The Project Gutenberg EBook of Scientific American Supplement, No. 647,
May 26, 1888, by Various
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Title: Scientific American Supplement, No. 647, May 26, 1888
Author: Various
Release Date: December 31, 2008 [EBook #27667]
Language: English
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[Illustration]
SCIENTIFIC AMERICAN SUPPLEMENT NO. 647
NEW YORK, MAY 26, 1888
Scientific American Supplement. Vol. XXV., No. 647.
Scientific American established 1845
Scientific American Supplement, $5 a year.
Scientific American and Supplement, $7 a year.
* * * * *
TABLE OF CONTENTS.
PAGE.
I. ARCHITECTURE.--Elements of Architectural Design.--By H. H.
Statham.--Continuation of this important contribution to
building art, Gothic, Roman, Romanesque, and Mediæval
architecture compared.--26 illustrations. 10339
The Evolution of the Modern Mill.--By C. J. H.
Woodbury.--Sibley College lecture treating of the
buildings for mills. 10329
II. CHEMISTRY.--An Automatic Still.--By T. Maben.--An improved
apparatus for making distilled water.--1 illustration. 10335
Testing Indigo Dyes.--Simple and practical chemical tests
of indigo products. 10342
III. CIVIL ENGINEERING.--Railway Bridge at Lachine.--Great
steel bridge across the St. Lawrence near Montreal.--2
illustrations. 10333
IV. ELECTRICITY.--Influence Machines.--By Mr. James
Wimshurst.--A London Royal Institution lecture, of great
value as giving a full account of the recent forms of
generators of static electricity.--14 illustrations. 10327
V. HYGIENE.--The Care of the Eyes.--By Prof. David Webster,
M.D.--A short and thoroughly practical paper on the all
important subject of preservation of sight. 10341
VI. MECHANICAL ENGINEERING.--Economy Trials of a
Non-condensing Steam Engine.--By Mr. P. W. Winans,
M.I.C.E.--Interesting notes on testing steam engines. 10331
The Mechanical Equivalent of Heat.--By Prof. De Volson
Wood.--A review of Mr. Hanssen's recent paper, with
interesting discussion of the problem. 10331
VII. METEOROLOGY.--The Meteorological Station on Mt. Santis.--A
new observatory recently erected in Switzerland, at an
elevation of 8,202 feet above the sea.--1 illustration. 10341
VIII. NAVAL ENGINEERING.--Improved Screw Propeller.--Mr. B.
Dickinson's new propeller.--Its form and peculiarities and
results.--4 illustrations. 10333
IX. PHOTOGRAPHY.--Manufacture of Photographic Sensitive
Plates.--Description of a factory recently erected for
manufacturing dry plates.--The arrangement of rooms,
machinery, and process.--10 illustrations. 10336
X. TECHNOLOGY.--Cotton Seed Oil.--How cotton seed oil is
made, and the cost and profits of the operation. 10335
Improved Dobby.--An improved weaving apparatus described
and illustrated.--1 Illustration. 10333
Sulphur Mines in Sicily.--By Philip Carroll, U. S. Consul,
Florence.--How sulphur is made in Sicily, percentage,
composition of the ore, and full details. 10334
The Use of Ammonia as a Refrigerating Agent.--By Mr. T. B.
Lightfoot, M.I.C.E.--An elaborate discussion of the theory
and practice of ammonia refrigerating, including the
hydrous and anhydrous systems, with conditions of economy. 10337
* * * * *
INFLUENCE MACHINES.[1]
[Footnote 1: Lecture delivered at the Royal Institution, April
27, 1888. For the above and for our illustrations we are indebted
to _Engineering_.]
BY MR. JAMES WIMSHURST.
I have the honor this evening of addressing a few remarks to you upon
the subject of influence machines, and the manner in which I propose
to treat the subject is to state as shortly as possible, first, the
historical portion, and afterward to point out the prominent
characteristics of the later and the more commonly known machines. The
diagrams upon the screen will assist the eye to the general form of
the typical machines, but I fear that want of time will prevent me
from explaining each of them.
In 1762 Wilcke described a simple apparatus which produced electrical
charges by influence, or induction, and following this the great
Italian scientist Alexander Volta in 1775 gave the electrophorus the
form which it retains to the present day. This apparatus may be viewed
as containing the germ of the principle of all influence machines yet
constructed.
Another step in the development was the invention of the doubler by
Bennet in 1786. He constructed metal plates which were thickly
varnished, and were supported by insulating handles, and which were
manipulated so as to increase a small initial charge. It may be better
for me to here explain the process of building up an increased charge
by electrical influence, for the same principle holds in all of the
many forms of influence machines.
This Volta electrophorus, and these three blackboards, will serve for
the purpose. I first excite the electrophorus in the usual manner, and
you see that it then influences a charge in its top plate; the charge
in the resinous compound is known as negative, while the charge
induced in its top plate is known as positive. I now show you by this
electroscope that these charges are unlike in character. Both charges
are, however, small, and Bennet used the following system to increase
them.
Let these three boards represent Bennet's three plates. To plate No. 1
he imparted a positive charge, and with it he induced a negative
charge in plate No. 2. Then with plate No. 2 he induced a positive
charge in plate No. 3. He then placed the plates Nos. 1 and 3
together, by which combination he had two positive charges within
practically the same space, and with these two charges he induced a
double charge in plate No. 2. This process was continued until the
desired degree of increase was obtained. I will not go through the
process of actually building up a charge by such means, for it would
take more time than I can spare.
In 1787 Carvallo discovered the very important fact that metal plates
when insulated always acquire slight charges of electricity; following
up those two important discoveries of Bennet and Carvallo, Nicholson
in 1788 constructed an apparatus having two disks of metal insulated
and fixed in the same plane. Then by means of a spindle and handle, a
third disk, also insulated, was made to revolve near to the two fixed
disks, metallic touches being fixed in suitable positions. With this
apparatus be found that small residual charges might readily be
increased. It is in this simple apparatus that we have the parent of
influence machines (see Fig. 1), and as it is now a hundred years
since Nicholson described this machine in the Phil. Trans., I think it
well worth showing a large sized Nicholson machine at work to-night
(see Fig. 11, above).
[Illustration: Figs. 1-9.]
In 1823 Ronalds described a machine in which the moving disk was
attached to and worked by the pendulum of a clock. It was a
modification of Nicholson's doubler, and he used it to supply
electricity for telegraph working. For some years after these machines
were invented no important advance appears to have been made, and I
think this may be attributed to the great discoveries in galvanic
electricity which were made about the commencement of this century by
Galvani and Volta, followed in 1831 to 1857 by the magnificent
discoveries of Faraday in electro-magnetism, electro-chemistry, and
electro-optics, and no real improvement was made in influence machines
till 1860, in which year Varley patented a form of machine shown in
Fig. 2. It also was designed for telegraph working.
In 1865 the subject was taken up with vigor in Germany by Toepler,
Holtz, and other eminent men. The most prominent of the machines made
by them are figured in the diagrams (Figs. 3 to 6), but time will not
admit of my giving an explanation of the many points of interest in
them; it being my wish to show you at work such of the machines as I
may be able, and to make some observations upon them.
In 1866 Bertsch invented a machine, but not of the multiplying type;
and in 1867 Sir William Thomson invented the form of machine shown in
Fig. 7, which, for the purpose of maintaining a constant potential in
a Leyden jar, is exceedingly useful.
The Carre machine was invented in 1868, and in 1880 the Voss machine
was introduced, since which time the latter has found a place in many
laboratories. It closely resembles the Varley machine in appearance,
and the Toepler machine in construction.
In condensing this part of my subject, I have had to omit many
prominent names and much interesting subject matter, but I must state
that in placing what I have before you, many of my scientific friends
have been ready to help and to contribute, and, as an instance of
this, I may mention that Prof. Sylvanus P. Thompson at once placed all
his literature and even his private notes of reference at my service.
I will now endeavor to point out the more prominent features of the
influence machines which I have present, and, in doing so, I must ask
a moment's leave from the subject of my lecture to show you a small
machine made by that eminent worker Faraday, which, apart from its
value as his handiwork, so closely brings us face to face with the
imperfect apparatus with which he and others of his day made their
valuable researches.
The next machine which I take is a Holtz. It has one plate revolving,
the second plate being fixed. The fixed plate, as you see, is so much
cut away that it is very liable to breakage. Paper inductors are fixed
upon the back of it, while opposite the inductors, and in front of the
revolving plate, are combs. To work the machine (1) a specially dry
atmosphere is required; (2) an initial charge is necessary; (3) when
at work the amount of electricity passing through the terminals is
great; (4) the direction of the current is apt to reverse; (5) when
the terminals are opened beyond the sparking distance, the excitement
rapidly dies away; (6) it does not part with free electricity from
either of the terminals singly.
It has no metal on the revolving plates, nor any metal contacts; the
electricity is collected by combs which take the place of brushes, and
it is the break in the connection of this circuit which supplies a
current for external use. On this point I cannot do better than quote
an extract from page 339 of Sir William Thomson's "Papers on
Electrostatics and Magnetism," which runs: "Holtz's now celebrated
electric machine, which is closely analogous in principle to Varley's
of 1860, is, I believe, a descendant of Nicholson's. Its great power
depends upon the abolition by Holtz of metallic carriers and metallic
make-and-break-contacts. It differs from Varley's and mine by leaving
the inductors to themselves, and using the current in the connecting
arc."
In respect to the second form of Holtz machine (Fig. 4) I have very
little information, for since it was brought to my notice nearly six
years ago I have not been able to find either one of the machines or
any person who had seen one. As will be seen by the diagram, it has
two disks revolving in opposite directions, it has no metal sectors
and no metal contacts. The "connecting arc circuit" is used for the
terminal circuit. Altogether I can very well understand and fully
appreciate the statement made by Professor Holtz in _Uppenborn's
Journal_ of May, 1881, wherein he writes that "for the purpose of
demonstration I would rather be without such machines."
The first type of Holtz machine has now in many instances been made up
in multiple form, within suitably constructed glass cases, but when so
made up, great difficulty has been found in keeping each of the many
plates to a like excitement. When differently excited, the one set of
plates furnished positive electricity to the comb, while the next set
of plates gave negative electricity; as a consequence, no electricity
passed the terminal.
To overcome this objection, to dispense with the dangerously cut
plates, and also to better neutralize the revolving plate, throughout
its whole diameter, I made a large machine having twelve disks 2 ft. 7
in. in diameter, and in it I inserted plain rectangular slips of glass
between the disks, which might readily be removed; these slips carried
the paper inductors. To keep all the paper inductors on one side of
the machine to a like excitement, I connected them together by a metal
wire. The machine so made worked splendidly, and your late president,
Mr. Spottiswoode, sent on two occasions to take note of my successful
modifications. The machine is now ten years old, but still works
perfectly. I will show you a smaller sized one at work.
The next machine for observations is the Carre (Fig. 8). It consists
essentially or a disk of glass which is free to revolve without touch
or friction. At one end of a diameter it moves near to the excited
plate of a frictional machine, while at the opposite end of the
diameter is a strip of insulting material, opposite which, and also
opposite the excited amalgam plate, are combs for conducting the
induced charges, and to which the terminals are metallically
connected; the machine works well in ordinary atmosphere, and
certainly is in many ways to be preferred to the simple frictional
machine. In my experiments with it I found that the quantity of
electricity might be more than doubled by adding a segment of glass
between the amalgam cushions and the revolving plate. The current in
this type of machine is constant.
The Voss machine has one fixed plate and one revolving plate. Upon the
fixed plate are two inductors, while on the revolving plate are six
circular carriers. Two brushes receive the first portions of the
induced charges from the carriers, which portions are conveyed to the
inductors. The combs collect the remaining portion of the induced
charge for use as an outer circuit, while the metal rod with its two
brushes neutralizes the plate surface in a line of its diagonal
diameter. When at work it supplies a considerable amount of
electricity. It is self-exciting in ordinary dry atmosphere. It freely
parts with its electricity from either terminal, but when so used the
current frequently changes its direction, hence there is no certainty
that a full charge has been obtained, nor whether the charge is of
positive or negative electricity.
I next come to the type of machine with which I am more closely
associated, and I may preface my remarks by adding that the invention
sprang solely from my experience gained by constantly using and
experimenting with the many electrical machines which I possessed. It
was from these I formed a working hypothesis which led me to make my
first small machine. It excited itself when new with the first
revolution. It so fully satisfied me with its performance that I had
four others made, the first of which I presented to this Institution.
Its construction is of a simple character. The two disks of glass
revolve near to each other and in opposite directions. Each disk
carries metallic sectors; each disk has its two brushes supported by
metal rods, the rods to the two plates forming an angle of 90 deg.
with each other. The external circuit is independent of the brushes,
and is formed by the combs and terminals.
[Illustration: Fig. 10.]
The machine is self-exciting under all conditions of atmosphere, owing
probably to each plate being influenced by and influencing in turn its
neighbor, hence there is the minimum surface for leakage. When
excited, the direction of the current never changes; this circumstance
is due, probably, to the circuit of the metallic sectors and the make
and break contacts always being closed, while the combs and the
external circuit are supplemental, and for external use only. The
quantity of electricity is very large and the potential high. When
suitably arranged, the length of spark produced is equal to nearly the
radius of the disk. I have made them from 2 in. to 7 ft. in diameter,
with equally satisfactory results. The diagram, Fig. 9, shows the
distribution of the electricity upon the plate surfaces when the
machine is fully excited. The inner circle of signs corresponds with
the electricity upon the front surface of the disk. The two circles of
signs between the two black rings refer to the electricity between the
disks, while the outer circle of signs corresponds with the
electricity upon the outer surface of the back disk. The diagram is
the result of experiments which I cannot very well repeat here this
evening, but in support of the distribution shown on the diagram, I
will show you two disks at work made of a flexible material, which
when driven in one direction close together at the top and the bottom,
while in the horizontal diameter they are repelled. When driven in the
reverse direction, the opposite action takes place.
I have also experimented with the cylindrical form of the machine (see
Fig. 10). The first of these I made in 1882, and it is before you. The
cylinder gives inferior results to the simple disks, and is more
complicated to adjust. You notice I neither use nor recommend
vulcanite, and it is perhaps well to caution my hearers against the
use of that material for the purpose, for it warps with age, and when
left in the daylight it changes and becomes useless.
[Illustration: Figs. 11 & 12.]
I have now only to speak of the larger machines. They are in all
respects made up with the same plates, sectors, and brushes as were
used by me in the first experimental machines, but for convenience
sake they are fitted in numbers within a glass case. One machine has
eight plates of 2 ft. 4 in. diameter; it has been in the possession of
the Institution for about three years. A second, which has been made
for this lecture, has twelve disks, each 2 ft. 6 in. in diameter. The
length of spark from it is 13-5/8 in. (see Fig. 12). During the
construction of the machine every care was taken to avoid electrical
excitement in any of its parts, and after its completion several
friends were present to witness the fitting of the brushes and the
first start. When all was ready the terminals were connected to an
electroscope, and the handle was moved so slowly that it occupied
thirty seconds in moving one-half revolution, and at that point
violent excitement appeared.
The machine has now been standing with its handle secured for about
eight hours. No excitement is apparent, but still it may not be
absolutely inert. Of this each one present must judge, but I will
connect it with this electroscope (Figs. 13 and 14), and then move the
handle slowly, so that you may see when the excitement commences and
judge of its absolutely reliable behavior as an instrument for public
demonstration. I may say that I have never, under any condition, found
this type of machine to fail in its performance.
[Illustration: Fig. 13.]
[Illustration: Fig. 14.]
I now propose to show you the beautiful appearances of the discharge,
and then, in order that you may judge of the relative capabilities of
each of these three machines, we will work them all at the same time.
The large frictional machine which is in use for this comparison is so
well known by you that a better standard could not be desired.
In conclusion, I may be permitted to say that it is fortunate I had
not read the opinions of Sir William Thomson and Professor Holtz, as
quoted in the earlier part of my lecture, previous to my own practical
experiments. For had I read such opinions from such authorities, I
should probably have accepted them without putting them to practical
test. As the matter stands, I have done those things which they said I
ought not to have done, and I have left undone those which they said I
ought to have done, and by so doing I think you must freely admit that
I have produced an electric generating machine of great power, and
have placed in the hands of the physicist, for the purposes of public
demonstration or original research, an instrument more reliable than
anything hitherto produced.
* * * * *
VIOLET COPYING INK.--Dissolve 40 parts of extract of logwood, 5 of
oxalic acid and 30 parts of sulphate of aluminium, without heat, in
800 parts of distilled water and 10 parts of glycerine; let stand
twenty-four hours, then add a solution of 5 parts of bichromate of
potassium in 100 parts of distilled water, and again set aside for
twenty-four hours. Now raise the mixture once to boiling in a bright
copper boiler, mix with it, while hot, 50 parts of wood vinegar, and
when cold put into bottles. After a fortnight decant it from the
sediment. In thin layers this ink is reddish violet; it writes dark
violet and furnishes bluish violet copies.
* * * * *
SIBLEY COLLEGE LECTURES.--1887-88.
BY THE CORNELL UNIVERSITY NON-RESIDENT LECTURERS IN MECHANICAL
ENGINEERING.
THE EVOLUTION OF THE MODERN MILL.[1]
[Footnote 1: The lecture was illustrated by about fifty views on
the screen, which cannot be reproduced here, showing photographs
of mills and mechanical drawings of the methods of construction
alluded to in the lecture.]
BY C. J. H. WOODBURY, BOSTON, MASS.
The great factories of the textile industries in this country are
fashioned after methods peculiarly adapted to the purposes for which
they are designed, particularly as regards the most convenient placing
of machinery, the distribution of power, the relation of the several
processes to each other in the natural sequence of manufacture, and
the arrangement of windows securing the most favorable lighting. The
floors and roofs embody the most economical distribution of material,
and the walls furnish examples of well known forms of masonry
originating with this class of buildings.
These features of construction have not been produced by a stroke of
genius on the part of any one man. There has been no Michael Angelo,
no Sir Christopher Wren, whose epitaph bids the reader to look around
for a monument; but the whole has been a matter of slow, steady
growth, advancing by hair's breadth; and, as the result of continual
efforts to adapt means to ends, an inorganic evolution has been
effected, resulting in the survival of the fittest, and literally
pushing the weaker to the wall.
This advance in methods has, like all inventions, resulted in the
impairment of invested capital. There are hundreds of mill buildings,
the wonder of their day, now used for storage because they cannot be
employed to sufficient advantage in manufacturing purposes to compete
with the facilities furnished by mills of later design. Thus their
owners have been compelled to erect new buildings, and, as far as the
original purpose of manufacturing is concerned, to abandon their old
mills.
In the case of a certain cotton mill built about thirty years ago, and
used for the manufacture of colored goods of fancy weave, the owners
added to the plant by constructing a one story mill, which proved to
be peculiarly adapted to this kind of manufacture, by reason of added
stability, better light, and increased facilities for transferring the
stock in process of manufacture; and they soon learned not only that
the old mill could not compete with the new one, but that they could
not afford to run it at any price; the annual saving in the cost of
gas, as measured by the identical meter used to measure the supply to
the old mill, being six per cent. on the cost of the new mill.
In another instance, one of two cordage mills burned, and a new mill
of one story construction was erected in its place. The advantage of
manufacture therein was so great that the owners of the property
changed the remaining old mill into a storehouse; and now, as they
wish to increase their business, it is to be torn down as a cumberer
of the ground, to make room for a building of similar construction to
the new mill.
It is true that such instances pertain more particularly to industries
and lines of manufacture where competition is close and conditions are
exacting. Still they apply in a greater or less degree to nearly every
industrial process in which a considerable portion of the expense of
manufacture consists in the application of organized labor to machines
of a high degree of perfection.
These changes have been solely due to the differences in the
conditions imposed by improvement in the methods of manufacture. The
early mills of this country were driven by water power, and situated
where that could be developed in the easiest manner. They were
therefore placed in the narrow valleys of rapid watercourses. The
method of applying water power in that day being strictly limited to
placing the overshot or breast wheel in the race leading from the
canal to the river, the mill was necessarily placed on a narrow strip
of land between these two bodies of water, with the race-way running
under the mill.
To meet these conditions of location, which was limited to this strip
of land, the mill must be narrow and short, and the requisite floor
area must be obtained by adding to the number of stories. It was
essential that the roof of such a mill should be strong and well
braced in order to sustain the excessive stress brought to bear upon
it. The old factory roof was a curious structure, with eaves springing
out of the edge of hollow cornices, the roof rising sharply until
about six feet above the attic floor, with an upright course of about
three feet, filled with sashes reaching to a second roof, which, at a
more moderate pitch than the first slope, trended to the ridge.
The attic was reduced to an approximately square room, by placing
sheathing between the columns underneath the sashes, and ceiling
underneath the collar beams above; thus forming a cock-loft above and
concealed spaces at the sides which diminished the practically
available floor space in the attic. This cock-loft and these concealed
spaces became receptacles for rubbish and harbors for vermin, both of
which were frequent causes of fire.
The floors of such a mill were similar in their arrangement to those
of a dwelling. Joists connecting the beams supported the floor; and
the under side was covered over by sheathing or lath and plaster, thus
forming, as in the case of the roof, hollow spaces which were a source
of danger. This method caused at the same time an extravagant
distribution of material, by the prodigal use of lumber and the
unnecessary thickness of such floors, and entailed an excessive amount
of masonry in the walls.
