its temperature satisfactorily if water vapour is allowed to
act upon a mass of carbide--assuming, of course, that the reaction
proceeds at any moderate speed, _e.g._, at a rate much above that
required to supply one or two burners with gas.
The decomposition which with perfect chemical accuracy has been stated to
occur quantitatively between 36 parts by weight, of water and 64 parts of
calcium carbide scarcely ever takes place in so simple a fashion in an
actual generator. Owing to the heat developed when carbide is in excess,
about half the water is converted into vapour; and so the reaction
proceeds in two stages: half the water added reacting with the carbide as
a liquid, the other half, in a state of vapour, afterwards reacting
similarly, [Footnote: This secondary reaction is manifestly only another
variety of the phenomenon known as "after-generation" (cf. _ante_).
After-generation is possible between calcium carbide and mechanically
damp slaked lime, between carbide and damp gas, or between carbide and
calcium hydroxide, as opportunity shall serve. In all cases the carbide
must be in excess.] or hardly reacting at all, as the case may be.
Suppose a vessel, A B, somewhat cylindrical in shape, is charged with
carbide, and that water is admitted at the end called A. Suppose now (1)
that the exit for gas is at the opposite end, B. As the lumps near A are
attacked by half the liquid introduced, while the other half is changed
into steam, a current, of acetylene and water vapour travels over the
charge lying between the decomposing spot and the end B. During its
passage the second half of the water, as vapour, reacts with the excess
of carbide, the first make of acetylene being dried, and more gas being
produced. Thus a second quantity of heat is developed, equal by theory to
that previously evolved; but a second elevation in temperature, far more
serious, and far less under control, than the former also occurs; and
this is easily sufficient to determine some of those undesirable effects
already described. Digressing for a moment, it may be admitted that the
desiccation of the acetylene produced in this manner is beneficial, even
necessary; but the advantages of drying the gas at this period of its
treatment are outweighed by the concomitant disadvantages and by the
later inevitable remoistening thereof. Suppose now (2) that both the
water inlet and the gas exit of the carbide cylinder are at the same end,
A. Again half the added water, as liquid, reacts with the carbide it
first encounters, but the hot stream of damp gas is not permitted to
travel over the rest of the lumps extending towards B: it is forced to
return upon its steps, leaving B practically untouched. The gas
accordingly escapes from the cylinder at A still loaded with water
vapour, and for a given weight of water introduced much less acetylene is
evolved than in the former case. The gas, too, needs drying somewhere
else in the plant; but these defects are preferable to the apparent
superiority of the first process because overheating is, or can be, more
thoroughly guarded against.
PRESSURE IN GENERATORS.--Inasmuch as acetylene is prone to dissociate or
decompose into its elements spontaneously whenever its pressure reaches 2
atmospheres or 30 lb. per square inch, as well as when its temperature at
atmospheric pressure attains 780° C., no pressure approaching that of 2
atmospheres is permissible in the generator. A due observance of this
rule, however, unlike a proper maintenance of a low temperature in an
acetylene apparatus, is perfectly easy to arrange for. The only reason
for having an appreciable positive pressure in any form of generating
plant is that the gas may be compelled to travel through the pipes and to
escape from the burner orifices; and since the plant is only installed to
serve the burners, that pressure which best suits the burners must be
thrown by the generator or its holder. Therefore the highest pressure it
is ever requisite to employ in a generator is a pressure sufficient
(_a_) to lift the gasholder bell, or to raise the water in a
displacement holder, (_b_) to drive the gas through the various
subsidiary items in the plant, such as washers and purifiers, (_c_)
to overcome the friction in the service-pipes, [Footnote: This friction
manifestly causes a loss of pressure, _i.e._, a fall in pressure, as
a gas travels along a pipe; and, as will be shown in Chapter VII., it is
the fall in pressure in a pipe rather than the initial pressure at which
a gas enters a pipe that governs the volume of gas passing through that
pipe. The proper behaviour and economic working of a burner (acetylene or
other, luminous or incandescent) naturally depend upon the pressure in
the pipe to which the burner is immediately attached being exactly suited
to the design of that burner, and have nothing to do with the fall in
pressure occurring in the delivery pipes. It is therefore necessary to
keep entirely separate the ideas of proper burner pressure and of maximum
desirable fall in pressure within the service due to friction.] and
(d) to give at the points of combustion a pressure which is
required by the particular burners adopted. In all except village or
district installations, (_c_) may be virtually neglected. When the
holder has a rising bell, (_a_) represents only an inch or so of
water; but if a displacement holder is employed the pressure needed to
work it is entirely indeterminate, being governed by the size and shape
of the said holder. It will be argued in Chapter III. that a rising
holder is always preferable to one constructed on the displacement
principle. The pressure (d) at the burners may be taken at 4
inches of water as a maximum, the precise figure being dependent upon the
kind of burners--luminous, incandescent, boiling, &c.--attached to the
main. The pressure (_b_) also varies according to circumstances, but
averages 2 or 3 inches. Thus a pressure in the generator exceeding that
of the atmosphere by some 12 inches of water--_i.e._, by about 7
oz., or less than half a pound per square inch--is amply sufficient for
every kind of installation, the less meritorious generators with
displacement holders only excepted. This pressure, it should be noted, is
the net or effective pressure, the pressure with which the gas raises the
liquid in a water-gauge glass out of the level while the opposite end of
the water column is exposed to the atmosphere. The absolute pressure in a
vessel containing gas at an effective pressure of 12 inches of water is 7
oz. plus the normal, insensible pressure of the atmosphere itself--say
15-1/4 lb. per square inch. The liquid in a barometer which measures the
pressure of the atmosphere stands at a height of 30 inches only, because
that liquid is mercury, 13.6 times as heavy as water. Were it filled with
water the barometer would stand at (30 X 13.6) = 408 inches, or 34 feet,
approximately. Gas pressures are always measured in inches of water
column, because expressed either as pounds per square inch or as inches
of mercury, the figures would be so small as to give decimals of unwieldy
length.
It would of course be perfectly safe so to arrange an acetylene plant
that the pressure in the generating chamber should reach the 100 inches
of water first laid down by the Home Office authorities as the maximum
allowable. There is, however, no appreciable advantage to be gained by so
doing, or by exceeding that pressure which feeds the burners best. Any
higher original pressure involves the use of a governor at the exit of
the plant, and a governor is a costly and somewhat troublesome piece of
apparatus that can be dispensed with in most single installations by a
proper employment of a well-balanced rising holder.
CHAPTER III
THE GENERAL PRINCIPLES OF ACETYLENE GENERATION--ACETYLENE GENERATING
APPARATUS
Inasmuch as acetylene is produced by the mere interaction of calcium
carbide and water, that is to say, by simply bringing those two
substances in the cold into mutual contact within a suitable closed
space, and inasmuch as calcium carbide can always be purchased by the
consumer in a condition perfectly fit for immediate decomposition, the
preparation of the gas, at least from the theoretical aspect, is
characterised by extreme simplicity. A cylinder of glass or metal, closed
at one end and open at the other, filled with water, and inverted in a
larger vessel containing the same liquid, may be charged almost
instantaneously with acetylene by dropping into the basin a lump of
carbide, which sinks to the bottom, begins to decompose, and evolves a
rapid current of gas, displacing the water originally held in the
inverted cylinder or "bell." If a very minute hole is drilled in the top
of the floating bell, acetylene at once escapes in a steady stream, being
driven out by the pressure of the cylinder, the surplus weight of which
causes it to descend into the water of the basin as rapidly as gas issues
from the orifice. As a laboratory experiment, and provided the bell has
been most carefully freed from atmospheric air in the first instance,
this escaping gas may be set light to with a match, and will burn with a
more or loss satisfactory flame of high illuminating power. Such is an
acetylene generator stripped of all desirable or undesirable adjuncts,
and reduced to its most elementary form; but it is needless to say that
so simple an apparatus would not in any way fulfil the requirements of
everyday practice.
Owing to the inequality of the seasons, and to the irregular nature of
the demand for artificial light and heat in all households, the capacity
of the plant installed for the service of any institution or district
must be amply sufficient to meet the consumption of the longest winter
evening--for, as will be shown in the proper place, attempts to make an
acetylene generator evolve gas more quickly than it is designed to do are
fraught with many objections--while the operation of the plant, must be
under such thorough control that not only can a sudden and unexpected
demand for gas be met without delay, but also that a sudden and
unexpected interruption or cessation of the demand shall not be followed
by any disturbance in the working of the apparatus. Since, on the one
hand, acetylene is produced in large volumes immediately calcium carbide
is wetted with water, so that the gas may be burnt within a minute or two
of its first evolution; and, on the other, that acetylene once prepared
can be stored without trouble or appreciable waste for reasonable periods
of time in a water-sealed gasholder closely resembling, in everything but
size, the holders employed on coal-gas works; it follows that there are
two ways of bringing the output of the plant into accord with the
consumption of the burners. It is possible to make the gas only as and
when it is required, or it is possible in the space of an hour or so,
during the most convenient part of the day, to prepare sufficient to last
an entire evening, storing it in a gasholder till the moment arrives for
its combustion. It is clear that an apparatus needing human attention
throughout the whole period of activity would be intolerable in the case
of small installations, and would only be permissible in the case of
larger ones if the district supplied with gas was populous enough to
justify the regular employment of two men at least in or about the
generating station. But with the conditions obtaining in such a country
as Great Britain, and in other lands where coal is equally cheap and
accessible, if a neighbourhood was as thickly populated as has been
suggested, it would be preferable on various grounds to lay down a coal-
gas or electricity works; for, as has been shown in the first chapter,
unless a very material fall in the price of calcium carbide should take
place--a fall which at present is not to be expected--acetylene can only
be considered a suitable and economical illuminant and heating agent for
such places as cannot be provided cheaply with coal-gas or electric
current. To meet this objection, acetylene generators have been invented
in which, broadly speaking, gas is only produced when it is required,
control of the chemical reaction devolving upon some mechanical
arrangement. There are, therefore, two radically different types of
acetylene apparatus to be met with, known respectively as "automatic" and
"non-automatic" generators. In a non-automatic generator the whole of the
calcium carbide put into the apparatus is more or less rapidly
decomposed, and the entire volume of gas evolved from it is collected in
a holder, there to await the moment of consumption. In an automatic
apparatus, by means of certain devices which will be discussed in their
proper place, the act of turning on a burner-tap causes some acetylene to
be produced, and the act of turning it off brings the reaction to an end,
thus obviating the necessity for storage. That, at any rate, is the
logical definition of the two fundamentally different kinds of generator:
in automatic apparatus the decomposition of the carbide is periodically
interrupted in such fashion as more or less accurately to synchronise
with the consumption of gas; in the non-automatic variety decomposition
proceeds without a break until the carbide vessels are empty.
Unfortunately a somewhat different interpretation of these two words has
found frequent acceptance, a generator being denominated non-automatic or
automatic according as the holder attached to it is or is not large
enough to store the whole of the acetylene which the charge of carbide is
capable of producing if it is decomposed all at once. Apart from the fact
that a holder, though desirable, is not an absolutely indispensable part
of an acetylene plant, the definition just quoted was sufficiently free
from objection in the earliest days of the industry; but now efficient
commercial generators are to be met with which become either automatic or
non-automatic according to the manner of working them, while some would
be termed non-automatic which comprise mechanism of a conspicuously self-
acting kind.
AUTOMATIC AND NON-AUTOMATIC GENERATORS.--Before proceeding to a detailed
description of the various devices which may be adopted to render an
acetylene generator automatic in action, the relative advantages of
automatic and non-automatic apparatus, irrespective of type, from the
consumer's point of view may be discussed. The fundamental idea
underlying the employment of a non-automatic generator is that the whole
of the calcium carbide put into the apparatus shall be decomposed into
acetylene as soon after the charge is inserted as is natural in the
circumstances; so that after a very brief interval of time the generating
chambers shall contain nothing but spent lime and water, and the holder
be as full of gas as is ever desirable. In an automatic apparatus, the
fundamental idea is that the generating chamber, or one at least of
several generating chambers, shall always contain a considerable quantity
of undecomposed carbide, and some receptacle always contain a store of
water ready to attack that carbide, so that whenever a demand for gas
shall arise everything may be ready to meet it. Inasmuch as acetylene is
an inflammable gas, it possesses all the properties characteristic of
inflammable gases in general; one of which is that it is always liable to
take fire in presence of a spark or naked light, and another of which is
that it is always liable to become highly explosive in presence of a
naked light or spark if, accidentally or otherwise, it becomes mixed with
more than a certain proportion of air. On the contrary, in the complete
absence of liquid or vaporised water, calcium carbide is almost as inert
a body as it is possible to imagine: for it will not take fire, and
cannot in any circumstances be made to explode. Hence it may be urged
that a non-automatic generator, with its holder always containing a large
volume of the actually inflammable and potentially explosive acetylene,
must invariably be more dangerous than an automatic apparatus which has
less or practically no ready-made gas in it, and which simply contains
water in one chamber and unaltered calcium carbide in another. But when
the generating vessels and the holder of a non-automatic apparatus are
properly designed and constructed, the gas in the latter is acetylene
practically free from air, and therefore while being, as acetylene
inevitably is, inflammable, is devoid of explosive properties, always
assuming, as must be the case in a water-sealed holder, that the
temperature of the gas is below 780° C.; and also assuming, as must
always be the case in good plant, that the pressure under which the gas
is stored remains less than two atmospheres absolute. It is perfectly
true that calcium carbide is non-inflammable and non-explosive, that it
is absolutely inert and incapable of change; but so comprehensive an
assertion only applies to carbide in its original drum, or in some
impervious vessel to which moisture and water have no access. Until it is
exhausted, an automatic acetylene generator contains carbide in one place
and water in another, dependence being put upon some mechanical
arrangement to prevent the two substances coming into contact
prematurely. Many of the devices adopted by builders of acetylene
apparatus for keeping the carbide and water separate, and for mixing them
in the requisite quantities when the proper time arrives, are as
trustworthy, perhaps, as it is possible for any automatic gear to be; but
some are objectionably complicated, and a few are positively inefficient.
There are two difficulties which the designer of automatic mechanism has
to contend with, and it is doubtful whether he always makes a sufficient
allowance for them. The first is that not only must calcium carbide and
liquid water be kept out of premature contact, but that moisture, or
vapour of water, must not be allowed to reach the carbide; or
alternatively, that if water vapour reaches the carbide too soon, the
undesired reaction shall not determine overheating, and the liberated gas
be not wasted or permitted to become a source of danger. The second
difficulty encountered by the designer of automata is so to construct his
apparatus that it shall behave well when attended to by completely
unskilled labour, that it shall withstand gross neglect and resist
positive ill-treatment or mismanagement. If the automatic principle is
adopted in any part of an acetylene apparatus it must be adopted
throughout, so that as far as possible--and with due knowledge and skill
it is completely possible--nothing shall be left dependent upon the
memory and common sense of the gasmaker. For instance, it must not be
necessary to shut a certain tap, or to manipulate several cocks before
opening the carbide vessel to recharge it; it must not be possible for
gas to escape backwards out of the holder; and either the carbide-feed
gear or the water-supply mechanism (as the case may be) must be
automatically locked by the mere act of taking the cover off the carbide
store, or of opening the sludge-cock at the bottom. It would be an
advantage, even, if the purifiers and other subsidiary items of the plant
were treated similarly, arranging them in such fashion that gas should be
automatically prevented from escaping out of the rest of the apparatus
when any lid was removed. In fact, the general notion of interlocking,
which has proved so successful in railway signal-cabins and in
carburetted water gas-plant for the prevention of accidents duo to
carelessness or overnight, might be copied in principle throughout an
acetylene installation whenever the automatic system is employed.
It is no part of the present argument, to allege that automatic
generators are, and must always be, inherently dangerous. Automatic
devices of a suitable kind may be found in plenty which are remarkably
simple and highly trustworthy; but it would be too bold a statement to
say that any such arrangement is incapable of failure, especially when
put into the hands of a person untrained in the superintendence of
machinery. The more reliable a piece of automatic mechanism proves itself
to be, the more likely is it to give trouble and inconvenience and
utterly to destroy confidence when it does break down; because the better
it has behaved in the past, and the longer it has lasted without
requiring adjustment, the less likely is it that the attendant will be at
hand when failure occurs. By suitable design and by an intelligent
employment of safety-valves and blow-off pipes (which will be discussed
in their proper place) it is quite easy to avoid the faintest possibility
of danger arising from an increase of pressure or an improper
accumulation of gas inside the plant or inside the building containing
the plant; but every time such a safety-valve or blow-off pipe comes into
action a waste of gas occurs, which means a sacrifice of economy, and
shows that the generator is not working as it should.
As glass is a fragile and brittle substance, and as it is not capable of
bearing large, rapid, and oft-repeated alterations of temperature in
perfect safety, it is not a suitable material for the construction of
acetylene apparatus or of portions thereof. Hence it follows that a
generator must be built of some non-transparent material which prevents
the interior being visible when the apparatus is at work. Although it is
comparatively easy, by the aid of a lamp placed outside the generator-
shed in such a position as to throw its beams of light through a window
upon the plant inside, to charge a generator after dark; and although it
is possible, without such assistance, by methodical habits and a
systematic arrangement of utensils inside the building to charge a
generator even in perfect darkness, such an operation is to be
deprecated, for it is apt to lead to mistakes, it prevents any slight
derangement in the installation from being instantly noticed, and it
offers a temptation to the attendant to break rules and to take a naked
light with him. On all those grounds, therefore, it is highly desirable
that every manipulation connected with a generator shall be effected
during the daytime, and that the apparatus-house shall be locked up
before nightfall. But owing to the irregular habits engendered by modern
life it is often difficult to know, during any given day, how much gas
will be required in the ensuing evening; and it therefore becomes
necessary always to have, as ready-made acetylene, or as carbide in a
proper position for instant decomposition, a patent or latent store of
gas more than sufficient in quantity to meet all possible requirements.
Now, as already stated, a non-automatic apparatus has its store of
material in the form of gas in a holder; and since this is preferably
constructed on the rising or telescopic principle, a mere inspection of
the height of the bell--on which, if preferred, a scale indicating its
contents in cubic feet or in burner-hours may be marked--suffices to show
how near the plant is to the point of exhaustion. In many types of
automatic apparatus the amount of carbide remaining undecomposed at any
moment is quite unknown, or at best can only be deduced by a tedious and
inexact calculation; although in some generators, where the store of
carbide is subdivided into small quantities, or placed in several
different receptacles, an inspection of certain levers or indicators
gives an approximate idea as to the capacity of the apparatus for further
gas production. In any case the position of a rising holder is the most
obvious sign of the degree of exhaustion of a generator; and therefore,
to render absolutely impossible a failure of the light during an evening,
a non-automatic generator fitted with a rising holder is best.
Since calcium carbide is a solid body having a specific gravity of 2.2,
water being unity, and since 1 cubic foot of water weighs 62.4 lb., in
round numbers 137 lb. of _compact_ carbide only occupy 1 cubic foot
of space. Again, since acetylene is a gas having a specific gravity of
0.91, air being unity, and since the specific gravity of air, water being
unity, is 0.0013, the specific gravity of acetylene, water being unity,
is roughly O.00116. Hence 1 cubic foot of acetylene weighs roughly 0.07
lb. Furthermore, since 1 lb. of good carbide evolves 5 cubic feet of gas
on decomposition with water, acetylene stored at atmospheric pressure
occupies roundly 680 times as much space as the carbide from which it has
been evolved. This figure by no means represents the actual state of
affairs in a generator, because, as was explained in the previous
chapter, a carbide vessel cannot be filled completely with solid; and,
indeed, were it so "filled," in ordinary language, much of its space
would be still occupied with air. Nevertheless it is incontrovertible
that an acetylene plant calculated to supply so many burners for so long
a period of time must be very much larger if it is constructed on the
non-automatic principle, when the carbide is decomposed all at once, than
if the automatic system is adopted, when the solid remains unattacked
until a corresponding quantity of gas is required for combustion. Clearly
it is the storage part of a non-automatic plant alone which must be so
much larger; the actual decomposing chambers may be of the same size or
even smaller, according to the system of generation to which the
apparatus belongs. In practice this extra size of the non-automatic plant
causes it to exhibit two disadvantages in comparison with automatic
apparatus, disadvantages which are less serious than they appear, or than
they may easily be represented to be. In the first place, the non-
automatic generator requires more space for its erection. If acetylene
were an illuminating agent suitable for adoption by dwellers in city or
suburb, where the back premises and open-air part of the messuage are
reduced to minute proportions or are even non-existent, this objection
might well be fatal. But acetylene is for the inhabitant of a country
village or the occupier of an isolated country house; and he has usually
plenty of space behind his residence which he can readily spare. In the
second place, the extra size of the non-automatic apparatus makes it more
expensive to construct and more costly to instal. It is more cosily to
construct and purchase because of its holder, which must be well built on
a firm foundation and accurately balanced; it is more costly to instal
because a situation must be found for the erection of the holder, and the
apparatus-house may have to be made large enough to contain the holder as
well as the generator itself. As regards the last point, it may be said
at once that there is no necessity to place the holder under cover: it
may stand out of doors, as coal-gas holders do in England, for the seal
of the tank can easily be rendered frost-proof, and the gas itself is not
affected by changes of atmospheric temperature beyond altering somewhat
in volume. In respect of the other objections, it must be remembered that
the extra expense is one of capital outlay alone, and therefore only
increases the cost of the light by an inappreciable amount, representing
interest and depreciation charges on the additional capital expenditure.
The increased cost of a year's lighting due to these charges will amount
to only 10 or 15 per cent, on the additional capital sunk. The extra
capital sunk does not in any way increase the maintenance charges; and
if, by having a large holder, additional security and trustworthiness are
obtained, or if the holder leads to a definite, albeit illusive, sense of
extra security and trustworthiness, the additional expenditure may well
be permissible or even advantageous.
The argument is sometimes advanced that inasmuch as for the same, or a
smaller, capital outlay as is required to instal a non-automatic
apparatus large enough to supply at one charging the maximum amount of
light and heat that can ever be needed on the longest winter's night, an
automatic plant adequate to make gas for two or three evenings can be
laid down, the latter must be preferable, because the attendant, in the
latter case, will only need to enter the generator-house two or three
times a week. Such an argument is defective because it ignores the
influence of habit upon the human being. A watch which must be wound
every day, or a clock which must be wound every week, on a certain day of
the week, is seldom permitted to run down; but a watch requiring to be
re-wound every other day, or a fourteen-day clock (used as such), would
rarely be kept going. Similarly, an acetylene generator might be charged
once a week or once a day without likelihood of being forgotten; but the
operation of charging at irregular intervals would certainly prove a
nuisance. With a non-automatic apparatus containing all its gas in the
holder, the attendant would note the position of the bell each morning,
and would introduce sufficient carbide to fill the holder full, or partly
full, as the case might be; with an automatic apparatus he would be
tempted to trust that the carbide holders still contained sufficient
material to last another night.
The automatic system of generating acetylene has undoubtedly one
advantage in those climates where frost tends to occur frequently, but
only to prevail for a short period. As the apparatus is in operation
during the evening hours, the heat evolved will, or can be made to,
suffice to protect the apparatus from freezing until the danger has
passed; whereas if the gas is generated of a morning in a non-automatic
apparatus the temperature of the plant may fall to that of the atmosphere
before evening, and some portion may freeze unless special precautions
are taken to protect it.
It was shown in Chapter II that overheating is one of the chief troubles
to be guarded against in acetylene generators, and that the temperature
attained is a function of the speed at which generation proceeds. Seeing
that in an automatic apparatus the rate of decomposition depends on the
rate at which gas is being burnt, while in a non-automatic generator it
is, or may be, under no control, the critic may urge that the reaction
must take place more slowly and regularly, and the maximum temperature
therefore be lower, when the plant works automatically. This may be true
if the non-automatic generator is unskilfully designed or improperly
manipulated; but it is quite feasible to arrange an apparatus, especially
one of the carbide-to-water or of the flooded-compartment type, in such
fashion that overheating to an objectionable extent is rendered wholly
impossible. In a non-automatic apparatus the holder is nothing but a
holder and may be placed wherever convenient, even at a distance from the
generating plant; in an automatic apparatus the holder, or a small
similarly constructed holder placed before the main storage vessel, has
to act as a water-supply governor, as the releasing gear for certain
carbide-food mechanism, or indeed as the motive power of such mechanism;
and accordingly it must be close to the water or carbide store, and more
or less intimately connected by means of levers, or the like, with the
receptacle in which decomposition occurs. Sometimes the holder surrounds,
or is otherwise an integral part of, the decomposing chamber, the whole
apparatus being made self-contained or a single structure with the object
of gaining compactness. But it is evident that such methods of
construction render additionally awkward, or even hazardous, any repair
or petty operation to the generating portion of the plant; while the more
completely the holder is isolated from the decomposing vessels the more
easily can they be cleaned, recharged, or mended, without blowing off the
stored gas and without interfering with the action of any burners that
may be alight at the time. Owing to the ingenuity of inventors, and the
experience they have acquired in the construction of automatic acetylene
apparatus during the years that the gas has been in actual employment, it
is going too far boldly to assert that non-automatic generators are
invariably to be preferred before their rivals. Still in view of the
nature of the labour which is likely to be bestowed on any domestic
plant, of the difficulty in having repairs or adjustments done quickly in
outlying country districts, and of the inconvenience, if not risk,
attending upon any failure of the apparatus, the greater capital outlay,
and the larger space required by non-automatic generators are in most
instances less important than the economy in space and prime cost
characteristic of automatic machines when the defects of each are weighed
fairly in the balance. Indeed, prolonged experience tends to show that a
selection between non-automatic and automatic apparatus may frequently be
made on the basis of capacity. A small plant is undoubtedly much more
convenient if automatic; a very large plant, such as that intended for a
public supply, is certainly better if non-automatic, but between these
two extremes choice may be exercised according to local conditions.
CONTROL OF THE CHEMICAL REACTION.--Coming now to study the principles
underlying the construction of an acetylene generator more closely it
will be seen that as acetylene is produced by bringing calcium carbide
into contact with water, the chemical reaction may be started either by
adding the carbide to the water, or by adding the water to the carbide.
Similarly, at least from the theoretical aspect, the reaction, may be
caused to stop by ceasing to add carbide to water, or by ceasing to add
water to carbide. Apparently if water is added by degrees to carbide,
until the carbide is exhausted, the carbide must always be in excess; and
manifestly, if carbide is added in small portions to water, the water
must always be in excess, which, as was argued in Chapter II., is
emphatically the more desirable position of affairs. But it in quite
simple to have carbide present in large excess of the water introduced
when the whole generator is contemplated, and yet to have the water
always in chemical excess in the desired manner; because to realise the
advantages of having water in excess, it is only necessary to subdivide
the total charge of carbide into a number of separate charges which are
each so small that more than sufficient water to decompose and flood one
of them is permitted to enter every time the feed mechanism comes into
play, or (in a non-automatic apparatus) every time the water-cock is
opened; so arranging the charges that each one is protected from the
water till its predecessor, or its predecessor, have been wholly
decomposed. Thus it is possible to regard either the carbide or the water
as the substance which has to be brought into contact with the other in
specified quantity. It is perhaps permissible to repeat that in the
construction of an automatic generator there is no advantage to be gained
from regulating the supply of both carbide and water, because just as the
mutual decomposition will begin immediately any quantity of the one meets
any quantity of the other, so the reaction will cease (except in one case
owing to "after-generation") directly the whole of that material which is
not in chemical excess has been consumed-quite independently of the
amount of the other material left unattacked. Being a liquid, and
possessing as such no definite shape or form of its own irrespective of
the vessel in which it is held, water is by far the more convenient of
the two substances to move about or to deliver in predetermined volume to
the decomposing chamber. A supply of water can be started instantaneously
or cut oil as promptly by the movement of a cock or valve of the usual
description; or it may be allowed to run down a depending pipe in
obedience to the law of gravitation, and stopped from running down such a
pipe by opposing to its passage a gas pressure superior to that
gravitational force. In any one of several obvious ways the supply of
water to a mass of carbide may be controlled with absolute certainty, and
therefore it should apparently follow that the make of acetylene should
be under perfect control by controlling the water current. On the other
hand, unless made up into balls or cartridges of some symmetrical form,
calcium carbide exists in angular masses of highly irregular shape and
size. Its lumps alter in shape and size directly liquid water or moisture
reaches them; a loose more or loss gritty powder, or a damp cohesive mud,
being produced which is well calculated to choke any narrow aperture or
to jam any moving valve. It is more difficult, therefore, by mechanical
agency to add a supply of carbide to a mass of water than to introduce a
supply of water to a stationary mass of carbide; and far more difficult
still to bring the supply of carbide under perfect control with the
certainty that the movement shall begin and stop immediately the proper
time arrives.
But assuming the mechanical difficulties to be satisfactorily overcome,
the plan of adding carbide to a stationary mass of water has several
chemical advantages, first, because, however the generator be
constructed, water will be in excess throughout the whole time of gas
production; and secondly, because the evolution of acetylene will
actually cease completely at the moment when the supply of carbide is
interrupted. There is, however, one particular type of generator in which
as a matter of fact the carbide is the moving constituent, viz., the
"dipping" apparatus (cf. _infra_), to which these remarks do not
apply; but this machine, as will be seen directly, is, illogically
perhaps, but for certain good reasons, classed among the water-to-carbide
apparatus. All the mechanical advantages are in favour, as just
indicated, of making water the moving substance; and accordingly, when
classified in the present manner, a great majority of the generators now
on the markets are termed water-to-carbide apparatus. Their disadvantages
are twofold, though these may be avoided or circumvented: in all types
save one the carbide is in excess at the immediate place and time of
decomposition; and in all types without exception the carbide in the
whole of the generator is in excess, so that the phenomenon of "after-
generation" occurs with more or less severity. As explained in the last
chapter, after-generation is the secondary production of acetylene which
takes place more or less slowly after the primary reaction is finished,
proceeding either between calcium hydroxide, merely damp lime, or damp
gas and calcium carbide, with an evolution of more acetylene. As it is
possible, and indeed usual, to fit a holder of some capacity even to an
automatic generator, the simple fact that more acetylene is liberated
after the main reaction is over does not matter, for the gas can be
safely stored without waste and entirely without trouble or danger. The
real objection to after-generation is the difficulty of controlling the
temperature and of dissipating the heat with which the reaction is
accompanied. It will be evident that the balance of advantage, weighing
mechanical simplicity against chemical superiority, is somewhat even
between carbide-to-water and water-to-carbide generators of the proper
type; but the balance inclines towards the former distinctly in the ease
of non-automatic apparatus, and points rather to the latter when
automatism is desired. In the early days of the industry it would have
been impossible to speak so favourably of automatic carbide-to-water
generators, for they were at first constructed with absurdly complicated
and unreliable mechanism; but now various carbide-feed gears have been
devised which seem to be trustworthy even when carbide not in cartridge
form is employed.
NON-AUTOMATIC CARBIDE-TO-WATER GENERATORS.--There is little to be said in
the present place about the principles underlying the construction of
non-automatic generators. Such apparatus may either be of the carbide-to-
water or the water-to-carbide type. In the former, lumps of carbide are
dropped by hand down a vertical or sloping pipe or shoot, which opens at
its lower end below the water-level of the generating chamber, and which
is fitted below its mouth with a deflector to prevent the carbide from
lodging immediately underneath that mouth. The carbide falls through the
water which stands in the shoot itself almost instantaneously, but during
its momentary descent a small quantity of gas is evolved, which produces
an unpleasant odour unless a ventilating hood is fixed above the upper
end of the tube. As the ratio of cubical contents to superficial area of
a lump is greater as the lump itself is larger, and as only the outer
surface of the lump can be attacked by the water in the shoot during its
descent, carbide for a hand-fed carbide-to-water generator should be in
fairly large masses--granulated material being wholly unsuitable--and
this quite apart from the fact that large carbide is superior to small in
gas-making capacity, inasmuch as it has not suffered the inevitable
slight deterioration while being crushed and graded to size. If carbide
is dropped too rapidly into such a generator which is not provided with a
false bottom or grid for the lumps to rest upon, the solid is apt to
descend among a mass of thick lime sludge produced at a former operation,
which lies at the bottom of the decomposing chamber; and here it may be
protected from the cooling action of fresh water to such an extent that
its surface is baked or coated with a hard layer of lime, while
overheating to a degree far exceeding the boiling-point of water may
occur locally. When, however, it falls upon a grid placed some distance
above the bottom of the water vessel, the various convection currents set
up as parts of the liquid become warm, and the mechanical agitations
produced by the upward current of gas rinse the spent lime from the
carbide, and entirely prevent overheating, unless the lumps are
excessively large in size. If the carbide charged into a hand-fed
generator is in very large lumps there is always a possibility that
overheating may occur in the centre of the masses, due to the baking of
the exterior, even if the generator is fitted with a reaction grid.
Manifestly, when carbide in lumps of reasonable size is dropped into
excess of water which is not merely a thick viscid cream of lime, the
temperature cannot possibly exceed the boiling-point--_i.e._, 100°
C.--provided always the natural convection currents of the water are
properly made use of.
The defect which is, or rather which may be, characteristic of a hand-fed
carbide-to-water generator is a deficiency of gas yield due to
solubility. At atmospheric temperatures and pressure 10 volumes of water
dissolve 11 volumes of acetylene, and were the whole of the water in a
large generator run to waste often, a sensible loss of gas would ensue.
If the carbide falls nearly to the bottom of the water column, the rising
gas is forced to bubble through practically the whole of the liquid, so
that every opportunity is given it to dissolve in the manner indicated
till the liquid is completely saturated. The loss, however, is not nearly
so serious as is sometimes alleged, because (1) the water becomes heated
and so loses much of its solvent power; and (2) the generator is worked
intermittently, with sufficiently long intervals to allow the spent lime
to settle into a thick cream, and only that thick cream is run off, which
represents but a small proportion of the total water present. Moreover, a
hand-fed carbide-to-water generator will work satisfactorily with only
half a gallon [Footnote: The United States National Board of Fire
Underwriters stipulates for the presence of 1 (American) gallon of water
for every 1 lb. of carbide before such an apparatus is "permitted." This
quantity of liquid might retain nearly 4 per cent. of the total acetylene
evolved. Even this is an exaggeration; for neither her, nor in the
corresponding figure given in the text, is any allowance made for the
diminution in solvent power of the water as it becomes heated by the
reaction.] of liquid present for every 1 lb. of carbide decomposed, and
were all this water run off and a fresh quantity admitted before each
fresh introduction of carbide, the loss of acetylene by dissolution could
not exceed 2 per cent. of the total make, assuming the carbide to be
capable of yielding 5 cubic feet of gas per lb. Admitting, however, that
some loss of gas does occur in this manner, the defect is partly, if not
wholly, neutralised by the concomitant advantages of the system: (1)
granted that the generator is efficiently constructed, decomposition of
the carbide is absolutely complete, so that no loss of gas occurs in this
fashion; (2) the gas is evolved at a low temperature, so that it is
unaccompanied, by products of polymerisation, which may block the leading
pipes and must reduce the illuminating power; (3) the acetylene is not
mixed with air (as always happens at the first charging of a water-to-
carbide apparatus), which also lowers the illuminating power; and (4) the
gas is freed from two of its three chief impurities, viz., ammonia and
sulphuretted hydrogen, in the generating chamber itself. To prevent the
loss of acetylene by dissolution, carbide-to-water generators are
occasionally fitted with a reaction grid placed only just below the
water-level, so that the acetylene has no more than 1 inch or so of
liquid to bubble through. The principle is wrong, because hot water being
lighter than cold, the upper layers may be raised to the boiling-point,
and even converted into steam, while the bulk of the liquid still remains
cold; and if the water actually surrounding the carbide is changed into
vapour, nearly all control over the temperature attending the reaction is
lost.
The hand-fed carbide-to-water generator is very simple and, as already
indicated, has proved itself perhaps the best type of all for the
construction of very large installations; but the very simplicity of the
generator has caused it more than once to be built in a manner that has
not given entire satisfaction. As shown at L in Fig. 6, p. 84, the
generator essentially consists of a closed cylindrical vessel
communicating at its top with a separate rising holder. At one side as
drawn, or disposed concentrically if so preferred, is an open-mouthed
pipe or shoot (American "shute") having its lower open extremity below
the water-level. Into this shoot are dropped by hand or shovel lumps of
carbide, which fall into the water and there suffer decomposition. As the
bottom of the shoot is covered with water, which, owing to the small
effective gas pressure in the generator given by the holder, stands a few
inches higher in the shoot than in the generator, gas cannot escape from
the shoot; because before it could do so the water in the generator would
have to fall below the level of the point _a_, being either driven
out through the shoot or otherwise. Since the point _b_ of the shoot
extends further into the generator than _a_, the carbide drops
centrally, and as the bubbles of gas rise vertically, they have no
opportunity of ascending into the shoot. In practice, the generator is
fitted with a conical bottom for the collection of the lime sludge and
with a cock or other aperture at the apex of the cone for the removal of
the waste product. As it is not desirable that the carbide should be
allowed to fall directly from the shoot into the thicker portion of the
sludge within the conical part of the generator, one or more grids is
usually placed in the apparatus as shown by the dotted lines in the
sketch. It does not seem that there is any particular reason for the
employment of more than one grid, provided the size of the carbide
decomposed is suited to the generator, and provided the mesh of the grid
is suited to the size of the carbide. A great improvement, however, is
made if the grid is carried on a horizontal spindle in such a way that it
can be rocked periodically in order to assist in freeing the lumps of
carbide from the adhering particles of lime. As an alternative to the
movable grid, or even as an adjunct thereto, an agitator scraping the
conical sides of the generator may be fitted which also assists in
ensuring a reasonably complete absence of undecomposed carbide from the
sludge drawn off at intervals. A further point deserves attention. If
constructed in the ideal manner shown in Fig. 6 removal of some of the
sludge in the generator would cause the level of the liquid to descend
and, by carelessness, the level might fall below the point _a_ at
the base of the shoot. In these circumstances, if gas were unable to
return from the holder, a pressure below that of the atmosphere would be
established in the gas space of the generator and air would be drawn in
through the shoot. This air might well prove a source of danger when
generation was started again. Any one of three plans may be adopted to
prevent the introduction of air. A free path may be left on the gas-main
passing from the generator to the holder so that gas may be free to
return and so to maintain the usual positive pressure in the decomposing
vessel; the sludge may be withdrawn into some vessel so small in capacity
that the shoot cannot accidentally become unsealed; or the waterspace of
the generator may be connected with a water-tank containing a ball-valve
attached to a constant service of water be that liquid runs in as quickly
as sludge is removed, and the level remains always at the same height.
The first plan is only a palliative and has two defects. In the first
place, the omission of any non-return valve between, the generator and
the next item in the train of apparatus is objectionable of itself; in
the second place, should a very careless attendant withdraw too much
liquid, the shoot might become unsealed and the whole contents of the
holder be passed into the air of the building containing the apparatus
through the open mouth of the shoot. The second plan is perfectly sound,
but has the practical defect of increasing the labour of cleaning the
generator. The third plan is obviously the best. It can indeed be adopted
where no real constant service of water is at hand by connecting the
generator to a water reservoir of relatively large size and by making the
latter of comparatively large transverse area, in proportion to its
depth; so that the escape of even a largo volume of water from the
reservoir may not involve a large reduction in the level at which it
stands there.
The dust that always clings to lumps of carbide naturally decomposes with
extreme rapidity when the material is thrown into the shoot of a carbide-
to-water generator, and the sudden evolution of gas so produced has on
more than one occasion seriously alarmed the attendant on the plant.
Moreover, to a trifling extent the actual superficial layers of the
carbide suffer attack before the lumps reach the true interior of the
generator, and a small loss of gas thereby occurs through the open mouth
of the shoot. To remove these objections to the hand-fed generator it has
become a common practice in large installations to cause the lower end of
the shoot to dip under the level of some oil contained in an appropriate
receptacle, the carbide falling into a basket carried upon a horizontal
spindle. The basket and its support are so arranged that when a suitable
charge of carbide has been dropped into it, a partial rotation of an
external hand-wheel lifts the basket and carbide out of the oil into an
air-tight portion of the generator where the surplus oil can drain away
from the lumps. A further rotation of the hand-wheel then tips the basket
over a partition inside the apparatus, allowing the carbide to fall into
the actual decomposing chamber. This method of using oil has the
advantage of making the evolution of acetylene on a large scale appear to
proceed more quietly than usual, and also of removing the dust from the
carbide before it reaches the water of the generator. The oil itself
obviously does not enter the decomposing chamber to any appreciable
extent and therefore does not contaminate the final sludge. The whole
process accordingly lies to be favourably distinguished from those other
methods of employing oil in generators or in the treatment of carbide
which are referred to elsewhere in this book.
NON-AUTOMATIC WATER-TO-CARBIDE GENERATORS.--The only principle underlying
the satisfactory design of a non-automatic water-to-carbide generator is
to ensure the presence of water in excess at the spot where decomposition
is taking place. This may be effected by employing what is known as the
"flooded-compartment" system of construction, _i.e._, by subdividing
the total carbide charge into numerous compartments arranged either
vertically or horizontally, and admitting the water in interrupted
quantities, each more than sufficient thoroughly to decompose and
saturate the contents of one compartment, rather than in a slow, steady
stream. It would be quite easy to manage this without adopting any
mechanism of a moving kind, for the water might be stored in a tank kept
full by means of a ball-valve, and admitted to an intermediate reservoir
in a slow, continuous current, the reservoir being fitted with an
inverted syphon, on the "Tantalus-cup" principle, so that it should first
fill itself up, and then suddenly empty into the pipe leading to the
carbide container. Without this refinement, however, a water-to-carbide
generator, with subdivided charge, behaves satisfactorily as long as each
separate charge of carbide is so small that the heat evolved on its
decomposition can be conducted away from the solid through the water-
jacketed walls of the vessel, or as the latent heat of steam, with
sufficient rapidity. Still it must be remembered that a water-to-carbide
generator, with subdivided charge, does not belong to the flooded-
compartment type if the water runs in slowly and continuously: it is then
simply a "contact" apparatus, and may or may not exhibit overheating, as
well as the inevitable after-generation. All generators of the water-to-
carbide type, too, must yield a gas containing some air in the earlier
portions of their make, because the carbide containers can only be filled
one-third or one-half full of solid. Although the proportion of air so
passed into the holder may be, and usually is, far too small in amount to
render the gas explosive or dangerous in the least degree, it may well be
sufficient to reduce the illuminating power appreciably until it is swept
out of the service by the purer gas subsequently generated. Moreover, all
water-to-carbide generators are liable, as just mentioned, to produce
sufficient overheating to lower the illuminating power of the gas
whenever they are wilfully driven too fast, or when they are reputed by
their makers to be of a higher productive capacity than they actually
should be; and all water-to-carbide generators, excepting those where the
carbide is thoroughly soaked in water at some period of their operation,
are liable to waste gas by imperfect decomposition.
DEVICES TO SECURE AUTOMATIC ACTION,--The devices which are commonly
employed to render a generator automatic in action, that is to say, to
control the supply of one of the two substances required in the
intermittent evolution of gas, may be divided into two broad classes: (A)
those dependent upon the position of a rising-holder bell, and (B) those
dependent upon the gas pressure inside the apparatus. As the bell of a
rising holder descends in proportion as its gaseous contents are
exhausted, it may (A^1) be fitted with some laterally projecting pin
which, arrived at a certain position, actuates a series of rods or
levers, and either opens a cock on the water-supply pipe or releases a
mechanical carbide-feed gear, the said cock being closed again or the
feed-gear thrown out of action when the pin, rising with the bell, once
more passes a certain position, this time in its upward path. Secondly
(A^2), the bell may be made to carry a perforated receptacle containing
carbide, which is dipped into the water of the holder tank each time the
bell falls, and is lifted out of the water when it rises again. Thirdly
(A^3), by fitting inside the upper part of the bell a false interior,
conical in shape, the descent of the bell may cause the level of the
water in the holder tank to rise until it is above some lateral aperture
through which the liquid may escape into a carbide container placed
elsewhere. These three methods are represented in the annexed diagram
(Fig. 1). In Al the water-levels in the tank and bell remain always at
_l_, being higher in the tank than in the bell by a distance
corresponding with the pressure produced by the bell itself. As the bell
falls a pin _X_ moves the lever attached to the cock on the water-
pipe, and starts, or shuts off, a current passing from a store-tank or
reservoir to a decomposing vessel full of carbide. It is also possible to
make _X_ work some releasing gear which permits carbide to fall into
water--details of this arrangement are given later on. In A^1 the water
in the tank serves as a holder seal only, a separate quantity being
employed for the purposes of the chemical reaction. This arrangement has
the advantage that the holder water lasts indefinitely, except for
evaporation in hot weather, and therefore it may be prevented from
freezing by dissolving in it some suitable saline body, or by mixing with
it some suitable liquid which lowers its point of solidification. It will
be observed, too, that in A^1 the pin _X_, which derives its motive
power from the surplus weight of the falling bell, has always precisely
the same amount of work to do, viz., to overcome the friction of the plug
of the water-cock in its barrel. Hence at all times the pressure
obtaining in the service-pipe is uniform, except for a slight jerk
momentarily given each time the cock is opened or closed. When _X_
actuates a carbide-feed arrangement, the work it does may or may not vary
on different occasions, as will appear hereafter. In A^2 the bell itself
carries a perforated basket of carbide, which is submerged in the water
when the bell falls, and lifted out again when it rises. As the carbide
is thus wetted from below, the lower portion of the mass soon becomes a
layer of damp slaked lime, for although the basket is raised completely
above the water-level, much liquid adheres to the spent carbide by
capillary attraction. Hence, even when the basket is out of the water,
acetylene is being produced, and it is produced in circumstances which
prevent any control over the temperature attained. The water clinging to
the lower part of the basket is vaporised by the hot, half-spent carbide,
and the steam attacks the upper part, so that polymerisation of the gas
and baking of the carbide are inevitable. In the second place, the
pressure in the service-pipe attached to A^2 depends as before upon the
net weight of the holder bell; but here that net weight is made up of the
weight of the bell itself, that of the basket, and that of the carbide it
contains. Since the carbide is being gradually converted into damp slaked
lime, it increases in weight to an indeterminate extent as the generator
in exhausted; but since, on the other hand, some lime may be washed out
of the basket each time it is submerged, and some of the smaller
fragments of carbide may fall through the perforations, the basket tends
to decrease in weight as the generator is exhausted. Thus it happens in
A^2 that the combined weight of bell plus basket plus contents is wholly
indefinite, and the pressure in the service becomes so irregular that a
separate governor must be added to the installation before the burners
can be expected to behave properly. In the third place, the water in the
tank serves both for generation and for decomposition, and this involves
the employment of some arrangement to keep its level fairly constant lest
the bell should become unsealed, while protection from frost by saline or
liquid additions is impossible. A^2 is known popularly as a "dipping"
generator, and it will be seen to be defective mechanically and bad
chemically. In both A^1 and A^2 the bell is constructed of thin sheet-
metal, and it is cylindrical in shape; the mass of metal in it is
therefore negligible in comparison with the mass of water in the tank,
and so the level of the liquid is sensibly the same whether the bell be
high or low. In A^3 the interior of the bell is fitted with a circular
plate which cuts off its upper corners and leaves a circumferential space
_S_ triangular in vertical section. This space is always full of
air, or air and water, and has to be deducted from the available storage
capacity of the bell. Supposing the bell transparent, and viewing it from
above, its effective clear or internal diameter will be observed to be
smaller towards the top than near the bottom; or since the space _S_
is closed both against the water and against the gas, the walls of the
bell may be said to be thicker near its top. Thus it happens that as the
bell descends into the water past the lower angle of _S_, it begins
to require more space for itself in the tank, and so it displaces the
water until the levels rise. When high, as shown in the sketch marked
A^3(a), the water-level is at _l_, below the mouth of a pipe
_P_; but when low, as in A^3(b), the water is raised to the point
_l'_, which is above _P_. Water therefore flows into _P_,
whence it reaches the carbide in an attached decomposing chamber. Here
also the water in the tank is used for decomposition as well as for
sealing purposes, and its normal level must be maintained exactly at
_l_, lest the mouth of _P_ should not be covered whenever the
bell falls.
[Illustration: FIG. 1.--TYPICAL METHODS OF AUTOMATIC GENERATION
CONTROLLED BY BELL GASHOLDER.]
The devices employed to render a generator automatic which depend upon
pressure (B) are of three main varieties: (B^1) the water-level in the
decomposing chamber may be depressed by the pressure therein until its
surface falls below a stationary mass of carbide; (B^2) the level in a
water-store tank may be depressed until it falls below the mouth of a
pipe leading to the carbide vessel; (B^3) the current of water passing
down a pipe to the decomposing chamber may be interrupted by the action
of a pressure superior to the force of gravitation. These arrangements
are indicated roughly in Fig. 2. In B^1, D is a hollow cylinder closed at
all points except at the cock G and the hole E, which are always below
the level of the water in the annulus F, the latter being open to the air
at its top. D is rigidly fastened to the outer vessel F so that it cannot
move vertically, and the carbide cage is rigidly fastened to D. Normally
the water-levels are at _l_, and the liquid has access to the
carbide through perforations in the basket. Acetylene is thus produced;
but if G is shut, the gas is unable to escape, and so it presses
downwards upon the water until the liquid falls in D to the dotted line
_l"_, rising in F to the dotted line _l'_. The carbide is then
out of water, and except for after-generation, evolution of gas ceases.
On opening G more or less fully, the water more or less quickly reaches
its original position at _l_, and acetylene is again produced.
Manifestly this arrangement is identical with that of A^2 as regards the
periodical immersion of the carbide holder in the liquid; but it is even
worse than the former mechanically because there is no rising holder in
B^1, and the pressure in the service is never constant. B^2 represents
the water store of an unshown generator which works by pressure. It
consists of a vessel divided vertically by means of a partition having a
submerged hole N. One-half, H, is cloned against the atmosphere, but
communicates with the gas space of the generator through L; the other
half, K, is open to the air. M is a pipe leading water to the carbide.
When gas is being burnt as fast as, or faster than, it is being evolved,
the pressure in the generator is small, the level of the water stands at
_l_, and the mouth of M is below it. When the pressure rises by
cessation of consumption, that pressure acts through L upon the water in
H, driving it down in H and up in K till it takes the positions
_l"_, and _l'_, the mouth of M being then above the surface. It
should be observed that in the diagrams B^1 and B^3, the amount of
pressure, and the consequent alteration in level, is grossly exaggerated
to gain clearness; one inch or less in both cases may be sufficient to
start or retard evolution of acetylene. Fig. B^3 is somewhat ideal, but
indicates the principle of opposing gas pressure to a supply of water
depending upon gravitation; a method often adopted in the construction of
portable acetylene apparatus. The arrangement consists of an upper tank
containing water open to the air, and a lower vessel holding carbide
closed everywhere except at the pipe P, which leads to the burners, and
at the pipe S, which introduces water from the store-tank. If the cock at
T is closed, pressure begins to rise in the carbide holder until it is
sufficient to counterbalance the weight of the column of water in the
pipe S, when a further supply is prevented until the pressure sinks
again. This idea is simply an application of the displacement-holder
principle, and as such is defective (except for vehicular lamps) by
reason of lack of uniformity in pressure.
[Illustration: FIG. 2.--TYPICAL METHODS OF AUTOMATIC GENERATION
CONTROLLED BY INTERNAL GAS PRESSURE.]
DISPLACEMENT GASHOLDERS.--An excursion may here be made for the purpose
of studying the action of a displacement holder, which in its most
elementary form is shown at C. It consists of an upright vessel open at
the top, and divided horizontally into two equal portions by a partition,
through which a pipe descends to the bottom of the lower half. At the top
of the closed lower compartment a tube is fixed, by means of which gas
can be introduced below the partition. While the cock is open to the air,
water is poured in at the open top till the lower compartment is
completely full, and the level of the liquid is at _l_. If now, gas
is driven in through the side tube, the water is forced downwards in the
lower half, up through the depending pipe till it begins to fill the
upper half of the holder, and finally the upper half is full of water and
the lower half of gas an shown by the levels _l'_ and _l"_. But
the force necessary to introduce gas into such an apparatus, which
conversely is equal to the force with which the apparatus strives to
expel its gaseous contents, measured in inches of water, is the distance
at any moment between the levels _l'_ and _l"_; and as these
are always varying, the effective pressure needed to fill the apparatus,
or the effective pressure given by the apparatus, may range from zero to
a few inches less than the total height of the whole holder. A
displacement holder, accordingly, may be used either to store a varying
quantity of gas, or to give a steady pressure just above or just below a
certain desired figure; but it will not serve both purposes. If it is
employed as a holder, it in useless as a governor or pressure regulator;
if it is used as a pressure regulator, it can only hold a certain fixed
volume of gas. The rising holder, which is shown at A^1 in Fig. 1
(neglecting the pin X, &c.) serves both purposes simultaneously; whether
nearly full or nearly empty, it gives a constant pressure--a pressure
solely dependent upon its effective weight, which may be increased by
loading its crown or decreased by supporting it on counterpoises to any
extent that may be required. As the bell of a rising holder moves, it
must be provided with suitable guides to keep its path vertical; these
guides being arranged symmetrically around its circumference and carried
by the tank walls. A fixed control rod attached to the tank over which a
tube fastened to the bell slides telescope-fashion is sometimes adopted;
but such an arrangement is in many respects less admirable than the
former.
Two other devices intended to give automatic working, which are scarcely
capable of classification among their peers, may be diagrammatically
shown in Fig. 3. The first of these (D) depends upon the movements of a
flexible diaphragm. A vessel (_a_) of any convenient size and shape
is divided into two portions by a thin sheet of metal, leather,
caoutchouc, or the like. At its centre the diaphragm is attached by some
air-tight joint to the rod _c_, which, held in position by suitable
guides, is free to move longitudinally in sympathy with the diaphragm,
and is connected at its lower extremity with a water-supply cock or a
carbide-feed gear. The tube _e_ opens at its base into the gas space
of the generator, so that the pressure below the diaphragm in _a_ is
the same as that elsewhere in the apparatus, while the pressure in
_a_ above the diaphragm is that of the atmosphere. Being flexible
and but slightly stretched, the diaphragm is normally depressed by the
weight of _c_ until it occupies the position _b_; but if the
pressure in the generator (_i.e._, in _e_) rises, it lifts the
diaphragm to somewhat about the position _b'_--the extent of
movement being, as usual, exaggerated in the sketch. The movement of the
diaphragm is accompanied by a movement of the rod _c_, which can be
employed in any desirable way. In E the bell of a rising holder of the
ordinary typo is provided with a horizontal striker which, when the bell
descends, presses against the top of a bag _g_ made of any flexible
material, such as india-rubber, and previously filled with water. Liquid
is thus ejected, and may be caused to act upon calcium carbide in some
adjacent vessel. The sketch is given because such a method of obtaining
an intermittent water-supply has at one time been seriously proposed; but
it is clearly one which cannot be recommended.
[Illustration: FIG. 3.--TYPICAL METHODS OF AUTOMATIC GENERATION
CONTROLLED BY A FLEXIBLE DIAPHRAM OR BAG.]
ACTION OF WATER-TO-CARBIDE GENERATORS.--Having by one or other of the
means described obtained a supply of water intermittent in character, it
remains to be considered how that supply may be made to approach the
carbide in the generator. Actual acetylene apparatus are so various in
kind, and merge from one type to another by such small differences, that
it is somewhat difficult to classify them in a simple and intelligible
fashion. However, it may be said that water-to-carbide generators,
_i.e._, such as employ water as the moving material, may be divided
into four categories: (F^1) water is allowed to fall as single drops or
as a fine stream upon a mass of carbide--this being the "drip" generator;
(F^2) a mass of water is made to rise round and then recede from a
stationary vessel containing carbide--this being essentially identical in
all respects save the mechanical one with the "dip" or "dipping"
generator shown in A^2, Fig. 1; (F^3) a supply of water is permitted to
rise round, or to flow upon, a stationary mass of carbide without ever
receding from the position it has once assumed--this being the "contact"
generator; and (F^4) a supply of water is admitted to a subdivided charge
of carbide in such proportion that each quantity admitted is in chemical
excess of the carbide it attacks. With the exception of F^2, which has
already been illustrated as A^2 Fig. 1, or as B^1 in Fig. 2, these
methods of decomposing carbide are represented in Figs. 4 and 5. It will
be observed that whereas in both F^1 and F^3 the liberated acetylene
passes off at the top of the apparatus, or rather from the top of the
non-subdivided charge of carbide, in F^1 the water enters at the top, and
in F^3 it enters at the bottom. Thus it happens that the mixture of
acetylene and steam, which is produced at the spot where the primary
chemical reaction is taking place, has to travel through the entire mass
of carbide present in a generator belonging to type F^3, while in F^1 the
damp gas flows directly to the exit pipe without having to penetrate the
lumps of solid. Both F^1 and F^3 exhibit after-generation caused by a
reaction between the liquid water mechanically clinging to the mass of
spent lime and the excess of carbide to an approximately equal extent;
but for the reason just mentioned, after-generation due to a reaction
between the vaporised water accompanying the acetylene first evolved and
the excess of carbide is more noticeable in F^3 than in F^1; and it is
precisely this latter description of after-generation which leads to
overheating of the most ungovernable kind. Naturally both F^1 and F^3 can
be fitted with water jackets, as is indicated by the dotted lines in the
second sketch; but unless the generating chamber in quite small and the
evolution of gas quite slow, the cooling action of the jacket will not
prove sufficient. As the water in F^1 and F^3 is not capable of backward
motion, the decomposing chambers cannot be employed as displacement
holders, as is the case in the dipping generator pictured at B^1, Fig. 2.
They must be coupled, accordingly, to a separate holder of the
displacement or, preferably, of the rising type; and, in order that the
gas evolved by after-generation may not be wasted, the automatic
mechanism must cut off the supply of water to the generator by the time
that holder is two-thirds or three-quarters full.
[Illustration: FIG. 4.--TYPICAL METHODS OF DECOMPOSING CARBIDE (WATER TO
CARBIDE).]
[Illustration: FIG. 5.--TYPICAL METHODS OF DECOMPOSING CARBIDE (WATER TO
CARBIDE).]
The diagrams G, H, and K in Figs. 4 and 5 represent three different
methods of constructing a generator which belongs either to the contact
type (F^3) if the supply of water is essentially continuous, _i.e._,
if less is admitted at each movement of the feeding mechanism than is
sufficient to submerge the carbide in each receptacle; or to the flooded-
compartment type (F') if the water enters in large quantities at a time.
In H the main carbide vessel is arranged horizontally, or nearly so, and
each partition dividing it into compartments is taller than its
predecessor, so that the whole of the solid in (1) must be decomposed,
and the compartment entirely filled with liquid before it can overflow
into (2), and so on. Since the carbide in all the later receptacles is
exposed to the water vapour produced in that one in which decomposition
is proceeding at any given moment, at least at its upper surface, some
after-generation between vapour and carbide occurs in H; but a partial
control over the temperature may be obtained by water-jacketing the
container. In G the water enters at the base and gas escapes at the top,
the carbide vessels being disposed vertically; hero, perhaps, more after-
generation of the same description occurs, as the moist gas streams round
and over the higher baskets. In K, the water enters at the top and must
completely fill basket (1) before it can run down the depending pipe into
(2); but since the gas also leaves the generator at the top, the later
carbide receptacles do not come in contact with water vapour, but are
left practically unattacked until their time arrives for decomposition by
means of liquid water. K, therefore, is the best arrangement of parts to
avoid after-generation, overheating, and polymerisation of the acetylene
whether the generator be worked as a contact or as a flooded-compartment
apparatus; but it may be freely admitted that the extent of the
overheating due to reaction between water vapour and carbide may be kept
almost negligible in either K, H, or G, provided the partitions in the
carbide container be sufficient in number--provided, that is to say, that
each compartment holds a sufficiently small quantity of carbide; and
provided that the quantity of water ultimately required to fill each
compartment is relatively so large that the temperature of the liquid
never approaches the boiling-point where vaporisation is rapid. The type
of generator indicated by K has not become very popular, but G is fairly
common, whilst H undoubtedly represents the apparatus which is most
generally adopted for use in domestic and other private installations in
the United Kingdom and the Continent of Europe. The actual generators
made according to the design shown by H usually have a carbide receptacle
designed in the form of a semi-cylindrical or rectangular vessel of steel
sliding fairly closely into an outside container, the latter being either
built within the main water space of the entire apparatus or placed
within a separate water-jacketed casing. Owing to its shape and the
sliding motion with which the carbide receptacle is put into the
container these generators are usually termed "drawer" generators. In
comparison with type G, the drawer generator H certainly exhibits a lower
rise in temperature when gas is evolved in it at a given speed and when
the carbide receptacles are constructed of similar dimensions. It is very
desirable that the whole receptacle should be subdivided into a
sufficient number of compartments and that it should be effectively
water-cooled from outside. It would also be advantageous if the water-
supply were so arranged that the generator should be a true flooded-
compartment apparatus, but experience has nevertheless shown that
generators of type H do work very well when the water admitted to the
carbide receptacle, each time the feed comes into action, is not enough
to flood the carbide in one of the compartments. Above a certain size
drawer generators are usually constructed with two or even more complete
decomposing vessels, arrangements being such that one drawer can be taken
out for cleaning, whilst the other is in operation. When this is the case
a third carbide receptacle should always be employed so that it may be
dry, lit to receive a charge of carbide, and ready to insert in the
apparatus when one of the others is withdrawn. The water-feed should
always be so disposed that the attendant can see at a glance which of the
two (or more) carbide receptacles is in action at any moment, and it
should be also so designed that the supply is automatically diverted to
the second receptacle when the first is wholly exhausted and back again
to the first (unless there are more than two) when the carbide in the
second is entirely gasified. In the sketches G, H, and K, the total space
occupied by the various carbide receptacles is represented as being
considerably smaller than the capacity of the decomposing chamber. Were
this method of construction copied in actual acetylene apparatus, the
first makes of gas would be seriously (perhaps dangerously) contaminated
with air. In practice the receptacles should fit so tightly into the
outer vessel and into one another that when loaded to the utmost extent
permissible--space being left for the swelling of the charge and for the
passage of water and gas--but little room should be left for the
retention of air in the chamber.
ACTION OF CARBIDE-TO-WATER GENERATORS.--The methods which may be adopted
to render a generator automatic when carbide is employed as the moving
material are shown at M, N, and P, in Fig. 6; but the precise devices
used in many actual apparatus are so various that it is difficult to
portray them generically. Moreover it is desirable to subdivide automatic
carbide-to-water generators, according to the size of the carbide they
are constructed to take, into two or three classes, which are termed
respectively "large carbide-feed," "small carbide-feed," and "granulated
carbide-feed" apparatus. (The generator represented at L does not really
belong to the present class, being non-automatic and fed by hand; but the
sketch is given for completeness.) M is an automatic carbide-feed
generator having its store of carbide in a hopper carried by the rising-
holder bell. The hopper is narrowed at its mouth, where it is closed by a
conical or mushroom valve _d_ supported on a rod held in suitable
guides. When the bell falls by consumption of gas, it carries the valve
and rod with it; but eventually the button at the base of _c_
strikes the bottom of the generator, or some fixed distributing plate,
and the rod can descend no further. Then, when the bell falls lower, the
mushroom _d_ rises from its seat, and carbide drops from the hopper
into the water. This type of apparatus has the defect characteristic of
A^2, Fig. 1; for the pressure in the service steadily diminishes as the
effective weight of bell plus hopper decreases by consumption of carbide.
But it has also two other defects--(1) that ordinary carbide is too
irregular in shape to fall smoothly through the narrow annular space
between the valve and its seat; (2) that water vapour penetrates into the
hopper, and liberates some gas there, while it attacks the lumps of
carbide at the orifice, producing dust or causing them to stick together,
and thus rendering the action of the feed worse than ever. Most of these
defects can be avoided by using granulated carbide, which is more uniform
in size and shape, or by employing a granulated and "treated" carbide
which has been dipped in some non-aqueous liquid to make it less
susceptible to the action of moisture. Both these plans, however, are
expensive to adopt; first, because of the actual cost of granulating or
"treating" the carbide; secondly, because the carbide deteriorates in
gas-making capacity by its inevitable exposure to air during the
granulating or "treating" process. The defects of irregularity of
pressure and possible waste of gas by evolution in the hopper may be
overcome by disposing the parts somewhat differently; making the holder
an annulus round the hopper, or making it cylindrical with the hopper
inside. In this case the hopper is supported by the main portion of the
apparatus, and does not move with the bell: the rod and valve being given
their motion in some fashion similar to that figured. Apparatus designed
in accordance with the sketch M, or with the modification just described,
are usually referred to under the name of "hopper" generators. On several
occasions trouble has arisen during their employment owing to the jamming
of the valve, a fragment of carbide rather larger than the rest of the
material lodging between the lips of the hopper and the edges of the
mushroom valve. This has been followed by a sudden descent of all the
carbide in the store into the water beneath, and the evolution of gas has
sometimes been too rapid to pass away at the necessary speed into the
holder. The trouble is rendered even more serious should the whole charge
of carbide fall at a time when, by neglect or otherwise, the body of the
generator contains much lime sludge, the decomposition then proceeding
under exceptionally bad circumstances, which lead to the production of an
excessively high temperature. Hopper generators are undoubtedly very
convenient for certain purposes, chiefly, perhaps, for the construction
of table-lamps and other small installations. Experience tends to show
that they may be employed, first, provided they are designed to take
granulated carbide--which in comparison with larger grades is much more
uniform and cylindrical in shape--and secondly, provided the quantity of
carbide in the hopper does not exceed a few pounds. The phenomenon of the
sudden unexpected descent of the carbide, popularly known as "dumping,"
can hardly be avoided with carbide larger in size than the granulated
variety; and since the results of such an accident must increase in
severity with the size of the apparatus, a limit in their capacity is
desirable.
[Illustration: FIG. 6.--TYPICAL METHODS OF DECOMPOSING CARBIDE (CARBIDE
TO WATER).]
When it is required to construct a carbide-feed generator of large size
or one belonging to the large carbide-feed pattern, it is preferable to
arrange the store in a different manner. In N the carbide is held in a
considerable number of small receptacles, two only of which are shown in
the drawing, provided with detachable lids and hinged bottoms kept shut
by suitable catches. At proper intervals of time those catches in
succession are knocked on one side by a pin, and the contents of the
vessel fall into the water. There are several methods available for
operating the pins. The rising-holder bell may be made to actuate a train
of wheels which terminate in a disc revolving horizontally on a vertical
axis somewhere just below the catches; and this wheel may bear an
eccentric pin which hits each catch as it rotates. Alternatively the
carbide boxes may be made to revolve horizontally on a vertical axis by
the movements of the bell communicated through a clutch; and thus each
box in succession may arrive at a certain position where the catch is
knocked aside by a fixed pin. The boxes, again, may revolve vertically on
a horizontal axis somewhat like a water-wheel, each box having its bottom
opened, or, by a different system of construction, being bodily upset,
when it arrives at the bottom of its circular path. In no case, however,
are the carbide receptacles carried by the bell, which is a totally
distinct part of the apparatus; and therefore in comparison with M, the
pressure given by the bell is much more uniform. Nevertheless, if the
system of carbide boxes moves at all, it becomes easier to move by
decrease in weight and consequent diminution in friction as the total
charge is exhausted; and accordingly the bell has less work to do during
the later stages of its operation. For this reason the plan actually
shown at N is preferable, since the work done by the moving pin,
_i.e._, by the descending bell, is always the same. P represents a
carbide-feed effected by a spiral screw or conveyor, which, revolved
periodically by a moving bell, draws carbide out of a hopper of any
desired size and finally drops it into a shoot communicating with a
generating chamber such as that shown in L. Here the work done by the
bell is large, as the friction against the blades of the screw and the
walls of the horizontal tube is heavy; but that amount of work must
always be essentially identical. The carbide-feed may similarly be
effected by means of some other type of conveyor instead of the spiral
screw, such as an endless band, and the friction in these cases may be
somewhat less than with the screw, but the work to be done by the bell
will always remain large, whatever type of conveyor may be adopted. A
further plan for securing a carbide-feed consists in employing some
extraneous driving power to propel a charge of carbide out of a reservoir
into the generator. Sometimes the propulsive effort is obtained from a
train of clockwork, sometimes from a separate supply of water under high
pressure. The clockwork or the water power is used either to drive a
piston travelling through the vessel containing the carbide so that the
proper quantity of material is dropped over the open mouth of a shoot, or
to upset one after another a series of carbide receptacles, or to perform
some analogous operation. In these cases the pin or other device fitted
to the acetylene apparatus itself has nothing to do beyond releasing the
mechanism in question, and therefore the work required from the bell is
but small. The propriety of employing a generator belonging to these
latter types must depend upon local conditions, _e.g._, whether the
owner of the installation has hydraulic power on a small scale (a
constant supply of water under sufficient pressure) at disposal, or
whether he does not object to the extra labour involved in the periodical
winding up of a train of clockwork.
It must be clear that all these carbide-feed arrangements have the defect
in a more or less serious degree of leaving the carbide in the main
storage vessel exposed to the attack of water vapour rising from the
decomposing chamber, for none of the valves or operating mechanism can be
made quite air-tight. Evolution of gas produced in this way does not
matter in the least, because it is easy to return the gas so liberated
into the generator or into the holder; while the extent of the action,
and the consequent production of overheating, will tend to be less than
in generators such as those shown in G and H of Figs. 4 and 5, inasmuch
as the large excess of water in the carbide-feed apparatus prevents the
liquid arriving at a temperature at which it volatilises rapidly. The
main objection to the evolution of gas in the carbide vessel of a
carbide-to-water generator depends on the danger that the smooth working
of the feed-gear may be interfered with by the formation of dust or by
the aggregation of the carbide lumps.
USE OF OIL IN GENERATORS.--Calcium carbide is a material which is only
capable of attack for the purpose of evolving acetylene by a liquid that
is essentially water, or by one that contains some water mixed with it.
Oils and the like, or even such non-aqueous liquids as absolute alcohol,
have no effect upon carbide, except that the former naturally make it
greasy and somewhat more difficult to moisten. This last property has
been found of service in acetylene generation, especially on the small
scale; for if carbide is soaked in, or given a coating of, some oil, fat,
or solid hydrocarbon like petroleum, cocoanut oil, or paraffin wax, the
substance becomes comparatively indifferent towards water vapour or the
moisture present in the air, while it still remains capable of complete,
albeit slow, decomposition by liquid water when completely immersed
therein. The fact that ordinary calcium carbide is attacked so quickly by
water is really a defect of the substance; for it is to this extreme
rapidity of reaction that the troubles of overheating are due. Now, if
the basket in the generator B^1 of Fig. 2, or, indeed, the carbide store
in any of the carbide-to-water apparatus, is filled with a carbide which
has been treated with oil or wax, as long as the water-level stands at
_l'_ and _l"_ or the carbide still remains in the hopper, it is
essentially unattacked by the vapour arising from the liquid; but
directly the basket is submerged, or the lumps fall into the water,
acetylene is produced, and produced more slowly and regularly than
otherwise. Again, oils do not mix with water, but usually float thereon,
and a mass of water covered by a thick film or layer of oil does not
evaporate appreciably. If, now, a certain quantity of oil, say lamp
paraffin or mineral lubricating oil, is poured on to the water in B^1,
Fig. 2, it moves upwards and downwards with the water. When the water
takes the position _l_, the oil is driven upwards away from the
basket of carbide, and acetylene is generated in the ordinary manner; but
when the water falls to _l"_ the oil descends also, rinses off much
of the adhering water from the carbide lumps, covers them with a greasy
film, and almost entirely stops generation till it is in turn washed off
by the next ascent of the water. Similarly, if the carbide in generators
F, G, and H (also K) has been treated with a solid or semi-solid grease,
it is practically unattacked by the stream of warm damp gas, and is only
decomposed when the liquid itself arrives in the basket. For the same
reason treated carbide can be kept for fairly long periods of time, even
in a drum with badly fitting lid, without suffering much deterioration by
the action of atmospheric moisture. The problem of acetylene generation
is accordingly simplified to a considerable degree by the use of such
treated carbide, and the advantage becomes more marked as the plant
decreases in size till a portable apparatus is reached, because the
smaller the installation the more relatively expensive or inconvenient is
a large holder for surplus gas. The one defect of the method is the extra
cost of such treated carbide; and in English conditions ordinary calcium
carbide is too expensive to permit of any additional outlay upon the
acetylene if it is to compete with petroleum or the product of a tiny
coal-gas works. The extra cost of using treated carbide falls upon the
revenue account, and is much more noticeable than that of a large holder,
which is capital expenditure. When fluid oil is employed in a generator
of type B^1, evolution of gas becomes so regular that any holder beyond
the displacement one which the apparatus itself constitutes is actually
unnecessary, though still desirable; but B^1, with or without oil, still
remains a displacement apparatus, and as such gives no constant pressure.
It must be admitted that the presence of oil so far governs the evolution
of gas that the movement of the water, and the consequent variation of
pressure, is rendered very small; still a governor or a rising holder
would be required to give the best result at the burners. One point in
connexion with the use of liquid oil must not be overlooked, viz., the
extra trouble it may give in the disposal of the residues. This matter
will be dealt with more fully in Chapter V.; here it is sufficient to say
that as the oil does not mix with the water but floats on the surface,
care has to be taken that it is not permitted to enter any open stream.
The foregoing remarks about the use of oil manifestly only apply to those
cases where it is used in quantity and where it ultimately becomes mixed
with the sludge or floats on the water in the decomposing chamber. The
employment of a limpid oil, such as paraffin, as an intermediate liquid
into which carbide is introduced on its way to the water in the
decomposing vessel of a hand-fed generator in the manner described on
page 70 is something quite different, because, except for trifling
losses, one charge of oil should last indefinitely.
RISING GASHOLDERS.--Whichever description of holder is employed in an
acetylene apparatus, the gas is always stored over, or in contact with, a
liquid that is essentially water. This introduces three subjects for
consideration: the heavy weight of a large body of liquid, the loss of
gas by dissolution in that liquid, and the protection of that liquid from
frost in the winter. The tanks of rising holders are constructed in two
different ways. In one the tank is a plain cylindrical vessel somewhat
larger in diameter than the bell which floats in it; and since there must
be nearly enough water in the tank to fill the interior of the bell when
the latter assumes its lowest position, the quantity of water is
considerable, its capacity for dissolving acetylene is large, and the
amount of any substance that may have to be added to it to lower its
freezing-point becomes so great as to be scarcely economical. All these
defects, including that of the necessity for very substantial foundations
under the holder to support its enormous weight, may be overcome by
adopting the second method of construction. It is clear that the water in
the centre of the tank is of no use,--all that is needed being a narrow
trough for the bell to work in. Large rising holders are therefore
advantageously built with a tank formed in the shape of an annulus, the
effective breadth of which is not more than 2 or 3 inches, the centre
portion being roofed over so as to prevent escape of gas. The same
principle may be retained with modified details by fitting inside a plain
cylindrical tank a "dummy" or smaller cylinder, closed by a flat or
curved top and fastened water- and air-tight to the bottom of the main
vessel. The construction of annular tanks or the insertion of a "dummy"
may be attended with difficulty if the tank is wholly or partly sunk
below the ground level, owing to the lifting force of water in the
surrounding soil. Where a steel tank is sunk, or a masonry tank is
constructed, regard must be paid, both in the design of the tank and in
the manner of construction, to the level of the underground water in the
neighbourhood, as in certain cases special precautions will be needed to
avoid trouble from the pressure of the water on the outside of the tank
until it is balanced by the pressure of the water with which the tank is
filled. So far as mere dissolution of gas is concerned, the loss may be
reduced by having a circular disc of wood, &c., a little smaller in
diameter than the boll, floating on the water of a plain tank.
EFFECT OF STORAGE IN GASHOLDER ON ACETYLENE.--It is perfectly true, as
has been stated elsewhere, that the gas coming from an acetylene
generator loses some of its illuminating power if it is stored over water
for any great length of time; such loss being given by Nichols as 94 per
cent, in five months, and having been found by one of the authors as 0.63
per cent. per day--figures which stand in fair agreement with one
another. This wastage is not due to any decomposition of the acetylene in
contact with water, but depends on the various solubilities of the
different gases which compose the product obtained from commercial
calcium carbide. Inasmuch as an acetylene evolved in the best generator
contains some foreign ingredients, and inasmuch as an inferior product
contains more (_cf._ Chapter V.), the contents of a holder are never
pure; but as those contents are principally made up of acetylene itself,
that gas stands at a higher partial pressure in the holder than the
impurities. Since acetylene is more soluble in water than any of its
diluents or impurities, sulphuretted hydrogen and ammonia excepted, and
since the solubility of all gases increases as the pressure at which they
are stored rises, the true acetylene in an acetylene holder dissolves in
the water more rapidly and comparatively more copiously than the
impurities; and thus the acetylene tends to disappear and the impurities
to become concentrated within the bell. Simultaneously at the outer part
of the seal, air is dissolved in the water; and by processes of diffusion
the air so dissolved passes through the liquid from the outside to the
inside, where it escapes into the bell, while the dissolved acetylene
similarly passes from the inside to the outside of the seal, and there
mingles with the atmosphere. Thus, the longer a certain volume of
acetylene is stored over water, the more does it become contaminated with
the constituents of the atmosphere and with the impurities originally
present in it; while as the acetylene is much more soluble than its
impurities, more gas escapes from, than enters, the holder by diffusion,
and so the bulk of stored gas gradually diminishes. However, the figures
previously given show that this action is too slow to be noticeable in
practice, for the gas is never stored for more than a few days at a time.
The action cannot be accepted as a valid argument against the employment
of a holder in acetylene plant. Such deterioration and wastage of gas may
be reduced to some extent by the use of a film of some cheap and
indifferent oil floating on the water inside an acetylene holder; the
economy being caused by the lower solubility of acetylene in oils than in
aqueous liquids not saturated with some saline material. Probably almost
any oil would answer equally well, provided it was not volatile at the
temperature of the holder, and that it did not dry or gum on standing,
_e.g._, olive oil or its substitutes; but mineral lubricating oil is
not so satisfactory. It is, however, not necessary to adopt this method
in practice, because the solvent power of the liquid in the seal can be
reduced by adding to it a saline body which simultaneously lowers its
freezing-point and makes the apparatus more trustworthy in winter.
FREEZING OF GASHOLDER SEAL.--The danger attendant upon the congelation of
the seal in an acetylene holder is very real, not so much because of the
fear that the apparatus may be burst, which is hardly to be expected, as
because the bell will be firmly fixed in a certain position by the ice,
and the whole establishment lighted by the gas will be left in darkness.
In these circumstances, hurried and perhaps injudicious attempts may be
made to thaw the seal by putting red-hot bars into it or by lighting
fires under it, or the generator-house may be thoughtlessly entered with
a naked light at a time when the apparatus is possibly in disorder
through the loss of storage-room for the gas it is evolving. Should a
seal ever freeze, it must be thawed only by the application of boiling
water; and the plant-house must be entered, if daylight has passed, in
perfect darkness or with the assistance of an outside lamp whining
through a closed window. [Footnote: By "closed window" is to be
understood one incapable of being opened, fitted with one or two
thicknesses of stout glass well puttied in, and placed in a wall of the
house as far as possible from the door.] There are two ways of preventing
the seal from freezing. In all large installations the generator-house
will be fitted with a warm-water heating apparatus to protect the portion
of the plant where the carbide is decomposed, and if the holder is also
inside the same building it will naturally be safe. If it is outside, one
of the flow-pipes from the warming apparatus should be led into and round
the lowest part of the seal, care being taken to watch for, or to provide
automatic arrangements for making good, loss of water by evaporation. If
the holder is at a distance from the generator-house, or if for any other
reason it cannot easily be brought into the warming circuit, the seal can
be protected in another way; for unlike the water in the generator, the
water in the holder-seal will perform its functions equally well however
much it be reduced in temperature, always providing it is maintained in
the liquid condition. There are numerous substances which dissolve in, or
mix with, water, and yield solutions or liquids that do not solidify
until their temperature falls far below that of the natural freezing-
point. Assuming that those substances in solution do not attack the
acetylene, nor the metal of which the holder is built, and are not too
expensive, choice may be made between them at will. Strictly speaking the
cost of using them is small, because unless the tank is leaky they last
indefinitely, not evaporating with the water as it is vaporised into the
gas or into the air. The water-seal of a holder standing within the
generator-house may eventually become so offensive to the nostrils that
the liquid has to be renewed; but when this happens it is due to the
accumulation in the water of the water-soluble impurities of the crude
acetylene. If, as should be done, the gas is passed through a washer or
condenser containing much water before it enters the holder the
sulphuretted hydrogen and ammonia will be extracted, and the seal will
not acquire an obnoxious odour for a very long time.
Four principal substances have been proposed for lowering the freezing-
point of the water in an acetylene-holder seal; common salt (sodium
chloride), calcium chloride (not chloride of lime), alcohol (methylated
spirit), and glycerin. A 10 per cent. solution of common salt has a
specific gravity of 1.0734, and does not solidify above -6° C. or 21.2°
F.; a 15 per cent. solution has a density of 1.111, and freezes at -10°
C. or 14° F. Common salt, however, is not to be recommended, as its
solutions always corrode iron and steel vessels more or less quickly.
Alcohol, in its English denatured form of methylated spirit, is still
somewhat expensive to use, but it has the advantage of not increasing the
viscosity of the water; so that a frost-proof mixture of alcohol and
water will flow as readily through minute tubes choked with needle-
valves, or through felt and the like, or along wicks, as will plain
water. For this reason, and for the practically identical one that it is
quite free from dirt or insoluble matter, diluted spirit is specially
suitable for the protection of the water in cyclists' acetylene lamps,
[Footnote: As will appear in Chapter XIII., there is usually no holder in
a vehicular acetylene lamp, all the water being employed eventually for
the purpose of decomposing the carbide. This does not affect the present
question. Dilute alcohol does not attack calcium carbide so energetically
as pure water, because it stands midway between pure water and pure
alcohol, which is inert. The attack, however, of the carbide is as
complete as that of pure water, and the slower speed thereof is a
manifest advantage in any holderless apparatus.] where strict economy is
less important than smooth working. For domestic and larger installations
it is not indicated. As between calcium chloride and glycerin there is
little to choose; the former will be somewhat cheaper, but the latter
will not be prohibitively expensive if the high-grade pure glycerins of
the pharmacist are avoided. The following tables show the amount of each
substance which must be dissolved in water to obtain a liquid of definite
solidifying point. The data relating to alcohol were obtained by Pictet,
and those for calcium chloride by Pickering. The latter are materially
different from figures given by other investigators, and perhaps it would
be safer to make due allowance for this difference. In Germany the
Acetylene Association advocates a 17 per cent. solution of calcium
chloride, to which Frank ascribes a specific gravity of 1.134, and a
freezing-point of -8° C. or 17.6° F.
_Freezing-Points of Dilute Alcohol._
_________________________________________________________
| | | |
| Percentage of | Specific Gravity. | Freezing-point. |
| Alcohol. | | |
|_______________|___________________|_____________________|
| | | | |
| | | Degs. C. | Degs. F. |
| 4.8 | 0.9916 | -2.0 | +28.4 |
| 11.3 | 0.9824 | 5.0 | 23.0 |
| 16.4 | 0.9761 | 7.5 | 18.5 |
| 18.8 | 0.9732 | 9.4 | 15.1 |
| 20.3 | 0.9712 | 10.6 | 12.9 |
| 22.1 | 0.9689 | 12.2 | 10.0 |
| 24.2 | 0.9662 | 14.0 | 6.8 |
| 26.7 | 0.9627 | 16.0 | 3.2 |
| 29.9 | 0.9578 | 18.9 | -2.0 |
|_______________|___________________|__________|__________|
_Freezing-Points of Dilute Glycerin._
_________________________________________________________
| | | |
| Percentage of | Specific Gravity. | Freezing-point. |
| Glycerin. | | |
|_______________|___________________|_____________________|
| | | | |
| | | Degs. C. | Degs. F. |
| 10 | 1.024 | -1.0 | +30.2 |
| 20 | 1.051 | 2.5 | 27.5 |
| 30 | 1.075 | 6.0 | 21.2 |
| 40 | 1.105 | 17.5 | 0.5 |
| 50 | 1.127 | 31.3 | -24.3 |
|_______________|___________________|__________|__________|
_Freezing-Points of Calcium Chloride Solutions._
_________________________________________________________
| | | |
| Percentage of | Specific Gravity. | Freezing-point. |
| CaCl_2. | | |
|_______________|___________________|_____________________|
| | | | |
| | | Degs. C. | Degs. F. |
| 6 | 1.05 | -3.0 | +26.6 |
| 8 | 1.067 | 4.3 | 24.3 |
| 10 | 1.985 | 5.9 | 21.4 |
| 12 | 1.103 | 7.7 | 18.1 |
| 14 | 1.121 | 9.8 | 14.4 |
| 16 | 1.140 | 12.2 | 10.0 |
| 18 | 1.159 | 15.2 | 4.6 |
| 20 | 1.170 | 18.6 | -1.5 |
|_______________|___________________|__________|__________|
Calcium chloride will probably be procured in the solid state, but it can
be purchased as a concentrated solution, being sold under the name of
"calcidum" [Footnote: This proprietary German article is a liquid which
begins to solidify at -42° C. (-43.6° F.), and is completely solid at
-56° C. (-69)° F.). Diluted with one-third its volume of water, it
freezes between -20° and -28° C. (-4° and-l8.4° F.). The makers recommend
that it should be mixed with an equal volume of water. Another material
known as "Gefrierschutzflüssigkeit" and made by the Flörsheim chemical
works, freezes at -35° C. (-3° F.). Diluted with one-quarter its volume
of water, it solidifies at -18° C. (-0.4° F.); with equal parts of water
it freezes at -12° C. (10.4° F.). A third product, called "calcidum
oxychlorid," has been found by Caro and Saulmann to be an impure 35 per
cent. solution of calcium chloride. Not one of these is suitable for
addition to the water used in the generating chamber of an acetylene
apparatus, the reasons for this having already been mentioned.] for the
protection of gasholder seals. Glycerin itself resembles a strong
solution of calcium chloride in being a viscid, oily-looking liquid; and
both are so much heavier than water that they will not mix with further
quantities unless they are thoroughly agitated therewith. Either may be
poured through water, or have water floated upon it, without any
appreciable admixture taking place; and therefore in first adding them to
the seal great care must be taken that they are uniformly distributed
throughout the liquid. If the whole contents of the seal cannot
conveniently be run into an open vessel in which the mixing can be
performed, the sealing water must be drawn off a little at a time and a
corresponding quantity of the protective reagent added to it. Care must
be taken also that motives of economy do not lead to excessive dilution
of the reagent; the seal must be competent to remain liquid under the
prolonged influence of the most severe frost ever known to occur in the
neighbourhood where the plant is situated. If the holder is placed out of
doors in an exposed spot where heavy rains may fall on the top of the
bell, or where snow may collect there and melt, the water is apt to run
down into the seal, diluting the upper layers until they lose the frost-
resisting power they originally had. This danger may be prevented by
erecting a sloping roof over the bell crown, or by stirring up the seal
and adding more preservative whenever it has been diluted with rain
water. Quite small holders would probably always be placed inside the
generator-house, where their seals may be protected by the same means as
are applied to the generator itself. It need hardly be said that all
remarks about the dangers incidental to the freezing of holder seals and
the methods for obviating them refer equally to every item in the
acetylene plant which contains water or is fitted with a water-sealed
cover; only the water which is actually used for decomposing the calcium
carbide cannot be protected from frost by the addition of calcium
chloride or glycerin--that water must be kept from falling to its natural
freezing-point. From Mauricheau-Beaupré's experiments, referred to on
page 106, it would appear that a further reason for avoiding an addition
of calcium chloride to the water used for decomposing carbide should lie
in the danger of causing a troublesome production of froth within the
generator.
