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Title: Chemistry
developed by facts and principles drawn chiefly from the non-metals
Author: John Howard Appleton
Release date: July 25, 2026 [eBook #79181]
Language: English
Original publication: Providence: Providence Lithograph Company, 1884
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*** START OF THE PROJECT GUTENBERG EBOOK CHEMISTRY ***
Transcriber’s Notes:
Underscores “_” before and after a word or phrase indicate _italics_
in the original text.
Equal signs “=” before and after a word or phrase indicate =bold=
in the original text.
Small capitals have been converted to SOLID capitals.
Illustrations have been moved so they do not break up paragraphs.
Deprecated spellings have been preserved.
Typographical and punctuation errors have been silently corrected.
[Illustration: A Chemist’s Work Bench.]
CHEMISTRY:
DEVELOPED BY
FACTS AND PRINCIPLES DRAWN CHIEFLY FROM THE NON-METALS,
BY
JOHN HOWARD APPLETON, A. M.,
_Professor of Chemistry in Brown University_.
AUTHOR OF
“THE YOUNG CHEMIST,”
“QUALITATIVE CHEMICAL ANALYSIS,”
“QUANTITATIVE CHEMICAL ANALYSIS.”
“THE LABORATORY HANDBOOK.”
PROVIDENCE:
PROVIDENCE LITHOGRAPH COMPANY.
1884.
OTHER WORKS ON CHEMISTRY
BY PROFESSOR APPLETON:
=I. The Young Chemist=: A book of chemical experiments for beginners in
Chemistry. It is composed almost entirely of experiments, those being
chosen that may be performed with very simple apparatus.
=II. Qualitative Analysis=: A brief but thorough manual for laboratory
use.
It gives full explanations and many chemical equations. The processes
of analysis are clearly stated and the whole subject is handled in a
manner that has been highly commended.
=III. Quantitative Analysis=: The treatment of the subject is such as
to afford an acquaintance with the best methods of determining all the
principal elements, as well as with the most important type-processes
both of gravimetric and volumetric analysis.
THE EXPLANATIONS ARE DIRECT AND CLEAR so that a pupil is enabled to
work intelligently _even without the constant guidance of the teacher_.
By this means the book is adapted for self-instruction of teachers and
others who require this kind of help to enable them to advance beyond
their present attainments.
=IV. The Laboratory Handbook=: An annual publication containing many
convenient tables for laboratory use. New tables are constantly
introduced, and changes are made in order to keep the matter abreast of
the latest discoveries.
COPYRIGHT, 1884,
BY
JOHN HOWARD APPLETON.
PRINTED AND ELECTROTYPED BY
E. A. JOHNSON & CO.,
PROVIDENCE, R. I.
PREFACE.
This little book has been prepared as a popular introduction to the
study of chemistry.
It is probably needless to recommend the _subject_: chemistry is
recognized as a science of such general interest, such wide usefulness,
and such universal application, that no intelligent person can endure
long to remain ignorant of its principal facts and laws.
This book treats principally of the _non-metals_; it is believed to be
the verdict of authors and teachers of experience, that these furnish
the most suitable material for a beginner in the study of chemistry;
these best present the fundamental facts and principles of the science,
and they do it in connection with objects and phenomena easily
accessible to almost every civilized human being.
The author contemplates the preparation hereafter of a book of similar
general character, only having its principal facts drawn from the
chemistry of the _metals_.
In writing this book it has been the effort to treat the subject in
a style that shall be attractive to the general reader; but it is
believed that in no case has scientific fact been sacrificed in the
interest of popular form.
The arrangement of matter in the book is in accordance with the
following plan: After the introductory chapters, which present the
general principles of chemical action, the chief non-metals are treated
in a scientific order as follows: the _monads_, hydrogen, chlorine,
bromine, iodine, and fluorine; then the _dyads_, oxygen and sulphur;
next the _triads_, boron, nitrogen; finally the _tetrads_, carbon and
silicon; thus including the four great groups into which the non-metals
are naturally arranged.
The _historical and biographical sketches_, that are distributed
through the book, have been introduced with the view of legitimately
helping to retain the reader’s attention. Most of the _experiments_
described are such as may be performed by any one possessed of
reasonable skill; it is believed that they will afford profitable
instruction as well as entertainment. Allusions to the _applications
of chemistry_ to the affairs of every-day life have been carefully
introduced and have been developed as fully as the circumstances seem
to warrant.
Perhaps some comment upon the _reading references_ (pp. 10, 17, 24, 27,
31, 38, 45, 56, 73, 84, 98, 111, 116, 133, 156, 161, 186, 196, 214)
is proper. They are largely from periodical publications, and it is
thought that they will be of service, especially to mature students.
Helps to reading are now viewed as among the most important offerings
of teachers to learners. The reading lists in this book point out some
papers which are selected as being chiefly popular in style; if these
lead the reader to consult the others he will find himself introduced
to some of the most important contributions to the knowledge of our
science.
BROWN UNIVERSITY, August, 1884.
CONTENTS.
CHAPTER I.—The scope of chemistry, 7
CHAPTER II.—The elementary substances, 12
CHAPTER III.—Names and symbols of elements, 19
CHAPTER IV.—Classification of the elementary
substances; metals and non-metals, 28
CHAPTER V.—Compound substances; examples of
binary and ternary compounds, 32
CHAPTER VI.—The construction of substances;
the mass, the molecule, the atom, 39
CHAPTER VII.—How chemical affinity works; the
modern atomic theory, 46
CHAPTER VIII.—Hydrogen; its discovery; method
of preparation; its properties, 58
CHAPTER IX.—Balloons; their invention and uses, 74
CHAPTER X.—Chlorine; its preparation and properties;
chlorohydric acid; bleaching-powder, 85
CHAPTER XI.—Bromine, 100
CHAPTER XII.—Iodine, 105
CHAPTER XIII.—Fluorine, 112
CHAPTER XIV.—Oxygen; its discovery; its preparation;
its properties; its relation to hydrogen; the compound
blowpipe; its relation to combustion in general, and
to animal respiration, 117
CHAPTER XV.—Water, its importance to living beings;
its terrestrial circulation; its influence on climate, 134
CHAPTER XVI.—Sulphur; sulphuretted hydrogen;
sulphur dioxide, 142
CHAPTER XVII.—Sulphur trioxide; manufacture of
sulphuric acid, 151
CHAPTER XVIII.—Boron, 157
CHAPTER XIX.—Nitrogen; its discovery; its properties;
compound with hydrogen; compounds with oxygen;
nitric acid, 162
CHAPTER XX.—The Atmosphere, 170
CHAPTER XXI.—Explosives; gunpowder; fireworks;
fulminates gun-cotton; nitroglycerine, 177
CHAPTER XXII.—Phosphorus; friction matches, 187
CHAPTER XXIII.—Carbon; charcoal; lamp-black; coal;
graphite; the diamond; other natural forms of carbon, 197
CHAPTER XXIV.—Compounds of carbon and oxygen, 215
CHAPTER XXV.—Illuminating gas, 221
CHAPTER XXVI.—Silicon, 228
CHEMISTRY.
CHAPTER I.
THE SCOPE OF CHEMISTRY.
Chemistry treats of all kinds of material substances. This is a very
broad assertion, but it appears to be true. The solid rock matter of
the earth and the wealth of living animal and vegetable substances
upon it undergo all their varied changes in subjection to chemical
laws. The same is true of the water and of all liquid things we know;
and the declaration applies yet further to the invisible gaseous mass
which surrounds and envelopes our terrestrial globe. This deeper but
thinner ocean which we call the atmosphere is also governed by chemical
law in all its varied relations to the living beings as well as to the
inanimate substances that have their existence within it. In thought we
may ascend above these solid, liquid and gaseous substances connected
with our earth. When thus we reach out to the heavenly bodies beyond,
we feel sure that these, possessing as they may, solid, liquid or
gaseous matter, are likewise controlled by chemical laws, and that
in their changes they exemplify with more or less fulness, distinct
chemical principles.
The Great Number of Different Substances in the Earth.
Here then it is intimated that chemistry relates to an enormous number
of substances. In fact the number of the various kinds of matter
already existing on our earth is so great that they have never been
so much as counted, much less described, in any list or volume; nay
more, doubtless many exist that human beings have never recognized at
all. This last statement refers not merely to such substances as may
be known only to savages dwelling beyond the reach of civilization and
commerce, nor yet to such as may be secreted in absolutely uninhabited
portions of the globe, nor even to those that exist so deep in the
earth that man’s power may never be sufficient to reach them. Probably
even some of the most humble and familiar natural things, such as
blades of wheat, petals of daisies, silks of corn, and the like,
contain small quantities of distinct and separate compounds that have
not yet been recognized as such by even the most skillful chemists.
But even compounds such as are described in books on chemistry are
exceedingly numerous; and further, the chemical laws now known
suggest the possibility of producing _artificially_ a great multitude
of substances not yet recognized, and even more than have yet been
produced in the great laboratory of nature.
How it Happens that there is such a Variety.
By searching aright for the secret of the countless number and the
rich and splendid variety of beings that nature and art present to the
curious gaze of man, a comprehensive answer is at last obtained.
Forms of ordinary matter may be compared to great cathedrals, like
those of Cologne and of Milan, which have been growing for centuries
and which by the combined labor of artists and artisans have at
length become intricate and beautiful structures, the admiration and
delight of the beholder. Just as these arise from the combination
in a multitude of ways of a comparatively small number of original
and fundamental substances—like stone, brick, iron, copper, plaster,
glass, wood—so all things known to chemists are made up of a few simple
substances, either existing alone or in richly various combination.
The simplest substances when alone are called the _chemical elements_
or elementary substances; the things resulting when different elements
are united together are called _compounds_. Thus metallic iron is
one familiar example of a chemical element; the oxygen gas of the
atmosphere is another example. A piece of iron exposed to damp air soon
becomes changed to a mass of iron-rust. This rust is a compound; it is
made up of iron and oxygen united together.
In the light of what has been said the chemical elements assume a new
and grand importance: they are the individuals chosen by the Creator to
be the foundation stones and the essential constituents of the glorious
natural edifices of his handiwork.
Again when the elementary individuals unite together they do so by
reason of the interaction of many and complex forces which reside,
almost like soul and spirit, within the elements.
These last remarks suggest the twofold character of chemical study. It
involves, _First_, the examination of elementary substances and their
compounds. _Secondly_, it requires a consideration of the many general
and special _laws and forces_ which determine the various possible
combinations.
READING REFERENCES.
In general, the first-mentioned books in each group are those which are
most accessible and at the same time most serviceable. Some rare and
costly books are mentioned, for the benefit of persons who have access
to large libraries.
Chemistry, General and Applied, Serial Publications.
=Chemical= News. (William Crookes, Ed.) London. Weekly.
(Commenced 1860.)
=Popular= Science News and Boston Journal of Chemistry.
Boston. Monthly. (Commenced 1867.)
=Journal= of the Chemical Society. London. Monthly.
———— Index to foregoing. 1841-1872: pp. 263.
=Annales= de Chimie et de Physique. Paris. Monthly.
———— Table des Tomes I à XXX. (1841-1851.) Paris, pp. 134.
———— Table Analytique des Tomes XXXI à LXIX. 3d Series.
(1851-1863.) Paris. pp. 474.
———— Table des Noms d’Auteurs et Table Analytique des Matieres.
(1864-1873.) 4th Series. Paris. pp. 249.
=Berichte= der Deutschen Chemischen Gesellschaft. Berlin.
(Commenced 1868.) 20 parts per year.
=Wagner=, Johannes R. v.—Jahres-Bericht über die Fortschritte
und Leistungen der chemischen Technologie. Leipzig.
Annual. (Commenced 1855; last vol. had 1,332 pp.)
———— Index to foregoing. Vols. I-X.
———— ” ” Vols. X-XX.
Dictionaries of Chemistry, etc.
=Watts=, Henry.—Dictionary of Chemistry and the allied branches
of other sciences. 8 vols. London. 1865-1875.
=Storer=, Frank H.—First Outlines of a Dictionary of
Solubilities of Chemical Substances. Cambridge. 1864.
=Wurtz=, Ad.—Dictionnaire de Chimie, pure et appliquée.
3 vols. Paris. 1870.
=Fehling=, Hermann v.—Neues Handwörterbuch der Chimie.
A to Morphin. Braunschweig. 1871—now issuing.
General Treatises on Chemistry.
=Roscoe=, H. E., and Schorlemmer, C.—A Treatise on Chemistry.
London and New York. 1878. Vol. I, pp. 771; Vol. II, part I,
pp. 504, part II, pp. 552; Vol. III, part I, pp 724.
(Now issuing.)
=Cooke=, Josiah P., Jr.—Principles of Chemical Philosophy.
Boston. 1881.
=Gmelin=, Leopold (Henry Watts, Tr.)—Hand-Book of Chemistry.
Printed for the Cavendish Society. 14 vols. London.
1848-1860.
=Graham-Otto’s= Ausführliches Lehrbuch der Chemie. 6 vols.
Braunschweig. 1857.
=Schützenberger=, P.—Traité de Chimie générale. 3 vols.
Paris. 1880.
CHAPTER II.
THE ELEMENTARY SUBSTANCES.
On the following page is a list of the sixty-six elementary substances
now generally recognized as such. Their respective symbols and their
atomic weights, both in exact and approximate numbers, are also given.
These substances, then, nearly seventy in number, are those from which
are made up all material things now known to man. While it is not
necessary for any one to retain such a list in memory, every person who
desires any considerable knowledge of chemistry should be acquainted
with each name and the symbol attached to it, and should know something
of the natural sources and the properties of the substances designated.
Six Suggestions Conveyed by this Table.
A careful and intelligent reading of the list affords several important
suggestions. The following are some of them:—
_First. The elements are not very numerous._ They are in fact very few,
as compared with the countless number of substances they may form by
their proper combinations.
_Second. They are however sufficiently numerous to produce the many
substances recognized in nature._ For, consider how human language may
have many words and yet all these may be spelled out by combinations
of few letters. Some English dictionaries register over a hundred
thousand words, yet these are all made by the combinations of less than
thirty letters. Now it is easy to comprehend how the few letters of an
alphabet may be even still further combined in various ways so as to
produce additional words almost without limit: in a similar manner it
may be easily imagined that the sixty-five elementary substances have
ample capabilities for giving rise not only to the compounds now known,
but to yet more and more, almost without limit. It is true that the
chemist discovers that some of the chemical elements appear to have a
limited power of union, but in others he finds an apparently unbounded
capacity to form new arrangements and combinations.
-------------------------------------------------------------------
The Chemist’s Elementary Substances.
===========+==================+================+===============
Name | | Exact | Approximate
of Element.| Atomic Symbol. | Atomic | Atomic Weight.
| | Weight. |
-----------+------------------+----------------+----------------
Aluminum | Al | 27.0090 | 27.
Antimony | Sb (Stibium) | 119.9550 | 120.
Arsenic | As | 74.9180 | 74.9
Barium | Ba | 136.7630 | 136.8
Bismuth | Bi | 207.5230 | 207.5
Boron | B | 10.9410 | 10.9
Bromine | Br | 79.7680 | 79.8
Cadmium | Cd | 111.8350 | 111.8
Caesium | Cs | 132.5830 | 132.6
Calcium | Ca | 39.9900 | 40.
Carbon | C | 11.9736 | 12.
Cerium | Ce | 140.4240 | 140.4
Chlorine | Cl | 35.3700 | 35.4
Chromium | Cr | 52.0090 | 52.
Cobalt | Co | 58.8870 | 58.9
Copper | Cu (Cuprum) | 63.1730 | 63.2
Didymium | D | 144.5730 | 144.6
Erbium | E | 165.8910 | 165.9
Fluorine | Fl | 18.9840 | 19.
Gallium | Ga | 68.8540 | 68.9
Glucinum | G or Be | |
| (Beryllium) | 9.0850 | 9.1
Gold | Au (Aurum) | 196.1550 | 196.2
Hydrogen | H | 1.0000 | 1.
Indium | In | 113.3980 | 113.4
Iodine | I | 126.5570 | 126.6
Iridium | Ir | 192.6510 | 192.7
Iron | Fe (Ferrum) | 55.9130 | 55.9
Lanthanum | La | 135.5260 | 138.5
Lead | Pb (Plumbum) | 206.4710 | 206.5
Lithium | Li | 7.0073 | 7.
Magnesium | Mg | 23.9590 | 24.
Manganese | Mn | 53.9060 | 53.9
Mercury | Hg (Hydrargyrum)| 199.7120 | 199.7
Molybdenum | Mo | 95.5270 | 95.5
Nickel | Ni | 57.9280 | 57.9
Niobium | Nb | 93.8120 | 93.8
Nitrogen | N | 14.0210 | 14.
Osmium | Os | 198.4940 | 198.5
Oxygen | O | 15.9633 | 16.
Palladium | Pd | 105.7370 | 105.7
Phosphorus | P | 30.9580 | 31.
Platinum | Pt | 194.4150 | 194.4
Potassium | K (Kalium) | 39.0190 | 39.
Rhodium | Rh | 104.0550 | 104.1
Rubidium | Rb | 85.2510 | 85.3
Ruthenium | Ru | 104.2170 | 104.2
Scandium | Sc | 43.9800 | 44.
Selenium | Se | 78.7970 | 78.8
Silicon | Si | 28.1950 | 28.2
Silver | Ag (Argentum) | 107.6750 | 107.7
Sodium | Na (Natrium) | 22.9980 | 23.
Strontium | Sr | 87.3740 | 87.4
Sulphur | S | 31.9840 | 32.
Tantalum | Ta | 182.1440 | 182.1
Tellurium | Te | 127.9600 | 128.
Thallium | Tl | 203.7150 | 203.7
Thorium | Th | 233.4140 | 233.4
Tin | Sn (Stannum) | 117.6980 | 117.7
Titanium | Ti | 47.9997 | 48.
Tungsten | W (Wolframium) | 183.6100 | 183.6
Uranium | U | 238.4820 | 238.5
Vanadium | Va | 51.2560 | 51.3
Ytterbium | Yb | 172.7610 | 172.8
Yttrium | Y | 89.8160 | 89.8
Zinc | Zn | 64.9045 | 64.9
Zirconium | Zr | 89.3670 | 89.4
-----------+------------------+----------------+-------------------
_Third. The elements are mostly uncommon._ Only about one-sixth of
them possess names that are familiar to ordinary readers. Thus carbon,
copper, gold, iron, lead, mercury, nickel, silver, sulphur, tin, zinc,
are almost the only ones in the list that can be said to suggest
familiar things. Indeed some members of this list exist in the earth
in extremely small quantities; but man by his ingenuity and industry
has gathered up even these and brought them near to the hand of every
civilized being. Thus gold exists in the earth—so far as man has access
to the earth—in only very minute amounts; yet gold has a multitude
of common uses beside its employment in coinage. Various forms of
decorative art, like gilded lettering on books, afford familiar
examples. So also mercury, which in the ordinary thermometer is very
familiar to every one, exists in the earth in but minute amounts.
When the chemist examines still more narrowly the composition of the
terrestrial globe, he discovers an inequality yet more extraordinary
than that hinted at. Thus it appears that probably one-half of our
entire planet consists of a single substance (that is, oxygen) and
that one-quarter of it consists of another single substance (that
is, silicon). Since an amount equal to three-quarters of the earth’s
matter, by weight, is made up of but two elements, the remaining ones
must necessarily exist in much smaller proportions.
The following table, given by Roscoe and Schorlemmer, shows the average
composition of the earth’s crust—so far as it is accessible to human
investigation by means at present known:
Percentage Composition of the Earth’s Solid Crust (by Weight).
Oxygen, 44.0 to 48.7 per cent.
Silicon, 22.8 36.2 ”
Aluminum, 9.9 6.1 ”
Iron, 9.9 2.4 ”
Calcium, 6.6 0.9 ”
Magnesium, 2.7 0.1 ”
Sodium, 2.4 2.5 ”
Potassium, 1.7 3.1 ”
————— —————
100.0 100.0
According to this table, the sum total of the amounts of _all the
elements not mentioned_ may be estimated as less than one-tenth of
one per cent. of the whole. This statement is rendered all the more
striking when it is considered that in this minute fractional part must
be included all coal and all the useful metals, except iron.
Another authority[1] declares that it is probable that an amount equal
to ninety-nine one-hundredths of the entire weight of the solid, liquid
and gaseous matter of our globe, is made up of only thirteen elementary
substances. The elements referred to and their relative proportions are
approximately represented in the diagram following:
[1] Professor J. P. Cooke.
Diagram of the Composition of our Globe (by Weight.)
+---------------------+---------------------+------------+
| | SULPHUR, HYDROGEN, | |
| | CHLORINE, NITROGEN, | 53 OTHERS |
| +---------------------+------------+
| | POTASSIUM, SODIUM, |
| | IRON, CARBON, |
| SILICON, ¼ +----------------------------------+
| | ALUMINUM, } |
| | MAGNESIUM, } ⅙ |
| | CALCIUM, } |
+---------------------+----------------------------------+
| |
| |
| |
| OXYGEN, ½ |
| |
| |
| |
+--------------------------------------------------------+
_Fourth. Most of the elements are metals._ This may not appear to the
ordinary reader until he is informed that terminations in _um_, as in
case of aluminum, barium, cadmium, calcium and others are intended to
suggest that the substances so designated are metals. Most of the other
elements having names not terminating in _um_ are called non-metals.
_Fifth. Each chemical element has an atomic symbol_, an abridgement, in
some form, of its name.
_Sixth. Each chemical element has an atomic weight._ As the atomic
weight of hydrogen is 1, without any fraction, it is easily understood
that the weight of one atom of hydrogen is taken as the unit of the
system. An inspection of the numbers given shows that in many cases the
atoms weigh amounts that are very nearly exact multiples of the weight
of an atom of hydrogen.
READING REFERENCES.
Atomic Weights, Calculations of
=Becker=, George F.—Atomic Weight Determinations: a digest of
the investigations published since 1814. (Published as Part IV
of the _Constants of Nature_, in Smithsonian Miscellaneous
Collections, No. 358.) 1880.
=Clarke=, Frank W.—A Recalculation of the Atomic Weights.
(Published as Part V of the _Constants of Nature_,
in Smithsonian Miscellaneous Collections, No. 441.) 1882.
———— Am. Chem. Jour. iii, 263. (1881.)
Atomic Weights, Periodicity of
=Meyer=, Lothar.—Chem. News, xli, 203.
Atomic Weights, Mendelejeff’s Law of
=Am.= Chem. Jour.—iii, 455.
=Cooke=, J. P.—Chem. Philosophy, p. 265.
=Wurtz=, Ad.—Atomic Theory, p. 154.
Atomic Weights, Arithmetical Relations of
=Hodges=, M. D. C.—Silliman’s Journal, 3d Ser. x, 277.
=Newlands=, J. A. R.—Chem. News, xlix, 198.
Atomic Weight of Oxygen.
=Odling=, W.—Jour. of Chem. Soc. of London, xi, 107.
Atomic Weight of Thallium.
=Cookes=, Wm.—Chem. News, xxix, 14, 29, 39, 55, 65, 75, 85,
97, 105, 115, 126, 137, 147, 157.
Atomic Weights, Prout’s Hypothesis of
=Cooke=, J. P.—Chemical Philosophy, 270.
=Clarke=, F. W.—Am. Chem. Journal, iii, 272. (1881.)
=Gerber=.—Silliman’s Journal, 3d Ser. xxvi, 236.
Atoms, Absolute Weight of
=Annaheim=, J.—Jour. of Chem. Soc. of London, xxxi, 31.
Elements, Defunct
=Bolton=, H. C.—American Chemist, i, 1.
Elements, Suggestions that Elements are Compound.
=Lockyer=, J. N.—Nature, Jan’y 2 and 9, also Nov. 6, 1879.
=Hastings=, C. S.—Criticism of above. Am. Chem. Jour., i, 15.
CHAPTER III.
NAMES AND SYMBOLS OF ELEMENTS.
Any history of the chemical elements, distinctly points to the enormous
stride which chemical discovery has taken within the last hundred
years. The dawn of this period was marked by many most important
results: among these may be mentioned the detection of the elementary
gases, oxygen, hydrogen and nitrogen. The light which these great
events threw upon the future of the science enabled the chemists
of that early period to perceive that the number of new compound
substances then discovered, and likely soon to be discovered, called
for a multitude of new terms. In 1787 the eminent French chemist,
Lavoisier, in committee with Guyton de Morveau and others of their
chemical associates of the French Academy, suggested a system by
which a considerable number of chemical compounds, both then known
and thereafter to be discovered, might be provided with names at
once convenient and suggestive. This system, slightly modified and
considerably extended—to accommodate the yet more widely expanding
needs of the science—affords the basis of the chemical language of
to-day.
A Few Principles of Chemical Language.
It is proposed to explain here a few of the first principles of
chemical nomenclature and notation; that is, to present a few of
the rules by which significant and useful _names and symbols_
are provided. These will be found to meet the wants of hitherto
inaccurately known substances, and even of those formerly unknown.
_First; the names of elementary substances long known are retained._
Thus, gold and silver are metals that were known in the earliest
historical periods, if not in prehistoric times; their names,
therefore, still remain in use.
_Second: the discoverers of new elementary substances assign the
names._ In so doing, they usually invent a name that suggests some
_fact_ connected with the substance itself. Thus the name nitrogen is
derived from two Greek words (νίτρον, _nitron_, mineral alkali, and
γεννάω, _gennao_, I produce) carrying the suggestion that the gas is
one of the constituents of nitre. The name hydrogen is derived from two
Greek words (ὕδωρ, _hydor_, water, and γεννάω, _gennao_, I produce,)
indicating that wherever water exists, hydrogen is an essential
constituent of it. So the name chlorine is derived from a Greek word
(χλωρός, _chloros_, green,) which reminds the chemist of the fact that
chlorine gas possesses a greenish color. The substance oxygen, however,
was named in a different manner. Its name is derived from two Greek
words (ὀξύς, _oxys_, acid, and γεννάω, _gennao_, I produce,) signifying
a generator of acids. It appears then, that in this case the name is
based, not on an easily verified fact, but upon a _theory_, current
when oxygen was discovered, of the action of the substance in question.
In a certain sense a name thus formed may be considered ill-advised.
Thus in the case in hand it has turned out that while oxygen is a
constituent of a majority of known acids, it is not essentially an
acidifying substance: many acids are known that contain no oxygen at
all, and again there are a multitude of compounds containing oxygen
that are not acids in any proper sense.
_Third; newly discovered metals are usually given names which, while
they suggest some property of the substance, have in addition the
termination, um._ Thus the metal thallium derives its name from a Greek
word (θάλλος, _thallos_, a green twig,) which carries the suggestion
of the fact that thallium and its compounds when highly heated evolve
light of a delicate green color. Again caesium, a newly discovered
metal, has a name derived from a Latin word (_caesius_, blue,) which
refers to the fact that caesium and its compounds when highly heated
afford light of a blue color. The termination _um_ is used for metals,
after the analogy of the Latin language which usually has its names of
metals end in _um_. Indeed the chemist often makes use of the Latin
names of even those metals that have been long known by more familiar
ones. Thus for gold the Latin word _aurum_ is used, for silver the
Latin word _argentum_, for lead the Latin word _plumbum_; it will
be seen later that slightly modified forms of these names are very
frequently employed when compounds of these metals are to be designated.
[Illustration: ANTOINE LAURENT LAVOISIER:
Born in Paris, August 26th, 1743; died on the scaffold in Paris, May
8th, 1794.]
Symbols used for Atoms.
Each elementary substance, or, strictly speaking, the minute quantity
of it represented by the term one atom, may be designated in brief by a
special letter or short group of letters called the symbol. The usual
symbol is the initial letter of the native or the Latin name of the
substance. Upon examining the list of elementary substances at page 13,
it will be seen that the following nine of the names begin with the
letter _C_; of course, therefore, in eight cases at least, the symbol
must contain an additional distinguishing letter:
Accordingly C indicates one atom of Carbon;
Ca ” ” Calcium;
Cd ” ” Cadmium;
Ce ” ” Cerium;
Cl ” ” Chlorine;
Co ” ” Cobalt;
Cr ” ” Chromium;
Cs ” ” Caesium;
Cu ” ” Copper (Latin word _cuprum_).
It also appears that in the case of metals, like iron and copper, known
to the ancients the symbols used are derived from the Latin names. The
use of these symbols made from letters—and therefore called literal
symbols, from the Latin word _litera_, a letter—will become apparent
as the reader advances; but it is easily perceived that they afford a
convenient abridgement of the longer titles of the elements.
The use of literal symbols as an abridgement of the chemical
nomenclature was first proposed by Berzelius, a Swedish chemist, whose
eminence in every branch of the science was such that the suggestion
here referred to constitutes one of the least of the many and
substantial grounds on which his fame rests.
READING REFERENCES.
Alchemy.
=Rodwell=, G. F.—The Birth of Chemistry. London. 1874.
=Draper=, J. C.—Amer. Chemist, v, 1.
=Mackay=, Charles.—Memoirs of Extraordinary Popular Delusions.
2 v. London. 1869. i, 93.
Berzelius.
=Wöhler=, F.—Early Recollections of Berzelius.
Am. Chemist, vi, 131.
Chemistry, History of
=Thomson=, Thomas.—History of Chemistry, 2 v. London. 1830.
=Hoefer=, F.—Histoire de la Physique et de la Chimie. Paris.
1872.
=Kopp=, Hermann.—Geschichte der Chemie. 4Th. Braunschweig.
1843.
———— Die Entwickelung der Chemie in der neueren Zeit. München.
1873.
=Bolton=, H. C.—Chem. News. xxxii, 36, 56, 68.
=Liebig=, J. v.—Familiar Letters on Chemistry.
=Whewell=, Wm.—History of the Inductive Sciences. 2 v.
New York. 1875. ii, 259.
[Illustration: JONS JAKOB BERZELIUS:
Born in East Gothland (in Sweden), Aug. 20, 1799; died Aug. 7, 1848.]
Lavoisier,
=Thomson=, Thomas,—History of Chemistry. 2 v.
London. 1830. ii, 75.
=Figuier=, L.—Vies des Savants Illustres du xviii siècle,
444.
=Brougham=, H.—Lives of Philosophers of the time of
George III. Edinburgh, 1872. 290.
Nomenclature.
=Morveau=, Guyton de.—Memoire sur les denominations chimiques,
la necessité d’en perfectionner le système, les règles pour y
parvenir, suivi d’un tableau d’une nomenclature chimique; Dijon.
1782.
=Lavoisier=, de Morveau, Fourcroy, Baumé, Hassenfratz, Adet
and others. Méthode de nomenclature chimique. Paris. 1787.
(The Boston Athenæum Library contains a copy of this work.)
CHAPTER IV.
CLASSIFICATION OF THE ELEMENTARY SUBSTANCES.
In speaking of the elementary substances some of them have been
referred to as metals. What then is the exact idea conveyed by this
designating term? Everyone can readily picture in his mind some metal
or metals like gold, silver, tin, zinc and others that have certain
common characteristics, such as great weight, and the peculiar
brilliancy and power of reflecting light which is described as metallic
lustre. Another well marked and widely recognized characteristic at
once thought of is the facility with which the substances ordinarily
known as metals maybe beaten or rolled into thin layers. This property,
called malleability, (a word derived from the Latin word _malleus_, a
hammer,) is not possessed in any striking degree by substances other
than metals. Thus sulphur is not malleable: quite the contrary, it
is very brittle. Charcoal, which consists mostly of the elementary
substance called carbon, is likewise not malleable; neither of these
last two substances would be likely to be considered by even an
ordinary observer as metals. In fact they are classed as non-metals by
the chemist. This division of the elementary substances into metals and
non-metals is dwelt upon, not because it can be called a very important
one, but because it is widely used in works on chemistry and because
in deciding to which of these two classes a given substance belongs,
ultimate dependence must be placed upon its chemical characteristics
rather than upon its mere mechanical properties.
The Meanings Associated with the Term Metal.
The principal properties referred to are best presented in three groups.
_First. Metallic Properties Associated with Mechanical Relations._
An elemental substance accepted as a metal must possess the property
of existing in a solid condition; a weight rather greater than that
of most well-known substances; considerable hardness, malleability,
ductility (that is the capability of being drawn out into fine wire).
_Second. Metallic Properties Associated with Physical Relations._
A metal should possess the metallic lustre; the power called opacity,
by reason of which it does not allow light to pass through it; the
noticeable capability of allowing heat to flow in it, called the power
of conducting heat; the ready capacity for allowing the electric
current to flow in it, called good conducting power for electricity.
_Third. Metallic Properties Associated with Chemical Relations._
A metal should possess the power and the tendency to readily form a
chemical union with oxygen; the chemical power to act upon compounds
containing hydrogen, in such a way as to turn the hydrogen out, and
take its place in the old compound and thus form a new one; the
relationship towards the electric current such that when the element
is subjected to the galvanic battery, it tends to gather about the
negative pole—in consequence of which characteristic it is usually
called electro-positive.
But while no known metal appears to possess the entire range of
properties with which in thought the ideal one is endowed, every
substance classified as a metal should possess many of them.
An illustration of what has been said may be found in metallic mercury.