Mills built after this manner were frequently in odd dimensions; and
the machinery was necessarily placed in diversified arrangement,
calling forth a similar degree of wasted skill as that used in making
a Chinese puzzle conform to its given boundaries. Their area depended
upon the topography of the site, and their height upon the owner's
pocket book. There was in Massachusetts a mill with ten floors, built
on land worth at that time ten cents or less per square foot, which
has been torn down and a new mill rebuilt in its place, because, since
the advent of modern mills, it has failed every owner by reason of the
excessive expenditure necessary for the distribution of power, for
supervision, and for the transfer of stock in process, in comparison
with the mills of their competitors, built with greater ground area
and less number of stories.
With the advent of the steam engine as prime mover in mills, and the
introduction of the turbine wheel with its trunk, affording greater
facilities in the application of water power, the character of these
buildings changed very materially, though still retaining many of
their old features. One of the first of these changes may be noticed
in the consideration which millwrights gave to the problem of fixing
upon the dimensions of a mill so as to arrange the machinery in the
most convenient manner. Although the floors were still hollow, there
was a better distribution of material, the joists being deeper, of
longer span, and resting upon the beams, thus avoiding the pernicious
method of wasting lumber, and guarding against fracture by tenoning
joists into the upper side of beams.
But this secondary type of mills was not honest in the matter of
design. The influence of architects who attempted effects not
accordant with or subservient to the practical use of the property is
apparent in such mills. The most frequent of these wooden efforts at
classic architecture was the common practice of representing a
diminutive Grecian temple surrounding a factory bell perched in mid
air. There were also windows with Romanesque arches copied from
churches, and Mansard roofs, exiled from their true function of
decorating the home, covering a factory without an answering line
anywhere on its flat walls.
I do not mean to criticise any of these elements of design in their
proper place and environment; but utility is the fundamental element
in design, and should be especially noticeable in a building
constructed for industrial purposes, and used solely as a source of
commercial profit in such applications. Its lines therefore fulfill
their true function in design in such measure as they suggest
stability and convenience; and this can be obtained in such structures
without the adoption of bad proportions offensive to the taste. In
fact, certain decorative effects have been made with good results; but
these have been wholly subordinate to the fundamental idea of utility.
The endurance with which brick will withstand frost and fires, and the
disintegrating forces of nature, in addition to its resistance to
crushing and the facility of construction, constitute very important
reasons for its value for building purposes. But the use of this has
been too often limited to plain brick in plain walls, whose monotony
portrayed no artistic effect beyond that furnished by a few
geometrical designs of the most primitive form of ornament, and
falling far short of what the practice of recent years has shown to be
possible with this material.
Additions of cast iron serve as ornaments only in the phraseology of
trade catalogues; and the mixture of stone with brick shows results in
flaring contrasts, producing harsh dissonance in the effect. The
facades of such buildings show that this is brick, this is stone, or
this is cast iron; but they always fail to impress the beholder with
the idea of harmonious design. The use of finer varieties of clay in
terra cotta figures laid among the brickwork furnishes a field of
architectural design hardly appreciated. The heavy mass of brick,
divided by regular lines of demarkation, serves as the groundwork of
such ornamentation, while the suitable introduction in the proper
places of the same material in terra cotta imparts the most
appropriate elements of beauty in design; for clay in both forms shows
alike its capacity for utility and decoration. The absorption of light
by both forms of this material abates reflection, and renders its
proportions more clearly visible than any other substance used in
building construction.
The modern mill has been evolved out of the various exacting
conditions developed in the effort to reduce the cost of production to
the lowest terms. These conditions comprise in a great measure
questions of stability, repairs, insurance, distribution of power, and
arrangement of machinery.
In presenting to your attention some of the salient features of modern
mill construction, I do not assume to offer a general treatise upon
the subject; but propose to confine myself to a consideration of some
topics which may not have been brought to your notice, as they are
still largely matters of personal experience which have not yet found
their way into the books on the subject. Much of this, especially the
drawings thrown on the screen, is obtained from the experience of the
manufacturers' mutual insurance companies, with which I am connected.
By way of explanation, I will say that these companies confine their
work to writing upon industrial property; and there is not a
mechanical process, or method of building, or use of raw material,
which does not have its relation to the question of hazard by fire, by
reason of the elements of relative danger which it embodies.
It is indeed fortunate that it has been found by experience that those
methods of building which are most desirable for the underwriter are
also equally advantageous for the manufacturer. There is no pretense
made at demands to compass the erection of fireproof buildings. In
fact, as I have once remarked, a fireproof mill is commercially
impossible, whatever effort may be made to overcome the constructive
difficulties in the way of erecting and operating a mill which shall
be all that the name implies. The present practice is to build a mill
of slow burning construction.
FOUNDATIONS.
In considering the elements of such buildings, I wish to devote a few
words to the question of foundations, because in the excessive loads
imposed by this class of buildings, and in the frequent necessity of
constructing them upon sites where alluvial drift or quicksands form
compressible foundations, there is afforded an opportunity for the
widest range of engineering skill in dealing with the problem. In such
instances, a settling of the building must be foreseen and provided
for, in order that it may be uniform under the whole structure. This
is generally accomplished by means of independent foundations under
the various points of pressure, arranged so as to give a uniform
intensity of pressure upon all parts of the foundation. It is
considered important to limit the load upon such foundations to two
tons a square foot, although loads frequently exceed this amount.
There is a large building in New York City which has recently been
reconstructed, and the foundations rearranged, where the load reached
to the enormous amount of six to ten tons per square foot. It was a
frequent occurrence in the class of high mills spoken of to impose
loads of so much greater intensity upon the wall foundation than upon
the piers under the columns of the mill, that the floors became much
lower at the walls than at the middle.
The stone for such foundations should be laid in cement rather than in
mortar, not merely because cement offers so much greater resistance to
crushing, but because its setting is due to chemical changes occurring
simultaneously throughout the mass. The hardening of mortar, on the
other hand, is due to the drying out of the water mechanically
contained with it, and its final setting is caused by the action of
the carbonic acid gas in the air.
Although quicksands are never to be desired, yet they will sustain
heavy loads if suitably confined. When inclined rock strata are met
with, all horizontal components of stress should be removed by cutting
steps so that the foundation stones shall lie upon horizontal beds.
Foundations are frequently impaired by the slow, insidious action of
springs or of water percolating from the canal which supplies the
water power for the mill; and the proper diversion of such streams
should be carefully provided for.
In the question of foundations, there is much of a general nature
which is applicable to all structures; but, at the same time, each
case requires independent consideration of the circumstances involved.
WALLS.
In addition to what has been said, there is but little for me to offer
on the subject of walls beyond the general question of stability. In
mill construction, walls of uniform thickness have been displaced by
pilastered walls, about sixteen inches thick at the upper story, and
increasing four inches in thickness with each story below.
The remainder of the walls is from four to six inches less in
thickness than at the pilasters. Frequently the outside dimensions of
these pilasters are somewhat increased, giving greater stability and
artistic effect. By leaving hollow flues within them, and using these
flues as conductors for heated air which may be forced in by a blower,
such pilasters afford a means for the most efficient method of warming
the building.
Consideration must be given to the contraction of brick masonry,
especially when an extension or addition is to be made to an older
building. This shrinkage amounts to about three-sixteenths of an inch
to the rod, an item which is of considerable importance in the floors
of high buildings, where the aggregate difference is very appreciable.
Some degree of annoyance is caused by neglect to consider this element
of shrinkage in reference to the window and door frames, which should
have a slight space above them allowing for such contraction. This
contraction is often the source of serious trouble in brick buildings
with stone faces, the shrinkage of the brick imposing excessive stress
on the stone. Instances of this are quite frequent, especially in
large public buildings, notably the capitol at Hartford and the public
building at Philadelphia, where the shivering of the joints of the
stone work gave undue alarm, on the general assumption that it
indicated a dangerous structural weakness. The difficulty has, I
believe, been entirely remedied in both cases.
The limit of good practice on loads upon brickwork is eight to ten
tons per square foot, although it is true that these loads are largely
exceeded at times. It is not to be shown, however, that the limits of
safety in regard to desirable construction should be confined to the
use of masonry for any low buildings. Structures which may be said to
be equal to those of brickwork, as far as commercial risk is
concerned, can be built wholly or in part of wood so as to conform to
all practical conditions of safety. This statement does not apply
except to low buildings of one or possibly two stories in height,
where the timber cannot be subjected to the intense blast of flame
occurring when a high building is on fire.
Mr. George H. Corliss, the eminent engine builder, of Providence,
first built a one-story machine shop, with brick walls extending only
to the base of the windows, above this the windows being very close
together, with solid timber construction between them.
Another method is to place upright posts reaching from the sill to the
roof timbers, and to lay three-inch plank on the outside of such posts
up to the line of the windows. A sheathing on the outside plank
between the timbers is laid vertically and fastened to horizontal
furring strips. In some instances a small amount of mortar is placed
over each of the furring strips. The reason for this arrangement is to
prevent the formation of vertical flues, which are such a potent
factor in the extension of fires.
WINDOWS.
Light is often limited or misapplied on account of faulty position or
size of windows. The use of pilastered walls permits the introduction
of larger windows, which are in most instances virtually double
windows, the two pairs of sashes being set in one frame separated by a
mullion. A more recent arrangement, widely adopted in English
practice, is to place a swinging sash at the top of the window, which
can be opened, when necessary, to assist in the ventilation, while the
main sashes of the window are permanently fixed.
Rough plate glass is used in such windows, because it gives a softer
and more diffused light, which is preferred to that from ordinary
clear glass. White glass may be rendered translucent by a coat of
white zinc and turpentine.
The top of a window should be as near the ceiling as practicable,
because light entering the upper portion of a room illuminates it more
evenly, and with less sharply marked shadows, than where the windows
are lower down.
The walls below the windows should be sloped, in order that there may
be no opportunity to use them as a resting place for material which
should be placed elsewhere.
FIRE WALLS.
Brick division walls should be built so as to constitute a fire wall
wherever it is practicable to do so. Such walls should project at
least three feet above the roof, and should be capped by stone, terra
cotta, or sheet metal. They must form a complete cut-off of all
combustible material, especially at the cornices.
FIRE DOORS.
All openings in such walls must be provided with such fireproof doors
as will prove reliable in time of need. Experience with iron doors of
various forms of construction show that they have been utterly
unreliable in resisting the heat of even a small fire. They will warp
and buckle so as to open the passageway and allow the fire to pass
through the doorway into the next room.
A door made of wood, completely enveloped by sheets of tinned iron,
and strongly fastened to the wall, has proved to resist fire better
than any door which can be applied to general use. I have seen such
doors in division walls where they had successfully resisted the flame
which destroyed four stories of a building filled with combustible
material, without imposing any injury upon the door except the removal
of the tin on the sheet iron; and the doors were kept in further
service without any repairs other than a coat of paint.
The reason for this resistance to fire is that the wood, being a poor
conductor of heat, will not warp and buckle under heat, and cannot
burn for lack of air to support combustion. A removal of the sheet
metal on such a door after a fire in a mill shows that the surface of
the wood is carbonized, not burned, reduced to charcoal, but not to
ashes.
Many fire doors are constructed and hung in such a manner that it is
doubtful whether they could withstand a fire serious enough to require
their services.
The door should be made of two thicknesses of matched pine boards of
well dried stock, and thoroughly fastened with clinched nails. It
should be covered with heavy tin, secured by hanging strips, and the
sheets lock-jointed to each other, with the edge sheets wrapping
around, so that no seam will be left on the edge.
Sliding doors are preferable to swinging doors for many reasons,
especially because they cannot be interfered with by objects on the
floor. But, if swinging doors are used, care should be taken that the
hinges and latches are very strong, and securely fastened directly to
the walls, and not to furring or anything in turn attached to the
walls. The portion of the fixtures attached to the doors must be
fastened by carriage bolts, and not by wood screws.
Sliding on trucks is the preferable method of hanging sliding doors,
inclined two and one half inches to the foot, and bolted to the wall.
The trucks should be heavy "barn door hangers," bolted to the door;
and a grooved door jamb, of wood, covered with tin similar to the
door, should receive it when shut. A step of wood will hold the door
against the wall when closed. A threshold in the doorway retards fire
from passing under the door, and also prevents the flow of water from
one room to another.
These doors are usually placed in pairs, and sometimes an automatic
sprinkler is placed between them.
Fire doors should always be closed at night. In some well ordered
establishments there is a printed notice over each door directing the
night watchmen to close such doors after them. In a storage warehouse
in Boston, the fire doors are connected with the watchman's electric
clock system, so that all openings of fire doors are matters of record
on the dial sheet.
Fire doors should certainly be closed at times of fire; yet, that such
doors are open at night fires, or left open by fleeing help at day
fires, is an old story with underwriters. A simple automatic device
can be used to shut such doors. It consists of two round pieces of
wood with a scarfed joint held by a ferrule, forming a strut which is
placed on two pins, keeping the door open, as other sticks have long
since served like purposes.
The peculiarity of this arrangement is that the ferrule is not
homogeneous, but is made up of four segments of brass soldered
together with the alloy fusible at 163 degrees Fahr., which is widely
known for its use in automatic sprinklers. When the solder yields, the
rod cripples, and the door rolls down the inclined rail and shuts. At
any time the door can be closed by removing one end of the rod from
one of the pins and allowing it to hang from the other pin.
MILL TOWERS.
Because of economic reasons for preserving the space within the walls
of the mill so that it may be to the greatest extent available for the
best arrangement of machinery, the stairways should be placed outside
of the building. Such stairways should not be spiral stairways, but
should be made in short straight runs with square landings, because in
the spiral stairway the portion of the stairs near the center is of so
much steeper pitch that it renders them dangerous when the help are
crowding out of the mill.
The wear of stairs from the tread of many feet presents a difficult
problem. A very common practice consists in covering each tread with a
thin piece of cast iron marked with diagonal scores, and generally
showing the name of the mill. These treads wear out in the course of
time, but for this use they answer very well, although somewhat
slippery.
A wood tread gives a more secure foothold upon the stairway; and in
some instances stairs have been protected by covering the treads with
boards of hard wood, containing grooves about three-eighths of an inch
deep, and of similar width, with a space of half an inch between them.
These boards are grooved on both sides and placed on the stairs. After
the front edge is worn, they are turned around so as to present the
other edge to the front, and, in course of time, turned from the
exposed side to do service in two positions on the other side. In this
manner these tread covers are exposed to wear in four different
positions.
Mill towers, besides containing the stairways, also serve other
purposes, as for cloak rooms for the help. They often contain a part
of the fire protective apparatus, carrying standpipes with hydrants at
each floor. For this use they are easily available, and furnish a line
of retreat in case a fire spreads to an extent beyond the ability of
the apparatus to cope with it. These towers also furnish an excellent
foundation for the elevated tank necessary for the supply of water for
the fire apparatus in places unprovided with an elevated reservoir.
In view of the terrible and deplorable accidents which have occurred
by reason of lack of proper stairway facilities at panics caused in
time of fire, I would repeat the words of the late Amos D. Lockwood,
the most eminent mill engineer which this country has yet produced,
when he said to the New England Cotton Manufacturers' Association,
"You have no moral right to build a mill employing a large number of
help, with only one tower containing the stairways for exit."
The statute laws of several of the States require fire escapes; but it
is a matter of fact that they are rarely used, because people are not
often cool enough to avail themselves of that opportunity of escape. I
know of one instance where a number of girls jumped out of a fourth
story window, because they did not think of the stairways, and did not
dare to use the fire escape. In that instance, none of the group
referred to tried to go down the stairs, which did furnish a perfectly
safe means of exit to a number of others.
Most of the fire escapes are put up so as to conform to the letter of
the law; and in such manner that no one but a sailor or an acrobat
would be likely to trust himself to them. In crowded city buildings,
and in other places where the ordinary means of escape are not in
duplicate, it is essential that fire escapes should be provided; but
it is a great deal better to make a mill building so that they shall
not be necessary as a matter of fact, even if they are put up to
conform to the requirements of statute law.
REAR TOWERS.
In addition to stairways, towers are placed at the rear of the mill,
for the purpose of accommodating the elevators and sanitary
arrangements. It is not desirable that elevators should be boxed or
surrounded with anything that would result in the construction of a
flue; but it is preferable that they pass directly through the floors,
with the openings protected by automatic hatchways which close
whenever the elevator car is absent. In the washroom, etc., in these
towers, it is desirable to protect the wood floors by means of a thin
layer of asphalt.
BASEMENT FLOORS.
There are difficulties connected with the floors on or near the
ground, by reason of the dry rot incident to such places. Dry rot
consists in the development of fungus growth from spores existing in
the wood, and waiting only the proper conditions for their
germination. The best condition for this germination is the exposure
to a slight degree of warmth and dampness. There have been many
methods of applying antiseptic processes for the preservation of wood;
but, irrespective of their varying degrees of merit, they have not
come into general use on account of their cost, odor, and solubility
in water.
It is necessary that wood should be freely exposed to circulation of
air, in order to preserve it under the ordinary conditions met with in
buildings. Whenever wood is sealed up in any way by paint or varnish,
unless absolutely seasoned, and in a condition not found in heavy
merchantable timber, dry rot is almost sure to ensue. Whitewash is
better.
There has recently been an instance of a very large building in New
York proving unsafe by reason of the dry rot generated in timbers
which have been completely sealed up by application of plaster of
Paris outside of the wire lath and plaster originally adopted as a
protection against fire. Wire lath and plaster is one of the best
methods of protecting timber against fire; and, if the outside is not
sealed by a plaster of stucco or some other impermeable substance, the
mortar will afford sufficient facilities for ventilation to prevent
the deposition of moisture, which will in turn generate dry rot.
Where beams pass into walls, ventilation should be assured by placing
a board each side of the beam while the walls are being built up, and
afterward withdrawing it. In the form of hollow walls referred to, it
is a common practice to run the end of the beam into the flue thus
formed, in order to secure ventilation.
I am well acquainted with a large mill property, one building of which
was erected a short time before the failure of the corporation, which
resulted in the whole plant remaining idle several years. After the
lapse of about five years this establishment was again put into
operation; but before the new mill could be safely filled with
machinery, it was necessary to remove all the beams which entered
walls and to substitute for them new ones, because the ends were so
thoroughly rotted that it would have been dangerous to impose any
further loads upon the floors. When floors are within a few feet of
the ground, unless the site be remarkably dry, it is essential to
provide for a circulation of air, which can be done very feasibly in a
textile mill by laying drain pipe through the upper part of the
underpinning, forming a number of holes leading into this space, and
then making a flue from this space to the picker room or any other
place requiring a large amount of air. The fans of the picker room,
drawing their supply from underneath the building, produce a
circulation of air which keeps the timber in good condition.
It is supposed by some that there is a difference in the quality of
timber according to the season in which it is felled, preference being
given to winter timber, on account of the greater amount of potash and
phosphoric acid which it is said to contain at that time. In some
parts of Europe it is a custom to specify that the lumber should have
been made from rafted timber, on account of the action of the water in
killing certain species of germs. Whatever may be the merits of either
of these two theories, the commercial lumber of the northern part of
this country is generally felled in winter and afterward rafted.
The action of lime in the preservation of wood has always been
attended with the most excellent results; although not suited to
places subject to the action of water, which dissolves the lime,
leaving the timber practically in its original condition. The
preservative action of lime upon wood is readily shown by the
admirable condition in which laths are always found. I doubt if any
one ever found a decayed lath in connection with plaster.
As an example of the action of lime as a preservative of lumber. I can
cite an instance of a mill in New Hampshire where the basement floor
was placed in 1856, the ledge in the cellar having been blasted out
for the purpose. The rock was very seamy, and abounded in water
issuing from springs or percolating from the canal supplying water to
the mill. The rock was blasted away to a grade two feet below the
floor, and most of the space filled up again by replacing the small
pieces of stone, so arranged as to form blind drains for the removal
of any water which might find its way under the floor.
Toward the top of this filling, finer stones were used, then about
three inches of gravel, which was covered with two inches of sand and
lime. Two years ago I was at this mill when some alterations requiring
the removal of the floor were in progress, and found that the lumber
was still in good, sound condition, except for a superficial decay on
the under side of the floor plank.
But there are frequent instances where it is necessary to place the
floor directly upon the earth, without any space or loose filling
underneath it, in order to save room, or to secure a firm support for
machinery. By way of information upon what has actually been
accomplished in this direction, I will cite instances of three floors
in such positions, all of which have to my knowledge fulfilled the
purpose for which they were designed.
The first instance is that of a basement floor laid twenty-one years
ago, a portion of which was made by excavating one foot below the
floor, six inches of coarse stone being filled in, then five inches of
coal tar concrete made up with coarse gravel, and finally about one
inch of fine gravel concrete. Before the concrete was laid, heavy
stakes were driven through the floor about three feet apart, to which
the floor timbers were nailed and leveled up. The concrete was then
filled in upon the floor timbers, and thoroughly tamped and rolled out
to the level of the top of the floor timbers. The under side of the
floor timbers was covered with hot coal tar.
This floor is still in good condition, and has not needed repairs
caused by the decay of the timber. Another portion of the floor laid
at the same time and in the same manner, with the exception that
cement concrete was used in the place of the coal tar, was entirely
rotted out in ten years.
Another floor was made in quite a similar manner. All soil and loam
was removed from the interior of the building; the whole surface was
brought up to the grade with a puddle of gravel and ashes; stakes two
and a half by four inches, and thirty inches in length, were driven
down; and nailing strips were secured to them. Over this puddled
surface a coat of concrete eight inches thick was laid, the top being
flush with the upper surface of the nailing strips. This concrete was
made of pebbles about two inches in diameter, well coated with coal
tar, and laid in place when hot. It was then packed together by being
tamped and rolled, and a thin covering of the tarred sand placed upon
the top, forming a smooth, hard surface. The first floor consisted of
two inches of matched spruce, grooved on both sides, and fitted with
hard pine splines, five-eighths by one and one-fourth inches. On the
top of this a hard pine 1¼ inch floor was laid over a course of
building paper.