It will be convenient to digress here for the purpose of considering how
the generators of an acetylene apparatus themselves should be protected
from frost; but it may be said at the outset that it is impossible to lay
down any fixed rules applicable to all cases, since local conditions,
such as climate, available resources, dimensions, and exposed or
protected position of the plant-house vary so largely in different
situations. In all important installations every item of the plant,
except the holder, will be collected in one or two rooms of a single
building constructed of brick or other incombustible material. Assuming
that long-continued frost reigns at times in the neighbourhood, the whole
of such a building, with the exception of one apartment used as a carbide
store only, is judiciously fitted with a heating arrangement like those
employed in conservatories or hothouses; a system of pipes in which warm
water is kept circulating being run round the walls of each chamber near
the floor. The boiler, heated with coke, paraffin, or even acetylene,
must naturally be placed in a separate room of the apparatus-house having
no direct (indoor) communication with the rooms containing the
generators, purifiers, &c. Instead of coils of pipe, "radiators" of the
usual commercial patterns may be adopted; but the immediate source of
heat should be steam, or preferably hot water, and not hot air or
combustion products from the stove. In exposed situations, where the
holder is out of doors, one branch of the flow-pipe should enter and
travel round the seal as previously suggested. Most large country
residences are already provided with suitable heating apparatus for
warming the greenhouses, and part of the heat may be capable of diversion
into the acetylene generator-shed if the latter is erected in a
convenient spot. In fact, if any existing hot-water warming appliances
are already at hand, and if they are powerful enough to do a little more
work, it may be well to put the generator-building in such a position
that it can be efficiently supplied with artificial warmth from those
boilers; for any extra length of main necessary to lead the gas into the
residence from a distant generator will cost less on the revenue account
than the fuel required to feed a special heating arrangement. In smaller
installations, especially such as are to be found in mild climates, it
may be possible to render the apparatus-house sufficiently frost-proof
without artificial heat by building it partly underground, fitting it
with a double skylight in place of a window for the entrance of daylight,
and banking up its walls all round with thick layers of earth. The house
must have a door, however, which must open outwards and easily, so that
no obstacle may prevent a hurried exit in emergencies. Such a door can
hardly be made very thick or double without rendering it heavy and
difficult to open; and the single door will be scarcely capable of
protecting the interior if the frost is severe and prolonged.
Ventilators, too, must be provided to allow of the escape of any gas that
may accidentally issue from the plant during recharging, &c.; and some
aperture in the roof will be required for the passage of the vent pipe or
pipes, which, in certain types of apparatus, move upwards and downwards
with the bell of the holder. These openings manifestly afford facilities
for the entry of cold air, so that although this method of protecting
generator-houses has proved efficient in many places, it can only be
considered inferior to the plan of installing a proper heating
arrangement. Occasionally, where local regulations do not forbid, the
entire generator-house may be built as a "lean-to" against some brick
wall which happens to be kept constantly warm, say by having a furnace or
a large kitchen stove on its other side.
In less complicated installations, where there are only two distinct
items in the plant to be protected from frost--generator and holder--or
where generator and holder are combined into one piece of apparatus,
other methods of warming become possible. As the reaction between calcium
carbide and water evolves much heat, the most obvious way of preventing
the plant from freezing is to economise that heat, _i.e._, to retain
as much of it as is necessary within the apparatus. Such a process,
clearly, is only available if the plant is suitable in external form, is
practically self-contained, and comprises no isolated vessels containing
an aqueous liquid. It is indicated, therefore, rather for carbide-to-
water generators, or for water-to-carbide apparatus in which the carbide
chambers are situated inside the main water reservoir--any apparatus, in
fact, where much water is present and where it is all together in one
receptacle. Moreover, the method of heat economy is suited for
application to automatic generators rather than to those belonging to the
opposite system, because automatic apparatus will be generating gas, and
consequently evolving heat, every evening till late at night--just at the
time when frost begins to be severe. A non-automatic generator will
usually be at work only in the mornings, and its store of heat will
accordingly be much more difficult to retain till nightfall. With the
object of storing up the heat evolved in the generator, it must be
covered with some material possessed of the lowest heat-conducting power
possible; and the proper positions for that material in order of
decreasing importance are the top, sides, and bottom of the plant. The
generator may either be covered with a thick layer of straw, carpet,
flannel, or the like, as is done in the protection of exposed water-
pipes; or it may be provided with a jacket filled with some liquid. In
view of the advisability of not having any organic or combustible
material near the generator, the solid substances just mentioned may
preferably be replaced by one of those partially inorganic compositions
sold for "lagging" steam-pipes and engine-cylinders, such as "Fossil
meal." Indeed, the exact nature of the lagging matters comparatively
little, because the active substance in retaining the heat in the
acetylene generator or the steam-pipe is the air entangled in the pores
of the lagging; and therefore the value of any particular material
depends mainly on its exhibiting a high degree of porosity. The idea of
fitting a water jacket round an acetylene generator is not altogether
good, but it may be greatly improved upon by putting into the jacket a
strong solution of some cheap saline body which has the property of
separating from its aqueous solution in the form of crystals containing
water of crystallisation, and of evolving much heat in so separating.
This method of storing much heat in a small space where a fire cannot be
lighted is in common use on some railways, where passengers' foot-warmers
are filled with a strong solution of sodium acetate. When sodium acetate
is dissolved in water it manifestly exists in the liquid state, and it is
presumably present in its anhydrous condition (i.e., not combined with
water of crystallisation). The common crystals are solid, and contain 3
molecules of water of crystallisation--also clearly in the solid state.
Now, the reaction
NaC_2H_3O_2 + 3H_2O = NaC_2H_3O_2.3H_2O
(anhydrous acetate) (crystals)
evolves 4.37 calories (Berthelot), or 1.46 calorie for each molecule of
water; and whereas 1 kilo. of water only evolves 1 large calorie of heat
as its temperature falls 1° C., 18 grammes of water (1 gramme-molecule)
evolve l.46 large calorie when they enter into combination with anhydrous
sodium acetate to assist in forming crystals--and this 1.46 calorie may
either be permitted to warm the mass of crystals, or made to do useful
work by raising the temperature of some adjacent substance. Sodium
acetate crystals dissolve in 3.9 parts by weight of water at 6° C. (43°
F.) or in 2.4 parts at 37° C. (99° F.). If, then, a jacket round an
acetylene apparatus is filled with a warm solution of sodium acetate
crystals in (say) 3 parts by weight of water, the liquid will crystallise
when it reaches some temperature between 99° and 43° F.; but when the
generator comes into action, the heat liberated will change the mass of
crystals into a liquid without raising its sensible temperature to
anything like the extent that would happen were the jacket full of simple
water. Not being particularly warm to the touch, the liquefied product in
the jacket will not lose much heat by radiation, &c., into the
surrounding air; but when the water in the generator falls again (after
evolution of acetylene ceases) the contents of the jacket will also cool,
and finally will begin to crystallise once more, passing a large amount
of low-temperature heat into the water of the generator, and safely
maintaining it for long periods of time at a temperature suitable for the
further evolution of gas. Like the liquid in the seal of an isolated
gasholder, the liquid in such a jacket will last indefinitely; and
therefore the cost of the sodium acetate in negligible.
Another method of keeping warm the water in any part of an acetylene
installation consists in piling round the apparatus a heap of fresh
stable manure, which, as is well known, emits much heat as it rots. Where
horses are kept, such a process may be said to cost nothing. It has the
advantage over methods of lagging or jacketing that the manure can be
thrown over any pipe, water-seal, washing apparatus, &c., even if the
plant is constructed in several separate items. Unfortunately the ammonia
and the volatile organic compounds which are produced during the natural
decomposition of stable manure tend seriously to corrode iron and steel,
and therefore this method of protecting an apparatus from frost should
only be employed temporarily in times of emergency.
CORROSION IN APPARATUS.--All natural water is a solution of oxygen and
may be regarded also as a weak solution of the hypothetical carbonic
acid. It therefore causes iron to rust more or less quickly; and since no
paint is absolutely waterproof, especially if it has been applied to a
surface already coated locally with spots of rust, iron and steel cannot
be perfectly protected by its aid. More particularly at a few inches
above and below the normal level of the water in a holder, therefore, the
metal soon begins to exhibit symptoms of corrosion which may eventually
proceed until the iron is eaten away or becomes porous. One method of
prolonging the life of such apparatus is to give it fresh coats of paint
periodically; but unless the old layers are removed where they have
cracked or blistered, and the rust underneath is entirely scraped off
(which is practically impossible), the new paint films will not last very
long. Another more elegant process for preserving any metal like iron
which is constantly exposed to the attack of a corrosive liquid, and
which is readily applicable to acetylene holders and their tanks, depends
on the principle of galvanic action. When two metals in good electrical
contact are immersed in some liquid that is capable of attacking both,
only that metal will be attacked which is the more electro-positive, or
which (the same thing in other words) is the more readily attacked by the
liquid, evolving the more heat during its dissolution. As long as this
action is proceeding, as long, that is, as some of the more electro-
positive material is present, the less electro-positive material will not
suffer. All that has to be done, therefore, to protect the walls of an
acetylene-holder tank and the sides of its bell is to hang in the seal,
supported by a copper wire fastened to the tank walls by a trustworthy
electrical joint (soldering or riveting it), a plate or rod of some more
electro-positive metal, renewing that plate or rod before it is entirely
eaten away. [Footnote: Contact between the bell and the rod may be
established by means of a flexible metallic wire; or a separate rod might
be used for the bell itself.] If the iron is bare or coated with lead
(paint may be overlooked), the plate may be zinc; if the iron is
galvanised, _i.e._, coated with zinc, the plate may be aluminium or
an alloy of aluminium and zinc. The joint between the copper wire and the
zinc or aluminium plate should naturally be above the water-level. The
foregoing remarks should be read in conjunction with what was said in
Chapter II., about the undesirability of employing a soft solder
containing lead in the construction of an acetylene generator. Here it is
proposed intentionally to set up a galvanic couple to prevent corrosion;
there, with the same object in view, the avoidances of galvanic action is
counselled. The reason for this difference is self-evident; here a
foreign metal is brought into electrical contact with the apparatus in
order that the latter may be made electro-negative; but when a joint is
soldered with lead, the metal of the generator is unintentionally made
electro-positive. Here the plant is protected by the preferential
corrosion of a cheap and renewable rod; in the former case the plant is
encouraged to rust by the unnecessary presence of an improperly selected
metal.
OTHER ITEMS IN GENERATING PLANT.--It has been explained in Chapter II.
that the reaction between calcium carbide and water is very tumultuous in
character, and that it occurs with great rapidity. Clearly, therefore,
the gas comes away from the generator in rushes, passing into the next
item of the plant at great speed for a time, and then ceasing altogether.
The methods necessarily adopted for purifying the crude gas are treated
of in Chapter V.; but it is manifest now that no purifying material can
prove efficient unless the acetylene passes through it at a uniform rate,
and at one which is as slow as other conditions permit. For this reason
the proper position of the holder in an acetylene installation is before
the purifier, and immediately after the condenser or washer which adjoins
the generator. By this method of design the holder is filled up
irregularly, the gas passing into it sometimes at full speed, sometimes
at an imperceptible rate; but if the holder is well balanced and guided
this is a matter of no consequence. Out of the holder, on the other hand,
the gas issues at a rate which is dependent upon the number and capacity
of the burners in operation at any moment; and in ordinary conditions
this rate is so much more uniform during the whole of an evening than the
rate at which the gas is evolved from the carbide, that a purifier placed
after the holder is given a far better opportunity of extracting the
impurities from the acetylene than it would have were it situated before
the holder, as is invariably the case on coal-gas works.
For many reasons, such as capacity for isolation when being recharged or
repaired, it is highly desirable that each item in an acetylene plant
shall be separated, or capable of separation, from its neighbours; and
this observation applies with great force to the holder and the
decomposing vessel of the generator. In all large plants each vessel
should be fitted with a stopcock at its inlet and, if necessary, one at
its outlet, being provided also with a by-pass so that it can be thrown
out of action without interfering with the rest of the installation. In
the best practice the more important vessels, such as the purifiers, will
be in duplicate, so that unpurified gas need not be passed into the
service while a solitary purifier is being charged afresh. In smaller
plants, where less skilled labour will probably be bestowed on the
apparatus, and where hand-worked cocks are likely to be neglected or
misused, some more, automatic arrangement for isolating each item is
desirable. There are two automatic devices which may be employed for the
purposes in view, the non-return valve and the water-seal. The non-return
valve is simply a mushroom or ball valve without handle, lifted off its
seat by gas passing from underneath whenever the pressure of the gas
exceeds the weight of the valve, but falling back on to its seat and
closing the pipe when the pressure decreases or when pressure above is
greater than that below. The apparatus works perfectly with a clean gas
or liquid which is not corrosive; but having regard to the possible
presence of tarry products, lime dust, or sludge, condensed water loaded
with soluble impurities, &c., in the acetylene, a non-return valve is not
the best device to adopt, for both it and the hand-worked cock or screw-
down valve are liable to stick and give trouble. The best arrangement in
all respects, especially between the generator and the holder, is a
water-seal. A water-seal in made by leading the mouth of a pipe
delivering gas under the level of water in a suitable receptacle, so that
the issuing gas has to bubble through the liquid. Gas cannot pass
backwards through the pipe until it has first driven so much liquid
before it that the level in the seal has fallen below the pipe's mouth;
and if the end of the pipe is vertical more pressure than can possibly be
produced in the apparatus is necessary to effect this. Omitting the side
tube _b_, one variety of water-seal is shown at D in Fig. 7 on page
103. The water being at the level _l_, gas enters at _a_ and
bubbles through it, escaping from the apparatus at _c_. It cannot
return from _c_ to _a_ without driving the water out of the
vessel till its level falls from _f_ to _g_; and since the area
of the vessel is much greater than that of the pipe, so great a fall in
the vessel would involve a far greater rise in _a_. It is clear that
such a device, besides acting as a non-return valve, also fulfils two
other useful functions: it serves to collect and retain all the liquid
matter that may be condensed in the pipe _a_ from the spot at which
it was originally level or was given a fall to the seal, as well as that
condensing in _c_ as far as the spot where _c_ dips again; and
it equally acts as a washer to the gas, especially if the orifice
_g_ of the gas-inlet pipe is not left with a plain mouth as
represented in the figure, but terminates in a large number of small
holes, the pipe being then preferably prolonged horizontally, with minute
holes in it so as to distribute the gas throughout the entire vessel.
Such an apparatus requires very little attention. It may with advantage
be provided with the automatic arrangement for setting the water-level
shown at _d_ and _e_. _d_ is a tunnel tube extending
almost to the bottom of the vessel, and _e_ is a curved run-off pipe
of the form shown. The lower part of the upper curve in _e_ is above
the level _f_, being higher than _f_ by a distance equal to
that of the gas pressure in the pipes; and therefore when water is poured
into the funnel it fills the vessel till the internal level reaches
_f_, when the surplus overflows of itself. The operation thus not
only adjusts the quantity of water present to the desired level so that
_a_ cannot become unsealed, but it also renews the liquid when it
has become foul and nearly saturated with dissolved and condensed
impurities from the acetylene. It would be a desirable refinement to give
the bottom of the vessel a slope to the mouth of _e_, or to some
other spot where a large-bore draw-off cock could be fitted for the
purpose of extracting any sludge of lime, &c., that may collect. By
having such a water-seal, or one simpler in construction, between the
generator and the holder, the former may be safely opened at any time for
repairs, inspection, or the insertion of a fresh charge of carbide while
the holder is full of gas, and the delivery of acetylene to the burners
at a specified pressure will not be interrupted. If a cock worked by hand
were employed for the separation of the holder from the generator, and
the attendant were to forget to close it, part or all of the acetylene in
the holder would escape from the generator when it was opened or
disconnected.
Especially when a combined washer and non-return valve follows
immediately after a generator belonging to the shoot type, and the mouth
of the shoot is open to the air in the plant-house, it is highly
desirable that the washer shall be fitted with some arrangement of an
automatic kind for preventing the water level rising much above its
proper position. The liquid in a closed washer tends to rise as the
apparatus remains in use, water vapour being condensed within it and
liquid water, or froth of lime, being mechanically carried forward by the
stream of acetylene coming from the decomposing chamber. In course of
time, therefore, the vertical depth to which the gas-inlet pipe in the
washer is sealed by the liquid increases; and it may well be that
eventually the depth in question, plus the pressure thrown by the holder
bell, may become greater than the pressure which can be set up inside the
generator without danger of gas slipping under the lower edge of the
shoot. Should this state of things arise, the acetylene can no longer
force its way through the washer into the holder bell, but will escape
from the mouth of the shoot; filling the apparatus-house with gas, and
offering every opportunity for an explosion if the attendant disobeys
orders and takes a naked light with him to inspect the plant.
It is indispensable that every acetylene apparatus shall be fitted with a
safety-valve, or more correctly speaking a vent-pipe. The generator must
have a vent-pipe in case the gas-main leading to the holder should become
blocked at any time, and the acetylene which continues to be evolved in
all water-to-carbide apparatus, even after the supply of water has been
cut off be unable to pass away. Theoretically a non-automatic apparatus
does not require a vent-pipe in its generator because all the gas enters
the holder immediately, and is, or should be, unable to return through
the intermediate water seal; practically such a safeguard is absolutely
necessary for the reason given. The holder must have a safety-valve in
case the cutting-off mechanism of the generator fails to act, and more
gas passes into it than it can store. Manifestly the pressure of the gas
in a water-sealed holder or in any generator fitted with a water-sealed
lid cannot rise above that corresponding with the depth of water in the
seal; for immediately the pressure, measured in inches of water, equals
the depth of the sealing liquid, the seal will be blown out, and the gas
will escape. Such an occurrence, however, as the blowing of a seal must
never be possible in any item of an acetylene plant, more especially in
those items that are under cover, for the danger that the issuing gas
might be fired or might produce suffocation would be extremely great.
Typical simple forms of vent-pipe suitable for acetylene apparatus are
shown in Fig. 7. In each case the pipe marked "vent" is the so-called
safety-valve; it is open at its base for the entry of gas, and open at
its top for the escape of the acetylene into the atmosphere, such top
being in all instances carried through the roof of the generator-house
into the open air, and to a spot distant from any windows of that house
or of the residence, where it can prove neither dangerous nor a nuisance
by reason of its odour. At A is represented the vent-pipe of a
displacement vessel, which may either be part of a displacement holder or
of a generator working on the displacement principle. The vent-pipe is
rigidly fixed to the apparatus. If gas is generated within the closed
portion of the holder or passes through it, and if the pressure so set up
remains less than that which is needed to move the water from the level
_l_ to the levels _l'_ and _l"_, the mouth of the pipe is
under water, and acetylene cannot enter it; but immediately such an
amount of gas is collected, or such pressure is produced that the
interior level sinks below _l"_, which is that of the mouth of the
pipe, it becomes unsealed, and the surplus gas freely escapes. There are
two minor points in connexion with this form of vent-pipe often
overlooked. At the moment when the water arrives at _l"_ in the
closed half of the apparatus, its level in the interior of the vent-pipe
stands at _l'_, identical with that in the open hall of the
apparatus (for the mouth of the vent-pipe and the water in the open hall
of the apparatus are alike exposed to the pressure of the atmosphere
only). When the water, then, descends just below _l"_ there is an
amount of water inside the pipe equal in height to the distance between
_l'_ and _l"_; and before the acetylene can escape, it must
either force this water as a compact mass out of the upper mouth of the
vent-pipe (which it is clearly not in a position to do), drive it out of
the upper mouth a little at a time, or bubble through it till the water
is gradually able to run downwards out of the pipe as its lower opening
is more fully unsealed. In practice the acetylene partly bubbles through
this water and partly drives it out of the mouth of the pipe; on some
occasions temporarily yielding irregular pressures at the burners which
cause them to jump, and always producing a gurgling noise in the vent-
pipe which in calculated to alarm the attendant. If the pipe is too small
in diameter, and especially if its lower orifice is cut off perfectly
horizontal and constricted slightly, the water may refuse to escape from
the bottom altogether, and the pipe will fail to perform its allotted
task. It is better therefore to employ a wide tube, and to cut off its
mouth obliquely, or to give its lower extremity the shape of an inverted
funnel. At the half of the central divided drawing marked B (Fig. 7) is
shown a precisely similar vent-pipe affixed to the bell of a rising
holder, which behaves in an identical fashion when by the rising of the
bell its lower end is lifted out of the water in the tank. The features
described above as attendant, upon the act of unsealing of the
displacement-holder vent-pipe occur here also, but to a less degree; for
the water remaining in the pipe at the moment of unsealing is only that
which corresponds with the vertical distance between _l'_ and
_l"_, and in a rising holder this is only a height always equal to
the pressure given by the bell. Nevertheless this form of vent-pipe
produces a gurgling noise, and would be better for a trumpet-shaped
mouth. A special feature of the pipe in B is that unless it is placed
symmetrically about the centre of the bell its weight tends to throw the
bell out of the vertical, and it may have to be supported at its upper
part; conversely, if the pipe is arranged concentrically in the bell, it
may be employed as part of the guiding arrangement of the bell itself.
Manifestly, as the pipe must be long enough to extend through the roof of
the generator-house, its weight materially increases the weight of the
bell, and consequently the gas pressure in the service; this fact is not
objectionable provided due allowance is made for it. So tall a vent-pipe,
however, seriously raises the centre of gravity of the bell and may make
it top-heavy. To work well the centre of gravity of a holder bell should
be as low as possible, any necessary weighting being provided
symmetrically about its circumference and close to its bottom edge. The
whole length of an ascending vent-pipe need not be carried by the rising
bell, because the lower portion, which must be supported by the bell, can
be arranged to slide inside a wider length of pipe which is fixed to the
roof of the generator-house at the point where it passes into the open
air.
[Illustration: FIG. 7.--TYPICAL FORMS OF VENT-PIPES OR SAFETY-VALVES.]
A refinement upon this vent-pipe is represented at C, where it is rigidly
fastened to the tank of the holder, and has its internal aperture always
above the level of the water in the apparatus. Rigidly fixed to the crown
of the bell is a tube of wider diameter, _h_, which is closed at its
upper end. _h_ is always full of gas, and its mouth is normally
beneath the level of the water in the seal; but when the bell rises to
its highest permissible position, the mouth of _h_ comes above the
water, and communication is opened between the holder and the outer
atmosphere. No water enters the vent-pipe from the holder, and therefore
no gurgling or irregular pressure is produced. Another excellent
arrangement of a vent-pipe, suggested by Klinger of Gumpoldskirchen, is
shown at D, a drawing which has already been partly considered as a
washer and water-seal. For the present purpose the main vessel and its
various pipes are so dimensioned that the vertical height _g_ to
_f_ is always appreciably greater than the gas pressure in the
service or in the generator or gasholder to which it is connected. In
these circumstances the gas entering at _a_ depresses the water in
the pipe below the level _f_ to an extent equal to the pressure at
which it enters that pipe--an extent normally less than the distance
_f_ to _g_; and therefore gas never passes into the body of the
vessel, but travels away by the side tube _b_ (which in former
references to this drawing was supposed to be absent). If, however, the
pressure at _a_ exceeds that of the vertical height _f_ to
_g_, gas escapes at _g_ through the water, and is then free to
reach the atmosphere by means of the vent _c_. As before, _d_
serves to charge the apparatus with water, and _e_ to ensure a
proper amount being added. Clearly no liquid can enter the vent-pipe in
this device. Safety-valves such as are added to steam-boilers and the
like, which consist of a weighted lever holding a conical valve down
against its seat, are not required in acetylene apparatus, for the
simpler hydraulic seals discussed above can always be fitted wherever
they may be needed. It should be noticed that these vent-pipes only come
into operation in emergencies, when they are required to act promptly. No
economy is to be effected by making them small in diameter. For obvious
reasons the vent-pipe of a holder should have a diameter equal to that of
the gas-inlet tube, and the vent-pipe of a generator be equal in size to
the gas-leading tube.
FROTHING IN GENERATORS.--A very annoying trouble which crops up every now
and then during the evolution of acetylene consists in the production of
large masses of froth within the generator. In the ordinary way,
decomposition of carbide is accompanied by a species of effervescence,
but the bubbles should break smartly and leave the surface of the liquid
reasonably free from foam. Sometimes, however, the bubbles do not break,
but a persistent "head" of considerable height is formed. Further
production of gas only increases the thickness of the froth until it
rises so high that it is carried forward through the gas-main into the
next item of the plant. The froth disappears gradually in the pipes, but
leaves in them a deposit of lime which sooner or later causes
obstructions by accumulating at the angles and dips; while during its
presence in the main the steady passage of gas to the holder is
interrupted and the burners may even be made to jump. Manifestly the
defect is chiefly, if not always, to be noticed in the working of
carbide-to-water generators. The phenomenon has been examined by
Mauricheau-Beaupré, who finds that frothing is not characteristic of pure
carbide and that it cannot be attributed to any of the impurities
normally present in commercial carbide. If, however, the carbide contains
calcium chloride, frothing is liable to occur. A 0.1 per cent. solution
of calcium chloride appears to yield some foam when carbide is decomposed
in it, and a 1 per cent. solution to foam in a pronounced manner. In the
absence of calcium chloride, the main cause of frothing seems to be the
presence in the generator of new paint or tar. If a generator is taken
into use before the paint in any part of it which becomes moistened by
warm lime-water has had opportunity of drying thoroughly hard, frothing
is certain to occur; and even if the carbide has been stored for only a
short time in a tin or drum which has been freshly painted, a production
of froth will follow when it is decomposed in water. The products of the
polymerisation of acetylene also tend to produce frothing, but not to
such an extent as the turpentine in paint and the lighter constituents of
coal-tar. Carbide stored even temporarily in a newly painted tin froths
on decomposition because it has absorbed among its pores some of the
volatile matter given off by the paint during the process of desiccation.
THE "DRY" PROCESS OF GENERATION.--A process for generating acetylene,
totally different in principle from those hitherto considered, has been
introduced in this country. According to the original patents of G. J.
Atkins, the process consisted in bringing small or powdered carbide into
mechanical contact with some solid material containing water, the water
being either mixed with the solid reagent or attached to it as water of
crystallisation. Such reagents indeed were claimed as crude starch and
the like, the idea being to recover a by-product of pecuniary value. Now
the process seems to be known only in that particular form in which
granulated carbide is treated with crystallised sodium carbonate,
_i.e._, common washing soda. Assuming the carbide employed to be
chemically pure and the reaction between it and the water of
crystallisation contained in ordinary soda crystals to proceed
quantitatively, the production of acetylene by the dry process should be
represented by the following chemical equation:
5CaC_2 + Na_2CO_3.10H_2O = 5C_2H_2 + 5Ca(OH)_2 + Na_2CO_3.
On calculating out the molecular weights, it will be seen that 286 parts
of washing soda should suffice for the decomposition of 320 parts of pure
calcium carbide, or in round numbers 9 parts of soda should decompose 10
parts of carbide. In practice, however, it seems to be found that from 1
to 1.5 parts of soda are needed for every part of carbide.
The apparatus employed is a metal drum supported on a hollow horizontal
spindle, one end of which is closed and carries a winch handle, and the
other end of which serves to withdraw the gas generated in the plant. The
drum is divided into three compartments by means of two vertical
partitions so designed that when rotation proceeds in one particular
direction portions of the two reagents stored in one end compartment pass
into the centre compartment; whereas when rotation proceeds in the
opposite direction, the material in the centre compartment is merely
mixed together, partly by the revolution of the drum, partly with the
assistance of a stationary agitator slung loosely from the central
spindle. The other end compartment contains coke or sawdust or other dry
material through which the gas passes for the removal of lime or other
dust carried in suspension as it issues from the generating compartment.
The gas then passes through perforations into the central spindle, one
end of which is connected by a packed joint with a fixed pipe, which
leads to a seal or washer containing petroleum. Approached from a
theoretical standpoint, it will be seen that this method of generation
entirely sacrifices the advantages otherwise accruing from the use of
liquid water as a means for dissipating the heat of the chemical
reaction, but on the other hand, inasmuch as the substances are both
solid, the reaction presumably occurs more slowly than it would in the
presence of liquid water; and moreover the fact that the water employed
to act upon the carbide is in the solid state and also more or less
combined with the rest of the sodium carbonate molecule, means that, per
unit of weight, the water decomposed must render latent a larger amount
of heat than it would were it liquid. Experiments made by one of the
authors of this book tend to show that the gas evolved from carbide by
the dry process contains rather less phosphorus than it might in other
conditions of generation, and as a fact gas made by the dry process is
ordinarily consumed without previous passage through any chemical
purifying agent. It is obvious, however, that the use of the churn
described above greatly increases the labour attached to the production
of the gas; while it is not clear that the yield per unit weight of
carbide decomposed should be as high as that obtained in wet generation.
The inventor has claimed that his by-product should be valuable and
saleable, apparently partly on the ground that it should contain caustic
soda. Evidence, however, that a reaction between the calcium oxide or
hydroxide and the sodium carbonate takes place in the prevailing
conditions is not yet forthcoming, and the probabilities are that such
decomposition would not occur unless the residue were largely diluted
with water. [Footnote: The oldest process employed for manufacturing
caustic soda consisted in mixing a solution of sodium carbonate with
quick or slaked lime, and it has been well established that the
causticisation of the soda will not proceed when the concentration of the
liquid is greater than that corresponding with a specific gravity of
about 1-10, _i.e._, when the liquid contains more than some 8 to 10
per cent, of sodium hydroxide.] Conversely there are some grounds for
believing that the dry residue is less useful than an ordinary wet
residue for horticultural purposes, and also for the production of
whitewash. From a financial standpoint, the dry process suffers owing to
the expense involved in the purchase of a second raw material, for which
but little compensation can be discovered unless it is proved that the
residue is intrinsically more valuable than common acetylene-lime and can
be sold or used advantageously by the ordinary owner of an installation.
The discarding of the chemical purifier at the present day is a move of
which the advantage may well be overrated.
ARTIFICIAL LIGHTING OF GENERATOR SHEDS.--It has already been argued that
all normal or abnormal operations in connexion with an acetylene
generating plant should be carried out, if possible, by daylight; and it
has been shown that on no account must a naked light ever be taken inside
the house containing such a plant. It will occasionally happen, however,
that the installation must be recharged or inspected after nightfall. In
order to do this in safety, a double window, incapable of being opened,
should be fitted in one wall of the house, as far as possible from the
door, and in such a position that the light may fall on to all the
necessary places. Outside this window may be suspended an ordinary hand-
lantern burning oil or paraffin; or, preferably, round this window may be
built a closed lantern into which some source of artificial light may be
brought. If the acetylene plant has an isolated holder of considerable
size, there is no reason at all why a connexion should not be made with
the service-pipes, and an acetylene flame be used inside this lantern;
but with generators of the automatic variety, an acetylene light is not
so suitable, because of the fear that gas may not be available precisely
at the moment when it is necessary to have light in the shed. It would,
however, be a simple matter to erect an acetylene burner inside the
lantern in such a way that when needed an oil-lamp or candle could be
used instead. Artificial internal light of any kind is best avoided; the
only kind permissible being an electric glow-lamp. If this is employed,
it should be surrounded by a second bulb or gas-tight glass jacket, and
preferably by a wire cage as well; the wires leading to it must be
carefully insulated, and all switches or cut-outs (which may produce a
spark) must be out of doors. The well-known Davy safety or miner's lamp
is not a trustworthy instrument for use with acetylene because of
(_a_) the low igniting-point of acetylene; (_b_) the high
temperature of its flame; and (_c_) the enormous speed at which the
explosive wave travels through a mixture of acetylene and air. For these
reasons the metallic gauze of the Davy lamp is not so efficient a
protector of the flame as it is in cases of coal-gas, methane, &c.
Moreover, in practice, the Davy lamp gives a poor light, and unless in
constant use is liable to be found out of order when required. It should,
however, be added that modern forms of the safety lamp, in which the
light is surrounded by a stout glass chimney and only sufficient gauze is
used for the admission of fresh air and for the escape of the combustion
products, appear quite satisfactory when employed in an atmosphere
containing some free acetylene.
CHAPTER IV
THE SELECTION OF AN ACETYLENE GENERATOR
In Chapter II. an attempt has been made to explain the physical and
chemical phenomena which accompany the interaction of calcium carbide and
water, and to show what features in the reaction are useful and what
inconvenient in the evolution of acetylene on a domestic or larger scale.
Similarly in Chapter III. have been described the various typical devices
which may be employed in the construction of different portions of
acetylene plant, so that the gas may be generated and stored under the
best conditions, whether it is evolved by the automatic or by the non-
automatic system. This having been done, it seemed of doubtful utility to
include in the first edition of this work a long series of illustrations
of such generators as had been placed on the markets by British, French,
German, and American makers. It would have been difficult within
reasonable limits to have reproduced diagrams of all the generators that
had been offered for sale, and absolutely impossible within the limits of
a single hand-book to picture those which had been suggested or patented.
Moreover, some generating apparatus appeared on the market ephemerally;
some was constantly being modified in detail so as to alter parts which
experience or greater knowledge had shown the makers to be in need of
alteration, while other new apparatus was constantly being brought out.
On these and other grounds it did not appear that much good purpose would
have been served by describing the particular apparatus which at that
time would have been offered to prospective purchasers. It seemed best
that the latter should estimate the value and trustworthiness of
apparatus by studying a section of it in the light of the general
principles of construction of a satisfactory generator as enunciated in
the book. While the position thus taken by the authors in 1903 would
still not be incorrect, it has been represented to them that it would
scarcely be inconsistent with it to give brief descriptions of some of
the generators which are now being sold in Great Britain and a few other
countries. Six more years' experience in the design and manufacture of
acetylene plant has enabled the older firms of manufacturers to fix upon
certain standard patterns for their apparatus, and it may confidently be
anticipated that many of these will survive a longer period. Faulty
devices and designs have been weeded out, and there are lessons of the
past as well as theoretical considerations to guide the inventor of a new
type of generator. On those grounds, therefore, an attempt has now been
made to give brief descriptions, with sectional views, of a number of the
generators now on the market in Great Britain. Moreover, as the first
edition of this book found many readers in other countries, in several of
which there is greater scope for the use of acetylene, it has been
decided to describe also a few typical or widely used foreign generators.
All the generators described must stand or fall on their merits, which
cannot be affected by any opinion expressed by the authors. In the
descriptions, which in the first instance have generally been furnished
by the manufacturers of the apparatus, no attempt has therefore been made
to appraise the particular generators, and comparisons and eulogistic
comments have been excluded. The descriptions, however, would
nevertheless have been somewhat out of place in the body of this book;
they have therefore been relegated to a special Appendix. It has, of
course, been impossible to include the generators of all even of the
English manufacturers, and doubtless many trustworthy ones have remained
unnoticed. Many firms also make other types of generators in addition to
those described. It must not be assumed that because a particular make of
generator is not mentioned it is necessarily faulty. The apparatus
described may be regarded as typical or well known, and workable, but it
is not by reason of its inclusion vouched for in any other respect by the
authors. The Appendix is intended, not to bias or modify the judgment of
the would-be purchaser of a generator, but merely to assist him in
ascertaining what generators there are now on the market.
The observations on the selection of a generator which follow, as well as
any references in other chapters to the same matter, have been made
without regard to particular apparatus of which a description may (or may
not) appear in the Appendix. With this premise, it may be stated that the
intending purchaser should regard the mechanism of a generator as shown
in a sectional view or on inspection of the apparatus itself. If the
generator is simple in construction, he should be able to understand its
method of working at a glance, and by referring it to the type
(_vide_ Chapter III.) to which it belongs, be able to appraise its
utility from a chemical and physical aspect from what has already been
said. If the generator is too complicated for ready understanding of its
mode of working, it is not unlikely to prove too complicated to behave
well in practice. Not less important than the mechanism of a generator is
good construction from the mechanical point of view, _i.e._, whether
stout metal has been employed, whether the seams and joints are well
finished, and whether the whole apparatus has been built in the workman-
like fashion which alone can give satisfaction in any kind of plant.
Bearing these points in mind, the intending purchaser may find assistance
in estimating the mechanical value of an apparatus by perusing the
remainder of this chapter, which will be devoted to elaborating at length
the so-called scientific principles underlying the construction of a
satisfactory generator, and to giving information on the mechanical and
practical points involved.
It is perhaps desirable to remark that there is scarcely any feature in
the generation of acetylene from calcium carbide and water--certainly no
important feature--which introduces into practice principles not already
known to chemists and engineers. Once the gas is set free it ranks simply
as an inflammable, moisture-laden, somewhat impure, illuminating and
heat-giving gas, which has to be dried, purified, stored, and led to the
place of combustion; it is in this respect precisely analogous to coal-
gas. Even the actual generation is only an exothermic, or heat-producing,
reaction between a solid and a liquid, in which rise of temperature and
pressure must be prevented as far as possible. Accordingly there is no
fundamental or indispensable portion of an acetylene apparatus which
lends itself to the protection of the patent laws; and even the details
(it may be said truthfully, if somewhat cynically) stand in patentability
in inverse ratio to their simplicity and utility.
During the early part of 1901 a Committee appointed by the British Home
Office, "to advise as to the conditions of safety to which acetylene
generators should conform, and to carry out tests of generators in the
market in order to ascertain how far those conform with such conditions,"
issued a circular to the trade suggesting that apparatus should be sent
them for examination. In response, forty-six British generators were
submitted for trial, and were examined in a fashion which somewhat
exceeded the instructions given to the Committee, who finally reported to
the Explosives Department of the Home Office in a Blue Book, No. Cd. 952,
which can be purchased through any bookseller. This report comprises an
appendix in which most of the apparatus are illustrated, and it includes
the result of the particular test which the Committee decided to apply.
Qualitatively the test was useful, as it was identical in all instances,
and only lacks full utility inasmuch as the trustworthiness of the
automatic mechanism applied to such generators as were intended to work
on the automatic system was not estimated. Naturally, a complete
valuation of the efficiency of automatic mechanism cannot be obtained
from one or even several tests, it demands long-continued watching; but a
general notion of reliability might have been obtained. Quantitatively,
however, the test applied by the Committee is not so free from reproach,
for, from the information given, it would appear to have been less fair
to some makers of apparatus than to others. Nevertheless the report is
valuable, and indicates the general character of the most important
apparatus which were being offered for sale in the United Kingdom in
1900-1901.
It is not possible to give a direct answer to the question as to which is
the best type of acetylene generator. There are no generators made by
responsible firms at the present time which are not safe. Some may be
easier to charge and clean than others; some require more frequent
attention than others; some have moving parts less likely to fail, when
handled carelessly, than others; some have no moving mechanism to fail.
For the illumination of a large institution or district where one man can
be fully occupied in attending to the plant, cleaning, lighting, and
extinguishing the lamps, or where other work can be found for him so as
to leave him an hour or so every day to look after the apparatus, the
hand-fed carbide-to-water generator L (Fig. 6) has many advantages, and
is probably the best of all. In smaller installations choice must be made
first between the automatic and the non-automatic principle--the
advantages most frequently lying with the latter. If a non-automatic
generator is decided upon, the hand carbide-feed or the flooded-
compartment apparatus is almost equally good; and if automatism is
desired, either a flooded-compartment machine or one of the most
trustworthy types of carbide-feed apparatus may be taken. There are
contact apparatus on the markets which appear never to have given
trouble, and those are worthy of attention. Some builders advocate their
own apparatus because the residue is solid and not a cream. If there is
any advantage in this arising from greater ease in cleaning and
recharging the generator and in disposing of the waste, that advantage is
usually neutralised by the fear that the carbide may not have been wholly
decomposed within the apparatus; and whereas any danger arising from
imperfectly spent carbide being thrown into a closed drain may be
prevented by flooding the residue with plenty of water in an open vessel,
imperfect decomposition in the generator means a deficiency in the amount
of gas evolved from a unit weight of solid taken or purchased. In fact,
setting on one side apparatus which belong to a notoriously defective
system and such as are constructed in large sizes on a system that is
only free from overheating, &c., in small sizes; setting aside all
generators which are provided with only one decomposing chamber when they
are of a capacity to require two or more smaller ones that can more
efficiently be cooled with water jackets; and setting aside any form of
plant which on examination is likely to exhibit any of the more serious
objections indicated in this and the previous chapters, there is
comparatively little to choose, from the chemical and physical points of
view, between the different types of generators now on the markets. A
selection may rather be made on mechanical grounds. The generator must be
well able to produce gas as rapidly as it will ever be required during
the longest or coldest evening; it must be so large that several more
brackets or burners can be added to the service after the installation is
complete. It must be so strong that it will bear careless handling and
the frequent rough manipulation of its parts. It must be built of stout
enough material not to rust out in a few years. Each and all of its parts
must be accessible and its exterior visible. Its pipes, both for gas and
sludge, must be of large bore (say 1 inch), and fitted at every dip with
an arrangement for withdrawing into some closed vessel the moisture, &c.,
that may condense. The number of cocks, valves, and moving parts must be
reduced to a minimum; cocks which require to be shut by hand before
recharging must give way to water-seals. It must be simple in all its
parts, and its action intelligible at a glance. It must be easy to
charge--preferably even by the sense of touch in darkness. It must be
easy to clean. The waste lime must be easily removed. It must be so
fitted with vent-pipes that the pressure can never rise above that at
which it is supposed to work. Nevertheless, a generator in which these
vent-pipes are often brought into use is badly constructed and wasteful,
and must be avoided. The water of the holder seal should be distinct from
that used for decomposing the carbide; and those apparatus where the
holder is entirely separated from the generator are preferable to such as
are built all in one, even if water-seals are fitted to prevent return of
gas. Apparatus which is supposed to be automatic should be made perfectly
automatic, the water or the carbide-feed being locked automatically
before the carbide store, the decomposing chamber, or the sludge-cock can
be opened. The generating chamber must always be in communication with
the atmosphere through a water-sealed vent-pipe, the seal of which, if
necessary, the gas can blow at any time. All apparatus should be fitted
with rising holders, the larger the better. Duplicate copies of printed
instructions should be demanded of the maker, one copy being kept in the
generator-house, and the other elsewhere for reference in emergencies.
These instructions must give simple and precise information as to what
should be done in the event of a breakdown as well as in the normal
manipulation of the plant. Technical expressions and descriptions of
parts understood only by the maker must be absent from these rules.
ADDENDUM.
BRITISH AND FOREIGN REGULATIONS FOR THE CONSTRUCTION AND INSTALLATION OF
ACETYLENE GENERATING PLANT
Dealing with the "conditions which a generator should fulfil before it
can be considered as being safe," the HOME OFFICE COMMITTEE of 1901
before mentioned write as follows:
1. The temperature in any part of the generator, when run at the maximum
rate for which it is designed, for a prolonged period, should not exceed
130° C. This may be ascertained by placing short lengths of wire, drawn
from fusible metal, in those parts of the apparatus in which heat is
liable to be generated.
2. The generator should have an efficiency of not less than 90 per cent.,
which, with carbide yielding 5 cubic feet per pound, would imply a yield
of 4.5 cubic feet for each pound of carbide used.
3. The size of the pipes carrying the gas should be proportioned to the
maximum rate of generation, so that undue back pressure from throttling
may not occur.
4. The carbide should be completely decomposed in the apparatus, so that
lime sludge discharged from the generator shall not be capable of
generating more gas.
5. The pressure in any part of the apparatus, on the generator side of
the holder, should not exceed that of 20 inches of water, and on the
service side of same, or where no gasholder is provided, should not
exceed that of 5 inches of water.
6. The apparatus should give no tarry or other heavy condensation
products from the decomposition of the carbide.
7. In the use of a generator regard should be had to the danger of
stoppage of passage of the gas and resulting increase of pressure which
may arise from the freezing of the water. Where freezing may be
anticipated, steps should be taken to prevent it.
8. The apparatus should be so constructed that no lime sludge can gain
access to any pipes intended for the passage of gas or circulation of
water.
9. The use of glass gauges should be avoided as far as possible, and,
where absolutely necessary, they should be effectively protected against
breakage.
10. The air space in a generator before charging should be as small as
possible.
11. The use of copper should be avoided in such parts of the apparatus as
are liable to come in contact with acetylene.
The BRITISH ACETYLENE ASSOCIATION has drawn up the following list of
regulations which, it suggests, shall govern the construction of
generators and the installation of piping and fittings:
1. Generators shall be so constructed that, when used in accordance with
printed instructions, it shall not be possible for any undecomposed
carbide to remain in the sludge removed therefrom.
2. The limit of pressure in any part of the generator shall not exceed
that of 20 inches of water, subject to the exception that if it be shown
to the satisfaction of the Executive of the Acetylene Association that
higher pressures up to 50 inches of water are necessary in certain
generators, and are without danger, the Executive may, with the approval
of the Home Office, grant exemption for such generators, with or without
conditions.
3. The limit of pressure in service-pipes, within the house, shall not
exceed 10 inches of water.
4. Except when used for special industrial purposes, such as oxy-
acetylene welding, factories, lighthouses, portable apparatus containing
not more than four pounds of carbide, and other special conditions as
approved by the Association, the acetylene plant, such as generators,
storage-holders, purifiers, scrubbers, and for washers, shall be in a
suitable and well-ventilated outhouse, in the open, or in a lean-to,
having no direct communication with a dwelling-house. A blow-off pipe or
safety outlet shall be arranged in such a manner as to carry off into the
open air any overmake of gas and to open automatically if pressure be
increased beyond 20 inches water column in the generating chamber or
beyond 10 inches in the gasholder, or beyond the depth of any fluid seal
on the apparatus.
5. Generators shall have sufficient storage capacity to make a serious
blow-off impossible.
6. Generators and apparatus shall be made of sufficiently strong material
and be of good workmanship, and shall not in any part be constructed of
unalloyed copper.
7. It shall not be possible under any conditions, even by wrong
manipulation of cocks, to seal the generating chamber hermetically.
8. It shall not be possible for the lime sludge to choke any of the gas-
pipes in the apparatus, nor water-pipes if such be alternately used as
safety-valves.
9. In the use of a generator, regard shall be had to the danger of
stoppage of passage of the gas, and resulting increase of pressure, which
may arise from the freezing of the water. Where freezing may be
anticipated, steps shall be taken to prevent it.
10. The use of glass gauges shall be avoided as far as possible, and
where absolutely necessary they shall be effectively protected against
breakage.
11. The air space in the generator before charging shall be as small as
possible, _i.e._, the gas in the generating chamber shall not
contain more than 8 per cent. of air half a minute after commencement of
generation. A sample of the contents, drawn from the holder any time
after generation has commenced, shall not contain an explosive mixture,
_i.e._, more than 18 per cent, of air. This shall not apply to the
initial charges of the gasholder, when reasonable precautions are taken.
12. The apparatus shall produce no tarry or other heavy condensation
products from the decomposition of the carbide.
13. The temperature of the gas, immediately on leaving the charge, shall
not exceed 212° F. (100° C.)
14. No generator shall be sold without a card of instructions suitable
for hanging up in some convenient place. Such instructions shall be of
the most detailed nature, and shall not presuppose any expert knowledge
whatever on the part of the operator.
15. Notice to be fixed on Generator House Door, "NO LIGHTS OR SMOKING
ALLOWED."
16. Every generator shall have marked clearly upon the outside a
statement of the maximum number of half cubic foot burners and the charge
of carbide for which it is designed.
17. The Association strongly advise the use of an efficient purifier with
generating plant for indoor lighting.
18. No composition piping shall be used in any part of a permanent
installation.
19. Before being covered in, all pipe-work (main and branches) shall be
tested in the following manner: A special acetylene generator, giving a
pressure of at least 10 inches water column in a gauge fixed on the
furthest point from the generator, shall be connected to the pipe-work.
All points shall be opened until gas reaches them, when they shall be
plugged and the main cock on the permanent generator turned off, but all
intermediate main cocks shall be open in order to test underground main
and all connexions. The gauge must not show a loss after generator has
been turned off for at least two hours.
20. After the fittings (pendants, brackets, &c.) have been fixed and all
burners lighted, the gas shall be turned off at the burners and the whole
installation shall be re-tested, but a pressure of 5 inches shall be
deemed sufficient, which shall not drop lower than to 4-1/2 inches on the
gauge during one hour's test.
21. No repairs to, or alterations in, any part of a generator, purifier,
or other vessel which has contained acetylene shall be commenced, nor,
except for recharging, shall any such part or vessel be cleaned out until
it has been completely filled with water, so as to expel any acetylene or
mixture of acetylene and air which may remain in the vessel, and may
cause a risk of explosion.
_Recommendation_.--It being the general practice to store carbide in
the generator-house, the Association recommend that the carbide shall be
placed on a slightly raised platform above the floor level.
THE BRITISH FIRE OFFICES COMMITTEE in the latest revision, dated July 15,
1907, of its Rules and Regulations _re_ artificial lighting on
insured premises, includes the following stipulations applicable to
acetylene:
Any apparatus, except as below, for generating, purifying, enriching,
compressing or storing gas, must be either in the open or in a building
used for such purposes only, not communicating directly with any building
otherwise occupied.
An acetylene portable apparatus is allowed, provided it holds a charge of
not more than 2 lb. of carbide.
A cylinder containing not more than 20 cubic feet of acetylene compressed
and (or) dissolved in accordance with an Order of Secretary of State
under the Explosives Act, 1875, is allowed.
The use of portable acetylene lamps containing charges of carbide
exceeding the limit of 2 lb. allowed under these Rules (the average
charge being about 18 lb.) is allowed in the open or in buildings in
course of erection.
Liquid acetylene must not be used or stored on the premises.
The pipe, whether flexible or not, connecting an incandescent gas lamp to
the gas-supply must be of metal with metal connexions.
(The reference in these Rules to the storage of carbide has been quoted
in Chapter II. (page 19).)
These rules are liable to revision from time to time.
The GERMAN ACETYLENE VEREIN has drawn up (December 1904) the following
code of rules for the construction, erection, and manipulation of
acetylene apparatus:
I. _Rules for Construction._
1. All apparatus for the generation, purification, and storage of
acetylene must be constructed of sheet or cast iron. Holder tanks may be
built of brick.
2. When bare, galvanised, or lead-coated sheet-iron is used, the sides of
generators, purifiers, condensers, holder tanks, and (if present) washers
and driers must be built with the following gauges as minima:
Holder bells. All other apparatus.
Up to 7 cubic feet capacity 0.75 mm. 1.00 mm.
From 7 to 18 " 1.00 1.25
From 18 to 53 " 1.25 1.50
Above 53 " 1.50 2.00
When not constructed of cast-iron, the bottoms, covers, and "manhole"
lids must be 0.5 mm. thicker in each respective size.
In all circumstances, the thickness of the walls--especially in the case
of apparatus not circular in horizontal section--must be such that
alteration in shape appears impossible, unless deformation is guarded
against in other ways.
Generators must be so constructed that when they are being charged the
carbide cannot fall into the residue which has already been gasified; and
the residues must always be capable of easy, complete, and safe removal.
3. Generators, purifiers, and holders must be welded, riveted or folded
at the seams; soft solder is only permissible as a tightening material.
4. Pipes delivering acetylene, or uniting the apparatus, must be cast- or
wrought-iron. Unions, cocks, and valves must not be made of copper; but
the use of brass and bronze is permitted.
5. When cast-iron is employed, the rules of the German Gas and Water
Engineers are to be followed.
6. In generators where the whole amount of carbide introduced is not
gasified at one time, it must be possible to add fresh water or carbide
in safety, without interfering with the action of the apparatus. In such
generators the size of the gasholder space is to be calculated according
to the quantity of carbide which can be put into the generator. For every
1 kilogramme of carbide the available gasholder space must be: for the
first 50 kilos., 20 litres; for the next 50 kilos., 15 litres; for
amounts above 100 kilos., 10 litres per kilo. [One kilogramme may be
taken as 2.2 lb., and 28 litres as 1 cubic foot.]
The generator must be large enough to supply the full number of normal
(10-litre) burners with gas for 5 hours; the yield of acetylene being
taken at 290 litres per kilo. [4.65 cubic feet per lb.]
The gasholder space of apparatus where carbide is not stored must be at
least 30 litres for every normal (10-litre) flame.
7. The gasholder must be fitted with an appliance for removing any gas
which may be generated (especially when the apparatus is first brought
into action) after the available space is full. This vent must have a
diameter at least equal to the inlet pipe of the holder.
8. Acetylene plant must be provided with purifying apparatus which
contains a proper purifying material in a suitable condition.
9. The dimensions of subsidiary apparatus, such as washers, purifiers,
condensers, pipes, and cocks must correspond with the capacity of the
plant.
10. Purifiers and washers must be constructed of materials capable of
resisting the attack of the substances in them.
11. Every generator must bear a plate giving the name of the maker, or
the seller, and the maximum number of l0-litre lights it is intended to
supply. If all the carbide put into the generator is not gasified at one
time, the plate must also state the maximum weight of carbide in the
charge. The gasholder must also bear a plate recording the maker's or
seller's name, as well as its storage capacity.
12. Rules 1 to 11 do not apply to portable apparatus serving up to two
lights, or to portable apparatus used only out of doors for the lighting
of vehicles or open spaces.
II. _Rules for Erection_
1. Acetylene apparatus must not be erected in or under rooms occupied or
frequented (passages, covered courts, &c.) by human beings. Generators
and holders must only be erected in apartments covered with light roofs,
and separated from occupied rooms, barns, and stables by a fire-proof
wall, or by a distance of 15 feet. Any wall is to be considered fire-
proof which is built of solid brick, without openings, and one side of
which is "quite free." Apparatus may be erected in barns and stables,
provided the space required is partitioned off from the remainder by a
fire-proof wall.
2. The doors of apparatus sheds must open outwards, and must not
communicate directly with rooms where fires and artificial lights are
used.
3. Apparatus for the illumination of showmen's booths, "merry-go-rounds,"
shooting galleries, and the like must be erected outside the tents, and
be inaccessible to the public.
4. Permanent apparatus erected in the open air must be at least 15 feet
from an occupied building.
5. Apparatus sheds must be fitted at their highest points with outlet
ventilators of sufficient size; the ventilators leading straight through
the roof into the open air. They must be so arranged that the escaping
gases and vapours cannot enter rooms or chimneys.
6. The contacts of any electrical warning devices must be outside the
apparatus shed.
7. Acetylene plants must be prevented from freezing by erection in frost-
free rooms, or by the employment of a heating apparatus or other suitable
appliance. The heat must only be that of warm water or steam. Furnaces
for the heating appliance must be outside the rooms containing
generators, their subsidiary apparatus, or holders; and must be separated
from such rooms by fire-proof walls.
8. In one of the walls of the apparatus shed--if possible not that having
a door--a window must be fitted which cannot be opened; and outside that
window an artificial light is to be placed. In the usual way acetylene
lighting may be employed; but a lamp burning paraffin or oil, or a
lantern enclosing a candle, must always be kept ready for use in
emergencies. In all circumstances internal lighting is forbidden.
9. Every acetylene installation must be provided with a main cock, placed
in a conveniently accessible position so that the whole of the service
may be cut off from the plant.
10. The seller of an apparatus must provide his customer with a sectional
drawing, a description of the apparatus, and a set of rules for attending
to it. These are to be supplied in duplicate, and one set is to be kept
hanging up in the apparatus shed.
III. Rules for Working the Apparatus.
1. The apparatus must only be opened by daylight for addition of water.
If the generator is one of those in which the entire charge of carbide is
not gasified at once, addition of fresh carbide must only be made by
daylight.
2. All work required by the plant, or by any portion of it, and all
ordinary attendance needed must be performed by daylight.
3. All water-seals must be carefully kept full.
4. When any part of an acetylene apparatus or a gas-meter freezes,
notwithstanding the precautions specified in II., 7, it must be thawed
only by pouring hot water into or over it; flames, burning fuel, or red-
hot iron bars must not be used.
5. Alterations to any part of an apparatus which involve the operations
of soldering or riveting, &c., _i.e._, in which a fire must be used,
or a spark may be produced by the impact of hammer on metal, must only be
carried out by daylight in the open air after the apparatus has been
taken to pieces. First of all the plant must be freed from gas. This is
to be done by filling every part with water till the liquid overflows,
leaving the water in it for at least five minutes before emptying it
again.
6. The apparatus house must not be used for any other operation, nor
employed for the storage of combustible articles. It must be efficiently
ventilated, and always kept closed. A notice must be put upon the door
that unauthorised persons are not permitted to enter.
7. It in forbidden to enter the house with a burning lantern or lamp, to
strike matches, or to smoke therein.
8. A search for leaks in the pipes must not be made with the aid of a
light.
9. Alterations to the service must not be made while the pipes are under
pressure, but only after the main cock has been shut.
10. If portable apparatus, such as described in I., 12, are connected to
the burners with rubber tube, the tube must be fortified with an internal
or external spiral of wire. The tube must be fastened at both ends to the
cocks with thread, copper wire, or with ring clamps.
11. The preparation, storage, and use of compressed or liquefied
acetylene is forbidden. By compressed acetylene, however, is only to be
understood gas compressed to a pressure exceeding one effective
atmosphere. Acetylene compressed into porous matter, with or without
acetone, is excepted from this prohibition.
12. In the case of plants serving 50 lights or less, not more than 100
kilos. of carbide in closed vessels may be kept in the apparatus house
besides the drum actually in use.
A fresh drum is not to be opened before the previous one has been two-
thirds emptied. Opened drums must be closed with an iron watertight lid
covering the entire top of the vessel.
In the case of apparatus supplying over 500 lights, only one day's
consumption of carbide must be kept in the generator house. In other
respects the store of carbide for such installations is to be treated as
a regular carbide store.
13. Carbide drums must not be opened with the aid of a flame or a red-hot
iron instrument.
14. Acetylene apparatus must only be attended to by trustworthy and
responsible persons.
The rules issued by the AUSTRIAN GOVERNMENT in 1905 for the installation
of acetylene plant and the use of acetylene are divided into general
enactments relating to acetylene, and into special enactments in regard
to the apparatus and installation. The general enactments state that:
1. The preparation and use of liquid acetylene is forbidden.
2. Gaseous acetylene, alone, in admixture, or in solution, must not be
compressed above 2 atmospheres absolute except under special permission.
3. The storage of mixtures of acetylene with air or other gases
containing or evolving free oxygen is forbidden.
4. A description of every private plant about to be installed must be
submitted to the local authorities, who, according to its size and
character, may give permission for it to be installed and brought into
use either forthwith or after special inspection. Important alterations
to existing plant must be similarly notified.
5. The firms and fitters undertaking the installation of acetylene plant
must be licensed.
The special enactments fall under four headings, viz., (_a_)
apparatus; (_b_) plant houses; (_c_) pipes; (_d_)
residues.
In regard to apparatus it is enacted that:
1. The type of apparatus to be employed must be one which has been
approved by one of certain public authorities in the country.
2. A drawing and description of the construction of the apparatus and a
short explanation of the method of working it must be fixed in a
conspicuous position under cover in the apparatus house. The notice must
also contain approved general information as to the properties of calcium
carbide and acetylene, precautions that must be observed to guard against
possible danger, and a statement of how often the purifier will require
to be recharged.
3. The apparatus must be marked with the name of the maker, the year of
its construction, the available capacity of the gasholder, and the
maximum generating capacity per hour.
4. Each constituent of the plant must be proportioned to the maximum
hourly output of gas and in particular the available capacity of the
holder must be 75 per cent. of the latter. The apparatus must not be
driven above its nominal productive capacity.
5. The productive capacity of generators in which the gasholder has to be
opened or the bell removed before recharging, or for the removal of
sludge, must not exceed 50 litres per hour, nor may the charge of carbide
exceed 1 kilo.
6. Generators exceeding 50 litres per hour productive capacity must be
arranged so that they can be freed from air before use.
7. Generators exceeding 1500 litres per hour capacity must be arranged so
that the acetylene, contained in the parts of the apparatus which have to
be opened for recharging or for the removal of sludge, can be removed
before they are opened.
8. Automatic generators of which the decomposing chambers are built
inside the gasholder must not exceed 300 litres per hour productive
capacity.
9. Generators must be arranged so that after-generation cannot produce
objectionable results.
10. The holder of carbide-to-water generators must be large enough to
take all the gas which may be produced by the introduction of one charge
of carbide without undue pressure ensuing.
11. The maximum pressure permissible in any part of the apparatus is 1.1
atmosphere absolute.
12. The temperature in the gas space of a generator must never exceed 80°
C.
13. Generating apparatus, &c., must be constructed in a workmanlike
manner of metal capable of resisting rust and distortion, and, where the
metal comes in contact with carbide or acetylene, it must not be one
(copper in particular) which forms an explosive compound with the gas.
Cocks and screw connexions, &c., of brass, bronze, &c., must always be
kept clean. Joints exposed to acetylene under pressure must be made by
riveting or welding except that in apparatus not exceeding 100 litres per
hour productive capacity double bending may be used.
14. Every apparatus must be fitted with a safety-valve or vent-pipe
terminating in a safe place in the open, and of adequate size.
15. Every apparatus must be provided with an efficient purifier so fitted
that it may be isolated from the rest of the plant and with due
consideration of the possible action of the purifying material upon the
metal used.
16. Mercury pressure gauges are prohibited. Liquid gauges, if used must
be double the length normally needed, and with a cock which in automatic
apparatus must be kept shut while it is in action.
17. Proper steps must always be taken to prevent the apparatus freezing.
In the absence of other precautions water-seals and pressure-gauges must
be filled with liquid having a sufficiently low freezing-point and
without action on acetylene or the containing vessel.
18. Signal devices to show the position of the gasholder bell must not be
capable of producing sparks inside the apparatus house.
19. Leaks must not be sought for with an open flame and repairs requiring
the use of a blow-pipe, &c., must only be carried out after the apparatus
has been taken to pieces or freed from gas by flooding.
20. Apparatus must only be attended to by trustworthy and responsible
adults.
21. Portable apparatus holding not more than 1 kilo. of carbide and of
not more than 50 litres per hour productive capacity, and apparatus fixed
and used out of doors are exempt from the foregoing regulations except
Nos. 11 and 12, and the first part of 13.
In regard to (_b_), plant houses, it is enacted that:
1. Rooms containing acetylene apparatus must be of ample size, used for
no other purpose, have water-tight floors, be warmed without fireplaces
or chimneys, be lighted from outside through an air-tight window by an
independent artificial light, have doors opening outwards, efficient
ventilation and a store of sand or like material for fire extinction.
Strangers must be warned away.
2. Apparatus of not more than 300 litres per hour productive capacity may
be erected in basements or annexes of dwelling houses, but if of over 50
litres per hour capacity must not be placed under rooms regularly
frequented. Rooms regularly frequented and those under the same must not
be used.
3. Apparatus of more than 300 litres per hour productive capacity must be
erected in an independent building at least 15 feet distant from other
property, which building, unless it is at least 30 feet distant, must be
of fire-proof material externally.
4. Gasholders exceeding 280 cubic foot in capacity must be in a detached
room or in the open and inaccessible to strangers, and at least 30 feet
from other property and with lightning conductors.
5. In case of fire the main cock must not be shut until it is ascertained
that no one remains in the room served with the gas.
6. All acetylene installations must be known to the local fire brigade.
In regard to (_c_), pipes, it is enacted that:
1. Mains for acetylene must be separated from the generating apparatus by
a cock, and under a five-minute test for pressure must not show a fall of
over eight-tenths inch when the pressure is 13.8 inches, or three times
the working pressure, whichever is greater.
2. The pipes must as a rule be of iron, though lead may be used where
they are uncovered and not exposed to risk of injury. Rubber connexions
may only be used for portable apparatus, and attached to a terminal on
the metal pipes provided with a cock, and be fastened at both ends so
that they will not slip off the nozzles.
In regard to (_d_), residues, it is enacted that special open or
well-ventilated pits must be provided for their reception when the
apparatus exceeds 300 litres per hour productive capacity. With smaller
apparatus they may be discharged into cesspools if sufficiently diluted.
The ITALIAN GOVERNMENT regulations in regard to acetylene plant are
divided into eight sections. The first of these relates to the production
and use of liquid and compressed acetylene. The production and use of
liquid acetylene is prohibited except under the provisions of the laws
relating to explosives. Neat acetylene must not be compressed to more
than l-1/2 atmospheres except that an absolute pressure of 10 atmospheres
is allowed when the gas is dissolved in acetone or otherwise rendered
free from risk. Mixtures of acetylene with air or oxygen are forbidden,
irrespective of the pressure or proportions. Mixtures of acetylene with
hydrocarbons, carbonic oxide, hydrogen and inert gases are permitted
provided the proportion of acetylene does not exceed 50 per cent. nor the
absolute pressure 10 atmospheres.
The second section relates to acetylene installations, which are
classified in four groups, viz., (_a_) fixed or portable apparatus
supplying not more than thirty burners consuming 20 litres per hour;
(_b_) private installations supplying between 30 and 200 such
burners; (_c_) public or works installations supplying between 30
and 200 such burners; (_d_) installations supplying more than 200
such burners.
The installations must comply with the following general conditions:
1. No part of the generator when working at its utmost capacity should
attain a temperature of more than 100° C.
2. The carbide must be completely decomposed in the apparatus so that no
acetylene can be evolved from the residue. The residues must be diluted
with water before being discharged into drains or cesspools, and sludge
storage-pits must be in the open.
3. The apparatus must preclude the escape of lime into the gas and water
connexions.
4. Glass parts must be adequately protected.
5. Rubber connexions between the generator, gasholder, and main are
absolutely prohibited with installations supplying more than 30 burners.
6. Cocks must be provided for cutting off the main and connexions from
the generator and gasholder.
7. Each burner must have an independent tap.
8. Generators of groups (_b_), (_c_), and (_d_) must be
constructed so that no after-generation of acetylene can take place
automatically and that any surplus gas would in any case be carried out
of the generator house by a vent-pipe.
The third section deals with generator houses, which must be well
ventilated and light; must not be used for any other purpose except to
store one day's consumption of carbide, not exceeding 300 kilos.; must be
fire-proof; must have doors opening outwards; and the vent-pipes must
terminate at a safe place in the open. Apparatus of group (_b_) must
not be placed in a dwelling-room and only in an adjoining room if the
gasholder is of less than 600 litres capacity. Apparatus of group
(_c_) must be in an independent building which must be at least 33
feet from occupied premises if the capacity of the gasholder is 6000
litres and upwards. Half this distance suffices for gasholders containing
600 to 6000 litres. These distances may be reduced at the discretion of
the local authorities provided a substantial partition wall at least 1
foot thick is erected. Apparatus of group (_d_) must be at least 50
feet from occupied premises and the gasholder and generator must not be
in the same building.
The fourth section deals with the question of authorisation for the
installation of acetylene plant. Apparatus of group (_a_) may be
installed without obtaining permission from any authorities. In regard to
apparatus of the other groups, permission for installation must be
obtained from local or other authorities.
The fifth section relates to the working of acetylene plant. It makes the
concessionaires and owners of the plant responsible for the manipulation
and supervision of the apparatus, and for the employment of suitable
operators, who must not be less than 18 years of age.
The sixth section relates to the inspection of acetylene plant from time
to time by inspectors appointed by the local or other authorities.
Apparatus of group (_a_) is not subject to these periodical
inspections.
The seventh section details the fees payable for the inspection of
installations and carbide stores, and fixes the penalties for non-
compliance with the regulations.
The eighth section refers to the notification of the position and
description of all carbide works, stores, and acetylene installations to
the local authorities.
The HUNGARIAN GOVERNMENT rules for the construction and examination of
acetylene plant forbid the use of copper and of its alloys; cocks,
however, may be made of a copper alloy. The temperature in the gas space
of a fixed generator must not exceed 50° C., in that of a portable
apparatus 80° C. The maximum effective pressure permissible is 0.15
atmosphere.
The CONSEIL D'HYGIÈNE DE LA SEINE IN FRANCE allows a maximum pressure of
1.5 metres, i.e., 59 inches, of water column in generators used for the
ordinary purposes of illumination; but apparatus intended to supply gas
to the low-pressure oxy-acetylene blowpipe (see Chapter IX.) may develop
up to 2.5 metres, or 98.5 inches of water pressure, provided copper and
its alloys are entirely excluded from the plant and from the delivery-
pipes.
The NATIONAL BOARD OF FIRE UNDERWRITERS OF THE UNITED STATES OF AMERICA
has issued a set of rules and requirements, of which those relating to
acetylene generators and plant are reproduced below. The underwriters
state that, "To secure the largest measure of safety to life and
property, these rules for the installation of acetylene gas machines must
be observed."
RULES FOR THE INSTALLATION AND USE OF ACETYLENE GAS GENERATORS.
[Footnote: The "gallon" of these rules is, of course, the American
gallon, which is equal to 0.83 English standard gallon.]
The use of liquid acetylene or gas generated therefrom is absolutely
prohibited.
Failure to observe these rules is as liable to endanger life as property.
To secure the largest measure of safety to life and property, the
following rules for the installation of acetylene gas machines must be
observed.
_Class A.--Stationary Automatic Apparatus._
1. FOUNDATIONS.--(_a_) Must, where practicable, be of brick, stone,
concrete or iron. If necessarily of wood they shall be extra heavy,
located in a dry place and open to the circulation of air.
The ordinary board platform is not satisfactory. Wooden foundations shall
be of heavy planking, joists or timbers, arranged so that the air will
circulate around them so as to form a firm base.
(_b_) Must be so arranged that the machine will be level and unequal
strain will not be placed on the generator or connexions.
2. LOCATION.--(_a_) Generators, especially in closely built up
districts should preferably be placed outside of insured buildings in
generator houses constructed and located in compliance with Rule 9.
(_b_) Generators must be so placed that the operating mechanism will
have room for free and full play and can be adjusted without artificial
light. They must not be subject to interference by children or careless
persons, and if for this purpose further enclosure is necessary, it must
be furnished by means of slatted partitions permitting the free
circulation of air.
(_c_) Generators which from their construction are rendered
inoperative during the process of recharging must be so located that they
can be recharged without the aid of artificial light.
(_d_) Generators must be placed where water will not freeze.
3. ESCAPES OR RELIEF-PIPES.--Each generator must be provided with an
escape or relief-pipe of ample size; no such pipe to be less than 3/4-
inch internal diameter. This pipe shall be substantially installed,
without traps, and so that any condensation will drain back to the
generator. It must be carried to a suitable point outside the building,
and terminate in an approved hood located at least 12 feet above ground
and remote from windows.
The hood must be constructed in such a manner that it cannot be
obstructed by rain, snow, ice, insects or birds.
4. CAPACITY.--(_a_) Must be sufficient to furnish gas continuously
for the maximum lighting period to all lights installed. A lighting
period of at least 5 hours shall be provided for in every case.
(_b_) Generators for conditions of service requiring lighting period
of more than 5 hours must be of sufficient capacity to avoid recharging
at night. The following ratings will usually be found advisable.
(i) For dwellings, and where machines are always used intermittently, the
generator must have a rated capacity equal to the total number of burners
installed.
(ii) For stores, opera houses, theatres, day-run factories, and similar
service, the generator must have a rated capacity of from 30 to 50 per
cent, in excess of the total number of burners installed.
(iii) For saloons and all night or continued service, the generator must
have a rated capacity of from 100 to 200 per cent. in excess of the total
number of burners installed.
(_c_) A small generator must never be installed to supply a large
number of lights, even though it seems probable that only a few lights
will be used at a time. _An overworked generator adds to the cost of
producing acetylene gas_.
5. CARBIDE CHARGES.--Must be sufficient to furnish gas continuously for
the maximum lighting period to all burners installed. In determining
charges lump carbide must be estimated as capable of producing 4-1/2
cubic foot of gas to the pound, commercial 1/4-inch carbide 4 cubic feet
of gas to the pound, and burners must be considered as requiring at least
25 per cent. more than their rated consumption of gas.
6. BURNERS.--Burners consuming one-half of a cubic foot of gas per hour
are considered standard in rating generators. Those having a greater or
less capacity will decrease or increase the number of burners allowable
in proportion.
Burners usually consume from 25 to 100 per cent. more than their rated
consumption of gas, depending largely on the working pressure. The so-
called 1/2-foot burner when operated at pressures of from 20- to 25-
tenths inches water column (2 to 2-1/2 inches) is usually used with best
economy.
7. PIPING.--(_a_) Connexions from generators to service-pipes must
be made with right and left thread nipples or long thread nipples with
lock nuts. All forms of unions are prohibited.
(_b_) Piping must, as far as possible, be arranged so that any
moisture will drain back to the generator. If low points occur of
necessity in any piping, they must be drained through tees into drip cups
permanently closed with screw caps or plugs. No pet-cocks shall be used.
(_c_) A valve and by-pass connexion must be provided from the
service-pipe to the blow-off for removing the gas from the holder in case
it should be necessary to do so.
(_d_) The schedule of pipe sizes for piping from generators to
burners should conform to that commonly used for ordinary gas, but in no
case must the feeders be smaller than three-eighths inch.
The following schedule is advocated:
3/8 inch pipe, 26 feet, three burners.
1/2 inch pipe, 30 feet, six burners.
3/4 inch pipe, 50 feet, twenty burners.
1 inch pipe, 70 feet, thirty-five burners.
1-1/4 inch pipe, 100 feet, sixty burners.
1-1/2 inch pipe, 150 feet, one hundred burners.
2 inch pipe, 200 feet, two hundred burners.
2-1/2 inch pipe, 300 feet, three hundred burners.
3 inch pipe, 450 feet, four hundred and fifty burners,
3-1/2 inch pipe, 500 feet, six hundred burners.
4 inch pipe, 600 feet, seven hundred and fifty burners.
(_e_) Machines of the carbide-feed type must not be fitted with
continuous drain connexions leading to sewers, but must discharge into
suitable open receptacles which may have such connections.
(_f_) Piping must be thoroughly tested both before and after the
burners have been installed. It must not show loss in excess of 2 inches
within twelve hours when subjected to a pressure equal to that of 15
inches of mercury.
(_g_) Piping and connexions must be installed by persons experienced
in the installation of acetylene apparatus.
8. CARE AND ATTENDANCE.--In the care of generators designed for a
lighting period of more than five hours always clean and recharge the
generating chambers at regular stated intervals, regardless of the number
of burners actually used.
Where generators are not used throughout the entire year always remove
all water and gas and clean thoroughly at the end of the season during
which they are in service.
It is usually necessary to take the bell portion out and invert it so as
to allow all gas to escape. This should never be done in the presence of
artificial light or fire of any kind.
Always observe a regular time, during daylight hours only, for attending
to and charging the apparatus.
In charging the generating chambers of water-feed machines clean all
residuum carefully from the containers and remove it at once from the
building. Separate from the mass any unslacked carbide remaining and
return it to the containers, adding now carbide as required. Be careful
never to fill the containers over the specified mark, as it is important
to allow for the swelling of the carbide when it comes in contact with
water. The proper action and economy of the machine are dependent on the
arrangement and amount of carbide placed in the generator. Carefully
guard against the escape of gas.
Whenever recharging with carbide always replenish the water-supply.
Never deposit residuum or exhausted material from water-feed machines in
sewer-pipes or near inflammable material.
Always keep water-tanks and water-seals filled with clean water.
Never test the generator or piping for leaks with a flame, and never
apply flame to an outlet from which the burner has been removed.
Never use a lighted match, lamp, candle, lantern or any open light near
the machine.
Failure to observe the above cautions is as liable to endanger life as
property.
9. OUTSIDE GENERATOR HOUSES.--(_a_) Outside generator houses should
not be located within 5 feet of any opening into, nor shall they open
toward any adjacent building, and must be kept under lock and key.
(_b_) The dimensions must be no greater than the apparatus requires
to allow convenient room for recharging and inspection of parts. The
floor must be at least 12 inches above grade and the entire structure
thoroughly weather-proof.
(_c_) Generator houses must be thoroughly ventilated, and any
artificial heating necessary to prevent freezing shall be done by steam
or hot-water systems.
(_d_) Generator houses must not be used for the storage of calcium
carbide except in accordance with the rules relating to that subject
(_vide_ Chapter II.).
_Class B.--Stationary Non-Automatic Apparatus_.
10. FOUNDATIONS.--(_a_) Must be of brick, stone or concrete.
(_b_) Must be so arranged that the machine will be level and so that
strain will not be brought upon the connexions.
11. GAS-HOUSES.--(_a_) Must be constructed entirely of non-
combustible material and must not be lighted by any system of
illumination involving open flames.
(_b_) Must be heated, where artificial heating is necessary to
prevent freezing, by steam or hot-water systems, the heater to be located
in a separate building, and no open flames to be permitted within
generator enclosures.
(_c_) Must be kept closed and locked excepting during daylight
hours.
(_d_) Must be provided with a permanent and effective system of
ventilation which will be operative at all times, regardless of the
periods of operation of the plant.
12. ESCAPE-PIPES.--Each generator must be provided with a vent-pipe of
ample size, substantially installed, without traps. It must be carried to
a suitable point outside the building and terminate in an approved hood
located at least 12 feet above ground and remote from windows.
The hood must be constructed in such a manner that it cannot be
obstructed by rain, snow, ice, insects or birds.
13. CARE AND MAINTENANCE.--All charging and cleaning of apparatus,
generation of gas and execution of repairs must be done during daylight
hours only, and generators must not be manipulated or in any way tampered
with in the presence of artificial light.
This will require gasholders of a capacity sufficient to supply all
lights installed for the maximum lighting period, without the necessity
of generation of gas at night or by artificial light.
In the operation of generators of the carbide-feed type it is important
that only a limited amount of carbide be fed into a given body of water.
An allowance of at least one gallon of generating water per pound of
carbide must be made in every case, and when this limit has been reached
the generator should be drained and flushed, and clean water introduced.
These precautions are necessary to avoid over-heating during generation
and accumulation of hard deposits of residuum in the generating chamber.
(Rule 14, referring to the storage of carbide, has been quoted in Chapter
II. (page 19)).
RULES FOR THE CONSTRUCTION OF GENERATORS.
The following Rules are intended to provide only against the more
hazardous defects usually noted in apparatus of this kind. The Rules do
not cover all details of construction nor the proper proportioning of
parts, and devices which comply with these requirements alone are not
necessarily suitable for listing as permissible for use. These points are
often only developed in the examination required before permission is
given for installation.
_Class A.--Stationary Apparatus for Isolated Installations._
15. GENERAL RULES. GENERATORS.--(_a_) Must be made of iron or steel,
and in a manner and of material to insure stability and durability.
(_b_) Must be automatically regulated and uniform in their action,
producing gas only as immediate consumption demands, and so designed that
gas is generated without producing sufficient heat to cause yellow
discoloration of residuum (which will occur at about 500° F.) or abnormal
pressure at any stage of the process when using carbide of any degree of
fineness.
The presence of excessive heat tends to change the chemical character of
the gas and may even cause its ignition, while in machines of the
carbide-feed type, finely divided carbide will produce excessive pressure
unless provision is made to guard against it.
(_c_) Must be so arranged that during recharging, back flow of gas
from the gasholder will be automatically prevented, or so arranged that
it will be impossible to charge the apparatus without first closing the
supply-pipe to the gasholder, and to the other generating chambers if
several are used.
This is intended to prevent the dangerous escape of gas.
(_d_) The water or carbide supply to the generating chamber must be
so arranged that gas will be generated long enough in advance of the
exhaustion of the supply already in the gasholder to allow the using of
all lights without exhausting such supply.
This provides for the continuous working of the apparatus under all
conditions of water-feed and carbide charge, and it obviates the
extinction of lights through intermittent action of the machine.
(_e_) No valves or pet-cocks opening into the room from the gas-
holding part or parts, the draining of which will allow an escape of gas,
are permitted, and condensation from all parts of the apparatus must be
automatically removed without the use of valves or mechanical working
parts.
Such valves and pet-cocks are not essential; their presence increases the
possibility of leakage. The automatic removal of condensation from the
apparatus is essential to the safe working of the machine.
U-traps opening into the room from the gas-holding parts must not be used
for removal of condensation. All sealed drip connexions must be so
arranged as to discharge gas to the blow-off when blown out, and the
seals must be self-restoring upon relief of abnormal pressure.
(_f_) The apparatus must be capable of withstanding fire from
outside causes.
Sheet-metal joints must be double-seamed or riveted and thoroughly
sweated with solder. Pipes must be attached to sheet-metal with lock-nuts
or riveted flanges.
This prohibits the use of wood or of joints relying entirely upon solder.
(_g_) Gauge glasses, the breakage of which would allow the escape of
gas, must not be used.
(_h_) The use of mercury seals is prohibited.
Mercury has been found unreliable as a seal in acetylene apparatus.(_i_)
Combustible oils must not be used in connexion with the
apparatus.
(_j_) The construction must be such that liquid seals shall not
become thickened by the deposit of lime or other foreign matter.
(_k_) The apparatus must be constructed so that accidental siphoning
of water will be impossible.
(_l_) Flexible tubing, swing joints, unions, springs, mechanical
check-valves, chains, pulleys, stuffing-boxes and lead or fusible piping
must not be used on acetylene apparatus except where failure of such
parts will not vitally affect the working or safety of the machine.
Floats must not be used excepting in cases where failure will result only
in rendering the machine inoperative.
(_m_) Every machine must be plainly marked with the maximum number
of lights it is designed to supply, the amount of carbide necessary for a
single charge, the manufacturer's name and the name of the machine.
16. GENERATING CHAMBERS.--(_a_) Must be constructed of galvanised
iron or steel not less than No. 24 U.S. Standard gauge in thickness for
capacities up to and including 20 gallons, not less than No. 22 U.S.
Standard gauge for capacities between 20 and 75 gallons, and not less
than No. 20 U.S. Standard gauge for capacities in excess of 75 gallons.
(_b_) Must each be connected with the gasholder in such a manner
that they will, at all times, give open connexion either to the gasholder
or to the blow-off pipe to the outer air.
This prevents dangerous pressure within or the escape of gas from the
generating chamber.
(_c_) Must be so constructed that not more than 5 pounds of carbide
can be acted upon at once, in machines which apply water in small
quantities to the carbide.
This tends to reduce the danger of overheating and excessive after-
generation by providing for division of the carbide charges in machines
of this type.
(_d_) Must be provided with covers having secure fastenings to hold
them properly in place and those relying on a water-seal must be
submerged in at least 12 inches of water. Water-seal chambers for covers
depending on a water-seal must be 1-1/2 inches wide and 15 inches deep,
excepting those depending upon the filling of the seal chambers for the
generation of gas, where 9 inches will be sufficient.
(_e_) Must be so designed that the residuum will not clog or affect
the working of the machine and can conveniently be handled and removed.
(_f_) Must be provided with suitable vent connexions to the blow-off
pipe so that residuum may be removed and the generating water replaced
without causing siphoning or introducing air to the gasholder upon
recharging.
This applies to machines of the carbide-feed type.
(_g_) Feed mechanism for machines of the carbide-feed type must be
so designed that the direct fall of carbide from the carbide holder into
the water of the generator is prevented at all positions of the feed
mechanisms; or, when actuated by the rise and fall of a gas-bell, must be
so arranged that the feed-valve will not remain open after the landing of
the bell, and so that the feed valve remains inoperative as long as the
filling opening on the carbide hopper remains open. Feed mechanisms must
always be far enough above the water-level to prevent clogging from the
accumulation of damp lime. For this purpose the distance should be not
less than 10 inches.
17. CARBIDE CHAMBERS.--(_a_) Must be constructed of galvanised iron
or steel not less than No. 24 U.S. Standard gauge in thickness for
capacities up to and including 50 pounds and not less than No. 22 U.S.
Standard gauge for capacities in excess of 50 pounds.
(_b_) Must have sufficient carbide capacity to supply the full
number of burners continuously and automatically during the maximum
lighting period.
This rule removes the necessity of recharging or attending to the machine
at improper hours. Burners almost invariably require more than their
rated consumption of gas, and carbide is not of staple purity, and there
should therefore be an assurance of sufficient quantity to last as long
as light is needed. Another important consideration is that in some
establishments burners are called upon for a much longer period of
lighting than in others, requiring a generator of greater gas-producing
capacity. Machines having several generating chambers must automatically
begin generation in each upon exhaustion of the preceding chamber.
(_c_) Must be arranged so that the carbide holders or charges may be
easily and entirely removed in case of necessity.
18. GASHOLDERS.--(_a_) Must be constructed of galvanised iron or
steel not less than No. 24 U.S. Standard gauge in thickness for
capacities up to and including 20 gallons, not less than No. 22 U.S.
Standard gauge for capacities between 20 and 75 gallons, and not less
than No. 20 U.S. Standard gauge for capacities in excess of 75 gallons.
Gas-bells, if used, may be two gauges lighter than holders.
Condensation chambers, if placed under holders, to be of same gauge as
holders.
(_b_) Must be of sufficient capacity to contain all gas generated
after all lights have been extinguished.
If the holder is too small and blows off frequently after the lights are
extinguished there is a waste of gas. This may suggest improper working
of the apparatus and encourage tampering.
(_c_) Must, when constructed on the gasometer principle, be so
arranged that when the gas-bell is filled to its maximum with gas at
normal pressure its lip or lower edge will extend at least 9 inches below
the inner water-level.
(_d_) Must, when constructed on the gasometer principle, have the
dimensions of the tank portion so related to those of the bell that a
pressure of at least 11 inches will be necessary before gas can be forced
from the holder.
(_e_) The bell portion of a gasholder constructed on the gasometer
principle must be provided with a substantial guide to its upward
movement, preferably in the centre of the holder, carrying a stop acting
to chock the bell 1 inch above the normal blow-off point.
This tends to insure the proper action of the bell and decreases the
liability of escaping gas.
(_f_) A space of at least three-quarters of an inch must be allowed
between the sides of the tank and the bell.
(_g_) All water-seals must be so arranged that the water-level may
be readily seen and maintained.
19. WATER-SUPPLY.--(_a_) The supply of water to the generator for
generating purposes must not be taken from the water-seal of any
gasholder constructed on the gasometer principle, unless the feed
mechanism is so arranged that the water-seals provided for in Rules 18,
(_c_), (_d_), and (_e_) may be retained under all
conditions. This provides for the proper level of water in the gasholder.
(_b_) In cases where machines of the carbide-feed type are supplied
with water from city water-mains or house-pipes, the pipe connexion must
discharge into the regularly provided filling trap on the generator and
not through a separate continuous connexion leading into the generating
chamber.
This is to prevent the expulsion of explosive mixtures through the
filling trap in refilling.
20. RELIEFS OR SAFETY BLOW-OFFS.--(_a_) Must in all cases be
provided, and must afford free vent to the outer air for any over-
production of gas, and also afford relief in case of abnormal pressure in
the machine.
Both the above-mentioned vents may be connected, with the same escape-
pipe.
(_b_) Must be of at least 3/4-inch internal diameter and be provided
with suitable means for connecting to the pipe loading outside of the
building.
(_c_) Must be constructed without valves or other mechanical working
parts.
(_d_) Apparatus requiring pressure regulators must be provided with
an additional approved safety blow-off attachment located between the
pressure regulator and the service-pipes and discharging to the outer
air.
This is intended to prevent the possibility of undue pressure in the
service-pipes due to failure of the pressure regulator.
21. PRESSURES.--(_a_) The working pressure at the generator must not
vary more than ten-tenths (1) inch water column under all conditions of
carbide charge and feed, and between the limits of no load and 50 per
cent. overload.
(_b_) Apparatus not requiring pressure regulators must be so
arranged that the gas pressure cannot exceed sixty-tenths (6) inches
water column.
This requires the use of the pressure relief provided for in Rule No. 20
(_a_).
(_c_) Apparatus requiring pressure regulators must be so arranged
that the gas pressure cannot exceed three pounds to the square inch.
The pressure limit of 3 pounds is taken since that is the pressure
corresponding to a water column about 6 feet high, which is about, the
limit in point of convenience for water-sealed reliefs.
22. AIR MIXTURES.--Generators must be so arranged as to contain the
minimum amount of air when first started or recharged, and no device or
attachment facilitating or permitting mixture of air with the gas prior
to consumption, except at the burners, shall be allowed.
Owing to the explosive properties of acetylene mixed with air, machines
must be so designed that such mixtures are impossible.
23. PURIFIERS.--(_a_) Must be constructed of galvanised iron or
steel not less than No. 24 U.S. Standard gauge in thickness.
(_b_) Where installed, purifiers must conform to the general rules
for the construction of other acetylene apparatus and allow the free
passage of gas.
(_c_) Purifiers must contain no carbide for drying purposes.
(_d_) Purifiers must be located inside of gasholders, or, where
necessarily outside, must have no hand-holes which can be opened without
first shutting off the gas-supply.
24. PRESSURE REGULATORS.--(_a_) Must conform to the rules for the
construction of other acetylene apparatus so far as they apply and must
not be subject to sticking or clogging.
(_b_) Must be capable of maintaining a uniform pressure, not varying
more than four-tenths inch water column, at any load within their rating.
(_c_) Must be installed between valves in such a manner as to
facilitate inspection and repairs.
_Class B.--Stationary Apparatus for Central Station Service._
Generators of over 300 lights capacity for central station service are
not required to be automatic in operation. Generators of less than 300
lights capacity must be automatic in operation and must comply in every
respect with the requirements of Class A.