From the fact that under ordinary conditions it is a liquid it is plain
that mercury must lack certain of the metallic properties referred
to; that is, it does not possess the solid form, it does not possess
hardness, it does not possess malleability, it does not possess
ductility. Yet if it is cooled to a low temperature—about forty degrees
below zero—it freezes, in other words becomes solid; then it possesses
many of the distinctly metallic features that it necessarily lacks when
in the ordinary liquid condition. Of course this liquid condition is a
mere incidental circumstance, due to the temperature which ordinarily
prevails upon our earth. If our ordinary temperature were slightly
lower than forty degrees below zero, mercury would then be commonly
known as a solid, hard, lustrous, heavy, malleable metal—capable of
course of melting with a slight accession of heat.
As a further illustration, in a somewhat different direction, mention
may be made of the metal lithium. This substance cannot be called
heavy, since it is lighter than water; indeed it is the lightest solid
known. But on the other hand it possesses in a striking degree those
chemical features of metals, such as strong affinity for oxygen and
tendency to combine with it, which have already been detailed in our
definition of the ideal metal.
The Term Non-metal.
The term non-metal is suggestive of a negative idea, and not of any
definite or positive one. In fact it is intended to intimate that
elementary substances of this class are those which do not properly
belong to the other. Sulphur and carbon have been already alluded to
as examples of non-metals; other non-metals, such as oxygen, hydrogen,
nitrogen and chlorine among the gases, bromine, a liquid, and iodine,
antimony, phosphorus among solids, are far less familiarly known to
most persons.
READING REFERENCES.
Elements, Classification of
=Williamson=, A. W.—Jour. of Chem. Soc. of London, xvii, 211.
Chemical Theory.
=Cooke=, Josiah P., Jr.—The New Chemistry. New York. 1874.
=Remsen=, Ira.—Principles of Theoretical Chemistry.
Philadelphia. 1883.
=Tilden=, William A.—Introduction to the Study of Chemical
Philosophy.
=Wurtz=, Ad. (Henry Watts, Tr.)—History of Chemical Theory.
London. 1869.
CHAPTER V.
COMPOUND SUBSTANCES.
In a previous chapter a list of elementary substances has been given.
All other matters known are compounds. From what has been said already,
it is evident that the compounds are very numerous, indeed that there
is practically no limit to the number of possible ones. These compounds
are all made up by the union of elementary substances in obedience to
the peculiar chemical forces that reside within them. Some compounds
have only two kinds of elements: they are called binaries. Some
compounds have three kinds of elements: they are called ternaries.
Other compounds may have four, five, six, or even more kinds of
elements grouped together to form one sort of substance. In this place
reference will be made principally to binaries and ternaries—that is to
the compounds of the simpler forms of constitution.
Examples of Binary Compounds.
In discussing binaries it will be well to give at the outset three or
four examples for the purpose of illustration.
_First._ The gas known as hydrogen and the gas known as chlorine
have the power of combining chemically and producing an entirely new
compound, a compound different from hydrogen and different from
chlorine yet containing portions of each of them. This compound is a
binary since it consists of but two kinds of elements. It has several
names, one of which is _hydric chloride_. The chemist frequently
represents what is evidently the smallest possible quantity of this
substance, and also its exact composition, by the expression
H Cl.
It is plain that this expression means a minute portion of substance
formed by the union of one atom of hydrogen, (expressed by H,) and one
atom of chlorine, (expressed by Cl).
_Second._ When sulphur burns in the air, it produces a blue flame.
At the same time a new and peculiar gas is formed which is easily
recognized by its choking odor, similar to that given off by a burning
sulphur match. Now this odor is one of the properties of a new compound
that has been formed: a compound different from sulphur, different from
oxygen, yet containing them both and produced by the union of them. The
compound is a binary because it contains but two kinds of elements. It
is called _sulphur dioxide_. The name is intended to suggest that there
are two atoms of oxygen to one of sulphur in the compound. This idea is
further conveyed by the abridged system of notation so commonly used
by chemists. Thus by this system the smallest possible quantity of the
compound in question is expressed as follows,
SO₂.
In this expression it is very plain that S stands for one atom of
sulphur, and O₂ for two atoms of oxygen.
_Third._ But sulphur may be made to combine with a still larger amount
of oxygen than it takes when it simply burns in the air. Then it forms
a compound called _sulphur trioxide_. This is still a binary, since it
contains nothing but sulphur and oxygen, that is only two elementary
substances. Expressed in the briefer form the smallest quantity of this
compound may be represented by the formula,
SO₃.
This expression means a compound arising from the union of one atom of
sulphur and three atoms of oxygen.
_Fourth._ When lead is heated to the melting point it is observed to
become coated with a constantly increasing mass of a kind of ashes. A
pound of the lead when heated in this way produces considerably more
than a pound of dross. The formation of this dross is explained by
the fact that when lead is heated it really burns, though of course
the rapidity of the burning depends upon the amounts of heat and air
to which the lead is subjected. Evidently the lead, in burning, has
something added to itself. That something is a gas which is ever
present in the atmosphere and which is called oxygen. The dross is a
chemical compound of lead and oxygen. It is called _plumbic oxide_, and
its smallest quantity is represented by the formula,
PbO.
In this formula it is easy to see that Pb stands for an atom of lead
(whose Latin name is _plumbum_), and O for an atom of oxygen. The dross
then is a binary compound.
A multitude of such examples of binary compounds might be given;
probably those already cited are sufficient for the present. It
will be advantageous to the reader to carefully learn the names and
the formulas of the binary compounds thus far given, since they are
selected examples which may be used again further on.
Examples of Ternary Compounds.
The ternary compounds are those which consist of three kinds of
elements; of course they are more complicated in structure than the
binaries. This fact, however, must not deter the reader from the
attempt to understand them at the outset, for the principal ternaries
are acids and salts, and everyone knows that acids and salts are among
the most important compounds which the chemist has to employ.
As examples of ternary acids mention will be made of two of the
principal ones used by the chemist.
And first, _nitric acid_ is a compound of hydrogen, nitrogen and
oxygen. The formula of the smallest individual portion of it is
HNO₃.
These letters signify that nitric acid contains one atom of hydrogen,
combined with one atom of nitrogen and three atoms of oxygen. Now this
nitric acid forms a great many salts. A simple example may be found in
that one containing silver. Thus when nitric acid and silver are warmed
together, either a part or the whole of the silver dissolves. A new
substance is produced which is commonly called nitrate of silver. By
the chemist it is oftener called argentic nitrate. Its solution may be
dried into the form of a white crystalline substance, one that has long
been accepted as a member of the class of salts. Its formula is
AgNO₃.
It is plain that this last formula is employed as a short way of
expressing that the salt is a compound of more than one kind of
element—of three kinds in fact—and that these elements are in the
proportions of one atom of silver, one atom of nitrogen, and three
atoms of oxygen.
Promise was made to refer to two important acids; _sulphuric acid_
is the second one. Commercially this substance is by far the most
important of all the acids. Indeed its manufacture is one branch of the
greatest chemical industry devised by man—the alkali trade. Evidently
it is important that the chemist should be thoroughly acquainted
with sulphuric acid, with its composition, its formula, its way of
chemically acting on other substances, and the things or products that
it gives rise to when it has opportunity so to act. Now sulphuric acid
has the formula
H₂SO₄.
This formula means that sulphuric acid is a ternary, being made up of
three different kinds of elements, namely two atoms of hydrogen, one
atom of sulphur and four atoms of oxygen.
Further sulphuric acid forms a multitude of salts. Thus it forms one
containing silver. This is commonly called sulphate of silver, though
the chemist generally calls it argentic sulphate. The formula of
argentic sulphate is
Ag₂SO₄
When this formula is firmly acquired by the reader so that he can
readily compare it with others already mentioned, a certain simple and
distinct relationship may be traced. Thus comparing
Argentic sulphate, Ag₂SO₄
with Sulphuric acid, H₂SO₄
it is evident that in the one, two atoms of silver have taken the
places of two atoms of hydrogen that appeared in the other. And such
is usually the case: when silver takes the place of hydrogen, it does
so, atom for atom. Indeed argentic nitrate, AgNO₃, already described,
illustrates this fact. It is a compound product closely related to
nitric acid, HNO₃, the only difference of construction being that here
also one atom of silver has taken the place of one atom of hydrogen.
The Purpose of this Chapter.
The purpose of this chapter has been to suggest a few facts respecting
the nature of chemical compounds and also to show how the science of
chemistry employs its peculiar language both in its longer and shorter
forms. This language is very comprehensive. In fact it is too elaborate
for full explanation here. The plan contemplated is to give at this
point a few hints as to its nature and scope, and to develop it only so
far as may be necessary to the succeeding stages of our progress.
It is proper to suggest at this point that no single scientific man—nor
society of them—can _enforce_ the use of any particular words upon
the great body of chemists. For this reason, as well as for others,
there still prevails the use of different chemical names for the same
substance. Thus the compound of hydrogen and chlorine first referred to
as represented by the formula HCl, has at least four widely used names:
_first_, a name merely suggestive of its component parts, that is
hydric chloride; _second_, names which suggests something in addition
to its component parts, namely that it is an acid, thus it is called
both chlorohydric acid and hydrochloric acid; _third_, an old fashioned
name, which still retains its hold upon the commercial world, namely,
muriatic acid.
This same general principle applies to a great many other substances,
and while it is true that it thus increases the number of names
in the chemical language, it likewise incidentally enriches that
language. For in many cases it has come to pass, little by little,
that these different names are appropriated to slightly differing
forms of the same substance, and so the name employed often conveys
to the intelligent chemist as definite a shade of meaning as do the
different synonyms used in the descriptions of every-day affairs by
any accomplished author. A single example will elucidate this point.
The term oil of vitriol would usually be defined as meaning sulphuric
acid. But the words sulphuric acid convey, strictly speaking, the same
meaning as the formula
H₂SO₄
This latter substance, however, is of very rare occurrence alone: it is
usually associated with varying quantities of water, and is then spoken
of as sulphuric acid of varying degrees of dilution. Now in commerce
the term oil of vitriol has come to be appropriated exclusively to that
dilution consisting of about
89 per cent. of sulphuric acid, H₂SO₄
with 11 per cent. of water, H₂O,
both taken by weight.
READING REFERENCES.
Notation, Chemical
=Frankland=, E.—Experimental Researches in Chemistry. 3.
London. 1877.
=Williamson=, A. W.—Jour. of Chem. Soc. of London, xvii, 421.
=Frankland=, E.—Loc. cit. xix, 372.
=Madan=, H. G.—Loc. cit. xxiii, 22.
=Council= Chem. Soc. of London.—Instructions to Abstractors
from Current Publications. (1879.) Chem. News. xlvii, 15.
CHAPTER VI.
THE CONSTRUCTION OF SUBSTANCES.
In order to understand the chemical construction of substances it is
necessary to consider three terms much used by the chemist: these terms
are,
Mass,
Molecule,
Atom.
Evidently the words relate to three grades of magnitude in which matter
is capable of existing; it is equally plain that of the series the mass
represents the largest individual portion of substance, and the atom
the smallest, while the molecule represents the intermediate one.
The Chemical Use of the Term Mass.
Whoever looks about him sees substances existing in masses. This is
true of vast mountain chains and equally true of the smallest grains of
matter that are recognized as the humblest components of those peaks.
But the smallest of these _visible_ masses is made up of particles
still more minute—yet perhaps of precisely the same kind. For the
chemist possesses means of subdivision of substances by which he may
make them into minute fractional parts that are measurable and are all
just alike, and he may continue this process long after the portions
have sunk below the reach and range of ordinary vision. A lump of pure
sugar as big as a cubic inch may be _mechanically_ divided by any
one into many smaller ones, each little one being easily recognized
by the ordinary senses as possessing the sweetness, the crystalline
construction, the whiteness, the solidity, the brilliancy, the power
of dissolving in water and indeed a great many other well-known
characteristics that pertain to sugar. But the chemist is able to
continue the subdivision of the sugar much further. This he does by
recourse to processes not exactly mechanical though closely allied to
them: by processes often called _physical_ as distinguished from purely
mechanical ones. He may thus reduce the sugar to fragments of such
extreme minuteness that while they do not impress our senses as larger
portions do, yet each fragment is capable of displaying to a competent
scientific observer the certain and sure chemical properties that
always belong to sugar, whether in large lumps or in small ones, and
which in fact belong to nothing but sugar.
Speaking generally, all particles producible by mechanical subdivision
are masses, while the same is true of most particles producible by
physical subdivision.
The Chemical Use of the Term Molecule.
But there is a point where any attempt at further scientific
subdivision results in a new and startling change: at this stage the
last individual that can properly be called sugar is dissected and
loses entirely the characteristics of sugar. The fragments produced by
the wreck of the last particle are of a new kind. They are
portions of carbon,
portions of hydrogen,
portions of oxygen.
This last particle of sugar is separated into its ultimate constituents
only by _chemical_ processes. This last particle before it is broken up
is called the _molecule_, the word meaning a little portion. The single
individual thing it refers to cannot be detected by the eye, nor can it
be in any way appreciated except by scientific means. But a chemical
change of _the last multitude of molecules at once_, is practicable
to everybody, and it is to a certain extent recognized by every one
who heats sugar until it turns to a charred mass. This charred mass is
mainly carbon—one of the components of the now ruined sugar—and it is
very unlike sugar in every way. The chemist can show that when sugar is
charred, the oxygen and the hydrogen go off mostly in the form of gases
or vapors, and that on this account they escape detection at the hands
of all ordinary observers.
The Chemical Use of the Term Atom.
It appears then that the chemist is able to subdivide molecules into
smaller parts. But he finds that further division is at a certain stage
forbidden him. He can take the oxygen out of the sugar, but he cannot
take anything but oxygen out of oxygen; he can take hydrogen out of
sugar, but he cannot take anything but hydrogen out of hydrogen; he can
take carbon out of sugar, but he cannot take anything but carbon out of
carbon.
As a result of all chemical study of common sugar the chemist has fixed
upon the following as expressing most closely the facts as he knows
them:
The formula
of one molecule of pure cane sugar, is
C₁₂H₂₂O₁₁
The chemical formula of any substance expresses much more than the
reader would at first imagine. Thus the formula C₁₂H₂₂O₁₁ conveys at
once to the chemist a series of facts, some of which may be amplified
as follows:—one molecule of sugar contains three kinds of substance:
carbon, hydrogen and oxygen:—each of these kinds of matter exists in
the molecule in separate minute portions such as in the present state
of human knowledge are divisible only in a limited way: thus the carbon
of one molecule of sugar is divisible into twelve parts, _and no
further_;
the hydrogen of one molecule of sugar is divisible into
twenty-two parts, _and no further_;
the oxygen of one molecule of sugar is divisible into
eleven parts, _and no further_.
Definition of the Term Atom.
Now at last the atom has been reached. It is that portion of any kind
of matter that is to human beings indivisible _in fact_. It has already
been stated that there are only sixty-six different kinds of atoms,
it appears then that there are only sixty-six kinds of matter that at
present cannot be chemically subdivided into different components.
It is true that some persons consider that certain intricate chemical
processes suggest that what have been here called indivisible atoms
are themselves really capable of yet further decomposition. Without
attempting here to sustain or to demolish this proposition or to say
what the future of chemical investigation may reveal, it may be safely
remarked that adequate proof has not yet been offered of the ability
of any one to successfully accomplish a decomposition of the sixty-six
atoms enumerated.
Plainly then just as bricks may be made into a building, and a series
of buildings may make a city, and a series of cities may exist in a
state, so atoms may combine together to form molecules, and molecules
may cohere together to form a mass, and visible masses may be placed
side by side and give rise to the ordinary objects recognized about
us. True the comparison suggested is not strictly carried out in all
particulars. But the difficulty not a serious one: for a city _might_
contain a multitude of houses each one so similar that no difference
could be distinguished between them, just as a mass of sugar does
in fact contain molecules of which each one is so like its neighbor
that the most refined chemical methods discover no difference between
them. Again these same houses _might_ be composed of combinations of
brick and other materials differing among themselves, but closely
corresponding in every house. So the molecule of sugar does contain
atoms of carbon, hydrogen and oxygen, the atoms of one kind differing
distinctly and absolutely from the atoms of the other kind.
But here the parallelism seems to cease. For while all bricks and
other components of a building are capable of being split into smaller
portions, the atoms composing the molecule are found by the chemist to
be absolutely indivisible in the present state of knowledge.
Employing still further the illustration already in hand it may be
added that just as the walls of a dwelling might contain bricks either
of the same kind as to their color, shape and weight, or else differing
in these or other respects, so a molecule may be a little group of
atoms of the same kind, or it may be a group of atoms of different
kinds. Thus the hydrogen gas molecule is composed of two atoms each
just alike, and each being hydrogen. This molecule is represented by
the formula
H₂ or H—H.
So a molecule of chlorine gas is composed of two atoms each just alike
and each being chlorine. This molecule is represented by the formula
Cl₂ or Cl—Cl.
Everything Built up of Atoms.
Now each of the sixty-six elementary substances has molecules composed
of atoms, and each molecule of a given element is composed of atoms
of the same kind. And further all the vast and countless myriad of
compound substances, whether buried in the heart of the solid earth,
whether drifting in the wandering courses of the ocean’s currents,
whether floating in the airy mass which is wrapped about our globe,
whether components of distant planets of unknown constituents, whether
parts of the seething mass which pours its volcanic torrents millions
of miles out from the surface of our central sun—all these substances
are constructed, so far as we know, of inconceivably minute atoms of
varying kinds bound together by chemical attraction into molecules, the
molecules being piled one upon another into those masses whose reaction
our dull senses can appreciate.
Atoms and Molecules Manifest Chemical Affinity.
But to the chemist, atoms, molecules and masses possess an interest of
another kind. Each atom and each molecule is endowed with an invisible,
occult power called _chemical affinity_. This power acts like an unseen
spirit possessed of likes and dislikes. By reason of it an atom of
hydrogen for example instantly binds itself to an atom of chlorine
whenever opportunity offers, but will never, even under the most
favorable circumstances, combine with an atom of gold.
Finally this attractive force is a kind of energy of which no true
explanation can be offered. All that human beings can do is to
attentively study it as it manifests itself in the relations of
elementary substances and compound substances one toward another.
Indeed one of the principal offices of chemistry is to study these
relationships as they develop. It is the multitude of possible
relationships and actions of which the numberless substances known are
capable, that gives to chemistry its great scope and variety and that
makes it such a vast field for experiment, for discovery of facts, and
for industrial application of them.
READING REFERENCES.
Atoms and Molecules.
=Barker=, G. F.—Amer. Chemist. Nov. 1876. p. ms. 164.
=Stoney=, Johnstone.—Phil. Mag. xxxvi, 141.
=Clerk=-Maxwell, J.—Encyclopædia Britannica,
_article_ Atoms.
———— Theory of Heat. New York. 1872.
=Thompson=, Sir Wm.—_Nature_. Mch. 1870.
=Tait=, P. G.—Recent Advances in Physical Science. London.
1876. p. 283.
=Mayer=, A. M.—Lecture Notes on Physics. p. 52.
=Cooke=, J. P.—The New Chemistry. New York. 1881. pp. 29-43.
———— American Cyclopædia, _article Molecule_.
CHAPTER VII.
HOW CHEMICAL AFFINITY WORKS.
It is an interesting fact that elements and compounds manifest an
exceedingly great variety of tendencies to combination. Fragments
of matter, so small that no eye perceives them, have, wrapped up in
themselves, a multitude of determinate powers. A given atom as of lead,
for example, will very readily combine with oxygen and with some other
substances, but it seems to absolutely refuse to combine with nitrogen.
So hydrogen will combine very readily with chlorine and with many other
elements, but it refuses to form any union with silver and with many
other elementary substances. It cannot be called a whim that determines
the kind of element or its amount that a certain substance will combine
with, though the likes and dislikes of atoms are in this respect
exceedingly marked and even incomprehensible. But however impossible
it may be _to explain_ an element’s friendly or unfriendly deportment
toward another, it is possible in each case to learn the facts with
certainty, for each atom possesses its true individuality and is always
constant and consistent in its affinities and hates.
It is the purpose of this chapter to present in an orderly manner some
of the peculiarities of this mysterious power of chemical affinity.
First. Each Kind of Atom Has Its Peculiar Chemical Affinities.
Chemical affinity seems to reside within the atom as a permanent, ever
present and guiding energy. Thus while iron oxidizes readily—that is
manifests under a multitude of common conditions a willingness to
combine with oxygen and form a new compound called oxide of iron, and
well-known under the name of iron-rust—gold on the other hand oxidizes
unwillingly; indeed in order to get it to combine with oxygen it must
be coaxed by means of circuitous and carefully planned devices. But
these atoms are always consistent in their action, for iron under any
and every condition oxidizes more readily than gold does.
Second. Chemical Affinity Acts Only Under Favorable Conditions.
While chemical action often works with most intense energy it does so
only when certain outside and incidental conditions are favorable.
Thus carbon has under certain conditions an affinity for oxygen and
manifests its tendency to combination, with an intensity that is
scarcely surpassed. In order however to awaken and vivify the dormant
inclination it must be stimulated by certain definite and favorable
conditions; the most important of these conditions is a certain
amount of warmth. The stores of fuel in our cellars—the coal and
the wood and all other combustible things—are surrounded by great
quantities of oxygen which winds its way, with every slightest stir
of the mobile air, in and out through all the crevices that the fuel
affords, passing continually in the immediate neighborhood of ample
quantities of atoms of carbon. But it does not ordinarily unite with
them. Subject the whole or any portion of these combustible things to
a slight rise in temperature—then the atoms of oxygen and the atoms of
carbon seem to arouse themselves from repose: they unite in friendly
and firm grasp, and what is called chemical union takes place. To the
ordinary observer the heat that is produced is the most notable sign of
this kind of combination. The chemist, however, discovers a yet more
conclusive evidence, for he finds that several kinds of new molecules
have been produced; one of these kinds, for example, is expressible by
the name carbon dioxide and by the formula CO₂. Evidently this formula
means that each atom of carbon has united with two atoms of oxygen. In
this familiar example heat is the agency that stimulates the atoms to
a display of the chemical force that previously was slumbering within
them.
Light and the electric current and the vital forces of animals and
plants, though acting in a manner less familiar to us, are energizers
of chemical affinity and all have their proper influence to make atoms
join in union; indeed in some cases they make atoms burst from each
others bonds and fly away to more congenial conditions.
Third. Each Atom Has a Certain Equivalence or Atom-Fixing Power.
The chemist also recognizes each atom as possessing certain peculiar
numerical preferences in its combinations; a manifestation of chemical
affinity called equivalence. Thus when carbon burns in a stove, by
reason of the air passing by it on its way to the chimney, it seizes
upon some of the oxygen atoms and _binds a definite number of them_
to itself. If there is much air, each atom of carbon of the millions
present, picks out two atoms of oxygen from the air; if there is but
little air, each atom of carbon has to be satisfied with one atom of
oxygen. Now in these two cases of course different substances are
formed. The first, whose composition is represented by the formula
CO₂, has already been spoken of as carbon dioxide. To the other, whose
composition is represented by the formula CO, is applied the name
carbon monoxide. Here then we see that _the same atom may sometimes
combine with two atoms of oxygen and sometimes with only one_.
Further the chemist knows four simple and familiar compounds whose
molecules illustrate very strikingly the difference of equivalence of
_different atoms_. These compounds are the following:
Chlorohydric acid (Hydric chloride), HCl or H—Cl
H— }
Water (Hydric oxide), H₂O or } O
H— }
H— }
Ammonia gas (Hydric nitride), H₃N or H— } N
H— }
H— }
Marsh gas (Hydric carbide), H₄C or H— } C
H— }
H— }
It has been found advisable to adopt the atom of hydrogen as the
standard of equivalence or atom-fixing power. It is plain that by
this method of comparison the atom chlorine may be said to have the
equivalence _one_, since it combines with one atom of hydrogen. And so
the atom oxygen may be said to have the equivalence _two_, since it
combines with two atoms of hydrogen. And the atom nitrogen may be said
to have the equivalence _three_, since it combines with three atoms
of hydrogen. And the atom carbon may be said to have the equivalence
_four_, since it combines with four atoms of hydrogen.
The language of chemistry sometimes presents the same observed facts
in a slightly different form, somewhat as follows: Chlorine is said
to have one point of attraction and is called a monad (a term derived
from the Greek word μονάς, _monas_, a unit). Oxygen is said to have
two points of attraction and is called a dyad (a term derived from the
Greek root δυάς, _dyas_, two). Nitrogen is said to have three points of
attraction and is called a triad (a term derived from the Greek word
τριάς, _trias_, a group of three). Carbon is said to have four points
of attraction and is called a tetrad (a term derived from the Greek
word τετράς, _tetras_, four).
While hydrogen as the basis of the system has the uniform equivalence
one, and is always a monad, and oxygen its close friend and ally has
always the equivalence two, and is always a dyad, most other elements
have some variety of equivalence. Thus chlorine has at different
times different equivalences, sometimes _one_, sometimes _three_, or
_five_, or _seven_. So nitrogen has at different times the different
equivalences, _one_, _three_, _five_. So carbon has sometimes an
equivalence _two_, sometimes _four_.
Fourth. Chemical Changes Neither Create nor Destroy Matter.
When chemical changes are produced by reason of the action of chemical
affinity, there is never either gain in weight or loss in weight. In
other words there is no creation of matter and no destruction of it.
In former times, people who observed the disappearance of solid matter
when charcoal burns, thought that the substance was destroyed—partly
if not wholly. The modern chemist finds, however, that the carbon is
only turned into the form of an invisible gas, and that by the use of
appropriate appliances he can find the weight of this gas, and compare
it with that of the carbon producing it. In the combustion of carbon
the chemical change is represented by the following equation:
=C= + =O₂= = =CO₂=
One atom of Two atoms of One molecule of
Carbon Oxygen Carbon dioxide
12 32 44
parts by weight. parts by weight. parts by weight.
\________________________________/ \_______________/
| |
44 44
This equation means that the chemist has discovered, by careful
experiments, that when any twelve parts by weight of carbon—say twelve
pounds—are completely burned, they always unite with thirty-two
corresponding parts of oxygen (in this case thirty-two pounds), and
they produce forty-four parts by weight of carbon dioxide (in this case
forty-four pounds).
And so in all chemical changes the substances taking part—whether
solid, liquid, or gaseous—may be weighed, and the sum of the weights
of all the matters finally produced is just equal to the sum of the
weights of the original factors.
Fifth. Chemical Changes are Often Attended by Displays of Force.
In many chemical changes the union of the atoms is attended with the
_production_ of heat, or electricity, or some other form of energy. Now
it is a law derived from modern discoveries that the amount of energy
given out by any chemical union is fixed and invariable, and that it is
just the same in amount as the quantity of that kind of energy that is
absorbed when such chemical action is reversed.
Sixth. Chemical Changes Produce Striking Results.
Each of the atoms of matter is in itself fixed and unchangeable and it
possesses through all its varied combinations an inherent character
which belongs to it and which no human being can permanently alter.
But when atoms unite to build up either simple or complex molecules,
the various original atomic characters are so blended and balanced and
reinforced as to afford in the molecular product an entirely new and
unexpected set of properties. An example of these principles is found
in the union of copper, sulphur, oxygen and hydrogen. These substances
may combine to form a new molecule which is called cupric sulphate, and
which has the composition expressed by the formula
CuSO₄ + 5H₂O.
Of the constituents of this molecule, copper is red, sulphur is yellow,
oxygen is colorless, hydrogen is colorless; but when they unite the
cupric sulphate formed is blue, that is its color is not that of
either of its constituents, nor is it intermediate between them. There
is simply a new and unexpected result, and one which in the present
state of knowledge cannot be explained; it can merely be recorded.
And this example is only one of a myriad. Throughout nature chemical
changes most marked—and to the human thought unexpected—arise from the
union of familiar elementary substances.
Seventh. Chemical Atoms Unite in Obedience to Definite Law.
Careful chemical study of the way in which atoms combine has developed
the following as a fundamental law of nature. The same chemical
compound always contains the same kind and number of elementary atoms,
and these atoms are united in the same proportions by weight. This law
is a formal statement of facts similar to those already referred to in
paragraphs _third_ and _fourth_ of this chapter. It does not therefore
seem to call for further explanation at this point.
The Modern Atomic Theory.
The same chemical study which has developed the truth of the law just
stated has also given rise to the modern atomic theory. The chemist is
constrained to believe that matter is composed of ultimate indivisible
particles called atoms. While these atoms are invisible to mortal eye
even with the help of the finest known optical appliances, yet when
their existence is once admitted this admission affords an explanation
that is a satisfactory one, and indeed the only one that harmonizes
with the multitude of observed chemical and physical laws.
This atomic theory, in its essential particulars, was suggested in
the early part of this century by Dr. John Dalton, who was a teacher
of mathematics in Manchester, England, and who died as recently as
in 1844. Dalton found recreation in chemical experiments, and the
mathematical turn of his mind led him to express the results of his
chemical analyses in a new numerical form. Thus previous to his time it
had been customary to express the composition of all substances in the
ordinary percentage form. Now Dalton found that _if some special weight
was adopted as the unit_, a variety of new and previously concealed
facts was revealed. The idea to be here conveyed is partially but
perhaps sufficiently expressed by the following examples derived from
the two compounds of carbon already referred to:
[Illustration: JOHN DALTON:
Born at Eaglesfield. (England.) Sept. 5th, 1766; died July 27th, 1844.]
Composition of the Two Compounds of Carbon and Oxygen.
+------------------------------------------------------+
| EXPRESSED IN PER CENTS. |
+------------------------------------------------------+
|_Carbon Monoxide (CO)._ _Carbon Dioxide (CO₂)._ |
|Carbon, 43 - per cent. 27 + per cent. |
|Oxygen, 57 + per cent. 73 - per cent. |
| ———— ———— |
| 100 100 |
+------------------------------------------------------+
+------------------------------------------------------+
| EXPRESSED IN DALTON’S FORM. |
+------------------------------------------------------+
|_Carbon Monoxide (CO)._ _Carbon Dioxide (CO₂)._ |
|Carbon, 12 parts by weight, 12 parts by weight. |
|Oxygen, 16 parts by weight. 32 parts by weight. |
| ——— ——— |
| 28 44 |
+------------------------------------------------------+
In Dalton’s expression it is at once evident that, as compared with
the weight of carbon, the amount of oxygen in carbon dioxide is
exactly twice what it is in carbon monoxide: but to the ordinary
unmathematical mind this fact is buried in the percentage statement.
Dalton’s experiments with still other compounds gave him results
showing a simplicity of relationships similar to that obtained from the
carbon compounds just referred to. To his mind these facts suggested
immediately the idea that an elementary substance is made up of atoms
each of a determinate weight, and that these atoms combine by wholes
and not by fractional parts, and that although it is impossible to
weigh any atom separately, yet _the weight ratios of a multitude of
them that combine as wholes_ express at once the weight ratios of
the atoms themselves. He thus got the idea of atomic weights and
constructed the first table of them. Since Dalton’s first declaration
of his atomic theory, the combining numbers of the different atoms
have been studied by chemists with the most thoughtful care and the
most painstaking methods known to modern science; and tables have been
constructed showing the combining numbers which are believed also
to be the true atomic weights for all the various elements thus far
recognized.
READING REFERENCES.
Atomic Constitution of Bodies.
=Saint-Venant.=—Jour. of Chem. Soc. of London. xxx,
pt. II, 472.
Atomic Philosophy.
———— Amer. Chemist, iii, 326.
Atomic Theory.
=Williamson=, A. W. (and others.)—Jour. of Chem. Soc.
of London. xxii, 328, 433.
=Wurtz=, Ad.—The Atomic Theory. New York. 1881.
Atomic Volumes, Etc.
=Avogadro.=—Annales de Chimie et de Physique.
3 Sér. xiv, 330; xxix, 248.
Atoms, Vortex Theory of
=Thomson=, Sir Wm.—Phil. Mag. 1867.
=Thompson=, J. J.—Science. iii, 289.
=Tait=, P. G.—Recent Advances in Physical Science.
London. 1876. p. 283.
Atomic Weights, Dalton’s First Table of
=Roscoe=, H. E.—Chem. News. xxx, 266.
Chemical Operations, Calculus of
=Brodie=, B. C.—Jour. of Chem. Soc. of London. xxi, 367.
Dalton, John
=Henry=, W. C.—Life of Dalton. London. 1854.
Definite Proportions, Variability in Law of
=Boutlerow.=—Silliman’s Journal. 3d Ser. xxvi, 63.
=Cooke=, J. P.—loc. cit. 310.
Equivalents of the Elements.
=Dumas=, J.—Annales de Chimie et de Physique. 3 Sér. lv, 129.
Energy.
=Stewart=, Balfour.—The Conservation of Energy. New York.
1874.
=Tait=, P. G.—Recent Advances in Physical Science. London.
1876. Encyclopædia Britannica. vol. viii.
Gaseous and Liquid States of Matter.
=Andrews=, T.—Jour. of Chem. Soc. of London. xxiii, 74; xxx,
pt. II, 159.
=Ramsey=, W.—Jour. of Chem. Soc. of London. xlii, 136.
Matter, Constitution of
=Ditte=, A.—Annales de Chimie et de Physique. 5 Sér. x, 145.
Nomenclature of Salts.
=Madan=, H. G.—Jour. of Chem. Soc. of London. xxiii, 22.
CHAPTER VIII.
HYDROGEN.