Another method, which is certainly more novel than either of the
others, consists in supporting a floor upon a bed of resin. The
underlying earth was removed, and replaced with spent moulding sand,
leaving trenches for the floor timbers, which were placed upon bricks
laid without mortar. Melted resin was poured into the space alongside
and underneath the timbers. The floor planks were then laid upon the
timbers, the tops of which were about half an inch above the level of
the sand. Holes were bored into the floor plank about four feet apart,
and melted resin then poured into the holes, so as to interpose a
layer of resin underneath the floor plank and beams. Upon this floor a
top floor of hard wood was laid in the usual manner. This floor has
been used for a number of years to support a large quantity of heavy
machine tools, principally planers, without yielding or depreciation
due to decay, and has proved to be most satisfactory.
In some instances asphaltum or coal tar concrete floors are not
covered with wood, although it is much more agreeable for the help to
stand upon wooden floors. It should be remembered that all these
compounds are readily softened by means of oil, and they should be
protected from oil by a coat of paint when not covered with wood; the
preferable method being to first apply a priming containing very
little oil, or a coat of shellac, and follow with some paint mixed up
with boiled linseed oil.
(_To be continued._)
* * * * *
THE MECHANICAL EQUIVALENT OF HEAT.
BY DE VOLSON WOOD, PROFESSOR OF ENGINEERING IN STEVENS INSTITUTE OF
TECHNOLOGY.
It is clearly intimated by Mr. Hanssen, in his determination of the
mechanical equivalent of heat, published in the Scientific American
Supplement, No. 642, April 21, 1888, that his object is to determine
the _absolute_ value of this constant. With his data he finds it to be
771.89 foot pounds. But the determination by direct experiment gives a
larger value. Thus, the most reliable experiments--those of Joule and
Rowland--give values exceeding by several units that found by Hanssen.
A committee of the British Association, appointed for this purpose,
reported in 1876 that sixty of the most reliable of Joule's
experiments gave the mean value 774.1. The experiments were made with
water at a temperature of about 60° F., according to the mercurial
thermometer, and reduced to its value at the temperature of melting
ice, according to the formula given by Regnault for the variation of
the specific heat of water at varying temperature under the constant
pressure of one atmosphere. According to this formula the specific
heat of water increases with the temperature above the melting point
of ice, so that the equivalent would be somewhat less at 32° F. than
at 60° F. It will be found in Regnault's _Relation des Experiences_
that he experimented on water at high temperatures, but more recently
Professor Rowland has found that the specific heat of water is
_greater_ at 40° F. than at 60° F., thus reversing between these
limits the law given by Regnault; the increase, as given by the most
probable values, being, roughly, about 1/250 of its value at 60° F.
The proper correction due to this cause would make the equivalent over
777 foot pounds, instead of 774.1. Professor Rowland's experiments,
when reduced to the same thermometer, same temperature, and same
latitude as Joule's, agreed very nearly with those of the latter,
being about 1/1000 part larger; so that the chief difference in the
ultimate values consists in the reductions for temperature and
latitude. The force of gravity being less for the lower latitudes, the
number representing the mechanical equivalent will be greater for the
latter, since the unit pound mass must fall through a greater number
of feet to equal the same work; so that the equivalent will be greater
at Paris than at Manchester. Professor Rowland also found that the
degrees on the air thermometer from 40° F. upward to above 60° F.
exceeded those on the mercurial thermometer throughout the
corresponding range, and that from 40° to 41° the degree was between
1/150 and 1/200 of a degree larger on the air thermometer than on the
mercurial. Although this fraction is too small to be observed by
ordinary means, yet, if it exists, it cannot be ignored if absolute
values are sought. Regnault employed the air thermometer in his
experiments, while Joule used the mercurial thermometer, and if
Joule's value 774.1 be increased by 1/200 of itself in order to reduce
it from the equivalent of the degree on the mercurial thermometer to
that on the air thermometer, we get 778 foot pounds, nearly. Rowland
found from his experiments that when reduced to the air thermometer
and to the latitude of Baltimore, the equivalent was nearly 783,
subject to small residual errors.
Nearly all writers upon this subject--except Rankine--have considered
that the mechanical equivalent of heat, in British units, was the
energy necessary to raise the temperature of one pound of water from
32° F. to 33° F., but Rankine defines it as the heat necessary to
increase the temperature of one pound of water one degree Fahrenheit
from that of maximum density, or from 39° F. to 40° F. For ordinary
practice it is immaterial which of these definitions is used, for the
errors resulting therefrom are much less than those resulting from
ordinary observations. But when the value is to be determined by
direct experiment at the standard temperature, Rankine's limits are
much to be preferred; for it is so very difficult to determine exact
values by observation when the substance is near the state bordering
on a change of state of aggregation, as that of changing from water to
ice. Observations made at about 60° F. were reduced by means of
Regnault's law for the specific heat of water, as has been stated,
which is expressed by the formula
4 9
c = 1 + ------ t + ------ t^{2}
10^{5} + 10^{7}
in which t denotes the temperature according to the Centigrade scale.
According to this law, the mechanical equivalent would not be 0.2 of a
foot pound greater at 5° C. (41° F.) than at 0° C. (32° F.); hence, if
this law were correct, it would make no practical difference whether
the temperature were at 0° C. or 5° C. This law makes the _computed_
value at 32° F. about 0.95 of a foot pound less than that determined
by experiment at 60° F.; whereas Rowland's experiments make it
_greater_ at 40° F. by more than four foot pounds, for the air
thermometer. In determining a _fixed_ value to be used for scientific
purposes, it is necessary to fix the place, the thermometer, and the
particular degree on the thermometer. The place may be known by its
latitude if reduced to the level of the sea. The air thermometer
agrees most nearly with that of the ideally perfect gas thermometer,
while the mercurial thermometer differs very much from it in some
cases. Thus, Regnault found that when the air thermometer indicated
630° F. above the melting point of ice (or 662° F.), the mercurial
thermometer indicated 651.9° above the same point (683.9° F.), a
difference of 22° F. It is apparent that the air thermometer furnishes
the best standard. As for the particular degree on the scale to be
used for the standard, it is apparent, from the observations above
made, that the temperature corresponding to that at or near the
maximum density of water is more desirable than that at the melting
point of ice. The fact, also, that the specific heats at constant
pressure and at constant volume are the same at the point of maximum
density, as shown by theory, is an additional argument in favor of
selecting this point for the standard. It thus appears that the
solution of this problem, which appears simple and very definite by
Mr. Hanssen's method, becomes intricate and, to a limited degree,
indeterminate when subjected to the refinements of direct experiment.
If the constants used by Hanssen are absolutely correct, then his
result must be unquestioned; but since physical constants are subject
to certain residual errors, one would as soon think of finding the
specific heat of air at constant volume, by using the value of the
mechanical equivalent as one of the elements, and trusting the result,
as he would to trust to the computed value of the mechanical
equivalent without subjecting it to the test of a direct experiment.
We will, therefore, examine the constants used to see if they are the
exact values of the quantities they represent.
He says they are universally accepted as correct; and this may be
true, when used for general purposes, and yet not be scientifically
exact. He uses 0.2377 as the specific heat of air. This is the value,
to four decimals, found by Regnault. Thus, Regnault gives for the mean
value of the specific heat of air
Between -30° C and + 10° C. 0.23771
" 0° C " 100° C. 0.23741
" 0° C " 200° C. 0.23751
And we know of no reason why one of these values should be used rather
than another, except that the mean of a large range of temperatures
may be more nearly correct than that of any other; and if this reason
determines our choice, the number 0.2375 would be used instead of
0.2377. Although this difference is small, yet the former value would
have reduced his result about 0.7 of a foot pound.
Again, he uses 0.1686 for the specific heat of air at constant volume.
The value of this constant has never been found to any degree of
accuracy by direct experiment, and we are still dependent upon the
method established by La Place and Poisson, according to which the
constant ratio of the specific heat of a gas at constant pressure to
that at constant volume is found by means of the velocity of sound in
the gas. The value of the ratio for air, as found in the days of La
Place, was 1.41, and we have 0.2377 ÷ 1.41 = 0.1686, the value used by
Clausius, Hanssen, and many others. But this ratio is not definitely
known. Rankine in his later writings used 1.408, and Tait in a recent
work gives 1.404, while some experiments give less than 1.4, and
others more than 1.41.
An error of one foot in a thousand in determining the velocity of
sound will affect the third decimal figure one or two units. A small
difference in the assumed weight of a cubic foot of air also affects
the result. M. Hanssen gives 0.080743 pound as the weight at 32° F.
under the pressure of one atmosphere; while Rankine gives 0.080728
pound. In my own computations I use 1.406 as a more probable value of
the constant sought. This will give for the specific heat of air at
constant pressure
0.2375 ÷ 1.406 = 0.1689
This is only 0.0003 of a unit greater than the value used by Hanssen,
but it would have given him nearly 775, instead of 771.89.
Again, he uses 491.4° F. for the absolute temperature of melting ice.
The exact value of this constant is unknown; but the mean value as
determined by Joule and Thomson, in their celebrated experiments with
porous plugs, was 492.66° F. This value would slightly change his
result. It will be seen from the above that a small change in the
constants used may affect by several units the computed value of the
mechanical equivalent. I have computed it, using 1.406 for the ratio
of the specific heat of air at constant pressure to that at constant
volume, 491.13° F. as the temperature of melting ice above the zero of
the _air_ thermometer, 26,214 feet for the height of a homogeneous
atmosphere, and 0.2375 for the specific heat of air, and I find, by
means of these constants, 778. If computed from the zero of the
absolute scale, 492.66° F., I find 777 to the nearest integer.
Recently I have used 778. If the value given by Rowland, about 783
according to the air thermometer at 39° F., should prove to be
correct, it seems probable that the constant 1.406 used above would be
reduced to about 1.403, or that the other constants must be changed by
a small amount. The height of the homogeneous atmosphere used above,
26,214 feet, is the value used by Rankine as deduced from Regnault's
figures, and only one foot less than the value used by Sir William
Thomson; but the figures used by Mr. Hanssen give 26,210½ feet.
The method above called Hanssen's is really that of Dr. Mayer (the
German professor), who in 1842 used it for determining the mechanical
equivalent; but on account of erroneous data, the value found by him
was much too small.
* * * * *
ECONOMY TRIALS OF A NON-CONDENSING STEAM ENGINE--SIMPLE, COMPOUND, AND
TRIPLE.[1]
[Footnote 1: Abstract of paper read before the Institution of
Civil Engineers, March 13.]
BY MR. P. W. WILLANS, M.I.C.E.
The author described a series of economy trials, non-condensing, made
with one of his central valve triple expansion engines, with one
crank, having three cylinders in line. By removing one or both of the
upper pistons, the engine could be easily changed into a compound or
into a simple engine at pleasure. Distinct groups of trials were thus
carried out under conditions very favorable to a satisfactory
comparison of results.
No jackets were used, and no addition had, therefore, to be made to
the figures given for feed water consumption on that account. Most of
the trials were conducted by the author, but check trials were made by
Mr. MacFarlane Gray, Prof. Kennedy, Mr. Druitt Halpin, Professor
Unwin, and Mr. Wilson Hartnell. The work theoretically due from a
given quantity of steam at given pressure, exhausting into the
atmosphere, was first considered.
By a formula deduced from the [theta] [phi] diagram of Mr. MacFarlane
Gray, which agreed in results with the less simple formulas of Rankine
and Clausius, the pound weight of steam of various pressures required
theoretically per indicated horse power were ascertained. (See annexed
table.)
A description was then given of the main series of trials, all at four
hundred revolutions per minute, of the appliances used, and of the
means taken to insure accuracy. A few of the results were embodied in
the table. The missing quantity of feed water at cut off, which, in
the simple trials, rose from 11.7 per cent. at 40 lb. absolute
pressure to nearly 30 per cent. at 110 lb. and at 90 lb. was 24.8 per
cent., was at 90 lb. only 5 per cent. in the compound trials. In the
latter, at 160 lb., it increased to 17 per cent., but, on repeating
the trial with triple expansion, it fell to 5.46 per cent. or to 4.43
per cent. in another trial not included in the table.
On the other hand, from the greater loss in passages, etc., the
compound engine must always give a smaller diagram, considered with
reference to the steam present at cut-off, than a simple engine, and a
triple a smaller diagram than a compound engine. Nevertheless, even at
80 lb. absolute pressure, the compound engine had considerable
advantage, not only from lessened initial condensation, but from
smaller loss from clearances, and from reducing both the amount of
leakage and the loss resulting from it. These gains became more
apparent with increasing wear. The greater surface in a compound
engine had not the injurious effect sometimes attributed to it, and
the author showed how much less the theoretical diagram was reduced by
the two small areas taken out of it in a compound engine than by the
single large area abstracted in a simple engine. The trials completely
confirmed the view that the compound engine owed its superiority to
reduced range of temperature. At the unavoidably restricted pressures
of the triple trials, the losses due to the new set of passages, etc.,
almost neutralized the saving in initial condensation, but with
increased pressure--say to 200 lb. absolute--there would evidently be
considerable economy. The figures of these trials showed that the loss
of pressure due to passages was far greater with high than with low
pressure steam, and that pipes and passages should be proportioned
with reference to the weight of steam passing, and not for a
particular velocity merely.
The author described a series of calorimetric tests upon a large scale
(usually with over two tons of water), the results of which were
stated to be very consistent. After comparing the dates of initial
condensation in cases where the density of steam, the area of exposed
surface, and the range of temperature were all variables, with other
cases (1) where the density was constant and (2) where the surface was
constant, the author concluded that, at four hundred revolutions per
minute, the amount of initial condensation depended chiefly on the
range of temperature in the cylinder, and not upon the density of the
steam or upon the extent of surface, and that its cause was probably
the alternate heating and cooling of a small body of water retained in
the cylinder. The effect of water, intentionally introduced into the
air cushion cylinder, corroborated the author's views, and he showed
how small a quantity of water retained in the cylinder would account
for the effects observed. At lower speeds surface might have more
influence. The favorable economical effect of high rotative speed,
_per se_, was very apparent.
In a trial with a compound engine, with 130 lb. absolute pressure, the
missing quantity at cut-off rose from 11.7 per cent. at 405
revolutions to 29.66 per cent. at 130 revolutions, the consumption of
feed water increasing from 20.35 lb. to 23.67 lb. This saving of 14
per cent. was due solely to increase of speed. Similar trials had been
made with a simple engine. In one simple trial at slow speed the
missing quantity rose to 44.5 per cent. of the whole feed water.
------------------------------+-----+------------+-------------+------+-------------+-------------+------
Intended mean | | | | | | |
admission pressure Lb.| 40 | 90 | 110 | 130 | 150 | 160 | 170
------------------------------+-----+------+-----+------+------+------+------+------+------+------+------
Simple, Compound, or Triple.| S. | S. | C. | S. | C. | C. | C. | T. | C. | T. | T.
Actual mean | | | | | | | | | | |
admission pressure Lb.|40.88| 92.65|87.54|106.3 |109.3 |130.6 |149.9 |151.9 |158.5 |158.1 |172.5
Percentage ratio of actual | | | | | | | | | | |
mean pressure, referred to | | | | | | | | | | |
low pressure piston, to | | | | | | | | | | |
theoretical mean pressure |98.2 |100 |91.3 |100.7 | 94.8 | 94.2 | 94.6 | 84.54| 95.9 | 85.3 | 85.2
Indicated horse power |16.51| 31.61|28.14| 33.5 | 33 | 36.31| 38.59| 35.69| 39.55| 35.56| 38.45
------------------------------+-----+------+-----+------+------+------+------+------+------+------+------
Feed water actually used per | | | | | | | | | | |
indicated H.P.H.-- | | | | | | | | | | |
Simple Lb.|42.76| 26.89| ... | 26 | ... | ... | ... | ... | ... | ... | ...
Compound Lb.| ... | ... |34.16| ... | 21.37| 20.35| 19.45| ... | 19.19| ... | ...
Triple Lb.| ... | ... | ... | ... | ... | ... | ... | 19.68| ... | 19.19| 18.45
Steam required theoretically | | | | | | | | | | |
per 1 H.P.H. Lb.|34.67| 19.24|19.86| 17.9 | 17.65| 16.25| 15.23| 15.16| 14.87| 14.9 | 14.36
Percentage efficiency |81.1 | 71.5 |82.2 | 68.8 | 82.5 | 80 | 78.3 | 77 | 77.4 | 77.6 | 77.8
------------------------------+-----+------+-----+------+------+------+------+------+------+------+------
Percentage of feed water | | | | | | | | | | |
missing at cut off in | | | | | | | | | | |
high pressure cylinder | ... | ... | ... | ... | ... | ... | ... | 5.33| ... | 6.84| 5.01
Ditto high pressure cylinder | ... | ... | 5 | ... | 9.5 | 11.7 | 15.1 | 14.84| 17 | 12.06| 15.33
Ditto low pressure cylinder |11.7 | 24.8 |15.2 | 29.56| 16.25| 19.1 | 20.6 | 22.12| 21.3 | 22.11| 24.21
Percentage of feed water | | | | | | | | | | |
missing at end of stroke | | | | | | | | | | |
in low pressure cylinder |10.4 | 18.83|14.25| 21.53| 16.59| 17.55| 20.69| 18.01| 19.55| 18.81| 19.25
------------------------------+-----+------+-----+------+------+------+------+------+------+------+------
The author compared a series of compound trials, at different powers,
with 130 lb. absolute pressure, and various ratios of expansion, with
a series giving approximately the same powers at a constant ratio of
expansion, but with varying pressures, being practically a trial of
automatic expansion against throttling. Starting with 40 indicated
horse power, 130 lb. absolute pressure, four expansions, and a
consumption of 20.75 lb. of water, the plan of varying the expansion,
as compared with throttling, showed a gain of about 7 per cent. at 30
indicated horse power, but of a very small percentage when below half
power. If the engine had an ordinary slide valve, the greater
friction, added to irregular motion, would probably neutralize the
saving, while if the engine were one in which initial condensation
assumed more usual proportions, the gain would be probably on the side
of variable pressure. Even as it was, the diagrams showed that the
missing quantity became enormously large as the expansion increased.
Judging only by the feed water accounted for by the indicator, the
automatic engine appeared greatly the more economical, but actual
measurement of the feed water disproved this. The position of the
automatic engine was, however, relatively more favorable when simple
than when compound.
In conclusion, the author referred to a trial with a condensing
engine, at 170 lb. absolute pressure, in which the feed water used was
15.1 lb., a result evidently capable of further improvement, and to an
efficiency trial of a combined central valve engine and Siemens'
dynamo, made for the Admiralty, at various powers. At the highest
power the ratio of external electrical horse power to indicated horse
power in the engine was 82.3 per cent. Taking the thermo-dynamic
efficiency of the engine at 80 per cent., that of the combined
apparatus would be nearly 66 per cent.
* * * * *
RAILWAY BRIDGE AT LACHINE.
The subject of our large illustration this week is a large steel
bridge carrying the Central Pacific Railway over the St. Lawrence
River at Lachine, near Montreal. The main features of this really
magnificent structure are the two great channel spans, each 408 feet
long. It will be noticed that the design combines, in a very ingenious
manner, an upper and a lower deck structure, the railway track being
laid on the top of the girders forming the side spans, and on the
lower flanges of the channel spans, which are crossed by continuous
girders, 75 feet deep, over the central pier, and supported by
brackets as shown. The upper of our two engravings shows the method of
constructing the principal spans, which were built outward from the
side piers, while the work on the center pier was extended on each
side to meet. It was built at the works of the Dominion Bridge
Company, Montreal, from the design of Mr. C. Shaler Smith, the
well-known American bridge engineer.--_Engineering._
[Illustration]
* * * * *
IMPROVED SCREW PROPELLER.
While the last few years have seen great advances made in the designs
of steamships and of their engines, little or nothing has been done in
the way of improving the screw propeller. As a general rule it would
appear to be taken for granted that no radical improvement could be
made in the form of the propeller, although various metals have been
introduced in its manufacture with the view of increasing its
efficiency. For sea-going steamers, however, the shape remains the
same, the variation chiefly relating to the number of blades employed.
A striking departure from ordinary practice, however, has of late been
made by Mr. B. Dickinson, who has invented a screw propeller which, on
practical trial, has given an efficiency far in advance of the
ordinary screw. This new propeller we illustrate here in Figs. C and
D, while Fig. A shows an ordinary propeller. The Dickinson propeller
illustrated has six blades, giving a surface of 30 square feet; it is
right handed, and has pitch of 15 ft. and a diameter of 10 ft. 6 in.
The ordinary screw propeller shown at Fig. A is right handed and two
bladed, with a pitch at the boss of 13 ft. 6 in. and at the tip of 15
ft. It has a diameter of 10 ft. 9 in. and 32 square ft. of surface.
The projected area looking forward is 22 square ft. and the projected
area looking athwartship 22.84 square feet. The most graphic way of
illustrating the principle of Mr. Dickinson's propeller is to take a
two bladed propeller of the ordinary type as shown at Fig. A in the
annexed cuts, and divide into three sections as in Fig. B, then move
section No. 1 to the line position on the shaft of No. 3, and No. 3 to
that of No. 1, No. 2 remaining stationary. The effect of this
interchange will be that (having regard to the circle of rotation) No.