25. GENERAL RULES. GENERATORS.--(_a_) Must be substantially
constructed of iron or steel and be protected against depreciation by an
effective and durable preventive of corrosion.
Galvanising is strongly recommended as a protection against oxidation,
and it may to advantage be reinforced by a thorough coating of asphaltum
or similar material.
(_b_) Must contain no copper or alloy of copper in contact with
acetylene, excepting in valves.
(_c_) Must be so arranged that generation will take place without
overheating; temperatures in excess of 500° F. to be considered
excessive.
(_d_) Must be provided with means for automatic removal of
condensation from gas passages.
(_e_) Must be provided with suitable protection against freezing of
any water contained in the apparatus.
No salt or other corrosive chemical is permissible as a protection
against freezing.
(_f_) Must in general comply with the requirements governing the
construction of apparatus for isolated installations so far as they are
applicable.
(_g_) Must be so arranged as to insure correct procedure in
recharging and cleaning.
(_h_) Generators of the carbide-feed type must be provided with some
form of approved measuring device to enable the attendant to determine
when the maximum allowable quantity of carbide has been fed into the
generating chamber.
In the operation of generators of this type an allowance of at least 1
gallon of clean generating water per pound of carbide should be made, and
the generator should be cleaned after slaking of every full charge. Where
lump carbide is used the lumps may become embedded in the residuum, if
the latter is allowed to accumulate at the bottom of the generating
chamber, causing overheating from slow and restricted generation, and
rendering the mass more liable to form a hard deposit and bring severe
stresses upon the walls of the generator by slow expansion.
26. GENERATING CHAMBERS.--(_a_) Must each be connected with the
gasholder in such a manner that they will, at all times, give open
connexion either to the gasholder or to the blow-off pipe into the outer
air.
(_b_) Must be so arranged as to guard against appreciable escape of
gas to the room at any time during the introduction of the charges.
(_c_) Must be so designed that the residuum will not clog or affect
the operation of the machine and can conveniently be handled and removed.
(_d_) Must be so arranged that during the process of cleaning and
recharging the back-flow of gas from the gasholder or other generating
chambers will be automatically prevented.
27. GASHOLDERS.--(_a_) Must be of sufficient capacity to contain at
least 4 cubic feet of gas per 1/2-foot burner of the rating.
This is to provide for the requisite lighting period without the
necessity of making gas at night, allowance being made for the
enlargement of burners caused by the use of cleaners.
(_b_) Must be provided with suitable guides to direct the movement
of the bell throughout its entire travel.
28. PRESSURE RELIEFS.--Must in all cases be provided, and must be so
arranged as to prevent pressure in excess of 100-tenths (10) inches water
column in the mains.
29. PRESSURES.--Gasholders must be adjusted to maintain a pressure of
approximately 25-tenths (2.5) inches water column in the mains.
CHAPTER V
THE TREATMENT OF ACETYLENE AFTER GENERATION
IMPURITIES IN CALCIUM CARBIDE.--The calcium carbide manufactured at the
present time, even when of the best quality commercially obtainable, is
by no means a chemically pure substance; it contains a large number of
foreign bodies, some of which evolve gas on treatment with water. To a
considerable extent this statement will probably always remain true in
the future; for in order to make absolutely pure carbide it would be
necessary for the manufacturer to obtain and employ perfectly pure lime,
carbon, and electrodes in an electric furnace which did not suffer attack
during the passage of a powerful current, or he would have to devise some
process for simultaneously or subsequently removing from his carbide
those impurities which were derived from his impure raw materials or from
the walls of his furnace--and either of these processes would increase
the cost of the finished article to a degree that could hardly be borne.
Beside the impurities thus inevitably arising from the calcium carbide
decomposed, however, other impurities may be added to acetylene by the
action of a badly designed generator or one working on a wrong system of
construction; and therefore it may be said at once that the crude gas
coming from the generating plant is seldom fit for immediate consumption,
while if it be required for the illumination of occupied rooms, it must
invariably be submitted to a rigorous method of chemical purification.
IMPURITIES OF ACETYLENE.--Combining together what may be termed the
carbide impurities and the generator impurities in crude acetylene, the
foreign bodies are partly gaseous, partly liquid, and partly solid. They
may render the gas dangerous from the point of view of possible
explosions; they, or the products derived from them on combustion, may be
harmful to health if inspired, injurious to the fittings and decorations
of rooms, objectionable at the burner orifices by determining, or
assisting in, the formation of solid growths which distort the flame and
so reduce its illuminating power; they may give trouble in the pipes by
condensing from the state of vapour in bends and dips, or by depositing,
if they are already solid, in angles, &c., and so causing stoppages; or
they may be merely harmful economically by acting as diluents to the
acetylene and, by having little or no illuminating value of themselves,
causing the gas to emit less light than it should per unit of volume
consumed, more particularly, of course, when the acetylene is not burnt
under the mantle. Also, not being acetylene, or isomeric therewith, they
require, even if they are combustible, a different proportion of oxygen
for their perfect combustion; and a good acetylene jet is only calculated
to attract precisely that quantity of air to the flame which a gas having
the constitution C_2H_2 demands. It will be apparent without argument
that a proper system of purification is one that is competent to remove
the carbide impurities from acetylene, so far as that removal is
desirable or necessary; it should not be called upon to extract the
generator impurities, because the proper way of dealing with them is, to
the utmost possible extent, to prevent their formation. The sole
exception to this rule is that of water-vapour, which invariably
accompanies the best acetylene, and must be partially removed as soon as
convenient. Vapour of water almost always accompanies acetylene from the
generator, even when the apparatus does not belong to those systems of
working where liquid water is in excess, this being due to the fact that
in a generator where the carbide is in excess the temperature tends to
rise until part of the water is vapourised and carried out of the
decomposing chamber before it has an opportunity of reacting with the
excess of carbide. The issuing gas is therefore more or less hot, and it
usually comes from the generating chamber saturated with vapour, the
quantity needed so to saturate it rising as the temperature of the gas
increases. Practically speaking, there is little objection to the
presence of water-vapour in acetylene beyond the fear of deposition of
liquid in the pipes, which may accumulate till they are partially or
completely choked, and may even freeze and burst them in very severe
weather. Where the chemical purifiers, too, contain a solid material
which accidentally or intentionally acts as a drier by removing moisture
from the acetylene, it is a waste of such comparatively expensive
material to allow gas to enter the purifier wetter than need be.
EXTRACTION OF MOISTURE.--In all large plants the extraction of the
moisture may take place in two stages. Immediately after the generator,
and before the washer if the generator requires such an apparatus to
follow it, a condenser is placed. Here the gas is made to travel somewhat
slowly through one or more pipes surrounded with cold air or water, or is
made to travel through a space containing pipes in which cold water is
circulating, the precise method of constructing the condenser being
perfectly immaterial so long as the escaping gas has a temperature not
appreciably exceeding that of the atmosphere. So cooled, however, the gas
still contains much water-vapour, for it remains saturated therewith at
the temperature to which it is reduced, and by the inevitable law of
physics a further fall in temperature will be followed by a further
deposition of liquid water from the acetylene. Manifestly, if the
installation is so arranged that the gas can at no part of the service
and on no occasion fall to a lower temperature than that at which it
issues from the condenser, the removal of moisture as effected by such a
condenser will be sufficient for all practical purposes; but at least in
all large plants where a considerable length of main is exposed to the
air, a more complete moisture extractor must be added to the plant, or
water will be deposited in the pipes every cold night in the winter. It
is, however, useless to put a chemical drier, or one more searching in
its action than a water-cooled condenser, at so early a position in the
acetylene plant, because the gas will be subsequently stored in a water-
sealed holder, where it will most probably once again be saturated with
moisture from the seal. When such generators are adopted as require to
have a specific washer placed after them in order to remove the water-
soluble impurities, _e.g._, those in which the gas does not actually
bubble through a considerable quantity of liquid in the generating
chamber itself, it is doubtful whether a separate condenser is altogether
necessary, because, as the water in the washer can easily be kept at the
atmospheric temperature (by means of water circulating in pipes or
otherwise), the gas will be brought to the atmospheric temperature in the
washer, and at that temperature it cannot carry with it more than a
certain fixed proportion of moisture. The notion of partially drying a
gas by causing it to pass through water may appear paradoxical, but a
comprehension of physical laws will show that it is possible, and will
prove efficient in practice, when due attention is given to the facts
that the gas entering the washer is hot, and that it is subsequently to
be stored over water in a holder.
GENERATOR IMPURITIES.--The generator impurities present in the crudest
acetylene consist of oxygen and nitrogen, _i.e._, the main
constituents of air, the various gaseous, liquid, and semi-solid bodies
described in Chapter II., which are produced by the polymerising and
decomposing action of heat upon the carbide, water, and acetylene in the
apparatus, and, whenever the carbide is in excess in the generator, some
lime in the form of a very fine dust. In all types of water-to-carbide
plant, and in some automatic carbide-feed apparatus, the carbide chamber
must be disconnected and opened each time a fresh charge has to be
inserted; and since only about one-third of the space in the container
can be filled with carbide, the remaining two-thirds are left full of
air. It is easy to imagine that the carbide container of a small
generator might be so large, or loaded with so small a quantity of
carbide, or that the apparatus might in other respects be so badly
designed, that the gas evolved might contain a sufficient proportion of
air to render it liable to explode in presence of a naked light, or of a
temperature superior to its inflaming-point. Were a cock, however, which
should have been shut, to be carelessly left open, an escape of gas from,
rather than an introduction of air into, the apparatus would follow,
because the pressure in the generator is above that of the atmosphere. As
is well known, roughly four-fifths by volume of the air consist of
nitrogen, which is non-inflammable and accordingly devoid of danger-
conferring properties; but in all flames the presence of nitrogen is
harmful by absorbing much of the heat liberated, thus lowering the
temperature of that flame, and reducing its illuminating power far more
seriously. On the other hand, a certain quantity of air in acetylene
helps to prevent burner troubles by acting as a mere diluent (albeit an
inferior one to methane or marsh-gas), and therefore it has been proposed
intentionally to add air to the gas before consumption, such a process
being in regular use on the large scale in some places abroad. As Eitner
has shown (Chapter VI.) that in a 3/4-inch pipe acetylene ceases to be
explosive when mixed with less than 47.7 per cent. of air, an amount of,
say, 40 per cent. or less may in theory be safely added to acetylene; but
in practice the amount of air added, if any, would have to be much
smaller, because the upper limit of explosibility of acetylene-air
mixtures is not rigidly fixed, varying from about 50 per cent. of air
when the mixture is in a small vessel, and fired electrically to about 25
per cent. of air in a large vessel approached with a flame. Moreover,
safely to prepare such mixtures, after the proportion of air had been
decided upon, would require the employment of some additional perfectly
trustworthy automatic mechanism to the plant to draw into the apparatus a
quantity of air strictly in accordance with the volume of acetylene made
--a pair of meters geared together, one for the gas, the other for the
air--and this would introduce extra complexity and extra expense. On the
whole the idea cannot be recommended, and the action of the British Home
Office in prohibiting the use of all such mixtures except those
unavoidably produced in otherwise good generators, or in burners of the
ordinary injector type, is perfectly justifiable. The derivation and
effect of the other gaseous and liquid generator impurities in acetylene
were described in Chapter II. Besides these, very hot gas has been found
to contain notable amounts of hydrogen and carbon monoxide, both of which
burn with non-luminous flames. The most plausible explanation of their
origin has been given by Lewes, who suggests that they may be formed by
the action of water-vapour upon very hot carbide or upon carbon separated
therefrom as the result of previous dissociation among the gases present;
the steam and the carbon reacting together at a temperature of 500° C. or
thereabouts in a manner resembling that of the production of water-gas.
The last generator impurity is lime dust, which is calcium oxide or
hydroxide carried forward by the stream of gas in a state of extremely
fine subdivision, and is liable to be produced whenever water acts
rapidly upon an excess of calcium carbide. This lime occasionally appears
in the alternative form of a froth in the pipes leading directly from the
generating chamber; for some types of carbide-to-water apparatus,
decomposing certain kinds of carbide, foam persistently when the liquid
in them becomes saturated with lime, and this foam or froth is remarkably
difficult to break up.
FILTERS.--It has just been stated that the purifying system added to an
acetylene installation should not be called upon to remove these
generator impurities; because their appearance in quantity indicates a
faulty generator, which should be replaced by one of better action. On
the contrary, with the exception of the gases which are permanent at
atmospheric temperature--hydrogen, carbon monoxide, nitrogen, and oxygen--
and which, once produced, must remain in the acetylene (lowering its
illuminating value, but giving no further trouble), extraction of these
generator impurities is quite simple. The dust or froth of lime will be
removed in the washer where the acetylene bubbles through water--the dust
itself can be extracted by merely filtering the gas through cotton-wool,
felt, or the like. The least volatile liquid impurities will be removed
partly in the condenser, partly in the washer, and partly by the
mechanical dry-scrubbing action of the solid purifying material in the
chemical purifier. To some extent the more volatile liquid bodies will be
removed similarly; but a complete extraction of them demands the
employment of some special washing apparatus in which the crude acetylene
is compelled to bubble (in finely divided streams) through a layer of
some non-volatile oil, heavy mineral lubricating oil, &c.; for though
soluble in such oil, the liquid impurities are not soluble in, nor do
they mix with, water; and since they are held in the acetylene as
vapours, a simple passage through water, or through water-cooled pipes,
does not suffice for their recovery. It will be seen that a sufficient
removal of these generator impurities need throw no appreciable extra
labour upon the consumer of acetylene, for he can readily select a type
of generator in which their production is reduced to a minimum; while a
cotton-wool or coke filter for the gas, a water washer, which is always
useful in the plant if only employed as a non-return valve between the
generator and the holder, and the indispensable chemical purifiers, will
take out of the acetylene all the remaining generator impurities which
need, and can, be extracted.
CARBIDE IMPURITIES.--Neglecting very minute amounts of carbon monoxide
and hydrogen (which may perhaps come from cavities in the calcium carbide
itself), as being utterly insignificant from the practical point of view,
the carbide impurities of the gas fall into four main categories: those
containing phosphorus, those containing sulphur, those containing
silicon, and those containing gaseous ammonia. The phosphorus in the gas
comes from calcium phosphide in the calcium carbide, which is attacked by
water, and yields phosphoretted hydrogen (or phosphine, as it will be
termed hereafter). The calcium phosphide, in its turn, is produced in the
electric furnace by the action of the coke upon the phosphorus in
phosphatic lime--all commercially procurable lime and some varieties of
coke (or charcoal) containing phosphates to a larger or smaller extent.
The sulphur in the gas comes from aluminium sulphide in the carbide,
which is produced in the electric furnace by the interaction of
impurities containing aluminium and sulphur (clay-like bodies, &c.)
present in the lime and coke; this aluminium sulphide is attacked by
water and yields sulphuretted hydrogen. Even in the absence of aluminium
compounds, sulphuretted hydrogen may be found in the gases of an
acetylene generator; here it probably arises from calcium sulphide, for
although the latter is not decomposed by water, it gradually changes in
water into calcium sulphydrate, which appears to suffer decomposition.
When it exists in the gas the silicon is derived from certain silicides
in the carbide; but this impurity will be dealt with by itself in a later
paragraph. The ammonia arises from the action of the water upon
magnesium, aluminium, or possibly calcium nitride in the calcium carbide,
which are bodies also produced in the electric furnace or as the carbide
is cooling. In the gas itself the ammonia exists as such; the phosphorus
exists mainly as phosphine, partly as certain organic compounds
containing phosphorus, the exact chemical nature of which has not yet
been fully ascertained; the sulphur exists partly as sulphuretted
hydrogen and partly as organic compounds analogous, in all probability,
to those of phosphorus, among which Caro has found oil of mustard, and
certain bodies that he regards as mercaptans. [Footnote: It will be
convenient to borrow the phrase used in the coal-gas industry, calling
the compounds of phosphorus other than phosphine "phosphorus compounds,"
and the compounds of sulphur other than sulphuretted hydrogen "sulphur
compounds." The "sulphur compounds" of coal-gas, however, consist mainly
of carbon bisulphide, which is certainly not the chief "sulphur compound"
in acetylene, even if present to any appreciable extent.] The precise way
in which these organic bodies are formed from the phosphides and
sulphides of calcium carbide is not thoroughly understood; but the system
of generation employed, and the temperature obtaining in the apparatus,
have much to do with their production; for the proportion of the total
phosphorus and sulphur found in the crude gas which exists as "compounds"
tends to be greater as the generating plant yields a higher temperature.
It should be noted that ammonia and sulphuretted hydrogen have one
property in common which sharply distinguishes them from the sulphur
"compounds," and from all the phosphorus compounds, including phosphine.
Ammonia and sulphuretted hydrogen are both very soluble in water, the
latter more particularly in the lime-water of an active acetylene
generator; while all the other bodies referred to are completely
insoluble. It follows, therefore, that a proper washing of the crude gas
in water should suffice to remove all the ammonia and sulphuretted
hydrogen from the acetylene; and as a matter of fact those generators in
which the gas is evolved in presence of a large excess of water, and in
which it has to bubble through such water, yield an acetylene practically
free from ammonia, and containing nearly all the sulphur which it does
contain in the state of "compounds." It must also be remembered that
chemical processes which are perfectly suited to the extraction of
sulphuretted hydrogen and phosphine are not necessarily adapted for the
removal of the other phosphorus and sulphur compounds.
WASHERS.--In designing a washer for the extraction of ammonia and
sulphuretted hydrogen it is necessary to see that the gas is brought into
most intimate contact with the liquid, while yet no more pressure than
can possibly be avoided is lost. Subdivision of the gas stream may be
effected by fitting the mouth of the inlet-pipe with a rose having a
large number of very small holes some appreciable distance apart, or by
bending the pipe to a horizontal position and drilling it on its upper
surface with numbers of small holes. Another method is to force the gas
to travel under a series of partitions extending just below the water-
level, forming the lower edges of those partitions either perfectly
horizontal or with small notches like the teeth of a saw. One volume of
pure water only absorbs about three volumes of sulphuretted hydrogen at
atmospheric temperatures, but takes up some 600 volumes of gaseous
ammonia; and as ammonia always accompanies the sulphuretted hydrogen, the
latter may be said to be absorbed in the washer by a solution of ammonia,
a liquid in which sulphuretted hydrogen is much more soluble. Therefore,
since water only dissolves about an equal volume of acetylene, the liquid
in the washer will continue to extract ammonia and sulphuretted hydrogen
long after it is saturated with the hydrocarbon. For this reason,
_i.e._, to avoid waste of acetylene by dissolution in the clean
water of the washer, the plan is sometimes adopted of introducing water
to the generator through the washer, so that practically the carbide is
always attacked by a liquid saturated with acetylene. Provided the liquid
in the generator does not become seriously heated, there is no objection
to this arrangement; but if the water is heated strongly in the generator
it loses much or all of its solvent properties, and the impurities may be
driven back again into the washer. Clearly if the waste lime of the
generator occurs as a dry or damp powder, the plan mentioned is not to be
recommended; but when the waste lime is a thin cream--water being in
large excess--it may be adopted. If the generator produces lime dust
among the gas, and if the acetylene enters the washer through minute
holes, a mechanical filter to remove the dust must be inserted between
the generator and the washer, or the orifices of the leading pipe will be
choked. Whenever a water-cooled condenser is employed after the
generator, in which the gas does not come in contact with the water, that
liquid may always be used to charge the generator. For compactness and
simplicity of parts the water of the holder seal is occasionally used as
the washing liquid, but unless the liquid of the seal is constantly
renewed it will thus become offensive, especially if the holder is under
cover, and it will also act corrosively upon the metal of the tank and
bell. The water-soluble impurities in acetylene will not be removed
completely by merely standing over the holder seal for a short time, and
it is not good practice to pass unnecessarily impure gas into a holder.
[Footnote: This is not a contradiction of what has been said in Chapter
III. about the relative position of holder and chemical purifiers,
because reference is now being made to ammonia and sulphuretted hydrogen
only.]
HARMFULNESS OF IMPURITIES.--The reasons why the carbide impurities must
be removed from acetylene before it is burned have now to be explained.
From the strictly chemical point of view there are three compounds of
phosphorus, all termed phosphoretted hydrogen or phosphine: a gas, PH_3;
a liquid, P_2H_4; and a solid, P_4H_2. The liquid is spontaneously
inflammable in presence of air; that is to say, it catches fire of itself
without the assistance of spark or flame immediately it comes in contact
with atmospheric oxygen; being very volatile, it is easily carried as
vapour by any permanent gas. The gaseous phosphine is not actually
spontaneously inflammable at temperatures below 100° C.; but it oxidises
so rapidly in air, even when somewhat diluted, that the temperature may
quickly rise to the point of inflammation. In the earliest days of the
acetylene industry, directly it was recognised that phosphine always
accompanies crude acetylene from the generator, it was believed that
unless the proportion were strictly limited by decomposing only a carbide
practically free from phosphides, the crude acetylene might exhibit
spontaneously inflammable properties. Lewes, indeed, has found that a
sample of carbide containing 1 per cent of calcium phosphide gave
(probably by local decomposition--the bulk of the phosphide suffering
attack first) a spontaneously inflammable gas; but when examining
specimens of commercial carbide the highest amount of phosphine he
discovered in the acetylene was 2.3 per cent, and this gas was not
capable of self-inflammation. According to Bullier, however, acetylene
must contain 80 per cent of phosphine to render it spontaneously
inflammable. Berdenich has reported a case of a parcel of carbide which
yielded on the average 5.1 cubic foot of acetylene per lb., producing gas
which contained only 0.398 gramme of phosphorus in the form of phosphine
per cubic metre (or 0.028 per cent. of phosphine) and was spontaneously
inflammable. But on examination the carbide in question was found to be
very irregular in composition, and some lumps produced acetylene
containing a very high proportion of phosphorus and silicon compounds. No
doubt the spontaneous inflammability was due to the exceptional richness
of these lumps in phosphorus. As manufactured at the present day, calcium
carbide ordinarily never contains an amount of phosphide sufficient to
render the gas dangerous on the score of spontaneous inflammability; but
should inferior material ever be put on the markets, this danger might
have to be guarded against by submitting the gas evolved from it to
chemical analysis. Another risk has been suggested as attending the use
of acetylene contaminated with phosphine (and to a minor degree with
sulphuretted hydrogen), viz., that being highly toxic, as they
undoubtedly are, the gas containing them might be extremely dangerous to
breathe if it escaped from the service, or from a portable lamp,
unconsumed. Anticipating what will be said in a later paragraph, the
worst kind of calcium carbide now manufactured will not yield a gas
containing more than 0.1 per cent. by volume of sulphuretted hydrogen and
0.05 per cent. of phosphine. According to Haldane, air containing 0.07
per cent. of sulphuretted hydrogen produces fatal results on man if it is
breathed for some hours, while an amount of 0.2 per cent. is fatal in 1-
1/2 minutes. Similar figures for phosphine cannot be given, because
poisoning therewith is very rare or quite unknown: the cases of "phossy-
jaw" in match factories being caused either by actual contact with yellow
phosphorus or by inhalation of its vapour in the elemental state.
However, assuming phosphine to be twice as toxic as sulphuretted
hydrogen, its effect in crude acetylene of the above-mentioned
composition will be equal to that of the sulphuretted hydrogen, so that
in the present connexion the gas may be said to be equally toxic with a
sample of air containing 0.2 per cent. of sulphuretted hydrogen, which
kills in less than two minutes. But this refers only to crude acetylene
undiluted with air; and being a hydrocarbon--being in fact neither oxygen
nor common air--acetylene is irrespirable of itself though largely devoid
of specific toxic action. Numerous investigations have been made of the
amount of acetylene (apart from its impurities) which can be breathed in
safety; but although these point to a probable recovery after a fairly
long-continued respiration of an atmosphere charged with 30 per cent. of
acetylene, the figure is not trustworthy, because toxicological
experiments upon animals seldom agree with similar tests upon man. If
crude acetylene were diluted with a sufficient proportion of air to
remove its suffocating qualities, the percentage of specifically toxic
ingredients would be reduced to a point where their action might be
neglected; and short of such dilution the acetylene itself would in all
probability determine pathological effects long before its impurities
could set up symptoms of sulphur and phosphorus poisoning.
Ammonia is objectionable in acetylene because it corrodes brass fittings
and pipes, and because it is partially converted (to what extent is
uncertain) into nitrous and nitric acids as it passes through the flame.
Sulphur is objectionable in acetylene because it is converted into
sulphurous and sulphuric anhydrides, or their respective acids, as it
passes through the flame. Phosphorus is objectionable because in similar
circumstances it produces phosphoric anhydride and phosphoric acid. Each
of these acids is harmful in an occupied room because they injure the
decorations, helping to rot book-bindings, [Footnote: It is only fair to
state that the destruction of leather bindings is commonly due to traces
of sulphuric acid remaining in the leather from the production employed
in preparing it, and is but seldom caused directly by the products of
combustion coming from gas or oil.] tarnishing "gold-leaf" ornaments, and
spoiling the colours of dyed fabrics. Each is harmful to the human
system, sulphuric and phosphoric anhydrides (SO_3, and P_4O_10) acting as
specific irritants to the lungs of persons predisposed to affections of
the bronchial organs. Phosphorus, however, has a further harmful action:
sulphuric anhydride is an invisible gas, but phosphoric anhydride is a
solid body, and is produced as an extremely fine, light, white voluminous
dust which causes a haze, more or less opaque, in the apartment.
[Footnote: Lewes suggests that ammonia in the gas burnt may assist in the
production of this haze, owing to the formation of solid ammonium salts
in the state of line dust.] Immediately it comes in contact with
atmospheric moisture phosphoric anhydride is converted into phosphoric
acid, but this also occurs at first as a solid substance. The solidity
and visibility of the phosphoric anhydride and acid are beneficial in
preventing highly impure acetylene being unwittingly burnt in a room;
but, on the other hand, being merely solids in suspension in the air, the
combustion products of phosphorus are not so easily carried away from the
room by the means provided for ventilation as are the products of the
combustion of sulphur. Phosphoric anhydride is also partly deposited in
the solid state at the burner orifices, perhaps actually corroding the
steatite jets, and always assisting in the deposition of carbon from any
polymerised hydrocarbons in the acetylene; thus helping the carbon to
block up or distort those orifices. Whenever the acetylene is to be burnt
on the incandescent system under a mantle of the Welsbach or other type,
phosphorus, and possibly sulphur, become additionally objectionable, and
rigorous extraction is necessary. As is well known, the mantle is
composed of the oxides of certain "rare earths" which owe their practical
value to the fact that they are non-volatile at the temperature of the
gas-flame. When a gas containing phosphorus is burnt beneath such a
mantle, the phosphoric anhydride attacks those oxides, partially
converting them into the respective phosphates, and these bodies are less
refractory. A mantle exposed to the combustion products of crude
acetylene soon becomes brittle and begins to fall to pieces, occasionally
showing a yellowish colour when cold. The actual advantage of burning
acetylene on the incandescent system is not yet thoroughly established--
in this country at all events; but it is clear that the process will not
exhibit any economy (rather the reverse) unless the plant is provided
with most capable chemical purifiers. Phosphorus, sulphur, and ammonia
are not objectionable in crude acetylene because they confer upon the gas
a nauseous odour. From a well-constructed installation no acetylene
escapes unconsumed: the gas remains wholly within the pipes until it is
burnt, and whatever odour it may have fails to reach the human nostrils.
A house properly piped for acetylene will be no more conspicuous by its
odour than a house properly piped for coal-gas. On the contrary, the fact
that the carbide impurities of acetylene, which, in the absolutely pure
state, is a gas of somewhat faint, hardly disagreeable, odour, do confer
upon that gas a persistent and unpleasant smell, is distinctly
advantageous; for, owing to that odour, a leak in the pipes, an unclosed
tap, or a fault in the generating plant is instantly brought to the
consumer's attention. A gas wholly devoid of odour would be extremely
dangerous in a house, and would have to be scented, as is done in the
case of non-carburetted water-gas when it is required for domestic
purposes.
AMOUNTS OF IMPURITIES AND SCOPE OF PURIFICATION.--Partly for the reason
which has just been given, and partly on the ground of expense, a
complete removal of the impurities from crude acetylene is not desirable.
All that need be done is to extract sufficient to deprive the gas of its
injurious effects upon lungs, decorations, and burners. As it stands,
however, such a statement is not sufficiently precise to be useful either
to consumers of acetylene or to manufacturers of plant, and some more or
less arbitrary standard must be set up in order to define the composition
of "commercially pure" acetylene, as well as to gauge the efficiency of
any process of purification. In all probability such limit may be
reasonably taken at 0.1 milligramme of either sulphur or phosphorus
(calculated as elementary bodies) per 1 litre of acetylene, _i.e._,
0.0-1.1 grain per cubic foot; a quantity which happens to correspond
almost exactly with a percentage by weight of 0.01. Owing to the atomic
weights of these substances, and the very small quantities being
considered, the same limit hardly differs from that of 0.01 per cent. by
weight of sulphuretted hydrogen or of phosphine--it being always
recollected that the sulphur and phosphorus do not necessarily exist in
the gas as simple hydrides. Keppeler, however, has suggested the higher
figure of 0.15 milligramme of either sulphur or phosphorus per litre of
acetylene (=0.066 grain per cubic foot) for the maximum amount of these
impurities permissible in purified acetylene. He adopts this standard on
the basis of the results of observations of the amounts of sulphur and
phosphorus present in the gas issuing from a purifier charged with
heratol at the moment when the last layer of the heratol is beginning to
change colour. No limit has been given for the removal of the ammonia,
partly because that impurity can more easily, and without concomitant
disadvantage, be extracted entirely; and partly because it is usually
removed in the washer and not in the true chemical purifier.
According to Lewes, the maximum amount of ammonia found in the acetylene
coming from a dripping generator is 0.95 gramme per litre, while in
carbide-to-water gas it is 0.16 gramme: 417 and 70.2 grains per cubic
foot respectively. Rossel and Landriset have found 4 milligrammes (1.756
grains [Footnote: Milligrammes per litre; grains per cubic foot. It is
convenient to remember that since 1 cubic foot of water weighs 62.321 x
16 - 997.14 avoirdupois ounces, grammes per litre are approximately equal
to oz. per cubic foot; and grammes per cubic metre to oz. per 1000 cubic
feet.]) to be the maximum in water-to-carbide gas, and none to occur in
carbide-to-water acetylene. Rossel and Landriset return the minimum
proportion of sulphur, calculated as H_2S, found in the gaseous state in
acetylene when the carbide has not been completely flooded with water at
1.18 milligrammes per litre, or 0.52 grain per cubic foot; and the
corresponding maxima at 1.9 milligrammes, or 0.84 grain. In carbide-to-
water gas, the similar maxima are 0.23 milligramme or 0.1 grain. As
already stated, the highest proportion of phosphine yet found in
acetylene is 2.3 per cent. (Lewes), which is equal to 32.2 milligrammes
of PH_3 per litre or 14.13 grains per cubic foot (Polis); but this sample
dated from 1897. Eitner and Keppeler record the minimum proportion of
phosphorus, calculated as PH_3, found in crude acetylene, as 0.45
milligramme per litre, and the maximum as 0.89 milligramme per litre; in
English terms these figures are 0.2 and 0.4 grain per cubic foot. On an
average, however, British and Continental carbide of the present day may
be said to give a gas containing 0.61 milligramme of phosphorus
calculated as PH_3 per litre and 0.75 milligramme of sulphur calculated
as H_2S. In other units these figures are equal to 0.27 grain of PH_3 and
0.33 grain of H_2S per 1 cubic foot, or to 0.041 per cent. by volume of
PH_3 and 0.052 per cent. of H_2S. Yields of phosphorus and sulphur much
higher than these will be found in the journals and books, but such
analytical data were usually obtained in the years 1896-99, before the
manufacture of calcium carbide had reached its present degree of
systematic control. A commercial specimen of carbide was seen by one of
the authors as late as 1900 which gave an acetylene containing 1.12
milligramme of elementary sulphur per litre, i.e., 0.096 per cent, by
volume, or 0.102 per cent, by volume of H_2S; but the phosphorus showed
the low figure of 0.36 milligramme per litre (0.031 per cent, of P or
0.034 per cent, of PH_3 by volume).
The British Acetylene Association's regulations relating to carbide of
calcium (_vide_ Chap. XIV.) contain a clause to the effect that
"carbide which, when properly decomposed, yields acetylene containing
from all phosphorus compounds therein more than 0.05 per cent, by volume
of phosphoretted hydrogen, may be refused by the buyer." This limit is
equivalent to 0.74 milligramme of phosphorus calculated as PH_3 per
litre. A latitude of 0.01 per cent, is, however, allowed for the
analysis, so that the ultimate limit on which carbide could be rejected
is: 0.06 volume per cent. of PH_3, or 0.89 milligramme of phosphorus per
litre.
The existence in appreciable quantity of combined silicon as a normal
impurity in acetylene seems still open to doubt. Calcium carbide
frequently contains notable quantities of iron and other silicides; but
although these bodies are decomposed by acids, yielding hydrogen
silicide, or siliciuretted hydrogen, they are not attacked by plain
water. Nevertheless Wolff and Gerard have found hydrogen silicide in
crude acetylene, and Lewes looks upon it as a common impurity in small
amounts. When it occurs, it is probably derived, as Vigouroux has
suggested, from "alloys" of silicon with calcium, magnesium, and
aluminium in the carbide. The metallic constituents of these substances
would naturally be attacked by water, evolving hydrogen; and the
hydrogen, in its nascent state, would probably unite with the liberated
silicon to form hydrogen silicide. Many authorities, including Keppeler,
have virtually denied that silicon compounds exist in crude acetylene,
while the proportion 0.01 per cent. has been given by other writers as
the maximum. Caro, however, has stated that the crude gas almost
invariably contains silicon, sometimes in very small quantities, but
often up to the limit of 0.8 per cent.; the failure of previous
investigators to discover it being due to faulty analytical methods. Caro
has seen one specimen of (bad) carbide which gave a spontaneously
inflammable gas although it contained only traces of phosphine; its
inflammability being caused by 2.1 per cent. of hydrogen silicide.
Practically speaking, all the foregoing remarks made about phosphine
apply equally to hydrogen silicide: it burns to solid silicon oxide
(silica) at the burners, is insoluble in water, and is spontaneously
inflammable when alone or only slightly diluted, but never occurs in good
carbide in sufficient proportion to render the acetylene itself
inflammable. According to Caro the silicon may be present both as
hydrogen silicide and as silicon "compounds." A high temperature in the
generator will favour the production of the latter; an apparatus in which
the gas is washed well in lime-water will remove the bulk of the former.
Fraenkel has found that magnesium silicide is not decomposed by water or
an alkaline solution, but that dilute hydrochloric acid acts upon it and
spontaneously inflammable hydrogen silicide results. If it may be assumed
that the other silicides in commercial calcium carbide also behave in
this manner it is plain that hydrogen silicide cannot occur in crude
acetylene unless the gas is supposed to be hurried out of the generator
before the alkaline water therein has had time to decompose any traces of
the hydrogen silicide which is produced in the favouring conditions of
high temperature sometimes prevailing. Mauricheau-Beaupré has failed to
find silica in the products of combustion of acetylene from carbide of
varying degrees of purity. He found, however, that a mixture of strong
nitric and hydrochloric acids (_aqua regia_), if contaminated with
traces of phosphoric acid, dissolved silica from the glass of laboratory
vessels. Consequently, since phosphoric acid results from the phosphine
in crude acetylene when the gas is passed through aqua regia, silica may
be found on subsequently evaporating the latter. But this, silica, he
found, was derived from the glass and not through the oxidation of
silicon compounds in the acetylene. It is possible that some of the
earlier observers of the occurrence of silicon compounds in crude
acetylene may have been misled by the solution of silica from the glass
vessels used in their investigations. The improbability of recognisable
quantities of silicon compounds occurring in acetylene in any ordinary
conditions of generation is demonstrated by a recent study by Fraenkel of
the composition of the deposit produced on reflectors exposed to the
products of combustion of a sample of acetylene which afforded a haze
when burnt. The deposit contained 51.07 per cent. of phosphoric acid, but
no silica. The gas itself contained from 0.0672 to 0.0837 per cent. by
volume of phosphine.
PURIFYING MATERIALS.--When acetylene first began to be used as a domestic
illuminant, most generator builders denied that there was any need for
the removal of these carbide impurities from the gas, some going so far
as to assert that their apparatus yielded so much purer an acetylene than
other plant, where purification might be desirable, that an addition of a
special purifier was wholly unnecessary. Later on the more responsible
members of the trade took another view, but they attacked the problem of
purification in a perfectly empirical way, either employing some purely
mechanical scrubber filled with some moist or dry porous medium, or
perhaps with coke or the like wetted with dilute acid, or they simply
borrowed the processes adopted in the purification of coal-gas. At first
sight it might appear that the more simple methods of treating coal-gas
should be suitable for acetylene; since the former contains two of the
impurities--sulphuretted hydrogen and ammonia--characteristic of crude
acetylene. After removing the ammonia by washing with water, therefore,
it was proposed to extract the sulphur by passing the acetylene through
that variety of ferric hydroxide (hydrated oxide of iron) which is so
serviceable in the case of coal-gas. The idea, however, was quite
unsound: first, because it altogether ignores the phosphorus, which is
the most objectionable impurity in acetylene, but is not present in coal-
gas; secondly, because ferric hydroxide is used on gasworks to extract in
a marketable form the sulphur which occurs as sulphuretted hydrogen, and
true sulphuretted hydrogen need not exist in well-generated and well-
washed acetylene to any appreciable extent; thirdly, because ferric
hydroxide is not employed by gasmakers to remove sulphur compounds (this
is done with lime), being quite incapable of extracting them, or the
analogous sulphur compounds of crude acetylene.
About the same time three other processes based on somewhat better
chemical knowledge were put forward. Pictet proposed leading the gas
through a strong solution of calcium chloride and then through strong
sulphuric acid, both maintained at a temperature of -20° to -40° C.,
finally washing the gas in a solution of some lead salt. Proof that such
treatment would remove phosphorus to a sufficient degree is not
altogether satisfactory; but apart from this the necessity of maintaining
such low temperatures, far below that of the coldest winter's night,
renders the idea wholly inadmissible for all domestic installations.
Willgerodt suggested removing sulphuretted hydrogen by means of potassium
hydroxide (caustic potash), then absorbing the phosphine in bromine
water. For many reasons this process is only practicable in the
laboratory. Bergé and Reychler proposed extracting both sulphuretted
hydrogen and phosphine in an acid solution of mercuric chloride
(corrosive sublimate). The poisonousness of this latter salt, apart from
all other objections, rules such a method out.
BLEACHING POWDER.--The next idea, first patented by Smith of Aberdeen,
but fully elaborated by Lunge and Cedercreutz, was to employ bleaching-
powder [Footnote: Bleaching-powder is very usually called chloride of
lime; but owing to the confusion which is constantly arising in the minds
of persons imperfectly acquainted with chemistry between chloride of lime
and chloride of calcium--two perfectly distinct bodies--the less
ambiguous expression "bleaching-powder" will be adopted here.] either in
the solid state or as a liquid extract. The essential constituent of
bleaching-powder from the present aspect is calcium hypochlorite, which
readily oxidises sulphuretted hydrogen, and more particularly phosphine,
converting them into sulphuric and phosphoric acids, while the acetylene
is practically unattacked. In simple purifying action the material proved
satisfactory; but since high-grade commercial bleaching-powder contains
some free chlorine, or some is set free from it in the purifier under the
influence of the passing gas, the issuing acetylene was found to contain
chlorine, free or combined; and this, burning eventually to hydrochloric
acid, is hardly less harmful than the original sulphur compounds.
Moreover, a mixture of acetylene, chlorine, and air is liable to catch
fire of itself when exposed to bright sunlight; and therefore the use of
a bleaching-powder purifier, or rather the recharging thereof, was not
unattended by danger in the early days. To overcome these defects, the
very natural process was adopted of diluting the bleaching-powder, such
diluent also serving to increase the porosity of the material. A very
unsuitable substance, however, was selected for the purpose, viz.,
sawdust, which is hygroscopic organic, and combustible. Owing to the
exothermic chemical action between the impurities of the acetylene and
the bleaching-powder, the purifying mass became heated; and thus not only
were the phenomena found in a bad generator repeated in the purifying
vessel, but in presence of air and light (as in emptying the purifier),
the reaction proceeded so rapidly that the heat caused inflammation of
the sawdust and the gas, at least on one occasion an actual fire taking
place which created much alarm and did some little damage. For a time,
naturally, bleaching-powder was regarded as too dangerous a material to
be used for the purification of crude acetylene; but it was soon
discovered that danger could be avoided by employing the substance in a
proper way.
HERATOL, FRANKOLINE, ACAGINE AND PURATYLENE.--Setting aside as unworthy
of attention certain compositions offered as acetylene purifying
materials whose constitution has not been divulged or whose action has
not been certified by respectable authority, there are now three
principal chemical reagents in regular use. Those are chromic acid,
cuprous chloride (sub- or proto-chloride of copper), and bleaching-
powder. Chromic acid is employed in the form of a solution acidified with
acetic or hydrochloric acid, which, in order to obtain the advantages
(_see_ below) attendant upon the use of a solid purifying material,
is absorbed in that highly porous and inert description of silica known
as infusorial earth or "kieselguhr." This substance was first recommended
by Ullmann, and is termed commercially "heratol" As sold it contains
somewhere about 136 grammes of chromic acid per kilo. Cuprous chloride is
used as a solution in strong hydrochloric acid mixed with ferric
chloride, and similarly absorbed in kieselguhr. From the name of its
proposer, this composition is called "frankoline." It will be shown in
Chapter VI. that the use of metallic copper in the construction of
acetylene apparatus is not permissible or judicious, because the gas is
liable to form therewith an explosive compound known as copper acetylide;
it might seem, therefore, that the employment of a copper salt for
purification courts accident. The objection is not sound, because the
acetylide is not likely to be produced except in the presence of ammonia;
and since frankoline is a highly acid product, the ammonia is converted
into its chloride before any copper acetylide can be produced. As a
special acetylene purifier, bleaching-powder exists in at least two chief
modifications. In one, known as "acagine," it is mixed with 15 per cent.
of lead chromate, and sometimes with about the same quantity of barium
sulphate; the function of the latter being simply that of a diluent,
while to the lead chromate is ascribed by its inventor (Wolff) the power
of retaining any chlorine that may be set free from the bleaching-powder
by the reduction of the chromic acid. The utility of the lead chromate in
this direction has always appeared doubtful; and recently Keppeler has
argued that it can have no effect upon the chlorine, inasmuch as in the
spent purifying material the lead chromate may be found in its original
condition unchanged. The second modification of bleaching-powder is
designated "puratylene," and contains calcium chloride and quick or
slaked lime. It is prepared by evaporating to dryness under diminished
pressure solutions of its three ingredients, whereby the finished
material is given a particularly porous nature.
It will be observed that both heratol and frankoline are powerfully acid,
whence it follows they are capable of extracting any ammonia that may
enter the purifier; but for the same reason they are liable to act
corrosively upon any metallic vessel in which they are placed, and they
therefore require to be held in earthenware or enamelled receivers. But
since they are not liquid, the casing of the purifier can be safely
constructed of steel or cast iron. Puratylene also removes ammonia by
virtue of the calcium chloride in it. Acagine would probably pass the
ammonia; but this is no real objection, as the latter can be extracted by
a preliminary washing in water. Heratol changes, somewhat obscurely, in
colour as it becomes spent, its original orange tint, due to the chromic
acid, altering to a dirty green, characteristic of the reduced salts of
chromium oxide. Frankoline has been asserted to be capable of
regeneration or revivification, _i.e._, that when spent it may be
rendered fit for further service by being exposed to the air for a time,
as is done with gas oxide; this, however, may be true to some extent with
the essential constituents of frankoline, but the process is not
available with the commercial solid product. Of all these materials,
heratol is the most complete purifier of acetylene, removing phosphorus
and sulphur most rapidly and thoroughly, and not appreciably diminishing
in speed or efficiency until its chromic acid is practically quite used
up. On the other hand, heratol does act upon pure acetylene to some
extent; so that purifiers containing it should be small in size and
frequently recharged. In one of his experiments Keppeler found that 13
per cent. of the chromic acid in heratol was wasted by reacting with
acetylene. As this waste of chromic acid involves also a corresponding
loss of gas, small purifiers are preferable, because at any moment they
only contain a small quantity of material capable of attacking the
acetylene itself. Frankoline is very efficacious as regards the
phosphorus, but it does not wholly extract the sulphur, leaving,
according to Keppeler, from 0.13 to 0.20 gramme of the latter in every
cubic metre of the gas. It does not attack acetylene itself; and if,
owing to its free hydrochloric acid, it adds any acid vapours to the
purified gas, these vapours may be easily removed by a subsequent passage
through a vessel containing lime or a carbide drier. Both being
essentially bleaching-powder, acagine and puratylene are alike in
removing phosphorus to a satisfactory degree; but they leave some sulphur
behind. Acagine evidently attacks acetylene to a slight extent, as
Keppeler has found 0.2 gramme of chlorine per cubic metre in the issuing
gas.
Although some of these materials attack acetylene slightly, and some
leave sulphur in the purified gas, they may be all considered reasonably
efficient from the practical point of view; for the loss of true
acetylene is too small to be noticeable, and the quantity of sulphur not
extracted too trifling to be harmful or inconvenient. They may be valued,
accordingly, mainly by their price, proper allowance being made for the
quantity of gas purified per unit weight of substance taken. This
quantity of gas must naturally vary with the proportion of phosphorus and
sulphur in the crude acetylene; but on an average the composition of
unpurified gas is what has already been given above, and so the figures
obtained by Keppeler in his investigation of the subject may be accepted.
In the annexed table these are given in two forms: (1) the number of
litres of gas purified by 1 kilogramme of the substance, (2) the number
of cubic feet purified per lb. It should be noted that the volumes of gas
refer to a laboratory degree of purification; in practice they may all be
increased by 10 or possibly 20 per cent.
_________________________________________________
| | | |
| | Litres | Cubic Feet |
| | per Kilogramme. | per Lb. |
|______________|___________________|______________|
| | | |
| Heratol | 5,000 | 80 |
| Frankoline | 9,000 | 144 |
| Puratylene | 10,000 | 160 |
| Acagine | 13,000 | 208 |
|______________|___________________|______________|
Another method of using dry bleaching-powder has been proposed by
Pfeiffer. He suggests incorporating it with a solution of some lead salt,
so that the latter may increase the capacity of the calcium hypochlorite
to remove sulphur. Analytical details as to the efficiency of this
process have not been given. During 1901 and 1902 Bullier and Maquenne
patented a substance made by mixing bleaching-powder with sodium
sulphate, whereby a double decomposition occurs, sodium hypochlorite,
which is equally efficient with calcium hypochlorite as a purifying
material, being produced together with calcium sulphate, which, being
identical with plaster of Paris, sets into a solid mass with the excess
of water present, and is claimed to render the whole more porous. This
process seemed open to objection, because Blagden had shown that a
solution of sodium hypochlorite was not a suitable purifying reagent in
practice, since it was much more liable to add chlorine to the gas than
calcium hypochlorite. The question how a solidified modification of
sodium hypochlorite would behave in this respect has been investigated by
Keppeler, who found that the Bullier and Maquenne material imparted more
chlorine to the gas which had traversed it than other hypochlorite
purifying agents, and that the partly foul material was liable to cause
violent explosions. About the same time Rossel and Landriset pointed out
that purification might be easily effected in all generators of the
carbide-to-water pattern by adding to the water of the generator itself a
quantity of bleaching-powder equivalent to 5 to 20 grammes for every 1
kilogramme of carbide decomposed, claiming that owing to the large amount
of liquid present, which is usually some 4 litres per kilogramme of
carbide (0.4 gallon per lb.), no nitrogen chloride could be produced, and
that owing to the dissolved lime in the generator, chlorine could not be
added to the gas. The process is characterised by extreme simplicity, no
separate purifier being needed, but it has been found that an
introduction of bleaching-powder in the solid condition is liable to
cause an explosive combination of acetylene and chlorine, while the use
of a solution is attended by certain disadvantages. Granjon has proposed
impregnating a suitable variety of wood charcoal with chlorine, with or
without an addition of bleaching-powder; then grinding the product to
powder, and converting it into a solid porous mass by the aid of cement.
The material is claimed to last longer than ordinary hypochlorite
mixtures, and not to add chlorine to the acetylene.
SUBSIDIARY PURIFYING MATERIALS.--Among minor reagents suggested as
purifying substances for acetylene may be mentioned potassium
permanganate, barium peroxide, potassium bichromate, sodium plumbate and
arsenious oxide. According to Benz the first two do not remove the
sulphuretted hydrogen completely, and oxidise the acetylene to some
extent; while potassium bichromate leaves some sulphur and phosphorus
behind in the gas. Sodium plumbate has been suggested by Morel, but it is
a question whether its action on the impurities would not be too violent
and whether it would be free from action on the acetylene itself. The use
of arsenious oxide dissolved in a strong acid, and the solution absorbed
in pumice or kieselguhr has been protected by G. F. Jaubert. The
phosphine is said to combine with the arsenic to form an insoluble
brownish compound. In 1902 Javal patented a mixture of 1 part of
potassium permanganate, 5 of "sulphuric acid," and 1 of water absorbed in
4 parts of infusorial earth. The acid constantly neutralised by the
ammonia of the crude gas is as constantly replaced by fresh acid formed
by the oxidation of the sulphuretted hydrogen; and this free acid, acting
upon the permanganate, liberates manganese peroxide, which is claimed to
destroy the phosphorus and sulphur compounds present in the crude
acetylene.
ÉPURÈNE.--A purifying material to which the name of épurène has been
given has been described, by Mauricheau-Beaupré, as consisting of a
mixture of ferric chloride and ferric oxide in the proportion of 2
molecules, or 650 parts, of the former with one molecule, or 160 parts,
of the latter, together with a suitable quantity of infusorial earth. In
the course of preparation, however, 0.1 to 0.2 per cent. of mercuric
chloride is introduced into the material. This mercuric chloride is said
to form an additive compound with the phosphine of the crude acetylene,
which compound is decomposed by the ferric chloride, and the mercuric
chloride recovered. The latter therefore is supposed to act only as a
carrier of the phosphine to the ferric chloride and oxide, by which it is
oxidised according to the equation:
8Fe_2Cl_6 + 4Fe_2O_3 + 3PH_3 = 12Fe_2Cl_4 + 3H_3PO_4.
Thus the ultimate products are phosphoric acid and ferrous chloride,
which on exposure to air is oxidised to ferric chloride and oxide. It is
said that this revivification of the fouled or spent épurène takes place
in from 20 to 48 hours when it is spread in the open in thin layers, or
it may be partially or wholly revivified _in situ_ by adding a small
proportion of air to the crude acetylene as it enters the purifier. The
addition of 1 to 2 per cent. of air, according to Mauricheau-Beaupré,
suffices to double the purifying capacity of one charge of the material,
while a larger proportion would achieve its continuous revivification.
Épurène is said to purify 10,000 to 11,000 litres of crude acetylene per
kilogramme, or, say, 160 to 176 cubic feet per pound, when the acetylene
contains on the average 0.05 per cent, by volume of phosphine.
For employment in all acetylene installations smaller than those which
serve complete villages, a solid purifying material is preferable to a
liquid one. This is partly due to the extreme difficulty of subdividing a
stream of gas so that it shall pass through a single mass of liquid in
small enough bubbles for the impurities to be removed by the time the gas
arrives at the surface. This time cannot be prolonged without increasing
the depth of liquid in the vessel, and the greater the depth of liquid,
the more pressure is consumed in forcing the gas through it. Perfect
purification by means of fluid reagents unattended by too great a
consumption of pressure is only to be effected by a mechanical scrubber
such as is used on coal-gas works, wherein, by the agency of external
power, the gas comes in contact with large numbers of solid surfaces kept
constantly wetted; or by the adoption of a tall tower filled with porous
matter or hollow balls over which a continuous or intermittent stream of
the liquid purifying reagent is made to trickle, and neither of these
devices is exactly suited to the requirements of a domestic acetylene
installation. When a solid material having a proper degree of porosity or
aggregation is selected, the stream of gas passing through it is broken
up most thoroughly, and by employing several separate layers of such
material, every portion of the gas is exposed equally to the action of
the chemical reagent by the time the gas emerges from the vessel. The
amount of pressure so consumed is less than that in a liquid purifier
where much fluid is present; but, on the other hand, the loss of pressure
is absolutely constant at all times in a liquid purifier, provided the
head of liquid is maintained at the same point. A badly chosen solid
purifying agent may exhibit excessive pressure absorption as it becomes
partly spent. A solid purifier, moreover, has the advantage that it may
simultaneously act as a drier for the gas; a liquid purifier, in which
the fluid is mainly water, obviously cannot behave in a similar fashion
For thorough purification it is necessary that the gas shall actually
stream through the solid material; a mere passage over its surface is
neither efficient nor economical of material.
DISPOSITION OF PURIFYING MATERIAL.--Although much has been written, and
some exaggerated claims made, about the maximum, volume of acetylene a
certain variety of purifying material will treat, little has been said
about the method in which such a material should be employed to obtain
the best results. If 1 lb. of a certain substance will purify 200 cubic
feet of normal crude acetylene, that weight is sufficient to treat the
gas evolved from 40 lb. of carbide; but it will only do so provided it is
so disposed in the purifier that the gas does not pass through it at too
high a speed, and that it is capable of complete exhaustion. In the coal-
gas industry it is usually assumed that four layers of purifying
material, each having a superficial area of 1 square foot, are the
minimum necessary for the treatment of 100 cubic feet of gas per hour,
irrespective of the nature of the purifying material and of the impurity
it is intended to extract. If there is any sound basis for this
generalization, it should apply equally to the purification of acetylene,
because there is no particular reason to imagine that the removal of
phosphine by a proper substance should occur at an appreciably different
speed from the removal of carbon dioxide, sulphuretted hydrogen, and
carbon bisulphide by lime, ferric oxide, and sulphided lime respectively,
Using the coal gas figures, then, for every 10 cubic feet of acetylene
generated per hour, a superficial area of (4 x 144 / 10) 57.6 square
inches of purifying material is required. In the course of Keppeler's
research upon different purifying materials it is shown that 400 grammes
of heratol, 360 grammes of frankoline, 250 grammes of acagine, and 230
grammes of puratylene each occupy a space of 500 cubic centimetres when
loosely loaded into a purifying vessel, and from these data, the
following table has been calculated:
__________________________________________________________
| | | | |
| | Weight | Weight | Cubic Inches |
| | per Gallon | per Cubic Foot | Occupied |
| | in Lbs. | in Lbs. | per Lb. |
|_____________|____________|________________|______________|
| | | | |
| Water | 10.0 | 62.321 | 27.73 |
| Heratol | 8.0 | 49.86 | 31.63 |
| Frankoline | 7.2 | 41.87 | 38.21 |
| Acagine | 6.0 | 31.16 | 55.16 |
| Puratylene | 4.6 | 28.67 | 60.28 |
|_____________|____________|________________|______________|
As regards the minimum weight of material required, data have been given
by Pfleger for use with puratylene. He states that 1 Kilogramme of that
substance should be present for every 100 litres of crude acetylene
evolved per hour, 4 kilogrammes being the smallest quantity put into the
purifier. In English units these figures are 1 lb. per 1.5 cubic feet per
hour, with 9 lb. as a minimum, which is competent to treat 1.1 cubic feet
of gas per hour. Thus it appears that for the purification of the gas
coming from any generator evolving up to 14 cubic feet of acetylene per
hour a weight of 9 lb of puratylene must be charged into the purifier,
which will occupy (60.28 / 9) 542 cubic inches of space; and it must be
so spread out as to present a total superficial area of (4 x 144 x 14 /
100) 80.6 square inches to the passing gas. It follows, therefore, that
the material should be piled to a depth of (542 / 80.6) 6.7 inches on a
support having an area of 80.6 square inches; but inasmuch as such a
depth is somewhat large for a small vessel, and as several layers are
better than one, it would be preferable to spread out these 540 cubic
inches of substance on several supports in such a fashion that a total
surface of 80.6 square inches or upwards should be exhibited. These
figures may obviously be manipulated in a variety of ways for the design
of a purifying vessel; but, to give an example, if the ordinary
cylindrical shape be adopted with four circular grids, each having a
clear diameter of 8 inches (_i.e._, an area of 50.3 square inches),
and if the material is loaded to a depth of 3 inches on each, there would
be a total volume of (50.3 x 3 x 4) = 604 cubic inches of puratylene in
the vessel, and it would present a total area of (50.3 x 4) = 201 square
inches to the acetylene. At Keppeler's estimation such an amount of
puratylene should weigh roughly 10 lb., and should suffice for the
purification of the gas obtained from 320 lb. of ordinary carbide; while,
applying the coal-gas rule, the total area of 201 square inches should
render such a vessel equal to the purification of acetylene passing
through it at a speed not exceeding (201 / 5.76) = 35 cubic feet per
hour. Remembering that it is minimum area in square inches of purifying
material that must govern the speed at which acetylene may be passed
through a purifier, irrespective probably of the composition of the
material; while it is the weight of material which governs the ultimate
capacity of the vessel in terms of cubic feet of acetylene or pounds of
carbide capable of purification, these data, coupled with Keppeler's
efficiency table, afford means for calculating the dimensions of the
purifying vessel to be affixed to an installation of any desired number
of burners. There is but little to say about the design of the vessel
from the mechanical aspect. A circular horizontal section is more likely
to make for thorough exhaustion of the material. The grids should be
capable of being lifted out for cleaning. The lid may be made tight
either by a clamp and rubber or leather washer, or by a liquid seal. If
the purifying material is not hygroscopic, water, calcium chloride
solution, or dilute glycerin may be used for sealing purposes; but if the
material, or any part of it, does absorb water, the liquid in the seal
should be some non-aqueous fluid like lubricating oil. Clamped lids are
more suitable for small purifiers, sealed lids for large vessels. Care
must be taken that condensation products cannot collect in the purifying
vessel. If a separate drying material is employed in the same purifier
the space it takes must be considered separately from that needed by the
active chemical reagent. When emptying a foul purifier it should be
recollected that the material may be corrosive, and being saturated with
acetylene is likely to catch fire in presence of a light.
Purifiers charged with heratol are stated, however, to admit of a more
rapid flow of the gas through them than that stated above for puratylene.
The ordinary allowance is 1 lb. of heratol for every cubic foot per hour
of acetylene passing, with a minimum charge of 7 lb. of the material. As
the quantity of material in the purifier is increased, however, the flow
of gas per hour may be proportionately increased, _e.g._, a purifier
charged with 132 lb. of heratol should purify 144 cubic feet of acetylene
per hour.
In the systematic purification of acetylene, the practical question
arises as to how the attendant is to tell when his purifiers approach
exhaustion and need recharging; for if it is undesirable to pass crude
gas into the service, it is equally undesirable to waste so comparatively
expensive a material as a purifying reagent. In Chapter XIV. it will be
shown that there are chemical methods of testing for the presence, or
determining the proportion, of phosphorus and sulphur in acetylene; but
these are not suitable for employment by the ordinary gas-maker. Heil has
stated that the purity of the gas may be judged by an inspection of its
atmospheric flame as given by a Bunsen burner. Pure acetylene gives a
perfectly transparent moderately dark blue flame, which has an inner cone
of a pale yellowish green colour; while the impure gas yields a longer
flame of an opaque orange-red tint with a bluish red inner zone. It
should be noted, however, that particles of lime dust in the gas may
cause the atmospheric flame to be reddish or yellowish (by presence of
calcium or sodium) quite apart from ordinary impurities; and for various
other reasons this appearance of the non-luminous flame is scarcely to be
relied upon. The simplest means of ascertaining definitely whether a
purifier is sufficiently active consists in the use of the test-papers
prepared by E. Merck of Darmstadt according to G. Keppeler's
prescription. These papers, cut to a convenient size, are put up in small
books from which they may be torn one at a time. In order to test whether
gas is sufficiently purified, one of the papers is moistened with
hydrochloric acid of 10 per cent. strength, and the gas issuing from a
pet-cock or burner orifice is allowed to impinge on the moistened part.
The original black or dark grey colour of the paper is changed to white
if the gas contains a notable amount of impurity, but remains unchanged
if the gas is adequately purified. The paper consists of a specially
prepared black porous paper which has been dipped in a solution of
mercuric chloride (corrosive sublimate) and dried. Moistening the paper
with hydrochloric acid provides in a convenient form for application
Bergé's solution for the detection of phosphine (_vide_ Chapter
XIV.). The Keppeler test-papers turn white when the gas contains either
ammonia, phosphine, siliciuretted hydrogen, sulphuretted hydrogen or
organic sulphur compounds, but with carbon disulphide the change is slow.
Thus the paper serves as a test for all the impurities likely to occur in
acetylene. The sensitiveness of the test is such that gas containing
about 0.15 milligramme of sulphur, and the same amount of phosphorus, per
litre (= 0.0655 grain per cubic foot) imparts in five minutes a distinct
white mark to the moistened part of the paper, while gas containing 0.05
milligramme of sulphur per litre (= 0.022 grain per cubic foot) gives in
two minutes a dull white mark visible only by careful inspection. If,
therefore, a distinct white mark appears on moistened Keppeler paper when
it is exposed for five minutes to a jet of acetylene, the latter is
inadequately purified. If the gas has passed through a purifier, this
test indicates that the material is not efficient, and that the purifier
needs recharging. The moistening of the Keppeler paper with hydrochloric
acid before use is essential, because if not acidified the paper is
marked by acetylene itself. The books of Keppeler papers are put up in a
case which also contains a bottle of acid for moistening them as required
and are obtainable wholesale of E. Merek, 16 Jewry Street, London, E.C.,
and retail of the usual dealers in chemicals. If Keppeler's test-papers
are not available, the purifier should be recharged as a matter of
routine as soon as a given quantity of carbide--proportioned to the
purifying capacity of the charge of purifying material--has been used
since the last recharging. Thus the purifier may conveniently contain
enough material to purify the gas evolved from two drums of carbide, in
which case it would need recharging when every second drum of carbide is
opened.
REGULATIONS AS TO PURIFICATION.--The British Acetylene
Association has issued the following set of regulations as to purifying
material and purifiers for acetylene:
Efficient purifying material and purifiers shall comply with the
following requirements:
(1) The purifying material shall remove phosphorus and sulphur compounds
to a commercially satisfactory degree; _i.e._, not to a greater
degree than will allow easy detection of escaping gas through its odour.
(2) The purifying material shall not yield any products capable of
corroding the gas-mains or fittings.
(3) The purifying material shall, if possible, be efficient as a drying
agent, but the Association does not consider this an absolute necessity.
(4) The purifying material shall not, under working conditions, be
capable of forming explosive compounds or mixtures. It is understood,
naturally, that this condition does not apply to the unavoidable mixture
of acetylene and air formed when recharging the purifier.
(5) The apparatus containing the purifying material shall be simple in
construction, and capable of being recharged by an inexperienced person
without trouble. It shall be so designed as to bring the gas into proper
contact with the material.
(6) The containers in purifiers shall be made of such materials as are
not dangerously affected by the respective purifying materials used.
(7) No purifier shall be sold without a card of instructions suitable or
hanging up in some convenient place. Such instructions shall be of the
most detailed nature, and shall not presuppose any expert knowledge
whatever on the part of the operator.
Reference also to the abstracts of the official regulations as to
acetylene installations in foreign countries given in Chapter IV. will
show that they contain brief rules as to purifiers.
DRYING.--It has been stated in Chapter III. that the proper position for
the chemical purifiers of an acetylene plant is after the holder; and
they therefore form the last items in the installation unless a "station"
governor and meter are fitted. It is therefore possible to use them also
to remove the moisture in the gas, if a material hygroscopic in nature is
employed to charge them. This should be true more particularly with
puratylene, which contains a notable proportion of the very hygroscopic
body calcium chloride. If a separate drier is desirable, there are two
methods of charging it. It may be filled either with some hygroscopic
substance such as porous calcium chloride or quicklime in very coarse
powder, which retains the water by combining with it; or the gas may be
led through a vessel loaded with calcium carbide, which will manifestly
hold all the moisture, replacing it by an equivalent quantity of
(unpurified) acetylene. The objection is sometimes urged against this
latter method, that it restores to the gas the nauseous odour and the
otherwise harmful impurities it had more or less completely lost in the
purifiers; but as regards the first point, a nauseous odour is not, as
has previously been shown, objectionable in itself, and as regards the
second, the amount of impurities added by a carbide drier, being strictly
limited by the proportion of moisture in the damp gas, is too small to be
noticeable at the burners or elsewhere. As is the case with purification,
absolute removal of moisture is not called for; all that is needed is to
extract so much that the gas shall never reach its saturation-point in
the inaccessible parts of the service during the coldest winter's night.
Any accessible length of main specially exposed to cold may be
safeguarded by itself; being given a steady fall to a certain point
(preferably in a frost-free situation), and there provided with a
collecting-box from which the deposited liquid can be removed
periodically with a pump or otherwise.
FILTRATION.--The gas issuing from the purifier or drier is very liable to
hold in suspension fine dust derived from the purifying or drying
material used. It is essential that thin dust should be abstracted before
the gas reaches the burners, otherwise it will choke the orifices and
prevent them functioning properly. Consequently the gas should pass
through a sufficient layer of filtering material after it has traversed
the purifying material (and drier if one is used). This filtering
material may be put either as a final layer in the purifier (or drier),
or in a separate vessel known as a filter. Among filtering materials in
common use may be named cotton-wool, fine canvas or gauze, felt and
asbestos-wool. The gas must be fairly well dried before it enters the
filter, otherwise the latter will become choked with deposited moisture,
and obstruct the passage of the gas.
Having now described the various items which go to form a well-designed
acetylene installation, it may be useful to recapitulate briefly, with
the object of showing the order in which they should be placed. From the
generator the gas passes into a condenser to cool it and to remove any
tarry products and large quantities of water. Next it enters a washing
apparatus filled with water to extract water-soluble impurities. If the
generator is of the carbide-to-water pattern, the condenser may be
omitted, and the washer is only required to retain any lime froth and to
act as a water-seal or non-return valve. If the generator does not wash
the gas, the washer must be large enough to act efficiently as such, and
between it and the condenser should be put a mechanical filter to extract
any dust. From the washer the acetylene travels to the holder. From the
holder it passes through one or two purifiers, and from there travels to
the drier and filter. If the holder does not throw a constant pressure,
or if the purifier and drier are liable to cause irregularities, a
governor or pressure regulator must be added after the drier. The
acetylene is then ready to enter the service; but a station meter (the
last item in the plant) is useful as giving a means of detecting any leak
in the delivery-pipes and in checking the make of gas from the amount of
carbide consumed. If the gas is required for the supply of a district, a
station meter becomes quite necessary, because the public lamps will be
fed with gas at a contract rate, and without the meter there would be no
control over the volume of acetylene they consume. Where the gas finally
leaves the generating-house, or where it enters the residence, a full-way
stopcock should be put on the main.
GENERATOR RESIDUES.--According to the type of generator employed the
waste product removed therefrom may vary from a dry or moist powder to a
thin cream or milk of lime. Any waste product which is quite liquid in
its consistency must be completely decomposed and free from particles of
calcium carbide of sensible magnitude; in the case of more solid
residues, the less fluid they are the greater is the improbability (or
the less is the evidence) that the carbide has been wholly spent within
the apparatus. Imperfect decomposition of the carbide inside the
generator not only means an obvious loss of economy, but its presence
among the residues makes a careful handling of them essential to avoid
accident owing to a subsequent liberation of acetylene in some
unsuitable, and perhaps closed, situation. A residue which is not
conspicuously saturated with water must be taken out of the generator-
house into the open air and there flooded with water, being left in some
uncovered receptacle for a sufficient time to ensure all the acetylene
being given off. A residue which is liquid enough to flow should be run
directly from the draw-off cock of the generator through a closed pipe to
the outside; where, if it does not discharge into an open conduit, the
waste-pipe must be trapped, and a ventilating shaft provided so that no
gas can blow back into the generator-house.
DISPOSAL OF RESIDUES.--These residues have now to be disposed of. In some
circumstances they can be put to a useful purpose, as will be explained
in Chapter XII.; otherwise, and always perhaps on the small scale--
certainly always if the generator overheats the gas and yields tar among
the spent lime--they must be thrown into a convenient place. It should be
remembered that although methods of precipitating sewage by adding lime,
or lime water, to it have frequently been used, they have not proved
satisfactory, partly because the sludge so obtained is peculiarly
objectionable in odour, and partly because an excess of lime yields an
effluent containing dissolved lime, which among other disadvantages is
harmful to fish. The plan of running the liquid residues of acetylene
manufacture into any local sewerage system which may be found in the
neighbourhood of the consumer's premises, therefore, is very convenient
to the consumer; but is liable to produce complaints if the sewage is
afterwards treated chemically, or if its effluent is passed untreated
into a highly preserved river; and the same remark applies in a lesser
degree if the residues are run into a private cesspool the liquid
contents of which automatically flow away into a stream. If, however, the
cesspool empties itself of liquid matter by filtration or percolation
through earth, there can be no objection to using it to hold the lime
sludge, except in so far as it will require more frequent emptying. On
the whole, perhaps the best method of disposing of these residues is to
run them into some open pit, allowing the liquid to disappear by
evaporation and percolation, finally burying the solid in some spot where
it will be out of the way. When a large carbide-to-water generator is
worked systematically so as to avoid more loss of acetylene by solution
in the excess of liquid than is absolutely necessary, the liquid residues
coming from it will be collected in some ventilated closed tank where
they can settle quietly. The clear lime-water will then be pumped back
into the generator for further use, and the almost solid sludge will be
ready to be carried to the pit where it is to be buried. Special care
must be taken in disposing of the residues from a generator in which oil
is used to control evolution of gas. Such oil floats on the aqueous
liquid; and a very few drops spread for an incredible distance as an
exceedingly thin film, causing those brilliant rainbow-like colours which
are sometimes imagined to be a sign of decomposing organic matter. The
liquid portions of these residues must be led through a pit fitted with a
depending partition projecting below the level at which the water is
constantly maintained; all the oil then collects on the first side of the
partition, only water passing underneath, and the oil may be withdrawn
and thrown away at intervals.
CHAPTER VI
THE CHEMICAL AND PHYSICAL PROPERTIES OF ACETYLENE
It will only be necessary for the purpose of this book to indicate the
more important chemical and physical properties of acetylene, and, in
particular, those which have any bearing on the application of acetylene
for lighting purposes. Moreover, it has been found convenient to discuss
fully in other chapters certain properties of acetylene, and in regard to
such properties the reader is referred to the chapters mentioned.
PHYSICAL PROPERTIES.--Acetylene is a gas at ordinary temperatures,
colourless, and, when pure, having a not unpleasant, so-called "ethereal"
odour. Its density, or specific gravity, referred to air as unity, has
been found experimentally by Leduc to be 0.9056. It is customary to adopt
the value 0.91 for calculations into which the density of the gas enters
(_vide_ Chapter VII.). The density of a gas is important not only
for the determination of the size of mains needed to convey it at a given
rate of flow under a given pressure, as explained in Chapter VII., but
also because the volume of gas which will pass through small orifices in
a given time depends on its density. According to Graham's well-known law
of the effusion of gases, the velocity with which a gas effuses varies
directly as the square root of the difference of pressure on the two
sides of the opening, and inversely as the square root of the density of
the gas. Hence it follows that the volume of gas which escapes through a
porous pipe, an imperfect joint, or a burner orifice is, provided the
pressure in the gas-pipe is the same, a function of the square root of
the density of the gas. Hence this density has to be taken into
consideration in the construction of burners, i.e., a burner required to
pass a gas of high density must have a larger orifice than one for a gas
of low density, if the rate of flow of gas is to be the same under the
same pressure. This, however, is a question for the burner manufacturers,
who already make special burners for gases of different densities, and it
need not trouble the consumer of acetylene, who should always use burners
devised for the consumption of that gas. But the Law of effusion
indicates that the volume of acetylene which can escape from a leaky
supply-pipe will be less than the volume of a gas of lower density,
_e.g._, coal-gas, if the pressure in the pipe is the same for both.
This implies that on an extensive distributing system, in which for
practical reasons leakage is not wholly avoidable, the loss of gas
through leakage will be less for acetylene than for coal-gas, given the
same distributing pressure. If _v_ = the loss of acetylene from a
distributing system and _v'_ = the loss of coal-gas from a similar
system worked at the same pressure, both losses being expressed in
volumes (cubic feet) per hour, and the coal-gas being assumed to have a
density of 0.04, then
(1) (_v_/_v'_) = (0.40 / 0.91)^(1/2) = 0.663
or, _v_ = 0.663_v'_,
which signifies that the loss of acetylene by leakage under the same
conditions of pressure, &c., will be only 0.663 times that of the loss of
coal-gas. In practice, however, the pressures at which the gases are
usually sent through mains are not identical, being greater in the case
of acetylene than in that of coal-gas. Formula (1) therefore requires
correction whenever the pressures are different, and calling the pressure
at which the acetylene exists in the main _p_, and the corresponding
pressure of the coal-gas _p'_, the relative losses by leakage are--
(2) (_v_/_v'_) = (0.40 / 0.91)^(1/2) x (_p_/_p'_)^(1/2)
_v_ = 0.663_v'_ x (_p_/_p'_)^(1/2)
It will be evident that whenever the value of the fraction
(_p_/_p'_)^(1/2), is less than 1.5, _i.e._, whenever the pressure of
the acetylene does not exceed double that of the coal-gas present in
pipes of given porosity or unsoundness, the loss of acetylene will be
less than that of coal-gas. This is important, especially in the case of
large village acetylene installations, where after a time it would be
impossible to avoid some imperfect joints, fractured pipes, &c.,
throughout the extensive distributing mains. The same loss of gas by
leakage would represent a far higher pecuniary value with acetylene than
with coal-gas, because the former must always be more costly per unit of
volume than the latter. Hence it is important to recognise that the rate
of leakage, _cteris paribus_, is less with acetylene, and it is
also important to observe the economical advantage, at least in terms of
gas or calcium carbide, of sending the acetylene into the mains at as low
a pressure as is compatible with the length of those mains and the
character of the consumers' burners. As follows from what will be said in
Chapter VII., a high initial pressure makes for economy in the prime cost
of, and in the expense of laying, the mains, by enabling the diameter of
those mains to be diminished; but the purchase and erection of the
distributing system are capital expenses, while a constant expenditure
upon carbide to meet loss by leakage falls upon revenue.
The critical temperature of acetylene, _i.e._, the temperature below
which an abrupt change from the gaseous to the liquid state takes place
if the pressure is sufficiently high, is 37° C., and the critical
pressure, _i.e._, the pressure under which that change takes place
at that temperature, is nearly 68 atmospheres. Below the critical
temperature, a lower pressure than this effects liquefaction of the gas,
_i.e._, at 13.5° C. a pressure of 32.77 atmospheres, at 0° C., 21.53
atmospheres (Ansdell, _cf._ Chapter XI.). These data are of
comparatively little practical importance, owing to the fact that, as
explained in Chapter XI., liquefied acetylene cannot be safely utilised.
The mean coefficient of expansion of gaseous acetylene between 0° C. and
100° C., is, under constant pressure, 0.003738; under constant volume,
0.003724. This means that, if the pressure is constant, 0.003738
represents the increase in volume of a given mass of gaseous acetylene
when its temperature is raised one degree (C.), divided by the volume of
the same mass at 0° C. The coefficients of expansion of air are: under
constant pressure, 0.003671; under constant volume, 0.003665; and those
of the simple gases (nitrogen, hydrogen, oxygen) are very nearly the
same. Strictly speaking the table given in Chapter XIV., for facilitating
the correction of the volume of gas measured over water, is not quite
correct for acetylene, owing to the difference in the coefficients of
expansion of acetylene and the simple gases for which the table was drawn
up, but practically no appreciable error can ensue from its use. It is,
however, for the correction of volumes of gases measured at different
temperatures to one (normal) temperature, and, broadly, for determining
the change of volume which a given mass of the gas will undergo with
change of temperature, that the coefficient of expansion of a gas becomes
an important factor industrially.
Ansdell has found the density of liquid acetylene to range from 0.460 at
-7° C. to 0.364 at +35.8° C., being 0.451 at 0° C. Taking the volume of
the liquid at -7° as unity, it becomes 1.264 at 35.8°, and thence Ansdell
infers that the mean coefficient of expansion per degree is 0.00489° for
the total range of pressure." Assuming that the liquid was under the same
pressure at the two temperatures, the coefficient of expansion per degree
Centigrade would be 0.00605, which agrees more nearly with the figure
0.007 which is quoted, by Fouché As mentioned before, data referring to
liquid (_i.e._, liquefied) acetylene are of no practical importance,
because the substance is too dangerous to use. They are, however,
interesting in so far as they indicate the differences in properties
between acetylene converted into the liquid state by great pressure, and
acetylene dissolved in acetone under less pressure; which differences
make the solution fit for employment. It may be observed that as the
solution of acetylene in acetone is a liquid, the acetylene must exist
therein as a liquid; it is, in fact, liquid acetylene in a state of
dilution, the diluent being an exothermic and comparatively stable body.
The specific heat of acetylene is given by M. A. Morel at 0.310, though
he has not stated by whom the value was determined. For the purpose of a
calculation in Chapter III. the specific heat at constant pressure was
assumed to be 0.25, which, in the absence of precise information, appears
somewhat more probable as an approximation to the truth. The ratio
(_k_ or C_p/C_v ) of the specific heat at constant pressure to that
at constant volume has been found by Maneuvrier and Fournier to be 1.26;
but they did not measure the specific heat itself. [Footnote: The ratio
1.26 _k_ or (C_p/C_v) has been given in many text-books as the value
of the specific heat of acetylene, whereas this value should obviously be
only about one-fourth or one-fifth of 1.26.
By employing the ordinary gas laws it is possible approximately to
calculate the specific heat of acetylene from Maneuvrier and Fournier's
ratio. Taking the molecular weight of acetylene as 26, we have
26 C_p - 26 C_v = 2 cal.,
and
C_p = 1.26 C_v.
From this it follows that C_p, _i.e._, the specific heat at constant
pressure of acetylene, should be 0.373.] It will be seen that this value
for _k_ differs considerably from the corresponding ratio in the
case of air and many common gases, where it is usually 1.41; the figure
approaches more closely that given for nitrous oxide. For the specific
heat of calcium carbide Carlson quotes the following figures:
0° 1000° 1500° 2000° 2500° 3000° 3500°
0.247 0.271 0.296 0.325 0.344 0.363 0.381
The molecular volume of acetylene is 0.8132 (oxygen = 1).
According to the international atomic weights adopted in 1908, the
molecular weight of acetylene is 26.016 if O = 16; in round numbers, as
ordinarily used, it is 26. Employing the latest data for the weight of 1
litre of dry hydrogen and of dry normal air containing 0.04 per cent. of
carbon dioxide at a temperature of 0° C. and a barometric pressure of 760
mm. in the latitude of London, viz., 0.089916 and 1.29395 grammes
respectively (Castell-Evans), it now becomes possible to give the weight
of a known volume of dry or moist acetylene as measured under stated
conditions with some degree of accuracy. Using 26.016 as the molecular
weight of the gas (O = 16), 1 litre of dry acetylene at 0° C. and 760 mm.
weighs 1.16963 grammes, or 1 gramme measures 0.854973 litre. From this it
follows that the theoretical specific gravity of the gas at 0°/0° C. is
0.9039 (air = 1), a figure which may be compared with Leduc's
experimental value of 0.9056. Taking as the coefficient of expansion at
constant pressure the figure already given, viz., 0.003738, the weights
and measures of dry and moist acetylene observed under British conditions
(60° F. and 30 inches of mercury) become approximately:
Dry. Saturated.
1 litre . . . 1.108 grm. . . 1.102 grm.
1 gramme . . . 0.902 litre. . . 0.907 litre.
1000 cubic feet . 69.18 lb. . . . 68.83 lb.
It should be remembered that unless the gas has been passed through a
chemical drier, it is always saturated with aqueous vapour, the amount of
water present being governed by the temperature and pressure. The 1 litre
of moist acetylene which weighs 1.102 gramme at 60° F. and 30 inches of
mercury, contains 0.013 gramme of water vapour; and therefore the weight
of dry acetylene in the 1 litre of moist gas is 1.089 gramme. Similarly,
the 68.83 pounds which constitute the weight of 1000 cubic feet of moist
acetylene, as measured under British standard conditions, are composed of
almost exactly 68 pounds of dry acetylene and 0.83 pound of water vapour.
The data required in calculating the mass of vapour in a known volume of
a saturated gas at any observed temperature and pressure, _i.e._, in
reducing the figures to those which represent the dry gas at any other
(standard) temperature and pressure, will be found in the text-books of
physical chemistry. It is necessary to recollect that since coal-gas is
measured wet, the factors given in the table quoted in Chapter XIV. from
the "Notification of the Gas Referees" simply serve to convert the volume
of a wet gas observed under stated conditions to the equivalent volume of
the same wet gas at the standard conditions mentioned.
HEAT OF COMBUSTION, &C--Based on Berthelot and Matignon's value for the
heat of combustion which is given on a subsequent page, viz., 315.7 large
calories per molecular weight of 26.016 grammes, the calorific power of
acetylene under different conditions is shown in the following table:
Dry. Dry. Saturated.
0° C. & 760 mm. 60° F & 30 ins. 60° F. & 30 ins.
1 gramme 12.14 cals. 12.14 cals. 12.0 cals.
1 litre 14.l9 " 13.45 " 13.22 "
1 cubic foot 40.19 " 380.8 " 374.4 "
The figures in the last column refer to the dry acetylene in the gas, no
correction having been made for the heat absorbed by the water vapour
present. As will appear in Chapter X., the average of actual
determinations of the calorific value of ordinary acetylene is 363 large
calories or 1440 B.Th.U. per cubic foot. The temperature of ignition of
acetylene has been generally stated to be about 480° C. V. Meyer and
Münch in 1893 found that a mixture of acetylene and oxygen ignited
between 509° and 515° C. Recent (1909) investigations by H. B. Dixon and
H. F. Coward show, however, that the ignition temperature in neat oxygen
is between 416° and 440° (mean 428° C.) and in air between 406° and 440°,
with a mean of 429° C. The corresponding mean temperature of ignition
found by the same investigators for other gases are: hydrogen, 585°;
carbon monoxide, moist 664°, dry 692°; ethylene, in oxygen 510°, in air
543°; and methane, in oxygen between 550° and 700°, and in air, between
650° and 750° C.
Numerous experiments have been performed to determine the temperature of
the acetylene flame. According to an exhaustive research by L. Nichols,
when the gas burns in air it attains a maximum temperature of 1900° C. ±
20°, which is 120° higher than the temperature he found by a similar
method of observation for the coal-gas flame (fish-tail burner). Le
Chatelier had previously assigned to the acetylene flame a temperature
between 2100° and 2400°, while Lewes had found for the dark zone 459°,
for the luminous zone 1410°, and for the tip 1517° C, Féry and Mahler
have also made measurements of the temperatures afforded by acetylene and
other fuels, some of their results being quoted below. Féry employed his
optical method of estimating the temperature, Mahler a process devised by
Mallard and Le Chatelier. Mahler's figures all relate to flames supplied
with air at a temperature of 0° C. and a constant pressure of 760 mm.
Hydrogen . . . . . . . . . . . 1900 1960
Carbon monoxide . . . . . . . . . -- 2100
Methane . . . . . . . . . . . -- _ 1850
Coal-gas (luminous) . . . . . . . . 1712 |
" (atmospheric, with deficient supply of air) . 1812 | 1950
" (atmospheric, with full supply of air) . . 1871 _|
Water-gas . . . . . . . . . . -- 2000
Oxy-coal-gas blowpipe . . . . . . . 2200 --
Oxy-hydrogen blowpipe . . . . . . . 2420 --
Acetylene . . . . . . . . . . 2548 2350
Alcohol . . . . . . . . . . . 1705 1700
Alcohol (in Denayrouze Bunsen) . . . . . 1862 --
Alcohol and petrol in equal parts . . . . 2053 --
Crude petroleum (American) . . . . . . -- 2000
Petroleum spirit " . . . . . . . -- 1920
Petroleum oil " . . . . . . . -- 1660
Catani has published the following determinations of the temperature
yielded by acetylene when burnt with cold and hot air and also with
oxygen:
Acetylene and cold air . . . . . . 2568° C.
" air at 500° C . . . . 2780° C.
" air at 1000° C . . . . 3000° C.
" oxygen . . . . . . 4160° C.
EXPLOSIVE LIMITS.--The range of explosibility of mixtures of acetylene
and air has been determined by various observers. Eitner's figures for
the lower and upper explosive limits, when the mixture, at 62.6° F., is
in a tube 19 mm. in diameter, and contains 1.9 per cent. of aqueous
vapour, are 3.35 and 52.3 per cent. of acetylene (_cf._ Chapter X.).
In this case the mixture was fired by electric spark. In wider vessels,
the upper explosive limit, when the mixture was fired by a Bunsen flame,
was found to be as high as 75 per cent. of acetylene. Eitner also found
that when 13 of the 21 volumes of oxygen in air are displaced by carbon
dioxide, a mixture of such "carbon dioxide air" with acetylene is
inexplosive in all proportions. Also that when carbon dioxide is added to
a mixture of acetylene and air, an explosion no longer occurs when the
carbon dioxide amounts to 46 volumes or more to every 54 volumes of air,
whatever may be the proportion of acetylene in the mixture. [Footnote:
According to Caro, if acetylene is added to a mixture composed of 55 per
cent. by volume of air and 45 per cent. of carbon dioxide, the whole is
only explosive when the proportion of acetylene lies between 5.0 and 5.8
per cent. Caro has also quoted the effect of various inflammable vapours
upon the explosive limits of acetylene, his results being referred to in
Chapter X.] These figures are valuable in connexion with the prevention
of the formation of explosive mixtures of air and acetylene when new
mains or plant are being brought into operation (_cf._ Chapter
VII.). Eitner has also shown, by direct investigation on mixtures of
other combustible gases and air, that the range of explosibility is
greatly reduced by increase in the proportion of aqueous vapour present.
As the proportion of aqueous vapour in gas standing over water increases
with the temperature the range of explosibility of mixtures of a
combustible gas and air is naturally and automatically reduced when the
temperature rises, provided the mixture is in contact with water. Thus at
17.0° C., mixtures of hydrogen, air, and aqueous vapour containing from
9.3 to 65.0 per cent, of hydrogen are explosive, whereas at 78.1° C.,
provided the mixture is saturated with aqueous vapour, explosion occurs
only when the percentage of hydrogen in the mixture is between 11.2 and
21.9. The range of explosibility of mixtures of acetylene and air is
similarly reduced by the addition of aqueous vapour (though the exact
figures have not been experimentally ascertained); and hence it follows
that when the temperature in an acetylene generator in which water is in
excess, or in a gasholder, rises, the risk of explosion, if air is mixed
with the gas, is automatically reduced with the rise in temperature by
reason of the higher proportion of aqueous vapour which the gas will
retain at the higher temperature. This fact is alluded to in Chapter II.
Acetone vapour also acts similarly in lowering the upper explosive limit
of acetylene (_cf._ Chapter XI.).
It may perhaps be well to indicate briefly the practical significance of
the range of explosibility of a mixture of air and a combustible gas,
such as acetylene. The lower explosive limit is the lowest percentage of
combustible gas in the mixture of it and air at which explosion will
occur in the mixture if a light or spark is applied to it. If the
combustible gas is present in the mixture with air in less than that
percentage explosion is impossible. The upper explosive limit is the
highest percentage of combustible gas in the mixture of it and air at
which explosion will occur in the mixture if a light or spark is applied
to it. If the combustible gas is present in the mixture with air in more
than that percentage explosion is impossible. Mixtures, however, in which
the percentage of combustible gas lies between these two limits will
explode when a light or spark is applied to them; and the comprehensive
term "range of explosibility" is used to cover all lying between the two
explosive limits. If, then, a naked light is applied to a vessel
containing a mixture of a combustible gas and air, in which mixture the
proportion of combustible gas is below the lower limit of explosibility,
the gas will not take fire, but the light will continue to burn, deriving
its necessary oxygen from the excess of air present. On the other hand,
if a light is applied to a vessel containing a mixture of a combustible
gas and air, in which mixture the proportion of combustible gas is above
the upper limit of explosibility, the light will be extinguished, and
within the vessel the gaseous mixture will not burn; but it may burn at
the open mouth of the vessel as it comes in contact with the surrounding
air, until by diffusion, &c., sufficient air has entered the vessel to
form, with the remaining gas, a mixture lying within the explosive
limits, when an explosion will occur. Again, if a gaseous mixture
containing less of its combustible constituent than is necessary to
attain the lower explosive limit escapes from an open-ended pipe and a
light is applied to it, the mixture will not burn as a useful compact
flame (if, indeed, it fires at all); if the mixture contains more of its
combustible constituent than is required to attain the upper explosive
limit, that mixture will burn quietly at the mouth of the pipe and will
be free from any tendency to fire back into the pipe--assuming, of
course, that the gaseous mixture within the pipe is constantly travelling
towards the open end. If, however, a gaseous mixture containing a
proportion of its combustible constituent which lies between the lower
and the upper explosive limit of that constituent escapes from an open-
ended pipe and a light is applied, the mixture will fire and the flame
will pass back into the pipe, there to produce an explosion, unless the
orifice of the said pipe is so small as to prevent the explosive wave
passing (as is the case with a proper acetylene burner), or unless the
pipe itself is so narrow as appreciably to alter the range of
explosibility by lowering the upper explosive limit from its normal
value.