This substance is one of the most interesting with which the chemist
has to deal. On account of its chemical and physical properties,
by reason of the many important compound substances into which it
enters, by reason of the part it has played in the history of chemical
progress, it is entitled to a large share of the student’s attention.
Meaning of the Word Hydrogen.
The name hydrogen was applied to it some time later than the first
recognition of the substance. The word is derived from two Greek words
(ὕδωρ, _hydor_, water, and γεννάω, _gennao_, I form or produce), the
word as a whole meaning _water former_. In fact hydrogen is in all
water wherever that substance exists. That this is a very comprehensive
expression appears when it is remembered that the atmosphere always
contains water diffused through it in the form of invisible vapor
even before that vapor is precipitated as the gentle dew, or the
crystalline snow, or the streaming rain. Again, water in seas and
oceans, lakes and rivers, is the mantle of nearly three-fourths of the
earth’s surface. Every living being on the dry land, whether animal or
vegetable, contains large quantities of water in its structure: the
blood of the higher animals is nearly nine-tenths water.
While water is the principal substance containing hydrogen, this gas
exists also as a constituent part of a great many other solid and
liquid matters found in the earth.
Why Free Hydrogen is not Found in the Earth.
Hydrogen scarcely ever exists on our globe alone, that is in the free
or uncombined condition. Indeed there are certain definite reasons why
it should not. These are based mainly upon the very strong chemical
affinity that hydrogen has for oxygen. Now, as has been declared
already, the latter substance is the most abundant element in nature,
and it exists in very large quantities in our atmosphere. Spread all
over the surface of the earth then, the free oxygen of the air stands
prepared to combine with hydrogen wherever the latter may be liberated.
Such combination might not occur, it is true, unless initiated by
influence of heat or some flame of fire; but owing to the constant
agitation of the air by reason of uniform currents like trade winds,
as well as those produced when the atmosphere is agitated by violent
storms, any mixture of hydrogen and oxygen would be likely soon to come
into contact with some flame or fire, and so these components would
enter into combination. Thus hydrogen would not be likely to remain
long uncombined even were it produced in considerable quantity by
natural terrestrial operations.
The Discoverer of Hydrogen.
Hydrogen was first distinctly described and its properties as a special
kind of gaseous matter clearly pointed out in the year 1766, by an
English chemist, the Honorable Henry Cavendish. This philosopher, the
son of Lord Charles Cavendish, and the grandson at once of the Duke of
Devonshire and the Duke of Kent, is one of the most curious characters
in the history of the natural sciences. He was of an exceptionally
careful, thorough and painstaking temper, which well fitted him for
the scientific pursuits which were the prime objects of his thoughts.
Sir Humphry Davy said of him: “The accuracy and beauty of his earlier
labors have remained unimpaired amidst the progress of discovery, and
their merits have been illustrated by discussion and exalted by time.”
In addition to his possession of many special aptitudes for the
exact studies to which he devoted his entire existence, it should be
recognized that he lived at a period that was remarkably favorable to
the pursuit of the natural sciences. The times, the state of knowledge,
the condition of society all over Europe seemed to be ripe for this
kind of progress, for in Scotland, in England, in France, in Germany,
in Sweden there appeared experimenters of unsurpassed skill, and
chemistry as a science had then its birth under most fortunate auspices.
Cavendish was very peculiar in his manners and habits, living in
great seclusion and retirement and in the most simple and methodical
manner; indeed his oddities attained for him the unenviable distinction
of a place in a book devoted to the lives of English eccentrics. In
that work, as well as in Dr. Wilson’s life of him, are many amusing
anecdotes of his way of life. One most remarkable episode was his
inheritance of wealth. Though poor in his youth he was suddenly made
rich in middle life by a bequest whose origin is scarcely known. M.
Biot neatly described him as “le plus riche de tous les savants, et
probablement aussi, le plus savant de tous les riches.” He lived on
however in as great seclusion as before, his chosen associates being
his flasks and his thermometers. His millions made no observable
impression upon his habits, notwithstanding at his death they made him
the largest holder of the stock of the Bank of England.
Lord Brougham says that Cavendish probably uttered fewer words in the
course of his life than any other man who ever lived to fourscore
years, not at all excepting the monks of La Trappe—who were bound to
perpetual silence except in cases of absolute necessity.
[Illustration: JOSEPH BLACK, M. D.
Born in Bordeaux, in 1728; died in Edinburgh, Nov. 26, 1799.]
Why Hydrogen was not Discovered Earlier.
Doubtless those prehistoric men who in earliest days looked about upon
the face of the earth, curiously examining their heritage from the
Creator, were familiar with water in its various forms. They must have
prized its bland and refreshing powers and have learned many of its
most important uses. But the idea that it is made up of more than one
kind of substance or matter was not suspected until very recent times,
and not proved until the masterly investigations of Cavendish clearly
set forth the facts. Indeed the very idea of a chemical compound, that
is of a substance as made up of inconceivably small portions of matter
in a union of almost inconceivable intimacy, an idea very familiar to
students of the present day, probably did not enter the minds even of
those profound thinkers who suggested the earlier atomic philosophies.
In fact the notion of chemical union is scarcely more than a century
old.
Moreover, hydrogen is a gas, and _the notion of gas_ is itself
decidedly a modern one. It was first stated in well-defined form in the
year 1752, by Dr. Joseph Black, professor in Glasgow and Edinburgh.
Black clearly and conclusively demonstrated the existence of _airs_ of
a different kind from that familiar to us in our atmosphere. It is true
Van Helmont and even others, fully one hundred years before Black’s
time, had known and stated more or less distinctly the existence of a
gas or air different from that we breathe, but owing to a variety of
circumstances these wonderful discoveries were allowed to relapse into
forgetfulness. Thus the human race lost for a century much advantageous
knowledge; but probably the general social advancement of those times
had not then prepared mankind for the benefits which the development of
modern chemistry has conferred upon the present citizens of the world.
Again, _experimenting_ with gases was not well understood until about
the year 1770, when Joseph Priestley invented that contrivance for
manipulating them known as the pneumatic trough, for which no better
substitute has yet been devised.
Further, in water—which has already been referred to as the most
abundant and widely diffused compound of hydrogen—the partner elements
are bound together by a chemical affinity that cannot be readily
overcome. This intensity of attractive force between the constituent
elements is therefore another reason why the true composition of
water was so long an unsolved riddle and why hydrogen was not earlier
recognized as a thing or kind of matter by itself, although in its
principal compound—one of the most admirable gifts of the Creator to
man—it was well-known from the first days of the human race.
How Hydrogen is Prepared.
Hydrogen may be obtained by the chemist in several ways:
_First._—There is a method of directly tearing the elements composing
water apart from each other. Considered theoretically this process is a
most direct and simple one. In order to realize its results, however,
advantage must be taken of the galvanic current. This force may be
obtained readily it is true: thus in most cases where two metals,
dipped in a liquid, are connected by a wire it is generated. But no one
knows fully what the current is. The words galvanic current and voltaic
current suggest the two investigators, Galvani and Volta, who were the
pioneers in this field, but they give nothing that can be called an
_explanation_ of the wondrous, invisible, imponderable form of energy
referred to. It is a force of an exceedingly interesting character and
about which a certain considerable body of knowledge has been collected.
Among the variety of facts known about it is that one which relates
to water; namely, when the poles or electrodes of a suitable galvanic
battery are dipped into a vessel of water, bubbles of gas may be seen
to flow freely from each of them. The gases may be collected in a
vessel placed over the electrodes, but the experimenter may well beware
of incautiously treating what has now been produced; he has obtained
a mixture of oxygen and hydrogen from the original water, and these
elements which he has rended apart from their more intimate union,
are ready upon the approach of the smallest flame to rush into union
again, with extraordinary violence, and in such a way as to produce a
tremendous explosion. In the act of this explosion, therefore, water is
again produced, first as expansive vapor, then condensible back to the
liquid drops whence it came.
[Illustration:
FIG. 6.—Apparatus for decomposition of water, (by action of two cells
of the Bunsen galvanic battery,) and for collection of hydrogen and
oxygen gases in separate receivers over the two electrodes of the
battery.]
If however the product from each electrode is collected _by itself in
a separate tube_, the one gas is found to be very different from the
other. The one is found to be hydrogen, the other oxygen. In accordance
with the formula H₂O—which it has before been stated represents the
composition of water—the hydrogen is found to be given off in a bulk
or volume that is twice as great as that of the oxygen obtained at the
same time from the same amount of water.
_Second._—Hydrogen may be obtained by bringing into contact with water
under proper conditions certain substances that have a very strong
affinity for its oxygen and at the same time but little affinity
for its hydrogen. Now every one is familiar with the fact that iron
rusts readily in the air. The chemist can demonstrate that this rust
is a compound of iron and oxygen. The union of these elements under
ordinary conditions suggests at once that that union arises from
an affinity between the iron and the oxygen. This affinity is much
greater at high temperatures, for it is well known that iron rusts
more violently when subjected to heat. These facts then are made use
of for the purpose of withdrawing oxygen from water and thus forcing
the hydrogen out in the free or uncombined condition so that it may be
obtained and experimented upon.
[Illustration:
FIG. 7.—Apparatus for preparation of hydrogen gas. Steam, generated
in the small retort, is conveyed through the tube placed in the
gas furnace; iron turnings within the tube being highly heated,
decompose the water-vapor, which thereby evolves hydrogen. The
liberated gas is collected in the little bell-glass.]
To produce hydrogen by this method, there must be provided a long
iron pipe which passes through a hot furnace; the pipe should contain
fragments of iron such as iron turnings, or iron filings, or pieces of
iron wire. Then a current of steam must be passed through the pipe.
The iron becomes red hot, and under these circumstances manifests more
affinity for the oxygen of the steam than the hydrogen does. The iron
then grasps the oxygen and holds it fast. As a result a peculiar kind
of oxide of iron of a black color is produced. Its chemical formula
is Fe₃O₄ and it is called by chemists ferroso-ferric oxide. The iron
has now taken the place as a partner of the oxygen that the hydrogen
formerly had. The hydrogen is thus cast out from its combination and
is set free as an uncombined gas, in which liberated condition it is
expelled at the end of the tube. The chemical action between the iron
and the steam may be represented by the following equation:
=Fe₃= + =4H₂O=
Three atoms of Four molecules of
Iron, Water,
168 72
parts by weight. parts by weight.
\____________________________________/
|
240
= =Fe₃O₄= + =4H₂=
One molecule of Four molecules of
Ferroso-ferric oxide, Hydrogen,
232 8
parts by weight. parts by weight.
\_________________________________________/
|
240
The gas produced as just described may be collected by adjusting a
suitable tube in connection with the pipe containing the iron. When
the gas is examined it is found to be in fact hydrogen. It will burn
with a blue flame and perform all the various actions that acknowledged
hydrogen will.
_Third._—There are other metals, not known to the common every-day
uses of life but still familiar to the chemist, which have far greater
affinity for oxygen than iron has. One such metal is that called
sodium. Its affinity for oxygen is so great that it cannot be long
preserved if exposed to the air: a block or lump of it would, in a day
or two in the open air, turn entirely to a mass of rust of sodium, that
is oxide of sodium. This metal therefore is preserved by the chemist
in bottles containing petroleum oil. The oil keeps the air away from
the metal; moreover the oil contains no oxygen in its composition as
many other liquids do. This metal sodium though heavier than the oil
is lighter than water. If thrown upon water it floats. But by virtue
of its intense affinity for oxygen, it at the same time decomposes the
water. It draws the oxygen to itself and it liberates the hydrogen.
Some chemical skill is requisite in the performance of this apparently
simple experiment, for occasionally the violent affinities involved
set the sodium and the hydrogen on fire and give rise to dangerous
explosions. When properly conducted, however, the hydrogen from this
process may be collected in a vessel and its various characteristics
displayed.[2]
[2] Appleton’s “Young Chemist,” Philadelphia, Cowperthwait & Co. pp.
26, 27, 28.
_Fourth._—The most common way of producing hydrogen is by bringing
together sulphuric acid and zinc. The formula for sulphuric acid is
H₂SO₄. Now the zinc has affinity for the compound radicle SO₄, known as
the sulphuric acid radicle. The chemical change is represented by the
following equation:
=Zn= + =H₂SO₄=
One atom of One molecule of
Zinc, Sulphuric acid,
65 98
parts by weight parts by weight
\___________________________________/
|
163
= =ZnSO₄= + =H₂=
One molecule of One molecule of
Zinc sulphate, Hydrogen,
161 2
parts by weight parts by weight
\_________________________________/
|
163
Here it is plain that by reason of its affinities the zinc has taken
the place of the hydrogen—or the place which the hydrogen formerly held
as related to the sulphuric acid radicle, SO₄—and that the hydrogen
thereby left without anything to combine with, appears as a free and
uncombined substance. The hydrogen produced by this method can be
readily collected and examined.
[Illustration:
FIG. 8.—Apparatus for production of hydrogen, by action of sulphuric
acid on zinc, and for collection of the gas in a receiver.]
Perhaps it ought to be stated that neither of the processes thus far
explained is likely to yield hydrogen in an absolutely pure condition.
The various substances used are likely themselves to contain associated
with them small amounts of other substances which give some impurity to
the gas evolved.
The Powers and Properties Manifested by Hydrogen.
Hydrogen has been seen, from the explanation already given, to be a
gas. Down to within a few years it resisted all attempts to liquify
it. Chemists submitted it to intense cold and enormous pressure and to
both these influences at the same time but without avail. Within a few
years, however, by use of ampler resources and contrivances for the
application of these condensing agencies, it has been brought down to
the liquid and perhaps even to the solid state.
As a gas it is colorless, odorless, tasteless.
Bulk for bulk it is the lightest substance known in nature. Thus a
quart of atmospheric air, light as it is, weighs over fourteen times
as much as a quart of hydrogen. A cubic inch of gold weighs more than
two hundred thousand times as much as a cubic inch of hydrogen. This
lightness is properly illustrated by inflating a soap bubble with
hydrogen rather than with air. When soap bubbles are filled with air
they fall, unless indeed carried upward by a temporary current; but
when filled with hydrogen they invariably rise with great rapidity.
By reason of this great lightness hydrogen was formerly used for the
inflating of balloons, but at the present day illuminating gas is so
much cheaper, that the latter is generally used, although it is much
heavier than hydrogen.
Diffusive Power of Hydrogen Gas.
It is not inappropriate to call attention here to certain interesting
relations that hydrogen manifests towards gases and solids. Thus
hydrogen possesses to a marked degree that curious facility of passing
into and permeating other gases which is spoken of as its _diffusive
power_. True, this power is possessed by all gases to a certain extent;
but in rapidity of action none approach hydrogen. As early as 1825 a
German chemist named Döbereiner announced his observations of this
power. He noticed that upon collecting some hydrogen in a cracked jar,
placed in a pneumatic trough, the hydrogen leaked out into the air more
rapidly than the air went in. So that in fact the water of the trough
rose on the inside of the jar. It has been since discovered that when
almost any two gases whatsoever, if only of different densities, are
separated by a partition having fine cracks or holes in it, the lighter
gas always moves out into the heavier one more rapidly than the heavier
gas moves in. As hydrogen is the lightest of all, of course it diffuses
into other gases with the greatest rapidity.
In liquids, hydrogen does not ordinarily dissolve in any considerable
quantity.
With solids however it displays some properties that are well nigh
incredible. Thus it has a very curious aptitude for passing into the
very interior of certain solid metals. The white, compact, solid
metal palladium, although it has no visible pores, has the power of
swallowing up into itself in some mysterious way nearly a thousand
times its bulk of this gas; and again a thin sheet of this same solid
metal, air-tight to all appearances, allows hydrogen to pass through it
as easily as a sieve does water.
The Most Interesting Chemical Property of Hydrogen.
By all means the most interesting chemical property of hydrogen is its
power to unite with oxygen. When it does so unite all the phenomena
of combustion appear. These phenomena are generally the production of
heat, light, flame, and the formation of some new chemical compound.
So then when hydrogen unites with oxygen, it burns, it gives out light
(although that light is of but feeble intensity), it gives out an
enormous quantity of heat, it forms an oxidized product. This product
is water, but water that—owing to the great heat of the combustion—is
raised to the form of invisible vapor. When however a jet of hydrogen
gas is burned under a bright but cool bell-glass, the deposit of mist
quickly formed on the inside of the glass shows that the vapor produced
by combustion has now condensed on the bell to minute liquid drops.
[Illustration:
FIG. 9.—A glass tube held over a hydrogen flame, for the purpose of
developing a musical note.]
In the matter of the heat involved, hydrogen has the distinction
of being above every other substance. One pound of hydrogen when
burned under favorable conditions evolves heat enough to raise over
_thirty-four thousand pounds_ of water from zero centigrade to one
degree centigrade, or nearly the same as from 32 degrees Fahrenheit
to 34 degrees Fahrenheit. This expression of the calorific power of
hydrogen has the same meaning as the following more technical one,
namely: burning hydrogen affords over thirty-four thousand thermal
units. Now carbon, a fuel which nature has provided, and which is
certainly admirably fitted to be man’s chief combustible, yields but
eight thousand thermal units of the kind just referred to, and for
purposes of comparison it maybe added that sulphur yields but two
thousand thermal units.
Hydrogen Cannot Supply the Uses of Atmospheric Air.
Notwithstanding the remarkable evidences of chemical affinity
suggested by what has just been said, hydrogen can in no sense act as
a substitute for the atmospheric air. Thus it does not support animal
life nor will it sustain the combustion of a candle. A living animal
immersed in a room full of hydrogen would be drowned in it; a burning
candle carried into such a chamber would be extinguished as if dipped
in water. In fact the comparison with drowning is very proper, for
in drowning a living animal the water does not chemically injure the
organism; the hydrogen and the water, in the cases supposed, have
similar action _in depriving both the animal and the taper of their
requisite oxygen_.
The Uses to Which Hydrogen May be Put.
[Illustration: FIG. 10.—Disposition of apparatus for the production of
water, by combustion of dry hydrogen in air.]
Hydrogen as the elementary gas finds but few applications in the arts.
It is true that from what has been said, it appears as if its wonderful
calorific power might be utilized in some of the arts where high
temperatures are requisite. But the cost and difficulties attending its
preparation, the liability to loss during its storage, and the danger
from explosion while in actual use, these and other circumstances have
led even the skilled artisan to content himself in most cases with
other though inferior materials. But if the reader has attentively
followed the introductory chapters of this work he must have perceived
that hydrogen is made of great service in many of the measurements
employed by the chemist. It has been noted that it is used as the
standard of _equivalence or atom-fixing power_. It has been spoken
of as the standard of _atomic weight_, and from what has appeared in
the remarks upon its lightness it will seem that it has been properly
adopted as the _standard of density for gases_.
READING REFERENCES.
Cavendish, Henry
=Brougham=, H.—Lives of Men of Letters and Science, etc.
p. 429.
=Timbs=, J.—English Eccentrics, etc. p. 132.
=Wilson=, George.—Life of Cavendish. London. 1851.
Black, Joseph
=Brougham=, H.—Lives of Men of Letters and Science, etc.
London. 1845 p. 324.
Diffusion of Gases.
=Graham=, T.—Elements of Chemistry. 2 v. London. 1850. i, 84.
———— Jour. of Chem. Soc. of London. xvii, 334.
Occlusion of Hydrogen by Palladium.
=Graham=, T.—Jour. of Chem. Soc. of London. xxii, 419.
CHAPTER IX.
BALLOONS.
The remarkable lightness of hydrogen early suggested the fitness of
that gas for the inflation of balloons. From the earliest ages men
have desired to navigate the air. The drudgery of land travelling over
hills and mountains, over marshes and streams, through jungles and
forests, has led men to prefer voyaging even by sea. Thus the people
of the United States crossed the stormy Atlantic in large numbers
long before they traversed the wilds of the American continent to the
Pacific coast; and the early voyagers from New York to the Golden Gate
of San Francisco preferred the water way, though it led them through
an enormous distance and around the perilous Cape Horn, rather than
undertake the shorter course over the Rocky Mountains. Even at a later
date, the sea voyage to Panama, and across the Isthmus, and again
by water way to San Francisco was the ordinary course until Pacific
railroads created a land pathway from one side of the continent to the
other. So men, envying the bird in its flight through the mobile air,
have desired yet more to conquer its smooth courses, just as their
keels have found a sliding pathway in the watery main. But no truly
successful air-voyaging was possible until about one hundred years ago.
[Illustration: FIG. 11.—One of the balloons of the Montgolfier
brothers.]
Invention of the Balloon.
In the year 1783 two brothers named Stephen Montgolfier and Joseph
Montgolfier, succeeded in sending up into the atmosphere the first
air-ship worthy of the name. They lived in France at a little town
named Annonay, situated about forty miles south of Lyons, and at
the junction of two small streams whose clear waters flow into the
river Rhone. Here the brothers carried on with increasing skill and
success the manufacture of paper, a business which their father had
conducted there before them, and which in fact is carried on by their
descendants of the same name even at the present day. The brothers,
Stephen and Joseph, were skillful mechanics, and one of them, it is
said, had studied Dr. Priestley’s work on “Different Kinds of Air.”
This seems to have led him to the idea of aerial navigation. However
that may be, it is a matter of history that on the 5th of June, 1783,
the two brothers sent up from Annonay a balloon about thirty-five
feet in diameter. Naturally it was made of paper, though lined with
linen. The ascensional power of this balloon was due to a proportional
lightening of the air within it by the influence of heat. The heat was
produced by the combustion of a large quantity of chopped straw, and
also from burning wool previously saturated with a little alcohol.
Probably the Montgolfier brothers did not then fully know why their
balloon ascended: they appear to have thought that it arose because of
the volumes of smoke that filled it. It is hardly probable that either
Stephen or Joseph Montgolfier thought at that time of using hydrogen
for their air-ship, notwithstanding its extraordinary lightness had
been a matter of public scientific knowledge for six or seven years.
This may seem the more strange in view of the admitted fact that as
early as 1767 Dr. Black, of Edinburgh, had publicly demonstrated that
a suitable vessel filled with hydrogen would ascend in the atmosphere
as cork does in water. Of course they did not think of employing
illuminating gas, because that substance was not then in public use.
The First Balloon Ascension in Paris.
The news of the wonderful and successful experiment at Annonay was
quickly sent to Paris, where it produced a profound sensation. The
interest extended from scientific men to the royal family and the
court, and indeed to the entire population of the capital. For the
French people—perhaps even more than other nations of Europe—seem
to have been particularly interested at this time in the study of
chemical and physical science. The king instantly issued a summons
for the Montgolfiers to come to Paris. But the Parisians could not
even await their arrival. The scientists of the capital, though but
partially informed as to the character of the experiments performed
at Annonay, at once set to work. They decided upon hydrogen gas as
probably the best fitted for their purposes. Whereupon they filled a
globular balloon with this gas, and prepared to try it in public upon
the Champ-de-Mars. It is said that three hundred thousand people—that
is, nearly half the population of Paris—gathered together, crowding
every adjacent avenue, to witness the unparalleled undertaking. The
liberation of the aerial messenger was announced to the public by a
salvo of artillery. The balloon immediately shot upward and, piercing
the clouds, was soon lost to view. When afterward it slowly descended
it reached the ground some fifteen miles from Paris. Here a troop of
peasants who detected the strange apparition, were at first struck
with alarm but quickly rallied, attacked the strange monster and of
course soon reduced it to shreds. The whole chain of circumstances
created so much excitement that the Government thought proper to issue
a proclamation upon the subject. A copy of this interesting document is
here presented in its original form. Perhaps some readers will find the
accompanying translation acceptable:
French Proclamation Respecting Balloons.
_Avertissement au peuple sur l’enlèvement des ballons ou
globes en l’air._
On a fait une découverte dont le gouvernement a jugé
convenable de donner connaissance, afin de prévenir les
terreurs qu’elle pourrait occasioner parmi le peuple. En
calculant la différence de pesanteur entre l’air appelé
inflammable et l’air de notre atmosphère, on a trouvé
qu’un ballon rempli de cet air inflammable devait s’élever
de lui-même dans le ciel jusqu’ au moment où les deux
airs seraient en équilibre, ce qui ne peut être qu’ à
une très grande hauteur. La première expérience a été
faite à Annonay, en Vivarais, par les sieurs Montgolfier,
inventeurs. Une globe de toile et de papier de cent cinq
pieds de circonférence, rempli d’air inflammable, s’éleva
lui-même à une hauteur qu’on n’a pu calculer. La même
expérience vient d’être renouvelée à Paris, le 27 août à
cinq heures du soir, en présence d’un nombre infini de
personnes. Un globe de taffetas enduit de gomme élastique,
de trente-six pieds de tour, s’est élevé du Champ-de-Mars
jusque dans les nues, où on l’a perdu de vue. On se propose
de répéter cette expérience avec des globes beaucoup plus
gros.
Chacun de ceux qui découvriront dans le ciel de pareils
globes, qui présentent l’aspect de la lune obscurcie, doit
donc être prévenir que, loin d’être un phénomène effrayant,
ce n’est qu’une machine toujours composée de taffetas ou de
toile légère recouverte de papier, qui ne peut causer aucun
mal, et dont il est à présumer qu’on fera quelque jour des
applications utiles aux besoins de la société.
_Lu et apprové,
ce 3 septembre, 1783._ DE SAUVIGNY.
_Notice to the public relative to the ascension of
balloons or globes into the air._
A discovery has been made to which the government considers
it advisable to call public attention, with a view of
preventing alarms which it otherwise might occasion among
the people. Upon calculating the difference of weight
between the gas called inflammable air and the air of
our atmosphere, it has been discovered that a balloon
filled with this inflammable air ought to rise of itself
to a height in the sky such that the air within and that
without will be in equilibrium, a condition which will
not be reached except at a very great elevation. The
first experiment of this sort has been made at Annonay,
in Vivarais, by the Messrs. Montgolfier, the inventors.
A globe of cloth and paper one hundred and five feet in
circumference and filled with inflammable air rose of itself
to a height which the observer could not calculate. The
same experiment has just been repeated at Paris on the 27th
of August at 5 o’clock in the afternoon, in presence of a
vast number of persons. A sphere of taffeta coated with gum
elastic, thirty-six feet in circumference, ascended from the
Champ-de-Mars even to the clouds, in which it became lost
to sight. It is contemplated repeating this experiment with
very much larger globes.
Anyone who discovers in the sky globes of this sort which
present the appearance of the moon when slightly obscured,
may therefore be warned that, far from being an alarming
phenomenon, this is nothing but a machine always constructed
of taffeta or of light cloth covered with paper, which
cannot do any injury, and which it is thought will assume at
some future time a form that will prove useful to the public.
_Read and approved,
September 3, 1783._ DE SAUVIGNY.
The enthusiasm created by the original experiment of the Montgolfier
brothers led soon after to the election of both of them to the Academy
of Sciences. Moreover their invention was not allowed to rest long in
its original form.
As early as November of the same year, 1783, two French gentlemen had
the courage to risk their lives in an ascension from Paris in a balloon
of the Montgolfier construction. They floated freely away and made
their landing in safety. One of them, however, De Rozier by name, on
a later occasion attempted to cross the Channel in a double balloon,
one part containing hydrogen, the other heated air in the Montgolfier
style. But at a great altitude the hydrogen balloon took fire from the
other, and De Rozier and his companion were dashed to pieces on the
rocks of the French coast. Since that early rash attempt thousands of
interesting and safe balloon ascensions have been made, and increased
knowledge of the scientific principles has largely contributed to the
pleasure and comfort of the aeronaut. Yet the contrivance has been in
most cases little more than a scientific toy.
[Illustration: FIG. 12.—Gay-Lussac and Biot making their balloon
ascension for scientific observations in 1804.]
The atmospheric air has thus far baffled the inventive power of man
to such an extent that the balloon as a mechanical contrivance has
been subjected to but few decided improvements since the Montgolfiers’
first experiments, and ascensions have afforded comparatively meagre
scientific or other results. Indeed the most of them have been
conducted for personal gratification or popular entertainment.
Of course there are marked exceptions. Thus on the 24th of August,
1804, two of the youngest but most distinguished of French physicists,
Messrs. Gay-Lussac and Biot, made an important ascension. Their voyage
was upon the suggestion of the French Academy of Sciences, and they
were well equipped with apparatus for making observations. Their
results, particularly in magnetism, showed the same laws prevailing
in the higher air as upon the earth. But as there were afterwards
expressed some doubts as to the accuracy of these observations,
Gay-Lussac made a later and higher ascent alone. On the 16th of
September he attained an altitude of twenty-three thousand feet, the
greatest reached up to that date. His experiments on this occasion
verified those made before. Of particular interest was his test of the
composition of the atmosphere. The bottle of air collected at this
great height was found upon analysis to possess the same proportional
amounts of oxygen and nitrogen as that collected at the surface of the
earth.[3]
[3] Of Gay-Lussac and this ascension there is told a pretty tale, which
I will not mar by making a translation:
“Parvenu à la hauteur de 7000 mètres, il voulut, dit-il, essayer de
monter plus haut, et se débarrassa de tous les objets dont il pouvait
rigoureusement se passer. Au nombre de ces objets figurait une chaise
en bois blanc, que le hasard fit tomber sur un buisson, tout près d’une
jeune fille qui gardait les moutons. Quel ne fut pas l’étonnement
de la bergère!—Comme eût dit Florian.—Le ciel était pur, le ballon
invisible.—Que penser de la chaise, si ce n’est qu’elle provenait du
paradis?—On ne pouvait objecter à cette conjecture que la grossièreté
du travail: les ouvriers, disaient les incrédules, ne pouvaient là-haut
être si inhabiles. La dispute en était là, lorsque les journaux, en
publiant toutes les particuliarités du voyage de Gay-Lussac, y mirent
fin, en rangeant parmi les effets naturels ce qui jusqu’ alors avait
parut un miracle.”—_Arago: Eloge de Gay-Lussac._
[Illustration: FIG. 17.—Microscopic despatches, received in Paris by
carrier pigeons, enlarged by the magic lantern.]
The height of this ascent has since been surpassed by Messrs. Glaisher
and Coxwell, of England, who on Sept. 5, 1862 attained an altitude of
about thirty-seven thousand feet.
Recent Use of Balloons.
Hydrogen is the lightest substance known, and this consideration
tends to make it a particularly favorable one for the inflation of
balloons. But we have seen that it was not until after the Montgolfier
experiments that hydrogen came into considerable use for this purpose.
Hydrogen is still occasionally prepared for purposes of this sort.
It is then produced by the action of sulphuric acid upon zinc. The
equation already given explaining this action is as follows:
=Zn= + =H₂SO₄=
One atom of One molecule of
Zinc, Sulphuric acid,
65 98
parts by weight. parts by weight.
\___________________________________/
|
163
= =ZnSO₄= + =H₂=
One molecule of One molecule of
Zinc sulphate, Hydrogen,
161 2
parts by weight. parts by weight.
\_____________________________________/
|
163
In case zinc is not at hand, iron turnings have been made to answer the
same purpose; and the chemical change in this event is represented by
an equation of very similar form:
=Fe= + =H₂SO₄=
One atom of One molecule of
Iron, Sulphuric acid,
56 98
parts by weight. parts by weight.
\___________________________________/
|
154
= =FeSO₄= + =H₂=
One molecule of One molecule of
Ferrous sulphate, Hydrogen,
152 2
parts by weight. parts by weight.
\_____________________________________/
|
154
Both of these methods of producing hydrogen are still somewhat used
where balloons have to be inflated at points distant from a city gas
supply. But the manufacture of illuminating gas is now so general,
even in small towns, that this substance is oftener used at the present
day. The superior convenience with which it may be obtained makes it
preferred to hydrogen, notwithstanding the greater ascensional power of
the latter substance.
[Illustration: FIG. 13.—Carrier pigeon having attached to his tail a
quill containing microscopic photographs of despatches to be sent into
Paris during the siege.]
[Illustration: FIG. 14.—The tube of quill containing messages as
attached to the tail-feathers of a carrier pigeon.]
Balloons have been used somewhat in recent wars. Thus they were found
of considerable service during the siege of Paris, particularly from
September 23, 1870, to January 28, 1871. During these last four months
of that siege sixty-two balloons left the city, and they carried out
above two million letters and a great many homing pigeons. Some of
the birds returned, escaping the Prussian sharp-shooters, and brought
with them letters and despatches, printed upon the thinnest of paper,
in the form of microscopic photographs. The balloons also took out of
Paris during the siege two especially notable passengers, the one, Leon
Gambetta, head of the provisional government, who left the city for the
purpose of conducting the public business in the provinces; the other,
Prof. Janssen, who had the courage to venture out in the darkness of
early morning so as to escape the rifles of the beleaguring forces.
His voyage was for the purpose of reaching the station in Algeria from
which he was to observe the total eclipse of the sun, to occur a few
weeks later, December 22, 1870. Readers who are interested in the use
of balloons during this memorable siege will find a most interesting
account in Mr. Glaisher’s book, _Travels in the Air_. It contains a
description of the manufacture of air-ships in Paris, together with a
list of the passengers and an account of the freight of those leaving
the city when other means of communication with the outside world were
cut off.
[Illustration: FIG. 15.—Owner’s name on the wing of a pigeon.]
[Illustration: FIG. 16.—Fac-simile of a microscopic despatch as sent by
carrier pigeon. Letters and messages, public or private, to the number
of about 5000, were printed on a large sheet of paper. Afterwards this
sheet was reduced by photography to the size and appearance shown
above.]