3, the rearmost section, will rotate in advance of No. 2, and No. 2 in
advance of No. 1 (see Fig. C). By this arrangement the water operated
on escapes freely astern from every blade--that from No. 1 passing in
the wake of No. 2, while that from Nos. 2 and 1 passes in the wake of
No. 3. Fig. D represents the blades with a wider spread as practically
used. The advantages claimed by Mr. Dickinson for his propeller, and
which are sufficiently important to be given in detail, are:
[Illustration: Figs. A-D.]
1. That the blades of each section, when the vessel is in motion,
necessarily cut solid, undisturbed water, each blade operating upon
precisely the same quantity of water as an individual broad blade
would do, though, of course, it parts with it in one-third of the
time.
2. That each sectional blade exerts the equivalent efficiency of the
first or entering third portion of the breadth of an ordinary
propeller blade, and that consequently the combined sections have
greater effective power. It is now regarded by experts as an
ascertained fact that the after or trailing portion of the broad blade
is relatively non-effective as compared with the forward or entering
portion.
3. When three blades are fitted, the spent water from No. 2 being
delivered immediately in the wake of No. 3, and that from No. 1 in the
wake of No. 2, has the effect of destroying or reducing to a minimum
the back draught of sections Nos. 2 and 3, No. 1 alone being subject
to this drawback. This is of greater importance than might at first
thought appear, as in cases where there are three or four blades
revolving in one plane, the water is drawn after the retreating blade,
lessening the resistance to the face of the advancing one.
4. That by the subdivision of the blades, as arranged spirally, the
water passing through within the radius of the propeller has its
resisting capacity more thoroughly worked out than is possible with
any propeller whose blades are all on the same plane. This view is
confirmed by the visibly increased rotation of the water in the wake
of the vessel.
5. That by broadening the blades or increasing the number of sections,
the diameter of the propeller may be proportionately diminished
without the sacrifice of engine power. This is often desirable with
vessels of light draught, the complete immersion of the screw being at
all times necessary to avoid waste of power.
6. The propeller being made and fitted on the shaft in sections, all
that is necessary in case of accident is to replace the broken
section. This in many cases could be done afloat.
7. The blades being arranged to take their water at different planes,
there is the greater certainty of one or other of the sections
operating upon what is termed the water of friction. This is
considered an advantage.
8. Where it is desirable, the blades of the different sections can be
made of varying breadth or pitch.
9. The principle of division into two or more sections applies equally
to two, three, or four bladed ordinary propellers.
10. The adoption of this principle does not entail any alteration or
enlargement of the screw space or bay as usually provided.
11. As a consequence of the freedom and rapidity with which the water
operated upon escapes from the narrow blades, the depression at the
stern of the vessel caused by the action of the ordinary propeller is
greatly reduced.
12. The vibration caused by this propeller is so slight as to be
hardly noticeable, thereby effecting a saving in the wear and tear of
the engine and machinery. This may also be a consideration in
promoting the comfort of passengers.
From a practical and working point of view we take Mr. Dickinson's
chief claims to be, in the first place, the yielding of a greater
speed per power employed, or an economy in obtaining an equal speed;
in the second, increased, rapidity in maneuvering and stopping a
vessel; and in the third, a reduction of vibration. In order to put
these claims to a practical and reliable comparative test, Messrs.
Weatherley, Mead & Hussey, of Saint Dunstan's Hill, London, placed at
the inventor's disposal two of their new steamers, the Herongate and
the Belle of Dunkerque. These are in every respect sister boats, and
were built in 1887 by Messrs. Short Brothers, and engined by Mr. John
Dickinson, of Sunderland. The Herongate was fitted about four months
ago with the largest propeller yet made on Mr. B. Dickinson's
principle, the Belle of Dunkerque having an ordinary four-bladed
propeller of the latest improved type. Every precaution was taken to
place the two vessels on the same footing for the purpose of a
comparative test, which was recently carried out. Both vessels
previously to the trial were placed on the gridiron, cleaned and
painted, their boilers opened out and scaled, their steam gauges
independently tested, and both vessels loaded with a similar cargo of
pitch, the only difference being that the Herongate carried 11 tons
more dead weight and had one inch more mean draught than the Belle of
Dunkerque, while the former had been running continuously for nine
months against the latter's two and a half months. On the day of the
trial the vessels were lying in the Lower Hope reach, and it was
decided to run them over the measured mile there with equal pressure
of steam. The order of running having been arranged, the Herongate got
under way first, the Belle of Dunkerque following over the same
course. Steaming down against tide, the Herongate is said to have come
round with remarkable ease and rapidity, and in turning on either
helm, whether with or against tide, to have shown a decided advantage.
Equally manifest, it is stated, was the superiority shown in bringing
up the vessel by reversing, when running at full speed, thus
confirming the very favorable reports previously received by the
owners from their captains since the Dickinson propeller was fitted to
the Herongate. Those who were on board her state that the vibration
was scarcely noticeable. From a statement submitted to us it is clear
that the Herongate had the turn of the scale against her in dead
weight and draught, vacuum, and diagrams taken, but notwithstanding
(making allowance for one faulty run due to the variations in tide)
she appears to have more than held her own in the matter of speed,
with a saving of 4½ and 3¼ revolutions per minute at 140 lb. and 160
lb. steam pressure respectively. This is further confirmed by the
results of a run made after the experiments were concluded, the two
vessels being placed in line, and fairly started for a half hour's run
over the flood with 150 lb. steam pressure. At the expiration of that
time the Herongate was judged to be leading by at least half a length,
her revolutions being 76, as against 80 in the Belle of Dunkerque. It
was agreed by all present at these trials that the propeller had
realized in full the three main working advantages claimed for it.
This being the first Dickinson propeller fitted to a sea-going vessel
of this size, it is quite within the limits of possibility that the
present results may be improved upon in further practice. In any case
we can but regard this propeller as a distinct and original departure
in marine propulsion, and we congratulate Mr. Dickinson on his present
success and promising future. Messrs. Weatherley, Mead & Hussey also
deserve credit for their discernment, and for the spirited manner in
which they have taken up Mr. Dickinson's ingenious invention. We
understand that they are so satisfied with the results that they
intend having one of their larger ocean-going steamers fitted with the
Dickinson propeller.--_Iron_.
* * * * *
IMPROVED DOBBY.
[Illustration]
At the Manchester Royal Jubilee Exhibition, Messrs. Butterworth &
Dickinson, Burnley, showed Catlow's patent dobby, which is illustrated
above, as applied to a strong calico loom. This dobby is a double lift
one, thus obtaining a wide shed, and the use of two lattice barrels
connected by gearing so that they both revolve in the same direction.
The jack lever is attached to the vertical levers, the top and bottom
catches being worked respectively by the two barrels, and connected
with the ends of the levers. To each of these catches a light blade
spring is attached, which insures them being sprung upon the top of
the knife, and thereby obtaining a certain lift. A series of wooden
jacks or levers are employed, so as to give a varying lift to the
front and back healds, in this way keeping the yarn in even tension,
and preventing slack sheds. The healds are drawn down by means of a
series of levers adjoining one another, and worked by means of a
rocking bar driven from the tappet shaft. When the shed is being
formed, the jacks are pushed down until it is fully open, and the warp
is thus drawn down with the same certainty as the upward movement is
made.--_Industries_.
* * * * *
[UNITED STATES CONSULAR REPORTS. SPECIAL ISSUE NO. 10.]
SULPHUR MINES IN SICILY.
BY PHILLIP CARROLL, U. S. CONSUL, PALERMO.
Sulphur, or brimstone, is a hard, brittle substance of various colors,
from brilliant yellow to dark brown, without smell when cool, of a
mild taste, and burns with a pale blue flame, emitting pungent and
suffocating fumes. Its specific gravity is from 1.9 to 2.1.
Sulphur exists more or less in all known countries, but the island of
Sicily, it is thought, is the only place where it is produced on a
large scale, and consequently that island appears to command the
market. Small quantities have been found in the north of Italy, the
Grecian Archipelago, Russia, Austria, Poland, France, Spain, eastern
shores of Egypt, Tunis, Iceland, Brazil, Central America, and the
United States. Large quantities are said to exist in various countries
of Asia, but it is understood to be impracticable to utilize the same,
consequent upon the distance from any commercial port and the absence
of rail or other roads.
Sulphur is of two kinds, one of which is of volcanic emanation, the
other being closely allied to sedimentary rocks. The latter is found
in Sicily, on the southern and central portions of the island. Mount
Etna, situated in the east, seems to exert no influence in the
formation of brimstone. There are various hypotheses relative to its
natural formation. Dr. Philip Swarzenburg attributes it to the
emanations of sulphur vapor expelled from metallic matter existing in
the earth, consequent upon the fire in the latter, while Professors
Hoffman and Bischoff ascribe it to the decomposition of sulphureted
hydrogen. Hoffman believes the sulphureted hydrogen must have passed
through the fissures of stratified rocks, but Bischoff is of opinion
that the sulphureted hydrogen must have been the result of the
decomposition of sulphate of lime in the presence of organic matter.
The theory of others is that sulphur owes its origin to the
combination of lacustrine deposits with vegetable matter, and others
again suppose that it is due to the action of the sea upon animal
remains. The huge banks of rock salt often met with in the vicinity of
sulphur mines, and which in some places stretch for a distance of
several miles, seem to indicate that the sea has worked its way into
the subsoil. Fish and insects, which are frequently found in strata of
tripoli, which lie under sulphur beds, induce the belief that lakes
formerly existed in Sicily.
The following is a list of the various strata which form part of the
crust of the earth in Sicily, according to Professor Mottura, an
Italian geologist:
_Pliocene._--Sandstone; coarse calcareous rock; marl.
_Upper Miocene._--Calcareous marl; gypsum, etc.; sulphur embedded in
calcareous limestone; silicious limestone; tripoli, containing fossils
of fish, insects' eggs, etc.
_Middle Miocene._--Sandstone containing quartz, intercalated with marl
of a saltish taste.
_Lower Miocene._--Rock salt; blue marl, containing petroleum and
bitumen; flintstone; ferruginous clay, mixed with aragonite and
bituminous schists; ferruginous and silicious sandstone.
_Eocene._--Limestone, containing diaspores and shells.
At times one or another of the strata disappears, while the order of
some is slightly reversed on account of the broken state of the crust.
Upon the whole, however, the above has been generally observed in the
various mines by the author referred to.
Sulphur mines have been operated in Sicily over three hundred years,
but until the year 1820 its exportation was confined to narrow limits.
At present the number of mines existing in Sicily is about three
hundred, nearly two hundred of which, being operated on credit, are,
it is understood, destined to an early demise. It is said that there
are about 30,000,000 tons of sulphur in Sicily at present, and that
the annual production amounts to about 400,000 tons. If this should be
true, taking the foregoing as a basis, the supply will become
exhausted in about seventy-five years.
In 1819 a law was passed in Italy, which is still in force, governing
mining in Sicily, which provides that should a land owner discover ore
in his property he would be the owner thereof, and should have the
right to mine, operate, or rent the property to others for that
purpose, but if he should decline to operate his mines or to rent them
to others to be operated, the state would rent them on its own
account.
Royalties vary from 12 to 45 per cent. They are paid according to the
quality of the ore and the facilities for producing sulphur; 25 per
cent. may, however, be taken as an average. There is a land tax of 36
per cent. of the net income, which is usually paid by the owners and
lessees of the mines, in proportion to the quantity of sulphur which
they produce. The export duty is 10 lire per ton. All mines are
inspected by government officials once a year, and the owners are
required to furnish the state with plans of the works and their
progress, with a view to insure the safety of the workmen and to
ascertain the extent of the property.
Those who rent their mines receive from 10 to 40 per cent. of the
sulphur produced. Leases are valid for such period as the contracting
parties may stipulate therein. The general limit, however, is nine
years. The average lease is 25 per cent., 40 per cent. being paid only
when the mines are very favorably situated and the production good.
Some lessees prefer paying a considerable sum in cash in advance, at
the beginning of the term of the lease, and giving 15 or 20 per cent.
in sulphur annually thereafter, instead of a higher percentage.
The external indications of the presence of sulphur are the appearance
of gypsum and sulphurous springs. These are indubitable signs of the
presence of sulphur, and when discovered the process resorted to here,
in order to reach the sulphur, is to bore a hole sufficiently large to
admit a man, after which steps are constructed in the passage in order
to facilitate the workmen in going to and fro. These steps extend
across the passage, and are about 25 centimeters high and 35 broad.
The inclination of the holes or passages varies from 30 to 50 degrees.
Upon attaining the depth of several meters water is often met with,
and in such considerable quantity that it is impossible to proceed.
Hence it becomes necessary to either pump the water out or retreat in
order to bore elsewhere. It is often necessary to bore several
passages in order to discover the ore or seam of sulphur. When,
however, it has been discovered the passages are made to follow its
direction, whether upward or downward. As the direction of seams is in
most cases irregular, that of the passages or galleries is likewise.
Where the ore is rich and the matrix yielding, the miners break it by
means of pick-axes and pikes, but when such is not the case gunpowder
is resorted to, the ore in this case being carried to the surface by
boys. The miners detach the ore from the surrounding material, and the
cavities which ensue in consequence assume the appearance of vast
caves, which are here and there supported by pillars of rock and ore
in order to keep them from falling or giving way. In order to
strengthen the galleries sterile rock is piled upon each side and
cemented with gypsum. In extensive mines, however, these supports and
linings are too weak, and not infrequently, as a result, the galleries
and caverns give way, occasionally causing considerable havoc among
the miners. Sulphur is found from the surface to a depth of 150
meters. The difficulties met with in operating mines are numerous, and
among the greatest in this category are water, land slides,
irregularity of seam, deleterious gases, hardness of rocks and
matrices. Of these difficulties, water is the most frequently met
with. Indeed, it is always present, and renders the constant use of
pumps necessary. At one time miners were allowed to dig where they
pleased so long as sulphur was extracted, the consequence being that
in groups of mines, the extent and direction of which being unknown to
their respective owners, one mine often fell into or upon another,
thus causing destruction to life and property. It was largely for this
reason, it is understood, that the government determined to require
owners and lessees of mines to furnish plans thereof to proper
authority, and directed that official inspection of the mines should
be made at stated periods. In order to comply with the decree of the
government it became necessary to employ mining engineers to draw the
plans, etc., and those employed were generally foreigners. In the
system of excavation described no steam power is employed. Pumping is
performed by means of primitive wooden hand pumps, and when sufficient
ore has been collected it is conveyed on the backs of boys to the
surface--a slow, costly, and difficult procedure. This system may,
however, be suitable to small mines, but in large mines there is no
economy in hand labor; indeed, much is lost in time and expense by it.
For this reason steam has been introduced into the larger and more
important mines. The machinery employed is a hoisting apparatus, with
a drum, around which a coil is wound, with the object of hoisting and
lowering trucks in vertical shafts. Steam pumps serve to extract the
water. The force of the hoisting apparatus varies from 15 to 50 horse
power. The fuel consumed is English and French coal, the former being
preferred, as it engenders greater heat. The cost of a ton of coal at
the wharf is $4.40, whereas in the interior of the island it costs
about $10. The shafts or pits are made in the ordinary way, great care
being taken in lining them with masonry in order to guard against land
slides. In level portions of the country vertical shafts are
preferred, but where the mine is situated upon a hill a debouch may
often be found below the sulphur seam, when an inclined plane is
preferred, the ore being placed in trucks and allowed to run down the
plane on rails until it reaches the exterior of the mine, where it
suddenly and violently stops, and as a result the trucks are emptied
of their load, when they are drawn up the plane to be refilled; and
thus the process goes on indefinitely. In these mines a gutter is made
in the inclined plane which carries off the water, thus dispensing
with the necessity of a pump and the requisites to operate it. The
galleries and inclined shafts are lined with beams of pine or larch,
which are brought hither from Sardinia, as Sicily possesses very
little timber. The mines are illuminated by means of iron oil lamps,
the wicks of which are exposed. The lamps are imported from Germany.
In certain cases an earthenware lamp, made on the island, and said to
be a facsimile of those used by the Phoenicians, is employed. This
lamp is made in the shape of a small bowl. It is filled with oil and a
wick inserted, which hangs or extends outward, and is thus ignited,
the flame being exposed to the air. Safety lamps are unknown, and
those described are generally secure. Few explosions take place--only
when confined carbonic hydrogen is met with in considerable
quantities, and when the ventilation is not good. In this case the
mine is easily ignited, and once on fire may burn for years. The only
practical expedient for extinguishing the fire is to close all inlets
and outlets in order to shut off the air. This, however, is difficult
and takes time. Notwithstanding the closing of communications, the
gases escape through the fissures and openings which obtain
everywhere, and the ingress of air makes it next to impossible to
extinguish the fire; hence it burns indefinitely or until the mine is
exhausted. Occasionally the burning of a mine results beneficially to
its owners, in that it dispenses with the necessity of smelting, and
produces natural, refined sulphur.
Galleries in extent are usually 1.20 by 1.80 meters, and when ore is
not found and it becomes necessary to extend the galleries, laborers
are paid in accordance with the progress they may make and the
character of the rock, earth, etc., through which it may be necessary
to cut, as follows:
Silicious limestone, 60 lire per meter; daily progress, 0.20 meter.
Gypsum, 50 lire per meter; daily progress, 0.30 meter.
Marl, 30 lire per meter; daily progress, 0.50 meter.
Clay, 15 lire per meter; daily progress, 1 meter.
Laborers working in the ore are paid 4.30 lire per ton. This includes
digging, extracting, and illumination. In some mines, however, the
laborers are paid when the sulphur is fused and ready for exportation.
One ton of sulphur, or its equivalent (say from 40 to 50 lire), is the
amount generally paid. In mines where this system obtains the
administration is only responsible for their maintenance. Each miner
produces on an average about 1½ tons of ore daily, and when the works
are not more than 40 meters in depth he employs one boy to assist him,
two boys when they reach 60 meters, and three when under 100 meters.
These boys are from seven to sixteen years of age, and are paid from
0.85 to 1.50 lire per day by the miner who employs them. They carry
from 1,000 to 1,500 pounds of ore daily, or in from six to eight
hours. The food consumed by miners is very meager, and consists of
bread, oil, wine, or water; occasionally cheese, macaroni, and
vegetables are added to the above.
Mining laborers generally can neither read nor write, and when
employed in mines distant from habitations or towns, live and sleep
therein, or in the open air, depending on the season or the weather.
In a few mines the laborers are, however, provided with suitable
dwelling places, and a relief fund is in existence for the succor of
the families of those who die in the service. This fund is greatly
opposed by the miners, from whose wages from 1 to 2 per cent. is
deducted for its maintenance. In the absence of a fund of this
character, the sick or infirm are abandoned by their companions and
left to die. Generally miners are inoffensive when fairly dealt with.
They are said to be indolent and dishonest as a rule. The managers of
mines receive from 3,000 to 5,000 lire per annum; chief miners from
1,500 to 2,500 lire; surveyors, 700 to 1,000 lire; and weighers and
clerks, from 1,000 to 2,000 lire per annum. The total number of mining
laborers in Sicily is estimated at about 25,000.
The ore for fusion of the first grade as to yield contains from 20 to
25 per cent. of sulphur, that of the second grade from 15 to 20 per
cent., and of the third grade 10 to 15 per cent. The usual means
adopted for extracting sulphur from the ore is heat, which attains the
height of 400 degrees Centigrade, smelting with the kiln, which in
Sicilian dialect is called a "calcarone." The "calcarone" is capable
of smelting several thousand tons of ore at a time and is operated in
the open air. Part of the sulphur is burned in the process of smelting
in order to liquefy the remainder. "Calcaroni" are situated as closely
to the mouth of a shaft as possible, and if practicable on the side of
a hill, in order that when the process of smelting is complete, the
sulphur may run down the hill in channels prepared for the purpose.
The shop of a "calcarone" is circular and the floor has an inclination
of from 10 to 15 degrees. A design of a "calcarone" is herewith
inclosed. The circular wall is made of rude stone work, cemented
together with gypsum. The thickness of the wall at the back is 0.50
meter, and from this it gradually becomes thicker until in front,
where it is 1 meter, when the diameter is to be 10 meters. In front of
the thickest part of the wall an opening is left, measuring 1.20
meters high and 0.25 meter broad.
Through this opening the liquid sulphur flows. Upon each side of this
opening two walls are built at right angles with the circular wall, in
order to strengthen the front of the kiln. These walls are 80
centimeters thick each and are roofed. A door is hinged to these
walls, thus forming a small room in front of each kiln in which the
keeper thereof resides from the commencement to the termination of the
flow of sulphur. The inclined floor of the kiln is made of stone work
and is covered with "ginesi," the name given to the refuse of a former
process of smelting. The stone work is 20 centimeters thick, and the
"ginesi" covering 25 centimeters, which gradually becomes thicker as
it approaches its lowest extremity. The front part of the circular
wall is 3.50 meters high and the back 1.80 meters. The interior of the
wall is plastered with gypsum in order to render it impermeable.
The cost of a "calcarone" of about 500 tons capacity is 800 lire. The
capacity varies from 40 to 5,000 tons, or more, depending upon
circumstances. If a mine is enabled to smelt the whole year round, the
smaller "calcaroni," being more easily managed, are preferred; the
inverse is the case as to the larger "calcaroni," when this is
impracticable. When a "calcarone" is situated within 100 meters of a
cereal farm, its operation is prohibited by law during the summer,
lest the fumes of the sulphur should destroy the crop.