By far the most potent factor in altering the range of explosibility of
any gas when mixed with air is the diameter of the vessel containing or
delivering such mixture. Le Chatelier has investigated this point in the
case of acetylene, and his values are reproduced overleaf; they are
comparable among themselves, although it will be observed that his
absolute results differ somewhat from those obtained by Eitner which are
quoted later:
_Explosive Limits of Acetylene mixed with Air._--(Le Chatelier.)
___________________________________________________________
| | | |
| | Explosive Limits. | |
| Diameter of Tube |_______________________| Range of |
| in Millimetres. | | | Explosibility. |
| | Lower. | Upper. | |
|__________________|___________|___________|________________|
| | | | |
| | Per Cent. | Per Cent. | Per Cent. |
| 40 | 2.9 | 64 | 61.1 |
| 30 | 3.1 | 62 | 58.9 |
| 20 | 3.5 | 55 | 51.5 |
| 6 | 4.0 | 40 | 36.0 |
| 4 | 4.5 | 25 | 20.5 |
| 2 | 5.0 | 15 | 10.0 |
| 0.8 | 7.7 | 10 | 2.3 |
| 0.5 | ... | ... | ... |
|__________________|___________|___________|________________|
Thus it appears that past an orifice or constriction 0.5 mm. in diameter
no explosion of acetylene can proceed, whatever may be the proportions
between the gas and the air in the mixture present.
With every gas the explosive limits and the range of explosibility are
also influenced by various circumstances, such as the manner of ignition,
the pressure, and other minor conditions; but the following figures for
mixtures of air and different combustible gases were obtained by Eitner
under similar conditions, and are therefore strictly comparable one with
another. The conditions were that the mixture was contained in a tube 19
mm. (3/4-inch) wide, was at about 60° to 65° F., was saturated with
aqueous vapour, and was fired by electric spark.
_Table giving the Percentage by volume of Combustible Gas in a Mixture
of that Gas and Air corresponding with the Explosive Limits of such a
Mixture._--(Eitner.)
____________________________________________________________________
| | | | |
| Description of | Lower | Upper | Difference between the |
| Combustible Gas. | Explosive | Explosive | Lower and Upper Limits, |
| | Limit. | Limit. | showing the range |
| | | | covered by the |
| | | | Explosive Mixtures. |
|__________________|___________|___________|_________________________|
| | | | |
| | Per Cent. | Per Cent. | Per Cent. |
| Carbon monoxide | 16.50 | 74.95 | 58.45 |
| Hydrogen | 9.45 | 66.40 | 57.95 |
| Water-gas | | | |
| (uncarburetted) | 12.40 | 66.75 | 54.35 |
| ACETYLENE | 3.35 | 52.30 | 48.95 |
| Coal-gas | 7.90 | 19.10 | 11.20 |
| Ethylene | 4.10 | 14.60 | 10.50 |
| Methane | 6.10 | 12.80 | 6.70 |
| Benzene (vapour) | 2.65 | 6.50 | 3.85 |
| Pentane " | 2.40 | 4.90 | 2.50 |
| Benzoline " | 2.40 | 4.90 | 2.50 |
|__________________|___________|___________|_________________________|
These figures are of great practical significance. They indicate that a
mixture of acetylene and air becomes explosive (_i.e._, will explode
if a light is applied to it) when only 3.35 per cent. of the mixture is
acetylene, while a similar mixture of coal-gas and air is not explosive
until the coal-gas reaches 7.9 per cent. of the mixture. And again, air
may be added to coal-gas, and it does not become explosive until the
coal-gas is reduced to 19.1 per cent. of the mixture, while, on the
contrary, if air is added to acetylene, the mixture becomes explosive as
soon as the acetylene has fallen to 52.3 per cent. Hence the immense
importance of taking precautions to avoid, on the one hand, the escape of
acetylene into the air of a room, and, on the other hand, the admixture
of air with the acetylene in any vessel containing it or any pipe through
which it passes. These precautions are far more essential with acetylene
than with coal-gas. The table shows further how great is the danger of
explosion if benzene, benzoline, or other similar highly volatile
hydrocarbons [Footnote: The nomenclature of the different volatile
spirits is apt to be very confusing. "Benzene" is the proper name for the
most volatile hydrocarbon derived from coal-tar, whose formula is C_6H_6.
Commercially, benzene is often known as "benzol" or "benzole"; but it
would be generally advantageous if those latter words were only used to
mean imperfectly rectified benzene, _i.e._, mixtures of benzene with
toluene, &c., such as are more explicitly understood by the terms "90.s
benzol" and "50.s benzol." "Gasoline," "carburine," "petroleum ether,"
"benzine," "benzoline," "petrol," and "petroleum spirit" all refer to
more or less volatile (the most volatile being mentioned first) and more
or less thoroughly rectified products obtained from petroleum. They are
mixtures of different hydrocarbons, the greater part of them having the
general chemical formula C_nH_2n+2 where n = 5 or more. None of them is a
definite chemical compound as is benzene; when n = 5 only the product is
pentane. These hydrocarbons are known to chemists as "paraffins,"
"naphthenes" being occasionally met with; while a certain proportion of
unsaturated hydrocarbons is also present in most petroleum spirits. The
hydrocarbons of coal-tar are "aromatic hydrocarbons," their generic
formula being C_nH_2^n-6, where n is never less than 6.] are allowed to
vaporise in a room in which a light may be introduced. Less of the vapour
of these hydrocarbons than of acetylene in the air of a room brings the
mixture to the lower explosive limit, and therewith subjects it to the
risk of explosion. This tact militates strongly against the use of such
hydrocarbons within a house, or against the use of air-gas, which, as
explained in Chapter I., is air more or less saturated with the vapour of
volatile hydrocarbons. Conversely, a combustible gas, such as acetylene,
may be safely "carburetted" by these hydrocarbons in a properly
constructed apparatus set up outside the dwelling-house, as explained in
Chapter X., because there would be no air (as in air-gas) in the pipes,
&c., and a relatively large escape of carburetted acetylene would be
required to produce an explosive atmosphere in a room. Moreover, the
odour of the acetylene itself would render the detection of a leak far
easier with carburetted acetylene than with air-gas.
N. Teclu has investigated the explosive limits of mixtures of air with
certain combustible gases somewhat in the same manner as Eitner, viz.: by
firing the mixture in an eudiometer tube by means of an electric spark.
He worked, however, with the mixture dry instead of saturated with
aqueous vapour, which doubtless helps to account for the difference
between his and Eitner's results.
_Table giving the Percentages by volume of Combustible Gas in a
Dehydrated Mixture of that Gas and Air between which the Explosive Limits
of such a Mixture lie._--(Teclu).
____________________________________________________________________
| | | |
| | Lower Explosive Limit. | Upper Explosive Limit. |
| Description of |________________________|________________________|
| Combustible Gas. | | |
| | Per Cent. of Gas. | Per Cent. of Gas. |
|__________________|________________________|________________________|
| | | |
| ACETYLENE | 1.53-1.77 | 57.95-58.65 |
| Hydrogen | 9.73-9.96 | 62.75-63.58 |
| Coal-gas | 4.36-4.82 | 23.35-23.63 |
| Methane | 3.20-3.67 | 7.46- 7.88 |
|__________________|________________________|________________________|
Experiments have been made at Lechbruch in Bavaria to ascertain directly
the smallest proportion of acetylene which renders the air of a room
explosive. Ignition was effected by the flame resulting when a pad of
cotton-wool impregnated with benzoline or potassium chlorate was fired by
an electrically heated wire. The room in which most of the tests were
made was 8 ft. 10 in. long, 6 ft. 7 in. wide, and 6 ft. 8 in. high, and
had two windows. When acetylene was generated in this room in normal
conditions of natural ventilation through the walls, the volume generated
could amount to 3 per cent. of the air-space of the room without
explosion ensuing on ignition of the wool, provided time elapsed for
equable diffusion, which, moreover, was rapidly attained. Further, it was
found that when the whole of the acetylene which 2 kilogrammes or 4.4 lb.
of carbide (the maximum permissible charge in many countries for a
portable lamp for indoor use) will yield was liberated in a room, a
destructive explosion could not ensue on ignition provided the air-space
exceeded 40 cubic metres or 1410 cubic feet, or, if the evolved gas were
uniformly diffused, 24 cubic metres or 850 cubic feet. When the walls of
the room were rendered impervious to air and gas, and acetylene was
liberated, and allowed time for diffusion, in the air of the room, an
explosion was observed with a proportion of only 2-1/2 per cent. of
acetylene in the air.
_Solubility of Acetylene in Various Liquids._
_____________________________________________________________________
| | | | |
| | | Volumes of | |
| | Tem- | Acetylene | |
| Solvent. |perature.|dissolved by| Authority. |
| | | 100 Vols. | |
| | | of Solvent.| |
|___________________________|_________|____________|__________________|
| | | | |
| | Degs. C | | |
| Acetone . . . . | 15 | 2500 | Claude and Hess |
| " . . . . | 50 | 1250 | " |
| Acetic acid; alcohol . | 18 | 600 | Berthelot |
| Benzoline; chloroform . | 18 | 400 | " |
| Paraffin oil . . . | 0 | 103.3 | E. Muller |
| " . . . | 18 | 150 | Berthelot |
| Olive oil . . . . | -- | 48 | Fuchs and Schiff |
| Carbon bisulphide . . | 18 | 100 | Berthelot |
| " tetrachloride . | 0 | 25 | Nieuwland |
| Water (at 4 65 atmospheres| | | |
| pressure) . . | 0 | 160 | Villard |
| " (at 755 mm. pressure)| 12 | 118 | Berthelot |
| " (760 mm. pressure) . | 12 | 106.6 | E. Müller |
| " " . | 15 | 110 | Lewes |
| " " . | 18 | 100 | Berthelot |
| " " . | -- | 100 | E. Davy (in 1836)|
| " " . | 19.5 | 97.5 | E. Müller |
| Milk of lime: about 10 | | | |
| grammes of calcium hy- | 5 | 112 | Hammerschmidt |
| droxide per 100 c.c. . | | | and Sandmann |
| " " " | 10 | 95 | " |
| " " " | 20 | 75 | " |
| " " " | 50 | 38 | " |
| " " " | 70 | 20 | " |
| " " " | 90 | 6 | " |
| Solution of common salt,5%| 19 | 67.9 | " |
| (sodium chloride) " | 25 | 47.7 | " |
| " 20%| 19 | 29.6 | " |
| " " | 25 | 12.6 | " |
| "(nearly saturated, | | | |
| 26%) . . | 15 | 20.6 | " |
| "(saturated, sp. gr.| | | |
| 1-21) . . | 0 | 22.0 | E. Müller |
| " " " | 12 | 21.0 | " |
| " " " | 18 | 20.4 | " |
| Solution of calcium | | | Hammerschmidt |
| chloride (saturated) . | 15 | 6.0 | and Sandmann |
| Bergé and Reychler's re- | | | |
| agent . . . . | -- | 95 | Nieuwland |
|___________________________|_________|____________|__________________|
SOLUBILITY.--Acetylene is readily soluble in many liquids. It is
desirable, on the one hand, as indicated in Chapter III., that the liquid
in the seals of gasholders, &c., should be one in which acetylene is
soluble to the smallest degree practically attainable; while, on the
other hand, liquids in which acetylene is soluble in a very high degree
are valuable agents for its storage in the liquid state. Hence it is
important to know the extent of the solubility of acetylene in a number
of liquids. The tabular statement (p. 179) gives the most trustworthy
information in regard to the solubilities under the normal atmospheric
pressure of 760 mm. or thereabouts.
The strength of milk of lime quoted in the above table was obtained by
carefully allowing 50 grammes of carbide to interact with 550 c.c. of
water at 5° C. A higher degree of concentration of the milk of lime was
found by Hammerschmidt and Sandmann to cause a slight decrease in the
amount of acetylene held in solution by it. Hammerschmidt and Sandmann's
figures, however, do not agree well with others obtained by Caro, who has
also determined the solubility of acetylene in lime-water, using first, a
clear saturated lime-water prepared at 20° C. and secondly, a milk of
lime obtained by slaking 10 grammes of quicklime in 100 c.c. of water. As
before, the figures relate to the volumes of acetylene dissolved at
atmospheric pressure by 100 volumes of the stated liquid.
_________________________________________________
| | | |
| Temperature. | Lime-water. | Milk of Lime. |
|_______________|_______________|_________________|
| | | |
| Degs C. | | |
| 0 | 146.2 | 152.6 |
| 5 | 138.5 | -- |
| 15 | 122.8 | 134.8 |
| 50 | 43.9 | 62.6 |
| 90 | 6.2 | 9.2 |
|_______________|_______________|_________________|
Figures showing the solubility of acetylene in plain water at different
temperatures have been published in Landolt-Börnstein's Physico-
Chemical Tables. These are reproduced below. The "Coefficient of
Absorption" is the volume of the gas, measured at 0° C. and a barometric
height of 760 mm. taken up by one volume of water, at the stated
temperature, when the gas pressure on the surface, apart from the vapour
pressure of the water itself, is 760 mm. The "Solubility" is the weight
of acetylene in grammes taken up by 100 grammes of water at the stated
temperature, when the total pressure on the surface, including that of
the vapour pressure of the water, is 760 mm.
_____________________________________________
| | | |
| Temperature. | Coefficient of | Solubility. |
| | Absorption. | |
|______________|________________|_____________|
| | | |
| Degs. C. | | |
| 0 | 1.73 | 0.20 |
| 1 | 1.68 | 0.19 |
| 2 | 1.63 | 0.19 |
| 3 | 1.58 | 0.18 |
| 4 | 1.53 | 0.18 |
| 5 | 1.49 | 0.17 |
| 6 | 1.45 | 0.17 |
| 7 | 1.41 | 0.16 |
| 8 | 1.37 | 0.16 |
| 9 | 1.34 | 0.15 |
| 10 | 1.31 | 0.15 |
| 11 | 1.27 | 0.15 |
| 12 | 1.24 | 0.14 |
| 13 | 1.21 | 0.14 |
| 14 | 1.18 | 0.14 |
| 15 | 1.15 | 0.13 |
| 16 | 1.13 | 0.13 |
| 17 | 1.10 | 0.13 |
| 18 | 1.08 | 0.12 |
| 19 | 1.05 | 0.12 |
| 20 | 1.03 | 0.12 |
| 21 | 1.01 | 0.12 |
| 22 | 0.99 | 0.11 |
| 23 | 0.97 | 0.11 |
| 24 | 0.95 | 0.11 |
| 25 | 0.93 | 0.11 |
| 26 | 0.91 | 0.10 |
| 27 | 0.89 | 0.10 |
| 28 | 0.87 | 0.10 |
| 29 | 0.85 | 0.10 |
| 30 | 0.84 | 0.09 |
|______________|________________|_____________|
Advantage is taken, as explained in Chapter XI., of the high degree of
solubility of acetylene in acetone, to employ a solution of the gas in
that liquid when acetylene is wanted in a portable condition. The
solubility increases very rapidly with the pressure, so that under a
pressure of twelve atmospheres acetone dissolves about 300 times its
original volume of the gas, while the solubility also increases greatly
with a reduction in the temperature, until at -80° C. acetone takes up
2000 times its volume of acetylene under the ordinary atmospheric
pressure. Further details of the valuable qualities of acetone as a
solvent of acetylene are given in Chapter XI., but it may here be
remarked that the successful utilisation of the solvent power of acetone
depends to a very large extent on the absolute freedom from moisture of
both the acetylene and the acetone, so that acetone of 99 per cent.
strength is now used as the solvent.
Turning to the other end of the scale of solubility, the most valuable
liquids for serving as seals of gasholders, &c., are readily discernible.
Far superior to all others is a saturated solution of calcium chloride,
and this should be selected as the confining liquid whenever it is
important to avoid dissolution of acetylene in the liquid as far as may
be. Brine comes next in order of merit for this purpose, but it is
objectionable on account of its corrosive action on metals. Olive oil
should, according to Fuchs and Schiff, be of service where a saline
liquid is undesirable; mineral oil seems useless. Were they concordant,
the figures for milk of lime would be particularly useful, because this
material is naturally the confining liquid in the generating chambers of
carbide-to-water apparatus, and because the temperature of the liquid
rises through the heat evolved during the generation of the gas
(_vide_ Chapters II. and III.). It will be seen that these figures
would afford a means of calculating the maximum possible loss of gas by
dissolution when a known volume of sludge is run off from a carbide-to-
water generator at about any possible temperature.
According to Garelli and Falciola, the depression in the freezing-point
of water caused by the saturation of that liquid with acetylene is 0.08°
C., the corresponding figure for benzene in place of water being 1.40° C.
These figures indicate that 100 parts by weight of water should dissolve
0.1118 part by weight of acetylene at 0° C., and that 100 parts of
benzene should dissolve about 0.687 part of acetylene at 5° C. In other
words, 100 volumes of water at the freezing-point should dissolve 95
volumes of acetylene, and 100 volumes of benzene dissolve some 653
volumes of the gas. The figure calculated for water in this way is lower
than that which might be expected from the direct determinations at other
temperatures already referred to; that for benzene may be compared with
Berthelot's value of 400 volumes at 18° C. Other measurements of the
solubility of acetylene in water at 0° C. have given the figure 0.1162
per cent. by weight.
TOXICITY.--Many experiments have been made to determine to what extent
acetylene exercises a toxic action on animals breathing air containing a
large proportion of it; but they have given somewhat inconclusive
results, owing probably to varying proportions of impurities in the
samples of acetylene used. The sulphuretted hydrogen and phosphine which
are found in acetylene as ordinarily prepared are such powerful toxic
agents that they would always, in cases of "acetylene" poisoning, be
largely instrumental in bringing about the effects observed. Acetylene
_per se_ would appear to have but a small toxic action; for the
principal toxic ingredient in coal-gas is carbon monoxide, which does not
occur in sensible quantity in acetylene as obtained from calcium carbide.
The colour of blood is changed by inhalation of acetylene to a bright
cherry-red, just as in cases of poisoning by carbon monoxide; but this is
due to a more dissolution of the gas in the haemoglobin of the blood, so
that there is much more hope of recovery for a subject of acetylene
poisoning than for one of coal-gas poisoning. Practically the risk of
poisoning by acetylene, after it has been purified by one of the ordinary
means, is _nil_. The toxic action of the impurities of crude
acetylene is discussed in Chapter V.
Acetylene is an "endothermic" compound, as has been mentioned in Chapter
II., where the meaning of the expression endothermic is explained. It has
there been indicated that by reason of its endothermic nature it is
unsafe to have acetylene at either a temperature of 780° C. and upwards,
or at a pressure of two atmospheres absolute, or higher. If that
temperature or that pressure is exceeded, dissociation (_i.e._,
decomposition into its elements), if initiated at any spot, will extend
through the whole mass of acetylene. In this sense, acetylene at or above
780° C., or at two or more atmospheres pressure, is explosive in the
absence of air or oxygen, and it is thereby distinguished from the
majority of other combustible gases, such as the components of coal-gas.
But if, by dilution with another gas, the partial pressure of the
acetylene is reduced, then the mixture may be subjected to a higher
pressure than that of two atmospheres without acquiring explosiveness, as
is fully shown in Chapter XI. Thus it becomes possible safely to compress
mixtures of acetylene and oil-gas or coal-gas, whereas unadmixed
acetylene cannot be safely kept under a pressure of two atmospheres
absolute or more. In a series of experiments carried out by Dupré on
behalf of the British Home Office, and described in the Report on
Explosives for 1897, samples of moist acetylene, free from air, but
apparently not purified by any chemical process, were exposed to the
influence of a bright red-hot wire. When the gas was held in the
containing vessel at the atmospheric pressure then obtaining, viz., 30.34
inches (771 mm.) of mercury, no explosion occurred. When the pressure was
raised to 45.34 inches (1150 mm.), no explosion occurred; but when the
pressure was further raised to 59.34 inches (1505 mm., or very nearly two
atmospheres absolute) the acetylene exploded, or dissociated into its
elements.
Acetylene readily polymerises when heated, as has been stated in Chapter
II., where the meaning of the term "polymerisation" has been explained.
The effects of the products of the polymerisation of acetylene on the
flame produced when the gas is burnt at the ordinary acetylene burners
have been stated in Chapter VIII., where the reasons therefor have been
indicated. The chief primary product of the polymerisation of acetylene
by heat appears to be benzene. But there are also produced, in some cases
by secondary changes, ethylene, methane, naphthalene, styrolene,
anthracene, and homologues of several of these hydrocarbons, while carbon
and hydrogen are separated. The production of these bodies by the action
of heat on acetylene is attended by a reduction of the illuminative value
of the gas, while owing to the change in the proportion of air required
for combustion (_see_ Chapter VIII.), the burners devised for the
consumption of acetylene fail to consume properly the mixture of gases
formed by polymerisation from the acetylene. It is difficult to compare
the illuminative value of the several bodies, as they cannot all be
consumed economically without admixture, but the following table
indicates approximately the _maximum_ illuminative value obtainable
from them either by combustion alone or in admixture with some non-
illuminating or feebly-illuminating gas:
________________________________________________
| | | |
| | | Candles per |
| | | Cubic Foot |
|______________|___________________|_____________|
| | | |
| | | (say) |
| Acetylene | C_2H_2 | 50 |
| Hydrogen | H_2 | 0 |
| Methane | CH_4 | 1 |
| Ethane | C_2H_6 | 7 |
| Propane | C_3H_8 | 11 |
| Pentane | C_5H_12 (vapour) | 35 |
| Hexane | C_6H_14 " | 45 |
| Ethylene | C_2H_4 | 20 |
| Propylene | C_3H_6 | 25 |
| Benzene | C_6H_6 (vapour) | 200 |
| Toluene | C_7H_8 " | 250 |
| Naphthalene | C_10H_8 " | 400 |
|______________|___________________|_____________|
It appears from this table that, with the exception of the three
hydrocarbons last named, no substance likely to be formed by the action
of heat on acetylene has nearly so high an illuminative value--volume for
volume--as acetylene itself. The richly illuminating vapours of benzene
and naphthalene (and homologues) cannot practically add to the
illuminative value of acetylene, because of the difficulty of consuming
them without smoke, unless they are diluted with a large proportion of
feebly- or non-illuminating gas, such as methane or hydrogen. The
practical effect of carburetting acetylene with hydrocarbon vapours will
be shown in Chapter X. to be disastrous so far as the illuminating
efficiency of the gas is concerned. Hence it appears that no conceivable
products of the polymerisation of acetylene by heat can result in its
illuminative value being improved--even presupposing that the burners
could consume the polymers properly--while practically a considerable
deterioration of its value must ensue.
The heat of combustion of acetylene was found by J. Thomson to be 310.57
large calories per gramme-molecule, and by Berthelot to be 321.00
calories. The latest determination, however, made by Berthelot and
Matignon shows it to be 315.7 calories at constant pressure. Taking the
heat of formation of carbon dioxide from diamond carbon at constant
pressure as 94.3 calories (Berthelot and Matignon), which is equal to
97.3 calories from amorphous carbon, and the heat of formation of liquid
water as 69 calories; this value for the heat of combustion of acetylene
makes its heat of formation to be 94.3 x 2 + 69 - 315.7 = -58.1 large
calories per gramme-molecule (26 grammes) from diamond carbon, or -52.1
from amorphous carbon. It will be noticed that the heat of combustion of
acetylene is greater than the combined heats of combustion of its
constituents; which proves that heat has been absorbed in the union of
the hydrogen and carbon in the molecule, or that acetylene is
endothermic, as elsewhere explained. These calculations, and others given
in Chapter IX., will perhaps be rendered more intelligible by the
following table of thermochemical phenomena:
_______________________________________________________________
| | | | |
| Reaction. | Diamond | Amorphous | |
| | Carbon. | Carbon. | |
|________________________________|_________|___________|________|
| | | | |
| (1) C (solid) + O . . . | 26.1 | 29.1 | ... |
| (2) C (solid) + O_2 . . . | 94.3 | 97.3 | ... |
| (3) CO + O (2 - 1) . . . | ... | ... | 68.2 |
| (4) Conversion of solid carbon | | | |
| into gas (3 - 1) . . . | 42.1 | 39.1 | ... |
| (5) C (gas) + O (1 + 4) . . | ... | ... | 68.2 |
| (6) Conversion of amorphous | | | |
| carbon to diamond . . | ... | ... | 3.0 |
| (7) C_2 + H_2 . . . . | -58.1 | -52.1 | ... |
| (8) C_2H_2 + 2-1/2O_2 . . | ... | ... | 315.7 |
|________________________________|_________|___________|________|
W. G. Mixter has determined the heat of combustion of acetylene to be
312.9 calories at constant volume, and 313.8 at constant pressure. Using
Berthelot and Matignon's data given above for amorphous carbon, this
represents the heat of formation to be -50.2 (Mixter himself calculates
it as -51.4) calories. By causing compressed acetylene to dissociate
under the influence of an electric spark, Mixter measured its heat of
formation as -53.3 calories. His corresponding heats of combustion of
ethylene are 344.6 calories (constant volume) and 345.8 (constant
pressure); for its heat of formation he deduces a value -7.8, and
experimentally found one of about -10.6 (constant pressure).
THE ACETYLENE FLAME.--It has been stated in Chapter I. that acetylene
burnt in self-luminous burners gives a whiter light than that afforded by
any other artificial illuminant, because the proportion of the various
spectrum colours in the light most nearly resembles the corresponding
proportion found in the direct rays of the sun. Calling the amount of
monochromatic light belonging to each of the five main spectrum colours
present in the sun's rays unity in succession, and comparing the amount
with that present in the light obtained from electricity, coal-gas, and
acetylene, Münsterberg has given the following table for the composition
of the several lights mentioned:
______________________________________________________________________
| | | | | |
| | Electricity | Coal-Gas | Acetylene | |
| |________________|__________________|_______________|_______|
| Colour | | | | | | | |
| in | | | | | | With | |
| Spectrum.| Arc. | Incan- | Lumin- | Incan- | Alone.| 3 per | Sun- |
| | | descent.| ous. | descent.| | Cent. | light.|
| | | | | | | Air. | |
|__________|______|_________|________|_________|_______|_______|_______|
| | | | | | | | |
| Red | 2.09 | 1.48 | 4.07 | 0.37 | 1.83 | 1.03 | 1 |
| Yellow | 1.00 | 1.00 | 1.00 | 0.90 | 1.02 | 1.02 | 1 |
| Green | 0.99 | 0.62 | 0.47 | 4.30 | 0.76 | 0.71 | 1 |
| Blue | 0.87 | 0.91 | 1.27 | 0.74 | 1.94 | 1.46 | 1 |
| Violet | 1.08 | 0.17 | 0.15 | 0.83 | 1.07 | 1.07 | 1 |
| Ultra- | | | | | | | |
| Violet | 1.21 | ... | ... | ... | ... | ... | 1 |
|__________|______|_________|________|_________|_______|_______|_______|
These figures lack something in explicitness; but they indicate the
greater uniformity of the acetylene light in its proportion of rays of
different wave-lengths. It does not possess the high proportion of green
of the Welsbach flame, or the high proportion of red of the luminous gas-
flame. It is interesting to note the large amount of blue and violet
light in the acetylene flame, for these are the colours which are chiefly
concerned in photography; and it is to their prominence that acetylene
has been found to be so very actinic. It is also interesting to note that
an addition of air to acetylene tends to make the light even more like
that of the sun by reducing the proportion of red and blue rays to nearer
the normal figure.
H. Erdmann has made somewhat similar calculation, comparing the light of
acetylene with that of the Hefner (amyl acetate) lamp, and with coal-gas
consumed in an Argand and an incandescent burner. Consecutively taking
the radiation of the acetylene flame as unity for each of the spectrum
colours, his results are:
__________________________________________________________________
| | | | |
| | | | Coal-Gas |
| Colour in | Wave-Lengths, | |_______________________|
| Spectrum | uu | Hefner Light | | |
| | | | Argand | Incandescent |
|___________|_______________|______________|________|______________|
| | | | | |
| Red | 650 | 1.45 | 1.34 | 1.03 |
| Orange | 610 | 1.22 | 1.13 | 1.00 |
| Yellow | 590 | 1.00 | 1.00 | 1.00 |
| Green | 550 | 0.87 | 0.93 | 0.86 |
| Blue | 490 | 0.72 | 1.27 | 0.92 |
| Violet | 470 | 0.77 | 1.35 | 1.73 |
|___________|_______________|______________|________|______________|
B. Heise has investigated the light of different flames, including
acetylene, by a heterochromatic photometric method; but his results
varied greatly according to the pressure at which the acetylene was
supplied to the burner and the type of burner used. Petroleum affords
light closely resembling in colour the Argand coal-gas flame; and
electric glow-lamps, unless overrun and thereby quickly worn out, give
very similar light, though with a somewhat greater preponderance of
radiation in the red and yellow.
____________________________________________________________________
| | | |
| | Percent of Total | |
| Light. | Energy manifested | Observer. |
| | as Light. | |
|____________________________|___________________|___________________|
| | | |
| Candle, spermaceti . . | 2.1 | Thomsen |
| " paraffin . . . | 1.53 | Rogers |
| Moderator lamp . . . | 2.6 | Thomsen |
| Coal-gas . . . . . | 1.97 | Thomsen |
| " . . . . . | 2.40 | Langley |
| " batswing . . . | 1.28 | Rogers |
| " Argand . . . | 1.61 | Rogers |
| " incandesce . . | 2 to 7 | Stebbins |
| Electric glow-lamp . . | about 6 | Merritt |
| " " . . | 5.5 | Abney and Festing |
| Lime light (new) . . . | 14 | Orehore |
| " (old) . . . | 8.4 | Orehore |
| Electric arc . . . . | 10.4 | Tyndall; Nakano |
| " . . . . | 8 to 13 | Marks |
| Magnesium light . . . | 12.5 | Rogers |
| Acetylene . . . . | 10.5 | Stewart and Hoxie |
| " (No. 0 slit burner | 11.35 | Neuberg |
| " (No. 00000 . . | | |
| Bray fishtail) | 13.8 | Neuberg |
| " (No. 3 duplex) . | 14.7 | Neuberg |
| Geissler tube . . . | 32.0 | Staub |
|____________________________|___________________|___________________|
Violle and Féry, also Erdmann, have proposed the use of acetylene as a
standard of light. As a standard burner Féry employed a piece of
thermometer tube, cut off smoothly at the end and having a diameter of
0.5 millimetre, a variation in the diameter up to 10 per cent. being of
no consequence. When the height of the flame ranged from 10 to 25
millimetres the burner passed from 2.02 to 4.28 litres per hour, and the
illuminating power of the light remained sensibly proportional to the
height of the jet, with maximum variations from the calculated value of
±0.008. It is clear that for such a purpose as this the acetylene must be
prepared from very pure carbide and at the lowest possible temperature in
the generator. Further investigations in this direction should be
welcome, because it is now fairly easy to obtain a carbide of standard
quality and to purify the gas until it is essentially pure acetylene from
a chemical point of view.
L. W. Hartmann has studied the flame of a mixture of acetylene with
hydrogen. He finds that the flame of the mixture is richer in light of
short wave-lengths than that of pure acetylene, but that the colour of
the light does not appear to vary with the proportion of hydrogen
present.
Numerous investigators have studied the optical or radiant efficiency of
artificial lights, _i.e._, the proportion of the total heat plus
light energy emitted by the flame which is produced in the form of
visible light. Some results are shown in the table on the previous page.
Figures showing the ratio of the visible light emitted by various
illuminants to the amount of energy expended in producing the light and
also the energy equivalent of each spherical Hefner unit evolved have
been published by H. Lux, whose results follow:
_______________________________________________________________________
| | | | | |
| | Ratio of | Ratio of | Mean | Energy |
| | Light | Light | Spherical | Equiva- |
| Light. | emitted to | emitted to | Illuminat- | lent to 1 |
| | Total | Energy | ing Power. | Spherical |
| | Radiation. | Impressed. | Hefners. | Hefner in |
| | | | | Watts. |
|____________________|____________|____________|____________|___________|
| | | | | |
| | Per Cent. | Per Cent. | | |
| Hefner lamp | 0.89 | 0.103 | 0.825 | 0.108 |
| Paraffin lamp, 14" | 1.23 | 0.25 | 12.0 | 0.105 |
| ACETYLENE, 7.2 | | | | |
| litre burner | 6.36 | 0.65 | 6.04 | 0.103 |
| Coal-gas incandes- | | | | |
| cent, upturned | 2.26-2.92 | 0.46 | 89.6 | 0.037 |
| " incandes- | | | | |
| cent, inverted | 2.03-2.97 | 0.51 | 82.3 | 0.035 |
| Carbon filament | | | | |
| glow-lamp | 3.2-2.7 | 2.07 | 24.5 | 0.085 |
| Nernst lamp | 5.7 | 4.21-3.85 | 91.9 | 0.073 |
| Tantalum lamp | 8.5 | 4.87 | 26.7 | 0.080 |
| Osram lamp | 9.1 | 5.36 | 27.4 | 0.075 |
| Direct-current arc | 8.1 | 5.60 | 524 | 0.047 |
| " " enclosed | 2.0 | 1.16 | 295 | 0.021 |
| Flame arc, yellow | 15.7 | 13.20 | 1145 | 0.041 |
| " " white | 7.6 | 6.66 | 760 | 0.031 |
| Alternating- | | | | |
| current arc | 3.7 | 1.90 | 89 | 0.038 |
| Uviol mercury | | | | |
| vapour lamp | 5.8 | 2.24 | 344 | 0.015 |
| Quartz lamp | 17.6 | 6.00 | 2960 | 0.014 |
|____________________|____________|____________|____________|___________|
CHEMICAL PROPERTIES.--It is unnecessary for the purpose of this work to
give an exhaustive account of the general chemical reactions of acetylene
with other bodies, but a few of the more important must be referred to.
Since the gases are liable to unite spontaneously when brought into
contact, the reactions between, acetylene and chlorine require attention,
first, because of the accidents that have occurred when using bleaching-
powder (_see_ Chapter V.) as a purifying material for the crude gas;
secondly, because it has been proposed to manufacture one of the products
of the combination, viz., acetylene tetrachloride, on a large scale, and
to employ it as a detergent in place of carbon tetrachloride or carbon
disulphide. Acetylene forms two addition products with chlorine,
C_2H_2Cl_2, and C_2H_2Cl_4. These are known as acetylene dichloride and
tetrachloride respectively, or more systematically as dichlorethylene and
tetrachlorethane. One or both of the chlorides is apt to be produced when
acetylene comes into contact with free chlorine, and the reaction
sometimes proceeds with explosive violence. The earliest writers, such as
E. Davy, Wöhler, and Berthelot, stated that an addition of chlorine to
acetylene was invariably followed by an explosion, unless the mixture was
protected from light; whilst later investigators thought the two gases
could be safely mixed if they were both pure, or if air was absent. Owing
to the conflicting nature of the statements made, Nieuwland determined in
1905 to study the problem afresh; and the annexed account is chiefly
based on his experiments, which, however, still fail satisfactorily to
elucidate all the phenomena observed. According to Nieuwland's results,
the behaviour of mixtures of acetylene and chlorine appears capricious,
for sometimes the gases unite quietly, although sometimes they explode.
Acetylene and chlorine react quite quietly in the dark and at low
temperatures; and neither a moderate increase in temperature, nor the
admission of diffused daylight, nor the introduction of small volumes of
air, is necessarily followed by an explosion. Doubtless the presence of
either light, air, or warmth increases the probability of an explosive
reaction, while it becomes more probable still in their joint presence;
but in given conditions the reaction may suddenly change from a gentle
formation of addition products to a violent formation of substitution
products without any warning or manifest cause. When the gases merely
unite quietly, tetrachlorethane, or acetylene tetrachloride, is produced
thus:
C_2H_2 + 2Cl_2 = C_2H_2Cl_4;
but when the reaction is violent some hexachlorethane is formed,
presumably thus:
2C_2H_2 + 5Cl_2 = 4HCl + C_2 + C_2Cl_6.
The heat evolved by the decomposition of the acetylene by the formation
of the hydrochloric acid in the last equation is then propagated amongst
the rest of the gaseous mixture, accelerating the action, and causing the
acetylene to react with the chlorine to form more hydrochloric acid and
free carbon thus;
C_2H_2 + Cl_2 = 2HCl + C_2.
It is evident that these results do not altogether explain the mechanism
of the reactions involved. Possibly the formation of substitution
products and the consequent occurrence of an explosion is brought about
by some foreign substance which acts as a catalytic agent. Such substance
may conceivably be one of the impurities in crude acetylene, or the solid
matter of a bleaching-powder purifying material. The experiments at least
indicate the direction in which safety may be sought when bleaching-
powder is employed to purify the crude gas, viz., dilution of the powder
with an inert material, absence of air from the gas, and avoidance of
bright sunlight in the place where a spent purifier is being emptied.
Unfortunately Nieuwland did not investigate the action on acetylene of
hypochlorites, which are presumably the active ingredients in bleaching-
powder. As will appear in due course, processes have been devised and
patented to eliminate all danger from the reaction between acetylene and
chlorine for the purpose of making tetrachlorethane in quantity.
Acetylene combines with hydrogen in the presence of platinum black, and
ethylene and then ethane result. It was hoped at one time that this
reaction would lead to the manufacture of alcohol from acetylene being
achieved on a commercial basis; but it was found that it did not proceed
with sufficient smoothness for the process to succeed, and a number of
higher or condensation products were formed at the same time. It has been
shown by Erdmann that the cost of production of alcohol from acetylene
through this reaction must prove prohibitive, and he has indicated
another reaction which he considered more promising. This is the
conversion of acetylene by means of dilute sulphuric acid (3 volumes of
concentrated acid to 7 volumes of water), preferably in the presence of
mercuric oxide, to acetaldehyde. The yield, however, was not
satisfactory, and the process does not appear to have passed beyond the
laboratory stage.
It has also been proposed to utilise the readiness with which acetylene
polymerises on heating to form benzene, for the production of benzene
commercially; but the relative prices of acetylene and benzene would have
to be greatly changed from those now obtaining to make such a scheme
successful. Acetylene also lends itself to the synthesis of phenol or
carbolic acid. If the dry gas is passed slowly into fuming sulphuric
acid, a sulpho-derivative results, of which the potash salt may be thrown
down by means of alcohol. This salt has the formula C_2H_4O_2,S_2O_6K_2,
and on heating it with caustic potash in an atmosphere of hydrogen,
decomposing with excess of sulphuric acid, and distilling, phenol results
and may be isolated. The product is, however, generally much contaminated
with carbon, and the process, which was devised by Berthelot, does not
appear to have been pursued commercially. Berthelot has also investigated
the action of ordinary concentrated sulphuric acid on acetylene, and
obtained various sulphonic derivatives. Schröter has made similar
investigations on the action of strongly fuming sulphuric acid on
acetylene. These investigations have not yet acquired any commercial
significance.
If a mixture of acetylene with either of the oxides of carbon is led
through a red-hot tube, or if a similar mixture is submitted to the
action of electric sparks when confined within a closed vessel at some
pressure, a decomposition occurs, the whole of the carbon is liberated in
the free state, while the hydrogen and oxygen combine to form water.
Analogous reactions take place when either oxide of carbon is led over
calcium carbide heated to a temperature of 200° or 250° C., the second
product in this case being calcium oxide. The equations representing
these actions are:
C_2H_2 + CO = H_2O + 3C
2C_2H_2 + CO_2 = 2H_2O + 5C
CaC_2 + CO = CaO + 3C
2CaC_2 + CO_2 = 2CaO + 5C
By urging the temperature, or by increasing the pressure at which the
gases are led over the carbide, the free carbon appears in the graphitic
condition; at lower temperatures and pressures, it is separated in the
amorphous state. These reactions are utilised in Frank's process for
preparing a carbon pigment or an artificial graphite (_cf._ Chapter
XII.).
Parallel decompositions occur between carbon bisulphide and either
acetylene or calcium carbide, all the carbon of both substances being
eliminated, while the by-product is either sulphuretted hydrogen or
calcium (penta) sulphide. Other organic bodies containing sulphur are
decomposed in the same fashion, and it has been suggested by Ditz that if
carbide could be obtained at a suitable price, the process might be made
useful in removing sulphur (_i.e._, carbon bisulphide and thiophen)
from crude benzol, in purifying the natural petroleum oil which contains
sulphur, and possibly in removing "sulphur compounds" from coal-gas.
COMPOUNDS WITH COPPER. By far the most important chemical reactions of
acetylene in connexion with its use as an illuminant or fuel are those
which it undergoes with certain metals, notably copper. It is known that
if acetylene comes in contact with copper or with one of its salts, in
certain conditions a compound is produced which, at least when dry, is
highly explosive, and will detonate either when warmed or when struck or
gently rubbed. The precise mechanism of the reaction, or reactions,
between acetylene and copper (or its compounds), and also the character
of the product, or products, obtained have been studied by numerous
investigators; but their results have been inconclusive and sometimes
rather contradictory, so that it can hardly be said that the conditions
which determine or preclude the formation of an explosive compound and
the composition of the explosive compound are yet known with certainty.
Copper is a metal which yields two series of compounds, cuprous and
cupric salts, the latter of which contain half the quantity of metal per
unit of acid constituent that is found in the former. It should follow,
therefore, that there are two compounds of copper with carbon, or copper
carbides: cuprous carbide, Cu_2C_2, and cupric carbide, CuC_2. Acetylene
reacts at ordinary temperatures with an ammoniacal solution of any cupric
salt, forming a black cupric compound of uncertain constitution which
explodes between 50° and 70° C. It is decomposed by dilute acids,
yielding some polymerised substances. At more elevated temperatures other
cupric compounds are produced which also give evidence of polymerisation.
Cuprous carbide or acetylide is the reddish brown amorphous precipitate
which is the ultimate product obtained when acetylene is led into an
ammoniacal solution of cuprous chloride. This body is decomposed by
hydrochloric acid, yielding acetylene; but of itself it is, in all
probability, not explosive. Cuprous carbide, however, is very unstable
and prone to oxidation; so that, given the opportunity, it combines with
oxygen or hydrogen, or both, until it produces the copper acetylide, or
acetylene-copper, which is explosive--a body to which Blochmann's formula
C_2H_2Cu_2O is generally ascribed. Thus it should happen that the exact
nature of the copper acetylene compound may vary according to the
conditions in which it has been formed, from a substance that is not
explosive at all at first, to one that is violently explosive; and the
degree of explosiveness should depend on the greater exposure of the
compound to air and moisture, or the larger amount of oxygen and moisture
in the acetylene during its contact with the copper or copper salt. For
instance, Mai has found that freshly made copper acetylide can be heated
to 60° C. or higher without explosion; but that if the compound is
exposed to air for a few hours it explodes on warming, while if warmed
with oxygen it explodes on contact with acetylene. It is said by Mai and
by Caro to absorb acetylene when both substances are dry, becoming so hot
as to explode spontaneously. Freund and Mai have also observed that when
copper acetylide which has been dried in contact with air for four or
five hours at a temperature of 50° or 60° C. is allowed to explode in the
presence of a current of acetylene, an explosion accompanied by light
takes place; but it is always local and is not communicated to the gas,
whether the latter is crude or pure. In contact with neutral or acid
solutions of cuprous salts acetylene yields various double compounds
differing in colour and crystallising power; but according to Chavastelon
and to Caro they are all devoid of explosive properties. Sometimes a
yellowish red precipitate is produced in solutions of copper salts
containing free acid, but the deposit is not copper acetylide, and is
more likely to be, at least in part, a copper phosphide--especially if
the gas is crude. Hence acid solutions or preparations of copper salts
may safely be used for the purification of acetylene, as is done in the
case of frankoline, mentioned in Chapter V. It is clear that the amount
of free acid in such a material is much more than sufficient to
neutralise all the ammonia which may accompany the crude acetylene into
the purifier until the material is exhausted in other respects; and
moreover, in the best practice, the gas would have been washed quite or
nearly free from ammonia before entering the purifier.
From a practical aspect the possible interaction of acetylene and
metallic copper has been investigated by Gerdes and by Grittner, whose
results, again, are somewhat contradictory. Gerdes exposed neat acetylene
and mixtures of acetylene with oil-gas and coal-gas to a pressure of nine
or ten atmospheres for ten months at ordinary summer and winter
temperatures in vessels made of copper and various alloys. Those metals
and alloys which resisted oxidation in air resisted the attack of the
gases, but the more corrodible substances were attacked superficially;
although in no instance could an explosive body be detected, nor could an
explosion be produced by heating or hammering. In further experiments the
acetylene contained ammonia and moisture and Gerdes found that where
corrosion took place it was due exclusively to the ammonia, no explosive
compounds being produced even then. Grittner investigated the question by
leading acetylene for months through pipes containing copper gauze. His
conclusions are that a copper acetylide is always produced if impure
acetylene is allowed to pass through neutral or ammoniacal solutions of
copper; that dry acetylene containing all its natural impurities except
ammonia acts to an equal extent on copper and its alloys, yielding the
explosive compound; that pure and dry gas does not act upon copper or its
alloys, although it is possible that an explosive compound may be
produced after a great length of time. Grittner has asserted that an
explosive compound may be produced when acetylene is brought into contact
with such alloys of copper as ordinary brass containing 64.66 per cent.
of copper, or red brass containing 74.46 per cent. of copper, 20.67 per
cent. of zinc, and 4.64 per cent. of tin; whereas none is obtained when
the metal is either "alpaca" containing 64.44 per cent. of copper, 18.79
per cent. of nickel, and 16.33 per cent. of zinc, or britannia metal
composed of 91.7 per cent. of copper and 8.3 per cent. of tin. Caro has
found that when pure dry acetylene is led for nine months over sheets or
filings of copper, brass containing 63.2 per cent. of copper, red brass
containing 73.8 per cent., so-called "alpaca-metal" containing 65.3 per
cent., and britannia metal containing 90.2 per cent. of copper, no action
whatever takes place at ordinary temperatures; if the gas is moist very
small quantities of copper acetylide are produced in six months, whatever
metal is tested, but the yield does not increase appreciably afterwards.
At high temperatures condensation occurs between acetylene and copper or
its alloys, but explosive bodies are not formed.
Grittner's statement that crude acetylene, with or without ammonia, acts
upon alloys of copper as well as upon copper itself, has thus been
corroborated by Caro; but experience renders it tolerably certain that
brass (and presumably gun-metal) is not appreciably attacked in practical
conditions. Gerdes' failure to obtain an explosive compound in any
circumstances may very possibly be explained by the entire absence of any
oxygen from his cylinders and gases, so that any copper carbide produced
remained unoxidised. Grittner's gas was derived, at least partially, from
a public acetylene supply, and is quite likely to have been contaminated
with air in sufficient quantity to oxidise the original copper compound,
and to convert it into the explosive modification.
For the foregoing reasons the use of unalloyed copper in the construction
of acetylene generators or in the subsidiary items of the plant, as well
as in burner fittings, is forbidden by statute or some quasi-legal
enactment in most countries, and in others the metal has been abandoned
for one of its alloys, or for iron or steel, as the case may be.
Grittner's experiments mentioned above, however, probably explain why
even alloys of copper are forbidden in Hungary. (_Cf._ Chapter IV.,
page 127.)
When acetylene is passed over finely divided copper or iron (obtained by
reduction of the oxide by hydrogen) heated to from 130° C. to 250° C.,
the gas is more or less completely decomposed, and various products,
among which hydrogen predominates, result. Ethane and ethylene are
undoubtedly formed, and certain homologues of them and of acetylene, as
well as benzene and a high molecular hydrocarbon (C_7H_6)_n termed
"cuprene," have been found by different investigators. Nearly the same
hydrocarbons, and others constituting a mixture approximating in
composition to some natural petroleums, are produced when acetylene is
passed over heated nickel (or certain other metals) obtained by the
reduction of the finely divided oxide. These observations are at present
of no technical importance, but are interesting scientifically because
they have led up to the promulgation of a new theory of the origin of
petroleum, which, however, has not yet found universal acceptance.
CHAPTER VII
MAINS AND SERVICE-PIPES--SUBSIDIARY APPARATUS
The process by which acetylene is produced, and the methods employed for
purifying it and rendering it fit for consumption in dwelling-rooms,
having been dealt with in the preceding pages, the present chapter will
be devoted to a brief account of those items in the plant which lie
between the purifier outlet and the actual burner, including the meter,
governor, and pressure gauge; the proper sizes of pipe for acetylene;
methods of laying it, joint-making, quality of fittings, &c.; while
finally a few words will be said about the precautions necessary when
bringing a new system of pipes into use for the first time.
THE METER.--A meter is required either to control the working of a
complete acetylene installation or to measure the volume of gas passing
through one particular pipe, as when a number of consumers are supplied
through separate services under agreement from a central supply plant.
The control which may be afforded by the inclusion of a meter in the
equipment of a domestic acetylene generating plant is valuable, but in
practice will seldom be exercised. The meter records check the yield of
gas from the carbide consumed in a simple and trustworthy manner, and
also serve to indicate when the material in the purifier is likely to be
approaching exhaustion. The meter may also be used experimentally to
check the soundness of the service-pipes or the consumption of a
particular burner or group of burners. Altogether it may be regarded as a
useful adjunct to a domestic lighting plant, provided full advantage is
taken of it. If, however, there is no intention to pay systematic
attention to the records of the meter, it is best to omit it from such an
installation, and so save its initial cost and the slight loss of
pressure which its use involves on the gas passing through it. A domestic
acetylene lighting plant can be managed quite satisfactorily without a
meter, and as a multiplication of parts is undesirable in an apparatus
which will usually be tended by someone not versed in technical
operations, it is on the whole better to omit the meter in such an
installation. Where the plant is supervised by a technical man, a meter
may advisedly be included in the equipment. Its proper position in the
train of apparatus is immediately after the purifier. A meter must not be
used for unpurified or imperfectly purified acetylene, because the
impurities attack the internal metallic parts and ultimately destroy
them. The supply of acetylene to various consumers from a central
generating station entails the fixing of a meter on each consumer's
service-pipe, so that the quantity consumed by each may be charged for
accordingly, just as in the case of public coal-gas supplies.
There are two types of gas-meter in common use, either of which may,
without essential alteration, be employed for measuring the volume of
acetylene passing through a pipe. It is unnecessary to refer here at
length to their internal mechanism, because their manufacture by other
than firms of professed meter-makers is out of the question, and the user
will be justified in accepting the mechanism as trustworthy and durable.
Meters can always be had stamped with the seal of a local authority or
other body having duly appointed inspectors under the Sales of Gas Act,
and the presence of such a stamp on a meter implies that it has been
officially examined and found to register quantities accurately, or not
varying beyond 2 per cent. in favour of the seller, or 3 per cent, in
favour of the consumer. [Footnote: It may be remarked that when a meter--
wet or dry--begins to register incorrectly by reason of old age or want
of adjustment, its error is very often in the direction that benefits the
customer, _i.e._, more gas passes through it than the dials record.]
Hence a "stamped" meter may be regarded for practical purposes as
affording a correct register of the quantities of gas passing through it.
Except that the use of unalloyed copper in any part of the meter where it
may come in contact with the gas must be wholly avoided, for the reason
that copper is inadmissible in acetylene apparatus (_see_ Chapter
VI.), the meters ordinarily employed for coal-gas serve quite well for
acetylene. Obviously, however, since so very much less acetylene than
coal-gas is consumed per burner, comparatively small meters only will be
required even for large installations of acetylene lighting. This fact is
now recognised by meter-makers, and meters of all suitable sizes can be
obtained. It is desirable, if an ordinary coal-gas meter is being bought
for use with acetylene, to have it subjected to a somewhat more rigorous
test for soundness than is customary before "stamping" but the makers
would readily be able to carry out this additional test.
The two types of gas-meter are known as "wet" and "dry." The case of the
wet meter is about hall-filled with water or other liquid, the level of
which has to be maintained nearly constant. Several ingenious devices are
in use for securing this constancy of level over a more or less extended
period, but the necessity for occasional inspection and adjustment of the
water-level, coupled with the stoppage of the passage of gas in the event
of the water becoming frozen, are serious objections to the employment of
the wet meter in many situations. The trouble of freezing may be avoided
by substituting for the simple water an aqueous solution of glycerin, or
mixture of glycerin with water, suitable strengths for which may be
deduced from the table relating to the use of glycerin in holder seals
given at the close of Chapter III. The dry meter, on the other hand, is
very convenient, because it is not obstructed by the effects of frost,
and because it acts for years without requiring attention. It is not
susceptible of adjustment for measuring with so high a degree of accuracy
as a good wet meter, but its indications are sufficiently correct to fall
well within the legalised deviations already mentioned. Such errors,
perhaps, are somewhat large for so costly and powerful a gas as
acetylene, and they would be better reduced; but it is not so very often
that a dry meter reaches its limit of inaccuracy. Whether wet or dry, the
meter should be fixed in a place where the temperature is tolerably
uniform, otherwise the volumes registered at different times will not
bear the same ratio to the mass of gas (or volume at normal temperature),
and the registrations will be misleading unless troublesome corrections
to compensate for changes of temperature are applied.
THE GOVERNOR, which can be dispensed with in most ordinary domestic
acetylene lighting installations provided with a good gasholder of the
rising-bell type, is designed to deliver the acetylene to a service-pipe
at a uniform pressure, identical with that under which the burners
develop their maximum illuminating efficiency. It must therefore both
cheek the pressure anterior to it whenever that is above the determined
limit to which it is set, and deliver to the efferent service-pipe
acetylene at a constant pressure whether all or any number of the burners
down to one only are in use. Moreover, when the pressure anterior to the
governor falls to or below the determined limit, the governor should
offer no resistance--entailing a loss of pressure to the passage of the
acetylene. These conditions, which a perfect governor should fulfil, are
not absolutely met by any simple apparatus at present in use, but so far
as practical utility is concerned service governors which are readily
obtainable are sufficiently good. They are broadly of two types, viz.,
those having a bell floating in a mercury seal, and those having a
diaphragm of gas-tight leather or similar material, either the bell or
the diaphragm being raised by the pressure of the gas. The action is
essentially the same in both cases: the bell or the diaphragm is so
weighted that when the pressure of the gas exceeds the predetermined
limit the diaphragm or bell is lifted, and, through an attached rod and
valve, brings about a partial closure of the orifice by which the gas
flows into the bell or the diaphragm chamber. The valve of the governor,
therefore, automatically throttles the gas-way more or less according to
the difference in pressure before and after the apparatus, until at any
moment the gas-way is just sufficient in area to pass the quantity of gas
which any indefinite number of burners require at their fixed working
pressure; passing it always at that fixed working pressure irrespective
of the number of burners, and maintaining it constant irrespective of the
amount of pressure anterior to the governor, or of any variations in that
anterior pressure. In most patterns of service governor weights may be
added when it is desired to increase the pressure of the effluent gas. It
is necessary, in ordering a governor for an acetylene-supply, to state
the maximum number of cubic feet per hour it will be required to pass,
and approximately the pressure at which it will be required to deliver
the gas to the service-pipe. This will usually be between 3 and 5 inches
(instead of about 1 inch in the case of coal-gas), and if the anterior
pressure is likely to exceed 10 inches, this fact should be stated also.
The mercury-seal governors are usually the more trustworthy and durable,
but they are more costly than those with leather diaphragms. The seal
should have twice or thrice the depth it usually has for coal-gas. The
governor should be placed where it is readily accessible to the man in
charge of the installation, but where it will not be interfered with by
irresponsible persons. In large installations, where a number of separate
buildings receive service-pipes from one long main, each service-pipe
should be provided with a governor.
GASHOLDER PRESSURE.--In drawing up the specification or scheme of an
acetylene installation, it is frequently necessary either to estimate the
pressure which a bell gasholder of given diameter and weight will throw,
or to determine what should be the weight of the bell of a gasholder of
given diameter when the gas is required to be delivered from it at a
particular pressure. The gasholder of an acetylene installation serves
not only to store the gas, but also to give the necessary pressure for
driving it through the posterior apparatus and distributing mains and
service-pipes. In coal-gas works this office is generally given over
wholly or in part to a special machine, known as the exhauster, but this
machine could not be advantageously employed for pumping acetylene unless
the installation were of very great magnitude. Since, therefore,
acetylene is in practice always forced through mains and service-pipes in
virtue of the pressure imparted to it by the gasholder and since, for
reasons already given, only the rising-bell type of gasholder can be
regarded as satisfactory, it becomes important to know the relations
which subsist between the dimensions and weight of a gasholder bell and
the pressure which it "throws" or imparts to the contained gas.
The bell must obviously be a vessel of considerable weight if it is to
withstand reasonable wear and tear, and this weight will give a certain
hydrostatic pressure to the contained gas. If the weight of the bell is
known, the pressure which it will give can be calculated according to the
general law of hydrostatics, that the weight of the water displaced must
be equal to the weight of the floating body. Supposing for the moment
that there are no other elements which will have to enter into the
calculation, then if _d_ is the diameter in inches of the
(cylindrical) bell, the surface of the water displaced will have an area
of _d^2_ x 0.7854. If the level of the water is depressed _p_
inches, then the water displaced amounts to _p_(_d^2_ x 0.7854)
cubic inches, and its weight will be (at 62° F.):
(0.7854_pd^2_ x 0.03604) = 0.028302_pd^2_ lb.
Consequently a bell which is _d_ inches in diameter, and gives a
pressure of _p_ inches of water, will weigh 0.028302_pd^2_ lb.
Or, if W = the weight of the bell in lb., the pressure thrown by it will
be W/0.028302_d^2_ or 35.333W/_d^2_. This is the fundamental
formula, which is sometimes given as _p_ = 550W/_d^2_, in which
W = the weight of the bell in tons, and _d_ the diameter in feet.
This value of _p_, however, is actually higher than the holder would
give in practice. Reductions have to be made for two influences, viz.,
the lifting power of the contained gas, which is lighter than air, and
the diminution in the effective weight of so much of the bell as is
immersed in water. The effect of these influences was studied by Pole,
who in 1839 drew up some rules for calculating the pressure thrown by a
gasholder of given dimensions and weight. These rules form the basis of
the formula which is commonly used in the coal-gas industry, and they may
be applied, _mutatis mutandis_, to acetylene holders. The
corrections for both the influences mentioned vary with the height at
which the top of the gasholder bell stands above the level of the water
in the tank. Dealing first with the correction for the lifting power of
the gas, this, according to Pole, is a deduction of _h_(1 -
_d_)/828 where _d_ is the specific gravity of the gas and
_h_ the height (in inches) of the top of the gasholder above the
water level. This strictly applies only to a flat-topped bell, and hence
if the bell has a crown with a rise equal to about 1/20 of the diameter
of the bell, the value of _h_ here must be taken as equal to the
height of the top of the sides above the water-level (= _h'_), plus
the height of a cylinder having the same capacity as the crown, and the
same diameter as the bell, that is to say, _h_=_h'_ +
_d_/40 where _d_ = the diameter of the bell. The specific
gravity of commercially made acetylene being constantly very nearly 0.91,
the deduction for the lifting power of the gas becomes, for acetylene
gasholders, 0.0001086_h_ + 0.0000027_d_, where _h_ is the
height in inches of the top of the sides of the bell above the water-
level, and _d_ is the diameter of the bell. Obviously this is a
negligible quantity, and hence this correction may be disregarded for all
acetylene gasholders, whereas it is of some importance with coal-gas and
other gases of lower specific gravity. It is therefore wrong to apply to
acetylene gasholders formulæ in which a correction for the lifting power
of the gas has been included when such correction is based on the average
specific gravity of coal-gas, as is the case with many abbreviated
gasholder pressure formulæ.
The correction for the immersion of the sides of the bell is of greater
magnitude, and has an important practical significance. Let H be the
total height in inches of the side of the gasholder, _h_ the height
in inches of the top of the sides of the gasholder above the water-level,
and _w_ = the weight of the sides of the gasholder in lb.; then, for
any position of the bell, the proportion of the total height of the sides
immersed (H - _h_)/H, and the buoyancy is (H - _h_)/H x
_w_/S + pi/4_d^2_, in which S = the specific gravity of the
material of which the bell is made. Assuming the material to be mild
steel or wrought iron, having a specific gravity of 7.78, the buoyancy is
(4_w_(H - _h_)) / (7.78Hpi_d^2_) lb. per square inch
(_d_ being inches and _w_ lb.), which is equivalent to
(4_w_(H - _h_)) / (0.03604 x 7.78Hpi_d^2_) =
(4.54_w_(H - _h_)) / (H_d^2_) inches of water. Hence the
complete formula for acetylene gasholders is:
_p_ = 35.333W / _d^2_ - 4.54_w_(H - _h_) /
H_d^2_
It follows that _p_ varies with the position of the bell, that is to
say, with the extent to which it is filled with gas. It will be well to
consider how great this variation is in the case of a typical acetylene
holder, as, if the variation should be considerable, provision must be
made, by the employment of a governor on the outlet main or otherwise, to
prevent its effects being felt at the burners.
Now, according to the rules of the "Acetylen-Verein" (_cf._ Chapter
IV.), the bells of holders above 53 cubic feet in capacity should have
sides 1.5 mm. thick, and crowns 0.5 mm. thicker. Hence for a holder from
150 to 160 cubic feet capacity, supposing it to be 4 feet in diameter and
about 12 feet high, the weight of the sides (say of steel No. 16 S.W.G. =
2.66 lb. per square foot) will be not less than 12 x 4pi x 2.66 = 401 lb.
The weight of the crown (say of steel No. 14 S.W.G. = 3.33 lb. per square
foot) will be not less than about 12.7 x 3.33 = about 42 lb. Hence the
total weight of holder = 401 + 42 = 443 lb. Then if the holder is full,
_h_ is very nearly equal to H, and _p_ = (35.333 x 443) / 48^2
= 6.79 inches. If the holder stands only 1 foot above the water-level,
then _p_ = 6.79 - (4.54 x 401 (144 - 12)) / (144 x 48^2) = 6.79 -
0.72 = 6.07 inches. The same result can be arrived at without the direct
use of the second member of the formula:
For instance, the weight of the sides immersed is 11 x 4pi x 2.66 = 368
lb., and taking the specific gravity of mild steel at 7.78, the weight of
water displaced is 368 / 7.78 = 47.3 lb. Hence the total effective weight
of the bell is 443 - 47.3 = 395.7 lb., and _p_ = (35.333 x 395.7) /
48^2 = 6.07 inches. [Footnote: If the sealing liquid in the gasholder
tank is other than simple water, the correction for the immersion of the
sides of the bell requires modification, because the weight of liquid
displaced will be _s'_ times as great as when the liquid is water,
if _s'_ is the specific gravity of the sealing liquid. For instance,
in the example given, if the sealing liquid were a 16 per cent. solution
of calcium chloride, specific gravity 1.14 (_vide_ p. 93) instead of
water, the weight of liquid displaced would be 1.14 (368 / 7.78) = 53.9
lb., and the total effective weight of the bell = 443 - 53.9 = 389.1 lb.
Therefore _p_ becomes = (35.333 x 389.1) / 48^2 = 5.97 inches,
instead of 6.07 inches.]
The value of _p_ for any position of the bell can thus be arrived
at, and if the difference between its values for the highest and for the
lowest positions of the bell exceeds 0.25 inch, [Footnote: This figure is
given as an example merely. The maximum variation in pressure must be
less than one capable of sensibly affecting the silence, steadiness, and
economy of the burners and stoves, &c., connected with the installation.]
a governor should be inserted in the main leading from the holder to the
burners, or one of the more or less complicated devices for equalising
the pressure thrown by a holder as it rises and falls should be added to
the holder. Several such devices were at one time used in connexion with
coal-gas holders, and it is unnecessary to describe them in this work,
especially as the governor is practically the better means of securing
uniform pressure at the burners.
It is frequently necessary to add weight to the bell of a small gasholder
in order to obtain a sufficiently high pressure for the distribution of
acetylene. It is best, having regard to the steadiness of the bell, that
any necessary weighting of it should be done near its bottom rim, which
moreover is usually stiffened by riveting to it a flange or curb of
heavier gauge metal. This flange may obviously be made sufficiently stout
to give the requisite additional weighting. As the flange is constantly
immersed, its weight must not be added to that of the sides in computing
the value of _w_ for making the correction of pressure in respect of
the immersion of the bell. Its effective weight in giving pressure to the
contained gas is its actual weight less its actual weight divided by its
specific gravity (say 7.2 for cast iron, 7.78 for wrought iron or mild
steel, or 11.4 for lead). Thus if _x_ lb. of steel is added to the
rim its weight in computing the value of W in the formula _p_ =
35.333W / _d_^2 should be taken as x - x / 7.78. If the actual
weight is 7.78 lb., the weight taken for computing W is 7.78 - 1 = 6.78
lb.
THE PRESSURE GAUGE.--The measurement of gas pressure is effected by means
of a simple instrument known as a pressure gauge. It comprises a glass U-
tube filled to about half its height with water. The vacant upper half of
one limb is put in communication with the gas-supply of which the
pressure is to be determined, while the other limb remains open to the
atmosphere. The difference then observed, when the U-tube is held
vertical, between the levels of the water in the two limbs of the tube
indicates the difference between the pressure of the gas-supply and the
atmospheric pressure. It is this _difference_ that is meant when the
_pressure_ of a gas in a pipe or piece of apparatus is spoken of,
and it must of necessity in the case of a gas-supply have a positive
value. That is to say, the "pressure" of gas in a service-pipe expresses
really by how much the pressure in the pipe _exceeds_ the
atmospheric pressure. (Pressures less than the atmospheric pressure will
not occur in connexion with an acetylene installation, unless the
gasholder is intentionally manipulated to that end.) Gas pressures are
expressed in terms of inches head or pressure of water, fractions of an
inch being given in decimals or "tenths" of an inch. The expression
"tenths" is often used alone, thus a pressure of "six-tenths" means a
pressure equivalent to 0.6 inch head of water.
The pressure gauge is for convenience provided with an attached scale on
which the pressures may be directly read, and with a connexion by which
the one limb is attached to the service-pipe or cock where the pressure
is to be observed. A portable gauge of this description is very useful,
as it can be attached by means of a short piece of flexible tubing to any
tap or burner. Several authorities, including the British Acetylene
Association, have recommended that pressure gauges should not be directly
attached to generators, because of the danger that the glass might be
fractured by a blow or by a sudden access of heat. Such breakage would be
followed by an escape of gas, and might lead to an accident. Fixed
pressure gauges, however, connected with every item of a plant are
extremely useful, and should be employed in all large installations, as
they afford great aid in observing and controlling the working, and in
locating the exact position of any block. All danger attending their use
can be obviated by having a stopcock between the gauge inlet and the
portion of the plant to which it is attached; the said stopcock being
kept closed except when it is momentarily opened to allow of a reading
being taken. As an additional precaution against its being left open, the
stopcock may be provided with a weight or spring which automatically
closes the gas-way directly the observer's hand is removed from the tap.
In the best practice all the gauges will be collected together on a board
fastened in some convenient spot on the wall of the generator-house, each
gauge being connected with its respective item of the plant by means of a
permanent metallic tube. The gauges must be filled with pure water, or
with a liquid which does not differ appreciably in specific gravity from
pure water, or the readings will be incorrect. Greater legibility will be
obtained by staining the water with a few drops of caramel solution, or
of indigo sulphate (indigo carmine); or, in the absence of these dyes,
with a drop or two of common blue-black writing ink. If they are not
erected in perfectly frost-free situations, the gauges may be filled with
a mixture of glycerin and pure alcohol (not methylated spirit), with or
without a certain proportion of water, which will not freeze at any
winter temperature. The necessary mixture, which must have a density of
exactly 1.00, could be procured from any pharmacist.
It is the pressure as indicated by the pressure gauge which is referred
to in this book in all cases where the term "pressure of the gas" or the
like is used. The quantity of acetylene which will flow in a given time
from the open end of a pipe is a function of this pressure, while the
quantity of acetylene escaping through a tiny hole or crack or a burner
orifice also depends on this total pressure, though the ratio in this
instance is not a simple one, owing to the varying influence of friction
between the issuing gas and the sides of the orifice. Where, however,
acetylene or other gas is flowing through pipes or apparatus there is a
loss of energy, indicated by a falling off in the pressure due to
friction, or to the performance of work, such as actuating a gas-meter.
The extent of this loss of energy in a given length of pipe or in a meter
is measured by the difference between the pressures of the gas at the two
ends of the pipe or at the inlet and outlet of the meter. This difference
is the "loss" or "fall" of pressure, due to friction or work performed,
and is spoken of as the "actuating" pressure in regard to the passage of
gas through the stretch of pipe or meter. It is a measure of the energy
absorbed in actuating the meter or in overcoming the friction. (Cf.
footnote, Chapter II., page 54.)
DIMENSIONS OF MAINS.--The diameter of the mains and service-pipes for an
acetylene installation must be such that the main or pipe will convey the
maximum quantity of the gas likely to be required to feed all the burners
properly which are connected to it, without an excessive actuating
pressure being called for to drive the gas through the main or pipe. The
flow of all gases through pipes is of course governed by the same general
principles; and it is only necessary in applying these principles to a
particular gas, such as acetylene, to know certain physical properties of
the gas and to make due allowance for their influence. The general
principles which govern the flow of a gas through pipes have been
exhaustively studied on account of their importance in relation to the
distribution of coal-gas and the supply of air for the ventilation of
places where natural circulation is absent or deficient. It will be
convenient to give a very brief reference to the way in which these
principles have been ascertained and applied, and then to proceed to the
particular case of the distribution of acetylene through mains and
service-pipes.
The subject of "The Motion of Fluids in Pipes" was treated in a lucid and
comprehensive manner in an Essay by W. Pole in the _Journal of Gas
Lighting_ during 1852, and his conclusions have been generally adopted
by gas engineers ever since. He recapitulated the more important points
of this essay in the course of some lectures delivered in 1872, and one
or other of these two sources should be consulted for further
information. Briefly, W. Pole treated the question in the following
manner:
The practical question in gas distribution is, what quantity of gas will
a given actuating pressure cause to flow along a pipe of given length and
given diameter? The solution of this question allows of the diameters of
pipes being arranged so that they will carry a required quantity of gas a
given distance under the actuating pressure that is most convenient or
appropriate. There are five quantities to be dealt with, viz.:
(1) The length of pipe = _l_ feet.
(2) The internal diameter of the pipe = _d_ inches.
(3) The actuating pressure = _h_ inches of head of water. (4) The
specific gravity or density of the gas = _d_ times that of air.
(5) The quantity of gas passing through the pipe--Q cubic feet per hour.
This quantity is the product of the mean velocity of the gas in the pipe
and the area of the pipe.
The only work done in maintaining the flow of gas along a pipe is that
required to overcome the friction of the gas on the walls of the pipe,
or, rather, the consequential friction of the gas on itself, and the laws
which regulate such friction have not been very exhaustively
investigated. Pole pointed out, however, that the existing knowledge on
the point at the time he wrote would serve for the purpose of determining
the proper sizes of gas-mains. He stated that the friction (1) is
proportional to the area of rubbing surface (viz., pi_ld_); (2)
varies with the velocity, in some ratio greater than the first power, but
usually taken as the square; and (3) is assumed to be proportional to the
specific gravity of the fluid (viz., _s_).
Thus the force (_f_) necessary to maintain the motion of the gas in
the pipe is seen to vary (1) as pi_ld_, of which pi is a constant;
(2) as _v^2_, where _v_ = the velocity in feet per hour; and
(3) as _s_. Hence, combining these and deleting the constant pi, it
appears that
_f_ varies as _ldsv^2_.
Now the actuating force is equal to _f_, and is represented by the
difference of pressure at the two ends of the pipe, _i.e._, the
initial pressure, viz., that at the place whence gas is distributed or
issues from a larger pipe will be greater by the quantity _f_ than
the terminal pressure, viz., that at the far end of the pipe where it
branches or narrows to a pipe or pipes of smaller size, or terminates in
a burner. The terminal pressure in the case of service-pipes must be
settled, as mentioned in Chapter II., broadly according to the pressure
at which the burners in use work best, and this is very different in the
case of flat-flame burners for coal-gas and burners for acetylene. The
most suitable pressure for acetylene burners will be referred to later,
but may be taken as equal to p_0 inches head of water. Then, calling the
initial pressure (_i.e._, at the inlet head of service-pipe) p_1, it
follows that p_1 - p_0 = _f_. Now the cross-section of the pipe has
an area (pi/4)_d^2_, and if _h_ represents the difference of
pressure between the two ends of the pipe per square inch of its area, it
follows that _f_ = _h(pi/4)d^2_. But since _f_ has been
found above to vary as _ldsv^2_ , it is evident that
_h(pi/4)d^2_ varies as _ldsv^2_.
Hence
_v^2_ varies as _hd/ls_,
and putting in some constant M, the value of which must be determined by
experiment, this becomes
_v^2_ = M_hd/ls_.
The value of M deduced from experiments on the friction of coal-gas in
pipes was inserted in this equation, and then taking Q = pi/4_d^2v_,
it was found that for coal-gas Q = 780(_hd/sl_)^(1/2)
This formula, in its usual form, is
Q = 1350_d^2_(_hd/sl_)^(1/2)
in which _l_ = the length of main in yards instead of in feet. This
is known as Pole's formula, and has been generally used for determining
the sizes of mains for the supply of coal-gas.
For the following reasons, among others, it becomes prudent to revise
Pole's formula before employing it for calculations relating to
acetylene. First, the friction of the two gases due to the sides of a
pipe is very different, the coefficient for coal-gas being 0.003, whereas
that of acetylene, according to Ortloff, is 0.0001319. Secondly, the
mains and service-pipes required for acetylene are smaller, _cateria
paribus_, than those needed for coal-gas. Thirdly, the observed
specific gravity of acetylene is 0.91, that of air being unity, whereas
the density of coal-gas is about 0.40; and therefore, in the absence of
direct information, it would be better to base calculations respecting
acetylene on data relating to the flow of air in pipes rather than upon
such as are applicable to coal-gas. Bernat has endeavoured to take these
and similar considerations into account, and has given the following
formula for determining the sizes of pipes required for the distribution
of acetylene:
Q = 0.001253_d^2_(_hd/sl_)^(1/2)
in which the symbols refer to the same quantities as before, but the
constant is calculated on the basis of Q being stated in cubic metres, l
in metres, and d and h in millimetres. It will be seen that the equation
has precisely the same shape as Pole's formula for coal-gas, but that the
constant is different. The difference is not only due to one formula
referring to quantities stated on the metric and the other to the same
quantities stated on the English system of measures, but depends partly
on allowance having been made for the different physical properties of
the two gases. Thus Bernat's formula, when merely transposed from the
metric system of measures to the English (_i.e._, Q being cubic feet
per hour, _l_ feet, and _d_ and _h_ inches) becomes
Q = 1313.5_d^2_(_hd/sl_)^(1/2)
or, more simply,
Q = 1313.4(_hd^5/sl_)^(1/2)
But since the density of commercially-made acetylene is practically the
same in all cases, and not variable as is the density of coal-gas, its
value, viz., 0.91, may be brought into the constant, and the formula then
becomes
Q = 1376.9(_hd^5/l_)^(1/2)
Bernat's formula was for some time generally accepted as the most
trustworthy for pipes supplying acetylene, and the last equation gives it
in its simplest form, though a convenient transposition is
d = 0.05552(Q^2_l/h_)^(1/5)
Bernat's formula, however, has now been generally superseded by one given
by Morel, which has been found to be more in accordance with the actual
results observed in the practical distribution of acetylene. Morel's
formula is
D = 1.155(Q^2_l/h_)^(1/5)
in which D = the diameter of the pipe in centimetres, Q = the number of
cubic metres of gas passing per hour, _l_ = the length of pipe in
metres, and _h_ = the loss of pressure between the two ends of the
pipe in millimetres. On converting tins formula into terms of the English
system of measures (_i.e._, _l_ feet, Q cubic feet, and
_h_ and _d_ inches) it becomes
(i) d = 0.045122(Q^2_l/h_)^(1/5)
At first sight this formula does not appear to differ greatly from
Bernat's, the only change being that the constant is 0.045122 instead of
0.05552, but the effect of this change is very great--for instance, other
factors remaining unaltered, the value of Q by Morel's formula will be
1.68 times as much as by Bernat's formula. Transformations of Morel's
formula which may sometimes be more convenient to apply than (i) are:
(ii) Q = 2312.2(_hd^5/l_)^(1/2)
(iii) _h_ = 0.000000187011(Q^2_l/d^5_)
and (iv) _l_ = 5,346,340(_hd^5_/Q^2)
In order to avoid as far as possible expenditure of time and labour in
repeating calculations, tables have been drawn up by the authors from
Morel's formulæ which will serve to give the requisite information as to
the proper sizes of pipes to be used in those cases which are likely to
be met with in ordinary practice. These tables are given at the end of
this chapter.
When dealing with coal-gas, it is highly important to bear in mind that
the ordinary distributing formulæ apply directly only when the pipe or
main is horizontal, and that a rise in the pipe will be attended by an
increase of pressure at the upper end. But as the increase is greater the
lower the density of the gas, the disturbing influence of a moderate rise
in a pipe is comparatively small in the case of a gas of so high a
density as acetylene. Hence in most instances it will be unnecessary to
make any allowance for increase of pressure due to change of level. Where
the change is very great, however, allowance may advisedly be made on the
following basis: The pressure of acetylene in pipes increases by about
one-tenth of an inch (head of water) for every 75 feet rise in the pipe.
Hence where acetylene is supplied from a gasholder on the ground-level to
all floors of a house 75 feet high, a burner at the top of the house will
ordinarily receive its supply at a pressure greater by one-tenth of an
inch than a burner in the basement. Such a difference, with the
relatively high pressures used in acetylene supplies, is of no practical
moment. In the case of an acetylene-supply from a central station to
different parts of a mountainous district, the variations of pressure
with level should be remembered.
The distributing formulæ also assume that the pipe is virtually straight;
bends and angles introduce disturbing influences. If the bend is sharp,
or if there is a right-angle, an allowance should be made if it is
desired to put in pipes of the smallest permissible dimensions. In the
case of the most usual sizes of pipes employed for acetylene mains or
services, it will suffice to reckon that each round or square elbow is
equivalent in the resistance it offers to the flow of gas to a length of
5 feet of pipe of the same diameter. Hence if 5 feet is added to the
actual length of pipe to be laid for every bond or elbow which will occur
in it, and the figure so obtained is taken as the value of _l_ in
formulæ (i), (ii), or (iii), the values then found for Q, _d_, or
_h_ will be trustworthy for all practical purposes.
It may now be useful to give an example of the manner of using the
foregoing formulæ when the tables of sizes of pipes are not available.
Let it be supposed that an institution is being equipped for acetylene
lighting; that 50 burners consuming 0.70 cubic foot, and 50 consuming
1.00 cubic foot of acetylene per hour may be required in use
simultaneously; that a pressure of at least 2-1/2 inches is required at
all the burners; that for sufficient reasons it is considered undesirable
to use a higher distributing pressure than 4 inches at the gasholder,
outlet of the purifiers, or initial governor (whichever comes last in the
train of apparatus); that the gasholder is located 100 feet from the main
building of the institution, and that the trunk supply-pipe through the
latter must be 250 feet in length, and the supplies to the burners,
either singly or in groups, be taken from this trunk pipe through short
lengths of tubing of ample size. What should be the diameter of the trunk
pipe, in which it will be assumed that ten bonds or elbows are necessary?
In the first instance, it is convenient to suppose that the trunk pipe
may be of uniform diameter throughout. Then the value of _l_ will be
100 (from gasholder to main building) + 250 (within the building) + 50
(equivalent of 10 elbows) = 400. The maximum value of Q will be (50 x
0.7) + (50 x 1.0) = 85; and the value of _h_ will be 1 - 2.5 - 1.5.
Then using formula (i), we have:
d = 0.045122((85^2 x 400)/1.5)^(1/5) = 0.045122(1,926,667)^(1/5)
= 0.045122 x 18.0713 = 0.8154.
The formula, therefore, shows that the pipe should have an internal
diameter of not less than 0.8154 inch, and consequently 1 inch (the next
size above 0.8154 inch) barrel should be used. If the initial pressure
(i.e., at outlet of purifiers) could be conveniently increased from 4 to
4.8 inches, 3/4 inch barrel could be employed for the service-pipe. But
if connexions for burners were made immediately the pipe entered the
building, these burners would then be supplied at a pressure of 4.2
inches, while those on the extremity of the pipe would, when all burners
were in use, be supplied at a pressure of only 2.5 inches. Such a great
difference of pressure is not permissible at the several burners, as no
type of burner retains its proper efficiency over more than a very
limited range of pressure. It is highly desirable in the case of the
ordinary Naphey type of burner that all the burners in a house should be
supplied at pressures which do not differ by more than half an inch;
hence the pipes should, wherever practicable, be of such a size that they
will pass the maximum quantity of gas required for all the burners which
will ever be in use simultaneously, when the pressure at the first burner
connected to the pipe after it enters the house is not more than half an
inch above the pressure at the burner furthermost removed from the first
one, all the burner-taps being turned on at the time the pressures are
observed. If the acetylene generating plant is not many yards from the
building to be supplied, it is a safe rule to calculate the size of pipes
required on the basis of a fall of pressure of only half an inch from the
outlet of the purifiers or initial governor to the farthermost burner.
The extra cost of the larger size of pipe which the application of this
rule may entail will be very slight in all ordinary house installations.
VELOCITY OF FLOW IN PIPES.--For various purposes, it is often desirable
to know the mean speed at which acetylene, or any other gas, is passing
through a pipe. If the diameter of the pipe is _d_ inches, its
cross-sectional area is _d^2_ x 0.7854 square inches; and since
there are 1728 cubic inches in 1 cubic foot, that quantity of gas will
occupy in a pipe whose diameter is _d_ inches a length of
1728/(_d^2_ x 0.7854) linear inches or 183/_d^2_^ linear feet.
If the gas is in motion, and the pipe is delivering Q cubic feet per
hour, since there are 3600 seconds of time in one hour, the mean speed of
the gas becomes
183/_d^2_ x Q/3600 = Q/(19 x 7_d^2_) linear feet per second.
This value is interesting in several ways. For instance, taking a rough
average of Le Chatelier's results, the highest speed at which the
explosive wave proceeds in a mixture of acetylene and air is 7 metres or
22 feet per second. Now, even if a pipe is filled with an acetylene-air
mixture of utmost explosibility, an explosion cannot travel backwards
from B to A in that pipe, if the gas is moving from A to B at a speed of
over 22 feet per second. Hence it may be said that no explosion can occur
in a pipe provided
Q/(19.7_d^2_) = 22 or more;
_i.e._, Q/_d^2_=433.4
In plain language, if the number of cubic feet passing through the pipe
per hour divided by the square of the diameter of the pipe is at least
433.4, no explosion can take place within that pipe, even if the gas is
highly explosive and a light is applied to its exit.
In Chapter VI. are given the explosive limits of acetylene-air mixtures
as influenced by the diameter of the tube containing them. If we
possessed a similar table showing the speed of the explosive wave in
mixtures of known composition, the foregoing formulæ would enable us to
calculate the minimum speed which would insure absence of explosibility
in a supply-pipe of any given diameter throughout its length, or at its
narrowest part. It would not, however, be possible simply by increasing
the forward speed of an explosive mixture of acetylene and air to a point
exceeding that of its explosion velocity to prevent all danger of firing
back in an atmospheric burner tube. A much higher pressure than is
usually employed in gas-burners, other than blowpipes, would be needed to
confer a sufficient degree of velocity upon the gas, a pressure which
would probably fracture any incandescent mantle placed in the flame.
SERVICE-PIPES AND MAINS.--The pipes used for the distribution of
acetylene must be sound in themselves, and their joints perfectly tight.
Higher pressures generally prevail in acetylene service-pipes within a
house than in coal-gas service-pipes, while slight leaks are more
offensive and entail a greater waste of resources. Therefore it is
uneconomical, as well as otherwise objectionable, to employ service-pipes
or fittings for acetylene which are in the least degree unsound.
Unfortunately ordinary gas-barrel is none too sound, nor well-threaded,
and the taps and joints of ordinary gas-fittings are commonly leaky.
Hence something better should invariably be used for acetylene. What is
known as "water" barrel, which is one gauge heavier than gas-barrel of
the same size, may be adopted for the service-pipes, but it is better to
incur a slight extra initial expense and to use "steam" barrel, which is
of still heavier gauge and is sounder than either gas or water-pipe. All
elbows, tees, &c., should be of the same quality. The fitters' work in
making the joints should be done with the utmost care, and the sloppy
work often passed in the case of coal-gas services must on no account be
allowed. It is no exaggeration to say that the success of an acetylene
installation, from the consumer's point of view, will largely, if not
principally, depend on the tightness of the pipes in his house. The
statement has been made that the "paint" used by gas-fitters,
_i.e._, the mixture of red and white lead ground in "linseed" oil,
is not suitable for employment with acetylene, and it has been proposed
to adopt a similar material in which the vehicle is castor-oil. No good
reason has been given for the preference for castor-oil, and the troubles
which have arisen after using ordinary paint may be explained partly on
the very probable assumption that the oil was not genuine linseed, and so
did not dry, and partly on the fact that almost entire reliance was
placed on the paint for keeping the joint sound. Joints for acetylene,
like those for steam and high-pressure water, must be made tight by using
well-threaded fittings, so as to secure metallic contact between pipe and
socket, &c.; the paint or spun-yarn is only an additional safeguard. In
making a faced joint, washers of (say, 7 lb) lead, or coils of lead-wire
arc extremely convenient and quite trustworthy; the packing can be used
repeatedly.
LEAKAGE.--Broadly speaking, it may be said that the commercial success of
any village acetylene-supply--if not that of all large installations--
depends upon the leakage being kept within moderate limits. It follows
from what was stated in Chapter VI. about the diffusion of acetylene,
that from pipes of equal porosity acetylene and coal-gas will escape at
equal rates when the effective pressure in the pipe containing acetylene
is double that in the pipe containing coal-gas. The loss of coal-gas by
leakage is seldom less than 5 per cent. of the volume passed into the
main at the works; and provided a village main delivering acetylene is
not unduly long in proportion to the consumption of gas--or, in other
words, provided the district through which an acetylene distributing main
passes is not too sparsely populated--the loss of acetylene should not
exceed the same figure. Caro holds that the loss of gas by leakage from a
village installation should be quoted in absolute figures and not as a
percentage of the total make as indicated by the works meter, because
that total make varies so largely at different periods of the year, while
the factors which determine the magnitude of the leakage are always
identical; and therefore whereas the actual loss of gas remains the same,
it is represented to be more serious in the summer than in the winter.
Such argument is perfectly sound, but the method of returning leakage as
a percentage of the make has been employed in the coal-gas industry for
many years, and as it does not appear to have led to any misunderstanding
or inconvenience, there is no particular reason for departing from the
usual practice in the case of acetylene where the conditions as to
uniform leakage and irregular make are strictly analogous.
Caro has stated that a loss of 15 to 20 litres per kilometre per hour
(_i.e._, of 0.85 to 1.14 cubic feet per mile per hour) from an
acetylene distributing main is good practice; but it should be noted that
much lower figures have been obtained when conditions are favourable and
when due attention has been devoted to the fitters' work. In one of the
German village acetylene installations where the matter has been
carefully investigated (Döse, near Cuxhaven), leakage originally occurred
at the rate of 7.3 litres per kilometre per hour in a main 8.5
kilometres, or 5.3 miles, long and 4 to 2 inches in diameter; but it was
reduced to 5.2 litres, and then to 3.12 litres by tightening the plugs of
the street lantern and other gas cocks. In British units, these figures
are 0.415, 0.295, and 0.177 cubic foot per mile per hour. By calculation,
the volume of acetylene generated in this village would appear to have
been about 23,000 cubic feet per mile of main per year, and therefore it
may be said that the proportion of gas lost was reduced by attending to
the cocks from 15.7 per cent, to 11.3 per cent, and then to 6.8 per cent.