The Centenary of Ballooning.
It is worthy of note that in August, 1883, the centenary of the
experiment of the Montgolfier brothers was celebrated by their
descendants and others at Annonay by a modern balloon ascension and
other fêtes. These included the dedication of a monument to the two
inventors. This monument is soon to be surmounted by a group in bronze
representing the two brothers inflating their first balloon.
READING REFERENCES.
Balloons, Their Early History.
=Figuier=, L.—Les Aérostats et les Aéronautes.
Revue des Deux Mondes. Oct. 1, 1850. p. 193.
[This interesting article will well repay the reader.]
=Blerzy=, H.—La Navigation Aérienne. Revue des Deux Mondes.
Nov. 1863. p. 279.
[Claim is here made, in a general way, that the original invention
of the balloon was made at the close of the 17th century by a
Portuguese named Gusmao.]
Balloons, Their Recent Uses.
=Glaisher=, James, and others.—Travels in the Air. London. 1871.
=Hofmann=, A. W.—Chem. News. xxxii, 231, 241, 255, 265.
Balloons, Centenary of Their Invention.
=London= Graphic. Aug 25, 1883.
Balloons, Popular Account of.
=Harper’s= Magazine. ii, 168, 323; xxxix, 145.
=Scribner’s= Monthly. i, 385.
Gay-Lussac.
=Arago=, D. F. J.—Oeuvres Completes. Paris. 1854-59. iii.
[The Boston Athenæum library has this work.]
CHAPTER X.
CHLORINE.
Chlorine is a substance of very great commercial importance on account
of its extensive use as a bleaching agent. Again it is a constituent of
common salt, and in this form of combination it is both of great value
as an article of food, and it is recognized as widely distributed. Thus
it exists in salt, whether that substance is in the brine of the ocean
or of mineral springs, or whether it occurs as a solid rock—as indeed
it does in some parts of the world. At Wieliczka, in Austria, mines of
solid salt have been worked for hundreds of years. So also at Cardona,
in Spain, are what may be called quarries of this valuable mineral;
while Cheshire, in England, furnishes immense solid deposits from which
salt is obtained to supply the enormous industrial establishments using
this substance for the production of chlorine and of compounds of
sodium.
Chlorine was first recognized as a distinct substance, by a European
chemist, Carl Wilhelm Scheele, known only to his neighbors as a humble
apothecary. Scheele was born at Stralsund, a seaport town of Pomerania,
situated on the little strait which leaves the island of Rügen in the
Baltic Sea. He spent the principal portion of his life in Sweden, and
on this account is often referred to as a Swedish chemist. Though
living in great obscurity, he yet made many discoveries in chemistry
which have rendered his name, otherwise almost unknown, one of the most
brilliant in the annals of this science.
It is related of Scheele that the King of Sweden, Gustavus III.,
while on a journey outside of his own dominions, heard so much of the
fame of this chemist, unknown to him before, that he regretted having
previously done nothing for him. He therefore commanded that Scheele
receive the honor of being created chevalier. “Scheele?” “Scheele?“
said the minister charged with this duty. “This is very singular; what
in the world has Scheele done?” The order was peremptory however, and
Scheele was knighted. But, as the reader may perhaps divine, the honor
designed for the acute discoverer fell upon another Scheele—not upon
that Scheele unknown at court but illustrious among the scientists of
Europe.
It was this obscure apothecary then, who added to the list of his
other investigations a study of the properties of what was ordinarily
considered a dull and uninteresting earthy substance called black
magnesia. This study was repaid by the revelation of no less than four
hitherto unknown substances: oxygen, barium, manganese, and finally
chlorine. Scheele obtained the chlorine in the year 1774 exactly as
it is done at the present day, namely, by bringing together the two
substances, now called chlorohydric acid and black oxide of manganese,
but then known as muriatic acid and black magnesia.
Scheele believed, and other celebrated chemists concurred in the
opinion, that the greenish gas that he discovered was a compound
substance. It was not until thirty-six years later, that is 1810, that
the distinguished English chemist, Sir Humphry Davy, demonstrated that
this gas is not a compound, but is in fact a simple or elementary
substance; and it was he who gave to it the name chlorine, a name
derived from a Greek word (χλωρός, chloros, meaning light green),
conveying an obvious and convenient reminder of one striking property
of the thing referred to.
[Illustration: SIR HUMPHRY DAVY, Bart.:
Born in Penzance, England, Dec. 17, 1778; died in Geneva, Switzerland,
May 29th, 1829.
“Davy, when not yet thirty-two years old, occupied, in the opinion of
all those who could judge of such labors, the first rank among the
chemists of this or any other age.”]
How Chlorine is Obtained.
The preparation of chlorine is a very simple matter. It may be
accomplished by placing some powdered black oxide of manganese, an
abundant mineral substance, in any deep glass vessel, and then adding
to it four or five times its weight of chlorohydric acid. Anyone who
performs the experiment will soon perceive the greenish gas rising
higher and higher in the vessel, and will soon discover its choking
and corrosive odor. Moreover the chlorine gas, which is two and a half
times as heavy as air, accumulates within the flask and stays there
some time. This is the process which has already been referred to as
that which first revealed the gas to Scheele, and this process, with
but slight modification, is that which to-day furnishes the enormous
quantities of chlorine demanded by modern industries.
The Characteristics of Chlorine.
The three most striking properties of chlorine are its noticeable
weight—greater than that of the air—its greenish color, and its
exceedingly irritating odor. Its influence on the animal organism is
very violent: more than one example can be produced of fatal results
following the inhalation of too large quantities of the gas. Thus
Pelletier, a French chemist, died at Bayonne from the effects of
inhaling a considerable quantity of chlorine, and Roe, a young Irish
chemist of Dublin, lost his life from the same cause, while studying
the properties of this gas.
Chlorine, as a _chemical agent_, manifests its activities in connection
with two principal properties, namely: its affinity for hydrogen
and its affinity for the metals. By this statement it is meant that
chlorine manifests a strong tendency to combine with hydrogen, and to
combine with metals, whenever these substances are accessible to it.
When it combines with hydrogen it forms the important compound
designated by the formula H Cl and called by the chemist chlorohydric
acid, but known in commerce as muriatic acid.
When chlorine combines with the metals it forms chlorides of them.
Thus with the metal sodium it forms the compound designated by the
formula NaCl and called by the chemist indifferently sodic chloride or
chloride of sodium; these will be recognized as the chemical names for
the important and well-known substance, common salt.
Chlorine and Hydrogen Combine.
Chlorine and hydrogen have a very strong tendency to combine with each
other. They manifest this tendency in a variety of ways. Thus, if the
two gases are prepared in a dark room, they may be there safely mixed
together in a glass vessel; but if the sunlight is allowed to enter and
fall upon the vessel, there is danger of its being shattered by the
explosive violence with which the hydrogen and chlorine immediately
unite. As a result of this combination, chlorohydric acid is produced.
The chemical change is represented by the following equation:
=H₂= + =Cl₂= = =2HCl=
One molecule of One molecule of Two molecules of
Hydrogen, Chlorine, Chlorohydric acid,
2 71 73
parts by weight. parts by weight. parts by weight.
\___________________________________/ \_______________/
| |
73 73
Again, when chlorine is brought in contact with vegetable or animal
substances, containing hydrogen, it proceeds to withdraw that hydrogen
for its own benefit, even though these vegetable and animal compounds
are thereby destroyed.
Although this operation, as well as the foregoing one, produces
chlorohydric acid, yet neither method is suitable for a determinate
preparation of that substance. It is usually better to prepare
chlorohydric acid in another way. Thus it is easily produced by the
action of sulphuric acid upon common salt.
Experimental Preparation of Chlorohydric Acid.
Any one who will take a little trouble may prepare chlorohydric acid in
the way indicated.
The experiment should be conducted as follows:
Place a small amount of common salt (NaCl) in a small retort; to it add
enough concentrated sulphuric acid to make a thin paste; connect the
neck of the retort with a clean test-tube containing a few drops of
water. Now gently heat the retort; chlorohydric acid will be formed and
will distil from the retort and condense in the receiver.
The chemical change is represented by the following equation:
=NaCl= + =H₂SO₄=
One molecule of One molecule of
Sodic chloride, Sulphuric acid,
58½ 98
parts by weight. parts by weight.
\____________________________________/
|
156½
= =HCl= + =HNaSO₄=
One molecule of One molecule of
Chlorohydric acid Hydro-Sodic sulphate
36½ 120
parts by weight. parts by weight.
\_______________________________________/
|
156½
The product of the foregoing experiment may be tested in three ways and
so shown to be in fact chlorohydric acid.
_First_: Take a minute drop on a glass rod and apply it to the tongue
and observe the sour or acid taste.
_Second_: Take a drop on a glass rod and touch it upon blue
litmus-paper. It should turn the paper red.
_Third_: Pour a few drops of the liquid into a solution of argentic
nitrate (that is, nitrate of silver) in a test-tube or other convenient
vessel: a white precipitate of argentic chloride will be formed.
[Illustration: FIG. 19.—Section of furnace used for manufacture of
chlorohydric acid. Common salt and sulphuric acid are placed in the
large retort A; upon heating, chlorohydric acid passes into the
receivers C, C, C.]
The method of producing chlorohydric acid just described and
illustrated, is followed in the manufacture of the substance for
general chemical purposes. It is also employed for the production of
the enormous quantities of it incidentally used in the manufacture of
bleaching-powder.
Experiments with Common Salt.
Chlorine has already been shown to combine with the metal silver
producing the compound designated by the formula AgCl, and called
argentic chloride and also chloride of silver. This substance may also
be prepared very easily somewhat as follows:
Make a solution of nitrate of silver. Prepare it either by dissolving
in water the crystals sold by apothecaries, or by dissolving a small
piece of silver in nitric acid. Then make a second clear solution,
by dissolving common salt in ordinary water. Add the salt solution
cautiously, drop by drop to the silver solution. There immediately
appear thick masses of white flakes which sooner or later fall to the
bottom of the vessel. These flakes consist of the argentic chloride
(AgCl), also called chloride of silver, already referred to.
The chemical change is represented by the following equation:
=AgNO₃= + =NaCl=
One molecule of One molecule of
Argentic nitrate, Sodic chloride,
169½ 58½
parts by weight. parts by weight.
\___________________________________/
|
228
= =AgCl= + =NaNO₃=
One molecule of One molecule of
Argentic chloride, Sodic nitrate,
143 85
parts by weight. parts by weight.
\____________________________________/
|
228
This white precipitate produced in this experiment possesses some
special interest from its use in photography. In fact chloride of
silver, as a thin film upon the surface of the photographic paper, is
the principal substance which, by its sensitiveness to light, produces
the photographic picture. In fact any one, who tries the experiment
last described, will soon observe, upon preserving the chloride of
silver so produced, that it rapidly grows dark upon exposure to
sunlight.
Bleaching-Powder.
The substance known as bleaching-powder may be spoken of in a general
way as consisting of lime saturated with chlorine. This description
points very justly to the method of producing the substance, but gives
no idea of the chemical arrangement of the constituents. Scheele
early noticed that chlorine gas possessed decided bleaching power, and
the French chemist, Berthollet, soon called attention to the possible
applications of the substance in the bleaching industries. But its
annoying odor made it impracticable to use chlorine on any large scale
in the state of gas, and forbade the use of it even when dissolved in
water. At length, twenty years after the discovery of the gas—that is
in 1798—the plan of absorbing chlorine in lime was hit upon, and here
may be discovered the beginnings of the bleaching-powder industry,
now one branch of the alkali trade, the greatest chemical industry
conducted by man. This bleaching-powder, at first a mere chemical
curiosity, is now manufactured by the thousands of tons, and is used in
the bleaching of cotton and linen goods, both in the form of cloth and
in the form of the various kinds of paper.
In another place reference is made to the vast proportions attained
by the alkali industry, meaning the manufacture of certain compounds
of sodium, the one produced in largest quantities being doubtless
sodic carbonate (Na₂CO₃), commonly called soda-ash. In trade this
substance is called an alkali because of certain alkaline properties
it possesses, but more strictly speaking it is called a salt—sometimes
an alkaline salt. In chemistry the single term alkali is reserved for
certain compounds called hydrates, of which indeed sodic hydrate—having
the formula NaOH, and often called caustic soda—is an appropriate
example. This latter compound is at present manufactured on a
large scale in connection with soda-ash. Now although the Leblanc
process—which has long been used for manufacturing soda-ash—is at
present meeting with a powerful and successful rival, yet the older
process has still a strong hold upon life in the fact that it gives
rise, as a convenient incidental product, to vast quantities of
chlorohydric acid. The meaning will be better understood when it
is explained that the first step of the Leblanc process is to add
sulphuric acid to common salt. Two substances are here produced:
the one is sodic sulphate, to be carried forward until it is turned
into sodic carbonate; the other substance is chlorohydric acid, a
compound largely used in the arts, and especially in the manufacture of
bleaching-powder.
[Illustration: FIG. 21.—Bleaching of pulp for manufacture of paper.]
[Illustration: FIG. 22.—Apparatus for producing bleaching-powder (by
passing chlorine gas, generated in A, upon quicklime spread upon the
shelves).]
In the production of bleaching-powder, the first step is to mingle
this chlorohydric acid and manganese dioxide. Chlorine gas is thus
generated, much as it is when the experiment is conducted on a small
scale as already described. The chlorine so generated is passed into
a chamber provided with shelves and containing slaked lime. Hereupon
the lime absorbs the chlorine, giving rise to a new substance called
bleaching-powder—also known as chloride of lime. From what has been
said it is evident that chemists know perfectly well what elementary
substances enter into this compound. But there are decided differences
of opinion as to the exact way in which the atoms are arranged.
Bleaching-powder is generally considered to be a chemical union of
calcic hypochlorite and calcic chloride with the addition of calcic
hydrate. The following representation may serve as a formula for the
compound:
CaCl₂O₂ + CaCl₂ + CaO₂H₂
(Calcic hypochlorite.) (Calcic chloride.) (Calcic hydrate.)
[Illustration: FIG 20.—Representation of the old method of bleaching
cotton and linen goods on lawns.]
[Illustration: FIG. 23.—Apparatus for “souring” cotton cloth by
passing it into dilute acid, before submitting it to the action of
bleaching-powder.]
The use of bleaching-powder offers certain advantages. The following
are some of them:
—The compound is itself white.
—It is a powder which can be easily handled, packed and transported.
—With reasonable precautions, the active bleaching agent chlorine is
retained by the powder in available form for a considerable length of
time.
—In actual use in the process of bleaching, the entire amount of
chlorine originally stored up in the powder may be liberated in contact
with the goods to be bleached.
—The liberation of this chlorine is easily affected. The addition of
almost any acid will accomplish it: even the carbon dioxide of the
atmosphere will suffice.
In the bleaching of cotton goods chlorine is not the only agent relied
upon, though it seems to be an essential one. At least three other
substances are employed to contribute to the bleaching. Each of them
either removes some colors or stains from the goods, or so modifies
them that the solution of bleaching-powder—one of the last agents to be
employed—can the easier finish its work. The three substances referred
to are milk of lime, diluted sulphuric acid, and sodic carbonate, also
called soda-ash.
The pieces of cloth, being sewed together into continuous strips many
miles in length, pass from one liquor to another, with washings in
water at proper times, until finally, after being fully whitened by the
chlorine preparation and then receiving the final washing in water,
they emerge from the works, completely bleached.
READING REFERENCES.
Alkali Trade, in its Various Branches.
=Claus=, C.—Chem. News. xxxviii, 263. (Ammonia soda.)
=Davis=, G. E.—Chem. News. xxxii, 164, 174, 187, 198, 210, 238.
=Hargreaves=, J.—Chem. News. xlii, 322.
=Kingzett=, Charles T.—The Alkali Trade. London, 1877.
=Lunge=, G.—Jour. of Chem. Soc. of London, xliv, 524, 528.
=Mactear=, J.—Chem. News. xxxv, 4, 14, 17, 23, 35; xxxvii, 16.
=Schmidt=, T.—Chem News. xxxviii, 203. (Ammonia soda.)
=Weldon=, W.—Chem. News. xlvii, 67, 79, 87.
(Present condition of soda industry.)
Bleaching Powder.
=Jurisch=, K.—Jour. of Chem. Soc. of London. xxxi, 350.
=Kingzett=, C. T.—_loc. cit._ xxviii, 404.
=Kopfer=, F.—_loc. cit._ xxviii, 713.
=Lunge=, G.—Chem. News. xliii, 1.
=Stahlschmidt=, C.—Jour. of Chem. Soc. of London. xxxi, 279.
=Wolters=, W.—_loc. cit._ xxviii, 404.
Chlorine Industry, Future of
=Hurter=, F.—Jour. of Chem. Soc. of London. xlvi, 225.
Chlorine, Preparation of
=Berthelot.=—Annales de Chimie et de Physique.
5 Sér. xxii, 464.
Davy, Sir Humphry.
=Davy=, John.—Collected Works and Memoirs of Sir H. Davy.
London, 1839.
=Paris=, John A.—Life of Sir Humphrey Davy. London, 1831.
=Brougham=, H.—Lives of Men of Letters, etc. London, 1845.
p. 448.
=Cooke=, J. P.—Scientific Culture. Boston, 1881. p. 11.
Salt Mines of Europe.
=Harper’s= Magazine, i, 759.
Scheele, C. W.
=Hoefer=, F.—Histoire de la Physique et de la Chimie. Paris,
1872. p. 497.
CHAPTER XI.
BROMINE.
Bromine is an elementary substance, which was first recognized as such
in the year 1826. It was detected by Antoine Jerome Balard, a French
chemist, who, at the age of twenty-four, was so fortunate and skillful
as to discover this interesting substance. He lived at Montpellier,
not far from Marseilles and but a few miles from the Mediterranean.
The waters of this great inland sea contain about one-tenth more
mineral salts than those of the larger oceans, and so it has long
been the custom along the southern coasts of France to evaporate
these waters for the production of common salt. After this principal
constituent is removed, there remains a strong brine called bittern.
While experimenting upon this bittern, Balard was struck by a peculiar
orange-red coloration of great intensity which appeared at certain
stages of his work. Upon further study, he was able to demonstrate that
this color was due to an elementary substance hitherto unrecognized.
Thus he had the felicity of securing for his name permanent renown as
one of the few philosophers who have been able to detect a new member
of that family of prime and fundamental materials from which is built
the structure of the universe.
It has already been stated that the elements at present acknowledged
are less than seventy in number, and some of these were known to
the ancients. In some cases, a single individual has been able to
recognize several new ones: thus Scheele has already been mentioned
as the discoverer of manganese, barium, and chlorine. So it appears
that of all the eminent men, whose conscientious labors contribute to
the building of the science of chemistry as a noble and harmonious
edifice, necessarily but few can possibly hope to attain the specially
conspicuous honor of having their names forever associated with the
first discovery of any of the primary elements. An interesting story is
told of the eminent German chemist, Justus von Liebig, in connection
with this particular subject. Some years before Balard’s discovery
there was sent to Liebig, from a German establishment where salt brines
were employed, a flask—whose contents were afterwards found to contain
bromine, or at least to be very rich in bromine—with the request that
he examine the contents. The general appearance of the substance
seemed to be that of chloride of iodine, and this circumstance led
Liebig to neglect making a more searching investigation. After Balard
had published his discovery, Liebig perceived his own unfortunate
oversight, and occasionally, of course not without some bitter regret,
he displayed to his friends this interesting flask, to show them how
one might fail to make a discovery of the first importance by reason of
some trifling oversight.[4]
[4] SCHUTZENBERGER, PAUL: _Traité de Chimie Générale_. Paris, 1880. i,
375.
Distribution of Bromine.
The name bromine is derived from a Greek word (βρῶμσς, _bromos_, a bad
smell) which suggests the very pungent odor of its vapor. The substance
occurs in the brine of the ocean and in that of mineral springs. But of
course it does not exist there in the uncombined form; instead it is
united with certain metals in the form of bromides. In sea-water the
principal bromide is bromide of magnesium (MgBr₂).
Experimental Preparation of Bromine.
Bromine may be prepared by anyone who is willing to take a little
trouble.
Place in any suitable glass vessel a small amount of manganese dioxide,
some potassic bromide (commonly known as bromide of potassium), then
some water, and finally a small quantity of chlorohydric acid. Bromine
is almost instantly liberated, and shows its presence by imparting
to the liquid an orange hue. If the vessel is covered lightly, and
then gentle heat is applied to it, the bromine will be expelled
from the liquid and will appear above it as a heavy vapor of a rich
reddish-brown color. Some care must be exercised however in conducting
this experiment, since the vapor is very irritating to the eyes and
also to the throat, and it has a general corrosive effect upon most
substances with which it comes in contact.
Chemical Properties of Bromine.
In its chemical relations bromine shows very decided resemblances to
chlorine, having affinities for the same substances, only less in
intensity. Since its discovery it has found a considerable number
of uses. Thus it is an important substance in the processes of
photography; and the enormous expansion and growth of this art within
a very few years has required in the aggregate large quantities of
bromine. The considerable demand for bromine, which at first increased
its price, has produced, as might have been anticipated, a stimulating
influence upon the manufacture of it. This has led to greatly increased
production of the substance, not only in Europe but also in the
United States. In Pennsylvania, Ohio, and West Virginia it has become
an important article of manufacture; in fact, the United States now
furnishes the largest proportion of the entire amount of the material
produced in the world.
One of the most important compounds of bromine is that produced by
its union with silver. We refer to argentic bromide (commonly called
bromide of silver, AgBr). This substance may be easily produced by the
following simple experiment.
[Illustration: FIG. 24.—Louis Jacques Mandé Daguerre, from whom the
daguerreotype was named: born at Cormeilles, (France,) 1789; died,
1851.]
To a solution of potassic bromide in water add a water solution of
argentic nitrate; a white, or yellowish-white precipitate immediately
appears.
The chemical change is represented by the following equation:
=KBr= + =AgNO₃=
One molecule of One molecule of
Potassic bromide, Argentic nitrate,
119 169½
parts by weight. parts by weight.
\____________________________________/
|
288½
= =AgBr= + =KNO₃=
One molecule of One molecule of
Argentic bromide, Potassic nitrate,
187½ 101
parts by weight. parts by weight.
\____________________________________/
|
288½
This argentic bromide produced, at first nearly white in color, has
the power of becoming black upon exposure to light, and it is this
important property which makes the substance suitable for use in the
processes of photography.
Again in the form of potassic bromide, bromine has had a very wide and
beneficent use as a remedial agent; it is still largely used in the
manufacture of the salt mentioned.
READING REFERENCE.
Liebig, His Life-Work in Chemistry. =Hofman=, A. W.—Jour. of Chem. Soc.
of London. xxviii, 1065.
[Illustration: FIG. 25.—Photographer at work in a room lighted through
a window of red glass. (Red glass cuts off the chief actinic, or
chemical, rays of sunlight.)]
CHAPTER XII.
IODINE.
Iodine belongs to what may be called a chemical family, the other
members being chlorine and bromine. All three of these elements are
found in sea-water, but in very different quantities. Thus chlorine
is extremely abundant; bromine is in the water in minute quantities,
while iodine exists there in amounts that are exceedingly small. They
all exist as salts, of which of course chloride of sodium is by far the
most abundant. It has already been shown that bromine is obtained from
sea-water, after enormous amounts of the water have been concentrated
by evaporation. But iodine, the third element of this group, exists
in sea-water in quantities so very minute that it cannot be extracted
from it at any practicable cost. Even the concentration method, just
alluded to, is not applicable in the case of iodine. It happens however
that sea-weeds have the power of extracting from sea-water even the
exceedingly minute amount of iodine, or of iodides, that the water
contains; and moreover when sea-weeds are burned, iodides are found in
their ashes.
The Discovery of Iodine.
The discovery of iodine is associated with the history of certain of
the most important and interesting products of the chemical arts. It
also has a striking connection with some of the political and military
affairs in France, and indeed in Europe, in the early years of the
present century. Finally, its great usefulness to mankind is in marked
contrast with the misfortunes that overtook its discoverer.
[Illustration: FIG. 26.—Gathering the harvest of sea-weed for the
manufacture of soda-ash.]
The discovery of iodine is directly referable to the old soda industry.
The term soda is a general one, and it was formerly used to include
several different chemical compounds manufactured from the ashes of
sea-weed. Decidedly the most important of these is sodic carbonate.
This substance has a well marked alkaline reaction, and although not
an alkali in the strictest chemical sense, it is yet the principal
product of that greatest of all the chemical industries known as the
alkali trade. (See pp. 94 and 99.) During the last sixty years, and
after many early trials and failures, the production of the various
alkaline compounds of sodium has risen to enormous proportions, such
that in England alone the daily product of sodic carbonate, the
principal one, is probably more than two thousand tons. This vast
amount of alkali is consumed by civilized peoples in some of their most
extensive industries such as the manufacture of soap and of glass,
and in many processes of bleaching. The extension of these branches of
business has of course gone hand in hand with the increased production
of alkali. Indeed, on the one side there has been a steady diminution
in price, and on the other a steady increase in consumption; probably
each circumstance may be considered as both cause and effect of the
other. Prior to 1793 however, the demands for alkali—vastly smaller
than to-day—were all satisfied by the material obtained from the ashes
of marine plants. Thus along the coasts of Great Britain, France,
and especially of Spain, sea-weed of various kinds was gathered as a
very important harvest. Some of the weed was used as a fertilizer of
the soil; more was dried and burned for the sake of the ashes. On the
British coast the ash was known as _kelp_; that produced on the coasts
of Normandy was called _varech_; and that produced on the Spanish coast
went by the name of _barilla_.
[Illustration: FIG. 27.—Varieties of sea-weed used to produce varech.]
Now one of the important indirect effects of the French Revolution was
that felt by the consumers of the old-fashioned alkali. In 1793 an
embargo was put upon the supply of alkaline ashes, such as kelp and
barilla, into France. But the French demand for alkali, not only for
ordinary purposes, but also for the production of the great amounts of
saltpetre required for the manufacture of gunpowder, was imperious.
The immediate effect, therefore, was to create the sudden development
of a process called the Leblanc method, by which alkaline compounds
of sodium are made from common salt. Notwithstanding the stimulus of
the prohibitory embargo and the fostering help of the government of
Napoleon Bonaparte, the complexity of the Leblanc process was such that
it was slow in gaining a foothold as a practical industrial method.
But after its first successful establishment as a regular business
and up to almost the present day the application of this process has
continually widened, and the method has held undivided sway in its
important field. In the year 1811 Bernard Courtois, a French chemist,
was engaged, just as other manufacturers were, in the production of
nitrate of potash, or saltpetre, for use in gunpowder. In the course of
this work he employed soda obtained from varech. In order to separate
the alkali from the varech in a more refined condition the raw varech
was subjected to a very careful purification. At certain stages of
his experiments Courtois discovered that the addition of sulphuric
acid gave rise to the production of a magnificent violet vapor. He
did not make the matter public however until late in the year 1813,
when he brought the subject to the attention of Sir Humphry Davy, the
distinguished English chemist, who was then visiting Paris. The next
year, 1814, the substance was carefully investigated by Gay-Lussac,
who gave to the world a very full description of its properties, and
who called it iodine from a Greek word (ἰοειδής, _ioeides_, violet
colored), suggesting the striking and characteristic color of its
vapor. The political events of 1815 ruined the business of Courtois,
and he sunk into poverty from which he was not able to recover, until
finally he died in 1838, poor and almost forgotten, leaving a widow who
was forced to win her bread by the labor of her hands.
Present Sources of Iodine.
Although kelp, varech and barilla are no longer used for the direct
purpose of affording alkali, they are still produced with a view to
their yielding iodine. On the rough and stormy coasts of Scotland,
Ireland, France and Spain, large quantities of sea-weeds are cast
ashore. They are collected, they are dried in the sun, they are then
burned, and their ashes are employed—but principally in the manufacture
of iodine. Thus on the coasts of Brittany and Normandy the occupation
of collecting weeds occupies three or four thousand families for the
larger part of the year.
Experimental Method of Preparing Iodine.
Iodine may be prepared in a manner closely resembling the process
already described for bromine; that is, by placing in a suitable glass
vessel a small amount of manganese dioxide, some potassic iodide
(commonly known as iodide of potassium), then some water, and finally
a small quantity of chlorohydric acid. Iodine is almost instantly
liberated, and shows its presence by imparting to the liquid a brownish
color. If the vessel is covered lightly and then gentle heat is applied
to it the iodine will be expelled and appear in the vessel above the
liquid as a heavy vapor of a rich violet color. This vapor readily
condenses on the upper and colder portions of the vessel in the form of
minute crystals of a color almost black. This is almost precisely the
method employed on the large scale for the production of iodine from
kelp.
[Illustration: FIG. 28.—Changing iodine to a violet vapor by means of
heat.]
Chemical Properties of Iodine.
The chemical characteristics of iodine are throughout closely allied to
those of chlorine and of bromine, only in general iodine may be said to
have weaker chemical affinities than either of the other two.
[Illustration: FIG. 29.—Apparatus used in the manufacturing process for
obtaining iodine. The retorts C, C, are surrounded by sand (sand-bath);
the heat drives iodine, in form of vapor, into the receivers, A, A,
where it solidifies.]
Iodine produces compounds of the same general type as the others,
and of this an example is found in argentic iodide. The following
method of producing it can be followed by almost any one. Prepare a
solution of nitrate of silver in water, and then add a water solution
of potassic iodide; a chemical change takes place, with the production
of a yellowish-white precipitate. This precipitate is argentic iodide.
Upon exposure to sunlight it readily changes in color, becoming almost
black. This is an important characteristic and is made use of, as is
the same property possessed by argentic bromide and also by argentic
chloride, in the production of the photograph. And while it is a fact,
and one well known, that many of the salts of silver blacken more or
less upon exposure to sunlight, it is found that the chloride, the
bromide, and the iodide, have properties particularly fitting them for
the purposes of photography. In discussing bromine, reference was made
to the influence of the great expansion of the photographic business;
and this circumstance has stimulated the demand for iodine just as for
bromine. It was also pointed out, that potassic bromide is an important
remedial agent; potassic iodide is likewise of great medicinal value.
Starch as a Test for Iodine.
Iodine, when in the free or uncombined condition, has a remarkable and
very peculiar way of attaching itself to granules of starch.
This property may be demonstrated by a simple and attractive
experiment. Thus if starch is boiled with water and then the hot mass
is poured into cold water, minute particles of starch distribute
themselves through the liquid. If to this liquid a very small amount
of free iodine, in the form of a solution, is added, the starch
instantly takes on a deep blue color. If to another portion of the same
or similar starch suspended in water, iodine is added _in a combined
form_—that is as potassic iodide for example—absolutely no change of
color is detected. These two experiments show that the iodine only
attacks starch when the iodine is _free and uncombined_.
READING REFERENCES.
Chlorine, Bromine, Iodine, and Fluorine.
=Mylius=, E.—Chem. News. xxxiii, 244, 253; xxxiv, 5, 13, 25,
33, 45, 55, 66, 78, 86, 118, 139, 149, 166, 180,
188, 197, 215, 233.
Iodine, Manufacture of
=Schmidt=, T.—Chem. News. xxxvii, 56.
=Stanford=, E. C. C.—_Loc. cit._ xxxv, 172.
CHAPTER XIII.
FLUORINE.
Of Fluorine it is necessary to made the remarkable statement that it
has never been known to be produced isolated, that is in a separate or
uncombined form. Many experiments have been performed for the purpose
of reaching this result, and though none of these have resulted in
the production of the element sought, they lead us to believe that
the element is a gas. For, if it were a solid or a liquid at ordinary
temperatures, it may be safely supposed that some processes that have
been devised would be capable of producing at least a small quantity
of the elementary substance, and that from this the observer would be
enabled to recognize and discover at least some of the properties of
the fluorine itself.
Properties of Fluorine.
There are a number of compounds known whose various properties, powers
of chemical interchange, and special molecular weights, clearly point
out the existence in them all of a certain peculiar element analogous
in many respects to chlorine, bromine, and iodine. To this element the
name fluorine has been given. Although, as before intimated, it has not
been known to have been obtained _liberated_, its properties in these
combined forms have been carefully studied and well made out. Thus,
like chlorine and its family associates it combines with hydrogen to
form an acid, fluohydric acid (HFl), properly comparable with the acids
formed by the three elements last discussed:
Chlorohydric acid, HCl.
Bromohydric acid, HBr.
Iodohydric acid, HI.
It also combines with the metals to form fluorides. The best example of
these fluorides is that compound in which fluorine most commonly occurs
in nature: that is fluor-spar, the mineral substance whose chemical
name is calcic fluoride, and whose composition is expressed by the
formula CaFl₂.
The property above all others that is characteristic of fluorine is,
however, its striking affinity for silicon. With this element it
readily combines under almost any circumstances. More wonderful still,
the compound produced with it is a gas. Now in general the compounds of
silicon are solids. These solids are many of them familiarly known in
those materials which constitute the principal portions of the stable
earth on which we tread, of the rock beneath it and of the enduring
mountain masses that here and there pierce through the soil and raise
their crests above the general level. The majority of these earthy and
rocky substances are silicates. It is apparent then that the compounds
of silicon are types of solidity and stability. They cannot be melted
except in the most powerful heating appliances, and the chemist can
hardly imagine conditions such as would change them into vapor. So
then it seems strange and almost contradictory that fluorine should
have the power of attacking compounds that seem to be the embodiments
of permanency itself;—yet it readily does so. Thus if fluohydric acid
comes in contact with silicon, whether that substance is in combination
as sand or as hard rocky minerals, the fluorine atoms pluck out the
silicon and then they fly away together in the form of gas or vapor.