When, however, the distance is greater from the farm or farms than 100
meters, smelting is permitted; but should any damage ensue to the
crops as a result of the fumes, the owners of the "calcaroni" are
required to liquidate it. Therefore the mines which are favorably
situated smelt the entire year, and employ "calcaroni" of from 40 to
500 tons, as there is less risk of a process failing, which
occasionally happens, and for the reason that the ore can be smelted
as soon as it is extracted; whereas, when kilns or "calcaroni" are
situated within or adjacent to the limit adverted to, they can only be
operated five or six months in the year, consequent upon which the ore
is necessarily stacked up all through the summer or until such time as
smelting may be commenced without endangering the crops, when it
becomes necessary to use "calcaroni" whose capacity amounts to several
thousand tons. As intimated, these large "calcaroni" are not so
manageable as those of smaller dimensions, and as a result many
thousands of tons of sulphur are lost in the process of smelting,
besides perhaps the loss of an entire year in labor. Again, the ore
deteriorates or depreciates when long exposed to the air and rain, all
of which, when practicable, render the kilns or "calcaroni" of the
smaller capacity more advantageous and lucrative to those operating
sulphur mines in Sicily. Smelting with a "calcarone" of 200 tons
capacity consumes thirty days, one of 800 tons 60 days, and with a
"calcarone" of 2,000 tons capacity from 90 to 120 days are consumed.
In loading or filling the "calcaroni," the larger blocks of ore are
placed at the bottom as well as against the mouth, in order to keep
the lower part of the kiln as cool as possible with a view of
preventing the liquid sulphur from becoming ignited as it passes down
to where it makes its exit, etc. The blocks of ore thus first placed
in position are, for obvious reasons, the most sterile. After the
foundation is thoroughly laid the building of the "pile" is proceeded
with, the larger blocks being placed in the center to form, as it
were, the backbone of the pile; the smaller blocks of ore are arranged
on the outside of these and in the interstices. The shape or form of
the pile when completed is similar to a truncated cone, and when
burning the kiln looks like a small volcano. When the kiln has been
filled with ore, the whole is covered with ginesi with a view of
preventing the escape of the fumes. The ore is then ignited by means
of bundles of straw, impregnated or saturated with sulphur, being held
above the thin portion of the top of the kiln, which is at once closed
with ginesi, and the "calcarone" is left to itself for about a week.
During the burning process the flames gradually descend, and the
sulphur contained in the ore is melted by the heat from above. In
about seven or eight days sulphuric fumes and sublimed sulphur
commence to escape, when it becomes necessary to add a new coat of
ginesi to the covering and thus prevent the destruction of vegetation
by the sulphur fumes. The mouth of the kiln, which has been left open
in order to create a draught, is closed up about this time with gypsum
plaster. When the sulphur is all liquefied it finds its way to the
most depressed part of the kiln, and there, upon encountering the
large sterile blocks, quite cold, already referred to, solidifies. It
is again liquefied by means of burning straw, whereupon an iron trough
is inserted into a mouth made in the kiln for the purpose, and the
reliquefied sulphur runs into it, from which it is immediately
collected into wooden moulds, called "gadite," and which have been
kept cool by being submerged in water. Upon its becoming thoroughly
cool the sulphur is taken out of the moulds referred to, and is now in
solid blocks, each weighing about 100 weight. Two of these blocks
constitute a load for a mule, and cost from 4 to 5 francs.
The above is the result when the operation succeeds; but this is not
always the case. At times the sulphur becomes solidified before it
reaches the mouth of the kiln, because of the heat not being
sufficient to keep it liquid in its passage thereto, and other
misfortunes not within control, and consequent upon the use of the
larger kilns, or "calcaroni."
When the sulphur ceases to run from the kiln, the process is complete.
The residue is left to cool, which consumes from one to two months.
The cooling process could be accomplished in much less time by
permitting the air to enter the kiln, but this would be destructive to
vegetation, and even to life, consequent upon the fumes of the
sulphur. The greatest heat at a given time in a kiln is calculated to
be above 650 degrees Centigrade--that is, at the close of the process.
This enormous heat is generally allowed to waste, whereas it is
understood it could be utilized in many ways. A gentleman of the name
of Gill is understood to have invented a recuperative kiln, which
will, if generally adopted, utilize the heat of former processes
named. A ton of ore containing about 25 per cent. of sulphur yields
300 pounds of sulphur. This is considered a good yield. When it yields
200 pounds it is considered medium, and poor when only 75 pounds.
Laborers are paid 0.40 lire per ton for loading and unloading kilns,
and from thirty to forty hands are employed at a time. The keeper of a
kiln receives from 2 to 2.50 lire per day.
Notwithstanding the "calcarone" has many defects, it is the simplest
and cheapest mode of smelting, and is preferred here to any other
system requiring machinery and skilled labor to operate it.
The following are the principal furnaces in use here: Durand's;
Hirzel; Gill and Kayser's system of fusion; Conby Bollman process;
Thomas steam process of smelting; and Robert Gill's recuperative
kilns.
There are seven qualities or grades of sulphur, viz.:
1. Sulphur almost chemically pure, of a very bright and yellow color.
_Second Best._--Slightly inferior to the first quality; bright and
yellow.
_Second Good._--Contains 4 to 5 per cent. of earthy matter, but is of
a bright yellow.
_Second Current._--Dirty yellow, containing more earthy matter than
that last named.
_Third Best._--Brownish yellow; this tint depends on the amount of
bitumen which it contains.
_Third Good._--Light brown, containing much extraneous matter.
_Third Current._--Brown and coarse.
These qualities are decided by color, not by test. The difference of
price is from 3 to 10 francs per ton. Manufacturers prefer the third
best, because of its containing more sulphuric acid and costing less
than the sulphur of better quality.
Sulphur is conveyed to the seaboard by rail, in carts, or on mules or
donkeys. Conveyance by cart, mule, or donkey is only resorted to when
the distance is short or from mines to railroad stations. The tariff
in the latter case is understood to be 1 lire per ton per mile. The
railroad tariff is 0.12 per ton per kilometer; but it is contemplated,
it is understood, to reduce this to 7 centimes in a short time. The
price per ton of sulphur is as follows:
At Porto At At
Grade. Empedocle. Licata. Catania.
Lire. Lire. Lire.
Second best 86.60 87.00 90.70
Second good 84.42 84.50 90.30
Second current 83.90 83.90 88.40
Third best 79.00 79.90 86.90
Third good 77.80 77.80 83.00
Third current 76.80 76.70
Sulphur free on board, brokerage, shipment, export duty, and all other
expenses included, costs 20 lire per ton in excess of the above
prices. Nearly all the sulphur exported from Palermo emanates from the
Lercara mines, in the province of Palermo, the price per ton being as
follows: first quality, 91.60 lire; second quality, 88.40. Sulphur is
usually conveyed in steamers to foreign countries from Sicilian ports.
The average freight per ton to New York is about as follows: From
Palermo, 8.70 lire; from Catania, 13.50 lire; from Girgenti, 16 lire.
An additional charge of 2.50 lire is made when the sulphur may be
destined for other ports in the United States.
Liebig once said that the degree of civilization of a nation and its
wealth could be seen in its consumption of sulphuric acid. Now,
although Italy produces immense quantities of sulphur, it cannot, on
account of the scarcity of fuel, and other obvious reasons perhaps,
compete with certain other countries in the manufacture and
consumption of sulphuric acid.
Sulphur is employed in the manufacture of sulphuric acid, and the
latter serves in the manufacture of sulphate of soda, chloridic acid,
carbonate of soda, azodic acid, ether, stearine candles, purification
of oils in connection with precious metals and electric batteries.
Nordhausen's sulphuric acid is employed in the manufacture of indigo.
Sulphate of soda is employed in the manufacture of artificial soda,
glassware, cold mixtures, and medicines. Carbonate of soda is used in
the manufacture of soap, bleaching wool, coloring and painting
tissues, and in the manufacture of fine crystal ware and the
preparation of borax. Chloric acid is used in the preparation of
chlorides with bioxide of manganese, and with chlorides in the
preparation of hypochlorides of lime, known in commerce under the name
of bleaching powder, and improperly called chloride of lime, which is
used as a disinfectant in contagious diseases, in bleaching stuffs,
and in the manufacture of paper from vegetable fibers, and in the
manufacture of gelatine extracted from bones, as well as in fermenting
molasses and in the manufacture of sugar from beet root. Sulphur is
also used in the preparation of gunpowder and oil of vitriol, and in
the manufacture of matches and cultivation of the vine.
In the year 1838 the Neapolitan government granted a monopoly to a
French company for the trade in sulphur. By the terms of the agreement
the producers were required to sell their sulphur to the company at
certain fixed prices, and the latter paid the government the sum of
$350,000 annually in consideration of this requirement. This, however,
was not a success, and tended to curtail the sulphur industry, and the
government, discovering the agreement to be against its interests,
annulled it, and established a free system of production, charging an
export tax per ton only. At that time sulphuric acid was derived
exclusively from sulphur. Hence the demand from all countries was
great, and the prices paid for sulphur were high. It was about this
period that the sulphur industry was at its zenith. The monopoly
having been abolished, every mine did its utmost to produce as much
sulphur as possible, and from the export duty exacted by the
government there accrued to it a much larger revenue than that which
it received during the period of the monopoly. The progress of science
has, however, modified the state of things since then, as sulphur can
now be obtained from pyrite or pyrite of iron. This discovery
immediately caused the price of sulphur to fall, and the great demand
therefore correspondingly ceased. In England, at the present time, it
is understood that two-thirds of the sulphuric acid used is
manufactured from pyrites. The decrease in prices caused many of the
mines to suspend operations, and as a result the sulphur remained idle
in stock. In 1884 an association was formed at Catania with a view to
buying up sulphur thus stored away at the mines and various ports at
low prices, and store it away until a favorable opportunity should
present itself for the sale thereof. This had the effect of increasing
the prices of sulphur in Sicily for some time, and the producers,
discovering that the methods of the association increased the foreign
demand for their produce as well as its prices, exported it directly
themselves, thus breaking up the association referred to, as it was no
longer a profitable concern.
The railroad system, which in later years has placed the most
important parts of Sicily in communication with the seaboard, has been
most beneficial to the sulphur industry. A great saving has been made
in transporting it to the ports. This was formerly (as stated)
accomplished by carts drawn by mules at an enormous expense, as the
roads were wretched, and unless some person of distinction
contemplated passing over them, repairs were unknown.
Palermo, March 20, 1888.
* * * * *
AN AUTOMATIC STILL.
BY T. MABEN.
The arrangement here described is one that may readily be adapted to,
and is specially suited for, the old fashioned stills which are in
frequent use among pharmacists for the purpose of distilling water.
The idea is extremely simple, but I can testify to its thorough
efficiency in actual practice. The still is of tinned copper, two
gallon capacity, and the condenser is the usual worm surrounded with
cold water.
The overflow of warm water from the condenser is not run into the
waste pipe as in the ordinary course, but carried by means of a bent
tube, A, B, C, to the supply pipe of the still. The bend at B acts as
a trap, which prevents the escape of steam.
[Illustration]
The advantages of this arrangement are obvious. It is perfectly
simple, and can be adapted at no expense. It permits of a continuous
supply of hot water to the still, so that the contents of the latter
may always be kept boiling rapidly, and as a consequence it condenses
the maximum amount of water with the minimum of loss of heat. If the
supply of water at D be carefully regulated, it will be found that a
continuous current will be passing into the still at a temperature of
about 180° F., or, if practice suggest the desirability of running in
the water at intervals, this can be easily arranged. It is necessary
that the level at A should be two inches or thereabout higher than the
level of the bend at C, otherwise there may not be sufficient head to
force a free current of water against the pressure of steam. It will
also be found that the still should only contain water to the extent
of about one-fourth of its capacity when distillation is commenced, as
the water in the condenser becomes heated much more rapidly than the
same volume is vaporized. By this expedient a still of two gallons
capacity will yield about half a dozen gallons per day, a much greater
quantity than could ever be obtained under the old system, which
required the still to be recharged with cold water every time one and
a half gallons had been taken off.
The objection to all such continuous or automatic arrangements is, of
course, that the condensed water contains all the free ammonia that
may have existed in the water originally, but it is only in cases
where the water is exceptionally impure that this disadvantage will
become really serious. The method here outlined has, no doubt,
occurred to many, and may probably be in regular use, but not having
seen any previous mention of the idea, I have thought that it might be
useful to some pharmacists who prepare their own distilled
water.--_Phar. Jour._
* * * * *
COTTON SEED OIL.
"Cotton seed oil," said Mr. A.E. Thornton, of the Atlanta mills, "is
one of the most valuable of oils because it is a neutral oil, that is,
neither acid nor alkali, and can be made to form the body of any other
oil. It assimilates the properties of the oil with which it is mixed.
For instance, olive oil. Cotton seed oil is taken and a little extract
of olives put in. The cotton oil takes up the properties of the
extract, and for all practical purposes it is every bit as good as the
pure olive oil. Then it is used in sweet oil, hair oil, and, in fact,
in nearly all others. A chemist cannot tell the prepared cotton oil
from olive oil except by exposing a saucerful of each, and the olive
oil becomes rancid much quicker than the cotton oil. The crude oil is
worth thirty cents a gallon, and even as it is makes the finest of
cooking lard, and enters into the composition of nearly all lard."
A visit to the mills showed how the oil is made. From the platform
where the seed is unloaded it is thrown into an elevator and carried
by a conveyor--an endless screw in a trough--to the warehouse. Then it
is distributed by the conveyor uniformly over the length of the
building--about 200 feet. The warehouse is nearly half filled now, and
thousands and thousands of bushels are lying in store. Another
elevator carries the seed up to the "sand screen." This is a revolving
cylinder made of wire cloth, the meshes being small enough to retain
the seed, which are inside the cylinder, but the sand and dirt escape.
Now the seeds start down an inclined trough. There is something else
to be taken out, and that is the screws and nails and rocks that were
too large to be sifted out with the sand and dirt. There is a hole in
the inclined trough, and up through that hole is blown a current of
air by a suction fan. If it were not for the fan, the cotton seed,
rocks, nails, and all would fall through. The current keeps up the
cotton seed, and they go on over, but it is not strong enough to keep
up the nails and pebbles, and they fall through. Now the seed, free of
all else, is carried by another elevator and endless screw conveyor to
the "linter." This is really nothing more than a cotton gin with an
automatic feed.
"HULLER" AND "HEATERS."
Then the seed is carried to the "huller," where it is crushed or
ground into a rough meal about as coarse as the ordinary corn "grits."
The next step is to separate the hulls from the kernels, all the oil
being in the kernel, so the crushed seed is carried to the
"separator." This is very much on the style of a sand screen, being a
revolving cylinder of wire cloth. The kernels, being smaller than the
broken hulls, fall through the broken meshes, and upon this principle
the hull is separated and carried direct to the furnace to be used as
fuel. The kernels are ground as fine as meal, very much as grist is
ground, between corrugated steel "rollers," and the damp, reddish
colored meal is carried to the "heater."
The "heater" is one iron kettle within another, the six inch steam
space between the kettles being connected direct with the boilers.
There are four of these kettles side by side. The meal is brought into
this room by an elevator, the first "heater" is filled, and for twenty
minutes the meal is subjected to a "dry cook," a steam cook, the steam
in the packet being under a pressure of forty-five pounds. Inside the
inner kettle is a "stirrer," a revolving arm attached at right angles
to a vertical shaft. The stirrer makes the heating uniform, and the
high temperature drives off all the water in the meal, while the
involatile oil all remains.
In five minutes the next heater is filled, in five minutes the next,
etc.
Now there are four "heaters," and as the last heater is filled--at the
end of twenty minutes--the first heater is emptied. Then at the end of
five minutes the first heater is filled, and the one next to it is
emptied, and the rotation is kept up, each heater full of meal being
"dry-cooked" for twenty minutes.
Corresponding to the four heaters are four presses. Each press
consists of six iron pans, shaped like baking pans, arranged one above
the other, and about five inches apart. The pans are shallow, and
around the edge of each is a semicircular trough, and at the lowest
point of the trough is a funnel-shaped hole to enable the oil to run
from one pan to the next lowest, and from the lowest pan to the
"receiving tanks" below.
PRESSING OUT THE OIL.
As soon as a "heater" is ready to be emptied, the meal is taken out
and put into six hair sacks, corresponding to the six pans in the
press. There are six hair mats about one foot wide and six long, one
side of each being coated with leather. The hair mat is about an inch
thick. Now the hair sack, containing ten and a half to eleven pounds
of heated steaming meal, is placed on one end of the mat, and the meal
distributed so as to make a pad or cushion of uniform thickness. The
pad of meal is not quite three feet long, a foot wide, and three
inches thick, and the hair mat is folded over, sandwiching the pad and
leaving the leather coating of the pad outside. In this form the six
loads are put into the six pans, and by means of a powerful hydraulic
press the pans are slowly pressed together. The oil begins trickling
out at the side, slowly at first, and then suddenly it begins running
freely. The pressure on the "loads" is 350 tons. After being pressed
about five minutes, the pressure is eased off and the "loads" taken
out. What had been a mushy pad three inches thick is a hard, compact
cake about three-quarters of an inch thick, and the sack is literally
glued to the cake. The crude oil has a reddish muddy color as it runs
into the tanks.
To one side were lying great heaps of sacks of yellowish meal--the
cakes which have been broken and ground up into meal. That, as
explained above, forms the body of all fertilizers. The following is a
summary of the work for the eight months' season at the Atlanta mills:
Fifteen thousand tons of seed used give:
Fifteen million pounds of hull.
Ten million three hundred and thirty-one thousand two hundred and
fifty pounds of meal.
Four million six hundred and sixty-eight thousand seven hundred and
fifty pounds of oil.
Three hundred thousand pounds of lint cotton.
The meal is worth at the rate of $6 for 700 pounds, or $88,603.58.
The oil is worth thirty cents a gallon, or seven and a half pounds, or
$186,750.
The lint is worth $18,000, making a total of $293,353, and that
doesn't include the 15,000,000 pounds of hull.--_Atlanta
Constitution._
* * * * *
MANUFACTURE OF PHOTOGRAPHIC SENSITIVE PLATES.
Quite recently Messrs. Marion & Company, London, began on their own
account to manufacture sensitive photographic plates by machinery, and
the operations are exceedingly delicate, for a single minute air
bubble or speck of dust on a plate may mar the perfection of a
picture. Their works for the purpose at Southgate were erected in the
summer of 1886, and were designed throughout by Mr. Alexander Cowan.
[Illustration: Fig. 1.]
Buildings of this kind have to be specially constructed, because some
of the operations have to be carried on in the absence of daylight,
and in that kind of non-actinic illumination which does not act upon
the particular description of sensitive photographic compound
manipulated. Glass and other materials have therefore to pass from
light to dark rooms through double doors or double sliding cupboards
made for the purpose, and the workshops have to be so placed in
relation to each other that the amount of lifting and the distance of
carriage of material shall be reduced to a minimum. Moreover, the
final drying of sensitive photographic plates takes place in absolute
darkness. Fig. 1 is a ground plan of the chief portion of the works.
In this cut, A is the manager's private office, B the counting house,
C the manager's laboratory, and D his dark room for private
experiment, which can thus be conducted without interfering with the
regular work of the establishment. E is the carpenter's shop and
packing room, F the albumen preparation room, G the engine room, with
its two doors; the position of the engine is marked at H. The main
building is entered through the door, K; the passage, L, is used for
the storage of glass, and has openings in the wall on one side to
permit the passage of glass into the cleaning room, M; this room is
illuminated by daylight. The plates, after being cleaned, pass into
the coating rooms, N and O, into which daylight is never admitted; the
coating machine is in the room, N, and three hand coating tables in
the room, O; both these rooms are illuminated by non-actinic light.
[Illustration: Fig. 2.]
[Illustration: Fig. 3.]
The walls of N and O are of brick, to keep these interior rooms as
cool as possible in hot weather, for the making of photographic plates
is more difficult in summer time, because the high temperature tends
to prevent the rapid setting of the gelatine emulsion upon them. At
the end of these rooms and communicating with both is the lift, P, by
which the coated plates are carried to the drying rooms above, which
there cover the entire area of the main building; they consist of two
rooms measuring 60 ft. by 30 ft., and are each 30 ft. high at the
highest part in the center of the building; these rooms are
necessarily kept in absolute darkness, except while the plates are
being stored therein or removed therefrom, and on such occasions
non-actinic light is used. After the plates are dry, they come down
the lift, Q, into the cutting and packing room, R, which is
illuminated by non-actinic light. In the drying rooms the batches of
plates are placed one after the other on tram lines at one end of the
room, and are gradually pushed to the other end of the building, so
that the first batches coated are the first to be ready to be taken
off when dry, and to be sent down the lift, Q. The plates in R, when
sufficiently packed to be safe from the action of daylight, are passed
through specially constructed openings into the outside packing room,
S, where they are labeled. The chemicals are kept in the room, U,
where they are weighed and measured ready for the making of the
photographic emulsion in the room, U. The next room, V, is for washing
small experimental batches of emulsion, and W is the large washing
room. The emulsion is then taken into the passage, X, communicating
with the two coating rooms. A centrifugal machine in the room, Y, is
used for extracting silver residues from waste materials, also for
freeing the emulsion from all soluble salts. Washing and cleaning in
general go on in the room, Z.
[Illustration: Fig. 4.]