At another village where the main was 2.5 kilometres long, tests
extending over two months, when the public lamps were not in use, showed
the leakage to be 4.4 litres per kilometre per hour, _i.e._, 1.25
cubic foot per mile per hour, when the annual make was roughly 46,000
cubic feet per mile of main. Here, the loss, calculated from the direct
readings of the works motor, was 4.65 per cent.
When all the fittings, burners excepted, have been connected, the whole
system of pipes must be tested by putting it under a gas (or air)
pressure of 9 or 12 inches of water, and observing on an attached
pressure gauge whether any fall in pressure occurs within fifteen minutes
after the main inlet tap has been shut. The pressure required for this
purpose can be obtained by temporarily weighting the holder, or by the
employment of a pump. If the gauge shows a fall of pressure of one
quarter of an inch or more in these circumstances, the pipes must be
examined until the leak is located. In the presence of a meter, the
installation can conveniently be tested for soundness by throwing into
it, through the meter, a pressure of 12 inches or so of water from the
weighted holder, then leaving the inlet cock open, and observing whether
the index hand on the lowest dial remains perfectly stationary for a
quarter of an hour--movement of the linger again indicating a leak. The
search for leaks must never be made with a light; if the pipes are full
of air this is useless, if full of gas, criminal in its stupidity. While
the whole installation is still under a pressure of 12 inches thrown from
the loaded holder, whether it contains air or gas, first all the likely
spots (joints, &c.), then the entire length of pipe is carefully brushed
over with strong soapy water, which will produce a conspicuous "soap-
bubble" wherever the smallest flaw occurs. The tightness of a system of
pipes put under pressure from a loaded holder cannot be ascertained
safely by observing the height of the bell, and noting if it falls on
standing. Even if there is no issue of gas from the holder, the position
of the bell will alter with every variation in temperature of the stored
gas or surrounding air, and with every movement of the barometer, rising
as the temperature rises and as the barometer falls, and _vice
versâ_, while, unless the water in the seal is saturated with
whatever gas the holder contains, the bell will steadily drop a little an
part of its contents are lost by dissolution in the liquid.
PIPES AND FITTINGS.--As a general rule it is unadvisable to use lead or
composition pipe for permanent acetylene connexions. If exposed, it is
liable to be damaged, and perhaps penetrated by a blow, and if set in the
wall and covered with paper or panel it is liable to be pierced if nails
or tacks should at any time be driven into the wall. There is also an
increased risk in case of fire, owing to its ready fusibility. If used at
all--and it has obvious advantages--lead or composition piping should be
laid on the surface of the walls, &c., and protected from blows, &c., by
a light wooden casing, outwardly resembling the wooden coverings for
electric lighting wires. It has been a common practice, in laying the
underground mains required for supplying the villages which are lighted
by means of acetylene from a central works in different parts of France,
to employ lead pipes. The plan is economical, but in view of the danger
that the main might be flattened by the weight of heavy traction-engines
passing over the roads, or that it might settle into local dips from the
same cause or from the action of subterranean water, in which dips water
would be constantly condensing in cold weather, the use of lead for this
purpose cannot be recommended. Steam-barrel would be preferable to cast
pipe, because permanently sound joints are easier to make in the former,
and because it is not so brittle.
The fittings used for acetylene must have perfectly sound joints and
taps, for the same reasons that the service-pipes must be quite sound.
Common gas-fittings will not do, the joints, taps, ball-sockets, &c., are
not accurately enough ground to prevent leakage. They may in many cases
be improved by regrinding, but often the plug and barrel are so shallow
that it is almost impossible to ensure soundness. It is therefore better
to procure fittings having good taps and joints in the first instance;
the barrels should be long, fairly wide, and there should be no sensible
"play" between plug and barrel when adjusted so that the plug turns
easily when lightly lubricated. Fittings are now being specially made for
acetylene, which is a step in the right direction, because, in addition
to superior taps and joints being essential, smaller bore piping and
smaller through-ways to the taps than are required for coal-gas serve for
acetylene. It is perhaps advisable to add that wherever a rigid bracket
or fitting will answer as well as a jointed one, the latter should on no
account be used; also water-slide pendants should never be employed, as
they are fruitful of accidents, and their apparent advantages are for the
most part illusory. Ball-sockets also should be avoided if possible; if
it is absolutely necessary to have a fitting with a ball-socket, the
latter should have a sleeve made of a short length of sound rubber-tubing
of a size to give a close fit, slipped over so as to join the ball
portion to the socket portion. This sleeve should be inspected once a
quarter at least, and renewed immediately it shows signs of cracking.
Generally speaking all the fittings used should be characterised by
structural simplicity; any ornamental or decorative effects desired may
be secured by proper design without sacrifice of the simplicity which
should always mark the essential and operative parts of the fitting.
Flexible connexions between the fixed service-pipe and a semi-portable or
temporary burner may at times be required. If the connexion is for
permanent use, it must not be of rubber, but of the metallic flexible
tubing which is now commonly employed for such connexions in the case of
coal-gas. There should be a tap between the service-pipe and the flexible
connexion, and this tap should be turned off whenever the burner is out
of use, so that the connexion is not at other times under the pressure
which is maintained in the service-pipes. Unless the connexion is very
short--say 2 feet or less--there should also be a tap at the burner.
These flexible connexions, though serviceable in the case of table-lamps,
&c., of which the position may have to be altered, are undesirable, as
they increase the risk attendant on gas (whether acetylene or other
illuminating gas) lighting, and should, if possible, be avoided. Flexible
connexions may also be required for temporary use, such as for conveying
acetylene to an optical lantern, and if only occasionally called for, the
cost of the metallic flexible tubing will usually preclude its use. It
will generally be found, however, that the whole connexion in such a case
can be of composition or lead gas-piping, connected up at its two ends by
a few inches of flexible rubber tubing. It should be carried along the
walls or over the heads of people who may use the room, rather than
across the floor, or at a low level, and the acetylene should be turned
on to it only when actually required for use, and turned off at the fixed
service-pipe as soon as no longer required. Quite narrow composition
tubing, say 1/4-inch, will carry all the acetylene required for two or
three burners. The cost of a composition temporary connexion will usually
be less than one of even common rubber tubing, and it will be safer. The
composition tubing must not, of course, be sharply bent, but carried by
easy curves to the desired point, and it should be carefully rolled in a
roll of not less than 18 inches diameter when removed. If these
precautions are observed it may be used very many times.
Acetylene service-pipes should, wherever possible, be laid with a fall,
which may be very slight, towards a small closed vessel adjoining the
gasholder or purifier, in order that any water deposited from the gas
owing to condensation of aqueous vapour may run out of the pipe into that
apparatus. Where it is impossible to secure an uninterrupted fall in that
direction, there should be inserted in the service-pipe, at the lowest
point of each dip it makes, a short length of pipe turned downwards and
terminating in a plug or sound tap. Water condensing in this section of
the service-pipe will then run down and collect in this drainage-pipe,
from which it can be withdrawn at intervals by opening the plug or tap
for a moment. The condensed water is thus removed from the service-pipe,
and does not obstruct its through-way. Similar drainage devices may be
used at the lowest points of all dips in mains, though there are special
seal-pots which take the place of the cock or plug used to seal the end
of the drainage-pipe. Such seal-pots or "syphons" are commonly used on
ordinary gas-distributing systems, and might be applied in the case of
large acetylene installations, as they offer facilities for removing the
condensed water from time to time in a convenient and expeditious manner.
EXPULSION OF AIR FROM MAINS.--After a service-pipe system has been proved
to be sound, it is necessary to expel the air from it before acetylene
can be admitted to it with a view to consumption. Unless the system is a
very large one, the expulsion of air is most conveniently effected by
forcing from the gasholder preliminary batches of acetylene through the
pipes, while lights are kept away from the vicinity. This precaution is
necessary because, while the acetylene is displacing the air in the
pipes, they will for some time contain a mixture of air and acetylene in
proportions which fall within the explosive limits of such a mixture. If
the escaping acetylene caught fire from any adjacent light under these
conditions, a most disastrous explosion would ensue and extend through
all the ramifications of the system of pipes. Therefore the first step
when a new system of pipes has to be cleared of air is to see that there
are no lights in or about the house--either fires, lamps, cigars or
pipes, candles or other flames. Obviously this work must be done in the
daytime and finished before nightfall. Burners are removed from two or
more brackets at the farthest points in the system from the gasholder,
and flexible connexions are temporarily attached to them, and led through
a window or door into the open air well clear of the house. One of the
brackets selected should as a rule be the lowest point supplied in the
house. The gasholder having been previously filled with acetylene, the
tap or taps on the pipe leading to the house are turned on, and the
acetylene is passed under slight pressure into the system of pipes, and
escapes through the aforesaid brackets, of which the taps have been
turned on, into the open. The taps of all other brackets are kept closed.
The gas should be allowed to flow thus through the pipes until about five
times the maximum quantity which all the burners on the system would
consume in an hour has escaped from the open brackets. The taps on these
brackets are then closed, and the burners replaced. Flexible tubing is
then connected in place of the burners to all the other brackets in the
house, and acetylene is similarly allowed to escape into the open air
from each for a quarter of an hour. All taps are then closed, and the
burners replaced; all windows in the house are left open wide for half an
hour to allow of the dissipation of any acetylene which may have
accumulated in any part of it, and then, while full pressure from the
gasholder is maintained, a tap is turned on and the gas lighted. If it
burns with a good, fully luminous flame it may be concluded that the
system of pipes is virtually free from air, and the installation may be
used forthwith as required. If, however, the flame is very feebly
luminous, or if the escaping gas does not light, lights must be
extinguished, and the pipes again blown through with acetylene into the
open air. The burner must invariably be in position when a light is
applied, because, in the event of the pipes still containing an explosive
mixture, ignition would not be communicated through the small orifices of
the burner to the mixture in the pipes, and the application of the light
would not entail any danger of an explosion.
Gasfitters familiar with coal-gas should remember, when putting a system
of acetylene pipes into use for the first time, that the range over which
mixtures of acetylene and air are explosive is wider than that over which
mixtures of coal-gas and air are explosive, and that greater care is
therefore necessary in getting the pipes and rooms free from a dangerous
mixture.
The mains for very large installations of acetylene--_e.g._, for
lighting a small town--may advisedly be freed from air by some other plan
than simple expulsion of the air by acetylene, both from the point of
view of economy and of safety. If the chimney gases from a neighbouring
furnace are found on examination to contain not more than about 8 per
cent of oxygen, they may be drawn into the gasholder and forced through
the pipes before acetylene is admitted to them. The high proportion of
carbon dioxide and the low proportion of oxygen in chimney gases makes a
mixture of acetylene and chimney gases non-explosive in any proportions,
and hence if the air is first wholly or to a large extent expelled from a
pipe, main, or apparatus, by means of chimney gases, acetylene may be
admitted, and a much shorter time allowed for the expulsion by it of the
contents of the pipe, before a light is applied at the burners, &c. This
plan, however, will usually only be adopted in the case of very large
pipes, &c.; but on a smaller scale the air may be swept out of a
distributing system by bringing it into connexion with a cylinder of
compressed or liquefied carbon dioxide, the pressure in which will drive
the gas to any spot where an outlet is provided. As these cylinders of
"carbonic acid" are in common employment for preparing aerated waters and
for "lifting" beer, &c., they are easy to hire and use.
TABLE (B).
Giving the Sizes of Pipe which should be used in practice for Acetylene
when the fall of pressure in the Pipe is not to exceed 0.1 inch. (Based
on Morel's formula.)
_________________________________________________________
| | |
| Cubic Feet of | Diameters of Pipe to be used up to |
| Acetylene | the lengths indicated. |
| which the Pipe |_______________________________________|
| is required to | | | | | |
| pass in | 1/4 | 3/8 | 1/2 | 3/4 | 1 |
| One Hour. | inch. | inch. | inch. | inch. | inch. |
|________________|_______|_______|_______|_______|_______|
| | | | | | |
| | Feet. | Feet. | Feet. | Feet. | Feet. |
| 1 | 520 | 3960 | 16700 | ... | ... |
| 2 | 130 | 990 | 4170 | ... | ... |
| 3 | 58 | 440 | 1850 | ... | ... |
| 4 | 32 | 240 | 1040 | ... | ... |
| 5 | 21 | 150 | 660 | 5070 | ... |
| 6 | 14 | 110 | 460 | 3520 | ... |
| 7 | 10 | 80 | 340 | 2590 | ... |
| 8 | ... | 62 | 260 | 1980 | ... |
| 9 | ... | 49 | 200 | 1560 | ... |
| 10 | ... | 39 | 160 | 1270 | 5340 |
| 15 | ... | 17 | 74 | 560 | 2370 |
| 20 | ... | 10 | 41 | 310 | 1330 |
| 25 | ... | ... | 26 | 200 | 850 |
| 30 | ... | ... | 18 | 140 | 590 |
| 35 | ... | ... | 13 | 100 | 430 |
| 40 | ... | ... | 10 | 79 | 330 |
| 45 | ... | ... | ... | 62 | 260 |
| 50 | ... | ... | ... | 50 | 210 |
|________________|_______|_______|_______|_______|_______|
TABLE (A).
Showing the Quantities [Q] (in cubic feet) of Acetylene which will pass
in One Hour through Pipes of various diameters (in inches) under
different Falls of Pressure. (Based on Morel's formula.)
____________________________________________________________________
| | | | | | | | | | | | |
| Diameter | | | | | | | | | | | |
| of Pipe | 1/4| 3/8| 1/2| 3/4 | 1 | 1 | 1 | 1 | 2 | 2 | 3 |
| [_d_] = | | | | | | 1/4 | 1/2| 3/4| | 1/2| |
| inches | | | | | | | | | | | |
|__________|____|____|____|_____|_____|_____|____|____|____|____|____|
| | |
| Length | |
| of Pipe | |
| [_l_] = | Fall of Pressure in the Pipe [_h_] = 0.10 inch. |
| Feet | |
|__________|_________________________________________________________|
| | | | | | | | | | | | |
| 10 | 7.2|19.9|40.8|112 |230 |405 | 635| 935|1305|2285|3600|
| 25 | 4.5|12.6|25.8| 71.2|146 |255 | 400| 590| 825|1445|2280|
| 50 | 3.2| 8.9|18.3| 50.3|103 |180 | 285| 420| 585|1020|1610|
| 100 | 2.3| 6.3|12.9| 35.6| 73.1|127 | 200| 295| 410| 720|1140|
| 200 | 1.6| 4.4| 9.1| 25.2| 51.7| 90.3| 142| 210| 290| 510| 805|
| 300 | 1.3| 3.6| 7.4| 20.5| 42.2| 73.7| 116| 171| 240| 415| 655|
| 400 | 1.1| 3.1| 6.4| 17.8| 36.5| 63.8| 100| 148| 205| 360| 570|
| 500 | 1.0| 2.8| 5.8| 15.9| 32.7| 57.1| 90| 132| 185| 320| 510|
|__________|____|____|____|_____|_____|_____|____|____|____|____|____|
| | |
| Length | |
| of Pipe | |
| [_l_] = | Fall of Pressure in the Pipe [_h_] = 0.25 inch. |
| Feet | |
|__________|_________________________________________________________|
| | | | | | | | | | | | |
| 25 | 7.2|19.9|40.8|112 |230 |405 | 635| 935|1305|2285|3600|
| 50 | 5.1|14.1|28.9| 79.6|163 |285 | 450| 660| 925|1615|2550|
| 100 | 3.6| 9.9|20.4| 56.3|115 |200 | 320| 470| 655|1140|1800|
| 250 | 2.3| 6.3|12.9| 35.6| 73.1|127 | 200| 295| 410| 720|1140|
| 500 | 1.6| 4.4| 9.1| 25.2| 51.7| 90.3| 142| 210| 290| 510| 805|
| 1000 | 1.1| 3.1| 6.4| 17.8| 36.5| 63.8| 100| 148| 205| 360| 570|
|__________|____|____|____|_____|_____|_____|____|____|____|____|____|
| | |
| Length | |
| of Pipe | |
| [_l_] = | Fall of Pressure in the Pipe [_h_] = 0.50 inch. |
| Feet | |
|__________|_________________________________________________________|
| | | | | | | | | | | | |
| 25 |10.2|28.1|57.8|159 |325 |570 | 900|1325|1850|3230|5095|
| 50 | 7.2|19.9|40.8|112 |230 |405 | 635| 935|1305|2285|3600|
| 100 | 5.1|14.1|28.9| 79.6|163 |285 | 450| 660| 925|1615|2550|
| 250 | 3.2| 8.9|18.3| 50.3|103 |180 | 285| 420| 585|1020|1610|
| 500 | 2.3| 6.3|12.9| 35.6| 73.1|127 | 200| 295| 410| 720|1140|
| 1000 | 1.6| 4.4| 9.1| 25.2| 51.7| 90.3| 142| 210| 290| 510| 805|
|__________|____|____|____|_____|_____|_____|____|____|____|____|____|
| | |
| Length | |
| of Pipe | |
| [_l_] = | Fall of Pressure in the Pipe [_h_] = 0.75 inch. |
| Feet | |
|__________|_________________________________________________________|
| | | | | | | | | | | | |
| 50 | 8.8|24.4|50.0|138 |280 |495 | 780|1145|1160|2800|4410|
| 100 | 6.2|17.2|35.4| 97.5|200 |350 | 550| 810|1130|1980|3120|
| 250 | 3.9|10.9|22.4| 61.7|126 |220 | 350| 510| 715|1250|1975|
| 500 | 2.8| 7.7|15.8| 43.6| 89.5|156 | 245| 360| 505| 885|1395|
| 1000 | 2.0| 5.4|11.2| 30.8| 63.3|110 | 174| 255| 360| 625| 985|
| 2000 | 1.4| 3.8| 7.9| 21.8| 44.8| 78.2| 123| 181| 250| 440| 695|
|__________|____|____|____|_____|_____|_____|____|____|____|____|____|
| | |
| Length | |
| of Pipe | |
| [_l_] = | Fall of Pressure in the Pipe [_h_] = 1.0 inch. |
| Feet | |
|__________|_________________________________________________________|
| | | | | | | | | | | | |
| 100 | 7.2|19.9|40.8|112 |230 |405 | 635| 935|1305|2285|3600|
| 250 | 4.5|12.6|25.8| 71.2|146 |255 | 400| 590| 825|1445|2280|
| 500 | 3.2| 8.9|18.3| 50.3|103 |180 | 285| 420| 585|1020|1610|
| 1000 | 2.3| 6.3|12.9| 35.6| 73.1|127 | 200| 295| 410| 720|1140|
| 2000 | 1.6| 4.4| 9.1| 25.2| 51.7| 90.3| 142| 210| 290| 510| 805|
| 3000 | 1.3| 3.6| 7.4| 20.5| 42.2| 73.7| 116| 171| 240| 415| 655|
|__________|_________________________________________________________|
| | |
| Length | |
| of Pipe | |
| [_l_] = | Fall of Pressure in the Pipe [_h_] = 1.5 inch. |
| Feet | |
|__________|_________________________________________________________|
| | | | | | | | | | | | |
| 250 | 5.6|15.4|31.6| 87.2|179 |310 | 495| 725|1010|1770|2790|
| 500 | 3.9|10.9|22.4| 61.7|126 |220 | 350| 510| 715|1250|1975|
| 1000 | 2.8| 7.7|15.8| 43.6| 89.5|156 | 245| 360| 505| 885|1395|
| 2000 | 2.0| 5.4|11.2| 30.8| 63.3|110 | 174| 255| 360| 625| 985|
| 3000 | 1.6| 4.4| 9.1| 25.2| 51.7| 90.3| 142| 210| 290| 510| 805|
| 4000 | 1.4| 3.8| 7.9| 21.8| 44.8| 78.2| 123| 181| 250| 440| 695|
|__________|____|____|____|_____|_____|_____|____|____|____|____|____|
| | |
| Length | |
| of Pipe | |
| [_l_] = | Fall of Pressure in the Pipe [_h_] = 2.0 inches. |
| Feet | |
|__________|_________________________________________________________|
| | | | | | | | | | | | |
| 500 | 4.5|12.6|25.8| 71.2|146 |255 | 400| 590| 825|1445|2280|
| 1000 | 3.2| 8.9|18.3| 50.3|103 |180 | 285| 420| 585|1020|1610|
| 2000 | 2.3| 6.3|12.9| 35.6| 73.1|127 | 200| 295| 410| 720|1140|
| 3000 | 1.8| 5.1|10.5| 29.1| 59.7|104 | 164| 240| 335| 590| 930|
| 4000 | 1.6| 4.4| 9.1| 25.2| 51.7| 90.3| 142| 210| 290| 510| 805|
| 5000 | 1.4| 4.0| 8.1| 22.5| 46.2| 80.8| 127| 187| 260| 455| 720|
| 6000 | 1.3| 3.6| 7.4| 20.5| 42.2| 73.7| 116| 171| 240| 415| 655|
|__________|____|____|____|_____|_____|_____|____|____|____|____|____|
NOTE.--In order not to impart to the above table the appearance of the
quantities having been calculated to a degree of accuracy which has no
practical significance, quantities of less than 5 cubic feet have been
ignored when the total quantity exceeds 200 cubic feet, and fractions of
a cubic foot have been included only when the total quantity is less than
100 cubic feet.
TABLE (C).
Giving the Sizes of Pipe which should be used in practice for Acetylene
when the fall of pressure in the Pipe is not to exceed 0.25 inch. (Based
on Morel's formula.)
____________________________________________________________________
| | |
| Cubic feet | |
| of | |
| Acetylene | Diameters of Pipe to be used up to the lengths stated.|
| which the | |
| Pipe is | |
| required |_______________________________________________________|
| to pass | | | | | | | | |
| in One | 1/4 | 1/2 | 3/4 | 1 | 1-1/4| 1-1/2| 1-3/4| 2 |
| Hour | inch.| inch.| inch.| inch.| inch.| inch.| inch.| inch.|
|____________|______|______|______|______|______|______|______|______|
| | | | | | | | | |
| | Feet.| Feet.| Feet.| Feet.| Feet.| Feet.| Feet.| Feet.|
| 2-1/2 | 1580 | 6680 | 50750| ... | ... | ... | ... | ... |
| 5 | 390 | 1670 | 12690| 53160| ... | ... | ... | ... |
| 7-1/2 | 175 | 710 | 5610| 23760| ... | ... | ... | ... |
| 10 | 99 | 410 | 3170| 13360| 40790| ... | ... | ... |
| 15 | 41 | 185 | 1410| 5940| 18130| 45110| ... | ... |
| 20 | 24 | 105 | 790| 3350| 10190| 25370| 54840| ... |
| 25 | 26 | 67 | 500| 2130| 6520| 16240| 35100| ... |
| 30 | 11 | 46 | 350| 1480| 4530| 11270| 24370| 47520|
| 35 | ... | 34 | 260| 1090| 3330| 8280| 17900| 34910|
| 40 | ... | 26 | 195| 830| 2550| 6340| 13710| 26730|
| 45 | ... | 20 | 155| 660| 2010| 5010| 10830| 21120|
| 50 | ... | 16 | 125| 530| 1630| 4060| 8770| 17110|
| 60 | ... | 11 | 88| 370| 1130| 2880| 6090| 11880|
| 70 | ... | ... | 61| 270| 830| 2070| 4470| 8730|
| 80 | ... | ... | 49| 210| 630| 1580| 3420| 6680|
| 90 | ... | ... | 39| 165| 500| 1250| 2700| 5280|
| 100 | ... | ... | 31| 130| 400| 1010| 2190| 4270|
| 150 | ... | ... | 14| 59| 180| 450| 970| 1900|
| 200 | ... | ... | ... | 33| 100| 250| 540| 1070|
| 250 | ... | ... | ... | 21| 65| 160| 350| 680|
| 500 | ... | ... | ... | ... | 16| 40| 87| 170|
| 1000 | ... | ... | ... | ... | ... | 10| 22| 42|
|____________|______|______|______|______|______|______|______|______|
TABLE (D).
Giving the Sizes of Pipe which should be used in practice for Acetylene
Mains when the fall of pressure in the Main is not to exceed 0.5 inch,
(Based on Morel's formula.)
____________________________________________________________________
| | |
| Cubic feet | |
| of | |
| Acetylene | Diameters of Pipe to be used up to the lengths stated.|
| which the | |
| Main is | |
| required |_______________________________________________________|
| to pass | | | | | | | | |
| in One | 3/4 | 1 | 1-1/4| 1-1/2| 1-3/4| 2 | 2-1/2| 3 |
| Hour | inch.| inch.| inch.| inch.| inch.| inch.| inch.| inch.|
|____________|______|______|______|______|______|______|______|______|
| | | | | | | | | |
| |Miles.|Miles.|Miles.|Miles.|Miles.|Miles.|Miles.|Miles.|
| 10 | 5.05 | ... | ... | ... | ... | ... | ... | ... |
| 25 | 0.80 | 2.45 | 6.15 | ... | ... | ... | ... | ... |
| 50 | 0.20 | 0.60 | 1.50 | 3.30 | 6.45 | ... | ... | ... |
| 100 | 0.05 | 0.15 | 0.35 | 0.80 | 1.60 | 4.95 |12.30 | ... |
| 200 | ... | 0.04 | 0.09 | 0.20 | 0.40 | 1.20 | 3.05 |12.95 |
| 300 | ... | ... | 0.04 | 0.09 | 0.18 | 0.55 | 1.35 | 5.75 |
| 400 | ... | ... | ... | 0.05 | 0.10 | 0.30 | 0.75 | 3.25 |
| 500 | ... | .. | ... | 0.03 | 0.06 | 0.20 | 0.50 | 2.05 |
| 750 | ... | ... | ... | ... | 0.03 | 0.08 | 0.20 | 0.80 |
| 1100 | ... | ... | ... | ... | ... | 0.05 | 0.12 | 0.50 |
| 1500 | ... | ... | ... | ... | ... | 0.02 | 0.05 | 0.23 |
| 2000 | ... | ... | ... | ... | ... | ... | 0.03 | 0.13 |
| 2500 | ... | ... | ... | ... | ... | ... | 0.02 | 0.08 |
| 5000 | ... | ... | ... | ... | ... | ... | ... | 0.03 |
|____________|______|______|______|______|______|______|______|______|
TABLE (E).
Giving the Sizes of Pipe which should be used in practice for Acetylene
Mains when the fall of pressure in the Main is not to exceed 1.0 inch.
(Based on Morel's formula.)
__________________________________________________________________
| | |
| Cubic feet | |
| of | |
| Acetylene |Diameters of Pipe to be used up to the lengths stated|
| which the | |
| Main is | |
| required |_____________________________________________________|
| to pass | | | | | | | | | |
| in One | 3/4 | 1 |1-1/4|1-1/2|1-3/4| 2 |2-1/2| 3 | 4 |
| Hour |inch.|inch.|inch.|inch.|inch.|inch.|inch.|inch.|inch.|
|____________|_____|_____|_____|_____|_____|_____|_____|_____|_____|
| | | | | | | | | | |
| |Miles|Miles|Miles|Mile.|Miles|Miles|Miles|Miles|Miles|
| 10 | 2.40|10.13|30.90| ... | ... | ... | ... | ... | ... |
| 25 | 0.38| 1.62| 4.94|12.30| ... | ... | ... | ... | ... |
| 50 | 0.09| 0.40| 1.23| 3.07| 6.65|12.96| ... | ... | ... |
| 100 | 0.02| 0.10| 0.30| 0.77| 1.66| 3.24| 9.88| ... | ... |
| 200 | ... | 0.02| 0.07| 0.19| 0.41| 0.81| 2.47| 6.15| ... |
| 300 | ... | 0.01| 0.03| 0.08| 0.18| 0.36| 1.09| 2.73|11.52|
| 400 | ... | ... | 0.0 | 0.05| 0.10| 0.20| 0.61| 1.53| 6.48|
| 500 | ... | ... | 0.0 | 0.03| 0.06| 0.13| 0.39| 0.98| 4.14|
| 750 | ... | ... | ... | 0.01| 0.03| 0.05| 0.17| 0.43| 1.84|
| 1000 | ... | ... | ... | ... | 0.01| 0.03| 0.10| 0.24| 1.03|
| 1500 | ... | ... | ... | ... | ... | 0.01| 0.01| 0.11| 0.46|
| 2000 | ... | ... | ... | ... | ... | ... | 0.02| 0.06| 0.26|
| 2500 | ... | ... | ... | ... | ... | ... | 0.01| 0.04| 0.16|
| 5000 | ... | ... | ... | ... | ... | ... | ... | 0.01| 0.04|
|____________|_____|_____|_____|_____|_____|_____|_____|_____|_____|
CHAPTER VIII
COMBUSTION OF ACETYLENE IN LUMINOUS BURNERS--THEIR DISPOSITION
NATURE OF LUMINOUS FLAMES.--When referring to methods of obtaining
artificial light by means of processes involving combustion or oxidation,
the term "incandescence" is usually limited to those forms of burner in
which some extraneous substance, such as a "mantle," is raised to a
brilliant white heat. Though convenient, the phrase is a mere convention,
for all artificial illuminants, even including the electric light, which
exhibit a useful degree of intensity depend on the same principle of
incandescence. Adopting the convention, however, an incandescent burner
is one in which the fuel burns with a non-luminous or atmospheric flame,
the light being produced by causing that flame to play upon some
extraneous refractory body having the property of emitting much light
when it is raised to a sufficiently high temperature; while a luminous
burner is one in which the fuel is allowed to combine with atmospheric
oxygen in such a way that one or more of the constituents in the gas
evolves light as it suffers combustion. From the strictly chemical point
of view the light-giving substance in the incandescent flame lasts
indefinitely, for it experiences no change except in temperature; whereas
the light-giving substance in a luminous flame lasts but for an instant,
for it only evolves light during the act of its combination with the
oxygen of the atmosphere. Any fluid combustible which burns with a flame
can be made to give light on the incandescent system, for all such
materials either burn naturally, or can be made to burn with a non-
luminous flame, which can be employed to raise the temperature of some
mantle; but only those fuels can be burnt on the self-luminous system
which contain some ingredient that is liberated in the elemental state in
the flame, the said ingredient being one which combines energetically
with oxygen so as to liberate much local heat. In practice, just as there
are only two or three substances which are suitable for the construction
of an incandescent mantle, so there is only one which renders a flame
usefully self-luminous, viz., carbon; and therefore only such fuels as
contain carbon among their constituents can be burnt so as to produce
light without the assistance of the mantle. But inasmuch as it is
necessary for the evolution of light by the combustion of carbon that
that carbon shall be in the free state, only those carbonaceous fuels
yield light without the mantle in which the carbonaceous ingredient is
dissociated into its elements before it is consumed. For instance,
alcohol and carbon monoxide are both combustible, and both contain
carbon; but they yield non-luminous flames, for the carbon burns to
carbon dioxide in ordinary conditions without assuming the solid form;
ether, petroleum, acetylene, and some of the hydrocarbons of coal-gas do
emit light on combustion, for part of their carbon is so liberated. The
quantity of light emitted by the glowing substance increases as the
temperature of that substance rises: the gain in light being equal to the
fifth or higher power of the gain in heat; [Footnote: Calculated from
absolute zero.] therefore unnecessary dissipation of heat from a flame is
one of the most important matters to be guarded against if that flame is
to be an economical illuminant. But the amount of heat liberated when a
certain weight (or volume) of a particular fuel combines with a
sufficient quantity of oxygen to oxidise it wholly is absolutely fixed,
and is exactly the same whether that fuel is made to give a luminous or a
non-luminous flame. Nevertheless the atmospheric flame given by a certain
fuel may be appreciably hotter than its luminous flame, because the
former is usually smaller than the latter. Unless the luminous flame of a
rich fuel is made to expose a wide surface to the air, part of its carbon
may escape ultimate combustion; soot or smoke may be produced, and some
of the most valuable heat-giving substance will be wasted. But if the
flame is made to expose a large surface to the air, it becomes flat or
hollow in shape instead of being cylindrical and solid, and therefore in
proportion to its cubical capacity it presents to the cold air a larger
superficies, from which loss of heat by radiation, &c., occurs. Being
larger, too, the heat produced is less concentrated.
It does not fall within the province of the present book to discuss the
relative merits of luminous and incandescent lighting; but it may be
remarked that acetylene ranks with petroleum against coal-gas,
carburetted or non-carburetted water-gas, and semi-water-gas, in showing
a comparatively small degree of increased efficiency when burnt under the
mantle. Any gas which is essentially composed of carbon monoxide or
hydrogen alone (or both together) burns with a non-luminous flame, and
can therefore only be used for illuminating purposes on the incandescent
system; but, broadly speaking, the higher is the latent illuminating
power of the gas itself when burnt in a non-atmospheric burner, the less
marked is the superiority, both from the economical and the hygienic
aspect, of its incandescent flame. It must be remembered also that only a
gas yields a flame when it is burnt; the flame of a paraffin lamp and of
a candle is due to the combustion of the vaporised fuel. Methods of
burning acetylene under the mantle are discussed in Chapter IX.; here
only self-luminous flames are being considered, but the theoretical
question of heat economy applies to both processes.
Heat may be lost from a flame in three several ways: by direct radiation
and conduction into the surrounding air, among the products of
combustion, and by conduction into the body of the burner. Loss of heat
by radiation and conduction to the air will be the greater as the flame
exposes a larger surface, and as a more rapid current of cold air is
brought into proximity with the flame. Loss of heat by conduction, into
the burner will be the greater as the material of which the burner is
constructed is a better conductor of heat, and as the mass of material in
that burner is larger. Loss of heat by passage into the combustion
products will also be greater as these products are more voluminous; but
the volume of true combustion products from any particular gas is a fixed
quantity, and since these products must leave the flame at the
temperature of that flame--where the highest temperature possible is
requisite--it would seem that no control can be had over the quantity of
heat so lost. However, although it is not possible in practice to supply
a flame with too little air, lest some of its carbon should escape
consumption and prove a nuisance, it is very easy without conspicuous
inconvenience to supply it with too much; and if the flame is supplied
with too much, there is an unnecessary volume of air passing through it
to dilute the true combustion products, which air absorbs its own proper
proportion of heat. It is only the oxygen of the air which a flame needs,
and this oxygen is mixed with approximately four times its volume of
nitrogen; if, then, only a small excess of oxygen (too little to be
noticeable of itself) is admitted to a flame, it is yet harmful, because
it brings with it four times its volume of nitrogen, which has to be
raised to the same temperature as the oxygen. Moreover, the nitrogen and
the excess of oxygen occupy much space in the flame, making it larger,
and distributing that fixed quantity of heat which it is capable of
generating over an unnecessarily large area. It is for this reason that
any gas gives so much brighter a light when burnt in pure oxygen than in
air, (1) because the flame is smaller and its heat more concentrated, and
(2) because part of its heat is not being wasted in raising the
temperature of a large mass of inert nitrogen. Thus, if the flame of a
gas which naturally gives a luminous flame is supplied with an excess of
air, its illuminating value diminishes; and this is true whether that
excess is introduced at the base of the actual flame, or is added to the
gas prior to ignition. In fact the method of adding some air to a
naturally luminous gas before it arrives at its place of combustion is
the principle of the Bunsen burner, used for incandescent lighting and
for most forms of warming and cooking stoves. A well-made modern
atmospheric burner, however, does not add an excess of air to the flame,
as might appear from what has been said; such a burner only adds part of
the air before and the remainder of the necessary quantity after the
point of first ignition--the function of the primary supply being merely
to insure thorough admixture and to avoid the production of elemental
carbon within the flame.
ILLUMINATING POWER.--It is very necessary to observe that, as the
combined losses of heat from a flame must be smaller in proportion to the
total heat produced by the flame as the flame itself becomes larger, the
more powerful and intense any single unit of artificial light is, the
more economical does it become, because economy of heat spells economy of
light. Conversely, the more powerful and intense any single unit of light
is, the more is it liable to injure the eyesight, the deeper and, by
contrast, the more impenetrable are the shadows it yields, and the less
pleasant and artistic is its effect in an occupied room. For economical
reasons, therefore, one large central source of light is best in an
apartment, but for physiological and æsthetic reasons a considerable
number of correspondingly smaller units are preferable. Even in the
street the economical advantage of the single unit is outweighed by the
inconvenience of its shadows, and by the superiority of a number of
evenly distributed small sources to one central large source of light
whenever the natural transmission of light rays through the atmosphere is
interfered with by mist or fog. The illuminating power of acetylene is
commonly stated to be "240 candles" (though on the same basis Wolff has
found it to be about 280 candles). This statement means that when
acetylene is consumed in the most advantageous self-luminous burner at
the most advantageous rate, that rate (expressed in cubic feet per hour)
is to 5 in the same ratio as the intensity of the light evolved
(expressed in standard candles) is to the said "illuminating power."
Thus, Wolff found that when acetylene was burnt in the "0000 Bray" fish-
tail burner at the rate of 1.377 cubic feet per hour, a light of 77
candle-power was obtained. Hence, putting x to represent the illuminating
power of the acetylene in standard candles, we have:
1.377 / 5 = 77 / x hence x = 280.
Therefore acetylene is said to have, according to Wolff, an illuminating
power of about 280 candles, or according to other observers, whose
results have been commonly quoted, of 240 candles. The same method of
calculating the nominal illuminating power of a gas is applied within the
United Kingdom in the case of all gases which cannot be advantageously
burnt at the rate of 5 cubic feet per hour in the standard burner
(usually an Argand). The rate of 5 cubic feet per hour is specified in
most Acts of Parliament relating to gas-supply as that at which coal-gas
is to be burnt in testings of its illuminating power; and the
illuminating power of the gas is defined as the intensity, expressed in
standard candles, of the light afforded when the gas is burnt at that
rate. In order to make the values found for the light evolved at more
advantageous rates of consumption by other descriptions of gas--such as
oil-gas or acetylene--comparable with the "illuminating power" of coal-
gas as defined above, the values found are corrected in the ratio of the
actual rate of consumption to 5 cubic feet per hour.
In this way the illuminating power of 240 candles has been commonly
assigned to acetylene, though it would be clearer to those unfamiliar
with the definition of illuminating power in the Acts of Parliament which
regulate the testing of coal-gas, if the same fact were conveyed by
stating that acetylene affords a maximum illuminating power of 48 candles
(_i.e._, 240 / 5) per cubic foot. Actually, by misunderstanding of
the accepted though arbitrary nomenclature of gas photometry, it has not
infrequently been assorted or implied that a cubic foot of acetylene
yields a light of 240 candle-power instead of 48 candle-power. It should,
moreover, be remembered that the ideal illuminating power of a gas is the
highest realisable in any Argand or flat-flame burner, while the said
burner may not be a practicable one for general use in house lighting.
Thus, the burners recommended for general use in lighting by acetylene do
not develop a light of 48 candles per cubic foot of gas consumed, but
considerably less, as will appear from the data given later in this
chapter.
It has been stated that in order to avoid loss of heat from a flame
through the burner, that burner should present only a small mass of
material (_i.e._, be as light in weight as possible), and should be
constructed of a bad heat-conductor. But if a small mass of a material
very deficient in heat-conducting properties comes in contact with a
flame, its temperature rises seriously and may approach that of the base
of the flame itself. In the case of coal-gas this phenomenon is not
objectionable, is even advantageous, and it explains why a burner made of
steatite, which conducts heat badly, in always more economical (of heat
and therefore of light) than an iron one. In the case of acetylene the
same rule should, and undoubtedly does, apply also; but it is
complicated, and its effect sometimes neutralised, by a peculiarity of
the gas itself. It has been shown in Chapters II. and VI. that acetylene
polymerises under the influence of heat, being converted into other
bodies of lower illuminating power, together with some elemental carbon.
If, now, acetylene is fed into a burner which, being composed of some
material like steatite possessed of low heat-conducting and radiating
powers, is very hot, and if the burner comprises a tube of sensible
length, the gas that actually arrives at the orifice may no longer be
pure acetylene, but acetylene diluted with inferior illuminating agents,
and accompanied by a certain proportion of carbon. Neglecting the effect
of this carbon, which will be considered in the following paragraph, it
is manifest that the acetylene issuing from a hot burner--assuming its
temperature to exceed the minimum capable of determining polymerisation--
may emit less light per unit of volume than the acetylene escaping from a
cold burner. Proof of this statement is to be found in some experiments
described by Bullier, who observed that when a small "Manchester" or
fish-tail burner was allowed to become naturally hot, the quantity of gas
needed to give the light of one candle (uncorrected) was 1.32 litres, but
when the burner was kept cool by providing it with a jacket in which
water was constantly circulating, only 1.13 litres of acetylene were
necessary to obtain the same illuminating value, this being an economy of
16 per cent.
EARLY BURNERS.--One of the chief difficulties encountered in the early
days of the acetylene industry was the design of a satisfactory burner
which should possess a life of reasonable length. The first burners tried
were ordinary oil-gas jets, which resemble the fish-tails used with coal-
gas, but made smaller in every part to allow for the higher illuminating
power of the oil-gas or acetylene per unit of volume. Although the flames
they gave were very brilliant, and indeed have never been surpassed, the
light quickly fell off in intensity owing to the distortion of their
orifices caused by the deposition of solid matter at the edges. Various
explanations have been offered to account for the precipitation of solid
matter at the jets. If the acetylene passes directly to the burner from a
generator having carbide in excess without being washed or filtered in
any way, the gas may carry with it particles of lime dust, which will
collect in the pipes mainly at the points where they are constricted; and
as the pipes will be of comparatively large bore until the actual burner
is readied, it will be chiefly at the orifices where the deposition
occurs. This cause, though trivial, is often overlooked. It will be
obviated whenever the plant is intelligently designed. As the phosphoric
anhydride, or pentoxide, which is produced when a gas containing
phosphorus burns, is a solid body, it may be deposited at the burner
jets. This cause may be removed, or at least minimised, by proper
purification of the acetylene, which means the removal of phosphorus
compounds. Should the gas contain hydrogen silicide siliciuretted
hydrogen), solid silica will be produced similarly, and will play its
part in causing obstruction. According to Lewes the main factor in the
blocking of the burners is the presence of liquid polymerised products in
the acetylene, benzene in particular; for he considers that these bodies
will be absorbed by the porous steatite, and will be decomposed under the
influence of heat in that substance, saturating the steatite with carbon
which, by a "catalytic" action presumably, assists in the deposition of
further quantities of carbon in the burner tube until distortion of the
flame results. Some action of this character possibly occurs; but were it
the sole cause of blockage, the trouble would disappear entirely if the
gas were washed with some suitable heavy oil before entering the burners,
or if the latter were constructed of a non-porous material. It is
certainly true that the purer is the acetylene burnt, both as regards
freedom from phosphorus and absence of products of polymerisation, the
longer do the burners last; and it has been claimed that a burner
constructed at its jets of some non-porous substance, e.g., "ruby," does
not choke as quickly as do steatite ones. Nevertheless, stoppages at the
burners cannot be wholly avoided by these refinements. Gaud has shown
that when pure acetylene is burnt at the normal rate in 1-foot Bray jets,
growths of carbon soon appear, but do not obstruct the orifices during
100 hours' use; if, however, the gas-supply is checked till the flame
becomes thick, the growths appear more quickly, and become obstructive
after some 60 hours' burning. On the assumption that acetylene begins to
polymerise at a temperature of 100° C., Gaud calculates that
polymerisation cannot cause blocking of the burners unless the speed of
the passing gas is so far reduced that the burner is only delivering one-
sixth of its proper volume. But during 1902 Javal demonstrated that on
heating in a gas-flame one arm of a twin, non-injector burner which had
been and still was behaving quite satisfactorily with highly purified
acetylene, growths were formed at the jet of that arm almost
instantaneously. There is thus little doubt that the principal cause of
this phenomenon is the partial dissociation of the acetylene (i.e.,
decomposition into its elements) as it passes through the burner itself;
and the extent of such dissociation will depend, not at all upon the
purity of the gas, but upon the temperature of the burner, upon the
readiness with which the heat of the burner is communicated to the gas,
and upon the speed at which the acetylene travels through the burner.
Some experiments reported by R. Granjon and P. Mauricheau-Beaupré in 1906
indicate, however, that phosphine in the gas is the primary cause of the
growths upon non-injector burners. According to these investigators the
combustion of the phosphine causes a deposit at the burner orifices of
phosphoric acid, which is raised by the flame to a temperature higher
than that of the burner. This hot deposit then decomposes some acetylene,
and the carbon deposited therefrom is rendered incombustible by the
phosphoric acid which continues to be produced from the combustion of the
phosphine in the gas. The incombustible deposit of carbon and phosphoric
acid thus produced ultimately chokes the burner.
It will appear in Chapter XI. that some of the first endeavours to avoid
burner troubles were based on the dilution of the acetylene with carbon
dioxide or air before the gas reached the place of combustion; while the
subsequent paragraphs will show that the same result is arrived at more
satisfactorily by diluting the acetylene with air during its actual
passage through the burner. It seems highly probable that the beneficial
effect of the earliest methods was due simply or primarily to the
dilution, the molecules of the acetylene being partially protected from
the heat of the burner by the molecules of a gas which was not injured by
the high temperature, and which attracted to itself part of the heat that
would otherwise have been communicated to the hydrocarbon. The modern
injector burner exhibits the same phenomenon of dilution, and is to the
same extent efficacious in preventing polymerisation; but inasmuch as it
permits a larger proportion of air to be introduced, and as the addition
is made roughly half-way along the burner passage, the cold air is more
effectual in keeping the former part of the tip cool, and in jacketing
the acetylene during its travel through the latter part, the bore of
which is larger than it otherwise would be.
INJECTOR AND TWIN-FLAME BURNERS.--In practice it is neither possible to
cool an acetylene burner systematically, nor is it desirable to construct
it of such a large mass of some good heat conductor that its temperature
always remains below the dissociation point of the gas. The earliest
direct attempts to keep the burner cool were directed to an avoidance of
contact between the flame of the burning acetylene and the body of the
jet, this being effected by causing the current of acetylene to inject a
small proportion of air through lateral apertures in the burner below the
point of ignition. Such air naturally carries along with it some of the
heat which, in spite of all precautions, still reaches the burner; but it
also apparently forms a temporary annular jacket round the stream of gas,
preventing it from catching fire until it has arrived at an appreciable
distance from the jet. Other attempts were made by placing two non-
injector jets in such mutual positions that the two streams of gas met at
an angle, there to spread fan-fashion into a flat flame. This is really
nothing but the old fish-tail coal-gas burner--which yields its flat
flame by identical impingement of two gas streams--modified in detail so
that the bulk of the flame should be at a considerable distance from the
burner instead of resting directly upon it. In the fish-tail the two
orifices are bored in the one piece of steatite, and virtually join at
their external ends; in the acetylene burner, two separate pieces of
steatite, three-quarters of an inch or more apart, carried by completely
separate supports, are each drilled with one hole, and the flame stands
vertically midway between them. The two streams of gas are in one
vertical plane, to which the vertical plane of the flame is at right
angles. Neither of these devices singly gave a solution of the
difficulty; but by combining the two--the injector and the twin-flame
principle--the modern flat-flame acetylene burner has been evolved, and
is now met with in two slightly different forms known as the Billwiller
and the Naphey respectively. The latter apparently ought to be called the
Dolan.
[Illustration: FIG. 8.--TYPICAL ACETYLENE BURNERS.]
The essential feature of the Naphey burner is the tip, which is shown in
longitudinal section at A in Fig. 8. It consists of a mushroom headed
cylinder of steatite, drilled centrally with a gas passage, which at its
point is of a diameter suited to pass half the quantity of acetylene that
the entire burner is intended to consume. The cap is provided with four
radial air passages, only two of which are represented in the drawing;
these unite in the centre of the head, where they enter into the
longitudinal channel, virtually a continuation of the gas-way, leading to
the point of combustion by a tube wide enough to pass the introduced air
as well as the gas. Being under some pressure, the acetylene issuing from
the jet at the end of the cylindrical portion of the tip injects air
through the four air passages, and the mixture is finally burnt at the
top orifice. As pointed out in Chapter VII., the injector jet is so small
in diameter that even if the service-pipes leading to the tip contain an
explosive mixture of acetylene and air, the explosion produced locally if
a light is applied to the burner cannot pass backwards through that jet,
and all danger is obviated. One tip only of this description evidently
produces a long, jet-like flame, or a "rat-tail," in which the latent
illuminating power of the acetylene is not developed economically. In
practice, therefore, two of these tips are employed in unison, one of the
commonest methods of holding them being shown at B. From each tip issues
a stream of acetylene mixed with air, and to some extent also surrounded
by a jacket of air; and at a certain point, which forms the apex of an
isosceles right-angled triangle having its other angles at the orifices
of the tips, the gas streams impinge, yielding a flat flame, at right-
angles, as mentioned before, to the plane of the triangle. If the two
tips are three-quarters of an inch apart, and if the angle of impingement
is exactly 90°, the distance of each tip from the base of the flame
proper will be a trifle over half an inch; and although each stream of
gas does take fire and burn somewhat before meeting its neighbour,
comparatively little heat is generated near the body of the steatite.
Nevertheless, sufficient heat is occasionally communicated to the metal
stems of these burners to cause warping, followed by a want of alignment
in the gas streams, and this produces distortion of the flame, and
possibly smoking. Three methods of overcoming this defect have been used:
in one the arms are constructed entirely of steatite, in another they are
made of such soft metal as easily to be bent back again into position
with the fingers or pliers, in the third each arm is in two portions,
screwing the one into the other. The second type is represented by the
original Phôs burner, in which the curved arms of B are replaced by a
pair of straight divergent arms of thin, soft tubing, joined to a pair of
convergent wider tubes carrying the two tips. The third type is met with
in the Drake burner, where the divergent arms are wide and have an
internal thread into which screws an external thread cut upon lateral
prolongations of the convergent tubes. Thus both the Phôs and the Drake
burner exhibit a pair of exposed elbows between the gas inlet and the two
tips; and these elbows are utilised to carry a screwed wire fastened to
an external milled head by means of which any deposit of carbon in the
burner tubes can be pushed out. The present pattern of the Phôs burner is
shown in Fig. 9, in which _A_ is the burner tip, _B_ the wire
or needle, and _C_ the milled head by which the wire is screwed in
and out of the burner tube.
[Illustration: FIG. 9.--IMPROVED PHÔS BURNER.]
[Illustration: FIG. 10.--"WONDER" SINGLE AND TWO-FLAME BURNERS.]
[Illustration: FIG. 11.--"SUPREMA" NO. 266651, TWO-FLAME BURNER.]
[Illustration: FIG. 12.--BRAY'S MODIFIED NAPHEY INJECTOR BURNER TIP.]
[Illustration: FIG. 13.--BRAY'S "ELTA" BURNER.]
[Illustration: FIG. 14.--BRAY'S "LUTA" BURNER.]
[Illustration: FIG. 15.--BRAY'S "SANSAIR" BURNER.]
[Illustration: FIG. 16.--ADJUSTABLE "KONA" BURNER.]
In the original Billwiller burner, the injector gas orifice was brought
centrally under a somewhat larger hole drilled in a separate sheet of
platinum, the metal being so carried as to permit entry of air. In order
to avoid the expense of the platinum, the same principle was afterwards
used in the design of an all-steatite head, which is represented at D in
Fig. 8. The two holes there visible are the orifices for the emission of
the mixture of acetylene with indrawn air, the proper acetylene jets
lying concentrically below these in the thicker portions of the heads.
These two types of burner have been modified in a large number of ways,
some of which are shown at C, E, and F; the air entering through saw-
cuts, lateral holes, or an annular channel. Burners resembling F in
outward form are made with a pair of injector jets and corresponding air
orifices on each head, so as to produce a pair of names lying in the same
plane, "end-on" to one another, and projecting at either side
considerably beyond the body of the burner; these have the advantage of
yielding no shadow directly underneath. A burner of this pattern, viz.,
the "Wonder," which is sold in this country by Hannam's, Ltd., is shown
in Fig. 10, alongside the single-flame "Wonder" burner, which is largely
used, especially in the United States. Another two-flame burner, made of
steatite, by J. von Schwarz of Nuremberg, and sold by L. Wiener of
London, is shown in Fig. 11. Burners of the Argand type have also been
manufactured, but have been unsuccessful. There are, of course, endless
modifications of flat-flame burners to be found on the markets, but only
a few need be described. A device, which should prove useful where it may
be convenient to be able to turn one or more burners up or down from the
same common distant spot, has been patented by Forbes. It consists of the
usual twin-injector burner fitted with a small central pinhole jet; and
inside the casing is a receptacle containing a little mercury, the level
of which is moved by the gas pressure by an adaptation of the
displacement principle. When the main is carrying full pressure, both of
the jets proper are alight, and the burner behaves normally, but if the
pressure is reduced to a certain point, the movement of the mercury seals
the tubes leading to the main jets, and opens that of the pilot flame,
which alone remains alight till the pressure is increased again. Bray has
patented a modification of the Naphey injector tip, which is shown in
Fig. 12. It will be observed that the four air inlets are at right-angles
to the gas-way; but the essential feature of the device is the conical
orifice. By this arrangement it is claimed that firing back never occurs,
and that the burner can be turned down and left to give a small flame for
considerable periods of time without fear of the apertures becoming
choked or distorted. As a rule burners of the ordinary type do not well
bear being turned down; they should either be run at full power or
extinguished completely. The "Elta" burner, made by Geo. Bray and Co.,
Ltd., which is shown in Fig. 13, is an injector or atmospheric burner
which may be turned low without any deposition of carbon occurring on the
tips. A burner of simple construction but which cannot be turned low is
the "Luta," made by the same firm and shown in Fig. 14. Of the non-
atmospheric type the "Sansair," also made by Geo. Bray and Co., Ltd., is
extensively used. It is shown in Fig. 15. In order to avoid the warping,
through the heat of the flame, of the arms of burners which sometimes
occurs when they are made of metal, a number of burners are now made with
the arms wholly of steatite. One of the best-known of these, of the
injector type, is the "Kona," made by Falk, Stadelmann and Co., of
London. It is shown in Fig. 16, fitted with a screw device for adjusting
the flow of gas, so that when this adjuster has been set to give a flame
of the proper size, no further adjustment by means of the gas-tap is
necessary. This saves the trouble of manipulating the tap after the gas
is lighted. The same adjusting device may also be had fitted to the Phôs
burner (Fig. 9) or to the "Orka" burner (Fig. 17), which is a steatite-
tip injector burner with metal arms made by Falk, Stadelmann and Co.,
Ltd. A burner with steatite arms, made by J. von Schwarz of Nuremberg,
and sold in this country by L. Wiener of London, is shown in Fig. 18.
[Illustration: FIG. 17.--"ORKA" BURNER.]
[Illustration: FIG. 18.--"SUPREMA" NO. 216469 BURNER.]
ILLUMINATING DUTY.--The illuminating value of ordinary self-luminous
acetylene burners in different sizes has been examined by various
photometrists. For burners of the Naphey type Lewes gives the following
table:
___________________________________________________________
| | | | | |
| | | Gas | | Candles |
| Burner. | Pressure, | Consumed, | Light in | per |
| | Inches | Cubic Feet | Candles. | Cubic Foot. |
| | | per Hour. | | |
|_________|___________|____________|__________|_____________|
| | | | | |
| No. 6 | 2.0 | 0.155 | 0.794 | 5.3 |
| " 8 | 2.0 | 0.27 | 3.2 | 11.6 |
| " 15 | 2.0 | 0.40 | 8.0 | 20.0 |
| " 25 | 2.0 | 0.65 | 17.0 | 26.6 |
| " 30 | 2.0 | 0.70 | 23.0 | 32.85 |
| " 42 | 2.0 | 1.00 | 34.0 | 34.0 |
|_________|___________|____________|__________|_____________|
From burners of the Billwiller type Lewes obtained in 1899 the values:
___________________________________________________________
| | | | | |
| | | Gas | | Candles |
| Burner. | Pressure, | Consumed, | Light in | per |
| | Inches | Cubic Feet | Candles. | Cubic Foot. |
| | | per Hour. | | |
|_________|___________|____________|__________|_____________|
| | | | | |
| No. 1 | 2.0 | 0.5 | 7.0 | 11.0 |
| " 2 | 2.0 | 0.75 | 21.0 | 32.0 |
| " 3 | 2.0 | 0.75 | 28.0 | 37.3 |
| " 4 | 3.0 | 1.2 | 48.0 | 40.0 |
| " 5 | 3.5 | 2.0 | 76.0 | 38.0 |
|_________|___________|____________|__________|_____________|
Neuberg gives these figures for different burners (1900) as supplied by
Pintsch:
______________________________________________________________________
| | | | | |
| | Gas | | Candles | |"w
| Burner. | Pressure, | Consumed, | Light in | per |
| | Inches | Cubic Feet | Candles. | Cubic Foot. |
| | | per Hour. | | |
|____________________|___________|____________|__________|_____________|
| | | | | |
| No. 0, slit burner | 3.9 | 1.59 | 59.2 | 37.3 |
| " 00000 fishtail | 1.6 | 0.81 | 31.2 | 38.5 |
| Twin burner No. 1 | 3.2 | 0.32 | 13.1 | 40.8 |
| " " " 2 | 3.2 | 0.53 | 21.9 | 41.3 |
| " " " 3 | 3.2 | 0.74 | 31.0 | 41.9 |
| " " " 4 | 3.2 | 0.95 | 39.8 | 41.9 |
|____________________|___________|____________|__________|_____________|
The actual candle-power developed by each burner was not quoted by
Neuberg, and has accordingly been calculated from his efficiency values.
It is noteworthy, and in opposition to what has been found by other
investigators as well as to strict theory, that Neuberg represents the
efficiencies to be almost identical in all sizes of the same description
of burner, irrespective of the rate at which it consumes gas.
Writing in 1902, Capelle gave for Stadelmann's twin injector burners the
following figures; but as he examined each burner at several different
pressures, the values recorded in the second, third, and fourth columns
are maxima, showing the highest candle-power which could be procured from
each burner when the pressure was adjusted so as to cause consumption to
proceed at the most economical rate. The efficiency values in the fifth
column, however, are the mean values calculated so as to include all the
data referring to each burner. Capelle's results have been reproduced
from the original on the basis that 1 _bougie décimale_ equals 0.98
standard English candle, which is the value he himself ascribes to it (1
_bougie décimale_ equals 1.02 candles is the value now accepted).
_____________________________________________________________________
| | | | | |
| Nominal | Best | Actual Consumption | Maximum | Average |
| Consumption,| Pressure| at Stated Pressure. | Light in | Candles per|
| Litres. | Inches. | Cubic Feet per Hour.| Candles. | Cubic Foot.|
|_____________|_________|_____________________|__________|____________|
| | | | | |
| 10 | 3.5 | 0.40 | 8.4 | 21.1 |
| 15 | 2.8 | 0.46 | 16.6 | 33.3 |
| 20 | 3.9 | 0.64 | 25.1 | 40.0 |
| 25 | 3.5 | 0.84 | 37.8 | 46.1 |
| 30 | 3.5 | 0.97 | 48.2 | 49.4 |
|_____________|_________|_____________________|__________|____________|
Some testings of various self-luminous burners of which the results were
reported by R. Granjon in 1907, gave the following results for the duty
of each burner, when the pressure was regulated for each burner to that
which afforded the maximum illuminating duty. The duty in the original
paper is given in litres per Carcel-hour. The candle has been taken as
equal to 0.102 Carcel for the conversion to candles per cubic foot.
___________________________________________________________________
| | | | |
| | Nominal | Best | Duty. Candles |
| Burner. | Consumption.| Pressure. | per cubic foot. |
|_______________________|_____________|__________ |_________________|
| | | | |
| | Litres. | Inches. | |
| Twin . . . . | 10 | 2.76 | 21.2 |
| " . . . . | 20 | 2.76 | 23.5 |
| " . . . . | 25 | 3.94 | 30.2 |
| " . . . . | 30 | 3.94-4.33 | 44.8 |
| ", (pair of flames) | 35 | 3.55-3.94 | 45.6 |
| Bray's "Manchester" | 6 | 1.97 | 18.8 |
| " | 20 | 1.97 | 35.6 |
| " | 40 | 2.36 | 42.1 |
| Rat-tail . . . | 5 | 5.5 | 21.9 |
| " . . . | 8 | 4.73 | 25.0 |
| Slit or batswing . | 30 | 1.97-2.36 | 37.0 |
|_______________________|_____________|___________|_________________|
Granjon has concluded from his investigations that the Manchester or
fish-tail burners are economical when they consume 0.7 cubic foot per
hour and when the pressure is between 2 and 2.4 inches. When these
burners are used at the pressure most suitable for twin burners their
consumption is about one-third greater than that of the latter per
candle-hour. The 25 to 35 litres-per-hour twin burners should be used at
a pressure higher by about 1 inch than the 10 to 20 litres-per-hour twin
burners.
At the present time, when the average burner has a smaller hourly
consumption than 1 foot per hour, it is customary in Germany to quote the
mean illuminating value of acetylene in self-luminous burners as being 1
Hefner unit per 0.70 litre, which, taking
1 Hefner unit = 0.913 English candle
1 English candle = 1.095 Hefner units,
works out to an efficiency of 37 candles per foot in burners probably
consuming between 0.5 and 0.7 foot per hour.
Even when allowance is made for the difficulties in determining
illuminating power, especially when different photometers, different
standards of light, and different observers are concerned, it will be
seen that these results are too irregular to be altogether trustworthy,
and that much more work must be done on this subject before the economy
of the acetylene flame can be appraised with exactitude. However, as
certain fixed data are necessary, the authors have studied those and
other determinations, rejecting some extreme figures, and averaging the
remainder; whence it appears that on an average twin-injector burners of
different sizes should yield light somewhat as follows:
_______________________________________________________
| | | |
| Size of Burner in | Candle-power | Candles |
| Cubic Feet per Hour. | Developed. | per Cubic Foot. |
|______________________|______________|_________________|
| | | |
| 0.5 | 18.0 | 35.9 |
| 0.7 | 27.0 | 38.5 |
| 1.0 | 45.6 | 45.6 |
|______________________|______________|_________________|
In the tabular statement in Chapter I. the 0.7-foot burner was taken as
the standard, because, considering all things, it seems the best, to
adopt for domestic purposes. The 1-foot burner is more economical when in
the best condition, but requires a higher gas pressure, and is rather too
powerful a unit light for good illuminating effect; the 0.5 burner
naturally gives a better illuminating effect, but its economy is
surpassed by the 0.7-foot burner, which is not too powerful for the human
eye.
For convenience of comparison, the illuminating powers and duties of the
0.5- and 0.7-foot acetylene burners may be given in different ways:
ILLUMINATING POWER OF SELF-LUMINOUS ACETYLENE.
_0.7-foot Burner._ | _Half-foot Burner._
|
1 litre = 1.36 candles. | 1 litre = 1.27 candles.
1 cubic foot = 38.5 candles. | 1 cubic foot = 35.9 candles.
1 candle = 0.736 litre. | 1 candle = 0.79 litre.
1 candle = 0.026 cubic foot. | 1 candle = 0.028 cubic foot.
If the two streams of gas impinge at an angle of 90°, twin-injector
burners for acetylene appear to work best when the gas enters them at a
pressure of 2 to 2.5 inches; for a higher pressure the angle should be
made a little acute. Large burners require to have a wider distance
between the jets, to be supplied with acetylene at a higher pressure, and
to be constructed with a smaller angle of impingement. Every burner, of
whatever construction and size, must always be supplied with gas at its
proper pressure; a pressure varying from time to time is fatal.
It is worth observing that although injector burners are satisfactory in
practice, and are in fact almost the only jets yet found to give
prolonged satisfaction, the method of injecting air below the point of
combustion in a self-luminous burner is in some respects wrong in
principle. If acetylene can be consumed without polymerisation in burners
of the simple fish-tail or bat's-wing type, it should show a higher
illuminating efficiency. In 1902 Javal stated that it was possible to
burn thoroughly purified acetylene in twin non-injector burners, provided
the two jets, made of steatite as usual, were arranged horizontally
instead of obliquely, the two streams of gas then meeting at an angle of
180°, so as to yield an almost circular flame. According to Javal,
whereas carbonaceous growths were always produced in non-injector
acetylene burners with either oblique or horizontal jets, in the former
case the growths eventually distorted the gas orifices, but in the latter
the carbon was deposited in the form of a tube, and fell off from the
burner by its own weight directly it had grown to a length of 1.2 or 1.5
millimetres, leaving the jets perfectly clear and smooth. Javal has had
such a burner running for 10 or 12 hours per day for a total of 2071
hours; it did not need cleaning out on any occasion, and its consumption
at the end of the period was the same as at first. He found that it was
necessary that the tips should be of steatite, and not of metal or glass;
that the orifices should be drilled in a flat surface rather than at the
apex of a cone, and that the acetylene should be purified to the utmost
possible extent. Subsequent experience has demonstrated the possibility
of constructing non-injector burners such as that shown in Fig. 13, which
behave satisfactorily even though the jets are oblique. But with such
burners trouble will inevitably ensue unless the gas is always purified
to a high degree and is tolerably dry and well filtered. Non-injector
burners should not be used unless special care is taken to insure that
the installation is consistently operated in an efficient manner in these
respects.
GLOBES, &C.--It does not fall within the province of the present volume
to treat at length of chimneys, globes, or the various glassware which
may be placed round a source of light to modify its appearance. It should
be remarked, however, that obedience to two rules is necessary for
complete satisfaction in all forms of artificial illumination. First, no
light much stronger in intensity than a single candle ought ever to be
placed in such a position in an occupied room that its direct rays can
reach the eye, or the vision will be temporarily, and may be permanently,
injured. Secondly, unless economy is to be wholly ignored, no coloured or
tinted globe or shade should ever be put round a source of artificial
light. The best material for the construction of globes is that which
possesses the maximum of translucency coupled with non-transparency,
_i.e._, a material which passes the highest proportion of the light
falling upon it, and yet disperses that light in such different
directions that the glowing body cannot be seen through the globe. Very
roughly speaking, plain white glass, such as that of which the chimneys
of oil-lamps and incandescent gas-burners are composed, is quite
transparent, and therefore affords no protection to the eyesight; a
protective globe should be rather of ground or opal glass, or of plain
glass to which a dispersive effect has been given by forming small prisms
on its inner or outer surface, or both. Such opal, ground, or dispersive
shades waste much light in terms of illuminating power, but waste
comparatively little in illuminating effect well designed, they may
actually increase the illuminating effect in certain positions; a tinted
globe, even if quite plain in figure, wastes both illuminating power and
effect, and is only to be tolerated for so-believed aesthetic reasons.
Naturally no globe must be of such figure, or so narrow at either
orifice, as to distort the shape of the unshaded acetylene flame--it is
hardly necessary to say this now, but some years ago coal-gas globes were
constructed with an apparent total disregard of this fundamental point.
CHAPTER IX
INCANDESCENT BURNERS--HEATING APPARATUS--MOTORS--AUTOGENOUS SOLDERING
MERITS OF LIGHTING BY INCANDESCENT MANTLES.--It has already been shown
that acetylene bases its chief claim for adoption as an illuminant in
country districts upon the fact that, when consumed in simple self-
luminous burners, it gives a light comparable in all respects save that
of cost to the light of incandescent coal-gas. The employment of a mantle
is still accompanied by several objections which appear serious to the
average householder, who is not always disposed either to devote
sufficient attention to his burners to keep them in a high state of
efficiency or to contract for their maintenance by the gas company or
others. Coal-gas cannot be burnt satisfactorily on the incandescent
system unless the glass chimneys and shades are kept clean, unless the
mantles are renewed as soon as they show signs of deterioration, and,
perhaps most important of all, unless the burners are frequently cleared
of the dust which collects round the jets. For this reason luminous
acetylene ranks with luminous coal-gas in convenience and simplicity,
while ranking with incandescent coal-gas in hygienic value. Very similar
remarks apply to paraffin, and, in certain countries, to denatured
alcohol. Since those latter illuminants are also available in rural
places where coal-gas is not laid on, luminous acetylene is a less
advantageous means of procuring artificial light than paraffin (and on
occasion than coal-gas and alcohol when the latter fuels are burnt under
the mantle), if the pecuniary aspect of the question is the only one
considered. Such a comparison, however, is by no means fair; for if coal-
gas, paraffin, and alcohol can be consumed on the incandescent system, so
can acetylene; and if acetylene is hygienically equal to incandescent
coal-gas, it is superior thereto when also burnt under the mantle.
Nevertheless there should be one minor but perfectly irremediable defect
in incandescent acetylene, viz., a sacrifice of that characteristic
property of the luminous gas to emit a light closely resembling that of
the sun in tint, which was mentioned in Chapter 1. Self-luminous
acetylene gives the whitest light hitherto procurable without special
correction of the rays, because its light is derived from glowing
particles of carbon which happen to be heated (because of the high flame
temperature) to the best possible temperature for the emission of pure
white light. The light of any combustible consumed on the "incandescent"
system is derived from glowing particles of ceria, thoria, or similar
metallic oxides; and the character or shade of the light they emit is a
function, apart from the temperature to which they are raised, of their
specific chemical nature. Still, the light of incandescent acetylene is
sufficiently pleasant, and according to Caro is purer white than that of
incandescent coal-gas; but lengthy tests carried out by one of the
authors actually show it to be appreciably inferior to luminous acetylene
for colour-matching, in which the latter is known almost to equal full
daylight, and to excel every form of artificial light except that of the
electric arc specially corrected by means of glass tinted with copper
salts.
CONDITIONS FOR INCANDESCENT ACETYLENE LIGHTING.--For success in the
combustion of acetylene on the incandescent system, however, several
points have to be observed. First, the gas must be delivered at a
strictly constant pressure to the burner, and at one which exceeds a
certain limit, ranging with different types and different sizes of burner
from 2 to 4 or 5 inches of water. (The authors examined, as long ago as
1903, an incandescent burner of German construction claimed to work at a
pressure of 1.5 inches, which it was almost impossible to induce to fire
back to the jets however slowly the cock was manipulated, provided the
pressure of the gas was maintained well above the point specified. But
ordinarily a pressure of about 4 inches is used with incandescent
acetylene burners.) Secondly, it is necessary that the acetylene shall at
all times be free from appreciable admixture with air, even 0.5 per cent,
being highly objectionable according to Caro; so that generators
introducing any noteworthy amount of air into the holder each time their
decomposing chambers are opened for recharging are not suitable for
employment when incandescent burners are contemplated. The reason for
this will be more apparent later on, but it depends on the obvious fact
that if the acetylene already contains an appreciable proportion of air,
when a further quantity is admitted at the burner inlets, the gaseous
mixture contains a higher percentage of oxygen than is suited to the size
and design of the burner, so that flashing back to the injector jets is
imminent at any moment, and may be determined by the slightest
fluctuation in pressure--if, indeed, the flame will remain at the proper
spot for combustion at all. Thirdly, the fact that the acetylene which is
to be consumed under the mantle must be most rigorously purified from
phosphorus compounds has been mentioned in Chapter V. Impure acetylene
will often destroy a mantle in two or three hours; but with highly
purified gas the average life of a mantle may be taken, according to
Giro, at 500 or 600 hours. It is safer, however, to assume a rather
shorter average life, say 300 to 400 burning hours. Fourthly, owing to
the higher pressure at which acetylene must be delivered to an
incandescent burner and to the higher temperature of the acetylene flame
in comparison with coal-gas, a mantle good enough to give satisfactory
results with the latter does not of necessity answer with acetylene; in
fact, the authors have found that English Welsbach coal-gas mantles of
the small sizes required by incandescent acetylene burners are not
competent to last for more than a very few hours, although, in identical
conditions, mantles prepared specially for use with acetylene have proved
durable. The atmospheric acetylene flame, too, differs in shape from an
atmospheric flame of coal-gas, and it does not always happen that a coal-
gas mantle contracts to fit the former; although it usually emits a
better light (because it fits better) after some 20 hours use than at
first. Caro has stated that to derive the best results a mantle needs to
contain a larger proportion of ceria than the 1 per cent. present in
mantles made according to the Welsbach formula, that it should be
somewhat coarser in mesh, and have a large orifice at the head. Other
authorities hold that mantles for acetylene, should contain other rare
earths besides the thoria and ceria of which the coal-gas mantles almost
wholly consist. It seems probable, however, that the composition of the
ordinary impregnating fluid need not be varied for acetylene mantles
provided it is of the proper strength and the mantles are raised to a
higher temperature in manufacture than coal-gas mantles by the use of
either coal-gas at very high pressure or an acetylene flame. The
thickness of the substance of the mantle cannot be greatly increased with
a view to attaining greater stability without causing a reduction in the
light afforded. But the shape should be such that the mantle conforms as
closely as possible to the acetylene Bunsen flame, which differs slightly
with different patterns of incandescent burner heads. According to L.
Cadenel, the acetylene mantle should be cylindrical for the lower two-
thirds of its length, and slightly conical above, with an opening of
moderate size at the top. The head of the mantle should be of slighter
construction than that of coal-gas mantles. Fifthly, generators belonging
to the automatic variety, which in most forms inevitably add more or less
air to the acetylene every time they are cleaned or charged, appear to
have achieved most popularity in Great Britain; and these frequently do
not yield a gas fit for use with the mantle. This state of affairs, added
to what has just been said, makes it difficult to speak in very
favourable terms of the incandescent acetylene light for use in Great
Britain. But as the advantages of an acetylene not contaminated with air
are becoming more generally recognised, and mantles of several different
makes are procurable more cheaply, incandescent acetylene is now more
practicable than hitherto. Carburetted acetylene or "carburylene," which
is discussed later, is especially suitable for use with mantle burners.
ATMOSPHERIC ACETYLENE BURNERS.--The satisfactory employment of acetylene
in incandescent burners, for boiling, warming, and cooking purposes, and
also to some extent as a motive power in small engines, demands the
production of a good atmospheric or non-luminous flame, _i.e._, the
construction of a trustworthy burner of the Bunsen type.
This has been exceedingly difficult to achieve for two reasons: first,
the wide range over which mixtures of acetylene and air are explosive;
secondly, the high speed at which the explosive wave travels through such
a mixture. It has been pointed out in Chapter VIII. that a Bunsen burner
is one in which a certain proportion of air is mixed with the gas before
it arrives at the actual point of ignition; and as that proportion must
be such that the mixture falls between the upper and lower limits of
explosibility, there is a gaseous mixture in the burner tube between the
air inlets and the outlet which, if the conditions are suitable, will
burn with explosive force: that is to say, will fire back to the air jets
when a light is applied to the proper place for combustion. Such an
explosion, of course, is far too small in extent to constitute any danger
to person or property; the objection to it is simply that the shock of
the explosion is liable to fracture the fragile incandescent mantle,
while the gas, continuing to burn within the burner tube (in the case of
a warming or cooking stove), blocks up that tube with carbon, and
exhibits the other well-known troubles of a coal-gas stove which has
"fired back."
It has been shown, however, in Chapter VI. that the range over which
mixtures of acetylene and air are explosive depends on the size of the
vessel, or more particularly on the diameter of the tube, in which they
are stored; so that if the burner tube between the air inlets and the
point of ignition can be made small enough in diameter, a normally
explosive mixture will cease to exhibit explosive properties. Manifestly,
if a tube is made very small in diameter, it will only pass a small
volume of gas, and it may be useless for the supply of an atmospheric
burner; but Le Chatelier's researches have proved that a tube may be
narrowed at one spot only, in such fashion that the explosive wave
refuses to pass the constriction, while the virtual diameter of the tube,
as far as passage of gas is concerned, remains considerably larger than
the size of the constriction itself. Moreover, inasmuch as the speed of
propagation of the explosion is strictly fixed by the conditions
prevailing, if the speed at which the mixture, of acetylene and air
travels from the air inlets to the point of ignition is more rapid than
the speed at which the explosion tends to travel from the point of
ignition to the air inlets, the said mixture of acetylene and air will
burn quietly at the orifice without attempting to fire backwards into the
tube. By combining together these two devices: by delivering the
acetylene to the injector jet at a pressure sufficient to drive the
mixture of gas and air forward rapidly enough, and by narrowing the
leading tube either wholly or at one spot to a diameter small enough, it
is easy to make an atmospheric burner for acetylene which behaves
perfectly as long as it is fairly alight, and the supply of gas is not
checked; but further difficulties still remain, because at the instant of
lighting and extinguishing, i.e., while the tap is being turned on or
off, the pressure of the gas is too small to determine a flow of
acetylene and air within the tube at a speed exceeding that of the
explosive wave; and therefore the act of lighting or extinguishing is
very likely to be accompanied by a smart explosion severe enough to split
the mantle, or at least to cause the burner to fire back. Nevertheless,
after several early attempts, which were comparative failures,
atmospheric acetylene burners have been constructed that work quite
satisfactorily, so that the gas has become readily available for use
under the mantle, or in heating stoves. Sometimes success has been
obtained by the employment of more than one small tube leading to a
common place of ignition, sometimes by the use of two or more fine wire-
gauze screens in the tube, sometimes by the addition of an enlarged head
to the burner in which head alone thorough mixing of the gas and air
occurs, and sometimes by the employment of a travelling sleeve which
serves more or less completely to block the air inlets.
DUTY OF INCANDESCENT ACETYLENE BURNERS.--Granting that the petty troubles
and expenses incidental to incandescent lighting are not considered
prohibitive--and in careful hands they are not really serious--
and that mantles suitable for acetylene are employed, the gas may be
rendered considerably cheaper to use per unit of light evolved by
consuming it in incandescent burners. In Chapter VIII. it was shown that
the modern self-luminous, l/2-foot acetylene burner emits a light of
about 1.27 standard English candles per litre-hour. A large number of
incandescent burners, of German and French construction, consuming from
7.0 to 22.2 litres per hour at pressures ranging between 60 and 120
millimetres have been examined by Caro, who has found them to give lights
of from 10.8 to 104.5 Hefner units, and efficiencies of from 2.40 to 5.50
units per litre-hour. Averaging his results, it may be said that
incandescent burners consuming from 10 to 20 litres per hour at pressures
of 80 or 100 millimetres yield a light of 4.0 Hefner units per litre-
hour. Expressed in English terms, incandescent acetylene burners
consuming 0.5 cubic foot per hour at a pressure of 3 or 4 inches give the
duties shown in the following table, which may advantageously be compared
with that printed in Chapter VIII., page 239, for the self-luminous gas:
ILLUMINATING POWER OF INCANDESCENT ACETYLENE.
HALF-FOOT BURNERS.
1 litre = 3.65 candles | 1 candle = 0.274 litre.
1 cubic foot = 103.40 candles. | 1 candle = 0.0097 cubic foot.
A number of tests of the Güntner or Schimek incandescent burners of the
10 and 15 litres-per-hour sizes, made by one of the authors in 1906, gave
the following average results when tested at a pressure of 4 inches:
_________________________________________________________________
| | | | |
| Nominal size | Rate of Consumption per | Light in | Duty |
| of Burner. | Hour | Candles | Candles per |
| | | | Cubic Foot |
|______________|_________________________|__________|_____________|
| | | | | |
| Litres. | Cubic Foot | Litres | | |
| 10 | 0.472 | 13.35 | 46.0 | 97.4 |
| 15 | 0.663 | 18.80 | 70.0 | 105.5 |
|______________|____________|____________|__________|_____________|
These figures indicate that the duty increases slightly with the size of
the burner. Other tests showed that the duty increased more considerably
with an increase of pressure, so that mantles used, or which had been
previously used, at a pressure of 5 inches gave duties of 115 to 125
candles per cubic foot.
It should be noted that the burners so far considered are small, being
intended for domestic purposes only; larger burners exhibit higher
efficiencies. For instance, a set of French incandescent acetylene
burners examined by Fouché showed:
_________________________________________________________________
| | | | | |
| Size of Burner | Pressure | Cubic Feet | Light in | Candles per |
| in Litres. | Inches. | per Hour. | Candles. | Cubic Feet. |
|________________|__________|____________|__________|_____________|
| | | | | |
| 20 | 5.9 | 0.71 | 70 | 98.6 |
| 40 | 5.9 | 1.41 | 150 | 106.4 |
| 70 | 5.9 | 2.47 | 280 | 113.4 |
| 120 | 5.9 | 4.23 | 500 | 118.2 |
|________________|__________|____________|__________|_____________|
By increasing the pressure at which acetylene is introduced into burners
of this type, still larger duties may be obtained from them:
_________________________________________________________________
| | | | | |
| Size of Burner | Pressure | Cubic Feet | Light in | Candles per |
| in Litres. | Inches. | per Hour. | Candles. | Cubic Feet. |
|________________|__________|____________|__________|_____________|
| | | | | |
| 55 | 39.4 | 1.94 | 220 | 113.4 |
| 100 | 39.4 | 3.53 | 430 | 121.8 |
| 180 | 39.4 | 6.35 | 820 | 129.1 |
| 260 | 27.6 | 9.18 | 1300 | 141.6 |
|________________|__________|____________|__________|_____________|
High-power burners such as these are only fit for special purposes, such
as lighthouse illumination, or optical lantern work, &c.; and they
naturally require mantles of considerably greater tenacity than those
intended for employment with coal-gas. Nevertheless, suitable mantles can
be, and are being, made, and by their aid the illuminating duty of
acetylene can be raised from the 30 odd candles per foot of the common
0.5-foot self-luminous jet to 140 candles or more per foot, which is a
gain in efficiency of 367 per cent., or, neglecting upkeep and sundries
and considering only the gas consumed, an economy of nearly 79 per cent.
In 1902, working apparently with acetylene dissolved under pressure in
acetone (_cf._ Chapter XI.), Lewes obtained the annexed results with
the incandescent gas:
________________________________________________________
| | | | |
| Pressure. | Cubic Feet | Candle Power | Candles per |
| Inches. | per Hour. | Developed. | Cubic Foot. |
|___________|_____________|______________|______________|
| | | | |
| 8 | 0.883 | 65 | 73.6 |
| 9 | 0.94 | 72 | 76.0 |
| 10 | 1.00 | 146 | 146.0 |
| 12 | 1.06 | 150 | 141.2 |
| 15 | 1.25 | 150 | 120.0 |
| 20 | 1.33 | 166 | 124.8 |
| 25 | 1.50 | 186 | 123.3 |
| 40 | 2.12 | 257 | 121.2 |
|___________|_____________|______________|______________|
It will be seen that although the total candle-power developed increases
with the pressure, the duty of the burner attained a maximum at a
pressure of 10 inches. This is presumably due to the fact either that the
same burner was used throughout the tests, and was only intended to work
at a pressure of 10 inches or thereabouts, or that the larger burners
were not so well constructed as the smaller ones. Other investigators
have not given this maximum of duty with a medium-sized or medium-driven
burner; but Lewes has observed a similar phenomenon in the case of 0.7 to
0.8 cubic foot self-luminous jets.
Figures, however, which seem to show that the duty of incandescent
acetylene does not always rise with the size of the burner or with the
pressure at which the gas is delivered to it, have been published in
connexion with the installation at the French lighthouse at Chassiron,
the northern point of the Island of Oléron. Here the acetylene is
generated in hand-fed carbide-to-water generators so constructed as to
give any pressure up to nearly 200 inches of water column; purified by
means of heratol, and finally delivered to a burner composed of thirty-
seven small tubes, which raises to incandescence a mantle 55 millimetres
in diameter at its base. At a pressure of 7.77 inches of water, the
burner passes 3.9 cubic feet of acetylene per hour, and at a pressure of
49.2 inches (the head actually used) it consumes 20.06 cubic feet per
hour. As shown by the following table, such increment of gas pressure
raises the specific intensity of the light, _i.e._, the illuminating
power per unit of incandescent surface, but it does not appreciably raise
the duty or economy of the gas. Manifestly, in terms of duty alone, a
pressure of 23.6 inches of water-column is as advantageous as the higher
Chassiron figures; but since intensity of light is an important matter in
a lighthouse, it is found better on the whole to work the generators at a
pressure of 49.2 inches. In studying these figures referring to the
French lighthouse, it is interesting to bear in mind that when ordinary
six-wick petroleum oil burners wore used in the same place, the specific
intensity of the light developed was 75 candle-power per square inch, and
when that plant was abandoned in favour of an oil-gas apparatus, the
incandescent burner yielded 161 candle-power per square inch;
substitution of incandescent acetylene under pressure has doubled the
brilliancy of the light.
___________________________________________________________
| | | |
| | Duty. | Intensity. |
| Pressure in Inches. | Candle-power per | Candle-power per |
| | Cubic Foot. | Square Inch. |
|_____________________|__________________|__________________|
| | | |
| 7.77 | 105.5 | 126.0 |
| 23.60 | 106.0 | 226.0 |
| 31.50 | 110.0 | 277.0 |
| 39.40 | 110.0 | 301.0 |
| 47.30 | 106.0 | 317.0 |
| 49.20 | 104.0 | 324.9 |
| 196.80 | 110.0 | 383.0 |
|_____________________|__________________|__________________|
When tested in modern burners consuming between 12 and 18 litres per hour
at a pressure of 100 millimetres (4 inches), some special forms of
incandescent mantles constructed of ramie fibre, which in certain
respects appears to be better suited than cotton for use with acetylene,
have shown the following degree of loss in illuminating power after
prolonged employment (Caro):
_Luminosity in Hefner Units._
________________________________________________________
| | | | | |
| Mantle. | New. | After | After | After |
| | | 100 Hours. | 200 Hours. | 400 Hours. |
|_________|_______|____________|____________|____________|
| | | | | |
| No. 1. | 53.2 | 51.8 | 50.6 | 49.8 |
| No. 2. | 76.3 | 75.8 | 73.4 | 72.2 |
| No. 3. | 73.1 | 72.5 | 70.1 | 68.6 |
|_________|_______|____________|____________|____________|
It will be seen that the maximum loss of illuminating power in 400 hours
was 6.4 per cent., the average loss being 6.0 per cent.
TYPICAL INCANDESCENT BURNERS.--Of the many burners for lighting by the
use of incandescent mantles which have been devised, a few of the more
widely used types may be briefly referred to. There is no doubt that
finality in the design of these burners has not yet been reached, and
that improvements in the direction of simplification of construction and
in efficiency and durability will continue to be made.
Among the early incandescent burners, one made by the Allgemeine Carbid
und Acetylen Gesellschaft of Berlin in 1900 depended on the narrowness of
the mixing tube and the proportioning of the gas nipple and air inlets to
prevent lighting-back. There was a wider concentric tube round the upper
part of the mixing tube, and the lower part of the mantle fitted round
this. The mouth of the mixing tube of this 10-litres-per-hour burner was
0.11 inch in diameter, and the external diameter of the middle
cylindrical part of the mixing tube was 0.28 inch. There was no gauze
diaphragm or stuffing, and firing-back did not occur until the pressure
was reduced to about 1.5 inches. The same company later introduced a
burner differing in several important particulars from the one just
described. The comparatively narrow stem of the mixing tube and the
proportions of the gas nipple and air inlets were retained, but the
mixing tube was surmounted by a wide chamber or burner head, in which
naturally there was a considerable reduction in the rate of flow of the
gas. Consequently it was found necessary to introduce a gauze screen into
the burner head to prevent firing back. The alterations have resulted in
the lighting duty of the burner being considerably improved. Among other
burners designed about 1900 may be mentioned the Ackermann, the head of
which consisted of a series of tubes from each of which a jet of flame
was produced, the Fouché, the Weber, and the Trendel. Subsequently a
tubular-headed burner known as the Sirius has been produced for the
consumption of acetylene at high pressure (20 inches and upwards).
The more recent burners which have been somewhat extensively used include
the "Schimek," made by W. Güntner of Vienna, which is shown in Fig. 19.
It consists of a tapering narrow injecting nozzle within a conical
chamber C which is open below, and is surmounted by the mixing tube over
which telescopes a tube which carries the enlarged burner head G, and the
chimney gallery D. There are two diaphragms of gauze in the burner head
to prevent firing back, and one in the nozzle portion of the burner. The
conical chamber has a perforated base-plate below which is a circular
plate B which rotates on a screw cut on the lower part of the nozzle
portion A of the burner. This plate serves as a damper to control the
amount of air admitted through the base of the conical chamber to the
mixing tube. There are six small notches in the lower edge of the conical
chamber to prevent the inflow of air being cut of entirely by the damper.