Again, fluohydric acid may be spoken of as the unique agent that
readily attacks glass and dissolves, and even destroys, this ordinarily
unchangeable substance.
Finally, there may be added what can be said of no other element,
namely: that fluorine is never known to form any compound with oxygen.
Discovery of Fluohydric Acid.
It is not easy to refer the first knowledge of fluorine to any
particular discoverer. Perhaps however renewed mention of the ingenious
Scheele is not out of place here; for it seems to have been he who
for the first time, and as early as 1771, recognized fluohydric acid
as a special acid. He called it fluoric acid, but he did not obtain
a correct idea of its composition. Scheele prepared the acid from a
well-known mineral, fluor-spar, and by the addition of sulphuric acid.
This operation cannot be performed to advantage in a glass or porcelain
vessel for they contain silicon, and as has been suggested already,
silicious matters are freely attacked by the acid produced. The
decomposition therefore is commonly conducted in a retort of lead, or
in one of platinum, and the acid produced is collected in a receiver,
also constructed of one of these metals.
[Illustration: FIG. 30.—Platinum retort and receiver shown with its
several parts separated.]
The chemical change is represented by the following equation:
=CaFl₂= + =H₂SO₄=
One molecule of One molecule of
Calcic fluoride, Sulphuric acid,
78 98
parts by weight. parts by weight.
\____________________________________/
|
176
= =2HFl= + =CaSO₄=
Two molecules of One molecule of
Fluohydric acid Calcic sulphate
40 136
parts by weight. parts by weight.
\___________________________________/
|
176
Ordinarily the product is a liquid, and consists of water holding in
solution the fluohydric acid (HFl). It is possible however to prepare
the acid free from water, and still in a liquid form. But in this
condition it is one of the most dangerous, poisonous, and corrosive
substances known. It produces painful burns if it falls upon the flesh,
and fatal results have been known to follow injuries received from it.
Thus in 1869, Professor Nicklès, an eminent French chemist, died from
injuries sustained by the accidental inhalation of fluohydric acid
vapor, while studying the properties of the substance.
Etching Glass by Fluohydric Acid.
The effect of fluohydric acid upon glass may be shown in attractive
form, and without much difficulty or danger, by the help of a small
dish of lead and a plate of glass to cover it. These being provided,
the experiment may be conducted somewhat as follows: Melt a little
beeswax upon the glass so that the wax may form a thin film upon one
side of it. Then allow the wax to cool and harden. Next, by use of
any convenient pointed instrument, draw some sketch or design deep
in the wax—in fact, to the surface of the glass. Next place some
powdered fluor-spar in the leaden dish, and add to it some concentrated
sulphuric acid. Now cover the dish, with the glass already prepared,
in such a way that the sketch or design is turned downward so as to
receive the fumes of fluohydric acid as they rise from the mixture in
the dish. It is easily understood from what has been said already that
the fluohydric acid will attack the glass, carrying away some of its
silicon in the form of gas or vapor. As a result of this action, minute
channels are formed in the glass. When the experiment is thought to be
sufficiently advanced, the wax may be removed from the plate by melting
it off or otherwise; thereupon it will be discovered that the glass has
actually become etched or engraved by the fluohydric acid gas.
[Illustration: FIG. 31.—Platinum retort and receiver shown as arranged
for production of fluohydric acid (HFl).]
In 1788 Puymaurin presented to the French Academy of Sciences such
a glass plate, upon which there was a beautiful fluoric etching
representing Chemistry and Genius weeping at the tomb of Scheele, who
had contributed so much to the history of fluohydric acid. “This work,”
says Haüy, “was of interest to the Academy on account of the fitness of
the subject as well as the elegance of its execution.”
Practical Application of Fluohydric Acid.
Fluohydric acid, formerly a mere chemical curiosity, has now become
a familiar article upon the shelves of the druggists. It is sold in
gutta-percha bottles with rubber stoppers. It is often used by jewelers
to correct errors in the application of silicious enamels upon their
work. Thus if the enamel has been incorrectly placed, it may be removed
by fluohydric acid and afterward a new portion may be introduced in
the proper position. Again, it is largely used in the decoration of
artistic glass objects, such as globes for gas chandeliers, and the
multitude of articles of table glass ware. In engraving such objects,
they are first covered with a suitable varnish that will resist the
fluohydric acid, then the design is drawn through the varnish with a
sharp needle; afterward the article is exposed to the gas and etched in
a manner similar to that already described.
[Illustration: FIG. 32.—Leaden tray and glass plate. The tray is
intended to receive the materials for production of fluohydric acid;
the plate is represented as covered with a varnish, through which a
sketch has been drawn, preparatory to etching.]
READING REFERENCES.
Fluohydric Acid.
=Gore=, G.—Jour. of Chem. Soc. of London. xxii, 368.
Fluorides.
=Fremy=, E.—Annales de Chimie et de Physique. 3 Sér. xlvii, 5.
CHAPTER XIV.
OXYGEN.
Oxygen may justly claim a high degree of importance as a subject for
the study alike of the professional chemist and the casual reader. This
importance depends upon a variety of considerations. Among them are
the surpassing abundance of the substance itself, the great number of
compounds into which it enters, the activity of its chemical powers,
and finally, the interesting circumstances under which its distinct
recognition, or, as perhaps we may say, its discovery, was attained.
Its great abundance has been pointed out already in the declaration
that oxygen makes up, by weight, fully one-half of our terrestrial
globe—including earth, ocean and air. The air is about one-fifth oxygen
by weight; all water, wherever existing, is sixteen-eighteenths oxygen
by weight, while quartz, sand, and other similar widespread and most
commonly occurring mineral matters, are a little more than one-half
oxygen. Other solid matters than the rocks, such as most parts of the
material structures of animal and vegetable beings, contain oxygen as
an important constituent element. While thus we have scanned the great
multitude of substances spread immediately about us by the hand of
nature, and found oxygen in them all, it is none the less true that
oxygen is an important factor in artificial products—that is, those
resulting from man’s manufacturing operations.
Chemical Activity of Oxygen.
Again, oxygen plays a part of exceeding activity in some of the
grandest chemical processes of nature and of the arts.
For example, it is essential to the vital processes of all animals.
Wherever a living being inhales the breath of life, whether from the
fresh air of the mountain tops, or from the populous streets of the
swarming metropolis, or from the solitary deck of the bark that creeps
with the ocean’s currents; or wherever the humbler servants of man’s
table find their way through unexplored depths of the ocean and pluck
from its waves the modicum of life-giving gas dissolved within them;
there is this wonderful agent, which has no substitute, sustaining
by active processes truly chemical, that vitality of man or of beast
which gives to nature its forms of highest beauty and most admirable
intelligence.
Again, oxygen is the necessary agent in all ordinary combustions. So
wherever a faggot, glowing beneficently in a sparsely peopled forest,
helps to sustain man’s vital spark; or, where in a highly civilized
community, the fires on the altars of modern industry draw from the
flinty rocks the metals that serve to give employment to millions of
children of toil;—there oxygen is ever active, the true supporter of
the combustion of all those flames which in the past have served as
signs of life and civilized activity, and which are still the best
symbols of vitality and intelligence.
The Discovery of Oxygen.
The first discovery of oxygen is usually attributed to Dr. Joseph
Priestley, an English clergyman and student of natural science. He
lived in a time when men’s minds all over Europe were strongly drawn
toward the pursuit of chemical knowledge. In fact, at almost the same
moment that Priestley was enthusiastically conducting his experiments,
Scheele was also producing oxygen in his apothecary’s chamber in
Sweden. And the brilliant Lavoisier, prominent among the men of
distinction who thronged the gay capital of France, was also working
in the same direction; it was he, who said about oxygen in one of his
own chemical works: “Cet air que nous avons decouvert presque en même
temps, Dr. Priestley, M. Scheele et moi,” so that he is sometimes
declared by his enthusiastic countrymen to be entitled to the merit of
the earliest discovery of this most magnificent of elements.
[Illustration: JOSEPH Priestley,
Born near Leeds, England, March 13, 1733; died in Northumberland, Pa.,
February 6, 1804.]
Priestley’s life included ample materials for a romance. On the one
hand, the ingenious discoverer in physics and chemistry and the friend
of that Benjamin Franklin—who was then minister at the brilliant
court of France from a handful of colonies that appeared capable of
being plucked up by the roots, but were instead destined to grow to
an unrivalled empire—himself a figure in a romance; and, on the other
side, a preacher to a dissenting congregation; a victim of public odium
for his liberal opinions on religious and political subjects; his house
set on fire by a mob, his apparatus wrecked, his library cast to the
winds; finally, an emigrant with his wife and children to an almost
unknown village in Pennsylvania, whose little burial-ground still gives
his bones repose;—these are but brief suggestions of the trials of this
perturbed spirit, in his life “sadly driven about and tossed,” now
cherished as one of those who in the realm of thought has made no mean
contribution to the glory of the English name.
Dr. Priestley prepared oxygen from red precipitate of mercury, a
substance now designated by the name mercuric oxide and by the formula
HgO. Heating this substance in a receiver and by means of a burning
glass or lens, he observed that a peculiar kind of air was evolved. He
further discovered that this air had an unusually stimulating influence
upon burning bodies, and was well suited for the respiration of living
animals. Priestley’s prime experiment was performed on the first day of
August, 1774, a date which may be accepted as almost the birthday of
modern chemistry.
Like many other great discoverers, Priestley was, to a certain degree,
anticipated. Thus a certain John Mayow, an English physician, fully a
hundred years before the time of Priestley’s experiment, enunciated the
doctrine that the atmosphere contains an air, in a certain sense the
essential food of animal life and of flame. But these wonderful views
of Mayow, brought forward too early for the state of thought at his
time, lay dormant and unproductive for an entire century.
First Method of Preparing Oxygen.
Oxygen may be prepared in many ways, but only two need receive
attention here. The first method is Priestley’s. If the red oxide of
mercury is heated over a powerful gas flame and in a tube of not easily
fusible glass, the oxygen passes from the metal and may be carried
by any small conducting tube into a convenient receiver filled with
water and standing in the _pneumatic trough_. If the gas so collected
is tested by means of a candle, having only a spark on its wick, the
oxygen is readily recognized by the fact that the taper promptly bursts
into a full and brilliant flame. This method is of historical interest
chiefly, though it may well attract some attention from the simplicity
of the chemical change involved. Thus this change is represented by the
following equation:
=2HgO= _heated_ = =O₂= + =2Hg=
Two molecules of One molecule of Two atoms of
Mercuric oxide, Oxygen, Mercury,
432 32 400
parts by weight. parts by weight. parts by weight.
\______________/ \____________________________________/
| |
432 432
A word about the pneumatic trough is not out of place here, because
this useful contrivance was the invention of Priestley. The name may
be appropriately applied to almost any vessel of water in which may
stand the open mouth of a bell-glass suitable for containing gas. The
water serves at once to seal the mouth of the jar, and also to afford a
material through which the exit tube of an appliance may be dipped, and
through which also the gas from the tube may freely and conveniently
flow into the bell-glass. Before Priestley’s time gases had been
collected in bladders or varnished bags, but the new contrivance
furnished a much superior means of detecting small quantities of gas
and working with them.
Second Method of Preparing Oxygen.
The second method, and that oftenest pursued, employs a salt not known
in Priestley’s time. This salt is called potassic chlorate and is
represented by the formula KClO₃.
This substance, when heated, evolves a large amount of oxygen, but it
does so with almost explosive violence.
The chemical change is represented by the following equation:
=2KClO₃= _heated_ = =2KCl= + =3O₂=
Two molecules of Two molecules of Three molecules of
Potassic chlorate, Potassic chloride, Oxygen,
245 149 96
parts by weight. parts by weight. parts by weight.
\______________/ \________________________________________/
| |
245 245
On the other hand, if the potassic chlorate is mixed with about
one-third of its weight of the earthy mineral known as black oxide of
manganese, (but called by the chemist, manganese dioxide,) the mixture
when heated evolves oxygen more slowly and continuously than the
chlorate alone—and it does it at a lower temperature. Strangely enough
however, the manganese dioxide appears to take either no _chemical_
part in the operation or else only a very obscure one. Indeed, some
other oxides will serve the same purpose, while they likewise appear to
undergo no chemical change.
In this method, as in the other, the oxygen gas produced may be
collected in a bell-glass over the pneumatic trough, and afterwards its
nature may be demonstrated as before by means of the taper having a
spark upon it.
The Properties of Oxygen.
It has been the custom of chemists to say of oxygen that it is a
_permanent gas_. The force of this expression is found in the fact
that until recently all attempts to liquefy it were futile. But recent
experiments, with apparatus capable of subjecting it at once to more
intense cold and to greater pressure than were ever before employed,
seem to demonstrate that it will turn to a liquid when these conditions
are carried to a sufficient extreme.
That oxygen is colorless and odorless appears plain from the properties
of the atmospheric air throughout which this gas is thoroughly diffused
and intimately intermingled, although it constitutes but one-fifth of
it.
Chemical Properties of Oxygen.
[Illustration: FIG. 34.—The rays of sunlight concentrated, by a lens,
upon a diamond placed in oxygen gas, with a view of proving the
combustibility of the gem.]
Of the chemical powers of oxygen the most striking and important seems
to be its marked tendency to combine with other elementary substances.
In many cases this combination does not commence except when the
substances are heated. Thus the noble buildings of a city are every
day and every night continuously and harmlessly bathed within and
without by that same oxygen, that, in time of conflagration, is ready
chemically to combine with their elements and as a result to reduce
the metropolis to ashes. But such combination, once inaugurated, often
itself affords sufficient heat not only to make the process continue,
but also to generate that flame or fire which is the token of what
is ordinarily called combustion. In this view, oxygen is often
spoken of as a supporter of combustion. That this property, known to
be associated with the atmospheric air, does in fact reside in the
oxygen of it, is to some extent proved by the more rapid and brilliant
combustion of the candle in pure oxygen.
Another interesting experiment is performed when a piece of charcoal,
which may be supported on a wire, is burned a little so as to acquire
a spark, and then is dipped in oxygen gas. The single coal would soon
cease to burn in atmospheric air, but it burns readily and brilliantly
in pure oxygen.
Even the diamond, the most compact and imperishable form of carbon
known, may burn in pure oxygen gas just as the most humble piece of
coal does, and the relationship of the gem to the commonplace fuel is
proved by this experiment.
[Illustration: FIG. 35.—The burning of a spiral of iron wire in a jar
of oxygen gas.]
Still another experiment in the same direction may be conducted with
sulphur. For this purpose a fragment of sulphur set on fire may be
dipped in a jar of pure oxygen. The sulphur burns with vastly increased
rapidity and with a violet flame much more brilliant than that of
sulphur burning in air.
Again, some substances not ordinarily considered combustible will burn
in oxygen gas. Thus a bundle of iron wire, to which a little lighted
chip is attached, itself takes fire and burns brilliantly when dipped
into oxygen gas.
The Products of Combustions in Oxygen.
As a necessary result of the combustion of substances in oxygen there
are produced a multitude of compounds called oxides.
This is true of the candle, which consists mainly of carbon and
hydrogen. When the candle burns, these two substances change into
oxides. The carbon produces carbon dioxide, whose formula is CO₂, and
which is familiarly known as carbonic acid gas. This oxide, it is
true, is not easily recognized by the ordinary observer because it is
an invisible gas, but the chemist can prove that it is in fact the
product of this combustion. At the same time the hydrogen produces an
oxide whose formula is H₂O and which will be recognized as the chemical
expression for water. And so water is in fact produced, though in the
form of vapor, by the burning candle.
Charcoal is composed almost entirely of what the chemist calls carbon,
and when it burns it produces the oxide called carbon dioxide (CO₂).
This is the same invisible gas that has already been declared to be
produced when the carbon of the candle is burned, and in this case as
in the other it is easy for the chemist to prove its presence.
In case of carbon, the chemical change is represented by the following
equation:
=C= + =O₂= = =CO₂=
One atom of One molecule of One molecule of
Carbon, Oxygen, Carbon dioxide,
12 32 44
Parts by weight. Parts by weight. Parts by weight.
\______________/ \____________________________________/
| |
44 44
And likewise when iron is burned, there is formed an oxide whose
composition is expressed by the formula, Fe₃O₄; (to this substance the
chemical name ferroso-ferric oxide is applied).
So when sulphur is burned, sulphur dioxide is formed (SO₂).
In this case the chemical change is represented by the following
equation:
=S= + =O₂= = =SO₂=
One atom of One molecule of One molecule of
Sulphur, Oxygen, Sulphur dioxide,
32 32 64
Parts by weight. Parts by weight. Parts by weight.
\_____________________________________/ \______________/
| |
64 64
Compound of Oxygen with Hydrogen.
[Illustration: FIG. 36.—Hydrogen gas, generated by use of zinc and
sulphuric acid, is then passed through a drying tube containing calcic
chloride (CaCl₂). By the act of combustion the union of the dried gas
with oxygen of the air produces drops of water.]
It has already been shown that the hydrogen escaping from a suitable
tube may be lighted in the air. If the burning jet is introduced into
oxygen gas the same combustion proceeds, only with greater energy. In
either case there is produced a compound of hydrogen and oxygen. This
compound is represented by the formula H₂O, a formula representing no
other than the familiar substance water. At the moment of combustion
of hydrogen very great heat is generated. In fact, a pound of hydrogen,
upon burning in pure oxygen, yields about four times as much heat
as a pound of pure carbon does in burning under the same favorable
conditions. Indeed, the pound of hydrogen, when in combustion, yields
more heat than a pound of any other substance known. On account of this
heat the water resulting from the burning hydrogen at first floats off
in the air in the form of vapor; but if the hydrogen flame is brought
in contact with some cooling surface, the water formed condenses in
drops upon it and thus it may be readily recognized as in its ordinary
form.
A great multitude of experiments show that the composition of water is
as follows:
+---------------------------------------------------------------+
| WATER IS MADE UP BY THE UNION OF, |
+----------+-------------------+---------------------+----------+
| | PARTS BY WEIGHT, | PARTS BY BULK, | ATOMS. |
+----------+-------------------+---------------------+----------+
| HYDROGEN,| 2 | 2 | 2 |
| | | | |
| OXYGEN, | 16 | 1 | 1 |
+----------+-------------------+---------------------+----------+
The composition of water, as displayed in the foregoing table, has
been demonstrated by analysis, this word meaning “the process of
taking apart.” Thus by chemical influences a portion of water may be
subdivided into its constituents and their amounts determined. On
the other hand the composition of water has also been made out by
synthesis, this word meaning “the process of putting things together.”
In this latter case, by putting together what are believed to be the
proper proportional amounts of hydrogen and oxygen to form water, and
then upon using some suitable means for bringing these things into a
state of true chemical combination, it has been found that they do
combine in fact to form water and in the proportions already given in
the table.
The Compound Blowpipe.
The fact of the enormous heat developed when hydrogen burns, was
known long ago, and it gave rise to the invention of a contrivance
for utilizing it. This has taken the form of the apparatus called the
compound blowpipe, also the oxy-hydrogen blowpipe.
[Illustration: FIG. 37.—Apparatus for analysis of water by use of the
galvanic battery.]
[Illustration: FIG. 38.—Apparatus devised by Dumas for determining the
composition of water.]
This blowpipe, as usually constructed, has a single jet or tip—to
which there is conveyed by separate tubes, on the one hand oxygen,
on the other hand hydrogen. The gases, when lighted, give rise to
a flame of but little luminous power but of intense heating power.
Many difficultly fusible metals, such as iron for instance, melt like
wax before it, while others, like lead and zinc, boil and vaporize
beneath its fervent breath. It must not be looked upon however as a
mere chemical toy; it has some uses in the arts. Of these one of the
most prominent is its application to the melting and refining of the
ores and alloys of platinum, substances which no ordinary furnace can
liquefy.
For purposes of this sort, a special furnace or crucible must be
provided, and it must be constructed of some substance that is itself
practically infusible. Such a material is found in quicklime (calcic
oxide, CaO), for this substance does not melt under the influence of
any known contrivance for producing heat. Moreover it does not conduct
heat rapidly, and thus any heat applied to the metal within, is not
subject to serious loss by being conducted away through the walls
of the vessel. For melting platinum then a crucible constructed of
quicklime, and having a cover of the same material, is employed. A
stream of burning gases from a compound blowpipe is forced through an
aperture in the crucible cover in such a way as to fall on the metal to
be melted.
[Illustration: FIG. 39.—Flame of the oxy-hydrogen blowpipe directed
upon a crucible in a furnace of lime.]
The Calcium Light.
Another interesting application of this blowpipe is found in the lime
light, an appliance also known as the calcium light and sometimes as
the Drummond light. In this apparatus, whatever may be its particular
form, the stream of burning gases is directed upon a small block or
cylinder of lime. Of course the block becomes highly heated,—in fact it
assumes a white heat, without melting; and while at this temperature it
gives out a dazzling light. This light has been utilized by architects
and engineers for carrying on important constructions during the
darkness of night. It is also often used in some of the finer forms of
the magic lantern, as for example in the various stereopticons used in
illustrated lectures. So numerous are the uses of the calcium light in
large cities that it has become a regular industry there to furnish
the oxygen and hydrogen gases in separate iron cylinders or cans,
into which they are pumped under great pressure.[5] (It is true that
illuminating gas is sometimes substituted for hydrogen with decided
economy in cost, and yet without serious loss of illuminating power.)
When the cylinders are in use the stop-cocks are slightly opened, and
the gases are under sufficient pressure to flow to the top of the
blowpipe as freely as can be desired.
[Illustration: FIG. 40.—Drummond light, or calcium light. The flame of
the oxy-hydrogen blowpipe directed against a block of lime renders the
latter intensely luminous.]
[5] DANGEROUS EXPLOSIBILITY OF MIXTURES OF OXYGEN AND HYDROGEN.—At
this point a warning should not be omitted, for mixtures of oxygen and
hydrogen gas, whether produced purposely or by accident, are capable
of very dangerous explosions. Even a soap bubble, inflated with the
mixed gases, and then lighted with a torch, explodes with tremendous
violence and a loud report. This result is all the more wonderful when
the extreme thinness and weakness of the filmy confining envelope is
considered. Such explosions are in entire harmony with the various
statements already made. For when the two gases combine, the intense
heat then generated gives rise to a momentary but enormous expansion
of the vapor of water produced by the combustion. The greatly expanded
vapor immediately strikes the air a sharp and violent blow. In
another instant however the vapor suddenly cools and condenses to an
exceedingly minute drop of liquid water. Immediately upon this effect,
the air that was previously forced outward immediately falls into the
vacancy left, and now a second blow results. It is these two violent
shocks the one following the other in almost instantaneous succession,
that produce the report; and to the same causes must be referred
the terribly destructive results of the accidental explosion of
considerable quantities of the mixed gases. It is plain therefore that
all contrivances, destined to employ these gases in close proximity,
must be handled with great caution when ready for use.
Oxygen as Related to Combustions in General.
But oxygen is prominent in many other combustions besides that of
hydrogen. Of course the best known and most common are those in which
the ordinary forms of fuel are the things burned. Here generally the
principal constituent of the combustible material is carbon.
Oxygen as Related to Animal Respiration.
Oxygen performs also one of its most important offices in connection
with the process of animal respiration. In the fulfillment of this
mission no element is known that can in any way act as a substitute.
The gas, which is to serve as the breath of life for the humblest as
well as the most exalted individuals of the animal creation, must
possess a combination of qualities truly marvellous when residing in
a single substance. Even a brief description of the ways in which it
discharges this delicate and manifold duty ought to substantiate the
general proposition.
Oxygen is qualified to sustain respiration by virtue of the exceeding
abundance of the atmospheric air, an abundance such that it extends
above our heads a distance of forty thousand times the height of a man.
Nor are the denizens of the sea forgotten, for oxygen possesses such
capacity for dissolving in water that there exists, absorbed in the
liquid of the rivers and oceans, enough of this vital gas to furnish
breath for all the finny tribes.
Again, the oxygen, so violent in its combinations, is yet bland enough
to pass through all the delicate passages leading into the lungs
without exciting the throat to the slightest cough; to filter through
the fine membranes of the lungs without doing an injury; to saturate
the blood, and to flow to every tissue and cell of the body, and not
only do no harm but everywhere accomplish a reviving work. It performs
throughout the animal frame a well regulated but no inconsiderable
combustion. Indeed the body of a living creature may be properly
looked upon as a kind of furnace, taking in air whose oxygen shall
sustain the combustion of worn-out parts. Nay more, these as they burn
do in their very death make as a final contribution the gift of that
warmth and glow which maintains the animal temperature at the vital
point.
While carrying out the important functions just referred to, oxygen
produces several gaseous substances, each of which, as if under the
constant direction of an ever watchful barometer, maintains its proper
bulk and pressure, so as to do no injury to the most delicate capillary
of a vein or to the tender walls of the smallest chambered cell of the
lungs. With each breath exhaled from the system, the blood, and thence
the lungs, discharge the gaseous products of the combustion already
described; plainly they do it somewhat in the same manner as a chimney
does in its proper action, only the lungs do their work in a far more
perfect way.
The parallelism is not strained here, for the burning of the animal
tissue in the body gives rise principally to the production of the gas
called carbon dioxide and the vapor of water, just as when a faggot
burns in the chimney-place, the carbon and the hydrogen of the wood
oxidize into the self-same products, both of which are wafted up the
flue and out into the great ocean of atmosphere beyond.
READING REFERENCES.
Gases, Liquefaction of
=Cailletet=, M.—Annales de Chimie et de Physique.
5 Sér. xv, 132.
———— Chem. News. xxxvii, 11.
=Coleman=, J. J.—Chem. News. xxxix, 87.
=Pictet=, R.—Annales de Chimie et de Physique.
5 Sér. xiii, 145.
———— Chem. News. xxxvii, 1, 23, 83.
=Roscoe and Schorlemmer.=—Chemistry. New York. 1878.
ii, pt. II, 516.
=Schutzenberger=, P.—Traité de Chimie Générale. i, 25.
Priestley, Joseph
=Brougham=, H.—Lives of Men of Letters, etc. p. 402.
———— Amer. Chemist. iv, 362-441; v, 11-35, 43, 210.
CHAPTER XV.
WATER.
As the most prominent compound of oxygen, water may properly receive
the reader’s attention at this time.
He who stands upon a high cliff and looks out upon the ocean,
experiences as one of his strongest impressions that of the
boundlessness of the expanse. And it is true that the area of
terrestrial waters is very wide, for in the aggregate their waves
cover more than three-fourths of the earth’s surface. But while their
superficial extent is so great, their depths are relatively but small.
When compared to the diameter of the earth the deepest ocean seems
shallow indeed. If the waters of the oceans were dried up or otherwise
wiped away, the roughness of the dry globe would be less relatively
than the roughness of an orange. In fact the total amount of water
actually existing upon the earth’s surface is less—relatively to the
entire mass of the globe—than the amount that would remain on an
orange after dipping it into a basin of water and then withdrawing
it. Notwithstanding these facts, the amount of water is so vast in
proportion to the littleness of human beings, and it has taken so
prominent a part in the phenomena observable by man, and it has been
such a powerful agent in the geological eras of the past, that it
is not surprising that its properties and history have excited the
interest of students and thinkers of all times. In the light of modern
chemical knowledge too, its various offices create an admiration that
is heightened, the more they are considered.
The chemical history, the characteristics, the properties, and the uses
of water, all these are important chemical topics; when one considers
further, the varied forms and uses in which this familiar substance is
employed in nature and in the arts, a subject is suggested that might
well furnish material for a volume. Plainly then only a few of its more
striking adaptations can be discussed here.
[Illustration: FIG. 41.—Egyptian Water-carrier.]
Importance of Water to Living Beings.
To living animals and plants water appears to be absolutely
indispensable. The reason for this is found not only in the fact
that water forms a necessary constituent part of most living beings,
but also because it serves as a sort of vehicle by virtue of whose
properties the vital processes are conducted and through which the
vital currents flow. It is easy to understand that if the atmospheric
air, which lies wrapped about our globe like a thin veil, were suddenly
wafted away, animal life would be instantly extinguished. Now, water is
not less essential than air. Banish water from the earth, and the life
of all animal and vegetable beings would instantly take its flight.
For the blood, that living tide which courses through the natural
gates and alleys of the body, contains water to the extent of nearly
seven-eighths of its weight. Again pure, unadulterated milk, rich as it
is in solid food materials dissolved or suspended within it, contains
not far short of 90 per cent of water. And further, an examination
of vegetable products reveals in them a preponderance of water such
as would not at first be suspected. Thus the following brief table
represents facts so surprising that it is at first difficult to accept
them:
Apples contain about 80 per cent of water.
Turnips ” ” 90 ” ” ” ”
Cucumbers ” ” 97 ” ” ” ”
Finally as an extreme example among the kingdoms of life it may
be mentioned that some forms of jelly-fish, as taken from their
appropriate home in the ocean, have been found to contain not less than
99 ⁹/₁₀ per cent. of water.[6]
[6] COOKE, JOSIAH P.: _Religion and Chemistry_. New York, 1864. p. 148.
The extraordinary and incredible proportion of water in living
beings is associated with the numerous, varied, and even apparently
contradictory offices to be performed by it, and the fitness of water
to fulfil these requirements is referable further to the curious and
interesting properties with which it is endowed. But it is so familiar
to every one and so bland in its action in its relation to most
well-known substances, that the ordinary observer fails to recognize
these properties and their marvellous adaptations.
One of the properties most appropriate for presentation in this
connection is the power water possesses of dissolving gases. It is
capable of storing up within itself, concealed from human view, almost
every gas with which it comes in contact. It displays this power upon
the atmospheric air, not only in its better known relations to man and
the higher animals, but also as respects the humbler population of the
globe. It will be seen by-and-by that the air consists in the main
of a mixture of two gases very different in their properties. One is
oxygen, the sustainer of animal respiration; the other, nitrogen, the
inactive substance existing in the air as a mere diluent of the active
oxygen. Now water possesses a very curious relation to these gases; it
naturally dissolves a larger proportion of oxygen than of nitrogen.
By reason of this property it acts upon the atmospheric air with a
selective effect highly suggestive of intelligent plan. For the gas
it selects to dissolve in larger proportional quantity is oxygen,—the
one absolutely needed to take the principal part in supporting the
respiration of the countless millions of fishes that make their natural
homes in all great bodies of water.
[Illustration: FIG. 43.—Arctic explorers employing dynamite to open a
channel through the ice.]
Terrestrial Circulation of Water.
Water is the chief liquid of the great globe itself. And it carries
on here a continued and beneficent circulation which may be properly
likened to that of the living animal and plant, except that it proceeds
on the cosmical scale. This circulation may be described as starting
in the depths of the ocean, where permanent currents are constantly
flowing in certain directions. These contribute to make the seas the
highways of navies even more completely than they would be if the
waters were always at rest. A yet more striking circulatory movement
is that initiated by the volumes of moisture which rise by constant
evaporation from the temperate as well as the tropical seas. This
water, ascending into the higher atmosphere, is carried by currents
of the air hither and thither and over the land, where by mountain
ranges or other natural means adequate to this purpose, it becomes
precipitated into a solid or liquid form. In this condensed form it
is recognized as beneficent when it is in cloud masses which delight
mankind with the purity of their fleecy whiteness, or the beauty of
their gorgeous coloring as well as when it is in the form of showers
which refresh the thirsty earth, or as the snow which protects it.
The rain and snow supply the numberless rivulets that contribute to
make up rivers, and these flow joyfully to the ocean and, mingling in
its waters, return to the source from which they came. Thus has been
pictured in brief an outline of the circulation previously suggested.
Water in the Solid Form.
Again, certain properties of water in the solid form are worthy of
presentation. Perhaps it is not inconsistent with the truth to say
that they are even more plainly beneficial. Thus in the form of snow,
water appears at first sight to be an emblem of cold. But when it
falls upon the earth it becomes a mantle or coverlet, which protects
the soil from the chilling effects of the wintry season and from that
rapid loss of heat by radiation off into space which the fields would
suffer without this protective coating. And so ice, as it forms on the
surface of lakes and ponds, manifests several remarkable properties.
Of these only two will be discussed here. They are both due to its
power of expanding at the moment of solidification. Most persons make
acquaintance with this characteristic of water by the inconvenient
bursting of pitchers and pipes, recognized as a disagreeable attendant
upon the winter’s cold. When looked upon with more fully instructed
eyes, however, it is discovered to be one feature of a remarkable
system which results in great benefit to the inhabitants of the earth.
For it is plain that as water in freezing expands, it thereby becomes
relatively lighter. On this account ice floats in water, whereas solid
substances generally sink in liquid matters of their own kind. Now the
ice formed upon lakes in the winter, stays at the top and thus protects
the water below from the chill of the colder air; so it prevents the
lakes from becoming uninhabitable to the fish. The same property
prevents a lake from becoming a mass of solid from the bottom upwards,
as would be the case if the ice upon freezing went to the bottom. The
summer’s sun would hardly be capable of thawing the solid masses so
formed. This same curious fact of the expansion of ice at the moment of
its formation contributes to the fertility of the soil. Thus the water
that penetrates the crevices of rocks, expands upon freezing, chipping
off those rocks, in fact pulverizing them little by little, and so
conveying fresh and valuable materials to the earth’s soils.