The glass for machine coating is cut to standard sizes at the
starting, instead of being coated in large sheets and cut afterward--a
practice somewhat common in this industry. The disadvantage of the
ordinary plan is that minute fragments of glass are liable to settle
upon the sensitive film and to cause spots and scratches during the
packing operations; any defect of this kind renders a plate worthless
to the photographer. When any breakages take place in the cutting, it
is best that they should occur at the outset, and not after the plate
has been coated with emulsion. The cutting when necessary is effected
by the aid of a "cutting board," Fig. 2, invented by Mr. Cowan, and
now largely in use in the photographic world. This appliance is used
to divide into two equal parts, with absolute exactness, any plate
within its capacity, and it is especially useful in dimly lighted
rooms. It consists of four rods pivoted together at the corners and
swinging on two centers, so that in the first position it is truly
square, and in other positions of rhomboid form, the two outer bars
approaching each other like those of a parallel ruler. The hinge flap
comes down on the exact center of the plate, minus the thickness of
the block holding the diamond. By this appliance plates can be cut in
either direction. Fig. 3 represents a similar arrangement for cutting
a number of very small plates out of one large one; in this the hinge
flap is made in the form of a gridiron, and the bars are spaced at
accurate distances, according to the size of the plate to be cut, so
that a plate 10 in. square, receiving four cuts in each direction,
will be divided into twenty-five small plates.
[Illustration: Fig. 5.]
Before being cleaned all sharp edges are roughly taken off those
plates intended for machine coating by girls, who rub the edges and
corners of the plates upon a stone; the plates are then cleaned by any
suitable method in use among photographers. The plates, now ready for
the coating room, have to be warmed to the temperature of the
emulsion, say from 80 deg. F. to 100 deg. F., before they pass to the
coating machine, the inventor of which, Mr. Cadett, having come to the
conclusion that, if the plates are not of the proper temperature, the
coating given will be uneven over various parts of the surface. The
plate-warming machine is represented in Fig. 4; it was designed by Mr.
A. Cowan, and made by his son, Mr. A. R. Cowan. It consists of a
trough 7 ft. long by 3 in. deep, forming a flat tank, through which
hot water passes by means of the circulating system shown in the
engraving. To facilitate the traveling of the glass plates without
friction the top of the tank is a sheet of plate glass bedded on a
sand bath. An assistant at one end places the glasses one after the
other on the warm glass slab, and by means of a movable slide pushes
them one at a time under the cover, which cover is represented raised
in the engraving to show the interior of the machine. After having put
one glass plate on the slide, another cannot be added until the man in
the dark room at the other end of the slide has taken off the farthest
warmed plate, because the slide has a reciprocating movement. This
heating apparatus is built at right angles to the coating machine in
the next room, in order to be conveniently placed in the present
building; but it is intended in future to use it as a part of the
coating machine itself, and to drive it at the same speed and with the
same gearing, so that the cold plates will be put on by hand at one
end, get warmed as they pass into the dark room, at the other end of
which they will be delivered by the machine in coated condition.
Underneath the heating table is a copper boiler, with its Bunsen's
burner of three concentric rings to get up the temperature quickly and
to give the power of keeping the water under the heating slab at a
definite temperature, as indicated by a thermometer. The cold water
tank of the system is represented against the wall in the cut.
[Illustration: Fig. 6.]
Fig. 5 represents the hot water circulating system outside the coating
rooms for keeping the gelatine emulsions in these dimly lighted
regions at a given temperature, without liberating the products of
combustion where the emulsion is manipulated. The temperature is
regulated automatically. It will be noticed where the pipes enter the
two coating rooms, and Fig. 6 shows the copper inside one of them
heated by the apparatus just described. The emulsion vessel in the
copper is surrounded by warm water, and the copper itself is jacketed
and connected with the hot water pipes, so forming part of the
circulating system.
[Illustration: Fig. 7.]
Fig. 7 is a general view of the coating machine recently invented by
Mr. Cadett, of the Greville Works, Ashtead, Surrey. The plates warmed
in the light room, as already described, are delivered near the end of
the coating table, where they are picked off a gridiron-like platform,
represented on the right hand side of the cut, and are placed by an
assistant one by one upon the parallel gauges shown at the beginning
of the machine proper; they are then carried on endless cords under
the coating trough described farther on. After they have been coated
they are carried onward upon a series of four broad endless bands of
absorbent cotton--Turkish toweling answers well--and this cotton is
kept constantly soaked with cold water, which flows over sheets of
accurately leveled plate glass below and in contact with the toweling;
the backs of the plates being thus kept in contact with fresh cold
water, the emulsion upon them is soon cooled down and is firmly set by
the time the plates have reached the end of the series of four wet
tables. They are then received upon one over which dry toweling
travels, which absorbs most of the moisture which may be clinging to
the backs of the plates; very little wet comes off the backs, so that
during a day's work it is not necessary to adopt special means to
redry this last endless band. What are technically known as "whole
plates," which are 8½ in. by 6½ in., are placed touching each other
end to end as they enter the machine, and they travel through it at
the rate of 720 per hour; smaller sizes are coated in proportion, the
smaller the plates the larger is the number coated in a given time.
The smaller plates pass through the machine in two parallel rows,
instead of in a single row, so that quarter plates, 4¼ in. by 3¼ in.,
are delivered at the end of the machine at the rate of 2,800 per hour,
keeping two attendants well employed in picking them up and placing
them in racks as quickly as they can do the work. The double row of
cords for carrying two lines of small plates through the machine is
represented in the engraving. Although the plates touch each other at
their edges on entering the machine, they are separated from each
other by short intervals after being coated; this is effected by
differential gearing. The water flowing over the tables for cooling
the plates is caught in receptacles below and carried away by pipes.
Between each of the tables is a little roller to enable small plates
to travel without tilting over the necessary gap between each pair of
bands.
[Illustration: Fig. 8.]
The feeding trough of Cadett's machine is represented in Fig. 8. The
plates, cleaned as already described, are carried upon the cords under
a brass roller, the weight of which causes sufficient friction to keep
the plates from tilting; they next pass under a soft camel's hair
brush to remove anything in the shape of dust or grit, and are then
coated. They afterward pass over a series of accurately leveled wheels
running in a tank of water kept exact by an automatic regulator at a
temperature of from 80 deg. Fah. to 100 deg. Fah., by means of a small
hot water circulating system. The emulsion trough is jacketed with hot
water at a constant temperature. This trough is silver plated inside,
because most metals in common use would spoil the emulsion by chemical
action. The trough is 16 in. long; it somewhat tapers toward the
bottom, and contains a series of silver pumps shown in the cut; the
whole of this series of pumps is connected with one long adjustable
crank when plates of the largest size have to be coated; when coating
plates of smaller sizes some of the pumps are detached. A chief object
of the machine is to deliver a carefully measured quantity of emulsion
upon each plate, and this is done by means of pumps, in order that the
quantity of emulsion delivered shall not be affected by changes in the
level of the emulsion in the trough; the quantity delivered is thus
independent of variations due to gravity or to the speed of the
machine. These pumps draw the emulsion from a sufficient depth in the
trough to avoid danger from the presence of air bubbles, and the
bottom of the trough is so shaped that should by chance any
sedimentary matter be present, it has a tendency to travel downward,
away from the bottoms of the pumps. There is a steady flow of emulsion
from the pumps to the delivery pipes, then it passes down a guide
plate of the exact width of the plate to be coated. Immediately in
front of the guide plate is a fixed silver cylinder, kept out of
contact with the plate by the thickness of a piece of fine and very
hard hempen cord, which can be renewed from time to time. These cords
keep the cylinder from scraping the emulsion off the plate, and they
help to distribute it in an even layer. There would be two lines upon
each plate where it is touched by the cords, were not the emulsion so
fluid as to flow over the cut-like lines made and close them up.
[Illustration: Fig. 9.]
The silver cylinder to a certain extent overcomes the effects of
irregularities in the glass plates, for the cylinder is jointed
somewhat in the cup and ball fashion, and is made in two or more
parts, which parts are held together by lengths of India rubber.
The arrangement is shown in section in Fig. 9, in which A is the hot
water jacket of the emulsion vessel; B, the crank driving the pumps;
C, a pump with piston in position; D, delivery tube of the pump; E,
the silver guide plate to conduct the emulsion down to the glass; F,
the spreading cylinder; G, the cords regulating the distance of the
cylinder from the glass plates; H, soft camel's hair brush; K,
friction roller; L L L, three plates passing under the emulsion tank;
M, knife edged wheels in the hot water tank, N; the "plucking roller,"
P, has a hot water tank of its own, and travels at slightly greater
speed than the other rollers; R is the beginning of the cooling bands;
T, the driving cords; and W, a level of the emulsion in the trough. Y
represents one of the bucket pistons of the pumps, detached. The
construction of the crank itself is such that, by adjustment of the
connecting rods, more or less emulsion may be put upon the plates. Mr.
Cowan, however, intends to adjust the pumps once for all, and to
regulate the amount of emulsion delivered upon the plates by means of
driving wheels of different diameters upon the cranks.
[Illustration: Fig. 10.]
Fig. 10 is a section of the hollow spreading cylinder, made of sheet
silver as thin as paper, so that its weight is light. For coating
large plates it is divided in the center, so as to adapt itself
somewhat to irregularities in the surface of each plate. In this case
it is supported by a third and central thread, as represented in the
cut. Otherwise the cylinder would touch the center of the plate. Its
two halves are held together by a slip of India rubber.--_The
Engineer_.
* * * * *
THE USE OF AMMONIA AS A REFRIGERATING AGENT.[1]
[Footnote 1: Paper lately read before the Civil and Mechanical
Engineers' Society.]
BY MR. T.B. LIGHTFOOT, M.I.C.E.
Within the last few years considerable progress has been made in the
application of refrigerating processes to industrial purposes, and the
demand for refrigerating apparatus thus created has led to the
production of machines employing various substances as the
refrigerating agent. In a paper read by the author before the
Institution of Mechanical Engineers, in May, 1886, these systems were
shortly described, and general comparisons given as to their
respective merits, scope of application, and cost of working. In the
present paper it is proposed to deal entirely with the use of ammonia
as a refrigerating agent, and to deal with it in a more full and
comprehensive manner than was possible in a paper devoted to the
consideration of a number of different systems and apparatus. In the
United States and in Germany, as well as to some extent elsewhere,
ammonia has been very generally employed for refrigerating purposes
during the last ten years or so. In this country, however, its
application has been extremely limited; and even at the present time
there are but few ammonia machines successfully at work in Great
Britain. No doubt this is, to a large extent, due to the fact that in
the United States and in Germany there existed certain stimulating
causes, both as regards climate and manufactures, while in this
country, on the other hand, these causes were present only in a
modified degree, or were absent altogether. The consequence was that
up to a comparatively recent date the only machine manufactured on
anything like a commercial scale was the original Harrison's ether
machine, first produced by Siebe, about the year 1857--a machine
which, though answering its purpose as a refrigerator, was both costly
to make and costly to work. In 1878 the desirability of supplementing
our then existing meat supply by means of the large stocks in our
colonies and abroad led to the rapid development of the special class
of refrigerating apparatus commonly known as the dry air refrigerator,
which, in the first instance, was specially designed for use on board
ship, where it was considered undesirable to employ chemical
refrigerants. Owing to their simplicity, and perhaps also to their
novelty, these cold air machines have very frequently been applied on
land, under circumstances in which the same result could have been
obtained with much greater economy by the use of ammonia or some other
chemical agent. Recently, however, more attention has been directed to
the question of economy, and consideration is now being given to the
applicability of certain machines to certain special purposes, with
the result that ammonia--which is the agent that, in our present state
of knowledge, gives as a rule the best results for large
installations, while on land at any rate its application for all
refrigerating purposes presents no unusual difficulties--promises to
become largely adopted. It is hoped, therefore, that the following
paper respecting its use will be of interest.
In all cases where a liquid is employed, the refrigerating action is
produced by the change in physical state from the liquid to the
vaporous form. It is, of course, well known that such a change can
only be brought about by the acquirement of heat; and for the purpose
of refrigeration (by which must be understood the abstraction of heat
at temperatures below the normal) it is obvious that, other things
being equal, that liquid is the best which has the highest heat of
vaporization, because with it the least quantity has to be dealt with
in order to produce a given result. In fact, however, liquids vary,
not only in the amount of heat required to vaporize them (this amount
also varying according to the temperature or pressure at which
vaporization occurs), but also in the conditions under which such
change can be effected. For instance, water has an extremely high
latent heat, but as its boiling point at atmospheric pressure is also
high, evaporation at such temperatures as would enable it to be used
for refrigerating purposes can only be effected under an almost
perfect vacuum. The boiling point of anhydrous ammonia, on the other
hand, is 37½° below zero F. at atmospheric pressure, and therefore for
all ordinary cooling purposes its evaporation can take place at
pressures considerably above that of our atmosphere. Some other agents
used for refrigerating purposes are methylic ether, Pictet's liquid,
sulphur dioxide, and ether. In this connection it should be stated
that Pictet's liquid is a compound of carbon dioxide and sulphur
dioxide, and is said to possess the property of having vapor tensions
not only much below those of pure carbon dioxide at equal
temperatures, but even below those of pure sulphur dioxide at
temperatures above 78° F. The considerations, therefore, which chiefly
influence the selection of a liquid refrigerating agent are:
1. The amount of heat required to effect the change from the liquid to
the vaporous state, commonly called the latent heat of vaporization.
2. The temperatures and pressures at which such change can be
effected.
This latter attribute is of twofold importance; for, in order to avoid
the renewal of the agent, it is necessary to deprive it of the heat
acquired during vaporization, under such conditions as will cause it
to assume the liquid form, and thus become again available for
refrigeration. As this rejection of heat can only take place if the
temperature of the vapor is somewhat above that of the cooling body
which receives the heat, and which, for obvious reasons, is in all
cases water, the liquefying pressure at the temperature of the cooling
water, and the facility with which this pressure can be reached and
maintained, is of great importance in the practical working of any
refrigerating apparatus. Ammonia in its anhydrous form, the use of
which is specially dealt with in this paper, is a liquid having at
atmospheric pressure a latent heat of vaporization of 900, and a
boiling point at the same pressure of 37½° below zero F. Water being
unity, the specific gravity of the liquid at a temperature of 40° F.
is 0.76, and the specific gravity of its vapor is 0.59, air being
unity. In the use of ammonia, two distinct systems are employed. So
far, however, as the mere evaporating or refrigerating part of the
process is concerned, it is the same in both. The object is to
evaporate the liquid anhydrous ammonia at such tension and in such
quantity as will produce the required cooling effect. The actual
tension under which this evaporation should be effected in any
particular case depends entirely upon the temperature at which the
acquirement of heat is to take place, or, in other words, on the
temperature of the material to be cooled. The higher the temperature,
the higher may be the evaporating pressure, and therefore the higher
is the density of the vapor, the greater the weight of liquid
evaporated in a given time, and the greater the amount of heat
abstracted. On the other hand, it must be remembered that, as in the
case of water, the lower the temperature of the evaporating liquid,
the higher is the heat of vaporization. It is in the method of
securing the rejection of heat during condensation of the vapor that
the two systems diverge, and it will be convenient to consider each of
these separately.
_The Absorption Process._--The principle employed in this process is
physical rather than mechanical. Ordinary ammonia liquor of commerce
of 0.880 specific gravity, which contains about 38 per cent. by weight
of pure ammonia and 62 per cent. of water, is introduced into a vessel
named the generator. This vessel is heated by means of steam
circulating through coils of iron piping, and a mixed vapor of ammonia
and water is driven off. This mixed vapor is then passed into a second
vessel, in order to be subjected to the cooling action of water. And
here, owing to the difference between the boiling points of water and
ammonia, fractional condensation takes place, the bulk of the water,
which condenses first, being caught and run back to the generator,
while the ammonia in a nearly anhydrous state is condensed and
collected in the lower part of the vessel.
This process of fractional condensation is due to Rees Reece, and
forms an important feature in the modern absorption machine. Prior to
the introduction of this invention, the water evaporated in the
generator was condensed with the ammonia, and interfered very
seriously with the efficiency of the process by reducing the power of
the refrigerating agent by raising its boiling point. In the improved
form of apparatus, ammonia is obtained in a nearly anhydrous
condition, and in this state passes on to the refrigerator. In this
vessel, which is in communication with another vessel called the
absorber, containing cold water or very weak ammonia liquor,
evaporation takes place, owing to the readiness with which cold water
or weak liquor absorbs the ammonia, water at 59° Fahr. absorbing 727
times its volume of ammonia vapor. The heat necessary to effect this
vaporization is abstracted from brine or other liquid, which is
circulated through the refrigerator by means of a pump. Owing to the
absorption of ammonia, the weak liquor in the absorber becomes
strengthened, and it is then pumped back into the generating vessel to
be again dealt with as above described.
The absorption apparatus, as applied for cooling purposes, consists of
a generator, which is a vessel of cast iron containing coils of iron
piping to which steam at any convenient pressure is supplied; an
analyzer, in which a portion of the water vapor is condensed, and from
which it flows back immediately into the generator; a rectifier and
condenser, in the upper portion of which a further condensation of
water vapor and a little ammonia takes place, the liquid thus formed
passing back by a pipe to the analyzer and thence to the generator,
while in the lower portion the ammonia vapor is condensed and
collected; and a refrigerator or cooler, into which the nearly
anhydrous liquid obtained in the condenser is admitted by a pipe and
regulating valve, and allowed to evaporate, the upper portion being in
communication with the absorber.
Through this vessel weak liquor, which has been deprived of its
ammonia in the generator, is continually circulated, after being first
cooled in an economizer by an opposite current of strong cold liquor
passing from the absorber to the generator, while, in addition, the
liquor in the absorber, which would become heated by the liberation of
heat due to the absorption and consequent liquefaction of the ammonia
vapor, is still further cooled by the circulation of cold water. As
the pressure in the absorber is much lower than that in the generator,
the strong liquor has to be pumped into the latter vessel, and for
this purpose pumps are provided. Though of necessity the various
operations have been described separately, the process is a continuous
one, strong liquor from the absorber being constantly pumped into the
generator through the heater or economizer, while nearly anhydrous
liquid ammonia is being continually formed in the condenser, then
evaporated in the refrigerator and absorbed by the cool weak liquor
passing through the absorber.
Putting aside the effect of losses from radiation, etc., all the heat
expended in the generator will be taken up by the water passing
through the condenser, less that portion due to the condensation of
the water vapor in the analyzer, and plus the amount due to the
difference between the temperature of the liquid as it enters the
generator and the temperature at which it leaves the condenser. In the
refrigerator the liquid ammonia, in becoming vaporized, will take up
the precise quantity of heat that was given off during its cooling and
liquefaction in the condenser, plus the amount due to the difference
in heat of vaporization, owing to the lower pressure at which the
change of state takes place in the refrigerator, and less the small
amount due to the difference in temperature between the vapor entering
the condenser and that leaving the refrigerator, less also the amount
necessary to cool the liquid ammonia to the refrigerator temperature.
When the vapor enters into solution with the weak liquor in the
absorber, the heat taken up in the refrigerator is imparted to the
cooling water, subject also to corrections for differences of pressure
and temperature. The sources of loss in such an apparatus are:
a. Radiation and conduction of heat from all vessels and pipes above
normal temperature, which can, to a large extent, be prevented by
lagging.
b. Conduction of heat from without into all vessels and pipes that are
below normal temperature, which can also to a large extent be
prevented by lagging.
c. Inefficiency of economizer, by reason of which heat obtained by the
expenditure of steam in the generator is passed on to the absorber and
there uselessly imparted to the cooling water.
d. The entrance of water into the refrigerator, due to the liquid
being not perfectly anhydrous.
e. The useless evaporation of water in the generator. With regard to
the amount of heat used, it will have been seen that the whole of that
required to vaporize the ammonia, and whatever water vapor passes off
from the generator, has to be supplied from without. Owing to the fact
that the heating takes place by means of coils, the steam passed
through may be condensed, and thus each pound can be made to give up
some 950 units of heat. With the absorption process worked by an
efficient boiler, it may be taken that 200,000 thermal units per hour
may be eliminated by the consumption of about 100 lb. of coal per
hour, with a brine temperature in the refrigerator of about 20° Fahr.
_Compression Process._--In this process ammonia is used in its
anhydrous form. So far as the action of the refrigerator is concerned,
it is precisely the same as it is in the case of the absorption
apparatus, but instead of the vapor being liquefied by absorption by
water, it is drawn from the refrigerator by a pump, by means of which
it is compressed and delivered into the condenser at such pressure as
to cause its liquefaction at the temperature of the cooling water. It
must be borne in mind, however, that allowance must be made for the
rise of temperature of the water passing through the condenser, and
also for the difference in temperature necessary in order to permit
the transfer of heat from one side of the cooling surface to the
other. In a compression machine the work applied to the pump may be
accounted for as follows:
a. Friction.
b. Heat rejected during compression and discharge.
c. Heat acquired by the ammonia in passing through the pump.
d. Work expended in discharging the compressed vapor from the pump.
But against this must be set the useful mechanical work performed by
the vapor entering the pump. The heat rejected in the condenser is the
heat of vaporization taken up in the refrigerator, less the amount due
to the higher pressure at which the change in physical state occurs,
plus the heat acquired in the pump, and less the amount due to the
difference between the temperature at which the vapor is liquefied in
the condenser and that at which it entered the pump. An ammonia
compression machine, as applied to ice making, contains ice-making
tanks, in which is circulated a brine mixture, uncongealable at any
temperature likely to be reached during the process. This brine also
circulates around coils of wrought iron pipes, in which the liquid
ammonia passing from the condenser is vaporized, the heat required for
this vaporization being obtained from the brine. A pump draws off the
ammonia vapor from the refrigerator coils, and compresses it into the
condenser, where, by means of the combined action of pressure and
cooling by water, it assumes a liquid form, and is ready to be again
passed on to the refrigerator for evaporation. The ammonia compression
process is more economical than the absorption process, and with a
good boiler and engine about 240,000 thermal units per hour can be
eliminated by the expenditure of 100 lb. of coal per hour, with a
brine temperature in the refrigerator of about 20° Fahr.