The mixing tube in both the 10-litre and the 15-litre burner is about
0.24 inch in internal diameter but the burner head is nearly 0.42 inch in
the 10-litre and 0.48 inch in the 15-litre burner. The opening in the
head of the burner through which the mixture of gas and air escapes to
the flame is 0.15 and 0.17 inch in diameter in these two sizes
respectively. The results of some testings made with Schimek burners have
been already given.
[Illustration: FIG. 19.--"SCHIMEK" BURNER.]
The "Knappich" burner, made by the firm of Keller and Knappich of
Augsburg, somewhat resembles the later pattern of the Allgemeine Carbid
und Acetylen Gesellschaft. It has a narrow mixing tube, viz., 0.2 inch in
internal diameter, and a wide burner head, viz., 0.63 inch in internal
diameter for the 25-litre size. The only gauze diaphragm is in the upper
part of the burner head. The opening in the cap of the burner head, at
which the gas burns, is 0.22 inch in diameter. The gas nipple extends
into a domed chamber at the base of the mixing tube, and the internal air
is supplied through four holes in the base-plate of that chamber. No
means of regulating the effective area of the air inlet holes are
provided.
The "Zenith" burner, made by the firm of Gebrüder Jacob of Zwickau, more
closely resembles the Schimek, but the air inlets are in the side of the
lower widened portion of the mixing tube, and are more or less closed by
means of an outside loose collar which may be screwed up and down on a
thread on a collar fixed to the mixing tube. The mixing tube is 0.24
inch, and the burner head 0.475 inch in internal diameter. The opening in
the cap of the burner is 0.16 inch in diameter. There is a diaphragm of
double gauze in the cap, and this is the only gauze used in the burner.
All the incandescent burners hitherto mentioned ordinarily have the gas
nipple made in brass or other metal, which is liable to corrosion, and
the orifice to distortion by heat or if it becomes necessary to remove
any obstruction from it. The orifice in the nipple is extremely small--
usually less than 0.015 inch--and any slight obstruction or distortion
would alter to a serious extent the rate of flow of gas through it, and
so affect the working of the burner. In order to overcome this defect,
inherent to metal nipples, burners are now constructed for acetylene in
which the nipple is of hard incorrodible material. One of these burners
has been made on behalf of the Office Central de l'Acétylène of Paris,
and is commonly known as the "O.C.A." burner. In it the nipple is of
steatite. On the inner mixing tube of this burner is mounted an elongated
cone of wire wound spirally, which serves both to ensure proper admixture
of the gas and air, and to prevent firing-back. There is no gauze in this
burner, and the parts are readily detachable for cleaning when required.
Another burner, in which metal is abolished for the nipple, is made by
Geo. Bray and Co., Ltd., of Leeds, and is shown in Fig. 20. In this
burner the injecting nipple is of porcelain.
[Illustration: FIG. 20.--BRAY'S INCANDESCENT BURNER.]
ACETYLENE FOR HEATING AND COOKING.--Since the problem of constructing a
trustworthy atmospheric burner has been solved, acetylene is not only
available for use in incandescent lighting, but it can also be employed
for heating or cooking purposes, because all boiling, most warming, and
some roasting stoves are simply arrangements for utilising the heat of a
non-luminous flame in one particular way. With suitable alterations in
the dimensions of the burners, apparatus for consuming coal-gas may be
imitated and made fit to burn acetylene; and as a matter of fact several
firms are now constructing such appliances, which leave little or nothing
to be desired. It may perhaps be well to insist upon the elementary point
which is so frequently ignored in practice, viz., that no stove, except
perhaps a small portable boiling ring, ought ever to be used in an
occupied room unless it is connected with a chimney, free from down-
draughts, for the products of combustion to escape into the outer air;
and also that no chimney, however tall, can cause an up-draught in all
states of the weather unless there is free admission of fresh air into
the room at the base of the chimney. Still, at the prices for coal,
paraffin oil, and calcium carbide which exist in Great Britain, acetylene
is not an economical means of providing artificial heat. If a 0.7 cubic
foot luminous acetylene burner gives a light of 27 candles, and if
ordinary country coal-gas gives light of 12 to 13 candles in a 5-foot
burner, one volume of acetylene is equally valuable with 15 or 16 volumes
of coal-gas when both are consumed in self-luminous jets; and if, with
the mantle, acetylene develops 99 candles per cubic foot, while coal-gas
gives in common practice 15 to 20 candles, one volume of acetylene is
equally valuable with 5 to 6-1/2 volumes of coal-gas when both are
consumed on the incandescent system; whereas, if the acetylene is burnt
in a flat flame, and the coal-gas under the mantle, 1 volume of the
former is equally efficient with 2 volumes of coal-gas as an artificial
illuminant. This last method of comparison being manifestly unfair,
acetylene may be said to be at least five times as efficient per unit of
volume as coal-gas for the production of light. But from the table given
on a later page it appears that as a source of artificial heat, acetylene
is only equal to about 2-3 times its volume of ordinary coal-gas.
Nevertheless, the domestic advantages of gas firing are very marked; and
when a properly constructed stove is properly installed, the hygienic
advantages of gas-firing are alone equally conspicuous--for the disfavor
with which gas-firing is regarded by many physicians is due to experience
gained with apparatus warming principally by convection [Footnote:
Radiant heat is high-temperature heat, like the heat emitted by a mass of
red-hot coke; convected heat is low-temperature heat, invisible to the
eye. Radiant heat heats objects first, and leaves them to warm the air;
convected heat is heat applied directly to air, and leaves the air to
warm objects afterwards. On all hygienic grounds radiant heat is better
than convected heat, but the latter is more economical. By an absurd and
confusing custom, that particular warming apparatus (gas, steam, or hot
water) which yields practically no radiant heat, and does all its work by
convection, is known to the trade as a "radiator."] instead of radiation;
or to acquaintance with intrinsically better stoves either not connected
to any flues or connected to one deficient in exhausting power. In these
circumstances, whenever an installation of acetylene has been laid down
for the illumination of a house or district, the merit of convenience may
outweigh the defect of extravagance, and the gas may be judiciously
employed in a boiling ring, or for warming a bedroom; while, if pecuniary
considerations are not paramount, the acetylene may be used for every
purpose to which the townsman would apply his cheaper coal-gas.
The difficulty of constructing atmospheric acetylene burners in which the
flame would not be likely to strike back to the nipple has already been
referred to in connexion with the construction atmospheric burners for
incandescent lighting. Owing, however, to the large proportions of the
atmospheric burners of boiling rings and stove and in particular to the
larger bore of their mixing tube, the risk of the flame striking back is
greater with them, than with incandescent lighting burners. The greatest
trouble is presented at lighting, and when the pressure of the gas-supply
is low. The risk of firing-back when the burner is lighted is avoided in
some forms of boiling rings, &c., by providing a loose collar which can
be slipped over the air inlets of the Bunsen tube before applying a light
to the burner, and slipped clear of them as soon as the burner is alight.
Thus at the moment of lighting, the burner is converted temporarily into
one of the non-atmospheric type, and after the flame has thus been
established at the head or ring of the burner, the internal air-supply is
started by removing the loose collar from the air inlets, and the flame
is thus made atmospheric. In these conditions it does not travel
backwards to the nipple. In other heating burners it is generally
necessary to turn on the gas tap a few seconds before applying a light to
the burner or ring or stove; the gas streaming through the mixing tube
then fills it with acetylene and air mixed in the proper working
proportions, and when the light is applied, there is no explosion in the
mixing tube, or striking-back of the flame to the nipple.
Single or two-burner gas rings for boiling purposes, or for heating
cooking ovens, known as the "La Belle," made by Falk Stadelmann and Co.,
Ltd., of London, may be used at as low a gas pressure as 2 inches, though
they give better results at 3 inches, which is their normal working
pressure. The gas-inlet nozzle or nipple of the burner is set within a
spherical bulb in which are four air inlets. The mixing tube which is
placed at a proper distance in front of the nipple, is proportioned to
the rate of flow of the gas and air, and contains a mixing chamber with a
baffling pillar to further their admixture. A fine wire gauze insertion
serves to prevent striking-back of the flame. A "La Belle" boiling ring
consumes at 3 inches pressure about 48 litres or 1.7 cubic feet of
acetylene per hour.
ACETYLENE MOTORS.--The question as to the feasibility of developing
"power" from acetylene, _i.e._, of running an engine by means of the
gas, may be answered in essentially identical terms. Specially designed
gas-engines of 1, 3, 6, or even 10 h.p. work perfectly with acetylene,
and such motors are in regular employment in numerous situations, more
particularly for pumping water to feed the generators of a large village
acetylene installation. Acetylene is not an economical source of power,
partly for the theoretical reason that it is a richer fuel even than
coal-gas, and gas-engines would appear usually to be more efficient as
the fuel they burn is poorer in calorific intensity, _i.e._, in
heating power (which is explosive power) per unit of volume. The richer,
or more concentrated, any fuel in, the more rapidly does the explosion in
a mixture of that fuel with air proceed, because a rich fuel contains a
smaller proportion of non-inflammable gases which tend to retard
explosion than a poor one; and, in reason, a gas-engine works better the
more slowly the mixture of gas and air with which it is fed explodes.
Still, by properly designing the ports of a gas-engine cylinder, so that
the normal amount of compression of the charge and of expansion of the
exploded mixture which best suit coal-gas are modified to suit acetylene,
satisfactory engines can be constructed; and wherever an acetylene
installation for light exists, it becomes a mere question of expediency
whether the same fuel shall not be used to develop power, say, for
pumping up the water required in a large country house, instead of
employing hand labour, or the cheaper hot-air or petroleum motor. Taking
the mean of the results obtained by numerous investigators, it appears
that 1 h.p.-hour can be obtained for a consumption of 200 litres of
acetylene; whence it may be calculated that that amount of energy costs
about 3d. for gas only, neglecting upkeep, lubricating material
(which would be relatively expensive) and interest, &c.
Acetylene Blowpipes--The design of a satisfactory blowpipe for use with
acetylene had at first proved a matter of some difficulty, since the jet,
like that of an ordinary self-luminous burner, usually exhibited a
tendency to become choked with carbonaceous growths. But when acetylene
had become available for various purposes at considerable pressure, after
compression into porous matter as described in Chapter XI, the troubles
were soon overcome; and a new form of blowpipe was constructed in which
acetylene was consumed under pressure in conjunction with oxygen. The
temperature given by this apparatus exceeds that of the familiar oxy-
hydrogen blowpipe, because the actual combustible material is carbon
instead of hydrogen. When 2 atoms of hydrogen unite with 1 of oxygen to
form 1 molecule of gaseous water, about 59 large calories are evolved,
and when 1 atom of solid amorphous carbon unites with 2 atoms of oxygen
to form 1 molecule of carbon dioxide, 97.3 calories are evolved. In both
cases, however, the heat attainable is limited by the fact that at
certain temperatures hydrogen and oxygen refuse to combine to form water,
and carbon and oxygen refuse to form carbon dioxide--in other words,
water vapour and carbon dioxide dissociate and absorb heat in the process
at certain moderately elevated temperatures. But when 1 atom of solid
amorphous carbon unites with 1 atom of oxygen to form carbon monoxide,
29.1 [Footnote: Cf. Chapter VI., page 185.] large calories are produced,
and carbon monoxide is capable of existence at much higher temperatures
than either carbon dioxide or water vapour. In any gaseous hydrocarbon,
again, the carbon exists in the gaseous state, and when 1 atom of the
hypothetical gaseous carbon combines with 1 atom of oxygen to produce 1
molecule of carbon monoxide, 68.2 large calories are evolved. Thus while
solid amorphous carbon emits more heat than a chemically equivalent
quantity of hydrogen provided it is enabled to combine with its higher
proportion of oxygen, it emits less if only carbon monoxide is formed;
but a higher temperature can be attained in the latter case, because the
carbon monoxide is more permanent or stable. Gaseous carbon, on the other
hand, emits more heat than an equivalent quantity of hydrogen, [Footnote:
In a blowpipe flame hydrogen can only burn to gaseous, not liquid,
water.] even when it is only converted into the monoxide. In other words,
a gaseous fuel which consists of hydrogen alone can only yield that
temperature as a maximum at which the speed of the dissociation of the
water vapour reaches that of the oxidation of the hydrogen; and were
carbon dioxide the only oxide of carbon, a similar state of affairs would
be ultimately reached in the flame of a carbonaceous gas. But since in
the latter case the carbon dioxide does not tend to dissociate
completely, but only to lose one atom of oxygen, above the limiting
temperature for the formation of carbon dioxide, carbon monoxide is still
produced, because there is less dissociating force opposed to its
formation. Thus at ordinary temperatures the heat of combustion of
acetylene is 315.7 calories; but at temperatures where water vapour and
carbon dioxide no longer exist, there is lost to that quantity of 315.7
calories the heat of combustion of hydrogen (69.0) and twice that of
carbon monoxide (68.2 x 2 = 136.4); so that above those critical
temperatures, the heat of combustion of acetylene is only 315.7 - (69.0 +
136.4) = 110.3. [Footnote: When the heat of combustion of acetylene is
quoted as 315.7 calories, it is understood that the water formed is
condensed into the liquid state. If the water remains gaseous, as it must
do in a flame, the heat of formation is reduced by about 10 calories.
This does not affect the above calculation, because the heat of
combustion of hydrogen when the water remains gaseous is similarly 10
calories less than 69, _i.e._, 59, as mentioned above in the text.
Deleting the heat of liquefaction of water, the calculation referred to
becomes 305.7 - (59.0 + l36.4) = 110.3 as before.] This value of 110.3
calories is clearly made up of the heat of formation of acetylene itself,
and twice the heat of conversion of carbon into carbon monoxide,
_i.e._, for diamond carbon, 58.1 + 26.1 x 2 = 110.3; or for
amorphous carbon, 52.1 + 29.1 x 2 = 110.3. From the foregoing
considerations, it may be inferred that the acetylene-oxygen blowpipe can
be regarded as a device for burning gaseous carbon in oxygen; but were it
possible to obtain carbon in the state of gas and so to lead it into a
blowpipe, the acetylene apparatus should still be more powerful, because
in it the temperature would be raised, not only by the heat of formation
of carbon monoxide, but also by the heat attendant upon the dissociation
of the acetylene which yields the carbon.
Acetylene requires 2.5 volumes of oxygen to burn it completely; but in
the construction of an acetylene-oxygen blowpipe the proportion of oxygen
is kept below this figure, viz., at 1.1 to 1.8 volumes, so that the
deficiency is left to be made up from the surrounding air. Thus at the
jet of the blowpipe the acetylene dissociates and its carbon is oxidised,
at first no doubt to carbon monoxide only, but afterwards to carbon
dioxide; and round the flame of the gaseous carbon is a comparatively
cool, though absolutely very hot jacket of hydrogen burning to water
vapour in a mixture of oxygen and air, which protects the inner zone from
loss of heat. As just explained, theoretical grounds support the
conclusions at which Fouché has arrived, viz., that the temperature of
the acetylene-oxygen blowpipe flame is above that at which hydrogen will
combine with oxygen to form water, and that it can only be exceeded by
those found in a powerful electric furnace. As the hydrogen dissociated
from the acetylene remains temporarily in the free state, the flame of
the acetylene blowpipe, possesses strong reducing powers; and this,
coupled probably with an intensity of heat which is practically otherwise
unattainable, except by the aid of a high-tension electric current,
should make the acetylene-oxygen blowpipe a most useful piece of
apparatus for a large variety of metallurgical, chemical, and physical
operations. In Fouché's earliest attempts to design an acetylene
blowpipe, the gas was first saturated with a combustible vapour, such as
that of petroleum spirit or ether, and the mixture was consumed with a
blast of oxygen in an ordinary coal-gas blow-pipe. The apparatus worked
fairly well, but gave a flame of varying character; it was capable of
fusing iron, raised a pencil of lime to a more brilliant degree of
incandescence than the eth-oxygen burner, and did not deposit carbon at
the jet. The matter, however, was not pursued, as the blowpipe fed with
undiluted acetylene took its place. The second apparatus constructed by
Fouché was the high-pressure blowpipe, the theoretical aspect of which
has already been studied. In this, acetylene passing through a water-seal
from a cylinder where it is stored as a solution in acetone (_cf._
Chapter XI.), and oxygen coming from another cylinder, are each allowed
to enter the blowpipe at a pressure of 118 to 157 inches of water column
(_i.e._, 8.7 to 11.6 inches of mercury; 4.2 to 5.7 lb. per square
inch, or 0.3 to 0.4 atmosphere). The gases mix in a chamber tightly
packed with porous matter such as that which is employed in the original
acetylene reservoir, and finally issue from a jet having a diameter of 1
millimetre at the necessary speed of 100 to 150 metres per second.
Finding, however, that the need for having the acetylene under pressure
somewhat limited the sphere of usefulness of his apparatus, Fouché
finally designed a low-pressure blowpipe, in which only the oxygen
requires to be in a state of compression, while the acetylene is drawn
directly from any generator of the ordinary pattern that does not yield a
gas contaminated with air. The oxygen passes through a reducing valve to
lower the pressure under which it stands in the cylinder to that of 1 or
1.5 effective atmosphere, this amount being necessary to inject the
acetylene and to give the previously mentioned speed of escape from the
blowpipe orifice. The acetylene is led through a system of long narrow
tubes to prevent it firing-back.
AUTOGENOUS SOLDERING AND WELDING.--The blowpipe is suitable for the
welding and for the autogenous soldering or "burning" of wrought or cast
iron, steel, or copper. An apparatus consuming from 600 to 1000 litres of
acetylene per hour yields a flame whose inner zone is 10 to 15
millimetres long, and 3 to 4 millimetres in diameter; it is sufficiently
powerful to burn iron sheets 8 to 9 millimetres thick. By increasing the
supply of acetylene in proportion to that of the oxygen, the tip of the
inner zone becomes strongly luminous, and the flame then tends to
carburise iron; when the gases are so adjusted that this tip just
disappears, the flame is at its best for heating iron and steel. The
consumption of acetylene is about 75 litres per hour for each millimetre
of thickness in the sheet treated, and the normal consumption of oxygen
is 1.7 times as much; a joint 6 metres long can be burnt in 1 millimetre
plate per hour, and one of 1.5 metres in 10 millimetre plate. In certain
cases it is found economical to raise the metal to dull redness by other
means, say with a portable forge of the usual description, or with a
blowpipe consuming coal-gas and air. There are other forms of low-
pressure blowpipe besides the Fouché, in some of which the oxygen also is
supplied at low pressure. Apart from the use of cylinders of dissolved
acetylene, which are extremely convenient and practically indispensable
when the blowpipe has to be applied in confined spaces (as in repairing
propeller shafts on ships _in situ_), acetylene generators are now
made by several firms in a convenient transportable form for providing
the gas for use in welding or autogenous soldering. It is generally
supposed that the metal used as solder in soldering iron or steel by this
method must be iron containing only a trifling proportion of carbon (such
as Swedish iron), because the carbon of the acetylene carburises the
metal, which is heated in the oxy-acetylene flame, and would thereby make
ordinary steel too rich in carbon. But the extent to which the metal used
is carburised in the flame depends, as has already been indicated, on the
proper adjustment of the proportion of oxygen to acetylene. Oxy-acetylene
autogenous soldering or welding is applicable to a great variety of work,
among which may be mentioned repairs to shafts, locomotive frames,
cylinders, and to joints in ships' frames, pipes, boilers, and rails. The
use of the process is rapidly extending in engineering works generally.
Generators for acetylene soldering or welding must be of ample size to
meet the quickly fluctuating demands on them and must be provided with
water-seals, and a washer or scrubber and filter capable of arresting all
impurities held mechanically in the crude gas, and with a safety vent-
pipe terminating in the open at a distance from the work in hand. The
generator must be of a type which affords as little after-generation as
possible, and should not need recharging while the blowpipe is in use.
There should be a main tap on the pipe between the generator and the
blowpipe. It does not appear conclusively established that the gas
consumed should have been chemically purified, but a purifier of ample
size and charged with efficient material is undoubtedly beneficial. The
blowpipe must be designed so that it remains sufficiently cool to prevent
polymerisation of the acetylene and deposition of the resultant particles
of carbon or soot within it.
It is important to remember that if a diluent gas, such as nitrogen, is
present, the superior calorific power of acetylene over nearly all gases
should avail to keep the temperature of the flame more nearly up to the
temperature at which hydrogen and oxygen cease to combine. Hence a
blowpipe fed with air and acetylene would give a higher temperature than
any ordinary (atmospheric) coal-gas blowpipe, just as, as has been
explained in Chapter VI., an ordinary acetylene flame has a higher
temperature than a coal-gas flame. It is likely that a blowpipe fed with
"Lindé-air" (oxygen diluted with less nitrogen than in the atmosphere)
and acetylene would give as high a limelight effect as the oxy-hydrogen
or oxy-coal-gas blowpipe.
CHAPTER X
CARBURETTED ACETYLENE
Now that atmospheric or Bunsen burners for the consumption of acetylene
for use in lighting by the incandescent system and in heating have been
so much improved that they seem to be within measurable reach of a state
of perfection, there appears to be but little use at the present time for
a modified or diluted acetylene which formerly seemed likely to be
valuable for heating and certain other purposes. Nevertheless, the facts
relating to this so-called carburetted acetylene are in no way traversed
by its failure to establish itself as an active competitor with simple
acetylene for heating purposes, and since it is conceivable that the
advantages which from the theoretical standpoint the carburetted gas
undoubtedly possesses in certain directions may ultimately lead to its
practical utilisation for special purposes, it has been deemed expedient
to continue to give in this work an account of the principles underlying
the production and application of carburetted acetylene.
It has already been explained that acetylene is comparatively a less
efficient heating agent than it is an illuminating material, because, per
unit of volume, its calorific power is not so much greater than that of
coal-gas as is its illuminating capacity. It has also been shown that the
high upper explosive limit of mixtures of acetylene and air--a limit so
much higher than the corresponding figure with coal-gas and other gaseous
fuels--renders its employment in atmospheric burners (either for lighting
or for heating) somewhat troublesome, or dependent upon considerable
skill in the design of the apparatus. If, therefore, either the upper
explosive limit of acetylene could be reduced, or its calorific value
increased (or both), by mixing with it some other gas or vapour which
should not seriously affect its price and convenience as a self-luminous
illuminant, acetylene would compare more favourably with coal-gas in its
ready applicability to the most various purposes. Such a method has been
suggested by Heil, and has been found successful on the Continent. It
consists in adding to the acetylene a certain proportion of the vapour of
a volatile hydrocarbon, so as to prepare what is called "carburetted
acetylene." In all respects the method of making carburetted acetylene is
identical with that of making "air-gas," which was outlined in Chapter
I., viz., the acetylene coming from an ordinary generating plant is led
over or through a mass of petroleum spirit, or other similar product, in
a vessel which exposes the proper amount of superficial area to the
passing gas. In all respects save one the character of the product is
similar to that of air-gas, _i.e._, it is a mixture of a permanent
gas with a vapour; the vapour may possibly condense in part within the
mains if they are exposed to a falling temperature, and if the product is
to be led any considerable distance, deposition of liquid may occur
(conceivably followed by blockage of the mains) unless the proportion of
vapour added to the gas is kept below a point governed by local climatic
and similar conditions. But in one most important respect carburetted
acetylene is totally different from air-gas: partial precipitation of
spirit from air-gas removes more or less of the solitary useful
constituent of the material, reducing its practical value, and causing
the residue to approach or overpass its lower explosive limit (_cf._
Chapter I.); partial removal of spirit from carburetted acetylene only
means a partial reconversion of the material into ordinary acetylene,
increasing its natural illuminating power, lowering its calorific
intensity somewhat, and causing the residue to have almost its primary
high upper explosive limit, but essentially leaving its lower explosive
limit unchanged. Thus while air-gas may conceivably become inefficient
for every purpose if supplied from any distance in very cold weather, and
may even pass into a dangerous explosive within the mains; carburetted
acetylene can never become explosive, can only lose part of its special
heating value, and will actually increase in illuminating power.
It is manifest that, like air-gas, carburetted acetylene is of somewhat
indefinite composition, for the proportion of vapour, and the chemical
nature of that vapour, may vary. 100 litres of acetylene will take up 40
grammes of petroleum spirit to yield 110 litres of carburetted acetylene
evidently containing 9 per cent. of vapour, or 100 litres of acetylene
may be made to absorb as much as 250 grammes of spirit yielding 200
litres of carburetted acetylene containing 50 per cent. of vapour; while
the petroleum spirit may be replaced, if prices are suitable, by benzol
or denatured alcohol.
The illuminating power of acetylene carburetted with petroleum spirit has
been examined by Caro, whose average figures, worked out in British
units, are:
ILLUMINATING POWER OF CARBURETTED ACETYLENE.
HALF-FOOT BURNERS.
_Self-luminous._ | _Incandescent_
1 litre = 1.00 candle. | 1 litre = 3.04 candles.
1 cubic foot = 28.4 candles. | 1 cubic foot = 86.2 candles.
1 candle = 1.00 litre. | 1 candle = 0.33 litre.
1 candle = 0.035 cubic foot. | 1 candle = 0.012 cubic foot.
Those results may be compared with those referring to air-gas, which
emits in incandescent burners from 3.0 to 12.4 candles per cubic foot
according to the amount of spirit added to the air and the temperature to
which the gas is exposed.
The calorific values of carburetted acetylene (Caro), and those of other
gaseous fuels are:
Large Calories per
_ Cubic Foot.
| (Lewes) . 320
| (Gand) . 403
Ordinary acetylene . . | (Heil) . 365
| ___
|_Mean . . 363
| Maximum . 680
Carburetted acetylene . . | Minimum . 467
(petroleum spirit) | ___
|_Mean . . 573
Carburetted acetylene (50 per cent. benzol by volume) 685
Carburetted acetylene (50 per cent. alcohol by volume) 364
Coal-gas (common, unenriched) . . . . . 150
_
| Maximum . 178
Air-gas, self-luminous flame | Minimum . 57
| ___
|_Mean . . . 114
_
| Maximum . 26
Air-gas, non-luminous flame | Minimum . 18
| ___
|_Mean . . . 22
Water-gas (Strache) from coke . . . . . 71
Mond gas (from bituminous coal) . . . . . 38
Semi-water-gas from coke or anthracite . . . 36
Generator (producer) gas . . . . . . 29
Besides its relatively low upper explosive limit, carburetted acetylene
exhibits a higher temperature of ignition than ordinary acetylene, which
makes it appreciably safer in presence of a naked light. It also
possesses a somewhat lower flame temperature and a slower speed of
propagation of the explosive wave when mixed with air. These data are:
______________________________________________________________________
| | | | |
| | Explosive | Temperature. | |
| | Limits. | Degrees C. | Explosive |
| |19 mm. Tube. | | Explosive |
| |_____________|__________________| Wave. |
| | | | | | Metres per |
| | | |Of Igni-| | Second. |
| |Lower.|Upper.| tion. |Of Flame.| |
|________________________|______|______|________|_________|____________|
| | | | | | |
| Acetylene (theoretical)| --- | --- | --- |1850-2420| --- |
| " (observed) | 3.35 | 52.3 | 480 |1630-2020| 0.18-100 |
| Carburetted \ from | 2.5 | 10.2 | 582 | 1620 | 3.2 |
| acetylene / . . to | 5.4 | 30.0 | 720 | 1730 | 5.3 |
| Carburetted acetylene\ | 3.4 | 22.0 | --- | 1820 | 1.3 |
| (benzol) . . . / | | | | | |
| Carburetted acetylene\ | 3.1 | 12.0 | --- | 1610 | 1.1 |
| (alcohol) . . . / | | | | | |
| Air-gas, self-luminous\|15.0 | 50.0 | --- |1510-1520| --- |
| flame . . . . /| | | | | |
| Coal-gas . . . | 7.9 | 19.1 | 600 | --- | --- |
|________________________|______|______|________|_________|____________|
In making carburetted acetylene, the pressure given by the ordinary
acetylene generator will be sufficient to drive the gas through the
carburettor, and therefore there will be no expense involved beyond the
cost of the spirit vaporised. Thus comparisons may fairly be made between
ordinary and carburetted acetylene on the basis of material only, the
expense of generating the original acetylene being also ignored. In Great
Britain the prices of calcium carbide, petroleum spirit, and 90s benzol
delivered in bulk in country places may be taken at 15£ per ton, and
1s. per gallon respectively, petroleum spirit having a specific
gravity of 0.700 and benzol of 0.88. On this basis, a unit volume (100
cubic metres) of plain acetylene costs 1135d., of "petrolised"
acetylene containing 66 per cent. of acetylene costs 1277d., and
of "benzolised" acetylene costs 1180d. In other words, 100 volumes
of plain acetylene, 90 volumes of petrolised acetylene, and 96 volumes of
benzolised acetylene are of equal pecuniary value. Employing the data
given in previous tables, it appears that 38.5 candles can be won from
plain acetylene in a self-luminous burner, and 103 candles therefrom in
an incandescent burner at the same price as 25.5-29.1 and 78-87 candles
can be obtained from carburetted acetylene; whence it follows that at
English prices petrolised acetylene is more expensive as an illuminant in
either system of combustion than the simple gas, while benzolised
acetylene, burnt under the mantle only, is more nearly equal to the
simple gas from a pecuniary aspect. But considering the calorific value,
it appears that for a given sum of money only 363 calories can be
obtained from plain acetylene, while petrolised acetylene yields 516, and
benzolised acetylene 658; so that for all heating or cooking purposes
(and also for driving small motors) carburetted acetylene exhibits a
notable economy. Inasmuch as the partial saturation of acetylene with any
combustible vapour is an operation of extreme simplicity, requiring no
power or supervision beyond the occasional recharging of the carburettor,
it is manifest that the original main coming from the generator supplying
any large establishment where much warming, cooking (or motor driving)
might conveniently be done with the gas could be divided within the
plant-house, one branch supplying all, or nearly all, the lighting
burners with plain acetylene, and the other branch communicating with a
carburettor, so that all, or nearly all, the warming and cooking stoves
(and the motor) should be supplied with the more economical carburetted
acetylene. Since any water pump or similar apparatus would be in an
outhouse or basement, and the most important heating stove (the cooker)
be in the kitchen, such an arrangement would be neither complicated nor
involve a costly duplication of pipes.
It follows from the fact that even a trifling proportion of vapour
reduces the upper limit of explosibility of mixtures of acetylene with
air, that the gas may be so lightly carburetted as not appreciably to
suffer in illuminating power when consumed in self-luminous jets, and yet
to burn satisfactorily in incandescent burners, even if it has been
generated in an apparatus which introduces some air every time the
operation of recharging is performed. To carry out this idea, Caro has
suggested that 5 kilos. of petroleum spirit should be added to the
generator water for every 50 cubic metres of gas evolved, _i.e._, 1
lb. per 160 cubic feet, or, say, 1 gallon per 1000 cubic feet, or per 200
lb. of carbide decomposed. Caro proposed this addition in the case of
central installations supplying a district where the majority of the
consumers burnt the gas in self-luminous jets, but where a few preferred
the incandescent system; but it is clearly equally suitable for
employment in all private plants of sufficient magnitude.
A lowering of the upper limit of explosibility is also produced by the
presence of the acetone which remains in acetylene when obtained from a
cylinder holding the compressed gas (_cf._ Chapter XI.). According
to Wolff and Caro such gas usually carries with it from 30 to 60 grammes
of acetone vapour per cubic metre, _i.e._, 1.27 grammes per cubic
foot on an average; and this amount reduces the upper limit of
explosibility by about 16 per cent., so that to this extent the gas
behaves more smoothly in an incandescent burner of imperfect design.
Lépinay has described some experiments on the comparative technical value
of ordinary acetylene, carburetted acetylene, denatured alcohol and
petroleum spirit as fuels for small explosion engines. One particular
motor of 3 (French) h.p. consumed 1150 grammes of petroleum spirit per
hour at full load; but when it was supplied with carburetted acetylene
its consumption fell to 150 litres of acetylene and 700 grammes of spirit
(specific gravity 0.680). A 1-1/4 h.p. engine running light required 48
grammes of 90 per cent. alcohol per horse-power-hour and 66 litres of
acetylene; at full load it took 220 grammes of alcohol and 110 litres of
acetylene. A 6 h.p. engine at full load required 62 litres of acetylene
carburetted with 197 grammes of petroleum spirit per horse-power-hour
(uncorrected); while a similar motor fed with low-grade Taylor fuel-gas
took 1260 litres per horse-power-hour, but on an average developed the
same amount of power from 73 litres when 10 per cent. of acetylene was
added to the gas. Lépinay found that with pure acetylene ignition of the
charge was apt to be premature; and that while the consumption of
carburetted acetylene in small motors still materially exceeded the
theoretical, further economics could be attained, which, coupled with the
smooth and regular running of an engine fed with the carburetted gas,
made carburetted acetylene distinctly the better power-gas of the two.
CHAPTER XI
COMPRESSED AND DISSOLVED ACETYLENE--MIXTURES WITH OTHER GASES
In all that was said in Chapters II., III., IV., and V. respecting the
generation and employment of acetylene, it was assumed that the gas would
be produced by the interaction of calcium carbide and water, either by
the consumer himself, or in some central station delivering the acetylene
throughout a neighbourhood in mains. But there are other methods of using
the gas, which have now to be considered.
COMPRESSED ACETYLENE.--In the first place, like all other gases,
acetylene is capable of compression, or even of conversion into the
liquid state; for as a gas, the volume occupied by any given weight of it
is not fixed, but varies inversely with the pressure under which it is
stored. A steel cylinder, for instance, which is of such size as to hold
a cubic foot of water, also holds a cubic foot of acetylene at
atmospheric pressure, but holds 2 cubic feet if the gas is pumped into it
to a pressure of 2 atmospheres, or 30 lb. per square inch; while by
increasing the pressure to 21.53 atmospheres at 0° C. (Ansdell, Willson
and Suckert) the gas is liquefied, and the vessel may then contain 1
cubic foot of liquid acetylene, which is equal to some 400 cubic feet of
gaseous acetylene at normal pressure. It is clear that for many purposes
acetylene so compressed or liquefied would be convenient, for if the
cylinders could be procured ready charged, all troubles incidental to
generation would be avoided. The method, however, is not practically
permissible; because, as pointed out in Chapters II. and VI., acetylene
does not safely bear compression to a point exceeding 2 atmospheres; and
the liability to spontaneous dissociation or explosion in presence of
spark or severe blow, which is characteristic of compressed gaseous
acetylene, is greatly enhanced if compression has been pushed to the
point of liquefaction.
However, two methods of retaining the portability and convenience of
compressed acetylene with complete safety have been discovered. In one,
due to the researches of Claude and Hess, the gas is pumped under
pressure into acetone, a combustible organic liquid of high solvent
power, which boils at 56° C. As the solvent capacity of most liquids for
most gases rises with the pressure, a bottle partly filled with acetone
may be charged with acetylene at considerable effective pressure until
the vessel contains much more than its normal quantity of gas; and when
the valve is opened the surplus escapes, ready for employment, leaving
the acetone practically unaltered in composition or quantity, and fit to
receive a fresh charge of gas. In comparison with liquefied acetylene,
its solution in acetone under pressure is much safer; but since the
acetone expands during absorption of gas, the bottle cannot be entirely
filled with liquid, and therefore either at first, or during consumption
(or both), above the level of the relatively safe solution, the cylinder
contains a certain quantity of gaseous acetylene, which is compressed
above its limit of safety. The other method consists in pumping acetylene
under pressure into a cylinder apparently quite full of some highly
porous solid matter, like charcoal, kieselguhr, unglazed brick, &c. This
has the practical result that the gas is held under a high state of
compression, or possibly as a liquid, in the minute crevices of the
material, which are almost of insensible magnitude; or it may be regarded
as stored in vessels whose diameter is less than that in which an
explosive wave can be propagated (_cf._ Chapter VI.).
DISSOLVED ACETYLENE.--According to Fouché, the simple solution of
acetylene in acetone has the same coefficient of expansion by heat as
that of pure acetone, viz., 0.0015; the corresponding coefficient of
liquefied acetylene is 0.007 (Fouché), or 0.00489 (Ansdell) _i.e._,
three or five times as much. The specific gravity of liquid acetylene is
0.420 at 16.4° C. (Ansdell), or 0.528 at 20.6° C. (Willson and Suckert);
while the density of acetylene dissolved in acetone is 0.71 at 15° C.
(Claude). The tension of liquefied acetylene is 21.53 atmospheres at 0°
C., and 39.76 atmospheres at 20.15° C. (Ansdell); 21.53 at 0° C., and
39.76 at 19.5° C. (Willson and Suckert); or 26.5 at 0° C., and 42.8 at
20.0° C. (Villard). Averaging those results, it may be said that the
tension rises from 23.2 atmospheres at 0° C. to 40.77 at 20° C., which is
an increment of 1/26 or 0.88 atmosphere, per 1° Centigrade; while, of
course, liquefied acetylene cannot be kept at all at a temperature of 0°
unless the pressure is 21 atmospheres or upwards. The solution of
acetylene in acetone can be stored at any pressure above or below that of
the atmosphere, and the extent to which the pressure will rise as the
temperature increases depends on the original pressure. Berthelot and
Vieille have shown that when (_a_) 301 grammes of acetone are
charged with 69 grammes of acetylene, a pressure of 6.74 atmospheres at
14.0° C. rises to 10.55 atmospheres at 35.7° C.; (_b_) 315 grammes
of acetone are charged with 118 grammes of acetylene, a pressure of 12.25
atmospheres at 14.0° C. rises to 19.46 at 36.0° C.; (_c_) 315
grammes of acetone are charged with 203 grammes of acetylene, a pressure
of 19.98 atmospheres at 13.0° C. rises to 30.49 at 36.0° C. Therefore in
(_a_) the increase in pressure is 0.18 atmosphere, in (_b_)
O.33 atmosphere, and in (_c_) 0.46 atmosphere per 1° Centigrade
within the temperature limits quoted. Taking case (_b_) as the
normal, it follows that the increment in pressure per 1° C. is 1/37
(usually quoted as 1/30); so that, measured as a proportion of the
existing pressure, the pressure in a closed vessel containing a solution
of acetylene in acetone increases nearly as much (though distinctly less)
for a given rise in temperature as does the pressure in a similar vessel
filled with liquefied acetylene, but the absolute increase is roughly
only one-third with the solution as with the liquid, because the initial
pressure under which the solution is stored is only one-half, or less,
that at which the liquefied gas must exist.
Supposing, now, that acetylene contained in a closed vessel, either as
compressed gas, as a solution in acetone, or as a liquid, were brought to
explosion by spark or shock, the effects capable of production have to be
considered. Berthelot and Vieille have shown that if gaseous acetylene is
stored at a pressure of 11.23 kilogrammes per square centimetre,
[Footnote: 1 kilo. per sq. cm. is almost identical with 1 atmosphere, or
15 lb. per sq. inch.] the pressure after explosion reaches 92.33
atmospheres on an average, which is an increase of 8.37 times the
original figure; if the gas is stored at 21.13 atmospheres, the mean
pressure after explosion is 213.15 atmospheres, or 10.13 times the
original amount. If liquid acetylene is tested similarly, the original
pressure, which must clearly be more than 21.53 atmospheres (Ansdell) at
0° C., may rise to 5564 kilos, per square centimetre, as Berthelot and
Vieille observed when a steel bomb having a capacity of 49 c.c. was
charged with 18 grammes of liquefied acetylene. In the case of the
solution in acetone, the magnitudes of the pressures set up are of two
entirely different orders according as the original pressure 20
atmospheres or somewhat less; but apart from this, they vary considerably
with the extent to which the vessel is filled with the liquid, and they
also depend on whether the explosion is produced in the solution or in
the gas space above. Taking the lower original pressure first, viz., 10
atmospheres, when a vessel was filled with solution to 33 per cent. of
its capacity, the pressure after explosion reached about 95 atmospheres
if the spark was applied to the gas space; but attained 117.4 atmospheres
when the spark was applied to the acetone. When the vessel was filled 56
per cent. full, the pressures after explosion reached about 89, or 155
atmospheres, according as the gas or the liquid was treated with the
spark. But when the original pressure was 20 atmospheres, and the vessel
was filled to 35 per cent. of its actual capacity with solution, the
final pressures ranged from 303 to 568 atmospheres when the gas was
fired, and from 2000 to 5100 when the spark was applied to the acetone.
Examining these figures carefully, it will be seen that the phenomena
accompanying the explosion of a solution of acetylene in acetone resemble
those of the explosion of compressed gaseous acetylene when the original
pressure under which the solution is stored is about 10 atmospheres; but
resemble those of the explosion of liquefied acetylene when the original
pressure of the solution reaches 20 atmospheres, this being due to the
fact that at an original pressure of 10 atmospheres the acetone itself
does not explode, but, being exothermic, rather tends to decrease the
severity of the explosion; whereas at an original pressure of 20
atmospheres the acetone does explode (or burn), and adds its heat of
combustion to the heat evolved by the acetylene. Thus at 10 atmospheres
the presence of the acetone is a source of safety; but at 20 atmospheres
it becomes an extra danger.
Since sound steel cylinders may easily be constructed to boar a pressure
of 250 atmospheres, but would be burst by a pressure considerably less
than 5000 atmospheres, it appears that liquefied acetylene and its
solution in acetone at a pressure of 20 atmospheres are quite unsafe; and
it might also seem that both the solution at a pressure of 10 atmospheres
and the simple gas compressed to the same limit should be safe. But there
is an important difference here, in degree if not in kind, because, given
a cylinder of known capacity containing (1) gaseous acetylene compressed
to 10 atmospheres, or (2) containing the solution at the same pressure,
if an explosion were to occur, in case (1) the whole contents would
participate in the decomposition, whereas in case (2), as mentioned
already, only the small quantity of gaseous acetylene above the solution
would be dissociated.
It is manifest that of the three varieties of compressed acetylene now
under consideration, the solution in acetone is the only one fit for
general employment; but it exhibits the grave defects (_a_) that the
pressure under which it is prepared must be so small that the pressure in
the cylinders can never approach 20 atmospheres in the hottest weather or
in the hottest situation to which they may be exposed, (_b_) that
the gas does not escape smoothly enough to be convenient from large
vessels unless those vessels are agitated, and (_c_) that the
cylinders must always be used in a certain position with the valve at the
top, lest part of the liquid should run out into the pipes. For these
reasons the simple solution of acetylene in acetone has not become of
industrial importance; but the processes of absorbing either the gas, or
better still its solution in acetone, in porous matter have already
achieved considerable success. Both methods have proved perfectly safe
and trustworthy; but the combination of the acetone process with the
porous matter makes the cylinders smaller per unit volume of acetylene
they contain. Several varieties of solid matter appear to work
satisfactorily, the only essential feature in their composition being
that they shall possess a proper amount of porosity and be perfectly free
from action upon the acetylene or the acetone (if present). Lime does
attack acetone in time, and therefore it is not a suitable ingredient of
the solid substance whenever acetylene is to be compressed in conjunction
with the solvent; so that at present either a light brick earth which has
a specific gravity of 0.5 is employed, or a mixture of charcoal with
certain inorganic salts which has a density of 0.3, and can be introduced
through a small aperture into the cylinder in a semi-fluid condition.
Both materials possess a porosity of 80 per cent., that is to say, when a
cylinder is apparently filled quite full, only 20 per cent, of the space
is really occupied by the solid body, the remaining 80 per cent, being
available for holding the liquid or the compressed gas. If all
comparisons as to degree of explosibility and effects of explosion are
omitted, an analogy may be drawn between liquefied acetylene or its
compressed solution in acetone and nitroglycerin, while the gas or
solution of the gas absorbed in porous matter resembles dynamite.
Nitroglycerin is almost too treacherous a material to handle, but as an
explosive (which in reason absorbed or dissolved acetylene is not)
dynamite is safe, and even requires special arrangements to explode it.
In Paris, where the acetone process first found employment on a large
scale, the company supplying portable cylinders to consumers uses large
storage vessels filled, as above mentioned, apparently full of porous
solid matter, and also charged to about 43 per cent, of their capacity
with acetone, thus leaving about 37 per cent. of the apace for the
expansion which occurs as the liquid takes up the gas. Acetylene is
generated, purified, and thoroughly dried according to the usual methods;
and it is then run through a double-action pump which compresses it first
to a pressure of 3.5 kilos., next to a pressure of 3.5 x 3.5 = 12 kilos,
per square centimetre, and finally drives it into the storage vessels.
Compression is effected in two stages, because the process is accompanied
by an evolution of much heat, which might cause the gas to explode during
the operation; but since the pump is fitted with two cylinders, the
acetylene can be cooled after the first compression. The storage vessels
then contain 100 times their apparent volume of acetylene; for as the
solubility of acetylene in acetone at ordinary temperature and pressure
is about 25 volumes of gas in 1 of liquid, a vessel holding 100 volumes
when empty takes up 25 x 43 = 1000 volumes of acetylene roughly at
atmospheric pressure; which, as the pressure is approximately 10
atmospheres, becomes 1000 x 10 = 10,000 volumes per 100 normal capacity,
or 100 times the capacity of the vessel in terms of water. From these
large vessels, portable cylinders of various useful dimensions, similarly
loaded with porous matter and acetone, are charged simply by placing them
in mutual contact, thus allowing the pressure and the surplus gas to
enter the small one; a process which has the advantage of renewing the
small quantity of acetone vaporised from the consumers' cylinders as the
acetylene is burnt (for acetone is somewhat volatile, cf. Chapter X.), so
that only the storage vessels ever need to have fresh solvent introduced.
Where it is procurable, the use of acetylene compressed in this fashion
is simplicity itself; for the cylinders have only to be connected with
the house service-pipes through a reducing valve of ordinary
construction, set to give the pressure which the burners require. When
exhausted, the bottle is simply replaced by another. Manifestly, however,
the cost of compression, the interest on the value of the cylinders, and
the carriage, &c., make the compressed gas more expensive per unit of
volume (or light) than acetylene locally generated from carbide and
water; and indeed the value of the process does not lie so much in the
direction of domestic illumination as in that of the lighting, and
possibly driving, of vehicles and motor-cars--more especially in the
illumination of such vehicles as travel constantly, or for business
purposes, over rough road surfaces and perform mostly out-and-home
journeys. Nevertheless, absorbed acetylene may claim close attention for
one department of household illumination, viz., the portable table-lamp;
for the base of such an apparatus might easily be constructed to imitate
the acetone cylinder, and it could be charged by simple connexion with a
larger one at intervals. In this way the size of the lamp for a given
number of candle-hours would be reduced below that of any type of actual
generator, and the troubles of after-generation, always more or less
experienced in holderless generators, would be entirely done away with.
Dissolved acetylene is also very useful for acetylene welding or
autogenous soldering.
The advantages of compressed and absorbed acetylene depend on the small
bulk and weight of the apparatus per unit of light, on the fact that no
amount of agitation can affect the evolution of gas (as may happen with
an ordinary acetylene generator), on the absence of any liquid which may
freeze in winter, and on there being no need for skilled attention except
when the cylinders are being changed. These vessels weigh between 2.5 and
3 kilos, per 1 litre capacity (normal) and since they are charged with
100 times their apparent volume of acetylene, they may be said to weigh 1
kilo, per 33 litres of available acetylene, or roughly 2 lb. per cubic
foot, or, again, if half-foot burners are used, 2 lb. per 36 candle-
hours. According to Fouché, if electricity obtained from lead
accumulators is compared with acetylene on the basis of the weight of
apparatus needed to evolve a certain quantify of light, 1 kilo, of
acetylene cylinder is equal to 1.33 kilos, of lead accumulator with arc
lamps, or to 4 kilos. of accumulator with glow lamps; and moreover the
acetylene cylinder can be charged and discharged, broadly speaking, as
quickly or as slowly as may be desired; while, it may be added, the same
cylinder will serve one or more self-luminous jets, one or more
incandescent burners, any number and variety of heating apparatus,
simultaneously or consecutively, at any pressure which may be required.
From the aspect of space occupied, dissolved acetylene is not so
concentrated a source of artificial light as calcium carbide; for 1
volume of granulated carbide is capable of omitting as much light as 4
volumes of compressed gas; although, in practice, to the 1 volume of
carbide must be added that of the apparatus in which it is decomposed.
LIQUEFIED ACETYLENE.--In most civilised countries the importation,
manufacture, storage, and use of liquefied acetylene, or of the gas
compressed to more than a fraction of one effective atmosphere, is quite
properly prohibited by law. In Great Britain this has been done by an
Order in Council dated November 26, 1897, which specifies 100 inches of
water column as the maximum to which compression may be pushed. Power
being retained, however, to exempt from the order any method of
compressing acetylene that might be proved safe, the Home Secretary
issued a subsequent Order on March 28, 1898, permitting oil-gas
containing not more than 20 per cent, by volume of acetylene (see below)
to be compressed to a degree not exceeding 150 lb. per square inch,
_i.e._, to about 10 atmospheres, provided the gases are mixed
together before compression; while a third Order, dated April 10, 1901,
allows the compression of acetylene into cylinders filled as completely
as possible with porous matter, with or without the presence of acetone,
to a pressure not exceeding 150 lb. per square inch provided the
cylinders themselves have been tested by hydraulic pressure for at least
ten minutes to a pressure not less than double [Footnote: In France the
cylinders are tested to six times and in Russia to five times their
working pressure.] that which it is intended to use, provided the solid
substance is similar in every respect to the samples deposited at the
Home Office, provided its porosity does not exceed 80 per cent., provided
air is excluded from every part of the apparatus before the gas is
compressed, provided the quantity of acetone used (if used at all) is not
sufficient to fill the porosity of the solid, provided the temperature is
not permitted to rise during compression, and provided compression only
takes place in premises approved by H.M.'s Inspectors of Explosives.
DILUTED ACETYLENE.--Acetylene is naturally capable of admixture or
dilution with any other gas or vapour; and the operation may be regarded
in either of two ways; (1) as a, means of improving the burning qualities
of the acetylene itself, or (2) as a means of conferring upon some other
gas increased luminosity. In the early days of the acetylene industry,
generation was performed in so haphazard a fashion, purification so
generally omitted, and the burners were so inefficient, that it was
proposed to add to the gas a comparatively small proportion of some other
gaseous fluid which should be capable of making it burn without
deposition of carbon while not seriously impairing its latent
illuminating power. One of the first diluents suggested was carbon
dioxide (carbonic acid gas), because this gas is very easy and cheap to
prepare; and because it was stated that acetylene would bear an addition
of 5 or even 8 per cent, of carbon dioxide and yet develop its full
degree of luminosity. This last assertion requires substantiation; for it
is at least a grave theoretical error to add a non-inflammable gas to a
combustible one, as is seen in the lower efficiency of all flames when
burning in common air in comparison with that which they exhibit in
oxygen; while from the practical aspect, so harmful is carbon dioxide in
an illuminating gas, that coal-gas and carburetted water-gas are
frequently most rigorously freed from it, because a certain gain in
illuminating power may often thus be achieved more cheaply than by direct
enrichment of the gas by addition of hydrocarbons. Being prepared from
chalk and any cheap mineral acid, hydrochloric by preference, in the
cold, carbon dioxide is so cheap that its price in comparison with that
of acetylene is almost _nil_; and therefore, on the above
assumption, 105 volumes of diluted acetylene might be made essentially
for the same price as 100 volumes of neat acetylene, and according to
supposition emit 5 per cent. more light per unit of volume.
It is reported that several railway trains in Austria are regularly
lighted with acetylene containing 0.4 to 1.0 per cent. of carbon dioxide
in order to prevent deposition of carbon at the burners. The gas is
prepared according to a patent process which consists in adding a certain
proportion of a "carbonate" to the generator water. In the United
Kingdom, also, there are several installations supplying an acetylene
diluted with carbon dioxide, the gas being produced by putting into that
portion of a water-to-carbide generator which lies nearest to the water-
supply some solid carbonate like chalk, and using a dilute acid to attack
the material. Other inventors have proposed placing a solid acid, like
oxalic, in the former part of a generator and decomposing it with a
carbonate solution; or they have suggested putting into the generator a
mixture of a solid acid and a solid soluble carbonate, and decomposing it
with plain water.
Clearly, unless the apparatus in which such mixtures as these are
intended to be prepared is designed with considerable care, the amount of
carbon dioxide in the gas will be liable to vary, and may fall to zero.
If any quantity of carbide present has been decomposed in the ordinary
way, there will be free calcium hydroxide in the generator; and if the
carbon dioxide comes into contact with this, it will be absorbed, unless
sufficient acid is employed to convert the calcium carbonate (or
hydroxide) into the corresponding normal salt of calcium. Similarly,
during purification, a material containing any free lime would tend to
remove the carbon dioxide, as would any substance which became alkaline
by retaining the ammonia of the crude gas.
It cannot altogether be granted that the value of a process for diluting
acetylene with carbon dioxide has been established, except in so far as
the mere presence of the diluent may somewhat diminish the tendency of
the acetylene to polymerise as it passes through a hot burner (_cf._
Chapter VIII.). Certainly as a fuel-gas the mixture would be less
efficient, and the extra amount of carbon dioxide produced by each flame
is not wholly to be ignored. Moreover, since properly generated and
purified acetylene can be consumed in proper burners without trouble, all
reason for introducing carbon dioxide has disappeared.
MIXTURES OF ACETYLENE AND AIR.--A further proposal for diluting acetylene
was the addition to it of air. Apart from questions of explosibility,
this method has the advantage over that of adding carbon dioxide that the
air, though not inflammable, is, in virtue of its contained oxygen, a
supporter of combustion, and is required in a flame; whereas carbon
dioxide is not only not a supporter of combustion, but is actually a
product thereof, and correspondingly more objectionable. According to
some experiments carried out by Dufour, neat acetylene burnt under
certain conditions evolved between 1.0 and 1.8 candle-power per litre-
hour; a mixture of 1 volume of acetylene with 1 volume of air evolved 1.4
candle-power; a mixture of 1 volume of acetylene with 1.2 volumes of air,
2.25 candle-power; and a mixture of 1 volume of acetylene with 1.3
volumes of air, 2.70 candle-power per litre-hour of acetylene in the
several mixtures. Averaging the figures, and calculating into terms of
acetylene (only) burnt, Dufour found neat acetylene to develop 1.29
candle-power per litre-hour, and acetylene diluted with air to develop
1.51 candle-power. When, however, allowance is made for the cost and
trouble of preparing such mixtures the advantage of the process
disappears; and moreover it is accompanied by too grave risks, unless
conducted on a largo scale and under most highly skilled supervision, to
be fit for general employment.
Fouché, however, has since found the duty, per cubic foot of neat
acetylene consumed in a twin injector burner at the most advantageous
rate of 3.2 inches, to be as follows for mixtures with air in the
proportions stated:
Percentage of air 0 17 27 33.5
Candles per cubic feet 38.4 36.0 32.8 26.0
At lower pressures, the duty of the acetylene when diluted appears to be
relatively somewhat higher. Figures which have been published in regard
to a mixture of 30 volumes of air and 70 volumes of acetylene obtained by
a particular system of producing such a mixture, known as the "Molet-
Boistelle," indicate that the admixture of air causes a slight increase
in the illuminating duty obtained from the acetylene in burners of
various sizes. The type of burner and the pressure employed in these
experiments were not, however, stated. This system has been used at
certain stations on the "Midi" railway in France. Nevertheless even where
the admixture of air to acetylene is legally permissible, the risk of
obtaining a really dangerous product and the nebulous character of the
advantages attainable should preclude its adoption.
In Great Britain the manufacture, importation, storage, and use of
acetylene mixed with air or oxygen, in all proportions and at all
pressures, with or without the presence of other substances, is
prohibited by an Order in Council dated July 1900; to which prohibition
the mixture of acetylene and air that takes place in a burner or
contrivance in which the mixture is intended to be burnt, and the
admixture of air with acetylene that may unavoidably occur in the first
use or recharging of an apparatus (usually a water-to-carbide generator),
properly designed and constructed with a view to the production of pure
acetylene, are the solitary exceptions.
MIXED CARBIDES.--In fact the only processes for diluting acetylene which
possess real utility are that of adding vaporised petroleum spirit or
benzene to the gas, as was described in Chapter X. under the name of
carburetted acetylene, and one other possible method of obtaining a
diluted acetylene directly from the gas-generator, to which a few words
will now be devoted. [Footnote: Mixtures of acetylene with relatively
large proportions of other illuminating gases, such as are referred to on
subsequent pages, are also, from one aspect, forms of diluted acetylene.]
Calcium carbide is only one particular specimen of a large number of
similar metallic compounds, which can be prepared in the electric
furnace, or otherwise. Some of those carbides yield acetylene when
treated with water, some are not attacked, some give liquid products, and
some yield methane, or mixtures of methane and hydrogen. Among the latter
is manganese carbide. If, then, a mixture of manganese carbide and
calcium carbide is put into an ordinary acetylene generator, the gas
evolved will be a mixture of acetylene with methane and hydrogen in
proportions depending upon the composition of the carbide mixture. It is
clear that a suitable mixture of the carbides might be made by preparing
them separately and bulking the whole in the desired proportions; while
since manganese carbide can be won in the electric furnace, it might be
feasible to charge into such a furnace a mixture of lime, coke, and
manganese oxide calculated to yield a simple mixture of the carbides or a
kind of double carbide. Following the lines which have been adopted in
writing the present book, it is not proposed to discuss the possibility
of making mixed carbides; but it may be said in brief that Brame and
Lewes have carried out several experiments in this direction, using
charges of lime and coke containing (_a_) up to 20 per cent. of
manganese oxide, and (_b_) more than 60 per cent. of manganese
oxide. In neither case did they succeed in obtaining a material which
gave a mixture of acetylene and methane when treated with water; in case
(_a_) they found the gas to be practically pure acetylene, so that
the carbide must have been calcium carbide only; in case (_b_) the
gas was mainly methane and hydrogen, so that the carbide must have been
essentially that of manganese alone. Mixed charges containing between 20
and 60 per cent. of manganese oxide remain to be studied; but whether
they would give mixed carbides or no, it would be perfectly simple to mix
ready-made carbides of calcium and manganese together, if any demand for
a diluted acetylene should arise on a sufficiently large scale. It is,
however, somewhat difficult to appreciate the benefits to be obtained
from forms of diluted acetylene other than those to which reference is
made later in this chapter.
There is, nevertheless, one modification of calcium carbide which, in a
small but important sphere, finds a useful _rôle_. It has been
pointed out that a carbide containing much calcium phosphide is usually
objectionable, because the gas evolved from it requires extra
purification, and because there is the (somewhat unlikely) possibility
that the acetylene obtained from such material before purification may be
spontaneously inflammable. If, now, to the usual furnace charge of lime
and coke a sufficient quantity of calcium phosphate is purposely added,
it is possible to win a mixture of calcium phosphide and carbide, or, as
Bradley, Read, and Jacobs call it, a "carbophosphide of calcium," having
the formula Ca_5C_6P_2, which yields a spontaneously inflammable mixture
of acetylene, gaseous phosphine, and liquid phosphine when treated with
water, and which, therefore, automatically gives a flame when brought
into contact with the liquid. The value of this material will be
described in Chapter XIII.
GAS-ENRICHING.--Other methods of diluting acetylene consist in adding a
comparatively small proportion of it to some other gas, and may be
considered rather as processes for enriching that other gas with
acetylene. Provided the second gas is well chosen, such mixtures exhibit
properties which render them peculiarly valuable for special purposes.
They have, usually, a far lower upper limit of explosibility than that of
neat acetylene, and they admit of safe compression to an extent greatly
exceeding that of acetylene itself, while they do not lose illuminating
power on compression. The second characteristic is most important, and
depends on the phenomena of "partial pressure," which have been referred
to in Chapter VI. When a single gas is stored at atmospheric pressure, it
is insensibly withstanding on all sides and in all directions a pressure
of roughly 15 lb. per square inch, which is the weight of the atmosphere
at sea-level; and when a mixture of two gases, X and Y, in equal volumes
is similarly stored it, regarded as an entity, is also supporting a
pressure of 15 lb. per square inch. But in every 1 volume of that mixture
there is only half a volume of X and Y each; and, ignoring the presence
of its partner, each half-volume is evenly distributed throughout a space
of 1 volume. But since the volume of a gas stands in inverse ratio to the
pressure under which it is stored, the half-volume of X in the 1 volume
of X + Y apparently stands at a pressure of half an atmosphere, for it
has expanded till it fills, from a chemical and physical aspect, the
space of 1 volume: suitable tests proving that it exhibits the properties
which a gas stored at a pressure of half an atmosphere should do.
Therefore, in the mixture under consideration, X and Y are both said to
be at a "partial pressure" of half an atmosphere, which is manifestly 7.5
lb. per square inch. Clearly, when a gas is an entity (either an element
or one single chemical compound) partial and total pressure are
identical. Now, it has been shown that acetylene ceases to be a safe gas
to handle when it is stored at a pressure of 2 atmospheres; but the limit
of safety really occurs when the gas is stored at a _partial_
pressure of 2 atmospheres. Neat acetylene, accordingly, cannot be
compressed above the mark 30 lb. shown on a pressure gauge; but diluted
acetylene (if the diluent is suitable) may be compressed in safety till
the partial pressure of the acetylene itself reaches 2 atmospheres. For
instance, a mixture of equal volumes of X and Y (X being acetylene)
contains X at a partial pressure of half the total pressure, and may
therefore be compressed to (2 / 1/2 =) 4 atmospheres before X reaches the
partial pressure of 2 atmospheres; and therewith the mixture is brought
just to the limit of safety, any effect of Y one way or the other being
neglected. Similarly, a mixture of 1 volume of acetylene with 4 volumes
of Y may be safely compressed to a pressure of (2 / 1/5 =) 10
atmospheres, or, broadly, a mixture in which the percentage of acetylene
is _x_ may be safely compressed to a pressure not exceeding (2 /
_x_/100) atmospheres. This fact permits acetylene after proper
dilution to be compressed in the same fashion as is allowable in the case
of the dissolved and absorbed gas described above.
If the latent illuminating power of acetylene is not to be wasted, the
diluent must not be selected without thought. Acetylene burns with a very
hot flame, the luminosity of which is seriously decreased if the
temperature is lowered. As mentioned in Chapter VIII., this may be done
by allowing too much air to enter the flame; but it may also be effected
to a certain extent by mixing with the acetylene before combustion some
combustible gas or vapour which burns at a lower temperature than
acetylene itself. Manifestly, therefore, the ideal diluent for acetylene
is a substance which possesses as high a flame temperature as acetylene
and a certain degree of intrinsic illuminating power, while the lower the
flame temperature of the diluent and the less its intrinsic illuminating
power, the less efficiently will the acetylene act as an enriching
material. According to Love, Hempel, Wedding, and others, if acetylene is
mixed with coal-gas in amounts up to 8 per cent. or thereabouts, the
illuminating power of the mixture increases about 1 candle for every 1
per cent. of acetylene present: a fact which is usually expressed by
saying that with coal-gas the enrichment value of acetylene is 1 candle
per 1 per cent. Above 8 per cent., the enrichment value of acetylene
rises, Love having found an increase in illuminating power, for each 1
per cent. of acetylene in the mixture, of 1.42 candles with 11.28 per
cent. of acetylene; and of 1.54 candles with 17.62 per cent. of
acetylene. Theoretically, if the illuminating power of acetylene is taken
at 240 candles, its enrichment value should be (240 / 100 =) 2.4 candles
per 1 per cent.; and since, in the case of coal-gas, its actual
enrichment value falls seriously below this figure, it is clear that
coal-gas is not an economical diluent for it. Moreover, coal-gas can be
enriched by other methods much more cheaply than with acetylene. Simple
("blue") water-gas, according to Love, requires more than 10 per cent. of
acetylene to be added to it before a luminous flame is produced; while a
mixture of 20.3 per cent. of acetylene and 79.7 per cent. of water-gas
had an illuminating power of 15.47 candles. Every addition to the
proportion of acetylene when it amounted to 20 per cent. and upwards of
the mixture had a very appreciable effect on the illuminating power of
the latter. Thus with 27.84 per cent. of acetylene, the illuminating
power of the mixture was 40.87 candles; with 38.00 per cent. of acetylene
it was 73.96 candles. Acetylene would not be an economical agent to
employ in order to render water-gas an illuminating gas of about the
quality of coal-gas, but the economy of enrichment of water-gas by
acetylene increases rapidly with the degree of enrichment demanded of it.
Carburetted water-gas which, after compression under 16 atmospheres
pressure, had an illuminating power of about 17.5 candles, was enriched
by additions of acetylene. 4.5 per cent. of acetylene in the mixture gave
an illuminating power of 22.69 candles; 8.4 per cent., 29.54 candles;
11.21 per cent., 35.05 candles; 15.06 per cent., 42.19 candles; and 21.44
per cent., 52.61 candles. It is therefore evident that the effect of
additions of acetylene on the illuminating power of carburetted water-gas
is of the same order as its effect on coal-gas. The enrichment value of
the acetylene increases with its proportion in the mixture; but only when
the proportion becomes quite considerable, and, therefore, the gas of
high illuminating power, does enrichment by acetylene become economical.
Methane (marsh-gas), owing to its comparatively high flame temperature,
and to the fact that it has an intrinsic, if small, illuminating power,
is a better diluent of acetylene than carbon monoxide or hydrogen, in
that it preserves to a greater extent the illuminative value of the
acetylene.
Actually comparisons of the effect of additions of various proportions of
a richly illuminating gas, such as acetylene, on the illuminative value
of a gas which has little or no inherent illuminating power, are largely
vitiated by the want of any systematic method for arriving at the
representative illuminative value of any illuminating gas. A statement
that the illuminating power of a gas is _x_ candles is, strictly
speaking, incomplete, unless it is supplemented by the information that
the gas during testing was burnt (1) in a specified type of burner, and
(2) either at a specified fixed rate of consumption or so as to afford a
light of a certain specified intensity. There is no general agreement,
even in respect of the statutory testing of the illuminating power of
coal-gas supplies, as to the observance of uniform conditions of burning
of the gas under test, and in regard to more highly illuminating gases
there is even greater diversity of conditions. Hence figures such as
those quoted above for the enrichment value of acetylene inevitably show
a certain want of harmony which is in reality due to the imperfection or
incompleteness of the modes of testing employed. Relatively to another,
one gas appears advantageously merely in virtue of the conditions of
assessing illuminating power having been more favourable to it. Therefore
enrichment values, such as those given, must always be regarded as only
approximately trustworthy in instituting comparisons between either
different diluent gases or different enriching agents.
ACETYLENE MIXTURES FOR RAILWAY-CARRIAGE LIGHTING.--In modern practice,
the gases which are most commonly employed for diluents of acetylene,
under the conditions now being considered, are cannel-coal gas (in
France) and oil-gas (elsewhere). Fowler has made a series of observations
on the illuminating value of mixtures of oil-gas and acetylene. 13.41 per
cent. of acetylene improved the illuminating power of oil-gas from 43 to
49 candles. Thirty-nine-candle-power oil-gas had its illuminating power
raised to about 60 candles by an admixture of 20 per cent. of acetylene,
to about 80 candles by 40 per cent. of acetylene, and to about 110
candles by 60 per cent. of acetylene. The difficulty of employing
mixtures fairly rich in acetylene, or pure acetylene, for railway-
carriage lighting, lies in the poor efficiency of the small burners which
yield from such rich gas a light of 15 to 20 candle-power, such as is
suitable for the purpose. For the lighting of railway carriages it is
seldom deemed necessary to have a flame of more than 20 candle-power, and
it is somewhat difficult to obtain such a flame from oil-gas mixtures
rich in acetylene, unless the illuminative value of the gas is wasted to
a considerable extent. According to Bunte, 15 volumes of coal-gas, 8
volumes of German oil-gas, and 1.5 volumes of acetylene all yield an
equal amount of light; from which it follows that 1 volume of acetylene
is equivalent to 5.3 volumes of German oil-gas.
A lengthy series of experiments upon the illuminating power of mixtures
of oil-gas and acetylene in proportions ranging between 10 and 50 per
cent. of the latter, consumed in different burners and at different
pressures, has been carried out by Borck, of the German State Railway
Department. The figures show that per unit of volume such mixtures may
give anything up to 6.75 times the light evolved by pure oil-gas; but
that the latent illuminating power of the acetylene is less
advantageously developed if too much of it is employed. As 20 per cent.
of acetylene is the highest proportion which may be legally added to oil-
gas in this country, Borck's results for that mixture may be studied:
______________________________________________________________________
| | | | | | | |
| | | | | | | Propor- |
| | | | Consump- | | Consump- | tionate |
| Kind of | No. of | Pres- | tion per | Candle- | tion per | Illum- |
| Burner. | Burner | sure. | Hour. | Power. | Candle- | inating |
| | | mm. | Litres. | | Hour. | Power |
| | | | | | Litres. | to Pure |
| | | | | | | Oil-Gas.|
|___________|________|_______|__________|_________|__________|_________|
| | | | | | | |
| Bray | 00 | 42 | 82 | 56.2 | 1.15 | 3.38 |
| " | 000 | 35 | 54 | 28.3 | 1.91 | 4.92 |
| " | 0000 | 35 | 43.3 | 16 | 2.71 | 4.90 |
| Oil-gas | | | | | | |
| burner | 15 | 24 | 21 | 7.25 | 2.89 | 4.53 |
| " " | 30 | 15 | 22 | 10.5 | 2.09 | 3.57 |
| " " | 40 | 16 | 33.5 | 20.2 | 1.65 | 3.01 |
| " " | 60 | 33 | 73 | 45.2 | 1.62 | 3.37 |
| |
| The oil-gas from which this mixture was prepared showing: |
| |
| Bray | 00 | 34 | 73.5 | 16.6 | 4.42 | ... |
| " | 000 | 30 | 48 | 6.89 | 6.96 | ... |
| " | 0000 | 28 | 39 | 3.26 | 11.6 | ... |
| Oil-gas | | | | | | |
| burner | 15 | 21 | 19 | 1.6 | 11.8 | ... |
| " " | 30 | 14 | 21.5 | 2.94 | 7.31 | ... |
| " " | 40 | 15 | 33 | 6.7 | 4.92 | ... |
| " " | 60 | 25 | 60 | 13.4 | 4.40 | ... |
|___________|________|_______|__________|_________|__________|_________|
It will be seen that the original oil-gas, when compressed to 10
atmospheres, gave a light of 1 candle-hour for an average consumption of
7.66 litres in the Bray burners, and for a consumption of 7.11 litres in
the ordinary German oil-gas jets; while the mixture containing 20 per
cent. of acetylene evolved the same amount of light for a consumption of
2.02 litres in Bray burners, or of 2.06 litres in the oil-gas jets.
Again, taking No. 40 as the most popular and useful size of burner, 1
volume of acetylene oil-gas may be said to be equal to 3 volumes of
simple oil-gas, which is the value assigned to the mixture by the German
Government officials, who, at the prices ruling there, hold the mixture
to be twice as expensive as plain oil-gas per unit of volume, which means
that for a given outlay 50 per cent. more light may be obtained from
acetylene oil-gas than from oil-gas alone.
This comparison of cost is not applicable, as it stands, to compressed
oil-gas, with and without enrichment by acetylene, in this country, owing
to the oils from which oil-gas is made being much cheaper and of better
quality here than in Germany, where a heavy duty is imposed on imported
petroleum. Oil-gas as made from Scotch and other good quality gas-oil in
this country, usually has, after compression, an illuminating duty of
about 8 candles per cubic foot, which is about double that of the
compressed German oil-gas as examined by Borck.
Hence the following table, containing a summary of results obtained by H.
Fowler with compressed oil-gas, as used on English railways, must be
accepted rather than the foregoing, in so far as conditions prevailing in
this country are concerned. It likewise refers to a mixture of oil-gas
and acetylene containing 20 per cent. of acetylene.
______________________________________________________________________
| | | | | | |
| | | | | | Ratio of |
| | |Consumption| |Candles per| Illuminating |
| Burner. |Pressure.| per Hour. |Candle| Cubic Foot| Power to that |
| | Inches. |Cubic Feet.|Power.| per Hour. |of Oil-gas [1] |
| | | | | | in the same |
| | | | | | Burner. |
|_____________|_________|___________|______|___________|_______________|
| | | | | | |
| Oil-gas . . | 0.7 | 0.98 | 12.5 | 12.72 | 1.65 |
| Bray 000 . | 0.7 | 1.17 | 14.4 | 12.30 | 1.57 |
| " 0000 . | 0.7 | 0.97 | 10.4 | 10.74 | 1.41 |
| " 00000 | 0.7 | 0.78 | 5.6 | 7.16 | 1.08 |
| " 000000 | 0.7 | 0.55 | 1.9 | 3.52 | 1.14 |
|_____________|_________|___________|______|___________|_______________|
[Footnote 1: Data relating to the relative pecuniary values of acetylene
(carburetted or not), coal-gas, paraffin, and electricity as heating or
illuminating agents, are frequently presented to British readers after
simple recalculation into English equivalents of the figures which obtain
in France and Germany. Such a method of procedure is utterly incorrect,
as it ignores the higher prices of coal, coal-gas, and especially
petroleum products on the Continent of Europe, which arise partly from
geographical, but mainly from political causes.]
The mixture was tried also at higher pressures in the same burners, but
with less favourable results in regard to the duty realised. The oil-gas
was also tried at various pressures, and the most favourable result is
taken for computing the ratio in the last column. It is evident from this
table that 1 volume of this acetylene-oil-gas mixture is equal at the
most to 1.65 volume of the simple oil-gas. Whether the mixture will prove
cheaper under particular conditions must depend on the relative prices of
gas-oil and calcium carbide at the works where the gas is made and
compressed. At the prevailing prices in most parts of Britain, simple
oil-gas is slightly cheaper, but an appreciable rise in the price of gas-
oil would render the mixture with acetylene the cheaper illuminant. The
fact remains, however, that per unit weight or volume of cylinder into
which the gas is compressed, acetylene oil-gas evolves a higher candle-
power, or the same candle-power for a longer period, than simple,
unenriched British oil-gas. Latterly, however, the incandescent mantle
has found application for railway-carriage lighting, and poorer
compressed gases have thereby been rendered available. Thus coal-gas, to
which a small proportion of acetylene has been added, may advantageously
displace the richer oil-gas and acetylene mixtures.
Patents have been taken out by Schwander for the preparation of a mixture
of acetylene, air, and vaporised petroleum spirit. A current of naturally
damp, or artificially moistened, air is led over or through a mass of
calcium carbide, whereby the moisture is replaced by an equivalent
quantity of acetylene; and this mixture of acetylene and air is
carburetted by passing it through a vessel of petroleum spirit in the
manner adopted with air-gas. No details as to the composition,
illuminating power, and calorific values of the gas so made have been
published. It would clearly tend to be of highly indefinite constitution
and might range between what would be virtually inferior carburetted
acetylene, and a low-grade air-gas. It is also doubtful whether the
combustion of such gas would not be accompanied by too grave risks to
render the process useful.
CHAPTER XII
SUNDRY USES
There are sundry uses for acetylene, and to some extent for carbide,
which are not included in what has been said in previous chapters of this
book; and to them a few words may be devoted.
In orchards and market gardens enormous damage is frequently done to the
crops by the ravages of caterpillars of numerous species. These
caterpillars cannot be caught by hand, and hitherto it has proved
exceedingly difficult to cope with them. However, when they have changed
into the perfect state, the corresponding butterflies and moths, like
most other winged insects, are strongly attracted by a bright light. As
acetylene can easily be burnt in a portable apparatus, and as the burners
can be supplied with gas at such comparatively high pressure that the
flames are capable of withstanding sharp gusts of wind even when not
protected by glass, the brilliant light given by acetylene forms an
excellent method of destroying the insects before they have had time to
lay their eggs. Two methods of using the light have been tried with
astonishing success: in one a naked flame is supported within some
receptacle, such as a barrel with one end knocked out, the interior of
which is painted heavily with treacle; in the other the flame is
supported over an open dish filled with some cheap heavy oil (or perhaps
treacle would do equally well). In the first case the insects are
attracted by the light and are caught by the adhesive surfaces; in the
second they are attracted and singed, and then drowned in, or caught by,
the liquid. Either a well-made, powerful, vehicular lamp with its bull's-
eye (if any) removed could be used for this purpose, or a portable
generator of any kind might be connected with the burner through a
flexible tube. It is necessary that the lights should be lit just before
dusk when the weather is fine and the nights dark, and for some twenty
evenings in June or July, exactly at the period of the year when the
perfect insects are coming into existence. In some of the vineyards of
Beaujolais, in France, where great havoc has been wrought by the pyralid,
a set of 10-candle-power lamps were put up during July 1901, at distances
of 150 yards apart, using generators containing 6 oz. of carbide, and
dishes filled with water and petroleum 18 or 20 inches in diameter. In
eighteen nights, some twenty lamps being employed, the total catch of
insects was 170,000, or an average of 3200 per lamp per night. At French
prices, the cost is reported to have been 8 centimes per night, or 32
centimes per hectare (2.5 acres). In Germany, where school children are
occasionally paid for destroying noxious moths, two acetylene lamps
burning for twelve evenings succeeded in catching twice as many insects
as the whole juvenile population of a village during August 1902. A
similar process has been recommended for the destruction of the malarial
mosquito, and should prove of great service to mankind in infected
districts. The superiority of acetylene in respect of brilliancy and
portability will at once suggest its employment as the illuminant in the
"light" moth-traps which entomologists use for entrapping moths. In these
traps, the insects, attracted by the light, flutter down panes of glass,
so inclined that ultimate escape is improbable; while they are protected
from injury through contact with the flame by moans of an intervening
sheet of glass.
Methods of spraying with carbide dust have been found useful in treating
mildew in vines; while a process of burying small quantities of carbide
at the roots has proved highly efficacious in exterminating phylloxera in
the French and Spanish vineyards. It was originally believed that the
impurities of the slowly formed acetylene, the phosphine in particular,
acted as toxic agents upon the phylloxera; and therefore carbide
containing an extra amount of decomposable phosphides was specially
manufactured for the vine-growers. But more recently it has been argued,
with some show of reason, that the acetylene itself plays a part in the
process, the effects produced being said to be too great to be ascribed
wholly to the phosphine. It is well known that many hydrocarbon vapours,
such as the vapour of benzene or of naphthalene, have a highly toxic
action on low organisms, and the destructive effect of acetylene on
phylloxera may be akin to this action.
As gaseous acetylene will bear a certain amount of pressure in safety--a
pressure falling somewhat short of one effective atmosphere--and as
pressure naturally rises in a generating apparatus where calcium carbide
reacts with water, it becomes possible to use this pressure as a source
of energy for several purposes. The pressure of the gas may, in fact, be
employed either to force a stream of liquid through a pipe, or to propel
certain mechanism. An apparatus has been constructed in France on the
lines of some portable fire-extinguishing appliances in which the
pressure set up by the evolution of acetylene in a closed space produces
a spray of water charged with lime and gas under the pressure obtaining;
the liquid being thrown over growing vines or other plants in order to
destroy parasitic and other forms of life. The apparatus consists of a
metal cylinder fitted with straps so that it can be carried by man or
beast. At one end it has an attachment for a flexible pipe, at the other
end a perforated basket for carbide introduced and withdrawn through a
"man-hole" that can be tightly closed. The cylinder is filled with water
to a point just below the bottom of the basket when the basket is
uppermost; the carbide charge is then inserted, and the cover fastened
down. As long as the cylinder is carried in the same position, no
reaction between the carbide and the water occurs, and consequently no
pressure arises; but on inverting the vessel, the carbide is wetted, and
acetylene is liberated in the interior. On opening the cock on the outlet
pipe, a stream of liquid issues and may be directed as required. By
charging the cylinder in the first place with a solution of copper
sulphate, the liquid ejected becomes a solution and suspension of copper
and calcium salts and hydroxides, resembling "Bordeaux mixture," and may
be employed as such. In addition, it is saturated with acetylene which
adds to its value as a germicide.
The effective gas pressure set up in a closed generator has also been
employed in Italy to drive a gas-turbine, and so to produce motion. The
plant has been designed for use in lighthouses where acetylene is burnt,
and where a revolving or flashing light is required. The gas outlet from
a suitably arranged generator communicates with the inlet of a gas-
turbine, and the outlet of the turbine is connected to a pipe leading to
the acetylene burners. The motion of the turbine is employed to rotate
screens, coloured glasses, or any desired optical arrangements round the
flames; or, in other situations, periodically to open and close a cock on
the gas-main leading to the burners. In the latter case, a pilot flame
fed separately is always alight, and serves to ignite the gas issuing
from the main burners when the cock is opened.
Another use for acetylene, which is only dependent upon a suitably
lowered price for carbide to become of some importance, consists in the
preparation of a black pigment to replace ordinary lampblack. One method
for this purpose has been elaborated by Hubou. Acetylene is prepared from
carbide smalls or good carbide, according to price, and the gas is pumped
into small steel cylinders to a pressure of 2 atmospheres. An electric
spark is then passed, and the gas, standing at its limit of safety,
immediately dissociates, yielding a quantitative amount of hydrogen and
free carbon. The hydrogen is drawn off, collected in holders, and used
for any convenient purpose; the carbon is withdrawn from the vessel, and
is ready for sale. At present the pigment is much too expensive, at least
in British conditions, to be available in the manufacture of black paint;
but its price would justify its employment in the preparation of the best
grades of printers' ink. One of the authors has examined an average
sample and has found it fully equal in every way to blacks, such as those
termed "spirit blacks," which fetch a price considerably above their real
value. It has a pure black cast of tint, is free from greasy matter, and
can therefore easily be ground into water, or into linseed oil without
interfering with the drying properties of the latter. Acetylene black has
also been tried in calico printing, and has given far better results in
tone and strength than other blacks per unit weight of pigment. It may be
added that the actual yield of pigment from creosote oils, the commonest
raw material for the preparation of lampblack ("vegetable black"), seldom
exceeds 20 or 25 per cent., although the oil itself contains some 80 per
cent, of carbon. The yield from acetylene is clearly about 90 per cent.,
or from calcium carbide nearly 37.5 per cent, of the original weight.
An objection urged against the Hubou process is that only small
quantities of the gas can be treated with the spark at one time; if the
cylinders are too large, it is stated, tarry by-products are formed. A
second method of preparing lampblack (or graphite) from acetylene is that
devised by Frank, and depends on utilising the reactions between carbon
monoxide or dioxide and acetylene or calcium carbide, which have already
been sketched in Chapter VI. When acetylene is employed, the yield is
pure carbon, for the only by-product is water vapour; but if the carbide
process is adopted, the carbon remains mixed with calcium oxide. Possibly
such a material as Frank's carbide process would give, viz., 36 parts by
weight of carbon mixed with 56 parts of quicklime or 60 parts of carbon
mixed with 112 parts of quicklime, might answer the purpose of a pigment
in some black paints where the amount of ash left on ignition is not
subject to specification. Naturally, however, the lime might be washed
away from the carbon by treatment with hydrochloric acid; but the cost of
such a purifying operation would probably render the residual pigment too
expensive to be of much service except (conceivably) in the manufacture
of certain grades of printers' ink, for which purpose it might compete
with the carbon obtainable by the Hubou process already referred to.
Acetylene tetrachloride, or tetrachlorethane, C_2H_2Cl_4, is now produced
for sale as a solvent for chlorine, sulphur, phosphorus, and organic
substances such as fats. It may be obtained by the direct combination of
acetylene and chlorine as explained in Chapter VI., but the liability of
the reaction to take place with explosive violence would preclude the
direct application of it on a commercial scale. Processes free from such
risk have now, however, been devised for the production of
tetrachlorethane. One patented by the Salzbergwerk Neu-Stassfurt consists
in passing acetylene into a mixture of finely divided iron and chloride
of sulphur. The iron acts as a catalytic. The liquid is kept cool, and as
soon as the acetylene passes through unabsorbed, its introduction is
stopped and chlorine is passed in. Acetylene and chlorine are then passed
in alternately until the liquid finally is saturated with acetylene. The
tetrachlorethane, boiling at 147° C., is then distilled off, and the
residual sulphur is reconverted to the chloride for use again in the
process. A similar process in which the chlorine is used in excess is
applicable also to the production of hexachlorethane.
Dependent upon price, again, are several uses for calcium carbide as a
metallurgical or reducing reagent; but as those are uses for carbide only
as distinguished from acetylene, they do not fall within the purview of
the present book.
When discussing, in Chapter III., methods for disposing of the lime
sludge coming from an acetylene generator, it was stated that on occasion
a use could be found for this material. If the carbide has been entirely
decomposed in an apparatus free from overheating, the waste lime is
recovered as a solid mass or as a cream of lime practically pure white in
colour. Sometimes, however, as explained in Chapter II., the lime sludge
is of a bluish grey tint, even in cases where the carbide decomposed was
of good quality and there was no overheating in the generator. Such
discoloration is of little moment for most of the uses to which the
sludge may be put. The residue withdrawn from a carbide-to-water
generator is usually quite fluid; but when allowed to rest in a suitable
pit or tank, it settles down to a semi-solid or pasty mass which contains
on a rough average 47 per cent. of water and 53 per cent. of solid
matter, the amount of lime present, calculated as calcium oxide, being
about 40 per cent. Since 64 parts by weight of pure calcium carbide yield
74 parts of dry calcium hydroxide, it may be said that 1 part of ordinary
commercial carbide should yield approximately 1.1 parts of dry residue,
or 2.1 parts of a sludge containing 47 per cent. of moisture; and sludge
of this character has been stated by Vogel to weigh about 22.5 cwt. per
cubic yard.
Experience has shown that those pasty carbide residues can be employed
very satisfactorily, and to the best advantage from the maker's point of
view, by builders and decorators for the preparation of ordinary mortar
or lime-wash. The mortar made from acetylene lime has been found equal in
strength and other properties to mortar compounded from fresh slaked
lime; while the distemper prepared by diluting the sludge has been used
most successfully in all places where a lime-wash is required,
_e.g._, on fruit-trees, on cattle-pens, farm-buildings, factories,
and the "offices" of a residence. Many of the village installations
abroad sell their sludge to builders for the above-mentioned purposes at
such a price that their revenue accounts are materially benefited by the
additional income. The sludge is also found serviceable for softening the
feed-water of steam boilers by the common liming process; although it has
been stated that the material contains certain impurities--notably "fatty
matter"--which becomes hydrolysed by the steam, yielding fatty acids that
act corrosively upon the boiler-plates. This assertion would appear to
require substantiation, but a patent has been taken out for a process of
drying the sludge at a temperature of 150° to 200° C. in order to remove
the harmful matter by the action of the steam evolved. So purified, it is
claimed, the lime becomes fit for treating any hard potable or boiler-
feed water. It is very doubtful, however, whether the intrinsic value of
acetylene lime is such in comparison with the price of fresh lime that,
with whatever object in view, it would bear the cost of any method of
artificial drying if obtained from the generators in a pasty state.
When, on the other hand, the residue is naturally dry, or nearly so, it
is exactly equal to an equivalent quantity of quick or slaked lime as a
dressing for soil. In this last connexion, however, it must be remembered
that only certain soils are improved by an addition of lime in any shape,
and therefore carbide residues must not be used blindly; but if analysis
indicates that a particular plot of ground would derive benefit from an
application of lime, acetylene lime is precisely as good as any other
description. Naturally a residue containing unspent carbide, or
contaminated with tarry matter, is essentially valueless (except as
mentioned below); while it must not be forgotten that a solid residue if
it is exposed to air, or a pasty residue if not kept under water, will
lose many of its useful properties, because it will be partially
converted into calcium carbonate or chalk.
Nevertheless, in some respects, the residue from a good acetylene
generator is a more valuable material, agriculturally speaking, than pure
lime. It contains a certain amount of sulphur, &c., and it therefore
somewhat resembles the spent or gas lime of the coal-gas industry. This
sulphur, together, no doubt, with the traces of acetylene clinging to it,
renders the residue a valuable material for killing the worms and vermin
which tend to infest heavily manured and under-cultivated soil. Acetylene
lime has been found efficacious in exterminating the "finger-and-toe" of
carrots, the "peach-curl" of peach-trees, and in preventing cabbages from
being "clubbed." It may be applied to the ground alone, or after
admixture with some soil or stable manure. The residue may also be
employed, either alone or mixed with some agglomerate, in the
construction of garden paths and the like.
If the residues are suitably diluted with water and boiled with (say)
twice their original weight of flowers of sulphur, the product consists
of a mixture of various compounds of calcium and sulphur, or calcium
sulphides--which remain partly in solution and partly in the solid state.