[Illustration: FIG. 42.—Water in the form of cumulus clouds.]
Water as Affecting Climate.
Further, the relations of water to heat are very interesting. “The
general aqueous circulation of the earth is a great steam-heating
apparatus, with its boiler in the tropics and its condensers all over
the globe. The sun’s rays make the steam. And wherever dew, rain
or snow fall, there heat, which came originally from the sun, and
which has been brought from the tropics concealed in the folds of the
vapor, is set free to warm the less favored regions of the earth. This
apparatus in nature, although so much simpler and working without
pipes, iron boiler or radiators, is exactly the same in principle
as the steam heater which may be seen at work in almost every large
factory.”[7] In other words, when water is changed into vapor in the
tropics, heat is not only requisite to the operation, but a definite
quantity of heat is actually stored up within the vapor so produced.
On the other hand, whenever in some cooler parts of the globe this
same portion of vapor condenses into the form of liquid, that heat
that was stored within it at the tropics is immediately evolved and
contributes something to the warmth of the region where condensation
takes place. Nay more, if the water, instead of falling as rain, falls
as snow a still larger amount of heat is by this means given out into
the atmosphere. This last statement is insensibly substantiated by the
expression often heard in winter, “the weather is too cold for snow.”
This common expression, translated into scientific language, means “the
air does not possess that amount of warmth that it would manifest if
snow were now condensing in the upper air and were ready to fall.”
[7] COOKE, JOSIAH P.: _Religion and Chemistry_. New York, 1884. p. 135.
It is not only with respect to those changes taking place when the
vapor of water changes to the liquid or the solid form that its heat
relations are beneficial to mankind. No lake can change one degree in
temperature—that is, grow warmer or cooler—without at the same time
exercising a contrarywise influence upon the air about it, and thus
a regulating one. In explanation of this declaration the following
statements may be made: When, in the intensely hot days of summer, a
lake or any mass of water become influenced by the high temperature, of
course its waters become warmer. But it is a curious fact that it takes
more heat to raise the temperature of water one degree than it does to
raise the temperature of the adjoining land one degree—or in fact to
raise any other substance known, one degree. Thus it appears that a
given amount of heat applied in a summer day to a lake will be absorbed
within the waters of that lake without raising the _temperature_ of
those waters to the extent that might be expected. So then in hot
weather the lake becomes an equalizer of temperature with a tendency in
the opposite direction, that is to cool the air about it. Now in cold
weather it becomes equally beneficial, only, as might be expected, in
the opposite direction. Thus the store of heat retained by the liquid
water is given out as the lake cools. For just as the water in order to
rise one degree in temperature requires, and indeed absorbs, more heat
than any other substance known, so naturally the same water, in cooling
one degree in temperature, freely gives out the amount of heat it had
previously stored within itself, which, as has been said is greater
than that stored up by any other substance known.
Water as a Working Contrivance.
When the moisture of the tropical oceans is taken up into the air by
evaporation, the sun has thereby done a truly stupendous amount of
_work_. For has it not lifted up high into the atmosphere an enormous
weight of this liquid material? Now as the vapor is wafted over the
land preparatory to falling as rain, it has acquired a position in
which it may do a great amount of work for human uses; for every
rain-drop, falling from its lofty position in the air, acquires thereby
a momentum which represents a quantity of force, minute in each
individual case but truly vast in the aggregate. Of this sum total but
a small portion is employed for man’s industrial uses; only a minute
fractional part is harnessed to the wheels that grind his food or weave
his clothing or transform the trees of the forest into his habitations;
yet the amount he does so employ—compelling it to do his work for
him—represents an enormous total quantity. All this work done, as well
as all that might be done, by the vast quantities of water allowed to
escape and violently run to waste, is referable back again to the sun
of the tropics, which has been enabled, by reason of the wonderful
properties of water, to store up all this power within it.
In view of what has been said, the sun and the water of the tropics may
be compared not inappropriately to the chief artificial contrivances
used in modern times for generating and applying mechanical
power—boiler and engine. As an ordinary steam-boiler imparts to water
the expansive and working power of steam, and again the ordinary
steam-engine utilizes this steam power so that it may be directly
applied to the labor of man’s workshops, so the sun of the tropics
lifts the water of the ocean high up into the air, and thus may be
likened to the boiler; while the rapidly running brooks may fitly
represent an engine in motion, ready to actuate any machine to which by
proper appliances it may be attached.
CHAPTER XVI.
SULPHUR.
Sulphur, in its aggregate in the earth is by no means an abundant
element. Thus its quantity is far inferior to that of oxygen, as is
strikingly illustrated by the diagram already presented. (See page 16.)
Yet sulphur was recognized by human beings thousands of years before
oxygen, which it has already been stated was discovered in 1774. The
comparative lateness of the discovery of this latter element, now
known to be that one which predominates largely over all others in the
earth, is due partly to the fact that free oxygen almost invariably
exists in gaseous form and that the idea or notion of gas is one of
recent growth. The fact that sulphur was recognized so much earlier
is due to many circumstances. _First_: It is found in the earth in
the solid condition—a form at once tangible and easy of recognition.
_Second_: Its yellow color helps to render it noticeable. _Third_: It
exists in the earth in countries which have long been the abode of
civilized beings. Thus it was early recognized in Italy. _Fourth_:
It occurs in deposits of such a character that it can be readily
obtained in a comparatively pure form from them. _Fifth_: It possesses
certain remarkable properties some of which would be easily detected
even by savage peoples, while others have for centuries excited great
interest in the minds of students of alchemy and chemistry. One of
these properties is the ease with which it assumes a liquid form—that
is, melts—when slightly heated. Another is the readiness with which it
takes fire and burns in the air. A third, closely connected with the
foregoing, is the striking blue flame produced when it burns. Still
another, and not less noticeable, is the choking and disagreeable odor
attendant upon this combustion.
Finally may be mentioned a circumstance which for a long time
contributed to make it peculiarly interesting to the alchemist, if not
to ordinary men: this is the fact that when sulphur is in the pure
form it may be burned away without leaving any ashes. In this respect
it differs from most other combustible materials. And this property
created the impression that sulphur is a sort of principle of fire, and
that it somehow exists in all combustible bodies. Indeed it is only for
about a hundred years that sulphur has been classified as a distinct
elementary form of matter. It is not intended to indicate here that the
strong interest of the alchemists in sulphur was mainly referable to
the circumstances of its combustibility. Its power of combination with
the metals was well known to them, and was recognized as a subject of
practical importance and one worthy of careful study and thought.
Natural Sources of Sulphur.
The principal supply of sulphur for commerce is obtained from the
volcanic districts of the island of Sicily. Here in fact there are
more than two hundred distinct establishments for production of the
substance, and they are capable of yielding about two hundred million
pounds of it per year.
The fact that sulphur is easily and widely recognized in the earth
has already been dwelt upon. But it occurs in nature in a great
variety of forms. The first and most striking form is that of free and
uncombined sulphur. In this condition it occurs either as masses or
as fine powder. Sometimes these materials possess the well-known and
easily recognized yellow color of sulphur; sometimes however the color
is white or otherwise disguised by reason of some peculiarity of the
sulphur itself or else because of the admixture of foreign substances.
Deposits of sulphur occur in the most considerable quantities in the
neighborhood of either active or extinct volcanoes. Thus sulphur earth
occurs near Vesuvius and Ætna, also in the vicinity of the volcanoes of
Iceland, in Central America and in the Sandwich Islands. In the region
of some extinct volcanoes the soil is impregnated with sulphur to the
depth of twenty or thirty feet and such soil is therefore a convenient
source of the element.
Purification of Natural Sulphur Ores.
In obtaining sulphur from the earth for commercial purposes, two simple
processes are resorted to. By the first method masses of the sulphur
earth are heaped up into a pile, in connection with a small amount of
fuel and over a shallow depression in the earth. Upon setting the mass
on fire, considerable quantities of sulphur escape combustion, and
so melt and run down to the ground below the heap. When the fire is
extinguished, the sulphur that collected beneath may be secured in a
form now only slightly impure.
[Illustration: FIG. 44. _Calcarone_ or heap of burning mineral from
which sulphur is obtained.]
[Illustration: FIG. 45.—Sketch illustrating the process of refining
sulphur.]
The second method of purification of the earth is still conducted
in Sicily in the following crude manner, though this is quite an
improvement upon that just described. A slightly inclined plane of
masonry is built upon the ground. Around the edges of this plane a low
wall is erected. At the lower side of the plane the wall is perforated.
Upon the surface of the plane large masses of sulphur earth are
carefully piled up so as to form a well-built heap. When it reaches
the proper height its outside is covered all over, first, with small
fragments of the same kind of earth, and then with its fine dust. Some
sulphur at the lower portion of the heap is then set on fire at several
points. The heat from the sulphur that burns melts other portions of
it, which then trickle down the spaces between the masses of rock.
This melted material, finding the bottom of the pile, runs freely to
the lowest portion of the platform, then through the perforations and
out into wooden boxes placed to receive it. The heap burns for two or
three weeks, at the end of which time the operation is finished. When
the mass is cool it is torn down, and a similar pile is erected from
fresh portions of the sulphur earth. The objectionable features of this
process are at least four. First, the consumption of sulphur as fuel
is a wasteful one. But in reply it may be said that no cheaper fuel
is accessible where this manufacture is carried on. Again, the great
volumes of sulphur dioxide given out by the burning _calcaroni_—as
the heaps are called—are injurious to the health of the workmen.
Further, these same products exercise a very destructive effect upon
all vegetation in their vicinity. In fact on this account the Italian
government has provided by law that this work shall not be carried on
at all between July 1st and December 31st. Finally the method is not as
successful with the richer ores, for they break down into powder which
it is difficult to utilize in the calcaroni.
A new and greatly improved method, and one which overcomes all the
objections above cited has recently been introduced. In this, the
ore is placed in perforated metal baskets and then immersed in tanks
containing hot solutions of calcic chloride. Under these conditions the
sulphur melts out from its ore and falls to the bottom of the tanks,
whence it is drawn out by stop-cocks in a comparatively pure form.
Sulphur is generally subjected to a still further purification. This
is conducted somewhat as follows. The crude sulphur, being melted in
a suitable retort and over a coal fire, changes into vapor and passes
into an apartment constructed of stone or brick, and prepared for the
purpose. In this apartment, the sulphur at first condenses on the walls
as minute yellow crystals or powder called flowers of sulphur. When the
first charge of sulphur in the retort has been completely vaporized
a new supply is allowed to run in, this time in the liquid form from
a small heater placed above the retort. The waste heat from the
furnace melts the sulphur in the heater, from which it flows into the
retort (by means of the tube shown in the diagram). When a sufficient
amount of flowers of sulphur has collected in the chamber, the fire is
extinguished. The purer product is then removed. Afterward the whole
operation is repeated.
The refining may be conducted so that the temperature of the condensing
apartment may rise considerably; in this case the vapor in it changes
to the liquid form. This liquid may be drawn off at the base of the
chamber into a small receiver, from which it is ladled into moulds,
which give it the form of cylinders known in trade as roll brimstone.
Natural Compounds of Sulphur.
Sulphur is also found in the earth in the form of certain chemical
compounds. Some of these are very widely distributed. They may be
divided into two classes. The first class—whose representatives are
by far the more abundant—includes the metallic sulphides, that is,
compounds formed by the direct union of sulphur with some metallic
substance. As examples of compounds of this class we mention:
Sulphide of iron (commonly called iron pyrites and having the formula
FeS₂).
Sulphide of lead (commonly called galena, and having the formula PbS).
Sulphide of zinc (commonly called blende, and having the formula ZnS).
Sulphide of mercury (commonly called cinnabar and having the formula
HgS).
Many other examples of similar import might be given, for it is a
well-known fact that most of the heavy metals occur in the earth in
combination with sulphur.
The other class of compounds also containing sulphur combined with the
metals has usually oxygen in addition. Two examples of this class may
be given here—calcic sulphate (commonly called _anhydrite_, and having
the formula CaSO₄); also baric sulphate (commonly called _heavy spar_,
and having the formula BaSO₄).
Sulphur is very widely distributed in animal and vegetable matters.
In these it exists, not as an uncombined element, but in union with
others. Indeed such compounds have many other elements besides the
sulphur, and they are characterized by decided complexity of structure.
But sulphur is oftener a component of animal matters than of vegetable.
The presence of sulphur in an egg is proved by an experiment of
every-day occurrence. That is to say, the silver spoon with which
the egg is eaten becomes blackened. This blackening is due to the
production of a new compound formed by a true union of sulphur from the
egg, with a part of the metal of the spoon. In fact the black material
is sulphide of silver, and it may be represented by the formula Ag₂S.
A French chemist has estimated that in the body of a human being of
ordinary size there exists, in the aggregate, not far from one quarter
of a pound of sulphur. To this, he adds the curious estimate that the
entire human population of France may be represented as containing not
far from nine millions of pounds of sulphur.
Chemical Properties of Sulphur.
The chemical properties of sulphur may be said to be its most important
and interesting ones. That it has a wide range of chemical aptitudes
is shown by the fact that it combines in simple forms of union with a
majority of the elements known. Thus it has strong affinities for most
of the metals. On the other hand it combines with various degrees of
attractive force with nearly all the non-metals as well.
Evidently then, sulphur forms a very large number of chemical
compounds. While the limits of this work are such as to make it
impossible to describe many of them, there are three that may with
propriety be briefly discussed in this place, and these are:
Sulphuretted hydrogen (H₂S),
Sulphur dioxide (SO₂),
Sulphur trioxide (SO₃).
Sulphuretted Hydrogen.
This substance is a colorless gas. It has an extremely offensive
odor; in fact it is a prominent component of that numerous group of
gaseous products of decomposition of animal matters that produce the
disagreeable smell attendant upon the decay of the latter.
Again, it is found in the waters of certain natural sulphur springs,
and it is a remedial agent of considerable value when properly applied
externally or when taken into the stomach. When received into the
lungs, however, it is decidedly poisonous.
A considerable number of simple experiments may be tried with it.
In these the gas used is generated by adding diluted sulphuric acid
to artificial ferrous sulphide. The ferrous sulphide is usually
manufactured by heating a mixture of roll brimstone and iron filings
in a sand crucible. In producing the gas, the chemical change is
represented by the following equation:
=FeS= + =H₂SO₄=
One molecule of One molecule of
Ferrous sulphide, Sulphuric acid,
88 98
parts by weight. parts by weight.
\___________________________________/
|
186
= =H₂S= + =FeSO₄=
One molecule of One molecule of
Sulphuretted hydrogen, Ferrous sulphate,
34 152
parts by weight. parts by weight.
\________________________________________/
|
186
For the purpose of the experiments here mentioned, a flask or bottle
may be used to prepare the gas and convey it into another bottle
containing water. In the water, the sulphuretted hydrogen gas dissolves
in such quantity that the solution so afforded may be conveniently
employed for showing the properties of the gas itself.
The following interesting experiments may be performed by use of this
solution:
1. Dissolve in water a small quantity of plumbic acetate, also called
sugar of lead. Filter this solution if convenient. To the clear liquid,
add some sulphuretted hydrogen water. A black precipitate of plumbic
sulphide (PbS) should immediately appear.
2. Dissolve in chlorohydric acid a fragment of white-arsenic not bigger
than a pin’s head. To the solution, freely add sulphuretted hydrogen
water. A beautiful lemon-yellow precipitate, consisting of arsenious
sulphide (As₂S₃), should result.
3. Dissolve in chlorohydric acid a minute quantity of tartar-emetic.
To the solution, freely add sulphuretted hydrogen water. A beautiful
orange red and flaky precipitate of antimonious sulphide (Sb₂S₃) should
appear.
4. Dissolve in water a minute fragment of cupric sulphate, commonly
called sulphate of copper or blue vitriol. To the solution, add some
of the sulphuretted hydrogen water. This should instantly give rise to
a black precipitate of cupric sulphide (CuS).
5. Dissolve in water a small quantity of zinc sulphate. To the
solution, freely add sulphuretted hydrogen water. There should appear
in this case a white precipitate consisting of zinc sulphide (ZnS).
These few experiments show that sulphuretted hydrogen is a convenient
substance for bringing sulphur into union with the metals, and,
moreover, they sustain the statements already presented, that many
metals show strong affinity for sulphur and marked tendencies to
combine with it. For these reasons sulphuretted hydrogen is much used
in chemical laboratories for distinguishing one metal from another.[8]
[8] See Appleton’s Qualitative Analysis, published by Cowperthwait &
Co., Philadelphia; p. 14.
Sulphur Dioxide.
When sulphur burns in oxygen gas or in atmospheric air, it gives rise
to a new gas of choking and offensive odor. This is the same substance
as that produced in the first stages of the burning of a sulphur match.
It is a substance of considerable importance in the arts, first,
because it is always produced in one stage of the process used in the
manufacture of sulphuric acid. Now sulphuric acid (commonly called oil
of vitriol) is a commercial product of enormous consumption. (See page
152.) Again, sulphur dioxide is used, as such, to a considerable extent
in the arts, the principal uses being in the bleaching of straw and
woolen goods. Chlorine as a bleaching agent has already been discussed,
but it is used mainly for the bleaching of cotton and linen goods; it
has an unfavorable and injurious action upon straw and woolen goods.
The way in which these latter are bleached by the use of sulphur may
be illustrated by a very simple experiment. Place a few fragments of
roll brimstone in a small crucible. Heat the crucible carefully until
the sulphur takes fire. Then cover the burning sulphur with a glass
lamp-chimney, or any other suitable contrivance. In the top of the
chimney hang a moistened carnation pink or other red flower. A few
minutes exposure to the gas, results in a partial bleaching of the
flower.
On a commercial scale, the sulphur bleaching process is conducted
in practically the same manner. For bleaching woolen goods there is
provided a small wooden house having a brick floor, with a small pit in
the centre. The goods are hung up in this house. The pit is filled with
sulphur which, when all is ready, is set on fire by throwing a piece
of red-hot iron upon it. Now the doors and windows of the house are
closed. Of course the sulphur burns into sulphur dioxide. The operation
is allowed to proceed without any further attention during one night.
The gas distributes itself throughout the goods and bleaches them. The
next morning the doors and windows are opened, and, when the fresh air
has driven the sulphur dioxide from the chamber, the goods are found
bleached. Everyone knows, however, that this bleaching has not the
permanence that chlorine bleaching has. Thus white flannels very soon
return to their original yellowish shade.
Sulphur dioxide is placed by the chemist in the class of acid
_anhydrides_. This term is intended to carry the meaning that
substances belonging to this class combine with water to form acids.
In accordance with this form of expression, sulphur dioxide is also
called _sulphurous anhydride_. Plainly this means that sulphur dioxide
with water will form an acid. Such seems to be indeed the case, for
water has the power of dissolving large quantities of sulphur dioxide,
and when it does so the water acquires the characteristics of an acid.
In fact it is then called sulphurous acid. The chemical change is
represented by the following equation:
=SO₂= + =H₂O= = =H₂SO₃=
One molecule of One molecule of One molecule of
Sulphur dioxide, Water, Sulphurous acid,
64 18 82
parts by weight. parts by weight. parts by weight.
\___________________________________/ \______________/
| |
82 82
One special characteristic which justifies the name sulphurous acid,
is the fact that the solution so produced has the power of producing a
series of salts as the other acids do. In this case, the salts have the
general name sulphites.
CHAPTER XVII.
SULPHUR TRIOXIDE.
Sulphur trioxide does not exist by itself in nature. Moreover it is but
little known even as an artificial product. It is not an article of
ordinary sale, though it is occasionally made by the chemist. Yet it
is a constituent part of one of the most important compounds known to
modern industry. That compound is sulphuric acid.
Sulphur trioxide is a white solid, but it cannot easily be kept so.
This is because it has very strong affinity for moisture. It fact it
readily absorbs that water-vapor which is distributed through the
atmosphere, even in dry weather and when the ordinary observer would
suppose that the air contained no moisture at all. When it absorbs
moisture it chemically combines with it, forming sulphuric acid.
The chemical change is represented by the following equation:
=SO₃= + =H₂O= = =H₂SO₄=
One molecule of One molecule of One molecule of
Sulphur trioxide, Water, Sulphuric acid,
80 18 98
parts by weight. parts by weight. parts by weight.
\____________________________________/ \_______________/
| |
98 98
On account of this reaction, sulphur trioxide is often spoken of as
sulphuric anhydride, the term anhydride being intended to suggest that
the substance so named is derived from an acid by the removal of water
from the latter. Thus sulphuric acid _minus_ water produces sulphuric
anhydride. And this harmonizes with what has before been declared,
namely, that sulphuric anhydride—or sulphur trioxide—_plus_ water
produces sulphuric acid.
Sulphuric Acid.
This substance is known to commerce chiefly under the name of oil
of vitriol. It is an oily liquid nearly twice as heavy as water. It
has very powerful chemical action upon most substances with which
it comes in contact. Moreover, its market price is very low, that
is, between one and two cents a pound at wholesale. To these two
facts last mentioned—that is, the marked chemical power and the low
price is referable the enormous demand for the substance. To be
sure, increase of demand and fall in price have a reciprocal action;
for even a slight cheapening of a substance widens considerably the
range of its possible uses and increases the amount consumed. Again,
increase of demand and consumption, lead manufacturers to increase
their production, a circumstance which is generally followed by lower
price. The manufacture of sulphuric acid exemplifies these well-known
principles of political economy. The manufacture of this substance has
risen within the last hundred years from almost nothing to a present
annual production of about nine hundred thousand tons in Great Britain
alone. The price meanwhile has fallen to about one-thirtieth of what it
was in the middle of the last century. At the present time the price
of oil of vitriol seems to be steadily decreasing, while the amount
produced is steadily increasing in England, France, Germany and the
United States—indeed in all countries pervaded by active industrial
enterprises. It will be generally admitted, as M. Dumas has said, that
the amount of sulphuric acid consumed affords a very precise measure
of the advancement in industrial arts of a given country or of a
historical epoch.
[Illustration: FIG. 48.—Section of chambers for manufacture of
sulphuric acid.]
Uses of Oil of Vitriol.
It would be difficult to enumerate the many industries that demand the
use of sulphuric acid. It must likewise be admitted that there are
but few manufacturing operations which do not directly or indirectly
involve its employment. The industries that stand in the front rank
as direct consumers of this acid are those that involve the following
processes, namely: the bleaching of cotton goods; the removal of
scale from iron in its various forms, such as castings, wire, etc.;
the changing of corn starch into the variety of sugar commonly called
glucose; the refining of bullion of gold and silver; the refining
of petroleum oil; last, but not least, the manufacture of chemical
fertilizers for agricultural use. Less directly, but still in enormous
quantities, it is used in the manufacture of soda-ash, and bleaching
powder already referred to as having reached an incredible consumption;
in the manufacture of alum; in the manufacture of both of the great
acids of commerce, chlorohydric acid and nitric acid, which must be
said to come next to sulphuric acid in usefulness; and finally, in
almost all the distinctly chemical industries.
Manufacture of Sulphuric Acid.
Notwithstanding the extremely low price of oil of vitriol and the
immense quantity of it manufactured, its production implies a series of
processes far more complicated than those involved in the preparation
of any other well-known acid. Moreover, although the various intricate
details of its preparation are matters of thorough _experimental_
knowledge to the producer, there are several steps which are not yet
clearly comprehended even by the most eminent chemists of the age.
The process of manufacture, as at present conducted, is properly
described as a continuous one. By this it is meant that the raw
materials are steadily introduced at one end of the apparatus used, and
the finished product is steadily drawn out at the other, the process
meanwhile going on without interruption, night and day, for years. In
order to a better comprehension of the process it is here described in
four stages.
In the first stage, sulphur is burned in a current of air. The material
employed is either partly refined Sicily sulphur, or what is largely
used at the present day, some mineral compound of sulphur, like the
iron and copper pyrites. In either case, sulphur dioxide (SO₂) is
formed. This is the well-known choking gas given out by a burning
sulphur match. As produced on a large scale the gas passes into a
series of enormous leaden chambers. These are, in fact, rectangular
rooms, often as large as one hundred and fifty feet long, twenty feet
wide and fifteen feet high. Generally at least three chambers are in
a series, connected by leaden pipes. Sulphur dioxide gas flows in a
steady stream into the series of chambers and toward the high chimney
of the works, whose draft produces the advance of gases through the
whole apparatus.
[Illustration: FIG. 46.—Section of building fitted for manufacture of
Sulphuric acid; _f_, furnace where sulphur is burned and oxides of
nitrogen are liberated; _k_, boiler from which steam is supplied to the
leaden chamber, _A_.]
The second stage is the most complicated one. It is the oxidizing of
the sulphur dioxide (SO₂) into sulphur trioxide (SO₃). This is indeed
accomplished by means of the oxygen of the air. But this oxygen is not
capable of _directly_ changing SO₂ into SO₃. Certain gaseous oxides of
nitrogen are forced into the chamber at this stage; and these have the
remarkable power on the one hand of taking oxygen to themselves from
the air, and on the other of imparting this oxygen to the compound SO₂
in such a way as to change it into the compound SO₃. Of course the air
is impoverished by the operation, a fact which necessitates a fresh
supply of it through the entire series of chambers.
The third stage is one whose principle has already been explained.
At various parts of the chamber, jets of steam are blown in. While
these aid mechanically in the progress of the gases through the entire
series, their main purpose is to furnish water which shall combine
with sulphuric anhydride to produce sulphuric acid.
Although this chemical change, represented by the following equation,
has been given before, it may not be improper to repeat it here:
=SO₃= + =H₂O= = =H₂SO₄=
One molecule of One molecule of One molecule of
Sulphur trioxide, Water, Sulphuric acid.
80 18 98
parts by weight. parts by weight. parts by weight.
\____________________________________/ \_______________/
| |
98 98
The effect of the steam is to give rise to a steady rain of oil of
vitriol in the chambers. Of course this liquid collects at the bottom.
Thence it is drawn off, for treatment in a fourth stage. It is plain
that up to this point the series of chemical reactions takes place in
what we may characterize as a vast but irregular tube, open at both
ends. This tube is enlarged here and there into great pockets which
constitute the chambers. It is bent into a form appropriate to the
conditions of the business. It is entered here and there by pipes for
introducing the agents whose proper interaction gives rise to the
product sought. It is also tapped for the purpose of drawing off the
acid generated. This open tube has its final exit into the atmosphere
through the tall chimney with which it is connected. It has its first
connection with the atmosphere at the open throat, which swallows at
once the vast volumes of sulphurous gas from the sulphur burned, and at
the same time levies upon the air to contribute its oxygen to produce
the substance which is the final purpose of the whole industry.
The fourth stage is the only one that may be properly said to be
disconnected from the others. The continuous process already described
cannot properly be made to produce acid of the strength demanded by
commerce. In the fourth stage then, the acid from the chambers is
boiled with a view of expelling some of the water in it, and thus of
producing a more concentrated product. This evaporation is itself
no inconsiderable portion of the business. It is conducted first in
shallow tanks of lead, and finally in costly stills of platinum. When
at length the acid in the platinum stills has attained the proper
degree of concentration, it is drawn out by means of a siphon tube,
and through a cooling tank of cold water, into the glass flasks called
carboys, in which it makes its appearance in commerce.
[Illustration: FIG. 47.—Section of apparatus used for concentrating
sulphuric acid. _A_, _A_, leaden pans in which the first evaporation is
conducted; _B_, platinum retort in which the concentrating is finished.]
Of course the account thus given is but a general sketch of this
great industry. Associated with the apparatus and the processes here
briefly described there are employed in actual working a multitude of
other devices and operations. Indeed it might be anticipated that the
successful conduct of a business of such magnitude and complexity would
draw upon the inventive resources of some of the best minds that have
been brought to bear upon chemical industries.
READING REFERENCES.
Sulphur Industry in Sicily.
=Barbaglia=, A.—Chem. News. xxxiv, 245; xxxv, 3, 28.
=Vincent=, C.—Am. Chem. Journal. vi, 63.
Sulphur, Extraction of.
=Sestini=, F.—Jour. of Chem. Soc. of London. xxviii, 335.
Sulphuric Acid.
=Affleck=, J.—Chem. News. xxxvii, 167, 192, 207.
=Hasenclever=, R.—Chem. News. xxxv, 48, 67, 88, 118, 183,
189, 214, 227.
CHAPTER XVIII.
BORON.
The white substance called borax has long been known to exist as a
solid deposit in the earth of many parts of the ancient East. But
its uses have increased a thousand fold as the result of the modern
discovery of new and far more abundant sources of it. Thus in the
manufacture of porcelain and in other of the industrial arts, and as a
remedial agency in medicine, borax has now come to be an important and
truly useful substance to mankind.
The knowledge of its composition is referable to a very recent date;
only in the present century its character as a true chemical salt was
fully made out. Borax is now recognized as sodic borate, which usually
exists in a form holding ten molecules of water of crystallization;
accordingly the chemical formula is Na₂B₄O₇ + 10 H₂O. From this it
appears that, in addition to the well-known substances sodium and
oxygen, borax contains a special and peculiar element called boron—a
name evidently derived from borax. Again, being a salt, the substance
must be viewed as containing an acid—or more properly speaking, the
representative of an acid. That this is indeed the fact may be readily
proved. If borax is dissolved in water in such a way as to form a
concentrated solution, then, upon addition of chlorohydric acid, a
solid substance separates out in pearly flakes; this upon subsequent
examination is found to be an acid. This solid acid has received the
name boric acid, and it may be represented by the formula H₃BO₃.
[Illustration: FIG. 49.—View among the Tuscan lagoni before the
introduction of the borax industry.]
[Illustration: FIG. 50.—View in Tuscany after the establishment of the
borax industry.]
Sources of Borax in Nature.
For a long time the only known source of borax was the natural crusts
of this substance found principally in the ground in certain parts of
Asia. At the present day, however, borax is obtained from Borax Lake,
in California, in very large quantities. In fact the commercial needs
of the United States for this substance, are readily supplied from
borax found within its own borders. The most interesting and important
step in connection with the preparation of borax dates back to about
the year 1776, when the fact was made public that certain lagoons in
Tuscany contained boric acid in their water. It was not until about
the year 1828, however, that the manufacture of boric acid from this
source was successful upon a large scale. In some of the Tuscan valleys
there are volcanic crevices in the earth, called _suffioni_. From
them steam escapes charged with certain compounds of boron. When this
steam is brought in contact with water, boric acid is liberated in the
water. The method of securing the acid is as follows: A ring of masonry
is built in a suitable place and so as to include several suffioni.
Sometimes new suffioni are artificially bored within this ring. Into
the basin so produced, water from some convenient spring is conducted.
The steam from the suffioni passing into the water, produces boric acid
there. When the water is sufficiently charged, it is made to flow as a
gentle cascade over a long series of shallow pans. The liquid readily
evaporates from these pans for under them also, steam from suffioni is
turned. It is indeed this last mentioned step in the manufacture, that
became the turning point which has lead to its successful prosecution.
The great cost of fuel for artificially evaporating the acid liquors,
rendered unprofitable the earlier attempts to utilize this source of
boric acid. A French gentleman, M. Larderel, suggested the use of steam
from suffioni for the evaporation of the liquids produced, and the
process was so successful that he quickly derived a colossal fortune
from its employment. At the same time he enriched the territory that
was previously not only desert and unproductive, but also was looked
upon by the inhabitants with superstitious dread and as little better
than the gate of the infernal regions. As a result of these inventions,
a barren and unfrequented territory has been changed to a seat of
thriving and beneficial industry. Finally, it is interesting to note
that for his services in developing the boric acid industry M. Larderel
was created Count of Monte-Cerboli by the Grand Duke of Tuscany.
READING REFERENCES.
Boric Acid, Manufacture of, etc.
=Payen.=—Annales de Chimie et de Physique. 3 Sér. i, 247;
ii, 322.
=Dieulafait=, L.—_loc. cit._ 5 Sér. xii, 318; xxv, 145.
Borax Lagoons of Tuscany.
=Harper’s= Magazine. i, 397.
CHAPTER XIX.
NITROGEN.
Nitrogen is an important constituent of our atmospheric air of which
it makes up about eighty per cent. The other twenty per cent., as has
already been stated, is oxygen. In the air the nitrogen is found in the
free or uncombined state, and we may reasonably suppose that it exists
here to fulfil some important offices. Unquestionably one of these is
that of diluting the oxygen, the energetic constituent of air, and
lessening its activities—for nitrogen itself is extremely inert. From
the part it performs in the atmosphere, nitrogen derives a considerable
portion of the interest with which it is invested.
Discovery of Nitrogen.