GENERAL CONSIDERATIONS.
From what has been said, it will have been seen that, so far as the
mere application is concerned, there is no difference whatever between
the absorption and compression processes. The following
considerations, therefore, which chiefly relate to the application of
refrigerating apparatus, will be dealt with quite independent of
either system. The application of refrigerating apparatus may roughly
be divided into the following heads:
a. Ice making.
b. The cooling of liquids.
c. The cooling of stores and rooms.
_Ice Making._--For this purpose two methods are employed, known as the
can and cell systems respectively. In the former, moulds of tinned
sheet copper or galvanized steel of the desired size are filled with
the water to be frozen, and suspended in a tank through which brine
cooled to a low temperature in the refrigerator is circulated. As soon
as the water is completely frozen, the moulds are removed, and dipped
for a long time into warm water, which loosens the blocks of ice and
enables them to be turned out. The thickness of the blocks exercises
an important influence upon the number of moulds required for a given
output, as a block 9 in. thick will take four or five times as long to
freeze solid as one of only 3 in. In the cell system a series of
cellular walls of wrought or cast iron are placed in a tank, the
distance between each pair of walls being from 12 to 16 in., according
to the thickness of the block required. This space is filled with the
water to be frozen. Cold brine circulates through the cells, and the
ice forms on the outer surfaces, gradually increasing in thickness
until the two opposite layers meet and join together. If thinner
blocks are required, the freezing process may be stopped at any time
and the ice removed. In order to detach the ice it is customary to cut
off the supply of cold brine and circulate brine at a higher
temperature through the cells. Ice frozen by either of the above
described methods from ordinary water is more or less opaque, owing to
the air liberated during the freezing process, little bubbles of which
are caught in the ice as it forms, and in order to produce transparent
ice it is necessary that the water should be agitated during the
freezing process in such a way as to permit the air bubbles to escape.
With the can system this is generally accomplished by means of arms
having a vertical or horizontal movement. These arms are either
withdrawn as the ice forms, leaving the block solid, or they are made
to work backward and forward in the center of the moulds, dividing the
block vertically into two pieces. With the cell system agitation is
generally effected by making a communication between the bottom of
each water space and a chamber below, in which a paddle or wood piston
is caused to reciprocate. The movement thus given to the water in the
chamber is communicated to that in the process of being frozen, and
the small bubbles of air are in this way detached and set free. The
ice which first forms on the sides of the moulds or cells is, as a
rule, sufficiently transparent even without agitation. The opacity
increases toward the center, where the opposing layers join, and it
is, therefore, more necessary to agitate toward the end of the
freezing process than at the commencement. As the capacity for holding
air in solution decreases if the temperature of the water is raised,
less agitation is needed in hot than in temperate climates.
Experiments have been made from time to time with the view of
producing transparent ice from distilled water, and so dispensing with
agitation. In this case the cost of distilling the water will have to
be added to the ordinary working expenses.
_Cooling of Liquids._--In breweries, distilleries, butter factories,
and other places where it is desired to have a supply of water or
brine for cooling and other purposes at a comparatively low
temperature, refrigerating machines may be advantageously applied. In
this case the liquid is passed through the refrigerator and then
utilized in any convenient manner.
_Cooling of Rooms._--For this purpose the usual plan is to employ a
circulation of cold brine through rows of iron piping, placed either
on the ceiling or on the walls of the rooms to be cooled. In this, as
in the other cases where brine is used, it is employed merely as a
medium for taking up heat at one place and transferring it to the
ammonia in the refrigerator, the ammonia in turn completing the
operation by giving up the heat to the cooling water during
liquefaction in the condenser. The brine pipes cool the adjacent air,
which, in consequence of its greater specific gravity, descends, being
replaced by warmer air, which in turn becomes cold, and so the process
goes on. Assuming the air to be sufficiently saturated, which is
generally the case, some of the moisture in it is condensed and frozen
on the surface of the pipes; and if the air is renewed in whole or in
part from the outside, or if the contents of the chamber are wet, the
deposit of ice in the pipes will in time become so thick as to
necessitate its being thawed off. This is accomplished by turning a
current of warm brine through the pipes. Another method has been
proposed, in which the brine pipes are placed in a separate
compartment, air being circulated through this compartment to the
rooms, and back again to the cooling pipes in a closed cycle by means
of a fan. This plan was tried on a large scale by Mr. Chambers at the
Victoria Docks, but for some reason or other was abandoned. One
difficulty is the collection of ice from the moisture deposited from
the air, which clogs up the spaces between the pipes, besides
diminishing their cooling power. This, in some cases, can be partially
obviated by using the same air over again, but in most instances
special means would have to be provided for frequent thawing off, the
pipes having, on account of economy of space and convenience, to be
placed so close together, and to be so confined in surface, that they
are much more liable to have their action interfered with than when
placed on the roof or walls of the room.
In addition to the foregoing there are, of course, many other
applications of ammonia refrigerating machines of a more or less
special nature, of which time will not permit even a passing
reference. Many of these are embraced in the second class, cold water
or brine being used for the cooling of candles, the separation of
paraffin, the crystallization of salts, and for many other purposes.
In the same way cold brine has been used with great success for
freezing quicksand in the sinking of shafts, the excavation being
carried out and the watertight tubing or lining put in while the
material is in a solid state. In a paper such as this it would be
quite impracticable to enter into details of construction, and the
author has therefore confined himself chiefly to principles of
working. In conclusion, however, it may be added that in ammonia
machines, whether on the absorption or compression systems, no copper
or alloy of copper can be used in parts subjected to the action of the
ammonia. Cast or wrought iron and steel may, however, be used,
provided the quality is good, but special care must be taken in the
construction of those parts of absorption machines which are subjected
to a high temperature. In both classes of apparatus first-class
materials and workmanship are most absolute essentials.
* * * * *
[Continued from Supplement, No. 646, p. 10319.]
ELEMENTS OF ARCHITECTURAL DESIGN.[1]
[Footnote 1: Delivered before the Society of Arts, London,
December 13, 1887. From the _Journal_ of the Society.]
BY H. H. STATHAM.
III.--CONTINUED.
The Romans, in their arched constructions, habitually strengthened the
point against which the vault thrust by adding columnar features to
the walls, as shown in Fig. 108; thus again making a false use of the
column in a way in which it was never contemplated by those who
originally developed its form. In Romanesque architecture the column
was no longer used for this purpose; its place was taken by a flat
pilaster-like projection of the wall (plan and section, Fig. 109),
which gave sufficient strength for the not very ambitious vaulted
roofs of this period, where often in fact only the aisles were
vaulted, and the center compartment covered with a wooden roof. At
first this pilaster-like form bore a reminiscence of a classic capital
as its termination; a moulded capping under the eaves of the building.
Next this capping was almost insensibly dropped, and the buttress
became a mere flat strip of wall. As the vaulting became bolder and
more ambitious, the buttress had to be made more massive and of
greater projection, to afford sufficient abutment to the vault, more
especially toward the lower part, where the thrust of the roof is
carried to the ground. Hence arose the tendency to increase the
projection of the buttress gradually downward, and this was done by
successive slopes or "set-offs," as they are termed, which assisted
(whether intentionally or not in the first instance) in further aiding
the correct architectural expression of the buttress. Then the
vaulting of the center aisle was carried so high and treated in so
bold a manner, with a progressive diminution of the wall piers (as the
taste for large traceried windows developed more and more), that a
flying buttress (see section, Fig. 110) was necessary to take the
thrust across to the exterior buttresses, and these again, under this
additional stress, were further increased in projection, and were at
the same time made narrower (to allow for all the window space that
was wanted between them), until the result was that the masses of
wall, which in the Romanesque building were placed longitudinally and
parallel to the axis of the building, have all turned about (Fig. 110,
plan) and placed themselves with their edges to the building to resist
the thrust of the roofing. The same amount of wall is there as in the
Romanesque building, but it is arranged in quite a new manner, in
order to meet the new constructive conditions of the complete Gothic
building.
[Illustration: Figs. 108-114.]
It will be seen thus how completely this important and characteristic
feature of Gothic architecture, the buttress, is the outcome of
practical conditions of construction. It is treated decoratively, but
it is itself a necessary engineering expedient in the construction.
The application of the same principle, and its effect upon
architectural expression, may be seen in some other examples besides
that of the buttress in its usual shape and position. The whole
arrangement and disposition of an arched building is affected by the
necessity of providing counterforts to resist the thrust of arches.
The position of the central tower, for instance, in so many cathedrals
and churches, at the intersection of the nave and transepts, is not
only the result of a feeling for architectural effect and the
centralizing of the composition, it is the position in which also the
tower has the cross walls of nave and transepts abutting against it in
all four directions: if the tower is to be placed over the central
roof at all, it could only be over this point of the plan. In the
Norman buildings, which in some respects were finer constructions than
those of later Gothic, the desire to provide a firm abutment for the
arches carrying the tower had a most marked effect on the
architectural expression of the interior. At Tewkesbury, for instance,
while the lower piers are designed in the usual way toward the north
and south sides (viz., as portions of a pier of nearly square
proportion standing under the angle of the tower), in the east and
west direction the tower piers run out into great solid masses of
wall, in order to insure a sufficient abutment for the tower arches.
On the north and south sides the solid transept walls were available
immediately on the other side of the low arch of the side aisle, but
on the east and west sides there were only the nave and choir arcades
to take the thrust of the north and south tower arches, and so the
Normans took care to interpose a massive piece of wall between, in
order that the thrust of the tower arches might be neutralized before
it could operate against the less solid arcaded portions of the walls.
This expedient, this great mass of wall introduced solely for
constructive reasons, adds greatly to the grandeur of the interior
architectural effect. The true constructive and architectural
perception of the Normans in this treatment of the lower piers is
illustrated by the curious contrast presented at Salisbury. There the
tower piers are rather small, the style is later, and the massive
building of the Normans had given way to a more graceful but less
monumental manner of building. Still the abutment of the tower arches
was probably sufficient for the weight of the tower as at first built;
but when the lofty spire was put on the top of this, its vertical
weight, pressing upon the tower arches and increasing their horizontal
thrust, actually thrust the nave and choir arcades out of the
perpendicular toward the west and east respectively, and there they
are leaning at a very perceptible angle away from the center of the
church--the architectural expression, in a very significant form, of
the neglect of balance of mass in construction.
But while the buttress in Gothic architecture has been in process of
development, what has the vault been doing? We left it (Fig. 92) in
the condition of a round wagon vault, intersected by another similar
vault at right angles. By that method of treatment we got rid of the
continuous thrust on the walls. But there were many difficulties to be
faced in the construction of vaulting after this first step had been
taken, difficulties which arose chiefly from the rigid and
unmanageable proportions of the circular arch, and which could not be
even partially solved till the introduction of the pointed arch. The
pointed arch is the other most marked and characteristic feature of
Gothic architecture, and, like the buttress, it will be seen that it
arose entirely out of constructive difficulties.
These difficulties were of two kinds; the first arose from the
tendency of the round arch, when on a large scale and heavily
weighted, to sink at the crown if there is even any very slight
settlement of the abutments. If we turn again to diagram 77, and
observe the nearly vertical line formed there by the joints of the
keystone, and if we suppose the scale of that arch very much increased
without increasing the width of each voussoir, and suppose it built in
two or three rings one over the other (which is really the
constructive method of a Gothic arch), we shall see that these joints
in the uppermost portion of the arch must in that case become still
more nearly vertical; in other words, the voussoirs almost lose the
wedge shape which is necessary to keep them in their places, and a
very slight movement or settlement of the abutments is sufficient to
make the arch stones lose some of their grip on each other and sink
more or less, leaving the arch flat at the crown. There can be no
doubt that it was the observance of this partial failure of the round
arch (partly owing probably to their own careless way of preparing the
foundations for their piers--for the mediæval builders were very bad
engineers in that respect) which induced the builders of the early
transitional abbeys, such as Furness and Fountains and Kirkstall, to
build the large arches of the nave pointed, though they still retain
the circular-headed form for the smaller arches in the same buildings,
which were not so constructively important. This is one of the
constructive reasons which led to the adoption of the pointed arch in
mediæval architecture, and one which is easily stated and easily
understood. The other influence is one arising out of the lengthened
conflict with the practical difficulties of vaulting, and is a rather
more complicated matter, which we must now endeavor to follow out.
[Illustration: Figs. 93-107.]
Looking at Fig. 92, it will be seen that in addition to the
perspective sketch of the intersecting arches, there is drawn under it
a plan, which represents the four points of the abutment of the arches
(identified in plan and perspective sketch as A, B, C, D), and the
lines which are taken by the various arches shown by dotted lines.
Looking at the perspective sketch, it will be apparent that the
intersection of the two cross vaults produces two intersecting arches,
the upper line of which is shown in the perspective sketch (marked _e_
and _f_); underneath, this intersection of the two arches, which forms a
furrow in the upper side of the construction, forms an edge which
traverses the space occupied by the plan of the vaulting as two
oblique arches, running from A to C and from B to D on the plan.
Although these are only lines formed by the intersection of two cross
arches, still they make decided arches to the eye, and form prominent
lines in the system of vaulting; and in a later period of vaulting
they were treated as prominent lines and strongly emphasized by
mouldings; but in the Roman and early Romanesque vaults they were
simply left as edges, the eye being directed rather to the vaulting
surfaces than to the edges. The importance of this distinction between
the vaulting surfaces and their meeting edges or _groins_[2] will be
seen just now. The edges, nevertheless, as was observed, do form
arches, and we have therefore a system of cross arches (A B and C D[3]
Fig. 95), two wall arches (A, D and B C), and two oblique arches (A C
and B D), which divide the space into four equal triangular portions;
this kind of vaulting being hence called _quadripartite_ vaulting. In
this and the other diagrams of arches on this page, the cross arches
are all shown in positive lines, and the oblique arches in dotted
lines.
[Footnote 2: A _groin_ is the edge line formed by the meeting and
intersection of any two arched surfaces. When this edge line is
covered and emphasized by a band of moulded stones forming an
arch, as it were, on this edge, this is called a _groin rib_.]
[Footnote 3: The "D" seems to have been accidentally omitted in
this diagram; it is of course the fourth angle of the plan.]
We have here a system in which four semicircular arches of the width
of A B are combined with two oblique arches of the width of A C,
springing from the same level and supposed to rise to the same height.
But if we draw out the lines of these two arches in a comparative
elevation, so as to compare their curves together, we at once find we
are in a difficulty. The intersection of the two circular arches
produces an ellipse with a very flat crown, and very liable to fail.
If we attempt to make the oblique arch a segment only of a large
circle, as in the dotted line at 94, so as to keep it the same level
as the other without being so flat at the top, the crown of the arch
is safer, but this can only be done at the cost of getting a queer
twist in the line of the oblique arch, as shown at D, Fig. 93. The
like result of a twist of the line of the oblique arch would occur if
the two sides of the space we are vaulting over were of different
lengths, i.e. if the vaulting space were otherwise than a square, as
long as we are using circular arches. If we attempt to make the
oblique arches complete circles, as at Fig. 96, we see that they must
necessarily rise higher than the cross and side arches, so that the
roof would be in a succession of domical forms, as at Fig. 97. There
is the further expedient of "stilting" the cross arches, that is,
making the real arch spring from a point above the impost and building
the lower portion of it vertical, as shown in Fig. 98. This device of
stilting the smaller arches to raise their crowns to the level of
those of the larger arches was in constant use in Byzantine and early
Romanesque architecture, in the kind of manner shown in the sketch,
Fig. 99; and a very clumsy and makeshift method of dealing with the
problem it is; but something of the kind was inevitable as long as
nothing but the round arch was available for covering contiguous
spaces of different widths. The whole of these difficulties were
approximately got over in theory, and almost entirely in practice, by
the adoption of the pointed arch. By its means, as will be seen in
Fig. 100, arches over spaces of different widths could be carried to
the same height, yet with little difference in their curves at the
springing, and without the necessity of employing a dangerously flat
elliptical form in the oblique arch. A sketch of the Gothic vault in
this form, and as the intersection of the surfaces of pointed vaults,
is shown in Fig. 101.
But now another and most important change was to come over the vault.
The mediæval architects were not satisfied with the mere edge left by
the Romans in their vaults, and even before the full Gothic period the
Roman builders had emphasized their oblique arches in many cases by
ponderous courses of moulded or unmoulded stone in the form of
vaulting ribs. These, in the case of Norman building, were probably
not merely put for the purpose of architectural expression, but also
because they afforded an opportunity of concealing behind the lines of
a regularly curved groin rib the irregular curves which were really
formed by the junction of the vaulting surfaces. But when the vault
become more manageable in its curves after the adoption of the pointed
arch, the groin rib became adopted in the early pointed vaulting as a
means of giving expression and carrying up the lines of the
architectural design. On its edge were stones moulded with the deep
undercut hollows of early English moulding, defining the curves of the
oblique as well as of the cross arches with strongly marked lines,
and, moreover, falling on a level with each other in architectural
importance; the oblique vault of the arch is no longer a secondary
line in the vaulting design; on the contrary, the cross arches are
usually omitted, as shown in Figs. 102 and 103 (view and plan of an
early Gothic quadripartite vault); so that the cross rib, which, in
the early Romanesque wagon vault (Fig. 90), was the one marked line on
the vaulting surface, has now been obliterated, and the line of the
oblique arch (E F, Figs. 102, 103) has taken its place.
The effect of the strongly marked lines of the groin ribs, radiating
from the cap of the shaft which was their architectural support, seems
to have been so far attractive to the mediæval builders that they soon
endeavored to improve upon it and carry it further by multiplying the
groin ribs. One of the stages of this progress is shown in Figs. 104,
105. Here it will be seen that the cross rib is again shown, and that
intermediate ribs have been introduced between it and the oblique rib.
The richness of effect of the vault is much heightened thereby; but a
very important modification in the mode of constructing it has been
introduced. As the groin ribs become multiplied, it came to be seen
that it was easier to construct them first, and fill in the spaces
afterward; accordingly the groin, instead of being, as it was in the
early days of vaulting, merely the line formed by the meeting of two
arch surfaces, became a kind of stone scaffolding or frame work,
between which the vaulting surfaces were filled in with lighter
material. This arrangement of course made an immense difference in the
whole principle of constructing the vault, and rendered it much more
ductile in the hands of the builder, more capable of taking any form
which he wished to impose on it, than when the vault was regarded and
built as an intersection of surfaces. There was still one difficulty,
however, one slight failure both practical and theoretical in the
vault architecture, which for a long time much exercised the minds of
the builders. The ribs of the vaulting being all of unequal length,
they had to assume different curves almost immediately on rising from
the impost; and as the mouldings of the ribs have to be run into each
other ("mitered" is the technical term) on the impost, there not being
room to receive them all separately, it was almost impossible to get
them to make their divergence from each other in a completely
symmetrical manner; the shorter ribs with the quicker curves parted
from each other at a lower point than the larger ones, and the
"miters" occurred at unequal heights. The effort to get over this
unsatisfactory and irregular junction of the ribs at the springing was
made first by setting back the feet of the shorter ribs on the impost
capping, somewhat in the rear of the feet of the larger ribs, so as to
throw their parting point higher up; but this also was only a
makeshift, which it was hoped the eye would pass over; and in fact it
is rarely noticeable except to those who know about it and look for
it. Still the defect was there, and was not got over until the idea
occurred of making all the ribs of the same curvature and the same
length, and intercepting them all by a circle at the apex of the
vault, as shown in Figs. 106, 107; the space between the circles at
the apex of the vault being practically a nearly flat surface or
_plafond_ held in its place by the arches surrounding it; though, for
effect, it is often treated otherwise in external appearance, being
decorated by pendants giving a reversed curve at this point, but which
of course are only ornamental features hung from the roof. If we look
again at Fig. 104, we shall see that this was a very natural
transition after all, for the arrangement of the ribs and vaulting
surfaces in that example is manifestly suggestive of a form radiating
round the central point of springing, though it only suggests that,
and does not completely realize it. But here came a further and very
curious change in the method of building the vault, for as the ribs
were made more numerous, for richness of effect, in this form of
vaulting, it was discovered that it was much easier to build the whole
as a solid face of masonry, working the ribs on the face of it. Thus
the ribs, which in the intermediate period were the constructive
framework of the vault, in the final form of fan vaulting came back to
their original use as merely a form of architectural expression, meant
to carry on the architectural lines of the design; and they perform,
on a larger scale and with a different expression, much the same kind
of function which the fluting lines performed in the Greek column. The
fan vault is therefore a kind of inverted dome, built up in courses on
much the same principle as a dome, but a convex curve internally,
instead of a concave one, the whole forming a series of inverted
conoid forms abutting against the wall at the foot and against each
other at their upper margins. This form of roof is wonderfully rich in
effect, and has the appearance of being a piece of purely artistic
work done for the pleasure of seeing it; yet, as we have seen, it is
in reality, like almost everything good in architecture, the logical
outcome of a contention with structural problems.
We have already noticed the suggestion, in early Gothic or Romanesque,
of the dividing up of a pier into a multiple pier, of which each part
supports a special member of the superstructure, as indicated in Fig.