This material, used either as a liquid spray or as a moist dressing, has
been said to prove a useful garden insecticide and weed-killer.
There are also numerous applications of the acetylene light, each of much
value, but involving no new principle which need be noticed. The light is
so actinic, or rich in rays acting upon silver salts, that it is
peculiarly useful to the photographer, either for portraiture or for his
various positive printing operations. Acetylene is very convenient for
optical lantern work on the small scale, or where the oxy-hydrogen or
oxy-coal-gas light cannot be used. Its intensity and small size make its
self-luminous flame preferable on optical grounds to the oil-lamp or the
coal-gas mantle; but the illuminating surface is nevertheless too large
to give the best results behind such condensers as have been carefully
worked to suit a source of light scarcely exceeding the dimensions of a
point. For lantern displays on very large screens, or for the projection
of a powerful beam of light to great distances in one direction (as in
night signalling, &c.), the acetylene blowpipe fed with pure oxygen, or
with air containing more than its normal proportion of oxygen, which is
discussed in Chapter IX., is specially valuable, more particularly if the
ordinary cylinder of lime is replaced by one of magnesia, zirconia, or
other highly refractory oxide.
CHAPTER XIII
PORTABLE ACETYLENE LAMPS AND PLANT
It will be apparent from what has been said in past chapters that the
construction of a satisfactory generator for portable purposes must be a
problem of considerable complexity. A fixed acetylene installation tends
to work the more smoothly, and the gas evolved therefrom to burn the more
pleasantly, the more technically perfect the various subsidiary items of
the plant are; that is to say, the more thoroughly the acetylene is
purified, dried, and delivered at a strictly constant pressure to the
burners and stoves. Moreover, the efficient behaviour of the generator
itself will depend more upon the mechanical excellence and solidity of
its construction than (with one or two exceptions) upon the precise
system to which it belongs. And, lastly, the installation will, broadly
speaking, work the better, the larger the holder is in proportion to the
demands ever made upon it; while that holder will perform the whole duty
of a gasholder more effectually if it belongs to the rising variety than
if it is a displacement holder. All these requirements of a good
acetylene apparatus have to be sacrificed to a greater or less extent in
portable generators; and since the sacrifice becomes more serious as the
generator is made smaller and lighter in weight, it may be said in
general terms that the smaller a portable (or, indeed, other) acetylene
apparatus is, the less complete or permanent satisfaction will it give
its user. Again, small portable apparatus are only needed to develop
intensities of light insignificant in comparison with those which may
easily be won from acetylene on a larger scale; they are therefore fitted
with smaller burners, and those burners are not merely small in terms of
consumption and illuminating power, but not infrequently are very badly
constructed, and are relatively deficient in economy or duty. Thus any
comparisons which may be made on lines similar to those adopted in
Chapter I., or between unit weights, volumes, or monetary equivalents of
calcium carbide, paraffin, candles, and colza oil, become utterly
incorrect if the carbide is only decomposed in a small portable generator
fitted with an inefficient jet; first, because the latent illuminating
power of the acetylene evolved is largely wasted; secondly, because any
gas produced over and above that capable of instant combustion must be
blown off from a vent-pipe; and thirdly, because the carbide itself tends
to be imperfectly decomposed, either through a defect in the construction
of the lamp, or through the brief and interrupted requirements of the
consumer.
In several important respects portable acetylene apparatus may be divided
into two classes from a practical point of view. There is the portable
table or stand lamp intended for use in an occupied room, and there is
the hand or supported lamp intended for the illumination of vehicles or
open-air spaces. Economy apart, no difficulty arises from imperfect
combustion or escape of unburnt gas from an outdoor lamp, but in a room
the presence of unburnt acetylene must always be offensive even if it is
not dangerous; while the combustion products of the impurities--and in a
portable generator acetylene cannot be chemically purified--are highly
objectionable. It is simply a matter of good design to render any form of
portable apparatus safe against explosion (employment of proper carbide
being assumed), for one or more vent-pipes can always be inserted in the
proper places; but from an indoor lamp those vent-pipes cannot be made to
discharge into a place of safety, while, as stated before, a generator in
which the vent-pipes come into action with any frequency is but an
extravagant piece of apparatus for the decomposition of so costly a
material as calcium carbide. Looked at from one aspect the holder of a
fixed apparatus is merely an economical substitute for the wasteful vent-
pipe, because it is a place in which acetylene can be held in reserve
whenever the make exceeds the consumption in speed. It is perhaps
possible to conceive of a large table acetylene lamp fitted with a water-
sealed rising holder; but for vehicular purposes the displacement holder
is practically the only one available, and in small apparatus it becomes
too minute in size to be of much service as a store for the gas produced
by after-generation. Other forms of holder have been suggested by
inventors, such as a collapsible bag of india-rubber or the like; but
rubber is too porous, weak, and perishable a material to be altogether
suitable. If it is possible, by bringing carbide and water into mutual
contact in predetermined quantities, to produce gas at a uniform rate,
and at one which corresponds with the requirements of the burner, in a
small apparatus--and experience has shown it to be possible within
moderately satisfactory limits--it is manifest that the holder is only
needed to take up the gas of after-generation; and in Chapters II. and
III. it was pointed out that after-generation only occurs when water is
brought into contact with an excess of carbide. If, then, the opposite
system of construction is adopted, and carbide is fed into water
mechanically, no after-generation can take place; and provided the make
of gas can be controlled in a small carbide-feed generator as accurately
as is possible in a small water-to-carbide generator, the carbide-feed
principle will exhibit even greater advantages in portable apparatus than
it does in plant of domestic size. Naturally almost every variety of
carbide-feeding gear, especially when small, requires or prefers
granulated (or granulated and "treated") carbide; and granulated carbide
must inevitably be considerably more expensive per unit of light evolved
than the large material, but probably in the application to which the
average portable acetylene apparatus is likely to be put, strict economy
is not of first consequence. In portable acetylene generators of the
carbide-feed type, the supply is generally governed by the movements of a
mushroom-headed or conical valve at the mouth of a conical carbide
vessel; such movements occurring in sympathy with the alterations in
level of the water in the decomposing chamber, which is essentially a
small displacement holder also, or being produced by the contraction of a
flexible chamber through which the gas passes on its way to the burner.
So far as it is safe to speak definitely on a matter of this kind, the
carbide-feed device appears to work satisfactorily in a stationary
(_e.g._, table) lamp; but it is highly questionable whether it could
be applied to a vehicular apparatus exposed to any sensible amount of
vibration. The device is satisfactory on the table of an occupied room so
far, be it understood, as any small portable generators can be: it has no
holder, but since no after-generation occurs, no holder is needed; still
the combustion products contaminate the room with all the sulphur and
phosphorus of the crude acetylene.
For vehicular lamps, and probably for hand lanterns, the water-to-carbide
system has practically no alternative (among actual generators), and
safety and convenience have to be gained at the expense of the carbide.
In such apparatus the supply of water is usually controlled ultimately by
pressure, though a hand-operated needle-valve is frequently put on the
water tube. The water actually reaches the carbide either by dropping
from a jet, by passing along, upwards or downwards, a "wick" such as is
used in oil-lamps, or by percolating through a mass of porous material
like felt. The carbide is held in a chamber closed except at the gas exit
to the burner and at the inlet from the water reservoir: so that if gas
is produced more rapidly than the burner takes it, more water is
prevented from entering, or the water already present is driven backwards
out of the decomposing chamber into some adjoining receptacle. It is
impossible to describe in detail all the lamps which have been
constructed or proposed for vehicular use; and therefore the subject must
be approached in general terms, discussing simply the principles involved
in the design of a safe portable generator.
In all portable apparatus, and indeed in generators of larger dimensions,
the decomposing chamber must be so constructed that it can never, even by
wrong manipulation, be sealed hermetically against the atmosphere. If
there is a cock on the water inlet tube which is capable of being
completely shut, there must be no cock between the decomposing chamber
and the burner. If there is a cock between the carbide vessel and the
burner, the water inlet tube must only be closed by the water, being
water-sealed, in fact, so that if pressure rises among the carbide the
surplus gas may blow the seal or bubble through the water in the
reservoir. If the water-supply is mainly controlled by a needle-valve, it
is useful to connect the burner with the carbide vessel through a short
length of rubber tube; and if this plan is adopted, a cock can, if
desired, be put close to the burner. The rubber should not be allowed to
form a bend hanging down, or water vapour, &c., may condense and
extinguish the flame. In any case there should be a steady fall from the
burner to the decomposing chamber, or to some separate catch-pit for the
products of condensation. Much of the success attainable with small
generators will depend on the water used. If it is contaminated with
undissolved matter, the dirt will eventually block the fine orifices,
especially the needle-valve, or will choke the pores of the wick or the
felt pad. If the water contains an appreciable amount of "temporary
hardness," and if it becomes heated much in the lamp, fur will be
deposited sooner or later, and will obviously give trouble. Where the
water reservoir is at the upper part of the lamp, and the liquid is
exposed to the heat of the flame, fur will appear quickly if the water is
hard. Considerable benefit would accrue to the user of a portable lamp by
the employment of rain water filtered, if necessary, through fabric or
paper. The danger of freezing in very severe weather may be prevented by
the use of calcium chloride, or preferably, perhaps, methylated spirit in
the water (_cf._ Chapter III., p. 92). The disfavour with which
cycle and motor acetylene lamps are frequently regarded by nocturnal
travellers, other than the users thereof, is due to thoughtless design in
the optical part of such lamps, and is no argument against the employment
of acetylene. By proper shading or deflection of the rays, the eyes of
human beings and horses can be sufficiently protected from the glare, and
the whole of the illumination concentrated more perfectly on the road
surface and the lower part of approaching objects--a beam of light never
reaching a height of 5 feet above the ground is all that is needed to
satisfy all parties.
As the size of the generator rises, conditions naturally become more
suited to the construction of a satisfactory apparatus; until generators
intended to supply light to the whole of (say) a railway carriage, or the
head and cab lamps of a locomotive, or for the outside and inside
lighting of an omnibus are essentially generators of domestic dimensions
somewhat altered in internal construction to withstand vibration and
agitation. As a rule there is plenty of space at the side of a locomotive
to carry a generator fitted with a displacement holder of sufficient
size, which is made tall rather than wide, to prevent the water moving
about more than necessary. From the boiler, too, steam can be supplied to
a coil to keep the liquid from freezing in severe weather. Such apparatus
need not be described at length, for they can be, and are, made on lines
resembling those of domestic generators, though more compactly, and
having always a governor to give a constant pressure. For carriage
lighting any ordinary type of generator, preferably, perhaps, fitted with
a displacement holder, can be erected either in each corridor carriage,
or in a brake van at the end of the train. Purifiers may be added, if
desired, to save the burners from corrosion; but the consumption of
unpurified gas will seldom be attended by hygienic disadvantages, because
the burners will be contained in closed lamps, ventilating into the
outside air. The generator, also, may conveniently be so constructed that
it is fed with carbide from above the roof, and emptied of lime sludge
from below the floor of the vehicle. It can hardly be said that the use
of acetylene generated on board adds a sensible risk in case of
collision. In the event of a subsequent fire, the gas in the generator
would burn, but not explode; but in view of the greater illuminating
power per unit volume of carbide than per equal volume of compressed oil-
gas, a portable acetylene generator should be somewhat less objectionable
than broken cylinders of oil-gas if a fire should follow a railway
accident of the usual kind. More particularly by the use of "cartridges"
of carbide, a railway carriage generator can be constructed of sufficient
capacity to afford light for a long journey, or even a double journey, so
that attention would be only required (in the ordinary way) at one end of
the line.
Passing on from the generators used for the lighting of vehicles and for
portable lamps for indoor lighting to the considerably larger portable
generators now constructed for the supply of acetylene for welding
purposes and for "flare" lamps, it will be evident that they may embody
most or all of the points which are essential to the proper working of a
fixed generator for the supply of a small establishment. The holder will
generally be of the displacement type, but some of these larger portable
generators are equipped with a rising holder. The generators are,
naturally, automatic in action, but may be either of the water-to-carbide
or carbide-to-water type--the latter being preferable in the larger sizes
intended for use with the oxy-acetylene blow-pipe for welding, &c., for
which use a relatively large though intermittent supply of acetylene is
called for. The apparatus is either carried by means of handles or poles
attached to it, or is mounted on a wheelbarrow or truck for convenience
of transport to the place where it is to be used. The so called "flare"
lamps, which are high power burners mounted, with or without a reflector,
above a portable generator, are extremely useful for lighting open spaces
where work has to be carried on temporarily after nightfall, and are
rapidly displacing oil-flares of the Lucigen type for such purposes.
The use of "cartridges" of calcium carbide has already been briefly
referred to in Chapters II. and III. These cartridges are usually either
receptacles of thin sheet-metal, say tin plate, or packages of carbide
wrapped up in grease proof paper or the like. If of metal, they may have
a lid which is detached or perforated before they are put into the
generator, or the generator (when automatic and of domestic size) may be
so arranged that a cartridge is punctured in one or more places whenever
more gas is required. If wrapped in paper, the cartridges may be dropped
into water by an automatic generator at the proper times, the liquid then
loosening the gum and so gaining access to the interior; or one spot may
be covered by a drape of porous material (felt) only, through which the
water penetrates slowly. The substance inside the cartridge may be
ordinary, granulated, or "treated" carbide. Cartridges or "sticks" of
carbide are also made without wrappings, either by moistening powdered
carbide with oil and compressing the whole into moulds, or by compressing
dry carbide dust and immersing the sticks in oil or molten grease. The
former process is said to cause the carbide to take up too much oil, so
that sticks made by the second method are reputed preferable. All these
cartridges have the advantage over common carbide of being more permanent
in damp air, of being symmetrical in shape, of decomposing at a known
speed, and of liberating acetylene in known quantity; but evidently they
are more expensive, owing to the cost of preparing them, &c. They may be
made more cheaply from the dust produced in the braking of carbide, but
in that case the yield of gas will be relatively low.
It is manifest that, where space is to spare, purifiers containing the
materials mentioned in Chapter V. can be added to any portable acetylene
apparatus, provided also that the extra weight is not prohibitive. Cycle
lamps and motor lamps must burn an unpurified gas unpurified from
phosphorus and sulphur; but it is always good and advisable to filter the
acetylene from dust by a plug of cotton wool or the like, in order to
keep the burners as clear as may be. A burner with a screwed needle for
cleaning is always advantageous. Formerly the burners used on portable
acetylene lamps were usually of the single jet or rat-tail, or the union
jet or fish tail type, and exhibited in an intensified form, on account
of their small orifices, all the faults of these types of burners for the
consumption of acetylene (see Chapter VIII.). Now, however, there are
numerous special burners adapted for use in acetylene cycle and motor
lamps, &c., and many of these are of the impinging jet type, and some
have steatite heads to prevent distortion by the heat. One such cycle-
lamp burner, as sold in England by L. Wiener, of Fore Street, London, is
shown in Fig. 21. A burner constructed like the "Kona" (Chapter VIII.) is
made in small sizes (6, 8 and 10 litres per hour) for use in vehicular
lamps, under the name of the "Konette," by Falk, Stadelmann and Co.,
Ltd., of London, who also make a number of other small impinging jet
burners. A single jet injector burner on the "Phôs" principle is made in
small sizes by the Phôs Co., of London, specially for use in lamps on
vehicles.
[Illustration: FIG. 21.--CYCLE-LAMP BURNER NO. 96042A.]
Nevertheless, although satisfactory medium-sized vehicular lamps for the
generation of acetylene have been constructed, the best way of using
acetylene for all such employments as these is to carry it ready made in
a state of compression. For railway purposes, where an oil-gas plant is
in existence, and where it is merely desired to obtain a somewhat
brighter light, the oil-gas may be enriched with 20 per cent. of
acetylene, and the mixed gas pumped into the same cylinders to a pressure
of 10 atmospheres, as mentioned in Chapter XI.; the only alteration
necessary being the substitution of suitable small burners for the common
oil-gas jets. As far as the plant is concerned, all that is required is a
good acetylene generator, purifier, and holder from which the acetylene
can be drawn or forced through a meter into a larger storage holder, the
meter being connected by gearing with another meter on the pipe leading
from the oil-gas holder to the common holder, so that the necessary
proportions of the two gases shall be introduced into the common holder
simultaneously. From this final holder the enriched gas will be pumped
into the cylinders or into a storage cylinder, by means of a thoroughly
cooled pump, so that the heat set free by the compression may be safely
dissipated.
Whenever still better light is required in railway carriages, as also for
the illumination of large, constantly used vehicles, such as omnibuses,
the acetone process (_cf._ Chapter XI.) exhibits notable advantages.
The light so obtained is the light of neat acetylene, but the gas is
acetylene having an upper limit of explosibility much lower than usual
because of the vapour of acetone in it. In all other respects the
presence of the acetone will be unnoticeable, for it is a fairly pure
organic chemical body, which burns in the flame completely to carbon
dioxide and water, exactly as acetylene itself does. If the acetylene is
merely compressed into porous matter without acetone, the gas burnt is
acetylene simply; but per unit of volume or weight the cylinders will not
be capable of developing so much light.
In the United States, at least one railway system (The Great Northern)
has a number of its passenger coaches lighted by means of plain acetylene
carried in a state of compression in cylinders without porous matter. The
gas is generated, filtered from dust, and stored in an ordinary rising
holder at a factory alongside the line; being drawn from this holder
through a drier to extract moisture, and through a safety device, by a
pump which, in three stages, compresses the acetylene into large storage
reservoirs. The safety device consists of a heavy steel cylinder filled
with some porous substance which, like the similar material of the
acetone cylinders, prevents any danger of the acetylene contained in the
water-sealed holder being implicated in an explosion starting backwards
from the compression, by extinguishing any spark which might be produced
there. The plant on the trains comprises a suitable number of cylinders,
filled by contact with the large stores of gas to a pressure of 10
atmospheres, pipes of fusible metal communicating with the lamps, and
ordinary half-foot acetylene burners. The cylinders are provided with
fusible plugs, so that, in the event of a fire, they and the service-
pipes would melt, allowing the gas to escape freely and burn in the air,
instead of exploding or dissociating explosively within the cylinders
should the latter be heated by any burning woodwork or the like. It is
stated that this plan of using acetylene enables a quantity of gas to be
carried under each coach which is sufficient for a run of from 53 to 70
hours' duration, or of over 3600 miles; that is to say, enables the
train, in the conditions obtaining on the line in question, to make a
complete "round trip" without exhaustion of its store of artificial
light. The system has been in operation for some years, and appears to
have been so carefully managed that no accident has arisen; but it is
clear that elements of danger are present which are eliminated when the
cylinders are loaded with porous matter and acetone. The use of a similar
system of compressed acetylene train lighting in South America has been
attended with a disastrous explosion, involving loss of life.
It may safely be said that the acetone system, or less conveniently
perhaps the mere compression into porous matter, is the best to adopt for
the table-lamp which is to be used in occupied rooms Small cylinders of
such shapes as to form an elegant base for a table-lamp on more or less
conventional lines would be easy to make. They would be perfectly safe to
handle. If accidentally or wilfully upset, no harm would arise. By
deliberate ill-treatment they might be burst, or the gas-pipe fractured
below the reducing valve, so that gas would escape under pressure for a
time; but short of this they would be as devoid of extra clangor in times
of fire as the candle or the coal-gas burner. Moreover, they would only
contaminate the air with carbon dioxide and water vapour, for the gas is
purified before compression; and modern investigations have conclusively
demonstrated that the ill effects produced in the air of an imperfectly
ventilated room by the extravagant consumption of coal-gas depend on the
accumulation of the combustion products of the sulphur in the gas rather
than upon the carbon dioxide set free.
One particular application of the portable acetylene apparatus is of
special interest. As calcium carbide evolves an inflammable gas when it
merely comes into contact with water, it becomes possible to throw into
the sea or river, by hand or by ejection from a mortar, a species of bomb
or portable generator which is capable of emitting a powerful beam of
light if only facilities are present for inflaming the acetylene
generated; and it is quite easy so to arrange the interior of such
apparatus that they can be kept ready for instant use for long periods of
time without sensible deterioration, and that they can be recharged after
employment. Three methods of firing the gas have been proposed. In one
the shock or contact with the water brings a small electric battery into
play which produces a spark between two terminals projecting across the
burner orifice; in the second, a cap at the head of the generator
contains a small quantity of metallic potassium, which decomposes water
with such energy that the hydrogen liberated catches fire; and in the
third a similar cap is filled with the necessary quantity of calcium
phosphide, or the "carbophosphide of calcium" mentioned in Chapter XI.,
which yields a flame by the immediate ignition of the liquid phosphine
produced on the attack of water. During the two or three seconds consumed
in the production of the spark or pilot flame, the water is penetrating
the main charge of calcium carbide in the interior of the apparatus,
until the whole is ready to give a bright light for a time limited only
by the capacity of the generator. It is obvious that such apparatus may
be of much service at sea: they may be thrown overboard to illuminate
separate lifebuoys in case of accident, or be attached to the lifebuoys
they are required to illuminate, or be used as lifebuoys themselves if
fitted with suitable chains or ropes; they may be shot ahead to
illuminate a difficult channel, or to render an enemy visible in time of
war. Several such apparatus have already been constructed and severely
tested; they appear to give every satisfaction. They are, of course, so
weighted that the burner floats vertically, while buoyancy is obtained
partly by the gas evolved, and partly by a hollow portion of the
structure containing air. Cartridges of carbide and caps yielding a self-
inflammable gas can be carried on board ship, by means of which the
torches or lifebuoys may be renewed after service in a few minutes' time.
CHAPTER XIV
VALUATION AND ANALYSIS OF CARBIDE
The sale and purchase of calcium carbide in this country will, under
existing conditions, usually be conducted in conformity with the set of
regulations issued by the British Acetylene Association, of which a copy,
revised to date, is given below:
"REGULATIONS AS TO CARBIDE OF CALCIUM."
1. The carbide shall be guaranteed by the seller to yield, when broken
to standard size, _i.e._, in lumps varying from 1 to 2-1/2 inches or
larger, not less than 4.8 cubic feet per lb., at a barometric pressure of
30 inches and temperature of 60° Fahr. (15.55° Centigrade). The actual
gas yield shall be deemed to be the gas yield ascertained by the analyst,
plus 5 per cent.
"Carbide yielding less than 4.8 cubic feet in the sizes given above shall
be paid for in proportion to the gas yield, _i.e._, the price to be
paid shall bear the same relation to the contract price as the gas yield
bears to 4.8 cubic feet per lb.
"2. The customer shall have the right to refuse to take carbide yielding
in the sizes mentioned above less than 4.2 cubic foot, per lb., and it
shall lie, in case of refusal and as from the date of the result, of the
analysis being made known to either party, at the risk and expense of the
seller.
"3. The carbide shall not contain higher figures of impurities than shall
from time to time be fixed by the Association.
"4. No guarantee shall be given for lots of less than 3 cwt., or for
carbide crushed to smaller than the above sizes.
"5. In case of dispute as to quality, either the buyer or the seller
shall have the right to have one unopened drum per ton of carbide, or
part of a ton, sent for examination to one of the analysts appointed by
the Association, and the result of the examination shall be held to apply
to the whole of the consignment to which the drum belonged.
"6. A latitude of 5 per cent, shall be allowed for analysis; consequently
differences of 5 per cent. above or below the yields mentioned in 1 and 2
shall not be taken into consideration.
"7. Should the yield of gas be less than 4.8 cubic feet less 5 per cent.,
the carriage of the carbide to and from the place of analysis and the
cost of the analysis shall be paid for by the seller. Should the yield be
more than 4.8 cubic feet less 5 per cent., the carriage and costs of
analysis shall be borne by the buyer, who, in addition, shall pay an
increase of price for the carbide proportionate to the gas yield above
4.8 cubic feet plus 5 per cent.
"8. Carbide of 1 inch mesh and above shall not contain more than 5 per
cent. of dust, such dust to be defined as carbide capable of passing
through a mesh of one-sixteenth of an inch.
"9. The seller shall not be responsible for deterioration of quality
caused by railway carriage in the United Kingdom, unless he has sold
including carriage to the destination indicated by the buyer.
"10. Carbide destined for export shall, in case the buyer desires to have
it tested, be sampled at the port of shipment, and the guarantee shall
cease after shipment.
"11. The analyst shall take a sample of not less than 1 lb. each from the
top, centre, and bottom of the drum. The carbide shall be carefully
broken up into small pieces, due care being taken to avoid exposure to
the air as much as possible, carefully screened and tested for gas yield
by decomposing it in water, previously thoroughly saturated by exposure
to acetylene for a period of not less than 48 hours.
"12. Carbide which, when properly decomposed, yields acetylene containing
from all phosphorus compounds therein more than .05 per cent. by volume
of phosphoretted hydrogen, may be refused by the buyer, and any carbide
found to contain more than this figure, with a latitude of .01 per cent.
for the analysis, shall lie at the risk and expense of the seller in the
manner described in paragraph 2.
"The rules mentioned in paragraph 7 shall apply as regards the carriage
and costs of analysis; in other words, the buyer shall pay these costs if
the figure is below 0.05 per cent. plus 0.01 per cent., and the seller if
the figure is above 0.05 per cent. plus 0.01 per cent.
"The sampling shall take place in the manner prescribed in paragraphs 5
and 11, and the analytical examination shall be effected in the manner
prescribed by the Association and obtainable upon application to the
Secretary."
* * * * *
The following is a translation of the corresponding rules issued by the
German Acetylene Association (_Der Deutsche Acetylenverein_) in
regard to business dealings in calcium carbide, as put into force on
April 1, 1909:
"REGULATIONS OF THE GERMAN ACETYLENE ASSOCIATION FOR TRADE IN CARBIDE.
"_Price_.
"The price is to be fixed per 100 kilogrammes (= 220 lb.) net weight of
carbide in packages containing about 100 kilogrammes.
"By packages containing about 100 kilogrammes are meant packages
containing within 10 per cent. above or below that weight.
"The carbide shall be packed in gas- and water-tight vessels of sheet-
iron of the strength indicated in the prescriptions of the carrying
companies.
"The prices for other descriptions of packing must be specially stated.
"_Place of Delivery_.
"For consignment for export, the last European shipping port shall be
taken as the place of delivery.
"_Quality_.
"Commercial carbide shall be of such quality that in the usual lumps of
15 to 80 mm. (about 3/5 to 3 inches) diameter it shall afford a yield of
at least 300 litres at 15° C. and 760 mm. pressure of crude acetylene per
kilogramme for each consignment (= 4.81 cubic feet at 60° F. and 30
inches per lb.). A margin of 2 per cent. shall be allowed for the
analysis. Carbide which yields less than 300 litres per kilogramme, but
not less than 270 litres (= 4.33 cubic feet) of crude acetylene per
kilogramme (with the above-stated 2 per cent. margin for analysis) must
be accepted by the buyer. The latter, however, is entitled to make a
proportionate deduction from the price and also to deduct the increased
freight charges to the destination or, if the latter is not settled at
the time when the transaction is completed, to the place of delivery.
Carbide which yields less than 270 litres of crude acetylene per
kilogramme need not be accepted.
"Carbide must not contain more than 5 per cent. of dust. By dust is to be
understood all which passes through a screen of 1 mm. (0.04 inch) square,
clear size of holes.
"Small carbide of from 4 to 15 mm. (= 1/6 to 3/5 inch) in size (and
intermediate sizes) must yield on the average for each delivery at least
270 litres at 15° C. and 760 mm. pressure of crude acetylene per
kilogramme (= 4.33 cubic feet at 60° F. and 30 inches per lb.) A margin
of 2 per cent. shall be allowed for the analysis. Small carbide of from 4
to 15 mm. in size (and intermediate sizes) which yields less than 270
litres but not less than 250 litres (= 4.01 cubic feet per lb.) of crude
acetylene per kilogramme (with the above-stated 2 per cent. margin for
analysis) must be accepted by the buyer. The latter, however, is entitled
to make a proportionate deduction from the price and also to deduct the
increased freight charges to the destination or, if the latter is not
settled at the time when the transaction is completed, to the place of
delivery. Small carbide of from 4 to 15 mm. in size (and intermediate
sizes) which yields less than 250 litres per kilogramme need not be
accepted.
"Carbide shall only be considered fit for delivery if the proportion of
phosphoretted hydrogen in the crude acetylene does not amount to more
than 0.04 volume per cent. A margin of 0.01 volume per cent. shall be
allowed for the analysis for phosphoretted hydrogen. The whole of the
phosphorus compounds contained in the gas are to be calculated as
phosphoretted hydrogen.
"_Period for Complaints._
"An interval of four weeks from delivery shall be allowed for complaints
for consignments of 5000 kilogrammes (= 5 tons) and over, and an interval
of two weeks for smaller consignments. A complaint shall refer only to a
quantity of carbide remaining at the time of taking the sample.
"_Determination of Quality._
"1. In case the parties do not agree that the consignee is to send to the
analyst for the determination of the quality one unopened and undamaged
drum when the consignment is less than 5000 kilogrammes, and two such
drums when it is over 5000 kilogrammes, a sample for the purpose of
testing the quality is to be taken in the following manner:
"A sample having a total weight of at least 2 kilogrammes (= 4.4 lb.) is
to be taken. If the delivery to be tested does not comprise more than ten
drums, the sample is to be taken from an unopened and undamaged drum
selected at random. With deliveries of more than ten drums, the sample is
to be drawn from not fewer than 10 per cent, of the lot, and from each of
the unopened and undamaged drums drawn for the purpose not less than 1
kilogramme (= 2.2 lb.) is to be taken.
"The sampling is to be carried out by a trustworthy person appointed by
the two parties, or by one of the experts regularly recognised by the
German Acetylene Association, thus: Each selected drum, before opening,
is to be turned over twice (to got rid of any local accumulation of dust)
and the requisite quantity is to be withdrawn with a shovel (not with the
hand) from any part of it. These samples are immediately shot into one or
more vessels which are closed air- and water-tight. The lid is secured by
a seal. No other description of package, such as cardboard cases, boxes,
&c., is permissible.
"If there is disagreement as to the choice of a trustworthy person, each
of the two parties is to take the required quantity, as specified above.
"2. The yield of gas and the proportion of phosphoretted hydrogen
contained in it are to be determined by the methods prescribed by the
German Acetylene Association. If there are different analyses giving non-
concordant results, an analysis is to be made by the German Acetylene
Association, which shall be accepted as final and binding.
"In cases, however, where the first analysis has been made in the
Laboratory of the German Acetylene Association and arbitration is
required, the decisive analysis shall be made by the Austrian Acetylene
Association. If one of the parties prevents the arbitrator's analysis
being carried out, the analysis of the other party shall be absolutely
binding on him.
"3. The whole of the cost of sampling and analysis is to be borne by the
party in the wrong."
* * * * *
The corresponding regulations issued by the Austrian Acetylene
Association (_Der Oesterreichische Acetylenverein_) are almost
identical with those of the German Association. They contain, however,
provisions that the price is to include packing, that the carbide must
not be delivered in lumps larger than the fist, that the sample may be
sealed in a glass vessel with well-ground glass stopper, that the sample
is to be transmitted to the testing laboratory with particulars of the
size of the lots and the number of drums drawn for sampling, and that the
whole of it is to be gasified in lots of upwards of 1 kilogramme (= 2.2
lb.) apiece.
In Italy, it is enacted by the Board of Agriculture, Commerce and
Industry that by calcium carbide is to be understood for legal purposes
also any other carbide, or carbide-containing mixture, which evolves
acetylene by interaction with water. Also that only calcium carbide,
which on admixture with water yields acetylene containing less than 1 per
cent. of its volume of sulphuretted hydrogen and phosphoretted hydrogen
taken together, may be put on the market.
It is evident from the regulations quoted that the determination of the
volume of gas which a particular sample of calcium carbide is capable of
yielding, when a given weight of it is decomposed under the most
favourable conditions, is a matter of the utmost practical importance to
all interested in the trafficking of carbide, _i.e._, to the makers,
vendors, brokers, and purchasers of that material, as well as to all
makers and users of acetylene generating plant. The regulations of the
British Association do not, however, give details of the method which the
analyst should pursue in determining the yield of acetylene; and while
this may to a certain extent be advantageously left to the discretion of
the competent analyst, it is desirable that the results of the experience
already won by those who have had special opportunities for practising
this branch of analytical work should be embodied in a set of directions
for the analysis of carbide, which may be followed in all ordinary
analyses of that material. By the adoption of such a set of directions as
a provisional standard method, disputes as to the quantity of carbide
will be avoided, while it will still be open to the competent analyst to
modify the method of procedure to meet the requirements of special cases.
It would certainly be unadvisable in the present state of our analytical
methods to accept any hard and fast of rules for analysis for determining
the quality of carbide, but it is nevertheless well to have the best of
existing methods codified for the guidance of analysts. The substance of
the directions issued by the German Association (_Der Deutsche
Acetylenverein_) is reproduced below.
"METHODS FOR THE DETERMINATION OF TILE YIELD OF GAS FROM CALCIUM CARBIDE.
"The greatest precision is attained when the whole of the sample
submitted to the analyst is gasified in a carbide-to-water apparatus, and
the gas evolved is measured in an accurately graduated gasholder.
"The apparatus used for this analysis must not only admit of all the
precautionary rules of gas-analytical work being observed, but must also
fulfil certain other experimental conditions incidental to the nature of
the analysis.
"(_a_) The apparatus must be provided with an accurate thermometer
to show the temperature of the confining water, and with a pressure
gauge, which is in communication with the gasholder.
"(_b_) The generator must either be provided with a gasholder which
is capable of receiving the quantity of gas evolved from the whole amount
of carbide, or the apparatus must be so constructed that it becomes
possible with a gasholder which in not too large (up to 200 litres = say
7 cubic feet capacity) to gasify a larger amount of carbide.
"(_c_) The generator must be constructed so that escape of the
evolved gas from it to the outer air is completely avoided.
"(_d_) The gasholder must be graduated in parts up to 1/4 per cent.
of its capacity, must travel easily, and be kept, as far as may be in
suspension by counterweighting.
"(_e_) The water used for decomposing the carbide and the confining
water must be saturated, before use, with acetylene, and, further, the
generator must, before the analysis proper, be put under the pressure of
the confining (or sealing) liquid."
The following is a description of a typical form of apparatus
corresponding with the foregoing requirements:
"The apparatus, shown in the annexed figure, consists of the generator A,
the washer B, and the gasholder C.
[Illustration: FIG. 22.--LARGE-SCALE APPARATUS FOR DETERMINING YIELD OF
GAS FROM CARBIDE.]
"The generator A consists of a cylindrical vessel with sloping bottom,
provided with a sludge outlet _a_, a gas exit-pipe _b_, and a
lid _b'_ fastened by screws. In the upper part ten boxes _c_
are installed for the purpose of receiving the carbide. The bottoms of
those boxes are flaps which rest through their wire projections on a
revolvable disc _d_, which is mounted on a shaft _l_. This
shaft passes through a stuffing-box to the outside of the generator and
can be rotated by moans of the chains _f_, the pulleys _g_ and
_h_, and the winch _i_. Its rotation causes rotation of the
disc _d_. The disc _d_, on which the bottoms of the carbide-
holders are supported, is provided with a slot _e_. On rotating the
disc, on which the supporting wires of the bottoms of the carbide-holders
rest, the slot is brought beneath these wires in succession; and the
bottoms, being thus deprived of their support, drop down. It is possible
in this way to effect the discharge of the several carbide-holders by
gradual turning of the winch _i_.
"The washer B is provided with a thermometer _m_ passing through a
sound stuffing-box and extending into the water.
"The gasholder C is provided with a scale and pointer, which indicate how
much gas there is in it. It is connected with the pressure-gauge
_n_, and is further provided with a control thermometer _o_.
The gas exit-pipe _q_ can be shut off by a cock. There is a cock
between the gasholder and the washer for isolating one from the other.
"The dimensions of the apparatus are such that each carbide-holder can
contain readily about half a kilogramme (say l lb.) of carbide. The
gasholder is of about 200 litres (say 7 cubic feet) capacity; and if the
bell is 850 mm. (= 33-1/2 inches) high, and 550 mm. (= 21-1/2 inches) in
diameter it will admit of the position being read off to within half a
litre (say 0.02 cubic foot)."
The directions of the German Association for sampling a consignment of
carbide packed in drums each containing 100 kilogrammes (say 2 cwt.) have
already been given in the rules of that body. They differ somewhat from
those issued by the British Association (_vide ante_), and have
evidently been compiled with a view to the systematic and rapid sampling
of larger consignments than are commonly dealt with in this country.
Drawing a portion of the whole sample from every tenth drum is
substantially the same as the British Association's regulations for cases
of dispute, viz., to have one unopened drum (_i.e._, one or two
cwt.) per ton of carbide placed at the analyst's disposal for sampling.
Actually the mode of drawing a portion of the whole sample from every
tenth vessel, or lot, where a large number is concerned, is one which
would naturally be adopted by analysts accustomed to sampling any other
products so packed or stored, and there in no reason why it should be
departed from in the case of large consignments of carbide. For lots of
less than ten drums, unless there is reason to suspect want of
uniformity, it should usually suffice to draw the sample from one drum
selected at random by the sampler. The analyst, or person who undertakes
the sampling, must, however, exercise discretion as to the scheme of
sampling to be followed, especially if want of uniformity of the several
lots constituting the consignment in suspected. The size of the lumps
constituting a sample will be referred to later.
The British Association's regulations lead to a sample weighing about 3
lb. being obtained from each drum. If only one drum is sampled, the
quantity taken from each position may be increased with advantage so as
to give a sample weighing about 10 lb., while if a large number of drums
is sampled, the several samples should be well mixed, and the ordinary
method of quartering and re-mixing followed until a representative
portion weighing about 10 lb. remains.
A sample representative of the bulk of the consignment having been
obtained, and hermetically sealed, the procedure of testing by means of
the apparatus already described may be given from the German
Association's directions:
"The first carbide receptacle is filled with 300 to 400 grammes (say 3/4
lb.) of any readily decomposable carbide, and is hung up in the apparatus
in such a position with regard to the slot _e_ on the disc _d_
that it will be the first receptacle to be discharged when the winch
_i_ is turned. The tin or bottle containing the sample for analysis
is then opened and weighed on a balance capable of weighing exactly to
1/2 gramme (say 10 grains). The carbide in it is then distributed
quickly, and as far as may be equally, into the nine remaining carbide
receptacles, which are then shut and hung up quickly in the generator.
The lid _b'_ is then screwed on the generator to close it, and the
empty tin or bottle, from which the sample of carbide has been removed,
is weighed.
"The contents of the first carbide receptacle are then discharged by
turning the winch _i_. Their decomposition ensures on the one hand
that the sealing water and the generating water are saturated with
acetylene, and on the other hand that the dead space in the generator is
brought under the pressure of the seal, so that troublesome corrections
which would otherwise be entailed are avoided. After the carbide is
completely decomposed, but not before two hours at least have elapsed,
the cock _p_ is shut, and the gasholder is run down to the zero mark
by opening the cock _q_. The cock _q_ is then shut, _p_ is
opened, and the analytical examination proper is begun by discharging the
several carbide receptacles by turning the winch _i_. After the
first receptacle has been discharged, five or ten minutes are allowed to
elapse for the main evolution of gas to occur, and the cock _p_ is
then shut. Weights are added to the gasholder until the manometer
_n_ gives the zero reading; the position of the gasholder C is then
read off, and readings of the barometer and of the thermometer _o_
are made. The gasholder is then emptied down to the zero mark by closing
the cock _p_ and opening _q_. When this is done _q_ is
closed and _p_ is opened, and the winch _i_ is turned until the
contents of the next carbide receptacle are discharged. This procedure is
followed until the carbide from the last receptacle has been gasified;
then, after waiting until all the carbide has been decomposed, but in any
case not less than two hours, the position of the gasholder is read, and
readings of the barometer and thermometer are again taken. The total of
the values obtained represents the yield of gas from the sample
examined."
The following example is quoted:
Weight of the tin received, with its contained |
carbide . . . . . ._| = 6325 grammes.
Weight of the empty tin . . . . = 1485 "
_______
Carbide used . . . = 4840 " = 10670 lb.
The carbide in question was distributed among the nine receptacles and
gasified. The readings were:
________________________________________________
| | | | |
| No. | Litres. | Degrees C. | Millimetres. |
|______|__________|______________|_______________|
| | | | |
| 1 | 152.5 | 13 | 762 |
| 2 | 136.6 | " | " |
| 3 | 138.5 | " | " |
| 4 | 161.0 | " | " |
| 5 | 131.0 | " | " |
| 6 | 182.5 | 13.5 | " |
| 7 | 146.0 | " | " |
| 8 | 163.0 | 14.0 | " |
| 9 | 178.5 | " | " |
|______|__________|______________|_______________|
After two hours, the total of the readings was 1395.0 litres at 13.5° C.
and 762 mm., which is equivalent to 1403.7 litres (= 49.57 cubic feet) at
15° C. and 760 mm. (or 60° F. and 30 inches; there is no appreciable
change of volume of a gas when the conditions under which it is measured
are altered from 15° C. and 760 mm. to 60° F. and 30 inches, or _vice
versâ_).
The yield of gas from this sample is therefore 1403.7/4.840 = 290 litres
at 15° C. and 760 mm. per kilogramme, or 49.57/10.67 = 4.65 cubic feet at
60° F. and 30 inches per pound of carbide. The apparatus described can,
of course, be used when smaller samples of carbide only are available for
gasification, but the results will be less trustworthy if much smaller
quantities than those named are taken for the test.
Other forms of carbide-to-water apparatus may of course be devised, which
will equally well fulfil the requisite conditions for the test, viz.,
complete decomposition of the whole of the carbide without excessive rise
of temperature, and no loss of gas by solution or otherwise.
An experimental wet gas-motor, of which the water-line has been
accurately set (by means of the Gas Referees' 1/12 cubic foot measure, or
a similar meter-proving apparatus), may be used in place of the graduated
gasholder for measuring the volume of the gas evolved, provided the rate
of flow of the gas does not exceed 1/6 cubic foot, or say 5 litres per
minute. If the generation of gas is irregular, as when an apparatus of
the type described above is used, it is advisable to insert a small
gasholder or large bell-governor between the washer and the meter. The
meter must be provided with a thermometer, according to the indications
of which the observed volumes must be corrected to the corresponding
volume at normal temperature.
If apparatus such as that described above is not available, fairly
trustworthy results for practical purposes may be obtained by the
decomposition of smaller samples in the manner described below, provided
these samples are representative of the average composition of the larger
sample or bulk, and a number of tests are made in succession and the
results of individual tests do not differ by more than 10 litres of gas
per kilogramme (or 0.16 cubic foot per pound) of carbide.
It is necessary at the outset to reduce large lumps of carbide in the
sample to small pieces, and this must be done with as little exposure as
possible to the (moist) air. Failing a good pulverising machine of the
coffee-mill or similar type, which does its work quickly, the lumps must
be broken as rapidly as possible in a dry iron mortar, which may with
advantage be fitted with a leather or india-rubber cover, through a hole
in which the pestle passes. As little actual dust as possible should be
made during pulverisation. The decomposition of the carbide is best
effected by dropping it into water and measuring the volume of gas
evolved with the precautions usually practised in gas analysis. An
example of one of the methods of procedure described by the German
Association will show how this test can be satisfactorily carried out:
"A Woulff's bottle, _a_ in the annexed figure, of blown glass and
holding about 1/4 litre is used as the generating vessel. One neck, about
15 mm. in internal diameter, is connected by flexible tubing with a
globular vessel _b_, having two tubulures, and this vessel is
further connected with a conical flask _c_, holding about 100 c.c.
The other neck is provided with tubing _d_, serving to convey the
gas to the inlet-tube, with tap _e_, of the 20-litre measuring
vessel _f_, which is filled with water saturated with acetylene, and
communicates through its lower tubulure with a similar large vessel
_g_. The generating vessel _a_ is charged with about 150 c.c.
of water saturated with acetylene. The vessel _f_ is filled up to
the zero mark by raising the vessel _g_; the tap _e_ is then
shut, and connexion is made with the tube _d_. Fifty grammes (or say
2 oz.) of the pulverised carbide are then weighed into the flask _c_
and this is connected by the flexible tubing with the vessel _b_.
The carbide is then decomposed by bringing it in small portions at a time
into the bulb _b_ by raising the flask _c_, and letting it drop
from _b_ into the generating vessel _a_, after having opened
the cock _e_ and slightly raised the vessel _f_. After the last
of the carbide has been introduced two hours are allowed to elapse, and
the volume of gas in _f_ is then read while the water stands at the
same level in _f_ and _g_, the temperature and pressure being
noted simultaneously."
A second, but less commendable method of decomposing the carbide is by
putting it in a dry two-necked bottle, one neck of which is connected
with _e_, and dropping water very slowly from a tap-funnel, which
enters the other neck, on to the carbide. The generating bottle should be
stood in water, in order to keep it cool, and the water should be dropped
in at the rate of about 50 c.c. in one hour. It will take about three
hours completely to gasify the 50 grammes of carbide under these
conditions. The gas is measured as before.
[Illustration: FIG. 23.--SMALL-SCALE APPARATUS FOR DETERMINING YIELD OF
GAS FROM CARBIDE.]
Cedercreutz has carried out trials to show the difference between the
yields found from large and small carbide taken from the same drum. One
sample consisted of the dust and smalls up to about 3/5 inch in size,
while the other contained large carbide as well as the small. The latter
sample was broken to the same size as the former for the analysis. Tests
were made both with a large testing apparatus, such as that shown in Fig.
22, and with a small laboratory apparatus, such as that shown in Fig. 23.
The dust was screened off for the tests made in the large apparatus. Two
sets of testings were made on different lots of carbide, distinguished
below as "A" and "B," and about 80 grammes wore taken for each
determination in the laboratory apparatus, and 500 grammes in the large
apparatus. The results are stated in litres (at normal temperature and
pressure) per kilogramme of carbide.
___________________________________________________________________
| | | |
| | "A" | "B" |
|_____________________________________________________|______|______|
| | | |
| Lot |Litres|Litres|
| Small carbide, unscreened, in laboratory \ (1) | 276 | 267 |
| apparatus . . . . . / (2) | 273 | 270 |
| Average sample of carbide, unscreened, in \ (1) | 318 | 321 |
| laboratory apparatus . . . / (2) | 320 | 321 |
| Small carbide, dust freed, in large apparatus (1) | 288 | 274 |
| Average sample of carbide, dust freed, in \ (2) | 320 | 322 |
| large apparatus . . . . / | | |
|_____________________________________________________|______|______|
As the result of the foregoing researches Cedercreutz has recommended
that in order to sample the contents of a drum, they should be tipped
out, and about a kilogramme (say 2 to 3 lb.) taken at once from them with
a shovel, put on an iron base and broken with a hammer to pieces of about
2/5 inch, mixed, and the 500 grammes required for the analysis in the
form of testing plant which he employs taken from this sample. Obviously
a larger sample can be taken in the same manner. On the other hand the
British and German Associations' directions for sampling the contents of
a drum, which have already been quoted, differ somewhat from the above,
and must generally be followed in cases of dispute.
Cedercreutz's figures, given in the above table, show that it would be
very unfair to determine the gas-making capacity of a given parcel of
carbide in which the lumps happened to vary considerably in size by
analysing only the smalls, results so obtained being possibly 15 per
cent. too low. This is due to two causes: first, however carefully it be
stored, carbide deteriorates somewhat by the attack of atmospheric
moisture; and since the superficies of a lump (where the attack occurs)
is larger in proportion to the weight of the lump as the lump itself is
smaller, small lumps deteriorate more on keeping than large ones. The
second reason, however, is more important. Not being a pure chemical
substance, the commercial material calcium carbide varies in hardness;
and when it is merely crushed (not reduced altogether to powder) the
softer portions tend to fall into smaller fragments than the hard
portions. As the hard portions are different in composition from the soft
portions, if a parcel is sampled by taking only the smalls, practically
that sample contains an excess of the softer part of the original
material, and as such is not representative. Originally the German
Acetylene Association did not lay down any rules as to the crushing of
samples by the analyst, but subsequently they specified that the material
should be tested in the size (or sizes) in which it was received. The
British Association, on the contrary, requires the sample to be broken in
small pieces. If the original sample is taken in such fashion as to
include large and small lumps as accurately as possible in the same
proportion as that in which they occur in the main parcel, no error will
be introduced if that sample is crushed to a uniform size, and then
subdivided again; but a small deficiency in gas yield will be produced,
which will be in the consumer's favour. It is not altogether easy to see
the advantage of the British idea of crushing the sample over the German
plan of leaving it alone; because the analytical generator will easily
take, or its parts could be modified to take, the largest lumps met with.
If the sample is in very large masses, and is decomposed too quickly,
polymerisation of gas may be set up; but on the other hand, the crushing
and re-sampling will cause wastage, especially in damp weather, or when
the sampling has to be done in inconvenient places. The British
Association requires the test to be made on carbide parcels ranging
between 1 and 2-1/2 inches or larger, because that is the "standard" size
for this country, and because no guarantee is to be had or expected from
the makers as to the gas-producing capacity of smaller material.
Manifestly, if a consumer employs such a form of generator that he is
obliged to use carbide below "standard" size, analyses may be made on his
behalf in the ordinary way; but he will have no redress if the yield of
acetylene is less than the normal. This may appear a defect or grievance;
but since in many ways the use of small carbide (except in portable
lamps) is not advantageous--either technically or pecuniarily--the rule
simply amounts to an additional judicious incentive to the adoption of
apparatus capable of decomposing standard-sized lumps. The German and
Austrian Associations' regulations, however, provide a standard for the
quality of granulated carbide.
It has been pointed out that the German Association's direction that the
water used in the testing should be saturated with acetylene by a
preliminary decomposition of 1/2 kilogramme of carbide is not wholly
adequate, and it has been suggested that the preliminary decomposition
should be carried out twice with charges of carbide, each weighing not
less than 1 per cent. of the weight of water used. A further possible
source of error lies in the fact that the generating water is saturated
at the prevailing temperature of the room, and liberates some of its
dissolved acetylene when the temperature rises during the subsequent
generation of gas. This error, of course, makes the yield from the sample
appear higher than it actually is. Its effects may be compensated by
allowing time for the water in the generator or gasholder to cool to its
original temperature before the final reading is made.
With regard to the measurement of the temperature of the evolved gas in
the bell gasholder, it is usual to assume that the reading of a
thermometer which passes through the crown of the gasholder suffices. If
the thermometer has a very long stem, so that the bulb is at about the
mid-height of the filled bell, this plan is satisfactory, but if an
ordinary thermometer is used, it is better to take, as the average
temperature of the gas in the holder, the mean of the readings of the
thermometer in the crown, and of one dipping into the water of the holder
seal.
The following table gives factors for correcting volumes of gas observed
at any temperature and pressure falling within its range to the normal
temperature (60° F.) and normal barometric height (30 inches). The normal
volume thus found is, as already stated, not appreciably different from
the volume at 15° C. and 760 mm. (the normal conditions adopted by
Continental gas chemists). To use the table, find the observed
temperature and the observed reading of the barometer in the border of
the table, and in the space where these vertical and horizontal columns
meet will be found a number by which the observed volume of gas is to be
multiplied in order to find the corresponding volume under normal
conditions. For intermediate temperatures, &c., the factors may be
readily inferred from the table by inspection. This table must only be
applied when the gas is saturated with aqueous vapour, as is ordinarily
the case, and therefore a drier must not be applied to the gas before
measurement.
Hammerschmidt has calculated a similar table for the correction of
volumes of gas measured at temperatures ranging from 0° to 30° C., and
under pressures from 660 to 780 mm., to 15° C. and 760 mm. It is based on
the coefficient of expansion of acetylene given in Chapter VI., but, as
was there pointed out, this coefficient differs by so little from that of
the permanent gases for which the annexed table was compiled, that no
appreciable error results from the use of the latter for acetylene also.
A table similar to the annexed but of more extended range is given in the
"Notification of the Gas Referees," and in the text-book on "Gas
Manufacture" by one of the authors.
The determination of the amounts of other gases in crude or purified
acetylene is for the most part carried out by the methods in vogue for
the analysis of coal-gas and other illuminating gases, or by slight
modifications of them. For an account of these methods the textbook on
"Gas Manufacture" by one of the authors may be consulted. For instance,
two of the three principal impurities in acetylene, viz., ammonia and
sulphuretted hydrogen, may be detected and estimated in that gas in the
same manner as in coal gas. The detection and estimation of phosphine
are, however, analytical operations peculiar to acetylene among common
illuminating gases, and they must therefore be referred to.
_Table to facilitate the Correction of the Volume of Gas at different
Temperatures and under different Atmospheric Pressures._
_____________________________________________________
| | |
| | THERMOMETER. |
| BAR.|_______________________________________________|
| | | | | | | |
| | 46° | 48° | 50° | 52° | 54° | 56° |
|_____|_______|_______|_______|_______|_______|_______|
| | | | | | | |
|28.4 | 0.979 | 0.974 | 0.970 | 0.965 | 0.960 | 0.955 |
|28.5 | 0.983 | 0.978 | 0.973 | 0.968 | 0.964 | 0.959 |
|28.6 | 0.986 | 0.981 | 0.977 | 0.972 | 0.967 | 0.962 |
|28.7 | 0.990 | 0.985 | 0.980 | 0.975 | 0.970 | 0.966 |
|28.8 | 0.993 | 0.988 | 0.984 | 0.979 | 0.974 | 0.969 |
|28.9 | 0.997 | 0.992 | 0.987 | 0.982 | 0.977 | 0.973 |
|29.0 | 1.000 | 0.995 | 0.990 | 0.986 | 0.981 | 0.976 |
|29.1 | 1.004 | 0.999 | 0.994 | 0.989 | 0.984 | 0.979 |
|29.2 | 1.007 | 1.002 | 0.997 | 0.992 | 0.988 | 0.982 |
|29.3 | 1.011 | 1.005 | 1.001 | 0.996 | 0.991 | 0.986 |
|29.4 | 1.014 | 1.009 | 1.004 | 0.999 | 0.995 | 0.990 |
|29.5 | 1.018 | 1.013 | 1.008 | 1.003 | 0.998 | 0.993 |
|29.6 | 1.021 | 1.016 | 1.011 | 1.006 | 1.001 | 0.996 |
|29.7 | 1.025 | 1.019 | 1.015 | 1.010 | 1.005 | 1.000 |
|29.8 | 1.028 | 1.023 | 1.018 | 1.013 | 1.008 | 1.003 |
|29.9 | 1.031 | 1.026 | 1.022 | 1.017 | 1.012 | 1.007 |
|30.0 | 1.035 | 1.030 | 1.025 | 1.020 | 1.015 | 1.010 |
|30.1 | 1.038 | 1.033 | 1.029 | 1.024 | 1.019 | 1.014 |
|30.2 | 1.042 | 1.037 | 1.032 | 1.027 | 1.022 | 1.017 |
|30.3 | 1.045 | 1.040 | 1.036 | 1.030 | 1.025 | 1.020 |
|30.4 | 1.049 | 1.044 | 1.039 | 1.034 | 1.029 | 1.024 |
|30.5 | 1.052 | 1.047 | 1.042 | 1.037 | 1.032 | 1.027 |
|_____|_______|_______|_______|_______|_______|_______|
_____________________________________________________
| | |
| | THERMOMETER. |
| BAR.|_______________________________________________|
| | | | | | | |
| | 58° | 60° | 62° | 64° | 66° | 68° |
|_____|_______|_______|_______|_______|_______|_______|
| | | | | | | |
|28.5 | 0.954 | 0.949 | 0.944 | 0.939 | 0.934 | 0.929 |
|28.6 | 0.958 | 0.953 | 0.947 | 0.943 | 0.938 | 0.932 |
|28.7 | 0.961 | 0.956 | 0.951 | 0.946 | 0.941 | 0.936 |
|28.8 | 0.964 | 0.959 | 0.954 | 0.949 | 0.944 | 0.939 |
|28.9 | 0.968 | 0.963 | 0.958 | 0.953 | 0.948 | 0.942 |
|29.0 | 0.971 | 0.966 | 0.961 | 0.956 | 0.951 | 0.946 |
|29.1 | 0.975 | 0.969 | 0.964 | 0.959 | 0.954 | 0.949 |
|29.2 | 0.978 | 0.973 | 0.968 | 0.963 | 0.958 | 0.952 |
|29.3 | 0.981 | 0.976 | 0.971 | 0.966 | 0.961 | 0.956 |
|29.4 | 0.985 | 0.980 | 0.975 | 0.969 | 0.964 | 0.959 |
|29.5 | 0.988 | 0.983 | 0.978 | 0.973 | 0.968 | 0.962 |
|29.6 | 0.992 | 0.986 | 0.981 | 0.976 | 0.971 | 0.966 |
|29.7 | 0.995 | 0.990 | 0.985 | 0.980 | 0.974 | 0.969 |
|29.8 | 0.998 | 0.993 | 0.988 | 0.983 | 0.978 | 0.972 |
|29.9 | 1.002 | 0.997 | 0.991 | 0.986 | 0.981 | 0.976 |
|30.0 | 1.005 | 1.000 | 0.995 | 0.990 | 0.985 | 0.979 |
|30.1 | 1.009 | 1.003 | 0.998 | 0.993 | 0.988 | 0.983 |
|30.2 | 1.012 | 1.007 | 1.002 | 0.996 | 0.991 | 0.986 |
|30.3 | 1.015 | 1.010 | 1.005 | 1.000 | 0.995 | 0.989 |
|30.4 | 1.019 | 1.014 | 1.008 | 1.003 | 0.998 | 0.993 |
|30.5 | 1.022 | 1.017 | 1.012 | 1.006 | 1.001 | 0.996 |
|_____|_______|_______|_______|_______|_______|_______|
_____________________________________________
| | |
| | THERMOMETER. |
| BAR.|_______________________________________|
| | | | | | |
| | 70° | 72° | 74° | 76° | 78° |
|_____|_______|_______|_______|_______|_______|
| | | | | | |
|28.4 | 0.921 | 0.915 | 0.910 | 0.905 | 0.900 |
|28.5 | 0.924 | 0.919 | 0.914 | 0.908 | 0.903 |
|28.6 | 0.927 | 0.922 | 0.917 | 0.912 | 0.906 |
|28.7 | 0.931 | 0.925 | 0.920 | 0.915 | 0.909 |
|28.8 | 0.934 | 0.929 | 0.924 | 0.918 | 0.913 |
|28.9 | 0.937 | 0.932 | 0.927 | 0.921 | 0.916 |
|29.0 | 0.941 | 0.935 | 0.930 | 0.925 | 0.919 |
|29.1 | 0.944 | 0.939 | 0.933 | 0.928 | 0.923 |
|29.2 | 0.947 | 0.942 | 0.937 | 0.931 | 0.926 |
|29.3 | 0.950 | 0.945 | 0.940 | 0.935 | 0.929 |
|29.4 | 0.954 | 0.949 | 0.943 | 0.938 | 0.932 |
|29.5 | 0.957 | 0.952 | 0.947 | 0.941 | 0.936 |
|29.6 | 0.960 | 0.955 | 0.950 | 0.944 | 0.939 |
|29.7 | 0.964 | 0.959 | 0.953 | 0.948 | 0.942 |
|29.8 | 0.967 | 0.962 | 0.957 | 0.951 | 0.946 |
|29.9 | 0.970 | 0.965 | 0.960 | 0.954 | 0.949 |
|30.0 | 0.974 | 0.968 | 0.963 | 0.958 | 0.952 |
|30.1 | 0.977 | 0.972 | 0.966 | 0.961 | 0.955 |
|30.2 | 0.980 | 0.975 | 0.970 | 0.964 | 0.959 |
|30.3 | 0.984 | 0.978 | 0.973 | 0.968 | 0.962 |
|30.4 | 0.987 | 0.982 | 0.976 | 0.971 | 0.965 |
|30.5 | 0.990 | 0.985 | 0.980 | 0.974 | 0.969 |
|_____|_______|_______|_______|_______|_______|
For the detection of phosphine, Bergé's solution may be used. It is a
"solution of 8 to 10 parts of corrosive sublimate in 80 parts of water
and 20 parts of 30 per cent. hydrochloric acid." It becomes cloudy when
gas containing phosphine is passed into it. It is, however, applied most
conveniently in the form of Keppeler's test-papers, which have been
described in Chapter V. Test-papers for phosphine, the active body in
which has not yet been divulged, have recently been produced for sale by
F. B. Gatehouse.
The estimation of phosphine will usually require to be carried out either
(1) on gas directly evolved from carbide in order to ascertain if the
carbide in question yields an excessive proportion of phosphine, or (2)
upon acetylene which is presumably purified, drawn either from the outlet
of the purifier or from the service-pipes, with the object of
ascertaining whether an adequate purification in regard to phosphine has
been accomplished. In either case, the method of estimation is the same,
but in the first, acetylene should be specially generated from a small
representative sample of the carbide and led directly into the apparatus
for the absorption of the phosphine. If the acetylene passes into the
ordinary gasholder, the amount of phosphine in gas drawn off from the
holder will vary from time to time according to the temperature and the
degree of saturation of the water in the holder-tank with phosphine, as
well as according to the amount of phosphine in the gas generated at the
time.
A method frequently employed for the determination of phosphine in
acetylene is one devised by Lunge and Cedercreutz. If the acetylene is to
be evolved from a sample of carbide in order to ascertain how much
phosphine the latter yields to the gas, about 50 to 70 grammes of the
carbide, of the size of peas, are brought into a half-litre flask, and a
tap-funnel, with the mouth of its stem contracted, is passed through a
rubber plug fitting the mouth of the flask. A glass tube passing through
the plug serves to convey the gas evolved to an absorption apparatus,
which is charged with about 75 c.c. of a 2 to 3 per cent. solution of
sodium hypochlorite. The absorption apparatus may be a ten-bulbed
absorption tube or any convenient form of absorption bulbs which subject
the gas to intimate contact with the solution. If acetylene from a
service-pipe is to be tested, it is led direct from the nozzle of a gas-
tap to the absorption tube, the outlet of which is connected with an
aspirator or the inlet of an experimental meter, by which the volume of
gas passed through the solution is measured. But if the generating flask
is employed, water is allowed to drop from the tap-funnel on to the
carbide in the flask at the rate of 6 to 7 drops a minute (the tap-funnel
being filled up from time to time), and all the carbide will thus be
decomposed in 3 to 4 hours. The flask is then filled to the neck with
water, and disconnected from the absorption apparatus, through which a
little air is then drawn. The absorbing liquid is then poured, and washed
out, into a beaker; hydrochloric acid is added to it, and it is boiled in
order to expel the liberated chlorine. It is then usual to precipitate
the sulphuric acid by adding solution of barium chloride to the boiling
liquid, allowing it to cool and settle, and then filtering. The weight of
barium sulphate obtained by ignition of the filter and its contents,
multiplied by 0.137, gives the amount of sulphur present in the acetylene
in the form of sulphuretted hydrogen. The filtrate and washings from this
precipitate are rendered slightly ammoniacal, and a small excess of
"magnesia mixture" is added; the whole is stirred, left to stand for 12
hours, filtered, the precipitate washed with water rendered slightly
ammoniacal, dried, ignited, and weighed. The weight so found multiplied
by 0.278 gives the weight of phosphorus in the form of phosphine in the
volume of gas passed through the absorbent liquid.
Objection may rightly be raised to the Lunge and Cedercreutz method of
estimating the phosphine in crude acetylene on the ground that explosions
are apt to occur when the gas is being passed into the hypochlorite
solution. Also it must be borne in mind that it aims at estimating only
the phosphorus which is contained in the gas in the form of phosphine,
and that there may also be present in the gas organic compounds of
phosphorus which are not decomposed by the hypochlorite. But when the
acetylene is evolved from the carbide in proper conditions for the
avoidance of appreciable heating it appears fairly well established that
phosphorus compounds other than phosphine exist in the gas only in
practically negligible amount, unless the carbide decomposed is of an
abnormal character. Various methods of burning the acetylene and
estimating the phosphorus in the products of combustion have, however
been proposed for the purpose of determining the total amount of
phosphorus in acetylene. Some of them are applicable to the simultaneous
determination of the total sulphur in the acetylene, and in this respect
become akin to the Gas Referees' method for the determination of the
sulphur compounds in coal-gas.
Eitner and Keppeler have proposed to burn the acetylene on which the
estimation is to be made in a current of neat oxygen. But this procedure
is rather inconvenient, and by no means essential. Lidholm liberated
acetylene slowly from 10 grammes of carbide by immersing the carbide in
absolute alcohol and gradually adding water, while the gas mixed with a
stream of hydrogen leading to a burner within a flask. The flow of
hydrogen was reduced or cut off entirely while the acetylene was coming
off freely, but hydrogen was kept burning for ten minutes after the flame
had ceased to be luminous in order to ensure the burning of the last
traces of acetylene. The products of combustion were aspirated through a
condenser and a washing bottle, which at the close were rinsed out with
warm solution of ammonia. The whole of the liquid so obtained was
concentrated by evaporation, filtered in order to remove particles of
soot or other extraneous matter, and acidified with nitric acid. The
phosphoric acid was then precipitated by addition of ammonium molybdate.
J. W. Gatehouse burns the acetylene in an ordinary acetylene burner of
from 10 to 30 litres per hour capacity, and passes the products of
combustion through a spiral condensing tube through which water is
dropped at the rate of about 75 c.c. per hour, and collected in a beaker.
The burner is placed in a glass bell-shaped combustion chamber connected
at the top through a right-angled tube with the condenser, and closed
below by a metal base through which the burner is passed. The amount of
gas burnt for one determination is from 50 to 100 litres. When the gas is
extinguished, the volume consumed is noted, and after cooling, the
combustion chamber and condenser are washed out with the liquid collected
in the beaker and finally with distilled water, and the whole, amounting
to about 400 c.c., is neutralised with solution of caustic alkali (if
decinormal alkali is used, the total acidity of the liquid thus
ascertained may be taken as a convenient expression of the aggregate
amount of the sulphuric, phosphoric and silicic acids resulting from the
combustion of the total corresponding impurities in the gas), acidified
with hydrochloric acid, and evaporated to dryness with the addition
towards the end of a few drops of nitric acid. The residue is taken up in
dilute hydrochloric acid; and silica filtered off and estimated if
desired. To the filtrate, ammonia and magnesia mixture are added, and the
magnesium pyrophosphate separated and weighed with the usual precautions.
Sulphuric acid may, if desired, be estimated in the filtrate, but in that
case care must be taken that the magnesia mixture used was free from it.
Mauricheau-Beaupré has elaborated a volumetric method for the estimation
of the phosphine in crude acetylene depending on its decomposition by a
known volume of excess of centinormal solution of iodine, addition of
excess of standard solution of sodium thiosulphate, and titrating back
with decinormal solution of iodine with a few drops of starch solution as
an indicator. One c.c. of centinormal solution of iodine is equivalent to
0.0035 c.c. of phosphine. This method of estimation is quickly carried
out and is sufficiently accurate for most technical purposes.
In carrying out these analytical operations many precautions have to be
taken with which the competent analyst is familiar, and they cannot be
given in detail in this work, which is primarily intended for ordinary
users of acetylene, and not for the guidance of analysts. It may,
however, be pointed out that many useful tests in connexion with
acetylene supply can be conducted by a trained analyst, which are not of
a character to be serviceable to the untrained experimentalist. Among
such may be named the detection of traces of phosphine in acetylene which
has passed through a purifier with a view to ascertaining if the
purifying material is exhausted, and the estimation of the amount of air
or other diluents in stored acetylene or acetylene generated in a
particular manner. Advice on these points should be sought from competent
analysts, who will already have the requisite information for the
carrying out of any such tests, or know where it is to be found. The
analyses in question are not such as can be undertaken by untrained
persons. The text-book on "Gas Manufacture" by one of the authors gives
much information on the operations of gas analysis, and may be consulted,
along with Hempel's "Gas Analysis" and Winkler and Lunge's "Technical Gas
Analysis."
APPENDIX
DESCRIPTIONS OF A NUMBER OF ACETYLENE GENERATORS AS MADE IN THE YEAR 1909
(_The purpose of this Appendix is explained in Chapter IV., page 111,
and a special index to it follows the general index at the end of this
book._)
AMERICA--CANADA.
_Maker_: SICHE GAS CO., LTD., GEORGETOWN, ONTARIO.
_Type_: Automatic; carbide-to-water.
The "Siche" generator made by this firm consists of a water-tank
_A_, having at the bottom a sludge agitator _N_ and draw-off
faucet _O_, and rigidly secured within it a bell-shaped generating
chamber _B_, above which rises a barrel containing the feed chamber
_C_, surmounted by the carbide chamber _D_. The carbide used is
granulated or of uniform size. In the generating chamber _B_ is an
annular float _E_, nearly filling the area of the chamber, and
connected, by two rods passing, with some lateral play, through apertures
in the conical bottom of the feed chamber _C_, to the T-shaped
tubular valve _F_. Consequently when the float shifts vertically or
laterally the rods and valves at once move with it. The angle of the cone
of the feed chamber and the curve of the tubular valve are based on the
angle of rest of the size of carbide used, with the object of securing
sensitiveness of the feed. The feed is thus operated by a very small
movement of the float, and consequently there is but very slight rise and
fall of the water in the generating chamber. Owing to the lateral play,
the feed valve rarely becomes concentric with its seat. There is a cover
_G_ over the feed valve _F_, designed to distribute the carbide
evenly about the feed aperture and to prevent it passing down the hollow
of the valve and the holes through which the connecting-rods pass. It
also directs the course of the evolved gas on its way to the service-pipe
through the carbide in the feed chamber _C_, whereby the gas is
dried. The carbide chamber _D_ has at its bottom a conical valve,
normally open, but closed by means of the spindle _H_, which is
engaged at its upper end by the closing screw-cap _J_, which is
furnished with a safelocking device to prevent its removal until the
conical valve is closed and the hopper chamber _D_ thereby cut off
from the gas-supply. The cap _J_, in addition to a leather washer to
make a gas-tight joint when down, has a lower part fitting to make an
almost gas-tight joint. Thus when the cap is off; the conical valve fits
gas-tight; when it is on and screwed down it is gas-tight; and when on
but not screwed down, it is almost gas-tight. Escape of gas is thus
avoided. A special charging funnel _K_, shown in half-scale, is
provided for inserting in place of the screw cap. The carbide falls from
the funnel into the chamber _D_ when the chain is pulled. A fresh
charge of carbide may be put in while the apparatus is in action. The
evolved gas goes into the chamber _C_ through a pipe, with cock, to
a dust-arrester _L_, which contains a knitted stocking lightly
filled with raw sheep's wool through which the gas passes to the service-
pipe. The dust-arrester needs its contents renewing once in one, two, or
three years, according to the make of gas. The pressure of the gas is
varied as desired by altering the height of water in the tank _A_.
When cleaning the machine, the water must never be run below the top of
the generating chamber.
[Illustration: FIG. 24.--"SICHE" GENERATOR.]
AMERICA--UNITED STATES.
_Maker:_ J. B. COLT CO., 21 BARCLAY STREET, NEW YORK.
_Type:_ Automatic; carbide-to-water.
The "Colt" generator made by this firm comprises a carbide hopper mounted
above a generating tank containing water, and an equalising bell
gasholder mounted above a seal-pot having a vent-pipe _C_
communicating with the outer air. The carbide hopper is charged with 1/4
x 1/12 inch carbide, which is delivered from it into the water in the
generating tank in small portions at a time through a double valve, which
is actuated through levers connected to the crown of the equalising
gasholder. As the bell of the gasholder falls the lever rotates a rock
shaft, which enters the carbide hopper, and through a rigidly attached
lever raises the inner plunger of the feed-valve. The inner plunger in
turn raises the concentric outer stopper, thereby leaving an annular
space at the base of the carbide hopper, through which a small delivery
of carbide to the water in the generating tank then ensues. The gas
evolved follows the course shown by the arrows in the figure into the
gasholder, and raises the bell, thereby reversing the action of the
levers and allowing the valve to fall of its own weight and so cut off
the delivery of carbide. The outer stopper of the valve descends before
the inner plunger and so leaves the conical delivery mouth of the hopper
free from carbide. The inner plunger, which is capped at its lower end
with rubber, then falls and seats itself moisture-tight on the clear
delivery mouth of the hopper. The weight of the carbide in the hopper is
taken by its sides and a projecting flange of the valve casing, so that
the pressure of the carbide at the delivery point is slight and uniform.
The outside of the delivery mouth is finished by a drip collar with
double lip to prevent condensed moisture creeping upwards to the carbide
in the hopper. A float in the generating tank, by its descent when the
water falls below a certain level, automatically draws a cut off across
the delivery mouth of the carbide hopper and so prevents the delivery of
carbide either automatically or by hand until the water in the generating
tank has been restored to its proper level. Interlocking levers, (11) and
(12) in the figure, prevent the opening of the feed valve while the cap
(10) of the carbide hopper is open for recharging the hopper. There is a
stirrer actuated by a handle (9) for preventing the sludge choking the
sludge cock. The gas passes into the gasholder through a floating seal,
which serves the dual purpose of washing it in the water of the gasholder
tank and of preventing the return of gas from the holder to the
generating tank. From the gasholder the gas passes to the filter (6)
where it traverses a strainer of closely woven cotton felt for the
purpose of the removal of any lime.
[Illustration: FIG. 25.--"COLT" GENERATING PLANT.]
Drip pipes (30) and (31) connected to the inlet- and outlet-pipes of the
gasholder are sealed in water to a depth of 6 inches, so that in the
event of the pressure in the generator or gasholder rising above that
limit the surplus gas blows through the seal and escapes through the
vent-pipe _C_. There is also a telescopic blow-off (32) and (33),
which automatically comes into play if the gasholder bell rises above a
certain height.
_Maker:_ DAVIS ACETYLENE CO., ELKHARDT, INDIANA.
_Type:_ Automatic; carbide-to-water.
The "Davis" generator made by this firm comprises an equalising bell
gasholder with double walls, the inner wall surrounding a central tube
rising from the top of the generating chamber, in which is placed a
water-sealed carbide chamber with a rotatory feeding mechanism which is
driven by a weight motor. The carbide falls from the chamber on to a wide
disc from which it is pushed off a lump at a time by a swinging
displacer, so arranged that it will yield in every direction and prevent
clogging of the feeding mechanism. Carbide falls from the disk into the
water of the generating chamber, and the evolved gas raises the bell and
so allows a weighted lever to interrupt the action of the clockwork,
until the bell again descends. The gas passes through a washer in the
gasholder tank, and then through an outside scrubber to the service-pipe.
There is an outside chamber connected by a pipe with the generating
chamber, which automatically prevents over-filling with water, and also
acts as a drainage chamber for the service- and blow-off-pipes. There is
an agitator for the residuum and a sludge-cock through which to remove
same. The feeding mechanism permits the discharge of lump carbide, and
the weight motor affords independent power for feeding the carbide, at
the same time indicating the amount of unconsumed carbide and securing
uniform gas pressure.
[Illustration: FIG. 26.--"DAVIS" GENERATOR.]
_Maker:_ SUNLIGHT GAS MACHINE CO., 49 WARREN STREET, NEW YORK.
_Type:_ Automatic; carbide-to-water.
The "Omega" apparatus made by this firm consists of a generating tank
containing water, and surmounted by a hopper which is filled with carbide
of 1/4-inch size. The carbide is fed from the hopper into the generating
tank through a mechanism consisting of a double oscillating cup so
weighted that normally the feed is closed. The fall of the bell of the
equalising gasholder, into which the gas evolved passes, operates a lever
_B_, which rotates the weighted cup in the neck of the hopper and so
causes a portion of carbide to fall into the water in the generating
tank. The feed-cup consists of an upper cup into which the carbide is
first delivered. It is then tipped from the upper cup into the lower cup
while, at the same time, further delivery from the hopper is prevented.
Thus only the portion of carbide which has been delivered into the lower
cup is emptied at one discharge into the generator. There is a safety
lock to the hopper cap which prevents the feeding mechanism coming into
operation until the hopper cap is screwed down tightly. Provision is made
for a limited hand-feed of carbide to start the apparatus. The gasholder
is fitted with a telescoping vent-pipe, by which gas escapes to the open
in the event of the bell being raised above a certain height. There is
also an automatic cut-off of the carbide feed, which comes into operation
it the gas is withdrawn too rapidly whether through leakage in the pipes
or generating plant, or through the consumption being increased above the
normal generating capacity of the apparatus. The gas evolved passes into
a condensing or washing chamber placed beneath the gasholder tank and
thence it travels to the gasholder. From the gasholder it goes through a
purifier containing "chemically treated coke and cotton" to the supply-pipe.
[Illustration: FIG. 27.--"OMEGA" GENERATOR.]
1 Vent-cock handle.
2 Residuum-cock handle.
3 Agitator handle.
4 Filling funnel.
5 Water overflow.
6 Hopper cap and lever.
7 Starting feed.
8 Rocker arm.
9 Feed connecting-rod.
A Pawl.
B Lever for working feed mechanism.
C Guide frame.
D Residuum draw-off cock.
G Chain from hopper cap to feed mechanism.
H Blow-off and vent-pipe connexion.
I Gas outlet from generator.
J Gas service-cock.
K Filling funnel for gasholder tank.
L Funnel for condensing chamber.
M Gas outlet at top of purifier.
N Guides on gas-bell.
O Crosshead on swinging pawl.
P Crane carrying pawl.
Q Shaft connecting feed mechanism.
R Plug in gas outlet-pipe.
S Guide-frame supports.
U Removable plate to clean purifier.
Z Removable plate to expose feed-cups for cleaning same.
AUSTRIA-HUNGARY
_Maker:_ RICH. KLINGER, GUMPOLDSKIRCHEN, NEAR VIENNA.
_Type:_ Non-automatic; carbide-to-water.
The generating plant made by this firm consists of the generator _A_
which is supported in a concrete water and sludge tank _B_, a
storage gasholder _J_, and purifiers _K_. In the top of the
generator are guide-ways _F_, through each of which is passed a
plunger _C_ containing a perforated cage charged with about 8 lb. of
lump carbide. The plungers are supported by ropes passing over pulleys
_D_, and when charged they are lowered through the guide-ways
_F_ into the water in the tank _B_. The charge of carbide is
thus plunged at once into the large body of water in the tank, and the
gas evolved passes through perforations in the washer _G_ to the
condenser _H_ and thence to the storage gasholder _J_. After
exhaustion of the charge the plungers are withdrawn and a freshly charged
cage of carbide inserted ready for lowering into the generating tank.
There is a relief seal _f_ through which gas will blow and escape by
a pipe _g_ to the open should the pressure within the apparatus
exceed the depth of the seal, viz., about 9 inches. There is a syphon pot
_N_ for the collection and withdrawal of condensed water. The sludge
is allowed to accumulate in the bottom of the concrete tank _B_
until it becomes necessary to remove it at intervals of about three
months. Water is added to the tank daily to replace that used up in the
generation of the gas. The gas passes from the storage holder through one
of the pair of purifiers _K_, with water-sealed lids, which are
charged with a chemical preparation for the removal of phosphoretted
hydrogen. This purifying material also acts as a desiccating agent. From
the purifiers the gas passes through the meter _L_ to the service-
pipes.
[Illustration: FIG. 28.--KLINGER'S GENERATING PLANT.]
BELGIUM.
_Maker_: SOC. AN. DE L'ACÉTYLITHE, 65 RUE DU MARCHE, BRUSSELS.
_Type_: Automatic; contact.
The generating apparatus made by this firm uses, instead of ordinary
carbide, a preparation known as "acétylithe," which is carbide treated
specially with mineral oil, glucose and sugar. The object of using this
treated carbide is to avoid the effects of the attack of atmospheric
humidity or water vapour, which, with ordinary carbide, give rise to the
phenomena of after-generation. The generator comprises a water-tank
_A_ with conical base, a basket _C_ containing the treated
carbide inserted within a cylindrical case _B_ which is open at the
bottom and is surmounted by a cylindrical filter _D_. At starting,
the tank _A_ is filled with water to the level _N N'_. The
water rises within the cylindrical case until it comes in contact with
the treated carbide, which thereupon begins to evolve gas. The gas passes
through the filter _D_, which is packed with dry cotton-wool, and
escapes through the tap _M_. As soon as the contained air has been
displaced by gas the outlet of the tap _M_ is connected by a
flexible tube to the pipe leading to a purifier and the service-pipe.
When the tap _M_ is closed, or when the rate of evolution of the gas
exceeds the rate of consumption, the evolved gas accumulates within the
cylindrical case _B_ and begins to displace the water, the level of
which within the case is lowered from _S S'_, first to _S1 S'1_
and ultimately to, say, _S2 S'2_. The evolution of gas is thereby
gradually curtailed or stopped until more is required for consumption.
The water displacement causes the water-level in the outer tank to rise
to _N1 N'1_ and ultimately to, say _N2 N'2_. The lime formed by
the decomposition of the carbide is loosened from the unattacked portion
and taken more or less into solution as sucrate of lime, which is a
soluble salt which the glucose or sugar in the treated carbide forms with
lime. The solution is eventually run off through the cock _R_. The
cover _T_ of the filter is screwed down on rubber packing until gas-
tight. The purifier is charged with puratylene or other purifying
material.
[Illustration: FIG. 29.--ACÉTYLITHE GENERATOR.]
_Maker_: L. DEBRUYNE, 22 PLACE MASUI, BRUSSELS.
_Type_: (1) Automatic; carbide-to-water.
The generating plant made by this firm, using granulated carbide,
comprises an equalising gasholder _E_ alongside a generating tank
_B_, which is surmounted by a closed carbide receptacle _A_ and
a distributing appliance. The carbide receptacle is filled with
granulated carbide and the lid _N_ screwed down; the carbide is then
withdrawn from the base of the receptacle by the distributing appliance
and discharged in measured quantities as required into the water in the
generating tank. The distributing appliance is actuated by a weighted
cord _H_ attached to the bell _I_ of the gasholder and
discharges at each time a quantity of carbide only sufficient nearly to
fill the gasholder with acetylene. The gas passes from the generator
through the pipe _J_ and seal-pot _D_, or bypass _F_, to
the gasholder. The generating tank is provided with a funnel _G_ for
replacing the water consumed, a sludge-stirrer and a draw-off cock
_L_, and a water-level cock _C_. The gas passes from the
gasholder through a purifier _K_, charged with heratol, to the
service-pipe.
[Illustration: FIG. 30.--L. DEBRUYNE'S GENERATING PLANT FOR GRANULATED
CARBIDE.]
(2) Automatic; carbide-to-water.
The "Debruyne" generator comprises an equalising bell gasholder _A_
placed alongside a generating tank _B_ containing water into which
lump carbide is discharged as necessary from each in turn of a series of
chambers mounted in a ring above the generating tank. The chambers are
removable for refilling, and when charged are hermetically sealed until
opened in turn above the shoot _C_, through which their contents are
discharged into the generating tank. The carbide contained in each
chamber yields sufficient gas nearly to fill the gasholder. The
discharging mechanism is operated through an arm _E_ attached to the
bell _G_ of the gasholder, which sets the mechanism in motion when
the bell has fallen nearly to its lowest position. The lip _L_
serves for renewing the water in the generator, and the gas evolved goes
through the pipe _K_ with tap _F_ to the gasholder. There is an
eccentric stirrer for the sludge and a large-bore cock for discharging
it. The gas passes from the gasholder through the pipe _J_ to the
purifier _H_, charged with heratol, and thence to the service-pipe.
[Illustration: FIG. 3l.--THE "DEBRUYNE" GENERATING PLANT FOR LUMP
CARBIDE.]
_Maker_: DE SMET VAN OVERBERGE, ALOST.
_Type_: (1) Automatic; carbide-to-water.
This generating apparatus comprises an equalising gasholder _A_
placed alongside a generating tank _B_, above which is mounted on a
rotating spindle a series of chambers _C_, arranged in a circle,
which are filled with carbide. The generating tank is closed at the top,
but on one side there is a shoot _D_ through which the carbide is
discharged from the chambers in turn into the water in the tank. The
series of chambers are rotated by means of a cord passing round a pulley
_E_ and having a weight _F_ at one end, and being attached to
the bell of the gasholder at the other. When the bell falls, owing to the
consumption of gas, to a certain low position, the carbide chamber, which
has been brought by the rotation of the pulley over the shoot, is opened
at the bottom by the automatic liberation of a catch, and its contents
are discharged into the generating tank. The contents of one carbide
chamber suffice to fill the gasholder to two-thirds of its total
capacity. The carbide chambers after filling remain hermetically closed
until the bottom is opened for the discharge of the carbide. There is a
sludge-cock _G_ at the bottom of the generating tank. The gas passes
from the gasholder through a purifier _H_, which is ordinarily
charged with puratylene.
[Illustration: FIG. 32.--AUTOMATIC GENERATING PLANT OF DE SMET VAN
OVERBERGE.]
(2) Non-automatic; carbide-to-water.
This apparatus comprises a storage bell gasholder _J_ placed
alongside a generating tank in the top of which is a funnel _E_ with
a counter-weighted lever pivoted on the arm _B_. The base of the
funnel is closed by a flap valve _C_ hinged at _D_. When it is
desired to generate gas the counter-weight _A_ of the lever is
raised and the valve at the bottom of the funnel is thereby opened. A
charge of carbide is then tipped into the funnel and drops into the water
in the generating tank. The valve is then closed and the gas evolved goes
through the pipe _G_ to the gasholder, whence it passes through a
purifier to the service-pipe. There is a sludge-cock on the generating
tank.
[Illustration: FIG. 33.--NON-AUTOMATIC GENERATING PLANT OF DE SMET VAN
OVERBERGE.]
_Maker_: SOC. AN. BELGE DE LA PHOTOLITHE, 2 RUE DE HUY, LIÉGE.
_Type_: Automatic; carbide-to-water.
The "Photolithe" generating plant made by this firm comprises an
equalising bell gasholder _A_ in the tank _O_, alongside a
generating tank _B_ which is surmounted by a carbide storage
receptacle divided into a number of compartments. These compartments are
fitted with flap bottoms secured by catches, and are charged with
carbide. Through the middle of the storage receptacle passes a spindle,
to the upper end of which is attached a pulley _b_. Round the pulley
passes a chain, one end of which carries a weight _n_, while in the
other direction it traverses guide pulleys and is attached to a loop on
the crown of the gasholder bell. When the bell falls below a certain
point owing to the consumption of gas, it pulls the chain and rotates the
pulley _b_ and therewith an arm _d_, which liberates the catch
supporting the flap-bottom of the next in order of the carbide
compartments. The contents of this compartment are thereby discharged
through the shoot _C_ into the generating tank _B_. The gas
evolved passes through the cock _R_ and the pipe _T_ into the
gasholder, the rise of the bell of which takes the pull off the chain and
allows the weight at its other end to draw it up until it is arrested by
the stop _f_. The arm _d_ is thereby brought into position to
liberate the catch of the next carbide receptacle. The generating tank is
enlarged at its base to form a sludge receptacle _E_, which is
provided with a sludge draw-off cock _S_ and a hand-hole _P_.
Between the generating tank proper and the sludge receptacle is a grid,
which is cleaned by means of a rake with handle _L_. The gas passes
from the gasholder through a purifier _H_ charged with puratylene,
to the service-pipe.
[Illustration: FIG. 34.--"PHOTOLITHE" GENERATING PLANT.]
The same firm also makes a portable generating apparatus in which the
carbide is placed in a basket in the crown of the bell of the gasholder.
This apparatus is supplied on a trolley for use in autogenous soldering
or welding.
FRANCE.
_Maker_: LA SOC. DES APPLICATIONS DE L'ACÉTYLÈNE, 26 RUE CADET,
PARIS.
_Type_: Automatic; carbide-to-water.
The "Javal" generating plant made by this firm consists of an equalising
bell gasholder _A_ in the tank _B_ with a series of buckets
_D_, with removable bottoms _h_, mounted on a frame _F_
round the guide framing of the holder. Alongside the gasholder stands the
generating tank _H_ with shoot _K_, into which the carbide
discharged from the buckets falls. On top of the generator is a tipping
water-bucket _I_ supplied with water through a ball cock. The bell
of the gasholder is connected by chains _a_ and _c_, and levers
_b_ and _d_ with an arm which, when the bell descends to a
certain point, comes in contact with the catch by which the bottom of the
carbide bucket is held in place, and, liberating the same, allows the
carbide to fall into the shoot. When the bell rises, in consequence of
the evolved gas, the ring of carbide buckets is rotated sufficiently to
bring the next bucket over the shoot. Thus the buckets are discharged in
turn as required through the rise and fall of the gasholder bell.