Perhaps the first clearly defined recognition of nitrogen as a
constituent of the air is referable to the genius of a wonderful man,
who, in obscurity and with the most imperfect appliances, obtained
an insight into the constitution of substances which has rarely been
surpassed. Reference is here made to the Swedish, or rather Prussian,
chemist Scheele, some of whose discoveries have been briefly adverted
to in earlier chapters. It has already been stated that the distinct
notion of a gas dates but little more than a hundred years back; and
this statement is intended to call to mind that brilliant period in the
history of chemistry when among others, Black in Scotland, Cavendish
and Priestley in England, Lavoisier and his worthy associates in
France, and finally, the sagacious Scheele in Sweden, were engaged in
a generous rivalry in chemical studies, which made the close of the
eighteenth century a period in the history of chemistry that will not
be forgotten so long as the science itself shall endure. At this time
unstinted effort was devoted, with ingenious but imperfect appliances,
to the study of gases. Of course the atmospheric air, as the gas most
vast in quantity, most accessible for experiment, most important in
its relation to the economy of living nature, received its full share
of attention. It was at this period that Dr. Rutherford, a professor
in the University of Edinburgh, demonstrated that after living animals
have breathed in a confined bulk or volume of air, there remains an
inert and peculiar gas behind. And Priestley showed that after the
burning of charcoal in a confined volume of air there remains a gaseous
material equal to about four-fifths of the amount of original air used.
But it was Scheele who first clearly pointed out that the air contained
a second distinct constituent that fails to support combustion and
animal respiration. And Lavoisier first proved this constituent to be
an elementary substance and he gave to it the name _azote_, which it
still retains in the French nomenclature of chemistry.
It is not forgotten that a critical examination of the history of
human knowledge respecting the atmosphere reveals the fact that a
wonderfully clear, even though incomplete, account of the functions
of the active constituent of the air was printed as early as the year
1669, by an English physician named John Mayow.[9] This affords another
illustration of the fact, recognized by all students of history, that
often in the progress of knowledge, before the clear and full dawn
there seems to be a twilight; at such a time, and before the darkness
has been fully dispelled, there have been found here and there men
gifted with supernatural vision who have been able to read the laws
of nature long before acknowledged philosophers even had found light
sufficient. And so the truths learned by Mayow, though clearly stated
by him, failed of recognition until they were rediscovered a hundred
years later. (See p. 121.)
[9] KOPP, HERMANN: _Geschichte der Chemie_. Dritter Theil. s. 193.
Preparation of Nitrogen.
Nitrogen is usually prepared from the air by the withdrawal of oxygen
from it. This withdrawal is effected by some substance which has a
strong affinity for oxygen.
Thus one method frequently resorted to for the preparation of nitrogen,
is to burn phosphorus in air. Phosphorus is placed in a little crucible
of porcelain and then floated upon a cork on the surface of water
in a pneumatic trough. A bell-glass of air is now inverted over the
phosphorus, after the latter has been set on fire. The phosphorus burns
at the expense of the oxygen in the bell-glass. Thus the oxygen is
little by little withdrawn and as a result the nitrogen is left.
[Illustration: FIG. 51.—Preparation of nitrogen from air, by absorbing
the oxygen by burning phosphorus.]
Another method for preparing nitrogen is based upon the same general
principle. It is the following: Pass a current of dry air through a
tube containing copper turnings heated to dull redness in a furnace.
Under these circumstances the copper absorbs oxygen from the air, and
leaves the nitrogen, which passes on to a receiver prepared for it.
Properties of Nitrogen.
Nitrogen prepared by these methods, or by any others, possesses the
following characteristics:
It is a gas that is colorless, odorless and tasteless. It is not
necessary to make any scientific demonstration of these facts, because
with every breath of air drawn into the lungs of a human being a large
quantity of nitrogen is inhaled, and it is easily perceived to be
without odor or taste, while a glance of the eye into the atmosphere
shows that, in moderate quantities at least, it is free from color.
Up to a period dating but a few years back, nitrogen was spoken of as
one of the permanent gases; and this word permanent was intended to
convey the idea that it is not condensable to the liquid form. It is
true that it was surmised that for every gas there must be a point
of very low temperature and very great pressure at which the gas
would assume the liquid form. Yet nitrogen, and two or three others,
successfully resisted all such attempts to liquefy them until toward
the close of the year 1878. Since that time, successful effort has been
made to bring to a higher degree of perfection the appliances used
for subjecting gases at once to intense cold and enormous pressure.
With these, it is believed that small amounts of nitrogen have been
liquefied. And it may even be said that there is now no permanent gas
known, but that all gaseous substances may in fact be liquefied.[10]
[10] SCRUTZENBERGER, PAUL: _Traité de Chimie Générale_, Paris, 1880, i,
30.
As a simple and uncombined substance, nitrogen is characterized by
extreme inactivity. It does not burn; it does not support combustion;
it cannot be made to enter into chemical union with other substances,
except by specially devised and circuitous processes.
While on the one hand inertness is the marked characteristic of the
nitrogen, on the other hand this element is a constituent of a very
large number of compounds. Moreover, these compounds are themselves
often characterized by a high degree of activity. Of the last two
declarations the first one seems to be inconsistent with the properties
of nitrogen in its elemental form. The second one seems inconsistent,
but less so when it is carefully considered. Thus the activity of
the compounds of nitrogen is to a certain extent referable to their
instability. The meaning of instability, as used here, is that the
compounds are easily decomposed; and this is because the inert
nitrogen readily lets go its hold upon the other elements. Whence it
appears, that the activity of the compounds, in reality referable to
the energetic action of the element or elements now loosed from the
nitrogen, rather than the nitrogen itself.
In nature, nitrogen is found as a constituent in some very important
compounds. Thus it seems to be an essential element of some of the
principal animal matters, such as muscular fibre and the material of
the brain. Again, it is a constituent of ammonia gas and also of a
multitude of compounds derived from it. Now these compounds are members
of a group of substances which serve as most valuable kinds of food for
living plants. So it may be said that both living animals and plants
seem to be in a peculiar way dependent upon nitrogen or nitrogenous
matters.
Compound of Nitrogen with Hydrogen.
Under favorable circumstances, nitrogen and hydrogen combine to form
the stable, interesting and important compound called ammonia gas and
having the formula NH₃.
While this gas may be produced by the direct union of the
constituents—that is when a mixture of nitrogen gas with hydrogen
gas has an electric discharge slowly passed through it—this is not
a common mode of procedure. Ammonia gas is oftener produced by a
natural or artificial decomposition of certain substances that contain
nitrogen and hydrogen among their constituents. As it has already
been stated that many animal matters contain nitrogen and hydrogen,
it follows that animal matters when decomposed, afford ammonia gas;
and so they do, in fact, whether the decomposition is in the course
of their natural decay, or whether it is conducted artificially, as
for example when _animal_ matters are heated in closed vessels to the
point of decomposition. Indeed ammonia gas and its important commercial
compounds were formerly produced in this last mentioned manner.
Ammonia gas—or some compound of it—is also formed, as may be readily
imagined from what has already been said, from decomposition of
_vegetable_ matters containing nitrogen. It is a fact that at the
present day the principal supplies of ammonia gas and its compounds
for the uses of commerce and the arts come from such a source, that
is from the artificial decomposition of bituminous coal. It is true
that in the ordinary sense coal is not vegetable matter. But careful
examination of it, shows that it is very directly derived from the
vegetation of ancient forests. The vegetable matter has been packed
away in the earth and has been subjected to water, heat and pressure
under such conditions that these agencies have changed it to the form
in which we find it. Now the coal-gas industry of the present day is
so conducted as to decompose coal and collect many of the products
of its decomposition. One of these products is ammonia gas. To the
decomposition of coal, therefore, the business world at present looks
for its supply of ammonia gas and the many compounds derived from it.
The name ammonia gas, indicates that it ordinarily exists in the
aeriform condition. It has a very pungent odor, well-known as that
evolved from smelling-salts. It dissolves in water with very great
facility and in very large quantities. It has a strong tendency to
combine with acids. This last fact may be easily illustrated by simple
experiments within the reach of almost any one.
Experiment with Ammonia.
Provide two wine-glasses or two shallow vessels of any sort. Into one
of them pour the liquid known as spirits of hartshorn, and called by
the chemist ammonic hydrate. Into the other pour some concentrated
chlorohydric acid. Abundant white clouds will quickly form above the
vessels and between them. These clouds are composed of minute particles
of a solid, called by the chemist ammonic chloride and expressed by the
formula NH₄Cl. The reason for their formation is this: from the spirits
of hartshorn escapes ammonia gas (NH₃); from the acid there constantly
escapes chlorohydric gas (HCl); the two gases meeting in the atmosphere
combine with energy, and form the smoky product referred to.
The chemical change is represented by the following equation:
=NH₃= + =HCl= = =NH₄Cl=
One molecule of One molecule of One molecule of
Ammonia gas, Chlorohydric acid, Ammonic chloride,
17 36½ 53½
parts by weight. parts by weight. parts by weight.
\____________________________________/ \______________/
| |
53½ 53⅓
The ammonic chloride thus produced is an article of commerce,
well-known under the name _sal ammoniac_. As has been said, it is a
solid and it belongs to the class of substances designated by chemists
as salts. In fact one of the most striking characteristics of ammonia
gas is its power to produce salts by union with acids. Here is a list
of three well-known salts of this sort:
With Chlorohydric acid, HCl it produces Ammonic chloride, NH₄Cl
” Nitric acid, HNO₃ it produces Ammonic nitrate, NH₄NO₃
” Sulphuric acid, H₂SO₄ it produces Ammonic sulphate, (NH₄)₂SO₄
Compounds of Nitrogen and Oxygen.
Nitrogen and oxygen ordinarily manifest scarcely any affinity for
each other. There are conditions however under which they unite; and
moreover they unite in different proportions so as to form at least
five different compounds. These may be presented in the form of the
following striking series:
Nitrogen protoxide (called laughing-gas,) N₂O.
Nitrogen dioxide, N₂O₂ (or NO).
Nitrogen trioxide or nitrous anhydride, N₂O₃.
Nitrogen tetroxide (brown fumes,) N₂O₄ (or NO₂).
Nitrogen pentoxide or nitric anhydride, N₂O₅.
Of these compounds, unquestionably the most important is nitric
anhydride—and this not on account of itself, for it is very rarely
produced either in the arts or in the investigator’s laboratory. Its
importance is referable to the fact that added to water, it produces
nitric acid.
This chemical change is represented by the following equation:
=N₂O₅= + =H₂O= = =2HNO₃=
One molecule of One molecule of Two molecules of
Nitric anhydride, Water, Nitric acid,
108 18 126
parts by weight. parts by weight. parts by weight.
\____________________________________/ \_______________/
| |
126 126
Nitric Acid.
This acid has been referred to in another place as one of three
principal acids of commerce. Certain of its most striking properties
may be displayed in an easy and interesting manner by any one. For this
purpose the following experiments are suggested:
_First experiment._—Nitric acid turns quill yellow.
Place a few fragments of white quill in a test-tube. Add a few drops
of nitric acid and then some water. Now warm the mixture. The quill
will be found to acquire a yellow color. Fill the tube with cold water
in order both to dilute the acid and to cool it. Pour away the liquid,
and wash the quill in water. The yellow color will be found to be
permanent. Many other animal matters are turned to a permanent yellow
color by nitric acid.
_Second experiment._—Nitric acid attacks copper with violence. There is
liberated by the process a gas called nitrogen dioxide (N₂O₂), which
is colorless but which becomes brown upon exposure to the atmospheric
air. The chemical change gives rise to a solution sometimes green and
sometimes blue, according to circumstances.
Place in a test-tube a small piece of metallic copper in the form of
either wire or foil. Add some nitric acid to the copper. Then warm it
gently until the copper disappears. The brown fumes will be recognized.
The colored solution of cupric nitrate, Cu(NO₃)₂ should also be noticed.
_Third experiment._—Nitric acid attacks zinc with great violence.
Try another experiment quite similar to that just described, only
employ zinc in place of copper. Brown fumes are evolved, and a
colorless solution is produced containing zinc nitrate, Zn(NO₃)₂.
_Fourth experiment._—Nitric acid attacks iron with violence.
Try another experiment, quite similar to the second and third, only
employ iron instead of the other metals mentioned. The fine iron wire
used by florists is suitable for this purpose. The same brown fumes
are evolved. A metallic nitrate is also produced; it is called ferric
nitrate and its formula is Fe₂(NO₃)₆. The solution is yellow, or but
slightly colored.
_Fifth experiment._—Nitric acid dissolves a nickel coin.
An experiment similar to those already detailed may be tried upon a
nickel coin; but it is not necessary to entirely dissolve the coin.
After the acid has acted for a few moments, water may be poured into
the tube so as to dilute the acid, and at the same time to cool it.
Then the liquid may be poured away and the coin withdrawn. In addition
to the brown fumes evolved, the feature most noticeable is the decided
green color of the solution. This is referable, to a considerable
degree at any rate, to the nickel present. Nickel imparts a green color
to most of its solutions.
These experiments suggest that nitric acid has a marked influence upon
the metals. This is in fact one of its prominent characteristics; and
it is largely used in the arts for the purpose of dissolving metals.
CHAPTER XX.
THE ATMOSPHERE.
The atmosphere or the air of our globe is the vast ocean of gaseous
matter at the bottom of which human beings, as well as other land
animals, dwell. While it is so thin that a vessel full of it is spoken
of in ordinary language as being empty, it yet possesses a reality
which it often displays in a very serious manner. Its presence is made
gently evident to human beings by the moderate resistance it offers to
them when they are in motion; but when itself is in motion with the
force of the hurricane or tornado, no solid matters can stand in its
path. Heavy railroad trains and massive buildings are hurled from their
positions and turned into miserable masses of wreckage, while even
strongly rooted forests are swept out of place by its vigorous breath.
The terribly destructive power of air at one moment and its mild and
subtle efficiency at another are very suggestive of the wonderful
adjustment of the forces residing in it. It is by the restrained action
of these forces that the atmospheric air is so admirably fitted to
perform its varied functions in connection with animal life. At the
same time it is so unobtrusive in its workings that its very existence
is at first scarcely noted. When at rest, it peacefully wraps the earth
about as in a gossamer veil, but when in angry agitation it scourges
country and city alike as with a whip of gigantic cables.
The height to which the atmospheric air extends above the earth is not
exactly known. But carefully devised experiments have shown that going
upward, its compactness or density diminishes very rapidly. Indeed
calculations based upon exact experiment show that at a height of fprty
miles, or thereabouts, from the surface of the earth, the air is so
highly rarified that practically it there comes to an end. In other
words, at this height a given bulk of space contains no more air than
exists in the so-called vacuum produced by a superior air-pump.
Weight of Air.
Notwithstanding the extreme tenuity of the gaseous medium in which
we live, it is capable of buoying up on its wings a multitude of
living beings of vast aggregate weight. It is firm enough to support
the millions of birds that sail in it, and the myriad of millions of
insects who yet more freely navigate it in search of food and warmth,
and in answer to the various needs of their existence.
One of the most striking evidences of the fact that air is indeed
a material substance is very easily discovered by showing that it
possesses weight. Thus suppose a properly constructed glass globe is
almost entirely emptied of air by the action of an efficient air-pump.
Suppose then that the globe is weighed. Next if it be connected with a
bell-glass containing ordinary atmospheric air over a pneumatic trough,
it may be readily seen that the air leaves the bell-glass in order to
pass into the globe. If this globe is now weighed again, it is found to
manifest a decided increase of weight. This increase is due to the air
it has received. By such means it may be easily shown that a cubic yard
of air weighs not far from two pounds.
Composition of Air.
The principal constituents of air are the two gases oxygen and
nitrogen; and of these the oxygen makes up about one-fifth and the
nitrogen about four-fifths of the whole. In addition to these principal
substances, however, certain others are always present, of which may be
specified vapor of water, carbon dioxide and ammonia gas; while more
minute quantities of a vast multitude of other gaseous substances find
a reservoir in the air. It is an unquestioned fact that the atmosphere
is likewise charged most of the time with still more minute quantities
of solid dust materials of various kinds. An example is found in the
common salt, blown up into the atmosphere from the ruffled surface of
the oceans. Now the oceans are spread over fully three-fourths of the
earth’s surface, and the winds, blowing upon the crested waves, not
only diffuse the salt over the oceans themselves but also carry it far
inland; accordingly spectrum analysis reveals the presence of salt in
almost all atmospheric air.
Just as the rivers of water flow to the ocean and bear along to
it debris of every kind—pulverized rock and earthy materials and
other washings from the soil, leaves of forests, impure products of
civilization thrown in from houses and manufacturing establishments—and
all these materials make their relatively minute contributions to the
impurities in the great ocean itself, so it is with the atmospheric
ocean. Thousands of millions of living animals pour out, with every
breath from the lungs, materials exhaled from their bodies. And so
wherever fuel is burned, or wherever manufacturing establishments
liberate gases or vapors, or even finely pulverized solids, these are
cast forth from the mouths of their reeking chimneys; and they all flow
into the great aerial sea. So then it is no unexpected circumstance
that the air should be a reservoir in which, in minute quantity, is
likely to exist every gaseous substance produced.
Offices of the Several Constituents of the Air.
The oxygen of the air is its most active constituent. This is the
substance that has already been described as essential for all
ordinary combustion and all animal respiration. By a great variety of
characteristics it is well fitted for these important offices.
The chief duty of the nitrogen appears to be to dilute the oxygen
and moderate the excessive activities that would be manifested if
the atmosphere consisted entirely of the active gas. Since iron and
other metals burn in pure oxygen, it is plain that in an atmosphere of
oxygen—containing no moderating gas like nitrogen—a fire once kindled
in a stove would not confine itself to its proper fuel, but would soon
spread to the metal of the stove itself, and so initiate conflagrations
that could hardly be restrained.
The _moisture_ in the air adds a number of wonderful and serviceable
characteristics to it. Thus it helps to retain the heat received from
the sun and so materially contributes to the sustenance of animal
and vegetable life. The heat of the sun penetrates our atmospheric
coverlet with great readiness and this heat is received by the surface
of the earth and thence is imparted to the layer of air immediately
upon it. Now the moisture contained in the atmosphere—and in principal
quantity in the portions of air closest to the earth—is one of the
chief agencies that prevent the immediate escape of that heat that the
solid earth has secured from the sun’s rays. And it is in the warm
layer of air so produced that animals and plants chiefly flourish.
Ascend a mountain’s side and a height is soon reached at which eternal
snow and cold prevail, where animal life cannot penetrate and even the
lowest forms of vegetable life can hardly make their residence. What
has thus far been said points out a valuable office of watery vapor
and one that is entirely in addition to that which this same material
performs as it floats in the clouds, ready to fall as beneficent
showers and then to proceed to the other steps in the progress of that
useful circulation which it performs as a liquid. But it may not be
out of place to mention here that the aqueous vapor in the atmosphere
appears to serve in another way for man’s pleasure, even though in this
particular no utility can be claimed. Thus the glories of sunrise and
sunset, which have delighted intelligent beings for so many ages, are
paintings upon the drapery of the firmament which the pencil of light
has been enabled to produce through the medium of the refractive power
of those gathering drops of water which float about in various forms
and combinations in the morning or the evening sky.
It has already been more than once declared that _carbon dioxide_
is poured out into the atmosphere by all the ordinary processes of
combustion. This is not only true of combustions such as those of coal
and wood and similar highly carbonaceous materials; it applies with
equal force to the animal body itself, which has been properly likened
to a furnace. The air taken into the lungs at each breath inspired,
supports during life a continual combustion, by reason of which,
minute fragments of the animal tissue are burned in all parts of the
system. One of the products of this burning is carbon dioxide, which
is carried to the lungs, thence to be exhaled as a waste product into
the atmosphere. It might at first be expected that this carbon dioxide
would accumulate and form a constantly increasing proportion of the
air. But it is one of the proper foods of vegetable life; for nature
has wonderfully provided that plants should thrive by the absorption
or inhalation of this particular gas. And so all the leaves in the
forest are continually cleansing the air of that carbon dioxide that
living animals have cast aside as a useless thing. And by a magnificent
alchemy, the result of a wonderful and beneficent plan, they turn this
waste matter of the animal frame into food for themselves, and they
cast out into the air as _their_ refuse that oxygen gas which living
animals demand. So then the two forms of living beings exist in a
harmonious partnership by reason of which each one is benefited.
An example similar to that just given with respect to carbon dioxide
is found in _ammonia gas_. This substance is one of the commonest
products of the decay and decomposition of animal matters. Wherever
animal waste is deposited upon the surface of the earth it quickly
evolves ammonia gas. This gas diffuses itself through the atmosphere
under the influence of conditions whereby it may perform an important
service; for it is always extremely soluble in water. And so as soon as
rain is condensed, whether in a gentle shower or in abundant torrents,
each drop in passing through the air gathers ammonia and carries it
down to the earth. Again, ammonia is one of the chief foods for plants.
And so the rain drops, charged with such ammonia as they have been
able to collect, bear it to the rootlets in the soil, as a valuable
and important food, and one which has been proved to have a most
stimulating influence upon their growth.
There is not opportunity here for a discussion of the offices and the
interplay of the other substances existing in atmospheric air; for they
are more local in their effects and more difficult to trace and to
describe.
The Air is not a Chemical Compound.
The importance of the atmosphere and its great abundance have naturally
led to most thorough scientific scrutiny of it. Thus the amounts of its
principal constituents have been studied with extreme care. One result
has been that the principal constituents—the oxygen and the nitrogen—
have been found to exist in air in proportions singularly constant in
amount. This fact indeed has suggested to some chemists the impression
that air is a true chemical compound. This latter suggestion appears
not to be sustained by the most rigid examinations that have been made.
In fact they give ample support to the opinion already declared—that
the air consists of a mass of merely mingled gases and that these gases
are uniformly maintained in their proper proportional amounts by the
beautiful interaction of the physical and chemical properties with
which they are endowed.
Fitness of Atmospheric Air for its Uses.
The statements already presented must have suggested to the reader
that the atmospheric air fulfils its offices in nature much as any
contrivance carefully devised by an intelligent framer would accomplish
the work for which it was planned. Beside those chemical adaptations
which have been the principal grounds upon which this line of thought
has been supported here, there are others which may be briefly
suggested.
By reason of the _mobility_ of air, as well as its tendencies to
expansion by heat, our atmosphere is necessarily in a state of most
intricate ebbing and flowing. One prominent effect of the motion thus
set up is to cause a transfer of warm air, and so a distribution of
heat, from more favored portions of the globe to the others.
This same result is also more completely attained by the influence of
the _specific heat_ of air. Atmospheric air has remarkable power, in
which it resembles to some extent water: to take up a very large amount
of _heat_ with but a slight rise in _temperature_; similarly a slight
fall of temperature is associated with a large evolution of heat.
By reason of these properties, air, like water, has an exceptional
storage power for heat. This contributes largely to the equalization of
climates.
The _elasticity_ of the atmosphere permits it to become a useful
servant of man in the transmission of sound. Thus human beings—and
with less distinctness most of the living creatures of the lower
orders—communicate their thoughts by means of spoken words through that
line of atmospheric air extending from them to their hearer or hearers.
Again the characteristics of the atmosphere are such that it _diffuses_
sunlight. By this is meant that in air, sunlight does not confine
itself to those strictly straight lines which it follows in empty
spaces. So then this property of air mitigates the blackness of shadows
and, for example, he who walks into a shady lane does not plunge into
absolute darkness, as he might if we were deprived of this beneficial
diffusing influence of the atmospheric air.
The two considerations last adduced contribute much towards making the
earth a cheerful home for human beings; for they aid materially in the
distribution of intelligible ideas. Moreover those properties of air by
virtue of which its undulating waves makes music possible, and further
those which permit the flight of light, and so allow of the existence
of the graphic arts, certainly make no mean contributions to the
happiness of man; and thus they help to furnish the earth as his place
of residence.
[Illustration: FIG. 53.—Display of fireworks on the Seine, Paris.]
CHAPTER XXI.
EXPLOSIVES.
The principal explosives owe their activity, to a very large degree, to
the presence of nitrogen in them; thus they may properly be discussed
in connection with that element.
The explosives of chief importance are four in number: gunpowder,
the fulminates, gun-cotton, nitroglycerine. While these substances
suggest at once the war-like uses to which they are put, it must not
be forgotten that they have also important applications in the arts
of peace. Thus enormous quantities of gunpowder and nitroglycerine
are used in blasting operations for purposes like the removal of rock
preparatory to laying foundations for large buildings, as well as in
excavations for railway cuttings and in the boring of tunnels; also in
the getting of building stone from quarries, the tearing of ore out
of mineral bearing veins in mining operations; and for loosening coal
in coal pits. Large quantities are likewise employed in pyrotechnics.
It must not be forgotten that fireworks are not only for purposes of
night illuminations and for public gratification in times of popular
rejoicings; they are also employed to a considerable extent for such
useful purposes as night signalling on vessels at sea.
Gunpowder.
Of the various explosives mentioned, gunpowder is the oldest. While the
invention of this substance has often been referred to Roger Bacon,
the celebrated English friar who died about 1292, it is now conceded
that though Bacon evidently knew the composition of it, the original
invention dates far earlier than his times. There seems foundation for
the belief that it is as old as a thousand years, while its use by
artillery at the battle of Crécy shows its employment in warfare for
over five hundred years. Bacon’s power of independent thought, placed
him so far in advance of the century in which he lived that he became
an object of persecution, but he is at present ranked as one of the
prominent figures of history. In his works Bacon refers to a substance
that seems to correspond to gunpowder, and in terms that suggest that
he considered it as a material of not uncommon knowledge in his day.
[Illustration: FIG. 52.—Roger Bacon, born near Ilchester, about 1214,
died probably at Oxford, in 1292.]
The principal constituents of gunpowder are three: potassic nitrate,
charcoal and sulphur. The chemical action between potassic nitrate
and charcoal in gunpowder may be better understood after a simple
experiment, which any one can try. The experiment referred to is as
follows: take a large piece of charcoal; heat it over a spirit lamp or
gas lamp until certain portions of it take fire so as to burn with a
slight glow; next sprinkle very carefully a small amount of powdered
potassic nitrate—also called both saltpetre and nitre—upon it. A
burning, something like that of gunpowder, only less violent, results.
The potassic nitrate has the formula KNO₃. When it falls upon the
glowing coal a portion of the oxygen leaves the other constituents and
accomplishes thereby a true combustion of the carbon. One important
factor in the operation is the element nitrogen; owing to the general
inertness of nitrogen it easily allows the escape of other elements
combined with it. So in case of the experiment just suggested, the
combustion of the charcoal is referable to oxygen liberated by
reason of the feeble affinity of one of the other constituents of
the potassic nitrate—that is, the nitrogen. Thus far the only thing
particularly suggested is the combustion that takes place; another
point of importance may be mentioned in this connection. If finely
powdered charcoal and potassic nitrate are thoroughly intermingled
and then set on fire in a closed vessel, a large amount of a gas,
that is, carbon dioxide, will be generated by the combustion; and
this gas may burst the vessel unless it is a very strong one. If,
however, the vessel has an opening supplied with a cork or plug, this
stopper will be violently driven out by reason of the explosive force
of the carbon dioxide generated. So in the preparation of gunpowder,
potassic nitrate, charcoal and the third substance sulphur, are finely
pulverized and carefully intermingled. Thus they are brought to a state
of thorough diffusion and intimate contact. The offices of carbon
and potassic nitrate have been already explained. The office of the
sulphur is principally to combine with the potassium of the potassic
nitrate, producing as a result a somewhat larger evolution of gas.
At all events, when gunpowder is consumed, two important results are
afforded. As already intimated, the first is the sudden liberation of
a very large amount of gas—carbon dioxide. The second is that this gas
is generated by a process of true combustion attended with great heat,
the latter contributing largely to the explosive force by reason of the
great expansion of the gaseous products, effected by the heating.
There are several different kinds of gunpowder, but they all consist
essentially of the constituents mentioned. Their differences are either
in the proportions of the constituents used or in the size of the
granules in which the powder is formed. Thus for some war purposes it
is requisite that the powder should burn very rapidly, while in others
it is required to burn slowly. For the purpose of regulating the rate
of combustion, the grains are made of various sizes. The smaller sizes
burn more quickly, while those of larger dimensions as well as those
more strongly compressed, burn more slowly.
While the exact chemical changes which take place when gunpowder burns,
are too complicated to admit of discussion here, they are in the main
those just explained.
Fireworks.
Gunpowder affords the basis of the pyrotechnic art. It is employed
also with the distinct intention of utilizing both of those prime
properties already referred to. That is to say, by reason of its
explosive force, gunpowder produces the various forms of _motion_
requisite in fireworks. By reason of the intense heat afforded by its
combustion, the various kinds of _light_ are producible. The truly
marvellous effects obtained by the skilled pyrotechnist involve the use
of a great multitude of substances and also an ingenious mechanical
combination of them. The effects he must produce require brilliant
light in various qualities and also upon occasions loud reports, as
the bursting of bombs and the like. So many forms and combinations of
fireworks are possible that no enumeration can be made here; moreover,
their infinite capabilities depend upon the inventive resources and
skill of the maker. In a brief description, the rocket may be taken
as the type of fireworks. It is often of most ingenious construction.
Thus it may be provided with many chambers, one connecting with another
by proper passages. In these passages are placed fuses so that the
fire shall run from one chamber to another in proper order. Of course
the main barrel contains a quickly burning gunpowder. This is for the
purpose of producing the ascent. It is well known that a pistol, a
rifle or a cannon, always experiences a strong recoil when fired. So
does a rocket; but the rocket is so constructed that the recoil is the
chief factor in its first discharge. That is, if the rocket is compared
to a cannon, the discharge is downward and the recoil upward, so that
in fact the ascent of the rocket is due to what may be called an
exceedingly powerful recoil. When the rocket is high in air, the fuse
connected with its principal barrel lights its subordinate chambers,
and these then exploding distribute into the sky the brilliant masses
of stars or other graceful pieces originally intended. The loud
reports that take place at such times are due to portions of violently
explosive substances within certain chambers; while the party-colored
lights produced are referable to the burning of substances which have
been carefully selected for the purpose. Thus the pyrotechnist has
recourse to mixtures of gunpowder and various other chemical substances
to produce colored fire. Finely powdered charcoal or lamp-black give
rise to a red fire; so also do most of the salts of strontium. Common
salt or powdered rosin give rise to yellow fire. Copper filings and
certain salts of copper produce greenish hues; so do salts of barium.
Zinc filings and chloride of copper, and certain others, produce blue
shades. Saltpeter in considerable quantity affords a delicate pink;
while iron filings and steel filings produce scintillations of great
brilliancy.
Fulminates.
The fulminates are substances that are so extremely unstable in
chemical character, that they require but a very slight mechanical
blow to decompose them. Two fulminates in particular may be mentioned:
fulminate of mercury and fulminate of silver. They are both viewed as
salts of a peculiar complex acid called fulminic acid. This acid is
a compound of carbon, hydrogen, oxygen and nitrogen. When silver or
mercury takes the place of the hydrogen in fulminic acid, the dangerous
salts just mentioned are obtained. Fulminating mercury is the one of
chief use. It is employed in percussion caps. A drop of gum is put
in the inside of the cap, then the exact amount of fulminate in the
form of a powder is allowed to fall into the gum; finally the whole is
allowed to harden. When the cap is used, a violent blow from the hammer
of the gun or pistol gives rise to the explosion of the fulminate,
and this communicates to the gunpowder of the cartridge to be fired.
Fulminating silver is too dangerous for use in percussion caps, but it
is employed in certain explosive toys like torpedoes.
Gun-Cotton.
Gun-cotton is a chemical modification of the ordinary cotton fibre.
This fibre when purified by chemical washings consists entirely of the
substance called cellulose. It is not different from certain other
vegetable fibres. It has the formula:
C₆H₅O₅H₅
which may also be represented as follows:
{ H
{ H
C₆H₅O₅ { H
{ H
{ H
When clean cotton is acted upon by strong nitric acid it undergoes the
wonderful chemical change to gun-cotton. Without material alteration
in its physical appearance there has been a chemical substitution
by reason of which a nitrogen compound has been introduced into the
chemical molecule, as a substitute in place of certain of the hydrogen
atoms originally present. Thus the formula of gun-cotton may be
represented as follows:
{ H
{ H
C₆H₅O₅ { NO₂
{ NO₂
{ NO₂
A comparison of this formula with the one given for pure cotton shows
that three atoms of hydrogen in the cotton have been replaced in the
gun-cotton by three molecules of the compound radicle NO₂. On this
account gun-cotton is often spoken of as trinitrocellulose. By reason
of this chemical substitution the cotton changes as if by magic
from the simple, safe material ordinarily known, to one of the most
dangerous of explosives. Thus Mr. Abel, the chemist to the English War
Department, who has made a series of most careful studies of gun-cotton
with reference to its use for war purposes, finds the explosive power
of gun-cotton to be more than fifty times that of gunpowder of equal
weight. One of the greatest objections to the use of gun-cotton is
found in the fact that upon keeping, it undergoes of itself a steady
decomposition resulting ultimately in dangerous explosions. This fact
appears to be likely to prevent the substance coming into general use.
[Illustration: FIG. 54.—Establishment for manufacture of dynamite, near
Turin.]
Nitroglycerine.
Glycerine—produced at present in enormous quantities from fats and
oils—is well known as a sweetish, oily and harmless substance.
Glycerine is composed of carbon, hydrogen and oxygen in proportions but
slightly different from those in cotton. Thus its formula is
C₃H₅O₃H₃.
If this bland and simple material is subjected to the action of
concentrated nitric acid, it undergoes a change very similar to that
recognized in the case of cotton and just described. It then produces a
compound called trinitroglycerine which, while it ranks as one of the
most powerful and useful explosives, is also associated with a long
list of horrible disasters produced by accidental, or in some cases
intentional, explosion of it.