90. The Gothic pier, in its development in this respect, affords a
striking example of that influence of the superstructure on the plan
which has before been referred to. The peculiar manner of building the
arch in Gothic work led almost inevitably to this breaking up of the
pier into various members. The Roman arch was on its lower surface a
simple flat section, the decorative treatment in the way of mouldings
being round the circumference, and not on the under side or _soffit_
of the arch, and in early Romanesque work this method was still
followed. The mediæval builders, partly in the first instance because
they built with smaller stones, adopted at an early period the plan of
building an arch in two or more courses or rings, one below and
recessed within the other. As the process of moulding the arch stones
became more elaborated, and a larger number of subarches one within
another were introduced, this characteristic form of subarches became
almost lost to the eye in the multiplicity of the mouldings used. But
up to nearly the latest period of Gothic architecture this form may
still be traced, if looked for, as the basis of the arrangement of the
mouldings, which are all formed by cutting out of so many square
sections, recessed one within the other. This will be more fully
described in the next lecture. We are now speaking more especially of
the pier as affected by this method of building the arches in recessed
orders. If we consider the effect of bringing down on the top of a
square capital an arch composed of two rings of squared stones, the
lower one only half the width (say) of the upper one, it will be
apparent that on the square capital the arch stones would leave a
portion of the capital at each angle bare, and supporting nothing.[4]
This looks awkward and illogical, and accordingly the pier is modified
so as to suit the shape of the arch. Figs. 111, 112, 113, and 114,
with the plans, B C D, accompanying them, illustrate this development
of the pier. Fig. 111 is a simple cylindrical pier with a coarsely
formed capital, a kind of reminiscence of the Doric capital, with a
plain Romanesque arch starting from it. Fig. 112, shown in plan at B,
is the kind of form (varied in different examples) which the pier
assumed in Norman and early French work, when the arch had been
divided into two recessed orders. The double lines of the arch are
seen springing from the cap each way, in the elevation of the pier. If
we look at the plan of the pier, we see that, in place of the single
cylinder, it is now a square with four smaller half cylinders, one on
each face. Of these, those on the right and left of the plan support
the subarches of the arcade; the one on the lower side, which we will
suppose to be looking toward the nave, supports the shaft which
carries the nave vaulting, and which stands on the main capital with a
small base of its own, as seen in Fig. 112--a common feature in early
work; and the half column on the upper side of the plan supports the
vaulting rib of the aisle. In Fig. 113 and plan C, which represents a
pier of nearly a century later, we see that the pier is broken up by
perfectly detached shafts, each with its own capital, and each
carrying a group of arch mouldings, which latter have become more
elaborated. Fig. 114 and plan D show a late Gothic fourteenth century
pier, in which the separate shafts have been abandoned, or rather
absorbed into the body of the pier, and the pier is formed of a number
of moulded projections, with hollows giving deep shadows between them,
and the capitals of the various members run into one another, forming
a complete cap round the pier. This pier shows a remarkable contrast
in every way to B, yet it is a direct development from the latter. In
this late form of pier, it will be observed that the projection, E,
which carries the vaulting ribs of the nave, instead of springing from
the capital, as in the early example, Fig. 111, springs from the
floor, and runs right up past the capital; thus the plan of the
vaulting is brought, as it were, down on to the floor, and the
connection between the roofing of its building and its plan is as
complete as can well be. In Fig. 113 the vaulting shaft is supposed to
stop short of the capital and to spring from a corbel in the wall,
situated above the limit of the drawing. This was a common arrangement
in the "Early English" and "Early Decorated" periods of Gothic, but it
is not so logical and complete, or so satisfactory either to the eye
or to the judgment, as starting the vaulting shaft from the floor
line. The connection between the roofing and the plan may be further
seen by looking at the portion of a mediæval plan given under Fig.
110, where the dotted lines represent the course of the groin ribs of
the roof above. It will be seen how completely these depend upon the
plan, so that it is necessary to determine how the roof in a vaulted
building is to be arranged before setting out the ground plan.
[Footnote 4: This was illustrated by diagrams on the wall at the
delivery of the lecture.]
Thus we see that the Gothic cathedral, entirely different in its form
from that of the Greek temple, illustrates, perhaps, even more
completely than the Greek style, the same principle of correct and
truthful expression of the construction of the building, and that all
the main features which give to the style its most striking and
picturesque effects are not arbitrarily adopted forms, but are the
result of a continuous architectural development based on the
development of the construction. The decorative details of the Gothic
style, though differing exceedingly from those of the Greek, are, like
the latter, conventional adaptations of suggestions from nature; and
in this respect again, as well as in the character of the mouldings,
we find both sides illustrating the same general principle in the
design of ornament, in its relation to position, climate, and
material; but this part of the subject will be more fully treated of
in the next lecture.
We have now arrived at a style of architectural construction and
expression which seems so different from that of Greek architecture,
which we considered in the last lecture, that it is difficult to
realize at first that the one is, in regard to some of its most
important features, a lineal descendant of the other. Yet this is
unquestionably the case. The long thin shaft of Gothic architecture is
descended, through a long series of modifications, from the single
cylindrical column of the Greek; and the carved mediæval capital,
again, is to be traced back to the Greek Corinthian capital, through
examples in early French architecture, of which a tolerably complete
series of modifications could be collected, showing the gradual change
from the first deviations of the early Gothic capital from its
classical model, while it still retained the square abacus and the
scroll under the angle and the symmetrical disposition of the leaves,
down to the free and unconstrained treatment of the later Gothic
capital. Yet with these decided relations in derivation, what a
difference in the two manners of building! The Greek building is
comparatively small in scale, symmetrical and balanced in its main
design, highly finished in its details in accordance with a
preconceived theory. The Gothic building is much more extensive in
scale, is not necessarily symmetrical in its main design, and the
decorative details appear as if worked according to the individual
taste and pleasure of each carver, and not upon any preconceived
theory of form or proportion. In the Greek building all the
predominant lines are horizontal; in the mediæval building they are
vertical. In the Greek building every opening is covered by a lintel;
in the Gothic building every opening is covered by an arch. No two
styles, it might be said, could be more strongly contrasted in their
general characteristics and appearance. Yet this very contrast only
serves to emphasize the more strongly the main point which I have been
wishing to keep prominent in these lectures--that architectural
design, rightly considered, is based on and is the expression of plan
and construction. In Greek columnar architecture the salient feature
of the style is the support of a cross lintel by a vertical pillar;
and the main effort of the architectural designer is concentrated on
developing the expression of the functions of these two essential
portions of the structure. The whole of the openings being bridged by
horizontal lintels, the whole of the main lines of the superstructure
are horizontal, and their horizontal status is as strongly marked as
possible by the terminating lines of the cornice--the whole of the
pressures of the superstructure are simply vertical, and the whole of
the lines of design of the supports are laid out so as to emphasize
the idea of resistance to vertical pressure. The Greek column, too,
has only one simple office to perform, that of supporting a single
mass of the superstructure, exercising a single pressure in the same
direction. In the Gothic building the main pressures are oblique and
not vertical, and the main feature of the exterior substructure, the
buttress, is designed to express resistance to an oblique pressure;
and no real progress was made with the development of the arched style
until the false use of the apparent column or pilaster as a buttress
was got rid of, and the true buttress form evolved. On the interior
piers of the arcade there is a resolution of pressures which
practically results in a vertical pressure, and the pier remains
vertical; but the pressure upon it being the resultant of a complex
collection of pressures, each of these has, in complete Gothic, its
own apparent vertical supporting feature, so that the plan of the
substructure becomes a logical representation of the main features and
pressures of the superstructure. The main tendency of the pointed
arched building is toward vertically, and this vertical tendency is
strongly emphasized and assisted by the breaking up of the really
solid mass of the pier into a number of slender shafts, which, by
their strongly marked parallel lines, lead the eye upward toward the
closing-in lines of the arcade and of the vaulted roof which forms the
culmination of the whole. The Greek column is also assisted in its
vertical expression by the lines of the fluting; but as the object of
these is only to emphasize the one office of the one column, they are
strictly subordinate to the main form, are in fact merely a kind of
decorative treatment of it in accordance with its function. In the
Gothic pier the object is to express complexity of function, and the
pier, instead of being a single fluted column, is broken up into a
variety of connected columnar forms, each expressive of its own
function in the design. It may be observed also that the Gothic
building, like the Greek, falls into certain main divisions arising
out of the practical conditions of its construction, and which form a
kind of "order" analogous to the classic order in a sense, though not
governed by such strict conventional rules. The classic order has its
columnar support, its beam, its frieze for decorative treatment. The
Gothic order has its columnar support, its arch (in place of the
beam), its decoratively treated stage (the triforium), occupying the
space against which the aisle roof abuts, and its clerestory, or
window stage. All these arise as naturally out of the conditions and
historical development of the structure in the Gothic case as in the
Greek one, but the Greek order is an external, the Gothic an internal
one. The two styles are based on constructive conditions totally
different the one from the other; their expression and character are
totally different. But this very difference is the most emphatic
declaration of the same principle, that architectural design is the
logical, but decorative, expression of plan and construction.
* * * * *
THE METEOROLOGICAL STATION ON MT. SANTIS.
[Illustration]
At the second International Meteorological Congress, in 1879, the
erection of an observatory on the top of a high mountain was
considered. The Swiss Meteorological Commission undertook to carry out
the project, and sent out circulars to different associations,
governments, and private individuals requesting single or yearly
contributions to aid in defraying the expense of the station. In
December, 1881, an extra credit of about $1,000 was granted by the
Bundesversammlung for the initial work on the station, which was
temporarily placed in the Santis Hotel, and a telegraph was put up
between that place and Weisbad in August, 1882, so that on September 1
of the same year the meteorological observations were begun.
At the end of August, 1885, this temporary arrangement expired, and
the enterprise could not be carried on unless the support of the same
was undertaken by the Union. On March 27, 1885, the Bundesversammlung
decided to take the necessary steps. Mr. Fritz Brunner, who died May
1, 1885, left a large legacy for the enterprise, making it possible to
build a special observatory.
For this purpose the northeast corner of the highest rocky peak was
blasted out and the building was so placed that the wall of rock at
the rear formed an excellent protection from the high west winds. By
the first of October, last year, the building was ready for occupancy,
and there was a quiet opening at which Mr. Potch, director of the Blue
Hill Observatory, near Boston, and others were present.
The building is 26 feet long, 19 feet deep, and 30 feet high, and is
very solid and massive, having been built of the limestone blasted
from the rock. It consists of a ground floor containing the telegraph
office, the observers' work room, and the kitchen and store rooms; the
first story, in which are the living and sleeping rooms for the
observers and their assistants; and the second story, living and
sleeping rooms for visiting scientists who come to make special
observations, and a reserve room. The barometer and barograph are
placed in the second story, at a height of about 8,202 feet above the
level of the sea, whereas in the hotel they were only about 8,093 feet
above the sea level. The flat roof, of wood and cement, which extends
very little above the plateau of the mountain top, is admirably
adapted for making observations in the open air. All the rooms in the
house are ceiled with wood, and the walls and floors of the ground
floor and first story and the ceilings of the second story are covered
with insulating material. The cost of the building, including the
equipments, amounted to about $11,200.
The fact that since the erection of the Santis station there has been
a still higher station constructed on Sonnblick (10,137 feet high)
does not decrease the value of the former, for the greater the number
of such elevated stations, the better will be the meteorological
investigations of the upper air currents. The present observer at
Santis is Mr. C. Saxer, who has endured the hardships and privations
of a long winter at the station.
The anemometer house, which is shown in our illustration, is connected
with the main house by a tunnel. Several times during the day records
are taken of the barometer, the thermometer, the weather vane, as well
as notes in regard to the condition of the weather, the clouds, fall
of rain or snow, etc. A registering aneroid barometer marks the
pressure of the atmosphere hourly, and two turning thermometers
register the temperature at midnight and at four o'clock in the
morning.--_Illustrirte Zeitung._
* * * * *
THE CARE OF THE EYES.[1]
[Footnote 1: From a paper by David Webster. M.D., professor of
ophthalmology in the New York Polyclinic and surgeon to the
Manhattan Eye and Ear Hospital, New York.]
BY PROF. DAVID WEBSTER, M.D.
"The light of the body is the eye." Of all our senses, sight, hearing,
touch, taste, and smell, the sight is that which seems to us the most
important. Through the eye, the organ of vision, we gain more
information and experience more pleasure, perhaps, than through any or
all our other organs of sense. Indeed, we are apt to depreciate the
value of our other senses when comparing them to the eyesight. It is
not uncommon to hear a person say, "I would rather die than be blind."
But no one says, "I would rather die than lose my hearing." As a
matter of fact, the person who is totally blind generally appears to
be more cheerful, happier, than one who is totally deaf. Deaf mutes
are often dull, morose, quick tempered, obstinate, self-willed, and
difficult to get along with, while the blind are not infrequently
distinguished for qualities quite the reverse. It is worthy of remark
that the eye is that organ of sense which is most ornamental as well
as useful, and the deprivation of which constitutes the most visible
deformity. But it is unnecessary to enter into a comparison of the
relative value of our senses or the relative misfortune of our loss of
any one of them. We need them all in our daily struggle for existence,
and it is necessary to our physical and mental well-being, as well as
to our success in life, that we preserve them all in as high a degree
of perfection as possible. We must not lose sight of the fact that all
our organs of sense are parts of one body, and that whatever we do to
improve or preserve the health of our eyes cannot do harm to any other
organ. We shall be able to "take care of our eyes" more intelligently
if we know something of their structure and how they perform their
functions. The eye is a hollow globe filled with transparent material
and set in a bony cavity of the skull, which, with the eyelids and
eyelashes, protect it from injury. It is moved at will in every
direction by six muscles which are attached to its surface, and is
lubricated and kept moist by the secretions of the tear gland and
other glands, which secretions, having done their work, are carried
down into the nose by a passage especially made for the purpose--the
tear duct. We are all familiar with the fact that our eyes are "to see
with," but in order to be able to take care of our eyes intelligently,
it is necessary to understand as far as possible how to see with them.
THE BACK WALL OF THE EYE.
It is a remarkable fact that every object we see has its picture
formed upon the back wall of our eyes. The eye is a darkened chamber,
and the whole of the front part of it acts as a lens to bring the rays
of light coming from objects we wish to see to a focus on its back
wall, thus forming a picture there as distinct as the picture formed
in the camera obscura of the photographer. This has not only been
proved by the laws of optics, but has been actually demonstrated in
the eyes of rabbits and other animals. Experimenters have held an
object before the eye of a rabbit for a few moments, and have then
killed the animal and removed the eye as quickly as possible, and laid
its back wall bare, and have distinctly seen there the picture of the
object upon which the eye had been fixed. It is a truly wonderful fact
that these pictures upon the back wall of the eye can be changed so
rapidly that the picture of the object last looked at disappears in an
instant and makes way for the picture of the next. We know that the
picture formed on the back wall of the eye is carried back to the
brain by the optic nerve, but there our knowledge stops. Science
cannot tell us how the brain, and through it the mind, completes the
act of seeing. It is there that the finite and the infinite touch,
and, as our minds are finite, we cannot comprehend the infinite.
But there is enough that we can understand, and it shall be my
endeavor in this paper to make some plain statements that will help as
a guide in the preservation of those wonderful and useful organs.
FAR AND NEAR SIGHTEDNESS.
We have to use our eyes for near and far distant vision. In gathering
pictures of distant objects the normally shaped eye puts forth little
or no effort. It is the near work, such as reading, sewing, or
drawing, that puts a real muscular strain upon the eyes. There are
certain rules that apply to the use of the eyes for such near work
regardless of the age of the person.
READING.
1. In reading, a book or newspaper should be held at a distance of
from ten to fifteen inches from the eyes. It is hardly necessary to
caution anybody not to hold the print further away than fifteen
inches. The only objection to holding ordinary print too far away is
that in so doing the pictures formed on the back wall of the eye are
too small to be readily and easily perceived, and the close attention
consequently necessary causes both the eyes and the brain to tire.
Most persons quickly find this out themselves, and the tendency is
rather to hold the book too near, for the nearer the object to the
eye, the larger its picture upon the retina, or back eye wall. But
here we encounter another danger. The nearer the object the eyes are
concentrated upon, the greater the muscular effort necessary; so that
by holding the book too near, the labor of reading is greatly
increased, and the long persistence in such a habit is likely to
produce weak eyes, and may, in some instances, lead to real
near-sightedness. When children are observed to have acquired this
habit and cannot be persuaded out of it, they should always be taken
to a physician skilled in the treatment of the eye for examination and
advice. A little attention at such a time may save them from a whole
lifetime of trouble with their eyes. Of course, the larger the print,
the farther it may be held from the eyes.
POSITION.
2. The position of the person with regard to the light should be so
that the latter will fall upon the page he is reading, and not upon
his eyes. It is generally considered most convenient to have the light
shine over the left shoulder, so that in turning the leaves of the
book, the shadow of the hand upon the page is avoided. It is not
always possible to do this, however, and, at the same time, to get
plenty of light upon the page. When one finds himself compelled to
face the light in reading, or in standing at a desk bookkeeping, he
should always contrive to shade his eyes from a direct light. This may
be done with a large eye shade projecting from the brow. A friend of
mine, a physician, is very fond of reading by a kerosene lamp, the
lamp being placed on a table by his side, and the direct light kept
from his eyes by means of a piece of cardboard stuck up by the lamp
chimney.
PROPER LIGHT.
3. The illumination should always be sufficient. Nothing is more
injurious to the eyes than reading by a poor light. Many persons
strain their eyes by reading on into the twilight as long as they
possibly can. They become interested and do not like to leave off.
Some read in the evening at too great a distance from the source of
light, forgetting that the quantity of light diminishes as the square
of the distance from the source of light increases. Thus, at four
feet, one gets only one-sixteenth part of the light upon his page that
he would at one foot. It is the duty of parents and others who have
charge of children to see to it that they do not injure their eyes by
reading by insufficient light, either daylight or artificial light.
There is a common notion that electric light is bad for the eyes. The
only foundation I can think of for such a notion is that it is trying
to the eyes to gaze directly at the bright electric light. It is bad
to gaze long at any source of light, and the brighter the source of
light gazed at, the worse for the eyes, the sun being the worst of
all. I have seen more than one person whose eyes were permanently
injured by gazing at the sun, during an eclipse or otherwise. As a
matter of fact, nothing short of sunlight is better than the
incandescent electric light to read by or to work by.
READING IN BED.
As to reading while lying down in bed or on a lounge, I can see no
objection to it so far as the eyes are concerned, provided the book is
held in such a position that the eyes do not have to be rolled down
too far. Unless the head is raised very high by pillows, however, it
will be found very fatiguing to hold the book high enough, not to
mention the danger of falling asleep, and of upsetting the lamp or
candle, and thus setting the bed on fire. Many persons permanently
weaken their eyes by reading to pass away the tedious hours during
recovery from severe illness. The muscles of the eyes partake of the
general weakness and are easily overtaxed. Persons in this condition
may be read to, but should avoid the active use of their own eyes.
READING IN RAIL CARS.
Reading while in the rail cars or in omnibuses is to be avoided. The
rapid shaking, trembling or oscillating motion of the cars makes it
very difficult to keep the eyes fixed upon the words, and is very
tiresome. I have seen many persons who attributed the failure of their
eyes to the daily habit of reading while riding to and from the city.
Children should be cautioned against reading with the head inclined
forward. The stooping position encourages a rush of blood to the head,
and consequently the eyes become congested, and the foundations for
near-sightedness are laid.
(_To be continued._)
* * * * *
TESTING INDIGO DYES.
The author deals with the question whether a sample of goods is dyed
with indigo alone or with a mixture of indigo and other blue coloring
matters. His method may be summarized as follows: Threads of the
material in question should give up no coloring matter to boiling
water. Alcohol at 50 and at 95 per cent. (by volume) ought to extract
no color, even if gently warmed (not boiled). Solution of oxalic acid
saturated in the cold, solution of borax, solution of alum at 10 per
cent., and solution of ammonium molybdate at 33-1/3 per cent. ought
not to extract any coloring matter at a boiling heat. The borax
extract, if subsequently treated with hydrochloric acid, should not
turn red, nor become blue on the further addition of ferric chloride.
Solutions of stannous chloride and ferric chloride with the aid of
heat ought entirely to destroy the blue coloring matter. Glacial
acetic acid on repeated boiling should entirely dissolve the coloring
matter. If the acetic extracts are mixed with two volumes of ether and
water is added, so as to separate out the ether, the water should
appear as a slightly blue solution, the main bulk of the indigo
remaining in suspension at the surface of contact of the ethereal and
watery stratum. This acid watery stratum should be colorless, and
should not assume any color if a little strong hydrochloric acid is
allowed to fall into it through the ether. No sulphureted hydrogen
should be evolved on boiling the yarn or cloth in strong hydrochloric
acid. On prolonged boiling, supersaturation with strong potassa in
excess, heating and adding a few drops of chloroform, no isonitrile
should be formed.--_W. Lenz_.
* * * * *
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TRANSCRIBER'S NOTES
1. Simple and obvious typographical errors have been corrected.
2. In the article "Manufacture of Photosensitive Plates", the original
text referred to room U twice. The first instance has been changed
to room T.
3. In the article "An Improved Screw Propeller", the text refers to the
propeller in figure A as being four bladed and also two bladed. It
is clearly two bladed and the reference to it being four-bladed has
been corrected.
End of the Project Gutenberg EBook of Scientific American Supplement, No.
647, May 26, 1888, by Various
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