[Illustration: FIG. 35.--"JAVAL" GENERATOR.]
The carbide falling from the opened bucket strikes the end _i_ of
the lever _k_, and thereby tips the water-bucket _I_ and
discharges its contents into the shoot of the generator. The rise in the
level of the water in the generator, due to the discharge of the water
from the bucket _I_, lifts the float _L_ and therewith, through
the attached rod and chain _u_, the ball _s_ of the valve
_t_. The sludge, which has accumulated in the base _N_ of the
generator from the decomposition of the previous portion of carbide, is
thereby discharged automatically into a special drain. The discharge-
valve closes automatically when the float _L_ has sunk to its
original level. The gas evolved passes from the generator through the
seal-pot _M_ and the pipe _r_ with cock _q_ into the
gasholder, from which it passes through the pipe _x_; with
condensation chamber and discharge tap _y_ into the purifier
_R_, which is charged with heratol.
_Maker_: L'HERMITE, LOUVIERS, EURE.
_Type_: (1) Automatic; carbide-to-water.
The generating plant known as "L'Éclair," by this firm comprises an
equalising bell gasholder _A_ floating in an annular water-seal
_N_, formed in the upper part of a generating tank _B_ into
which carbide enters through the shoot _K_. Mounted at the side of
the tank is the carbide delivery device, which consists of the carbide
containers _J_ supported on an axis beneath the water-sealed cover
_H_. The containers are filled with ordinary lump carbide when the
cover _H_ is removed. The tappet _O_ attached to the bell of
the gasholder come in contact with a pawl when the gasholder bell
descends to a certain level and thereby rotates a pinion on the
protruding end of the axis which carries the carbide containers _J_.
Each time the bell falls and the tappet strikes the pawl, one compartment
of the carbide containers discharges its contents down the shoot _K_
into the generating tank _B_. The gas evolved passes upwards and
causes the bell _A_ to rise. The gas is prevented from rising into
the shoot by the deflecting plates _G_. The natural level of the
water in the generating tank, when the apparatus is in use, is shown by
the dotted lines _L_. The lime sludge is discharged from time to
time through the cock _E_, being stirred up by means of the agitator
_C_ with handle _D_. When the sludge is discharged water is
added through _M_ to the proper level. The gas evolved passes from
the holder through the pipe with tap _F_ to the service-pipe. A
purifier is supplied if desired.
[Illustration: FIG. 36.--"L'ÉCLAIR," GENERATOR.]
_References_
A Gasholder.
B Generator.
C Agitator.
D Handle of agitator.
E Sludge-cock.
F Gas outlet.
G Deflecting plates.
H Cover.
I Carbide.
J Automatic distributor.
K Shoot.
L Water-level.
M Water-inlet.
N Water-seal.
O Tappet.
(2) Automatic; water-to-carbide; contact.
A generating plant known as "L'Étoile" made by this firm. A tappet on the
bell of an equalising gasholder depresses a lever which causes water to
flow into a funnel, the outlet of which leads to a generating chamber
containing carbide.
_Maker_: MAISON SIRIUS, FR. MANGIAMELI & CO., 34 RUE DES PETITS-
HÔTELS, PARIS.
_Type_: (1) Automatic; carbide-to-water.
The generating plant made by this firm comprises a drum-shaped carbide
holder mounted above a generating tank, a condenser, a washer, an
equalising gasholder, and a purifier. The drum _A_ is divided into
eight chambers _a_ each closed by a fastening on the periphery of
the drum. These chambers are packed with lump carbide, which is
discharged from them in turn through the funnel _B_ into the
generating tank, which is filled with water to the level of the overflow
cock _b_. A deflecting plate _d_ in the tank distributes the
carbide and prevents the evolved gas passing out by way of the funnel
_B_. The gas evolved passes through the pipe _O_ into the
condenser, which is packed with coke, through which the gas goes to the
pipe _E_ and so to the washer _P_ through the water, in which
it bubbles and issues by the pipe _G_ into the gasholder. The bell
_L_ of the gasholder is connected by a chain _C_ to the axis of
the drum _A_, on which is a pinion with pawl so arranged that the
pull on the chain caused by the fall of the bell of the gasholder rotates
the drum by 1/8 of a turn. The catch on the outside of the carbide
chamber, which has thereby been brought to the lowest position, is at the
same time freed, so that the contents of the chamber are discharged
through the funnel _B_. The evolved gas causes the bell to rise and
the drum remains at rest until, owing to the consumption of gas, the bell
again falls and rotates the drum by another 1/8 of a turn. Each chamber
of the drum holds sufficient carbide to make a volume of gas nearly equal
to the capacity of the gasholder. Thus each discharge of carbide very
nearly fills the gasholder, but cannot over-fill it. The bell is provided
with a vent-pipe _i_, which comes into operation should the bell
rise so high that it is on the point of becoming unsealed. From the
gasholder the gas passes through the pipe _J_, with cock _e_,
to the purifier, which is charged with frankoline, puratylene, or other
purifying material, whence it passes to the pipe _N_ leading to the
place of combustion. The generating tank is provided with a sludge-cock
_g_, and a cleaning opening with lid _f_. This generating plant
has been primarily designed for the use of acetylene for autogenous
welding, and is made also mounted on a suitable trolley for transport for
this purpose.
[Illustration: FIG. 37.--"SIRIUS" GENERATOR.]
(2) Automatic; carbide-to-water.
A later design of generating plant, known as the Type G, also primarily
intended for the supply of acetylene for welding, has the carbide store
mounted in the crown of the bell of the equalising gasholder, to the
framing of the tank of which are attached a purifier, charged with
frankoline, and a safety water-seal or valve. The whole plant is mounted
on a four-legged stand, and is provided with handles for carrying as a
whole without dismounting. It is made in two sizes, for charges of 5-1/2
and 11 lb. of carbide respectively.
GERMANY.
_Maker_: KELLER AND KNAPPICH, G.m.b.H., AUGSBURG.
_Type_: Non-automatic; carbide-to-water.
The "Knappich" generating plant made by this firm embodies a generating
tank, one-half of which is closed, and the other half of which is open at
the top, containing water. A small drum containing carbide is attached by
a clamp to the end of a lever which projects above the open half of the
tank. The lever is fastened to a horizontal spindle which is turned
through 180° by means of a counter-weighted lever handle. The carbide
container is thus carried into the water within the closed half of the
tank, and is opened automatically in transit. The carbide is thus exposed
to the water and the evolved gas passes through a pipe from the top of
the generating tank to a washer acting on the Livesey principle, and
thence to a storage gasholder. The use of closed carbide containers in
charging is intended to preclude the introduction of air into the
generator, and the evolution and escape of gas to the air while the
carbide is being introduced. Natural circulation of the water in the
generating tank is encouraged with a view to the dissipation of heat and
washing of the evolved gas. From the gasholder the gas passes in a
downward direction through two purifiers arranged in series, charged with
a material supplied under the proprietary name of "Carburylen." This
material is stated to act as a desiccating as well as a purifying agent.
The general arrangement of the plant is shown in the illustration. (Fig.
38).
[Illustration: FIG. 38.--"KNAPPICH" GENERATING PLANT.]
_Maker_: NORDISCHE AZETYLEN-INDUSTRIE; ALTONA-OTTENSEN.
_Type_: Automatic; water-to-carbide; "drawer."
The apparatus made by this firm consists of an equalising gasholder with
bell _D_ and tank _E_, a water-tank _O_, and two drawer
generators _C_ situated in the base of the gasholder tank. The
water-supply from the tank _O_ through the pipe _P_ with valve
_Q_ is controlled by the rise and fall of the bell through the
medium of the weight _J_ attached to the bell. When the bell
descends this weight rests on _K_ and so moves a counter-weighted
lever, which opens the valve _Q_. The water then flows through the
nozzle _B_ into one division of the funnel _A_ and down the
corresponding pipe to one of the generators. The generators contain trays
with compartments intended to be half filled with carbide. The gas
evolved passes up the pipe _T_ and through the seal _U_ into
the bell of the gasholder. There is a safety pipe _F_, the upper end
of which is carried outside the generator house. From the gasholder the
gas is delivered through the cock _M_ to a purifier charged with a
special purifying material mixed with cork waste and covered with
wadding. There is a drainage cock _N_ at the base of the purifier.
The nozzle _B_ of the water-supply pipe is shifted to discharge into
either compartment of the funnel _A_, according to which of the two
generators is required to be in action. The other generator may then be
recharged without interfering with the continuous working of the plant.
[Illustration: FIG. 39.--GENERATING PLANT OF THE NORDISCHE AZETYLEN-
INDUSTRIE.]
GREAT BRITAIN AND IRELAND.
_Maker:_ THE ACETYLENE CORPORATION OF GREAT BRITAIN LTD., 49
VICTORIA STREET, LONDON, S.W.
_Type:_ (1) Automatic; water-to-carbide; contact, superposed pans.
The "A1" generating plant made by this firm comprises a bell gasholder,
with central guide, standing alongside the generator. The generator
consists of a rectangular tank in which is a generating chamber having a
water-sealed lid with pressure test-cock _I_. Into the generating
chamber fit a number of pans _J_, which are charged with carbide.
Water is supplied to the generating chamber from an overhead tank
_B_ through the starting tap _D_ and the funnel _E_. It
flows out of the supply-pipe near the top of the generating chamber
through a slot in the side of the pipe facing the corner of the chamber,
so that it runs down the latter without splashing the carbide in the
upper pans. It enters first the lowest carbide pan through the
perforations, which are at different levels in the side of the pan. It
thus attacks the carbide from the bottom upwards. The evolved gas passes
from the generating chamber through a pipe opening near the top of the
same to the washer _A_, which forms the base of the generating tank.
It bubbles through the water in the washer, which therefore also serves
as a water-seal, and passes thence to the gasholder. On the bell of the
gasholder is an arm _C_ which, when the holder descends nearly to
its lowest point, depresses the rod _C_, which is connected by a
chain to a piston in the outlet-pipe from the water-tank _B_. The
fall of the gasholder thereby raises the piston and allows water to flow
out of the tank _B_ through the tap _D_ to the funnel _E_.
The generating tank is connected by a pipe, with tap _G_, with the
washer _A_, and the water in the generating tank is run off through
this pipe each time the generating chamber is opened for recharging,
thereby flushing out the washer _A_ and renewing the water in the
same. There is a sludge discharging tap _F_. With a view to the
ready dissipation of the heat of generation the generating chamber is
made rectangular and is placed in a water-tank as described. Some of the
heat of generation is also communicated to the underlying washer and
warms the water in it, so that the washing of the gas is effected by warm
water. Water condensing in the gasholder inlet-pipe falls downwards to
the washer. There is a water lip _H_ by which the level of the water
in the washer is automatically kept constant. The gasholder is provided
with a safety-pipe _K_, which allows gas to escape through it to the
open before the sides of the holder become unsealed, should the holder
for any reason become over-filled. The holder is of a capacity to take
the whole of the gas evolved from the carbide in one pan, and the water-
tank _B_ holds just sufficient water for the decomposition of one
charge of the generator. From the gasholder the gas passes through a
purifier, which is ordinarily charged with "Klenzal," and a baffle-box
for abstraction of dust, to the service-pipe. With plants intended to
supply more than forty lights for six hours, two or more generating
chambers are employed, placed in separate compartments of one rectangular
generating tank. The water delivery from the water-tank _B_ then
takes place into a trough with outlets at different levels for each
generating chamber. By inspection of this trough it may be seen at once
whether the charge in any generating chamber is unattacked, in course of
attack, or exhausted.
[Illustration: FIG. 40.--THE "A1" GENERATING PLANT OF THE ACETYLENE
CORPORATION OF GREAT BRITAIN, LTD.]
(2) Automatic; water-to-carbide; contact.
The same firm also makes the "Corporation Flexible-Tube Generator," which
is less costly than the "A1" (_vide supra_). The supply of water to
the generating vessels takes place from the tank of the equalising bell
gasholder and is controlled by a projection on the bell which depresses a
flexible tube delivering into the generating vessels below the level of
the water inlet to the tube.
(3) Automatic; water-to-carbide; "drawer."
The same firm also makes a generator known as the "A-to-Z," which is less
costly than either of the above. In it water is supplied from the tank of
a bell gasholder to a drawer type of generator placed in the base of the
gasholder tank. The supply of water is controlled by an external piston-
valve actuated through the rise and fall of the bell of the gasholder.
The flow of water to the generator is visible.
_Maker_: THE ACETYLENE GAS AND CARBIDE OF CALCIUM CO., PONTARDAWE,
R.S.O., GLAM.
_Type_: Automatic; water-to-carbide; flooded compartment.
The "Owens" generator made by this firm comprises an equalising bell
gasholder alongside which are placed two or more inclined generating
cylinders. The front lower end of each cylinder is fitted with a lid
which is closed by a screw clamp. There is inserted in each cylinder a
cylindrical trough, divided into ten compartments, each of which contains
carbide. Water is supplied to the upper ends of the cylinders from a
high-level tank placed at the back of the gasholder. In the larger sizes
the tank is automatically refilled from a water service through a
ball-cock. The outlet-valve of this tank is operated through a counter-
weighted lever, the unweighted end of which is depressed by a loop,
attached to the crown of the gasholder bell, when the bell has nearly
reached its lowest position. This action of the bell on the lever opens
the outlet-valve of the tank and allows water to flow thence into one of
the generating cylinders. It is discharged into the uppermost of the
compartments of the carbide trough, and when the carbide in that
compartment is exhausted it flows over the partition into the next
compartment, and so on until the whole trough is flooded. The gas passes
from the generating cylinders through a water-seal and a baffle plate
condenser placed within the water link of the gasholder to the bell of
the latter. There is a water seal on the water supply-pipe from the tank
to the generators, which would be forced should the pressure within the
generators for any reason become excessive. There is also a sealed vent-
pipe which allows of the escape of gas from the holder to the open should
the holder for any reason be over filled. The gas passes from the holder
through a purifier charged with "Owens" purifying material to the service
pipe. The plant is shown in Fig 41.
[Illustration: FIG. 41.--"OWENS" GENERATOR.]
_Maker_ ACETYLENE ILLUMINATING CO, LTD, 268-270 SOUTH LAMBETH ROAD,
LONDON, SW
_Type_ (1) Non automatic, carbide to water
The generator _A_ of this type made by this firm is provided with a
loading box _B_, with gas tight lid, into which the carbide is put.
It is then discharged by moving a lever which tilts the hinged bottom
_D_ of the box _B_, and so tips the carbide through the shoot
_E_ on to the conical distributor _F_ and into the water in the
generating chamber. There is a sludge cock _G_ at the base of the
generator. Gas passes as usual from the generator to a washer and storage
gasholder. Heratol is the purifying material supplied.
[Illustration: FIG. 42.--CARBIDE-TO-WATER GENERATOR OF THE ACETYLENE
ILLUMINATING CO., LTD.]
(2) Non-automatic; water-to-carbide; contact.
The generator _A_ is provided with a carbide container with
perforated base, and water is supplied to it from a delivery-pipe through
a scaled overflow. The gas evolved passes through the pipe _E_ to
the washer _B_, which contains a distributor, and thence to the
storage gasholder _G_. There is a sludge-cock _F_ at the base
of the generator. From the gasholder the gas passes through the purifier
_D_, charged with heratol, to the service-pipe.
[Illustration: FIG. 43.--WATER-TO-CARBIDE GENERATING PLANT OF THE
ACETYLENE ILLUMINATING CO., LTD.]
_Maker_: THE ALLEN CO., 106 VICTORIA STREET, LONDON, S.W.
_Type_: Automatic; water-to-carbide; contact, superposed trays.
The generating plant made by this firm comprises an equalising bell
gasholder, from the tank of which water is supplied through a flexible
tube to the top of a water-scaled generating chamber in which is a
vertical cylinder containing a cage packed with carbide. The open end of
the flexible tube is supported by a projection from the bell of the
gasholder, so that as the bell rises it is raised above the level of the
water in the tank and so ceases to deliver water to the generator until
the bell again falls. The water supplied flows by way of the water-seal
of the cover of the generating chamber to the cylinder containing the
carbide cage. Larger sizes have two generating chambers, and the nozzle
of the water delivery-pipe may be switched over from one to the other.
There is an overflow connexion which brings the second chamber
automatically into action when the first is exhausted. One chamber may be
recharged while the other is in action. Spare cylinders and cages are
provided for use when recharging. There is a cock for drawing off water
condensing in the outlet-pipe from the gasholder. The gas passes from the
holder to the lower part of a purifier with water-scaled cover, through
the purifying material in which it rises to the outlet leading to the
service-pipe. Purifying material under the proprietary name of the
"Allen" compound is supplied. The plant is shown in Fig. 44.
[Illustration: FIG. 44.--"ALLEN" FLEXIBLE-TUBE GENERATOR.]
Maker: THE BON-ACCORD ACETYLENE GAS CO., 285 KING STREET, ABERDEEN.
Type: Automatic; water-to-carbide; contact, superposed trays.
The "Bon Accord" generating plant made by this firm comprises an
equalising displacement gasholder _B_ immersed in a water-tank
_A_. Alongside the tank are placed two water-jacketed generating
chambers _G1_ and _G2_ containing cages _K_ charged with
carbide. Water passes from within the gasholder through the water inlet-
pipes _L1 L2_, the cock _H_, and the pipes _F1 F2_ to the
generating chambers, from which the gas evolved travels to the holder
_B_, in which it displaces water until the water-level falls below
the mouths of the pipes _L1_ and _L2_, and so cuts off the
supply of water to the generating chambers. The gas passes from the
holder _B_ through the pipe with outlet-cock _T_ to a washer
containing an acid solution for the neutralisation of ammonia, then
through a purifier containing a "special mixture of chloride of lime."
After that through a tower packed with lime, and finally through a
pressure regulator, the outlet of which is connected to the service-pipe.
There is an indicator _I_ to show the amount of gas in the holder.
One generator may be charged while the other is in action.
[Illustration: FIG. 45.--"BON-ACCORD" GENERATOR.]
_Maker_: FREDK. BRABY AND CO., LTD., ASHTON GATE WORKS, BRISTOL; AND
352-364 EUSTON ROAD, LONDON.
_Type:_ (I) Automatic; carbide-to-water.
The "A" type of generator made by this firm comprises an equalising bell
gasholder, round the bell of which are arranged a series of buckets which
are charged with carbide. Those buckets are discharged in turn as the
bell falls from time to time through a mechanism operated by a weight
suspended from a wire cord on a revolving spindle. The carbide is
discharged on to a different spot in the generating tank from each
bucket. There is a cock for the periodical removal of sludge. Gas passes
through a purifier charged with puratylene to the service-pipe. The
disposition of the parts of the plant and the operating mechanism arc
shown in the accompanying figure, which represents the generating
apparatus partly in elevation and partly in section. The carbide buckets
(1) are loosely hooked on the flat ring (2) bolted to the gasholder tank
(3). The buckets discharge through the annular water-space (4) between
the tank and the generator (5). The rollers (6), fitted on the generator,
support a ring (7) carrying radial pins (8) projecting outwards, one pin
for each bucket. The ring can travel round on the rollers. Superposed on
the ring is a tray (9) closed at the bottom except for an aperture
beneath the throat (11), on which is mounted an inclined striker (12),
which strikes the projecting tongues (1_a_) of the lids of the
buckets in turn. There is fixed to the sides of the generator a funnel
(13) with open bottom (13_a_) to direct the carbide, on to the
rocking grid (14) which is farther below the funnel than appears from the
figure. Gas passing up behind the funnel escapes through a duct (15) to
the gasholder. The ring (7) is rotated through the action of the weight
(16) suspended by the chain or rope (17) which passes round the shaft
(18), which is supported by the bracket (19) and has a handle for winding
up. An escapement, with upper limb (20_a_) and lower limb
(20_b_), is pivotally centred at (21) in the bracket (19) and
normally restrains the turning of the shaft by the weight. There is a
fixed spindle (24) supported on the bracket (23)--which is fixed to the
tank or one of the guide-rods--having centred on it a curved bar or
quadrant (25) running loose on the spindle (24) and having a crank arm
(26) to which is connected one end of a rod (27) which, at the other end,
is connected to the arm (28) of the escapement. The quadrant bears at
both extremities against the flat bar (29) when the bell (22) is
sufficiently raised. The bar (29) extends above the bell and carries an
arm (30) on which is a finger (30_a_). There is fixed on the shaft
(18) a wheel (31), with diagonal divisions or ways extending from side to
side of its rim, and stop-pins (32) on one side at each division. A
clutch prevents the rotation of the wheel during winding up.
[Illustration: FIG. 46.--THE "A" GENERATOR OF FRED K. BRABY AND CO.,
LTD.]
(2) Automatic; water-to-carbide; contact, superposed trays.
The type "B" generator made by this firm comprises an equalising bell
gasholder, a crescent-shaped feed water-tank placed on one side of the
gasholder, and mechanism for controlling a tap on the pipe by which the
feed water passes to a washer whence it overflows through a seal into a
horizontal generating chamber containing cells packed with carbide. The
mechanism controlling the water feed embodies the curved bar (25),
connecting-rod (27) and flat guide-bar (29) as used for controlling the
carbide feed in the "A" type of generator (Fig. 46). When the bell
descends water is fed into the washer, and the water-level of the seal is
thus automatically maintained. The gas evolved passes through a pipe,
connecting the seal on the top of the generating chamber with the washer,
into the gasholder. Plants of large size have two generating chambers
with connexions to a single washer.
_Maker:_ THE DARGUE ACETYLENE GAS CO., 57 GREY STREET, NEWCASTLE-ON-
TYNE.
_Type:_ Automatic; water-to-carbide; "drawer."
The "Dargue" acetylene generator made by this firm comprises an
equalising bell gasholder _B_ floating in a water-tank _A_,
which is deeper than is necessary to submerge the bell of the gasholder.
In the lower part of this tank are placed two or more horizontal
generating chambers which receive carbide-containing trays divided by
partitions into a number of compartments which are half filled with
carbide. Water is supplied from the gasholder tank through the tap
_E_ and pipe _F_ to the generating chambers in turn. It rises
in the latter and floods the first compartment containing carbide before
gaining access to the second, and so on throughout the series of
compartments. As soon as the carbide in the first generating chamber is
exhausted, the water overflows from it through the pipe with by-pass tap
_J_ to the second generating chamber. The taps _G_ and _H_
serve to disconnect one of the generating chambers from the water-supply
during recharging or while another chamber is in action. The gas evolved
passes from each generating chamber through a pipe _L_, terminating
in the dip-pipe _M_, which is provided with a baffle-plate having
very small perforations by which the stream of gas is broken up, thereby
subjecting it to thorough washing by the upper layers of water in the
gasholder tank. The washed gas, which thus enters the gasholder, passes
from it through the pipe _N_ with main cock _R_ to the service-
pipes. The water-supply to the generator is controlled through the tap
_E_, which is operated by a chain connected to an arm attached to
the bell of the gasholder.
The water in the gasholder tank is accordingly made to serve for the
supply of the generating chambers, for the washing of the gas, and as a
jacket to the generating chambers. The heat evolved by the decomposition
of the carbide in the latter creates a circulation of the water, ensuring
thereby thorough mixing of the fresh water, which is added from time to
time to replace that removed for the decomposition of the carbide, with
the water already in the tank. Thus the impurities acquired by the water
from the washing of the gas do not accumulate in it to such an extent as
to render it necessary to run off the whole of the water and refill,
except at long intervals. A purifier, ordinarily charged with puratylene,
is inserted in many cases after the main cock _R_. The same firm
makes an automatic generator on somewhat similar lines, specially
designed for use in autogenous welding, the smaller sizes of which are
readily portable.
[Illustration: FIG. 47.--"DARGUE" GENERATOR.]
_Maker_: J. AND J. DRUMMOND, 162 MARKET STREET, ABERDEEN.
_Type_: Automatic; water-to-carbide; contact.
The generating plant made by this firm comprises two or more generating
vessels _B_ in which carbide is contained in removable cases
perforated at different levels. Water is supplied to these generating
vessels, entering them at the bottom, from an elevated tank _A_
through a pipe _C_, in which is a tap _F_ connected by a lever
and chain _L_ with the bell _G_ of the equalising gasholder
_H_, into which the evolved gas passes. The lever of the tap
_F_ is counter-weighted so that when the bell _G_ descends the
tap is opened, and when the bell rises the tap is closed. The gas passes
from the generating chambers _B_ through the pipe _D_ to the
washer-cooler _E_ and thence to the gasholder. From the latter it
passes through the dry purifier _J_ to the service-pipe. The
gasholder bell is sealed in oil contained in an annular tank instead of
in the usual single-walled tank containing water. The purifying material
ordinarily supplied is puratylene. The apparatus is also made to a large
extent in a compact form specially for use on board ships.
[Illustration: FIG. 48.--J. AND J. DRUMMOND'S GENERATING PLANT.]
_Agents_: FITTINGS, LTD., 112 VICTORIA STREET, S.W.
_Type_: Automatic; carbide-to-water.
The "Westminster" generator supplied by this firm is the "Davis"
generator described in the section of the United States. The rights for
the sale of this generator in Great Britain are held by this firm.
_Maker_: LOCKERBIE AND WILKINSON, TIPTON, STAFFS.
_Type_: (1) Automatic; water-to-carbide; contact, superposed trays.
The "Thorscar" generator of this firm comprises an equalising gasholder,
the gas-space of the bell _B_ of which is reduced by conical upper
walls. When the bell descends and this lining enters the water in the
tank _A_ the displacement of water is increased and its level raised
until it comes above the mouths of the pipes _E_, through which a
portion then flows to the generators _D_. The evolution of the gas
in the latter causes the bell to rise and the conical lining to be lifted
out of the water, the level of which thereupon falls below the mouths of
the pipes _E_ in consequence of the reduced displacement of the
bell. The supply of water to the generators is thus cut off until the
bell again falls and the level of the water in the tank is raised above
the mouths of the pipes _E_. The generating chambers _D_ are
provided with movable cages _F_ in which the carbide is arranged on
trays. The gas evolved travels through a scrubbing-box _G_
containing charcoal, and the pipe _J_ with drainage-pipe _P_ to
the water-seal or washer _K_ inside the holder, into which it then
passes. The outlet-pipe for gas from the holder leads through the
condensing coil _L_ immersed in the water in the tank to the
condensed water-trap _N_, and thence by the tap _Q_ to the
supply-pipe. The generating chambers are water-jacketed and provided with
gauge-glasses _H_ to indicate when recharging is necessary, and also
with sludge-cocks _M_. The object of the displacement cone in the
upper part of the bell is to obtain automatic feed of water to the
carbide without the use of cocks or movable parts. There is a funnel-
shaped indicator in front of the tank for regulating the height of water
to a fixed level, and also an independent purifier, the purifying
material or which is supplied under the proprietary name of "Thorlite."
[Illustration: FIG. 49.--"THORSCAR" GENERATOR.]
(2) Non-automatic; water-to-carbide; "drawer."
This generating plant, the "Thorlite," comprises a water-tank _A_
from which water is admitted to the drawer generating chambers _B_,
one of which may be recharged while the other is in operation. The gas
evolved passes through a seal _C_ to the gasholder _D_, whence
it issues as required for use through the purifier _E_ to the
supply-pipe. For the larger sixes a vertical generating chamber is used.
The purifier and purifying material are the same as for the automatic
plant of the same firm.
[Illustration: FIG. 50.--"THORLITE" GENERATING PLANT.]
_Maker_: THE MANCHESTER ACETYLENE GAS CO., LTD., ACRE WORKS,
CLAYTON, MANCHESTER.
_Type_: Automatic; water-to-carbide; "drawer."
The plant made by this firm comprises an equalising gasholder _A_
from the tank of which water is supplied to generating cylinders _B_
placed at the side of the tank, the number of which varies with the
capacity of the plant. The cylinders receive tray carbide-containers
divided into compartments perforated at different levels so that they are
flooded in turn by the inflowing water. A weight _C_ carried by a
chain _D_ from one end of a lever _E_ pivoted to the framing of
the gasholder is supported by the bell of the gasholder when the latter
rises; but when the holder falls the weight _C_, coming upon the
lever _E_, raises the rod _F_, which thereupon opens the valve
_G_, which then allows water to flow from the gasholder tank through
the pipe _H_ to one of the generating cylinders. When the carbide in
the first cylinder is exhausted, the water passes on to a second. One
generating cylinder may be recharged while another is in action. The
rising of the holder, due to the evolved gas, causes the bell to support
the weight _C_ and thus closes the water supply-valve _G_. The
gas evolved passes through vertical condensers _J_ into washing-
boxes _K_, which are placed within the tank. The gas issues from the
washing-boxes into the gasholder bell, whence it is withdrawn through the
pipe _L_ which leads to the purifier. Puratylene is the purifying
material ordinarily supplied by this firm.
[Illustration: FIG. 51.--GENERATING PLANT OF THE MANCHESTER ACETYLENE GAS
CO., LTD.]
_Maker:_ R,. J. MOSS AND SONS, 98 SNOW HILL, BIRMINGHAM.
_Type:_ (1) Automatic; water-to-carbide; superposed trays.
The "Moss" generator, "Type A," made by this firm comprises an equalising
gasholder, four, three, or two generating chambers, and an intermediate
water-controlling chamber. Each generating chamber consists of a frame in
which are arranged about a central tube trays half filled with carbide,
having water inlet-holes at several different levels, and each divided
into two compartments. Over this frame is put a bell-shaped cover or cap,
and the whole is placed in an outer tank or bucket, in the upper part of
which is a water inlet-orifice. The water entering by this orifice passes
down the outside of the bell, forming a water-seal, and rises within the
bell to the perforations in the carbide trays from the lowest upwards,
and so reaches the carbide in successive layers until the whole has been
exhausted. The gas evolved passes through the central tube to a water-
seal and condensing tank, through which it escapes to the controlling
chamber, which consists of a small water displacement chamber, the gas
outlet of which is connected to the equalising gasholder. The bell of the
equalising gasholder is weighted or balanced so that when it rises to a
certain point the pressure is increased to a slight extent and
consequently the level of the water in the displacement controlling
chamber is lowered. In this chamber is a pipe perforated at about the
water-level, so that when the level is lowered through the increased
pressure thrown by the rising gasholder the water is below the
perforations and cannot enter the pipe. The pipe leads to the water
inlet-orifices of the generating tanks and when the equalising gasholder
falls, and so reduces the pressure within the controlling chamber, the
water in the latter rises and flows through the pipe to the generating
tanks. The water supplied to the carbide is thus under the dual control
of the controlling chamber and of the differential pressure within the
generating tank. The four generators are coupled so that they come into
action in succession automatically, and their order of operation is
naturally reversed after each recharging. An air-cock is provided in the
crown of the bell of each generator and, in case there should be need of
examination when charged, cocks are provided in other parts of the
apparatus for withdrawing water. There is a sludge-cock on each
generator. The gas passes from the equalising gasholder through a
purifier, for which the material ordinarily supplied is puratylene.
[Illustration: FIG. 52.--"MOSS TYPE A" GENERATOR.]
The "Moss Type B" generator is smaller and more compact than "Type A." It
has ordinarily only two generating chambers, and the displacement water
controlling chamber is replaced by a bell governor, the bell of which is
balanced through a lever and chains by a weight suspended over the bell
of the equalising gasholder, which on rising supports this counter-weight
and so allows the governor bell to fall, thereby cutting off the flow of
water to the generating chambers.
[Illustration: FIG 53.--"MOSS TYPE B" GENERATOR.]
The "Moss Type C" generator is smaller than either "Type A" or "B," and
contains only one generating chamber, which is suspended in a pocket in
the crown of the equalising gasholder. Water enters through a hole near
the top of the bucket of the generating chamber, when it descends with
the holder through the withdrawal of gas from the latter.
[Illustration: FIG 54.--"MOSS TYPE C" GENERATOR.]
(2) Semi-automatic; water-to-carbide; superposed trays.
The "Moss Semi-Non-Auto" generating plant resembles the automatic plant
described above, but a storage gasholder capable of holding the gas
evolved from one charging of the whole of the generating chambers is
provided in place of the equalising gasholder, and the generation of gas
proceeds continuously at a slow rate.
The original form of the "Acetylite" generator (_vide infra_)
adapted for lantern use is also obtainable of R. J. Moss and Sons.
_Maker:_ WM. MOYES AND SONS, 115 BOTHWELL STREET, GLASGOW.
_Type:_ Automatic; carbide-to-water.
The "Acetylite" generator made by this firm consists of an equalising
gasholder and one or more generating tanks placed alongside it. On the
top of each generating tank is mounted a chamber, with conical base,
charged with granulated carbide 1/8 to 1/2 inch in size. There is an
opening at the bottom of the conical base through which passes a rod with
conical head, which, when the rod is lowered, closes the opening. The rod
is raised and lowered through levers by the rise and fall of the bell of
the equalising gasholder, which, when it has risen above a certain point,
supports a counter-weight, the pull of which on the lever keeps the
conical feed-valve open. The gas evolved in the generating tanks passes
through a condensing chamber situated at the base of the tank into the
equalising gasholder and so automatically controls the feed of carbide
and the evolution of gas according to the rate of withdrawal of the gas
from the holder to the service-pipes. The water in the gasholder tank
acts as a scrubbing medium to the gas. The generating tanks are provided
with sludge-cocks and a tap for drawing off condensed water. The gas
passes from the equalising gasholder, through a purifier and dryer
charged with heratol or other purifying material to the service-pipes.
The original form of the "Acetylite" generator is shown in elevation and
vertical section in Fig. 55. Wm. Moyes and Sons now make it also with a
detached equalising gasholder connected with the generator by a pipe in
which is inserted a lever cock actuated automatically through a lever and
cords by a weight above the bell of the gasholder. Some other changes
have been made with a view to securing constancy of action over long
periods and uniformity of pressure. In this form the apparatus is also
made provided with a clock-work mechanism for the supply of lighthouses,
in which the light is flashed on periodically. The flasher is operated
through a pilot jet, which serves to ignite the gas at the burners when
the supply is turned on to them at the prescribed intervals by the clock-
work mechanism.
[Illustration: FIG. 55.--"ACETYLITE" GENERATOR.]
_Maker_: THE PHÔS CO., 205 AND 207 BALLS POND ROAD, LONDON, N.
_Type_: Non-automatic; water-to-carbide; drip.
The type "E" generator made by this firm consists of a generating chamber
placed below a water chamber having an opening with cap _E_ for
refilling. The generating chamber in closed by a door _B_, with
rubber washer _C_, held in position by the rod _A_, the ends of
which pass into slots, and the screw _A'_. The movable carbide
chamber _D_ has its upper perforated part half filled with carbide,
which is pressed upwards by a spring _D'_. The carbide chamber when
filled is placed in the generating chamber, which is closed, and the
lever _F_ of one of the taps _F'_ is turned from "off" to "on,"
whereupon water drips from the tank on to the carbide. The evolution of
gas is stopped by reversing the lever of the tap. The second tap is
provided for use when the evolution of gas, through the water-supply from
the first tap, has been stopped and it is desired to start the apparatus
without waiting for water from the first tap to soak through a layer of
spent carbide. The two taps are not intended for concurrent use. The
evolved gas passes through a purifier containing any suitable purifying
material to the pipes leading to the burners.
[Illustration: FIG. 56.--"PHÔS TYPE E" GENERATOR.]
_Maker:_ ROSCO ACETYLENE COMPANY, BELFAST.
_Type:_ Non-automatic; carbide-to-water
The "Rosco" generating plant made by this firm comprises a generating
tank _A_ which is filled with water to a given level by means of the
funnel-mouthed pipe _B_ and the overflow _O_. On the top of the
water-sealed lid of the generating tank is mounted the carbide feed-valve
_L_, which consists of a hollow plug-tap with handle _M_. When
the handle _M_ is turned upwards the hollow of the tap can be filled
from the top of the barrel with carbide. On giving the tap a third of a
turn the hollow of the plug is cut off from the outer air and is opened
to the generating tank so that the carbide contained in it is discharged
over a distributor _E_ on to the tray _N_ in the water in the
generating tank. The gas evolved passes through the scrubber and seal-pot
_J_ to the storage gasholder _Q_. From the latter the gas
passes through the dry purifier _T_ to the service-pipe. A sludge-
cock _P_ is provided at the bottom of the generating tank and is
stated to be available for use while generation of gas is proceeding. The
purifying material ordinarily supplied is "Roscoline."
[Illustration: FIG. 57.--"ROSCO" GENERATING PLANT.]
_Maker_: THE RURAL DISTRICTS GAS LIGHT CO., 28 VICTORIA STREET, S.W.
_Type_: Automatic; water-to-carbide; contact, superposed trays.
The "Signal-Arm" generating apparatus made by this firm comprises a bell
gasholder _A_, from the tank _B_ of which water is supplied
through a swivelled pipe _C_ to a generating chamber _D_. One
end of the swivelled pipe is provided with a delivery nozzle, the other
end is closed and counter-weighted, so that normally the open end of the
pipe is raised above the level of the water in the tank. A tappet
_E_ on the bell of the gasholder comes into contact with, and
depresses, the open end of the swivelled pipe when the bell falls below a
certain point. As soon as the open end of the swivelled pipe has thus
been lowered below the level of the water in the tank, water flows
through it into the funnel-shaped mouth _F_ of a pipe leading to the
bottom of the generating chamber. The latter is filled with cages
containing carbide, which is attacked by the water rising in the chamber.
The gas evolved passing into and raising the bell of the gasholder causes
the open end of the swivelled pipe to rise, through the weight of the
counterpoise _G_, above the level of the water in the tank and so
cuts off the supply of water to the generating chamber until the bell
again descends and depresses the swivelled pipe. The tappet on the bell
also displaces a cap _H_ which covers the funnel-shaped mouth of the
pipe leading to the generating chamber, which cap, except when the
swivelled supply-pipe is being brought into play, prevents any extraneous
moisture or other matter entering the mouth of the funnel. Between the
generating chamber and the gasholder is a three-way cock _J_ in the
gas connexion, which, when the gasholder is shut off from the generator,
brings the latter into communication with a vent-pipe _K_ leading to
the open. The gas passes from the holder to a chamber _L_ under
grids packed with purifying material, through which it passes to the
outlet of the purifier and thence to the service-pipe. Either heratol or
chloride of lime is used in the purifier, the lid of which, like the
cover of the generator, is water-sealed.
[Illustration: FIG. 58.--"SIGNAL-ARM" GENERATING PLANT.]
_Maker_: ST. JAMES' ILLUMINATING CO., LTD., 3 VICTORIA STREET,
LONDON, S.W.
_Type_: (1) Automatic; water-to-carbide; contact, superposed trays.
This plant consists of the generators _A_, the washer _B_, the
equalising gasholder _C_, the purifier _D_, and the water-tank
_E_. The carbide is arranged in baskets in the generators to which
water is supplied from the cistern _E_ through the pipe _F_.
The supply is controlled by means of the valve _H_, which is
actuated through the rod _G_ by the rise and fall of the gasholder
_C_. Gas travels from the gasholder through the purifier _D_ to
the service-pipe. The purifier is packed with heratol resting on a layer
of pumice. The washer _B_ contains a grid, the object of which is to
distribute the stream of gas through the water. There is a syphon-pot
_J_ for the reception of condensed moisture. Taps _K_ are
provided for shutting off the supply of water from the generators during;
recharging, and there is an overflow connexion _L_ for conveying the
water to the second generator as soon as the first is exhausted. There is
a sludge-cock _M_ at the base of each generator.
(2) Non-automatic; water-to-carbide; contact, superposed trays.
This resembles the preceding plant except that the supply of water from
the cistern to the generators takes place directly through the pipe
_N_ (shown in dotted lines in the diagram) and is controlled by hand
through the taps _K_. The automatic control-valve _H_ and the
rod _G_ are omitted. The gasholder _C_ is increased in size so
that it becomes a storage holder capable of containing the whole of the
gas evolved from one charging.
[Illustration: FIG. 59.--GENERATING PLANT OF THE ST. JAMES' ILLUMINATING
CO., LTD. (SECTIONAL ELEVATION AND PLAN.)]
_Maker_: THE STANDARD ACETYLENE CO., 123 VICTORIA STREET, LONDON,
S.W.
_Type_: (1) Non-automatic; carbide-to-water.
This plant comprises the generator _A_, the washer _B_, the
storage gasholder _C_, and the purifier _D_. The generator is
first filled with water to the crown of the cover, and carbide is then
thrown into the water by hand through the gas-tight lock, which is opened
and closed as required by the horizontal handle _P_. A cast-iron
grid prevents the lumps of carbide falling into the sludge in the conical
base of the generator. At the base of the cone is a sludge-valve
_G_. The gas passes from the generator through the pipe _H_
into the washer _B_, and after bubbling through the water therein
goes by way of the pipe _K_ into the gasholder _C_. The syphon-
pot _E_ is provided for the reception of condensed moisture, which
is removed from time to time by the pump _M_. From the gasholder the
gas flows through the valve _R_ to the purifier _D_, whence it
passes to the service-pipes. The purifier is charged with material
supplied under the proprietary name of "Standard."
[Illustration: FIG. 60.--CARBIDE-TO-WATER GENERATING PLANT OF THE STANDARD
ACETYLENE CO.]
(2) Automatic; water-to-carbide; contact, superposed trays.
This plant comprises the generators _A_, the washer _B_, the
equalising gasholder _C_, the purifier _D_, and the water-tank
_E_. The carbide is arranged on a series of wire trays in each
generator, to which water is supplied from the water-tank _E_
through the pipe _Y_ and the control-tap _U_. The gas passes
through the pipes _H_ to the washer _B_ and thence to the
holder _C_. The supply of water to the generators is controlled by
the tap _U_ which is actuated by the rise and fall of the gasholder
bell through the rod _F_. The gas passes, as in the non-automatic
plant, through a purifier _D_ to the service-pipes. Taps _W_
are provided for cutting off the flow of water to either of the
generators during recharging and an overflow pipe _h_ serves to
convey the water to the second generator as soon as the carbide in the
first is exhausted. A sludge-cook _G_ is put at the base of each
generator.
[Illustration: FIG. 61.--AUTOMATIC, WATER-TO-CARBIDE GENERATING PLANT OF
THE STANDARD ACETYLENE CO.]
(3) Non-automatic; water-to-carbide; contact, superposed-trays.
This apparatus resembles the preceding except that the supply of water to
the generators is controlled by hand through the taps _W_, the
control valve _U_ being omitted, and the gasholder _C_ being a
storage holder of sufficient dimensions to contain the whole of the
acetylene evolved from one charging.
_Maker_: THORN AND HODDLE ACETYLENE CO., 151 VICTORIA STREET, S.W.
_Type_: Automatic; water-to-carbide; "drawer."
The "Incanto" generating plant made by this firm consists of a rising
bell gasholder which acts mainly on an equaliser. The fall of the bell
depresses a ball valve immersed in the tank, and so allows water to flow
from the tank past an outside tap, which is closed only during
recharging, to a generating chamber. The generating chamber is horizontal
and is fixed in the base of the tank, so that its outer case is
surrounded by the water in the tank, with the object of keeping it cool.
The charge of carbide is placed in a partitioned container, and is
gradually attacked on the flooding principle by the water which enters
from the gasholder tank when the ball valve is depressed. The gas evolved
passes from the generating chamber by a pipe which extends above the
level of the water in the tank, and is then bent down so that its end
dips several inches below the level of the water. The gas issuing from
the end of the pipe is thus washed by the water in the gasholder tank.
From the gasholder the gas is taken off as required for use by a pipe,
the mouth of which is just below the crown of the holder. There is a lip
in the upper edge of the gasholder tank into which water is poured from
time to time to replace that consumed in the generation of the gas. There
are from one to three generating chambers in each apparatus according to
its size. The purifier is independent, and a purifying mixture under the
proprietary name of "Curazo" is supplied for use in it.
[Illustration: FIG. 62.--"INCANTO" GENERATOR.]
_Maker:_ WELDREN AND BLERIOT, 54 LONG ACRE, LONDON, W.C.
_Type:_ Automatic; contact.
This firm supplies the "Acétylithe" apparatus (_see_ Belgium).
INDEX
Absorbed acetylene,
Acagine,
Accidents, responsibility for,
Acetone, effect of, on acetylene,
solution of acetylene in,
Acetylene-copper,
Acetylene-oil-gas,
Acetylene Association (Austrian)--regulations as to carbide,
Acetylene Association (British)--analysis of carbide,
generator rules,
pressure gauges,
purification rules,
Acetylene Association (German)--analysis of carbide,
holders,
generator rules,
standard carbide,
Acetylene tetrachloride, production of,
Ackermann burner,
Advantages of acetylene, general,
hygienic,
intrinsic,
pecuniary,
"After generation,"
Air, admission of, to burners,
and acetylene, ignition temperature of,
composition of,
dilution of acetylene with, before combustion,
effect of acetylene lighting on,
coal-gas lighting on,
on illuminating power of acetylene,
paraffin lighting on,
in acetylene,
in flames, effect of,
in generators, danger of,
objections to,
in incandescent acetylene,
in service-pipes,
proportion of, rendering acetylene explosive,
removing, from pipes,
specific gravity of,
sterilised by flames,
Air-gas,
and acetylene, comparison between,
and carburetted acetylene, comparison between,
effect of cold on,
illuminating power of,
Alcohol, action of, on carbide,
for carburetting acetylene,
holder seals,
from acetylene, production of,
Allgemeine Carbid und Acetylen Gesellschaft burner,
Alloys, fusible, for testing generators,
Alloys of copper. See _Copper (alloyed)_
Aluminium sulphide, in carbide
America (U.S.), regulations of the National Board of Fire Underwriters,
American gallon, value of,
Ammonia, in acetylene,
in coal-gas,
removal of,
solubility of, in water,
Analysis of carbide,
Ansdell, compressed and liquid acetylene,
Anthracene, formation of, from acetylene,
Anti-freezing agents,
Area of purifiers,
Argand burners,
Aromatic hydrocarbons,
Arrangement of generating plant,
Arsenious oxide purifier,
Atkins, dry process of generation,
Atmospheric moisture and carbide,
Atomic weights,
Attention needed by generators,
Austrian Acetylene Association, regulations as to carbide,
Austrian Government Regulations,
Autogenous soldering and welding,
Automatic generators. See _Generators (automatic)_
B
Baking of carbide
Ball-sockets for acetylene,
Barium peroxide purifier,
sulphate in bleaching-powder,
Barrel, gas, for acetylene, quality of
Bell gasholders. See _Holders (rising)_
Benz purifying material,
Benzene,
for carburetting acetylene,
production of, from acetylene,
Benzine. See _Petroleum spirit_
Bergé, detection of phosphorus,
and Reychler, purification of acetylene,
and Reychler's reagent, solubility of acetylene in,
Bernat, formula for mains and pipes,
Berthelot, addition of chlorine to acetylene,
sodium acetate,
sulphuric acid and acetylene,
Berthelot and Matignon, thermochemical data,
and Vieille, dissolved acetylene,
Billwiller burners,
Black, acetylene,
Blagden, sodium hypochlorite,
Bleaching-powder purifier (simple),
Blochmann, copper acetylide,
Blow-off pipes. See _Vent-pipes_
Blowpipe, acetylene,
Boiling-ring,
Boistelle. See _Molet_
Borek, enrichment of oil-gas,
_Bougie décimale_,
Brackets for acetylene,
Bradley, Read, and Jacobs, calcium carbophosphide,
Brame and Lewes, manganese carbide,
Bray burners,
British Acetylene Association. See _Acetylene Association
(British)_,
Fire Offices Committee Regulations,
regulations. See _Acetylene Association (British); Home Office;
Orders in Council_
Bromine-water purifier,
Bullier, effect of heat on burners,
phosphorus in acetylene,
and Maquenne purifier,
Bunsen burner, principle of,
Bunte, enrichment of oil-gas,
Burner orifices and gas density,
Burners,
atmospheric,
principle of,
design of,
glassware for,
heating,
incandescent,
Ackermann,
Allgemeine Carbid und Acetylen Gesellschaft,
Bray,
firing back in,
Fouché,
Günther's,
illuminating power of,
Jacob, Gebrüder,
Keller and Knappich,
Knappich,
O.C.A.,
pressure for,
principles of construction of,
Schimek,
Sirius,
Trendel,
typical,
Weber,
Zenith,
self-luminous,
Argand,
as standard of light,
Billwiller,
Bray,
choking of,
corrosion of,
cycle,
Falk, Stadelmann and Co.'s,
Konette,
Phôs,
Wiener's,
Dolan,
Drake,
effect of heat on,
Elta,
Falk, Stadelmann and Co.'s,
firing back in,
fish-tail,
Forbes,
Hannam's,
illuminating power of,
self-luminous injector,
Javal,
Kona,
Luta,
Naphey,
Orka,
Phôs,
Pintsch,
pressure for,
rat-tail,
Sansair,
Schwarz's,
Stadelmann,
Suprema,
twin, angle of impingement in,
injector,
non-injector,
warping of,
Wiener's,
Wonder,
By-products, See also _Residues_
C
Cadenel, shape of incandescent acetylene mantle,
"Calcidum,"
Calcium carbide, action of heat on,
action of non-aqueous liquids on,
analysis of,
and carbon bisulphide, reaction between,
and hydroxide, reaction between,
and ice, reaction between,
and steam, reaction between,
and water, reaction between,
as drying material,
baking of,
balls and cartridges. See _Cartridges_
bulk of,
chemical properties of,
crushing of,
decomposition of,
by solids containing water,
heat evolved during,
imperfect,
speed of,
temperature attained during,
deterioration of, on storage,
drums of,
dust in,
explosibility of,
fire, risk of,
formula for,
granulated,
heat-conducting power of,
of formation of,
impurities in,
inertness of,
in residues,
physical properties of,
purity of,
quality, regulations as to,
sale and purchase of, regulations as to,
scented,
shape of lumps of,
sizes of,
small, yield of gas from,
specific gravity of,
heat of,
standard, British,
German,
"sticks,"
storage regulations for,
subdivided charges of,
sundry uses of,
swelling of, during decomposition,
"treated,"
yield of acetylene from,
Calcium carbophosphide,
Calcium chloride, cause of frothing in generators,
for seals,
purifier,
solubility of acetylene in,
Calcium hydroxide,
adhesion of, to carbide,
and carbide, reaction between,
milk of, solubility of acetylene in,
physical properties of,
space occupied by,
Calcium hypochlorite,
Calcium oxide,
and water, reaction between,
hydration of,
hygroscopic nature of,
physical properties of,
Calcium phosphide,
Calcium sulphide,
Calorie, definition of,
Calorific power of acetylene,
various gases,
Candle-power. See _Illuminating power_
Capelle, illuminating power of acetylene,
Carbide. See _Calcium carbide_
Carbide-containers,
air in,
filling of,
partitions in,
water-jacketing,
Carbide-feed generators. See _Generators (carbide-to-water)_
Carbide impurities in acetylene,
Carbide-to-water generators. See _Generators (carbide-to-water)_
Carbides, mixed,
Carbolic acid, production of, from acetylene,
Carbon, combustion of, in flames,
deposition of, in burners,
gaseous, heat of combustion of,
heat of combustion of,
vaporisation of,
pigment, production of,
Carbon bisulphide and acetylene, reaction between,
and calcium carbide, reaction between,
in coal-gas,
Carbon dioxide, addition of, to acetylene,
dissociation of,
effect of, on explosibility of acetylene,
for removing air from pipes,
heat of formation of,
produced by respiration,
benzene,
coal-gas,
in flame of acetylene,
Carbon monoxide, in acetylene,
heat of combustion of,
formation of,
temperature of ignition of,
Carbonic acid. See _Carbon dioxide_
Carburetted acetylene, composition of,
effect of cold on,
illuminating power of,
manufacture of,
pecuniary value of,
Carburetted water-gas, enrichment of,
Carburine. See _Petroleum spirit_
Carlson, specific heat of carbide,
Caro, acetone vapour in acetylene,
addition of petroleum spirit to generator water,
air in incandescent acetylene,
calorific power of gases,
colour of incandescent acetylene,
composition of mantles,
durability of mantles,
heat production in generators,
illuminating power of carburetted acetylene,
of incandescent acetylene,
oil of mustard,
silicon in crude acetylene,
Caro and Saulmann, "Calcidum,"
Carriage, cost of, and artificial lighting,
Cartridges of carbide,
Cast-iron pipe for acetylene,
Castor oil for acetylene joints,
Catani, temperature of acetylene flame,
Caustic potash purifier,
Cedercreutz, yield of gas from carbide,
and Lunge, purification,
Ceilings, blackening of,
Ceria, proportion of, in mantles,
Cesspools for residues,
Chandeliers, hydraulic, for acetylene,
Charcoal and chlorine purifier,
Charging generators after dark,
at irregular intervals,
Chassiron lighthouse,
Chemical formulæ, meaning of,
Chemical reactions and heat,
of acetylene,
Chimneys for stoves, &c.,
glass, for burners,
Chloride of lime. See _Bleaching-powder_
Chlorine and acetylene, compounds of,
and charcoal purifier,
in acetylene,
Chromic acid purifier,
Cigars, lighted, danger of,
Claude and Hess, dissolved acetylene,
Coal-gas, enrichment of, with acetylene,
illuminating power of,
impurities in,
vitiation of air by,
Cocks, hand-worked, in generators,
Coefficient of expansion of acetone,
air,
dissolved acetylene,
gaseous acetylene,
liquid acetylene,
simple gases,
Coefficient of friction of acetylene,
of coal-gas,
Coke filters for acetylene,
Cold, effect of, on acetylene,
on air-gas,
on carburetted acetylene,
on generation,
Colour judging by acetylene,
of acetylene flame,
of air-gas flame,
Colour of atmospheric acetylene flame,
of coal-gas flame,
of electric light,
of incandescent acetylene flame,
of spent carbide,
Combustion of acetylene,
deposit from,
Composition pipe for acetylene,
Compounds, endo- and exo-thermic,
explosive, of acetylene and copper,
"Compounds," of phosphorus and sulphur,
silicon,
Compressed acetylene,
Condensed matter in pipes, removal of,
Condensers,
Connexions, flexible, for acetylene,
Construction of generators, principles of,
regulations as to,
Contact generators,
Convection of heat,
Cooking-stoves,
Copper acetylide,
(alloyed) in acetylene apparatus,
(unalloyed) in acetylene apparatus,
and acetylene, reactions between,
carbides,
chloride purifier
Corrosion in apparatus,
avoidance of,
Corrosive sublimate purifier,
as test for phosphorus
Cost of acetylene lighting,
Cotton-wool filters for acetylene,
Council, Orders in. See _Orders in Council_
Counterpoises for rising holders,
Couples, galvanic,
Coward. See _Dixon_
Critical pressure and temperature of acetylene,
Crushing of carbide,
"Cuprene,"
Cuprous chloride purifier,
Cycle lamps,
burners for,
dilute alcohol for,
Cylinders for absorbed acetylene,
D
Davy, addition of chlorine to acetylene,
Davy's lamp for generator sheds,
Decomposing vessels. See _Carbide containers_
Decomposition of acetylene,
of carbide, See _Calcium carbide (decomposition of)_
De Forcrand, heat of formation of carbide,
Density. See _Specific gravity_
Deposit at burner orifices,
on reflectors from combustion of acetylene,
Deterioration of carbide in air,
Diameter of pipes and explosive limits,
Diaphragms, flexible, in generators,
Diffusion through gasholder seals,
Diluted acetylene,
Dimensions of mains and pipes,
Dipping generators,
Displacement gasholders. See _Holders (displacement)_
Dissociation of acetylene,
carbon dioxide,
water vapour,
Dissolution of acetylene, depression of freezing-point by,
of gas in generators,
Dissolved acetylene,
Dixon and Coward, ignition temperature of acetylene,
of various gases,
Dolan burners,
Doors of generator sheds,
Drainage of mains,
Drake burners,
Driers, chemical,
Dripping generators,
Drums of carbide,
Dry process of generation,
Dufour, addition of air to acetylene,
"Dummies" in gasholder tanks,
Dust and incandescent lighting,
in acetylene,
carbide,
E
Effusion of gases,
Eitner, explosive limits of acetylene,
and Keppeler, estimation of phosphine,
phosphorus in crude acetylene,
Electric lamps in generator sheds,
lighting, cost, and efficiency of,
Elta burner,
Endothermic compounds,
nature of acetylene,
Engines, use of acetylene in,
Enrichment, value of acetylene for,
with acetylene,
épurène purifying material,
Equations, chemical, meaning of,
Erdmann, acetylene as a standard of light,
colour of acetylene flame,
production of alcohol,
Ethylene, formation of from acetylene,
heats of formation and combustion of,
ignition temperature of,
Exhaustion of air by flames,
Exothermic compounds,
Expansion of gaseous acetylene, coefficient of,
of liquid acetylene coefficient of,
various coefficients of,
Explosibility of carbide,
Explosion of chlorine and acetylene,
of compressed acetylene,
Explosive compounds of acetylene and copper,
effects of acetylene dissociation,
limits, meaning of term,
of acetylene,
of various gases,
nature of acetylene,
wave, speed of, in gases,
Expulsion of air from mains,
F
Faced joints for acetylene,
Falk, Stadelmann and Co., boiling-ring,
burners,
cycle-lamp burner,
Ferric hydroxide purifier,
Fery, temperature of flames,
and Violle, acetylene as standard of light,
Filters for acetylene,
Filtration,
Fire Offices Committee Regulations (British),
risks of acetylene apparatus,
carbide,
flame illuminants,
Underwriters, United States, Regulations,
"Firing back" in incandescent burners,
self-luminous burners,
Fish, action of lime on,
Fittings for acetylene, quality of,
Flame, colour of, air-gas,
atmospheric acetylene,
coal-gas,
incandescent, acetylene,
self-luminous acetylene,
Flame illuminants, risk of fire with,
of acetylene containing air,
steadiness of acetylene,
Flame temperature of acetylene,
temperature of various gases,
Flames, distortion of, by solid matter,
effect of air on,
nitrogen on,
evolution of heat in,
light in,
jumping of,
liberation of carbon from,
loss of heat from,
shading of acetylene,
size of,
Flare lamps,
Flash-point of paraffin,
Flexible connexions for acetylene,
Floats in holder seals,
Flooded-compartment generators,
Flow of gases in pipes,
Flues for heating burners,
Fog, transmission of light through,
Forbes burner,
Foreign regulations,
Formulæ, meaning of chemical,
Fouché, absorbed acetylene,
burner,
dissolved acetylene,
illuminating power of acetylene air mixtures,
incandescent acetylene,
liquid acetylene,
oxy-acetylene blowpipe,
Fournier. See _Maneuvrier_
Fowler, enrichment of oil-gas,
Fraenkel, deposit on reflectors from combustion of acetylene,
silicon in acetylene,
France, regulations of the Conseil d'Hygiène de la Seine,
village acetylene mains in,
Frank, freezing-point of calcium chloride solutions,
preparation of black pigment,
purifier,
Frankoline,
Freezing of generators,
of holder seals,
Freezing of portable lamps,
of pressure-gauges,
Freezing-point, depression of by dissolution of acetylene,
of calcium chloride solutions,
of dilute alcohol,
of dilute glycerin,
Freund and Mai, copper acetylide,
Friction of acetylene, coefficient of,
coal-gas, coefficient of,
gas in pipes,
Frost, effect of, on air-gas,
on carburetted acetylene,
Froth, lime, in acetylene,
Frothing in generators,
Fuchs and Schiff, olive oil,
Furnace gases for removing air from pipes,
G
Gallon, American, value of,
Galvanic action,
Garelli and Falciola, depression of freezing-point by dissolution of
acetylene,
Gas barrel for acetylene, objection to,
drying of,
engines, acetylene for,
escape of, from generators,
firing, effects of,
volumes, correction of, for temperature and pressure,
yield of, from carbide,
determining,
standard,
Gases, calorific value of,
effusion of,
explosive limits of,
flame temperature of,
illuminating power of,
inflammable properties of,
speed of explosive wave in,
temperature of ignition of,
Gasfitters' paint,
Gasholders. See _Holders_
Gatehouse, F. B., test-papers,
J. W., estimation of phosphine,
Gaud, blocking of burners,
polymerisation of acetylene,
Generation, dry process of,
Generating plant, regulations as to construction of,
Generator impurities in acetylene,
pressure, utilisation of,
sheds,
lighting of,
smoking in,
water, addition of bleaching-powder to,
of petroleum spirit to,
Generators and holders, isolation of,
attention needed by,
Generators, charging after dark,
chemical reactions in,
construction of,
copper in,
corrosion in,
dissolution of gas in,
effect of tarry matter in,
escape of gas from,
failure of,
for analytical purposes,
for welding,
frothing in,
frozen, thawing of,
gauge of sheet-metal for,
heat dissipation in,
economy in,
produced in,
high temperatures and impurities in,
instructions for using,
joints in, making,
"lagging" for,
lead solder in,
materials for construction of,
maximum pressure in,
output of gas from,
overheating in,
polymerisation in,
pressure in,
protection of, from frost,
purchase of,
regulations as to,
American (National Board of Fire Underwriters),
Austrian Government,
British Acetylene Association,
Fire Offices Committee,
Home Office Committee(1901),
French (Council d' Hygiene de la Seine),
German Acetylene Association,
Hungarian Government,
Italian Government,
responsibility for accidents with,
selection of,
temperatures in,
typical,
vent-pipes for,
waste-pipes for,
water-jackets for,
water-scale in,
Generators (automatic),
advantages of,
carbide-to-water,
definition of,
flexible diaphragms for,
holders of,
interlocking in,
mechanism for,
pressure thrown by,
speed of reaction in,
store of gas in,
supply of water to,
use of oil in,
water-to-carbide,
worked by holder bell,
by pressure,
Generators (carbide-to-water),
advantages of,
frothing of,
grids for,
loss of gas in,
maximum temperature in,
pressure in,
quantity of water required by,
Generators (contact),
(dipping),
temperatures in,
(dripping),
temperatures in,
(flooded compartment),
(non-automatic),
advantages of,
carbide-to-water,
hand-charging of,
water required for,
definition of,
speed of reaction in,
water-to-carbide,
(portable),
(shoot),
(water-to-carbide),
overheating in,
with carbide in excess,
with water in excess,
Gerard, silicon in crude acetylene,
Gerdes, acetylene copper,
German Acetylene Association. (See _Acetylene Association, German_)
Gin, heat of formation of carbide,
Glassware, for burners,
Glow-lamps, electric, in generator sheds,
Glucose for treatment of carbide,
Glycerin for holder-seals,
for wet meters,
Governor, displacement holder as,
Governors,
Graham, effusion of gases,
Gramme-molecules,
Granjon, illuminating power of self-luminous burners,
phosphine in acetylene,
pressure,
purifier,
Granulated carbide. See _Calcium carbide, (granulated)_
Graphite, artificial, production of,
Grease for treatment of carbide,
Grids for carbide-to-water generators,
in purifiers,
Grittner, acetylene, and copper,
Guides for rising holders,
Güntner burner,
H
Haber, effect of heat on acetylene,
Haldane, toxicity of sulphuretted hydrogen,
Hammcrschmidt, correction of gas volumes,
and Sandmann, milk of lime,
Hannam's Ltd., burners,
Hartmann, acetylene flame,
Haze, on combustion of acetylene,
Heat absorbed during change of physical state,
action on acetylene. See _Overheating_
carbide,
and temperature, difference between,
conducting power of carbide
iron and steel,
water,
convected,
developed by acetylene lighting,
coal-gas lighting,
electric lighting,
paraffin lighting,
dissipation of, in generators,
economy in generators,
effect of, on acetylene. (See _Overheating_)
on burners,
evolution of, in flames,
expansion of gaseous acetylene by,
liquid acetylene by,
from acetylene, production of,
latent. See _Latent heat_
loss of, from flames,
of chemical reactions,
of combustion of acetylene,
carbon,
carbon monoxide,
ethylene,
of formation of acetylene,
calcium carbide,
hydroxide,
oxide,
carbon dioxide,
monoxide,
ethylene,
water,
of hydration of calcium oxide,
of reaction between carbide and calcium hydroxide,
between carbide and water,
of solution of calcium hydroxide,
of vaporisation of carbon,
water,
radiant,
specific. See _Specific heat_
Heating apparatus for generator sheds,
Hefner unit,
Heil, atmospheric acetylene flame,
carburetted acetylene,
Heise, acetylene flame,
Hempel, enrichment of coal-gas,
Heratol,
Hess. See _Claude_
Hexachlorethane, production of,
High houses, supply of acetylene to,
Holder-bells, for testing mains,
supplying water to automatic generators,
weighting of,
Holder-seals, freezing of,
level of liquid in,
liquids in,
and pressure,
solubility of acetylene in,
use of floats in,
liquids in, for decomposing carbide,
oil in,
water in, for washing the gas,
Holders (gas) and generators, isolation of,
and pressure, relationship between,
and purifiers, relative position of,
exposed, roofs over,
false interiors for,
freezing of,
gauge of sheet-metal for,
loss of pressure in,
moistening of gas in,
of automatic generators,
preservation of, from corrosion,
situation of,
size of,
vent-pipes for,
value of,
Holders (displacement),
action of,
pressure given by,
(rising),
guides and counterpoises for,
pressure thrown by,
equalisation of,
tanks for,
Home Office, maximum pressure permitted by,
prohibition of air in acetylene by,
Committee, 1901, recommendations,
report,
Home Secretary's Orders. See _Orders in Council_
Hoxie. See _Stewart_,
Hubou, acetylene black,
Hungarian rules for apparatus,
Hydraulic pendants for acetylene,
Hydrocarbons formed by polymerisation,
illuminating power of,
volatile, names of,
Hydrochloric acid in purified acetylene,
Hydrogen and acetylene, reactions between,
effect of, on acetylene flame,
ignition temperature of,
in acetylene,
liberated by heat from acetylene,
silicide in crude acetylene,
Hygienic advantages of acetylene,
I
Ice, reaction between carbide and,
Ignition temperature of acetylene,
various gases,
Illuminating power and illuminating effect,
definition of,
of acetylene, after storage,
carburetted,
effect of air on,
incandescent,
nominal,
self-luminous,
of acetylene-oil-gas,
of air-gas,
of polymerised acetylene,
of candles,
of coal-gas,
of electric lamps,
of hydrocarbons, various,
of paraffin,
Illumination, amount of, required in rooms,
of lighthouses,
of optical lanterns,
Impurities in acetylene, carbide,
detection and estimation of,
effect of, on air,
generator,
harmfullness of,
water soluble,
See also _Ammonia_ and _Sulphuretted hydrogen_
in coal-gas,
in purified acetylene,
maximum limits of,
Incandescent acetylene,
burners. See _Burners (incandescent)_
mantles,
Inertness of carbide,
Inflaming-point of acetylene,
Inflammability, spontaneous,
Installations, new, removal of air from,
Interlocking of automatic generators,
Iron and acetylene, reactions between,
and steel, heat-conducting power of,
silicide in carbide,
Insecticide, carbide residues as,
Isolation of apparatus parts,
Intensity, specific, of acetylene light,
of oil light,
Italian Government rules,
J
Jackets for generators,
Jacob, Gebrüder, burner,
Jacobs. See _Bradley_
Jaubert, arsenious oxide purifier,
Javal burners,
blocking of,
purifier,
Jet photometer of acetylene,
Joint-making in generators,
pipes,
K
Keller and Knappich burner,
Keppeler, lead chromate in acagine,
Keppeler, purification,
silicon in acetylene,
test-papers,
See also _Eitner_
Kerosene. See _Paraffin oil_
Klinger, vent-pipes,
Knappich burner,
Kona burner,
Konette cycle-lamp burner,
L
La Belle boiling ring,
Labour required in acetylene lighting,
Lagging for generators,
Lamps for generator sheds
paraffin,
portable,
acetone process for,
Landolt-Börnstein, solubility of acetylene in water,
Landriset. See _Rossel_
Lantern, optical, illumination of,
Latent heat,
Lead chromate in bleaching-powder,
objection to, in generators,
pipes for acetylene,
salts in bleaching-powder,
wire, &c., for faced joints,
Leakage of acetylene,
Leaks, search for,
Le Chatelier, explosive limits,
temperature of acetylene flame,
thermo-couple
Leduc, specific gravity of acetylene,
Lépinay, acetylene for engines,
Level alteration and pressure in mains,
Lewes, ammonia in crude acetylene,
blocking of burners,
haze,
heat of decomposition of carbide,
production in generators,
illuminating power of acetylene,
phosphorus in crude acetylene,
polymerisation of acetylene,
presence of hydrogen and carbon monoxide in acetylene,
reaction between carbide and calcium hydroxide,
silicon in crude acetylene,
temperature of acetylene flame,
Lewes and Brame, manganese carbide,
Lidholm, estimation of phosphine,
Lifebuoys, acetylene for,
Lifetime of burners,
mantles,
Lifting power of acetylene in holders,
Light, acetylene as a standard of,
colour of acetylene, incandescent,
self-luminous,
evolution of, in flames,
from acetylene, production of,
transmission of through fog,
Lights, single, disadvantages of,
strong and weak, comparison between,
Lighthouse illumination,
Lighting by acetylene, scope of,
of generator sheds,
Lime dust in acetylene,
reaction with sodium carbonate,
sludge. See _Residues_
solubility of, in sugar solutions,
water, solubility of gas in,
Lime-light, acetylene for the,
Limits, explosive, of acetylene,
Lindé-air,
Linseed oil for acetylene joints,
Liquid acetylene, properties of,
condensation in pipes,
in holder-seals and pressure,
in pressure-gauge,
Liquids, corrosive action of, on metals,
for seals,
purification by,
solubility of acetylene in,
Locomotive lighting,
Loss of gas in generators,
of pressure in holders,
in mains,
in purifiers,
on distribution,
Love, enrichment by acetylene,
Lubricating oil for seals,
Luminous burners. See _Burners, self-luminous_
Lunge and Cedercreutz, determination of phosphorus in acetylene,
purification,
Luta burner,
Lutes for holders. See _Seals_
M
Mahler, temperature of flames,
Mai and Freund, copper acetylide,
Mains, deposition of liquid in,
diameter of, and explosive limits,
dimensions of,
escapes from,
friction in,
laying of,
lead,
quality of,
removing air from,
testing of,
Make of acetylene from carbide,
in generators,
Manchester burners,
Maneuvrier and Fournier, specific heat of acetylene,
Manganese carbide,
Mantles for acetylene,
Manure for generator protection,
Manurial value of generator residue,
Maquenne. See _Bullier_
Marsh gas, enrichment with acetylene,
formed from acetylene,
Matignon. See _Berthelot_,
Mauricheau-Beaupré, épurène,
estimation of phosphine,
frothing in generators,
phosphine in acetylene,
silicon in acetylene,
Mechanism for automatic generators,
Mercaptans in acetylene,
Mercuric chloride purifier,
test for phosphorus,
Merck test-papers,
Metals for generators,
gauge of,
Meters for acetylene,
Methane, enrichment with acetylene,
formed from acetylene,
ignition temperature of,
Methylated spirit for generators,
for holder seals,
Meyer and Münch, ignition temperatures,
Mildew in vines, use of acetylene in,
Milk of lime, solubility of acetylene in,
Mineral oil for lighting. (See _Paraffin oil_)
for seals,
Miner's lamp for generator sheds,
Mist, transmission of light through,
Mixter, thermo-chemical data,
Mixtures of acetylene and air,
illuminating duty of,
Moisture, effect of, on carbide,
in acetylene,
Molecular volume of acetylene,
weight of acetylene,
weights, various,
Molet-Boistelle acetylene-air mixture,
Morel, formula for acetylene pipes,
sodium plumbate purifier,
specific heat of acetylene,
of carbide,
Mosquitoes, destruction of,
Moths, catching of,
Motion of fluids in pipes,
Motors, acetylene for,
Münch. See _Meyer_
Münsterberg, acetylene flame,
Mustard, oil of,
N
Naphey burners,
Naphthalene, formation of, from acetylene,
Neuberg, illuminating power of acetylene,
radiant efficiency of acetylene,
Nieuwland, mixtures of acetylene and chlorine,
Nichols, illuminating power of acetylene after storage,
temperature of acetylene flame,
Nickel and acetylene, reactions between,
Nipples, burner, materials for,
Nitrides in carbide,
Nitrogen in flames, effect of,
Non-automatic generators. See _Generators (non-automatic)_
Non-luminous acetylene flame, appearance of,
burners. See _Burners (atmospheric)_
Non-return valves,
O
O. C. A. burner,
Odour of acetylene,
Oil, action of, on carbide,
castor, for acetylene joints,
in generators,
in residues,
in seals,
linseed, for acetylene joints,
mustard,
olive, for seals,
(See also _Paraffin oil_)
Olive oil for seals,
Oil-gas, enrichment of,
Optical efficiency of acetylene,
Orders in Council, air in acetylene,
compression of absorbed acetylene,
acetylene-oil-gas,
neat acetylene,
Origin of petroleum,
Orka burner,
Ortloff, friction of acetylene,
Overheating in generators,
See also _Polymerisation_
Oxide of iron purifier,
Oxy-acetylene blowpipe,
Oxygen required for combustion of acetylene,
of benzene,
combustion of acetylene with,
flames burning in,
P
Paint, cause of frothing in generators,
gas-fitters',
Paraffin oil,
action of, on carbide,
flash-point of,
illuminating power of,
in residues,
lamps,
lighting, effect of on air,
heat developed by,
quality of different grades of,
use of in automatic generators,
seals,
Paraffin wax, treatment of carbide with,
Partial pressure,
Pendants, water-slide for acetylene,
Petroleum oil. See _Paraffin oil_
spirit, addition of, to generator water,
composition of,
for carburetted acetylene,
spirits, nomenclature of,
theory of origin of,
Pfeiffer, purifier,
Pfleger, puratylene,
Phenol, production of, from acetylene,
Phôs burners,
Phosphine, cause of deposit at burner orifices,
composition of,
in crude acetylene,
amount of,
toxicity of,
Phosphoretted hydrogen. See _Phosphine_
Phosphorus and incandescent mantles,
"compounds,"
in crude acetylene,
in purified acetylene,
detection and determination of,
removal of,
"Phossy-jaw,"
Photometer, jet of acetylene,
Phylloxera, use of acetylene for,
Physical properties of acetylene,
Pickering, freezing-points of calcium chloride solutions,
Pictet, freezing-points of dilute alcohol,
purification of acetylene,
Pintsch burners,
Pipes, blow-off. See _Vent-pipes_
diameter of, and explosive limits,
vent. See _Vent-pipes_ (See also _Mains_)
Plant, acetylene, fire risks of,
order of items in,
Platinum in burners,
Poisonous nature of acetylene,
Pole, motion of fluids in pipes,
pressure thrown by holders,
Polymerisation, definition of,
of acetylene,
See also _Overheating_
Porous matter, absorption of acetylene in,
Portable lamps,
acetone process for,
temperature in,
Potassium bichromate purifier,
hydroxide purifier,
permanganate purifier,
Power from acetylene, production of,
Precautions with generators,
with new installations,
Presence of moisture in acetylene,
Pressure and leakage,
after explosions of acetylene,
atmospheric,
automatic generators working by,
correction of gas volumes for,
critical, of acetylene,
definition of (gas),
for incandescent burners,
self-luminous burners,
gauge,
liquid for,
given by displacement holders,
rising holders,
in generators,
utilisation of,
in mains and pipes,
in purifiers, loss of,
irregular, caused by vent-pipes,
maximum safe, for acetylene,
necessity for regular,
partial,
regulators. See _Governors_
Protection of generators from frost,
holders from frost,
Puratylene,
Purchase of a generator,
carbide, regulations as to,
Purification by liquids and solids,
in portable lamps,
necessary extent of,
reasons for,
regulations as to,
speed of,
Purified acetylene, chlorine in,
hydrochloric acid in,
phosphorus in,
sulphur in,
Purifiers and holder, relative positions of,
construction of,
duplication of,
exhaustion of,
foul, emptying of,
loss of pressure in,
mechanical, for acetylene,
Purifying materials, density of,
efficiency of,
quantity required,
Pyralid, destruction of the,
Q
Quality of carbide, regulations as to,
Quicklime. See _Calcium oxide_
R
Radiant efficiency of acetylene,
heat,
Railway lighting by acetylene,
Ramie mantles for acetylene,
Range of explosibility, meaning of term,
of acetylene,
Rat-tail burner,
Reactions between copper and acetylene,
chemical, of acetylene,
physical, of acetylene,
Reaction grids in generators,
Read and Jacobs. See _Bradley_
Rod lead for acetylene joints,
Regulations, American (National Board of Fire Underwriters of U.S.A.),
Austrian Acetylene Association,
Government,
British Acetylene Association,
Fire Offices Committee,
Home Office Committee (1901),
for analysis of carbide,
for construction of generating plant,
for generators,
for purification,
for sale and purchase of carbide,
for sampling carbide,
for storing carbide,
French (Conseil d'Hygiène de la Seine),
German Acetylene Association,
Hungarian Government,
Italian Government,
Residue from dry process of generation,
Residues, carbide in,
colour of,
composition of,
consistency of,
disposal of,
containing oil,
manurial value of,
utilisation of,
Respiration of acetylene,
Reversibility of reaction between calcium oxide and water,
Reychler. See _Bergé_
Rising holders. See _Holders (rising)_
Rossel and Landriset, ammonia in crude acetylene,
purifier,
sulphur in crude acetylene,
Roofs over exposed holders,
Rooms, amount of illumination required in,
Rubber tubes for acetylene,
Ruby for burners,
Rules. See _Regulations_
S
Safety lamp, Davy's, for generator sheds,
valves. See _Vent-pipes_
Sale of carbide, regulations as to,
Salt, common, in holder-seals,
Salzbergwerk Neu Stassfurt, production of tetrachlorethane,
Sampling carbide,
Sandmann. See _Hammerschmidt_
Sansair burner,
Saulmann. See _Caro_
Sawdust in bleaching-powder,
Scale, water, in generators,
Scented carbide,
Schiff. See _Fuchs_
Schimek burner,
Schwander, carburetted acetylene,
Schwarz burners,
Seal-pots,
Seals (holder). See _Holder-seals_
Seams in generator-making,
Self-luminous burners. See _Burners (self-luminous)_
Sensible heat,
Separation of holder from generator,
Service-pipes. See _Mains_
Shoot generators,
Silicon compounds,
in acetylene,
in carbide,
Sirius burner,
Slaked lime. See _Calcium hydroxide_
Sludge. See _Residues_
Sludge-cocks, automatic locking of,
Sludge-pipes, blocked, clearance of,
Smell of crude and purified acetylene,
Smith, purification,
Smoke, production of, by flames,
Smoking, danger of, in generator sheds,
Soap, use of, in testing pipes,
Soda, washing, for decomposing carbide,
Sodium acetate solution for generator jackets,
Sodium carbonate and lime, reaction between,
crystallised, for decomposing carbide,
chloride for holder-seals,
solubility of acetylene in,
hypochlorite purifier,
plumbate purifier,
sulphate in bleaching-powder,
Soil, carbide residues as dressing for,
Solder in generators,
Soldering, autogenous,
Solids containing water, decomposition of carbide by,
purification by,
Solubility of acetylene,
in generators,
in holders,
in liquids,
Soot, production by, of flames,
Space occupied by purifying materials,
Sparks from steel tools, danger of,
Specific gravity and holder pressure,
leakage,
of acetylene, dissolved,
gaseous,
liquid,
of air,
of carbide,
of gases, and burner construction,
of water,
heat of acetylene,
of carbide,
heats, various,
intensity. See _Intensity, specific_
Speed of reactions between carbide, water, and calcium hydroxide,
of purification,
Spent lime. See _Residues_
Spontaneous inflammability,
Spraying apparatus,
Stable manure for warming generators,
Stadelmann burners,
Standard of illumination in rooms,
of light, acetylene as,
Steam, latent heat of, use of,
specific heat of,
reaction between carbide and,
Steam-barrel for acetylene mains,
Steatite for burners,
Steel, heat-conducting power of,
tools, danger of
Sterilisation of air by flames,
Stewart and Hoxie, radiant efficiency of acetylene,
Storage regulations for carbide,
vessels for carbide, temporary,
Styrolene. formation of, from acetylene,
Suckert. See _Willson_
Suffocation by acetylene,
Sugar solutions, solubility of lime in,
Sulphur "compounds,"
in coal-gas,
in crude acetylene,
in purified acetylene,
removal of,
Sulphuretted hydrogen, solubility of, in water,
toxicity of,
Sulphuric acid and acetylene, reactions between
as purifying material,
Superficial area in purifiers,
Supply of water to automatic generators,
Suprenia burners,
Swelling of carbide during decomposition,
Symbols, chemical, meaning of,
Syphons for removing water,
T
Table-lamps, acetone process for,
Tabular numbers,
Tanks for rising holders, construction of,
"Tantalus Cup,"
Taps for acetylene pipes,
Tar, cause of frothing in generators,
Tarry matter in generators,
Telescopic gasholders. _See Holder (rising)_
Temperature and heat, difference between,
correction of volumes for,
critical, of acetylene,
high, effect of, on acetylene. See _Polymerization_
of acetylene blowpipe,
flame,
of dissociation of acetylene,
of ignition of acetylene,
various gases,
of reaction between carbide and calcium hydroxide,
between carbide and water,
Temperatures in generators,
calculation of,
determination of,
Tension of liquid acetylene,
Test-papers,
Tetrachlorethane, production of,
Tetrachloride, acetylene, production of,
Thawing of frozen apparatus,
Thermo-chemical data,
Thermo-couple, Le Chatelier's,
Thomson, radiant efficiency of acetylene,
thermo-chemical data,
Tools, steel or iron, danger of,
Town supplies,
Toxicity of acetylene,
of sulphur and phosphorus compounds,
Train-lighting by acetylene,
Treated carbide. See _Calcium carbide (treated)_
Trondol burner,
Tubes, diameter of, and explosive limits,
Tubes for acetylene. See _Mains_
Tubing, flexible, for acetylene,
Typical generators,
U
Ullmax purifier,
Unaccounted-for gas,
Underwriters, United States Fire,
United States. See _America_
Uses, sundry, for acetylene,
V
Valuation of carbide,
Value of acetylene, hygienic,
enriching,
pecuniary,
of purifying materials,
Valves, screw-down, for generators,
Vapour, water, in acetylene, objections to,
removal of,
value of,
Vehicular lamps,
Ventilation of generator sheds,
Vent-pipes, economy of,
for carbide vessels,
generators,
holders,
noise in,
position of mouths of,
size of,
Vibration and incandescent lighting,
Vieille, dissolved acetylene,
Vigouroux, silicon in acetylene,
Village installations, mains for,
leakage in,
supplies,
Villard, liquid acetylene,
Vines, treatment by acetylene of, for mildew and phylloxera,
Violle and Féry, acetylene as standard of light,
Vitiation of air by flames,
Volume, alteration of, on dissociation,
and weight of acetylene,
molecular, of acetylene,
Volume of acetylene passing through pipes,
Volumes, gas, correction for temperature and pressure,
W
Washers, oil,
water,
Waste-pipes of generators,
Water and calcium oxide, reaction between,
and carbide, heat of reaction between,
boiling-point, evolution of gas at,
condensation of, in pipes,
consumption of, in generators,
convection currents in,
freezing-point, evolution of gas at,
heat absorbed in warming,
conducting power of,
of formation of,
in excess, generators with,
in holders, freezing of,
use for decomposition,
use for washing,
jackets for generators,
quality of, for portable generators,
quantity required in carbide-to-water generators,
scale in generators,
solubility of acetylene in,
of impurities in,
of load in,
specific gravity of,
supply for automatic generators,
non-automatic generators,
yield of gas per unit of,
Water-gas, enrichment with acetylene,
Water-seals, as not-return valves,
setting water-level in,
Water-slide pendants for acetylene,
Water-soluble impurities in acetylene,
See also _Ammonia and Sulphuretted hydrogen_
Water-to-carbide generators. See _Generators (water-to-carbide)_
Water-vapour, dissociation of,
existence of, at low temperatures,
in acetylene, objections to,
removal of,
value of,
reaction between carbide and,
Weber burner,
Wedding, enrichment of coal-gas,
Weed-killer, carbide residues as,
Weight and volume of acetylene,
Weights, atomic,
molecular,
Welding, acetylene,
White lead, for acetylene joints,
Wiener burners,
Willgerodt, purification,
Willson and Suckert, liquid acetylene,
Windows in generator sheds,
Winter, manipulation of generators during,
Wöhler, addition of chlorine to acetylene,
Wolff, acetone in acetylene,
illuminating power of acetylene,
purifier,
silicon in acetylene,
Wonder burner,
Work done in actuating automatic generators,
Y
Yield of gas, deficient, cause of,
from carbide,
determining,
(British standard),
(German standard),
from water,
Z
Zenith burner,
INDEX TO APPENDIX
A
"A" Generator (of Braby and Co., Ltd.),
"A1" generator (of Acetylene Corporation of Great Britain),
"A-to-Z" generator (of Acetylene Corporation of Great Britain),
Acetylene Corporation of Great Britain,
Acetylene Gas and Carbide of Calcium Co.,
Acetylene Illuminating Co., Ltd.,
"Acetylite" generator,
"Acétylithe" generator,
Acétylithe, Soc. An. de l',
Allen Co.,
"Allen" Flexible-tube generator,
"Allen" purifying material,
American generators,
Applications de l'Acétylène, La Soc. des.,
Austrian generator,
Automatic generators,
B
"B" generator (of Braby and Co., Ltd.),
Belgian generators,
Bon Accord Acetylene Gas Co.,
"Bon Accord" generator,
Braby, Frederick and Co., Ltd.,
British generators,
C
Canadian generators,
Carbide-to-water generators,
"Carburlen" purifying material,
Chloride of lime purifying material,
Colt Co., J. G.,
"Colt" generator,
Compartment, flooded, generator,
Contact generators,
Cork waste and wadding purifying material,
"Corporation Flexible Tube Generator,"
"Curaze" purifying material,
D
"Dargue" generator,
Dargue Acetylene Gas Co.,
Davis Acetylene Co.,
"Davis" generator,
Debruyne, L.,
Debruyne's generators,
Drawer generators,
Drip generator,
Drummond, J. and J.,
E
English generators,
F
Flooded compartment generator,
Fittings, Ltd.,
Frankoline purifying material,
French generators,
G
German generators,
H
Heratol, purifying material,
I
"Incanto" generator,
Irish generator,
J
"Javal" generator,
K
Keller and Knappich, G.m.b.H.,
"Klenzal" purifying material,
Klinger, Rich.,
Klinger's generator,
"Knappich" generator,
L
"L'Éclair" generator,
"L'Étoile" generator,
L'Hermite,
Lockerbie and Wilkinson,
M
Manchester Acetylene Gas Col., Ltd.,
Mangiameli, Fr. and Co.,
Moss, R. J. and Sons,
"Semi-Non-Auto" generator,
"Type A" generator,
"Type B" generator,
"Type C" generator,
Moyes Wm., and Sons,
N
Non-automatic generators,
Nordische Azetylen Industrie,
O
"Omega" generator,
Overberge, De Smet van,
"Owens" generator,
"Owens" purifying material,
P
Phôs Co.,
"Phôs Type E" generator,
"Photolithe" generator,
Photolithe, Soc. An. Belg de la,
Pumice purifying material,
Puratylene purifying material,
Purifying material, "Allen,"
"Carburylen,"
chloride of lime,
coke and cotton, chemically treated,
cork waste and wadding,
"Curaze,"
frankoline,
heratol,
"Klenzal,"
"Owens,"
pumice,
puratylene,
"Roscoline,"
"Standard,"
"Thorlite,"
R
Rosco Acetylene Co.,
"Rosco" generator,
"Roscoline" purifying material,
Rural Districts Gas Light Co.,
S
St. James' Illuminating Co., Ltd.,
Scotch generators,
Semi-automatic generator,
Siche Gas Co., Ltd.,
"Siche" generator,
"Signal-Arm" generator,
"Sirius" generator,
Sirius, Maison,
Standard Acetylene Co.,
"Standard" purifying material,
Sunlight Gas Machine Co.,
Superposed pans or trays,
T
"Thorlite" generator,
purifying material,
Thorn and Hoddle Co.,
"Thorscar" generator,
Trays, superposed,
U
United States generators,
W
Wadding and cork waste purifying material,
Water-to-carbide generators,
Weldhen and Bleriot,
Welsh generator,
"Westminster" generator,
End of the Project Gutenberg EBook of Acetylene, The Principles Of Its
Generation And Use, by F. H. Leeds and W. J. Atkinson Butterfield
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