Nitroglycerine is itself an oily material and was at first considerably
used in that form. The terrible accidents from transportation of the
article have given rise to the adoption of two means for lessening
the risks attending it. The first is the manufacture of the substance
in suitable localities—that is near to great public works in which it
is to be employed. And again the factories are so arranged that the
operation of the manufacture shall be conducted in small buildings
surrounded by earthworks sufficient to localize any explosion that
might unhappily occur.
At the manufactory of explosives at Ardeer on the Scotch coast, about
fifty miles from Glasgow, a most ingenious additional precaution is
taken. Here each laborer, as he enters the works in the morning, passes
into a cottage to change his dress. He dons a uniform of a special and
distinctive color—it may be scarlet, or bright blue or white or gray,
according to the department in which he is employed. Thus the policemen
who are constantly on duty can detect at once any employé who strays
into a department to which he does not belong and where his lack of
acquaintance with the processes might lead to a terrible accident.
[Illustration: FIG. 57.—Torpedo-boat attacking a large war vessel.]
Another special device is the invention of Albert Nobel, who has
been noted as the principal person by whose efforts nitroglycerine
has been introduced into the important uses which it finds at the
present day. This is the absorption of the liquid nitroglycerine in
some spongy material such as will serve as a safe and proper vehicle
for the explosive. The substance thus employed is a kind of fine
siliceous earth called diatomaceous earth, also infusorial earth. This
is a mineral material found in various parts of the world in somewhat
abundant deposits. Upon examination by the microscope it is found to be
composed of the mineral skeletons of microscopic organisms. The minute
cellular texture which this substance affords seems to be admirably
fitted to imbibe the liquid nitroglycerine, and assist in packing it in
proper cartridges. The explosive produced by the combination is the one
commonly known as dynamite.
[Illustration: FIG. 56.—Dynamite exploder.]
A peculiarity of nitroglycerine and dynamite is that they cannot be
fired in the ordinary fashion. That is, if a lighted match is brought
to them they may take fire and burn with perfect quietness. For their
_explosion_ they demand some kind of violent blow. For this reason
their cartridges have to be provided with special exploders. These are
small cases of gunpowder or perhaps fulminating materials, which may
be set on fire by means of a powder fuse or an electric current; their
explosion within the nitroglycerine mass determines a violent shock to
the latter. It is the concussion thus produced that is the appropriate
means of exploding the nitroglycerine or dynamite cartridges.
While the sad accidents with these materials have horrified the
whole world by their sudden and disastrous results it is too often
forgotten that their gigantic forces are day by day safely and quietly
contributing to the execution of great public works all over the
earth. Thus in the great rock tunnels of Mont-Cenis and St. Gothard,
which pierce the Alps, nitroglycerine and dynamite have done the work
of armies of men. In the St. Gothard tunnel more than two million
pounds of dynamite have been employed, and it has proved wonderfully
effective in advancing most arduous subterranean work. Unquestionably
the principal use of this explosive, as well as others, is in the
labors of peace. Still, nitroglycerine and dynamite have come into
great prominence by reason of their use in naval warfare. Torpedoes of
a great variety of forms are now constructed so that a quick moving
launch may steam up to a large ship of war, place close to her side one
of these dangerous contrivances and then quickly withdraw in time to
avoid the effects of the explosion which involves the great vessel in
devastating ruins. Torpedoes charged with nitroglycerine or dynamite,
are also used for the defence of harbors, being sometimes placed in
such a way that an enemy’s ship, in crossing the line formed by the
torpedoes, shall by that act explode one or more of them and produce
her own destruction.
READING REFERENCES.
Explosive Agents.
=Abel=, F. A.—Jour. of Chem. Soc. of London. xxiii, 41,
xxvii, 536.
—Chem. News.—xxxix, 165, 187, 198, 208.
Explosives, a New Class of
=Sprengel=, H.—Jour. of Chem. Soc. of London. xxvi, 796.
Explosives, Force of
=Berthelot.=—Annales de Chimie et de Physique.
4 Sér. xxiii, 223.
Explosives, in Blasting.
=Scribner’s= Monthly. iii, 33.
Greek Fire, (so called.)
=Lalanne=, L.—Annales de Chimie et de Physique.
3 Sér. iv, 433.
Gun-cotton, Manufacture and Composition of
=Abel=, F. A.—Journal of Chem. Soc. of London. xx, 311, 505.
Gunpowder, Chemical Theory of
=Debus=, H.—Chemical News. xlv, 91.
CHAPTER XXII.
PHOSPHORUS.
Phosphorus is a most interesting chemical element. This is because of
its exceptional chemical properties, the very important part it plays
in the chemistry of animal and vegetable life, and its employment in
the friction match, one of the most convenient and useful articles of
human invention.
Phosphorus appears to have been first prepared in the year 1669 by a
Hamburg merchant named Brandt who became fascinated with the study
of alchemy and pursued his experiments with the view of repairing
his broken fortunes by the discovery of the philosopher’s stone. The
happy discovery of phosphorus, while it did not enrich him, at least
preserved his name in the annals of chemistry. Brandt produced it by
a laborious process from certain animal matters. Notwithstanding the
remarkable properties of the substance and the extraordinarily useful
purposes to which modern scientific knowledge has applied it and its
compounds, phosphorus remained the merest toy for more than a hundred
years. In 1771 Scheele revealed to the world the fact that it may be
prepared from bone-ashes, that is from burnt bone, and this has ever
since been found to be its most convenient source.
The name phosphorus is derived from two Greek words (φῶς _phos_, light,
and, φέρω _phero_, I bear) which suggest one of its marked properties,
namely its power of continually affording light even though not set
on fire after the manner of ordinary illuminating materials. It is
true the light is feeble and chiefly noticeable in the dark. It is the
same, in fact, as that yielded in the dark by an ordinary friction
match when it is gently rubbed, but has not yet taken fire. This
light, however, is the product of a true combustion, only of a very
slow one; and again this burning of phosphorus is initiated by heat,
(though only a very moderate amount is required for it). Of course for
phosphorus much less heat is demanded than to set on fire our ordinary
combustibles.
Phosphorus, though very widely distributed in nature, is never found
free or uncombined. This fact is distinctly referable to the ease with
which the substance combines with oxygen; if it were found free at
any point on the surface of the earth, where it suffered exposure to
atmospheric air, it would of course quickly enter into combination with
oxygen.
Phosphorus exists occasionally in the earth in the state of
combination in very hard rocky masses, of which the mineral known as
apatite—composed mainly of calcic phosphate—is a good example. It is
also present in small quantities in almost all soils; and in minute
quantities in most natural waters, like river-water and sea-water.
One of the most familiar substances containing phosphorus is the
bony skeleton of the higher animals. Here also it exists as calcic
phosphate. It exists also in the brain, though in a form of chemical
combination not easily stated.
Further, it is a constituent of various portions of the vegetable
structure, especially of seeds.
The statements in the last two paragraphs have been presented with
the express purpose of calling attention to the important offices of
phosphorus in connection with animal and vegetable life. Thus exact
experiments have shown that plants cannot flourish in soils barren of
phosphates, and that the mere addition of almost any soluble phosphate
to an arid soil promptly stimulates the plant living upon it, into
more luxuriant growth. These facts have led to the introduction into
commerce of artificial fertilizers containing soluble phosphates as
their principal ingredients; and the manufacture of such fertilizers
has continually expanded, until now it is conducted by the principal
commercial nations on a truly gigantic scale. For the purpose of this
manufacture, _bones_ are particularly favorable because of their
porosity. In fact the surface of the world is ransacked to supply this
raw material. Thus from the deserts of Africa, bones are conveyed as
far as England to be manufactured into fertilizers; and so from the
great western plains of the United States, bones are brought to the
eastern centres for a like use.
The agricultural demand for phosphates of some sort has become so
imperious that even apatite is now largely used, notwithstanding the
difficulties that its exceedingly hard and compact structure place in
the way of the manufacturer.
From the plant, phosphorus finds its way in the form of food into the
animal system. The living animal appreciates this essential ingredient,
carefully selects it out from the food, and stores it up both in
its brain and in its bony framework. This framework is exceedingly
important as giving the requisite rigidity to the whole structure, and
the proper support for the action of the various muscles.
Phosphorus itself is prepared by a process too complicated for the
ordinary amateur chemist to repeat; indeed its preparation, even on
the large scale, presents serious difficulties. These are associated
with the great combustibility of the substance, which makes necessary
extraordinary precautions against fire. Again, laborers in phosphorus
works are subject to a painful and incurable disease called _phosphorus
necrosis_, which has a peculiar and destructive effect upon the bones
of the jaw. Finally, the chemical changes involved give rise to such
difficulties and complexities as force the manufacturer to unusual
watchfulness. In fact it has been recently stated that there are
scarcely more than two factories for phosphorus manufacture in the
world—one in England and one in France.
The element phosphorus, as ordinarily seen, has much the appearance of
wax. It has a white or amber color, and is translucent; it may be cut
with a knife much as wax cuts. It is ordinarily sold in the form of
cylinders of about half-an-inch in diameter. It is necessary to keep it
in vessels of water, for as already stated, if exposed to the air it
would oxidize. This oxidation, at first slow, increases in vigor from
the heat afforded by the earlier stages. After a short exposure to air,
portions of phosphorus spontaneously burst into flame. Evidently then,
phosphorus should not be handled except under water. Cases are recorded
of severe and even fatal burns—the result of handling phosphorus in the
air.
We may with propriety call attention here to another peculiarity
of phosphorus, which constitutes one of the remarkable features of
this interesting element. About thirty years ago, a Vienna chemist
discovered that when phosphorus is heated for a considerable length
of time, under conditions such that no gas is present which can act
chemically upon it, it undergoes a marked change in its properties.
Thus its color turns to red, and, strange to say, it loses altogether
that ready combustibility which is the most striking characteristic
of ordinary phosphorus. It may seem incredible that any such change
could in fact occur. But this red phosphorus has become an article
of considerable importance in commerce, and it is a well-established
fact that ordinary phosphorus may be turned into this modification
without any gain or loss of weight, and that, on the other hand, this
red phosphorus may be turned back again, by suitable processes, to the
ordinary form, also without gain or loss of weight. Phosphorus is not
the only elementary substance that is capable of this kind of change.
Indeed the general term _allotropism_ has been applied to the tendency
of elementary substances to undergo internal changes, by reason of
which their chemical properties are temporarily modified without gain
or loss of weight, and therefore independently of chemical combination
or decomposition.
[Illustration: FIG. 58.—Coignet’s apparatus for production of red
phosphorus. Ordinary phosphorus is placed in a cast-iron vessel _c_; it
is then heated ten or twelve days, an even temperature being maintained
by the two iron jackets, one enclosing sand, the other holding fusible
alloy.]
Chemical Properties of Phosphorus.
The chemical properties of phosphorus are wide in their range; that
is, it combines with many of the chemical elements. Thus it unites
with hydrogen in more than one proportion, and thereby forms several
compounds. As might be expected, they are all exceedingly combustible;
one of them in particular, called phosphuretted hydrogen, takes fire
at ordinary temperatures immediately upon coming in contact with
the atmosphere. Its production affords opportunity for a beautiful
experiment, though a somewhat dangerous one. When the gas is produced
in a retort, it may be made to bubble through water in the form of
vapor in company with various gases generated at the same time. Then,
as it reaches the surface, it instantly takes fire, the phosphorus
burning to a white, smoke-like substance which usually floats away in
forms similar to those of smoker’s rings. The smoke consists of minute
particles of a solid, called phosphorus pentoxide, and expressed by the
formula P₂O₅. This is evidently the product of the combustion of that
phosphorus which is a part of the inflammable gas. The shape of the
rings is due to a mere mechanical circumstance and the same in effect
as that afforded by the lips of the smoker while producing rings.
Indeed if a paper box, having a round hole on one side, be filled with
smoke of any kind, sharp blows upon the opposite side will drive out
portions of the smoke in such a way as to produce similar rings. Such
rings are often seen on a still day puffed out of the smokestack of
a locomotive, and they are sometimes produced by the discharge of a
cannon in still air. The fact is that in all these cases the portion
of smoke producing a ring advances through the opening with a sudden
impulse, the edge of the opening retarding those particles that pass
nearest to it. Thus the delayed particles acquire a tendency backward
and inward which starts them on the peculiar series of circular
courses, which in the grand aggregate give rise to the rings.
[Illustration: FIG. 59.—Phosphuretted hydrogen gas, of the
spontaneously inflammable variety, taking fire in air and forming
smoke-rings.]
As has more than once been stated, phosphorus has a marked affinity for
oxygen. It burns in any vessel containing air, combining with oxygen in
such a way as to readily deprive the air of the entire amount of this
element contained in it.
The chemical change is represented by the following equation:
=P₄= + =5O₂= = =2P₂O₅=
One molecule of Five molecules of Two molecules of
Phosphorus, Oxygen, Phosphorus pentoxide,
124 160 284
parts by weight. parts by weight. parts by weight.
\__________________________________/ \_________________/
| |
284 284
When the operation is performed in a tall jar, the oxide of phosphorus
produced falls as abundant flakes having a snow-like consistency. When
these flakes are thrown upon water they chemically combine with the
water, affording much heat and producing a hissing sound which is the
evidence of it. The liquid now acquires a sour taste referable to the
fact that phosphoric acid has been produced.
The chemical change is represented by the following equation:
=P₂O₅= + =3H₂O= = =2H₃PO₄=
One molecule of Three molecules of Two molecules of
Phosphorus pentoxide, Water, Phosphoric acid,
142 54 196
parts by weight. parts by weight. parts by weight.
\_______________________________________/ \_______________/
| |
196 196
Phosphoric acid is the starting point of an immense series of salts
called phosphates. One of these, calcic phosphate, we have already
referred to as existing in bones and in apatite.
Friction Matches.
The earliest method of producing flame appears to have been by the
friction of pieces of dry wood in contact with dry leaves or similarly
combustible substances. This method travelers have found to be still in
use among tribes of a low stage of development. The next method seems
to have been by the use of flint and steel and tinder. When the flint
is sharply struck against the steel, it tears off minute particles of
the metal, and these fragments are heated to the luminous point by the
violence of the stroke; if they are made to fall upon the tinder, this
easily combustible material takes fire; from its burning, a candle or
lamp may be lighted. But the flint and steel and tinder must be dry and
in good order to produce the best results; even then considerable skill
is demanded. So it is easy to see that mankind has often preferred to
_preserve a flame once lighted_, and then communicate this to another
and another from time to time, rather than to go to the trouble of
exciting a new combustion when fire was needed. And it is easy to
appreciate the usefulness to its possessor of a flame once kindled—and
the serious inconvenience resulting from its extinction. Thus we can
readily comprehend how nations have adopted fire as a sacred agent,
to be preserved continuously unextinguished, and to be guarded with
religious care.
The flint and steel method has ample illustration as to its principle,
not only in familiar cases like sparks from the horse’s hoof, but also
in many processes in factories and machine shops. Here it is well known
that the grindstones used for finishing articles of iron and steel send
off from their work an uninterrupted current of minute chips of the hot
and luminous metal.
The flint and steel method of obtaining fire held its own until about
sixty years ago. In 1829 a kind of chemical match was devised, and
soon after, in 1832, a true friction match containing phosphorus was
brought into use. The _principles_ upon which the phosphorus match
depend are but very slightly different from those involved in the use
of the flint and steel. Thus in the friction match the rubbing upon
the rough surface is a mechanical process which generates heat, just
as any blow or any friction does. In the case in question the amount
of heat is small, but it is sufficient to set on fire the small amount
of phosphorus on the tip of the match; the phosphorus sets on fire
the sulphur which coats over the end of the match; the sulphur in
burning sets on fire the wood of the match, and here the combustion has
reached a stage at which it is easily communicated to larger masses of
material. In the finer kinds of wooden matches, in order to avoid the
objectionable smell of the burning sulphur, this latter substance is
sometimes replaced by a thin coating of wax upon the end of the stick.
In this case, other chemicals are added to the tip of the match, in
order to make the combustion more active.
Friction matches of the ordinary kind are now so abundant and familiar
everywhere that the exceeding usefulness, convenience and importance
of the match as a device or invention, is apt to be overlooked. It is
not intended to dwell here upon this subject, however, for perhaps what
has been said of the appliances for lighting used in the past, renders
unnecessary further presentation of the principles utilized in the
little tapers of to-day.
As an article of manufacture, the individual match is so small that
it is not easy at first to appreciate the greatness of the commercial
interest it represents. Thus it is estimated that in Europe alone fifty
thousand persons are constantly employed in the manufacture of the
various kinds of matches. Again, though the amount of phosphorus used
in each match is very minute, its sum total is no less than a thousand
tons a year. The value of the annual product of this industry is not
far from fifty millions of dollars.
If there were introduced here an account describing at length the
manufacture of the friction match—commencing at the beginning with
the special kind of wood employed and the processes used for its
subdivision into the requisite fragments, continuing even so as to
explain the various contrivances for packing the finished product—that
description might be of interest; but the special topic seems to be
more properly the preparation and application of the material at the
tip of the match. The sticks having been prepared, they are placed, by
machine, in frames capable of containing large numbers of them. They
are first sulphured, that is their ends are dipped in melted sulphur
and it is allowed to harden upon them. For the finer grade of matches
however, the sulphur must be dispensed with, and instead the sticks are
dipped into melted wax.
In any case, they are next tipped with the highly inflammable material,
this process being called chemicking. The inflammable paste is prepared
in large quantities by mixing the proper ingredients in a kettle
surrounded by boiling water. First, a solution of an appropriate gum or
glue is made. When it has attained a proper consistency, the phosphorus
is introduced little by little. The whole mass is then slowly but
thoroughly agitated with a wooden stirrer until thephosphorus is
diffused through the mass. Finally, other ingredients, such as
potassic nitrate or binoxide of lead or manganese dioxide, which favor
combustion, are added; and certain coloring matters, such as Prussian
blue or vermilion, are introduced. Here is a German recipe for making
this paste:
Gum, 16 parts.
Phosphorus, 9 parts.
Potassic nitrate, 14 parts.
Manganese dioxide, 16 parts.
As has already been intimated, all of these substances, except the
phosphorus, may be replaced by others, according to the style of the
article to be manufactured or the views of the maker. The process of
chemicking consists in dipping the sulphured ends into the inflammable
paste, which for this purpose is spread out on a stone slab. Finally,
the tips are coated over with a thin varnish to protect them from
absorption of moisture.
[Illustration: FIG. 60.—Pan or water-bath, for melting and mixing the
inflammable paste for match tips.]
At present the manufacture of friction matches is carried on to a very
large extent in Sweden, and that country, it is now stated, produces
about seventy-five per cent of all the matches made in the world. In
Sweden, too, are largely manufactured what are called safety matches.
The safety matches are tipped with a composition of potassic chlorate,
potassic dichromate, red oxide of lead, and sulphide of antimony. Under
ordinary circumstances friction will not set these matches on fire.
In lighting, they must be rubbed on a prepared surface which contains
principally red phosphorus and sulphide of antimony. When the match is
rubbed upon this surface, the potassic chlorate of the match and the
red phosphorus of the friction-surface start a chemical combination
which extends to the other materials on the tip of the match. Safety
matches, then, involve an invention which in accomplishing its purpose,
affords a twofold advantage. In the first place, as the match lights
only on the prepared surface, the danger of conflagrations from
accidental ignition of them is very largely reduced. This costly
feature of the ordinary phosphorus match would be largely, if not
entirely, done away with by the general use of the safety match. In the
second place, the use of _red phosphorus_ has the advantage of saving
human lives in other ways. Thus it spares the operatives, employed
in this business, the liability to the phosphorus disease already
mentioned. Again, ordinary phosphorus is very poisonous; in fact the
tips of matches containing this substance have not only often produced
the death of children who have tasted them, but such matches have often
been used in cases of intentional suicide. Of course as safety matches
contain no phosphorus, these forms of poisoning cannot arise from them.
A flame of fire, as a visible and tangible thing, has in all ages
been accepted as a symbol which appropriately typifies enlightenment
of the mind and soul. This favorite and beautiful figure loses none
of its fitness when narrowed in its application to the aspects of
these subjects in their peculiarly modern forms. For in the friction
match, whose cheapness brings it to the hand of every human being
however low his degree, we may discover the type of that opportunity
for enlightenment offered to individuals whose circumstances seem most
humble and even forbidding. The one is the invention of modern science;
the other the gift of modern laws, of modern theories of the rights
of men, of modern schools, libraries, and newspapers, of the modern
printing press, telegraph, and railroad.
READING REFERENCE.
Friction Matches.
=Schrötter=, A. V.—Chem. News. xxxvi, 207, 219, 259.
CHAPTER XXIII.
CARBON.
Carbon exists in nature in a multitude of forms. It is rarely found in
the pure and uncombined condition, though certain well-known substances
possess it in large quantity.
Ordinary Charcoal.
[Illustration: FIG. 61.—Charcoal pit.]
Probably the most familiar and representative form of carbon is that
known as charcoal. But charcoal is rarely free from other chemical
elements, and a distinction ought to be made between it and the
absolutely pure form of the element under consideration. Charcoal is
produced by the partial decomposition, under the influence of heat, of
vegetable or animal substances. Thus charcoal is commonly prepared by
piling wood into a conical heap, then covering it with earth and sods,
and finally setting it on fire within. Certain portions of the wood are
thus burned, while others are only charred. The wood is decomposed by
the heat to which it is subjected; volatile materials generated by this
decomposition are expelled, while there is left behind a solid matter
consisting mainly of carbon, and called charcoal.
[Illustration: FIG. 62.—Tree trunks discovered in coal mines.]
Animal Charcoal.
The same general treatment of certain animal matters, such as waste
leather, gives rise to a finer kind of carbon called animal charcoal.
[Illustration: FIG. 63.—Charcoal burners at work.]
Again, when bones are partly burned, they produce what is called
bone-coal. The _mineral matter_ of the bone undergoes no change by the
heat; but the gelatinous matters which permeate it are decomposed, and
they leave behind them the carbon deposited upon this mineral matter.
Lamp-Black.
Another material, closely assimilated to those already spoken of, is
lamp-black. This is a product of the imperfect combustion of substances
like oil, tar, resin, and the like, which are very rich in carbon. The
tar or resin being set on fire is allowed to burn, but in an imperfect
way, and so as to evolve a dense black smoke. The smoke flows into
a chamber prepared for it, where the sooty material collects on the
floor and walls. It is afterwards scraped up and put into packages
for commercial distribution. In the English method of manufacture of
lamp-black, the smoke is made to pass through a series of heavy canvas
bags. From openings at the bottoms of the bags, the soot is afterward
drawn out for packing.
[Illustration: FIG. 64.—Manufacture of lamp-black.]
[Illustration: FIG. 65.—Bags in which lamp-black is collected in the
English process of manufacture.]
Coal.
Anthracite coal and bituminous coal are both well-known compounds of
carbon. Anthracite seems to be derived from bituminous coal which has
been subjected in the earth to heat and pressure under conditions
favorable to the expulsion of some of the more volatile constituents
of the original bituminous coal. Both of these combustibles, when
carefully studied, show distinct evidences of their vegetable origin.
Plainly they are accumulated masses of the remains of a rank vegetation
which flourished in an earlier period in the geological history of our
globe. Careful observations made in the mines have revealed in the coal
the existence of trunks of trees, branches, leaves, fruits, in various
conditions from the one extreme of comparatively perfect preservation,
to the other extreme in which the mineral preserves a mere impression
of the original vegetable matter. These remains have made it possible
to construct a complete botany of this period of geological history;
and with but a moderate aid of the imagination, artists have been able
to produce ideal landscapes representing these early forms of vegetable
life as they flourished in the ancient ages.
[Illustration: FIG. 66.—Imaginary landscape during the carboniferous
era.]
Graphite.
Closely allied to anthracite coal is that valuable material called
graphite. This a very compact and comparatively pure form of carbon.
It is familiarly known to every one in the black material used in lead
pencils. Graphite is commonly called black lead, though it is a well
established fact that it contains no lead at all. Strangely enough
graphite is remarkably incombustible under all ordinary circumstances.
It is also—like other forms of carbon—infusible at the highest
temperatures known. On account of these properties graphite finds use,
though it must be deemed a somewhat anomalous one, in the manufacture
of crucibles. When the precious metals are fused in such a crucible,
at a high temperature in a glowing furnace, an interesting paradox is
furnished. It is this: the coal—freely burning in the fire, and so
furnishing the intense heat desired—is fundamentally of precisely the
same chemical nature as the graphite of the crucible, which resists
the heat and the combustion, and, while allowing the metals to melt,
preserves them.
The Diamond.
The diamond is nearly pure carbon, crystallized. Perhaps it is not too
much to say that it is the most striking and wonderful of all the forms
of this interesting element. The costliness of the diamond is referable
largely to its great rarity; for it is found in comparatively few
portions of the earth.
The ancient Greeks and Romans highly prized the rare and precious
crystal, which they obtained from India, and it was worn by them
not only because of its costliness and beauty, but also because
they believed that it served as a potent charm against alarms and
enchantments; more important yet, they ascribed to it the power of
preserving the peace and harmony of the family circle. Upon this point
a French writer has wittily said: “Cette dernière vertu, je crois qu’il
la possède encore quand le mari est assez riche pour acheter le bijou
que sa femme ambitionne de porter!”
The East Indies, the Cape of Good Hope and the Brazils may be said to
be the principal sources of this gem. In Brazil the search for diamonds
is systematically conducted. The diamond bearing soils are carefully
pulverized in vessels of water, under the direction of experienced
inspectors. The work is done by slaves who prosecute their search under
the stimulus of the well understood rule that he who finds a diamond
weighing seventeen and one-half carats or more, publicly receives his
freedom as a reward. Notwithstanding the systematic labor applied to
the search for these gems and the fascination naturally attending
undertakings of this sort, the wealth of Brazil is derived to a vastly
greater extent from its agricultural products than from its mines.
Thus it is stated that from 1740 to 1822, a period of more than eighty
years, the diamond mines yielded but little more than $17,000,000.
On the other hand the value of coffee exported in a single year has
sometimes been double or even more than double this amount. Thus in
the year 1859 the coffee exported was valued at above $28,000,000;
and in 1873 the quantity of this article exported was valued at above
$60,000,000.
[Illustration: FIG. 68.—“The Sancy.”]
[Illustration: FIG. 69.—“The Polar Star.”]
[Illustration: FIG. 70.—“The Empress Eugenie” or “Pigott.”]
[Illustration: FIG. 71.—“The Koh-i-noor.”]
[Illustration: FIG. 72.—“The Star of the South.”]
[Illustration: FIG. 73.—“The Regent” or “Pitt.”]
[Illustration: FIG. 74.—“The Grand Duke of Tuscany.”]
[Illustration: FIG. 75.—“The Orloff.”]
[Illustration: FIG. 76.—“The Grand Mogul.”
The great diamonds of the world (natural size).]
[Illustration: FIG. 77.—Transportation of diamonds under military
protection.]
[Illustration: FIG. 79.—Diamond cutter at work.]
The larger gems are exceedingly rare. On this account the money value
of diamonds increases in a far more rapid ratio than the weight.
The Cutting of Diamonds.
[Illustration: FIG. 80.—Diamond known as “The Star of the South”;
before and after cutting.]
The cutting of diamonds as an art has been known for but a few
centuries, and the perfection with which it is at present conducted
is of much more recent date. Of course the process is an extremely
delicate and important one because it involves splitting off portions
of the gem so as to reduce it to the exact geometrical shape previously
decided upon. That form called the _brilliant_ is the one commonest
produced at the present day. The business of cutting diamonds has
been for a long time concentrated in the city of Amsterdam in Holland.
Here, among a Jewish population of twenty-eight thousand persons, ten
thousand are employed exclusively in working on diamonds. In many cases
diamonds are subject to a very large relative loss of weight by the
process of cutting. Thus the Koh-i-noor, when brought from India as a
gift from the East India Company to the English Crown, was in the rough
state and weighed one hundred and eighty-six carats. It was afterwards
cut in Amsterdam, by which process it suffered a loss of weight
variously stated as from eighty to one hundred carats. After the first
trimming, the gem is carefully polished by rubbing it gently against a
revolving plate upon which is a mixture of oil and diamond dust.
[Illustration: FIG. 81.—Diamond polisher at work.]
[Illustration: FIG. 67.—Diamond washing in Brazil.]
Up to the close of the last century the nature and composition of the
diamond had been a subject of interesting discussion among students
of natural science. At the period mentioned however, the question was
settled by Lavoisier and other scientific investigators, who clearly
proved that the diamond underwent complete combustion in oxygen and
that as a result carbon dioxide gas was generated.
[Illustration: FIG. 82.—The Koh-i-noor before cutting.]
[Illustration: FIG. 83.—The Koh-i-noor after cutting.]
Other Natural Forms of Carbon.
In addition to the well-known forms of matter containing carbon, and
already described, there are yet many others.
Thus it is found in the atmosphere, as has already been explained,
in the form of carbon dioxide. This gas exists in the air in small
relative proportion, but in enormous aggregate amount.
As a natural carbonaceous substance petroleum, too, ought not to be
forgotten. This wonderful and useful substance stored up beneath the
surface of the earth, in incredibly large quantities, owes its chief
value to its wealth of carbon. It is composed of carbon and hydrogen,
but the former is the constituent to which is referable the beautiful
light it affords.
Again, the marble and the limestones of the globe contain enormous
quantities of carbon. These minerals consist principally of calcic
carbonate (Ca CO₃); and the carbon makes up about one-eight of this
substance. Since some whole mountain chains consist chiefly of
limestone or marble, it is plain that the total amount of carbon in
these forms must be very large.
[Illustration: FIG. 84.—View in the vicinity of the Pennsylvania oil
wells.]
With few exceptions, all animal and vegetable matters contain carbon—a
substance which appears to perform its most important offices in
connection with the kingdoms of life. Indeed it has been called the
characteristic element of animal and vegetable compounds. So vast is
the variety of these compounds already recognized that it is hardly
conceivable that man can ever be able to acquire an acquaintance with
all those as yet undetected.
[Illustration: FIG. 85.—Automatic regulator whereby the carbon pencils
of the electric light are maintained at the proper distance apart.]
Infusibility of Carbon.
Carbon differs from most solid substances in the fact that it is
infusible at the highest temperatures to which it has yet been
subjected. And since in the elementary form it has not been changed
to the liquid state, much less has it been brought to the _gaseous_
condition. Indeed this stability and fixedness of carbon is one of its
most valuable attributes. Thus this characteristic is a principal one
that renders it specially appropriate for use in the pencils employed
in electric lighting. It is true these pencils slowly burn away. But
some combustion ought to be expected when it is remembered that the
electric current, flowing from one pencil to the other, affords an
intense heat as well as brilliant light. But it is a general law that
substances give out the most intensely brilliant white light when they
neither liquefy nor volatilize, and to this principle—exemplified in
the carbon pencils—must be referred the brilliancy of the electric
light.
Decolorizing Power of Carbon.
Carbon, whether in the form of wood charcoal, animal charcoal, or
bone-coal, has a wonderful power of decolorizing liquids. Even more
compact carbonaceous matter, such as anthracite coal, possesses this
same property though, as might be expected, to a much inferior degree.
Thus if a colored solution is strained through a considerable quantity
of one of these forms of carbon, the latter substance absorbs the
coloring matter and the liquid passes through practically colorless.
On account of this wonderful power bone-coal is used in the arts in
enormous quantity in many processes where liquids must be decolorized.
The sugar refining industry affords a prominent example upon this
point. Here, enormous quantities of bone-coal are used for the purpose
of whitening the syrups before crystallizing the sugar.
[Illustration: FIG. 86.—Magnified view of the carbon terminals used for
the production of the electric light.]
[Illustration: FIG. 87.—Excavations carried on at night by aid of the
electric light.]
Charcoal has also a similar, and yet more striking, property of
absorbing offensive gases. Thus, tainted meat packed in freshly burned
charcoal quickly loses its odor—which is absorbed by the coal—and the
meat then becomes sweet and wholesome.
Chemical Properties of Carbon.
The chemical properties of carbon are by no means less wonderful
than the characteristics already referred to. It is very inert at
low temperatures; but at high temperatures, it manifests chemical
activities of extraordinary vigor. Thus at high temperatures carbon
withdraws oxygen from almost any other elements known, in this way
manifesting chemical force superior to that possessed by any of them.
[Illustration: FIG. 88.—Colored liquid filtered through charcoal, and
thereby decolorized.]
The Great Number of Compounds Formed by Carbon.
The vast number of the compounds of carbon seems to be referable to
two fundamental properties with which it is endowed by nature. One of
these is the fact that the atom of carbon possesses four points of
attraction. This matter need not be explained here as it has already
been discussed at sufficient length. But the fact may be conveniently
represented to the eye by a symbol like the following:
|
——C——
|
The other property referred to is this: carbon—unlike most other
elements—has a peculiar capacity by virtue of which atoms of it may
join together in either short or long chains, and afterwards may
gather other elements to the various parts of the chain. One among the
many ways in which carbon takes part in forming such compounds may be
represented by the simple diagram shown in the margin:
|
——C——
|
——C——
|
——C——
|
——C——
|
——C——
|
The number of compounds of this character already known to chemists is
very large; it suggests the probability that there is no distinct limit
to the number of atoms that may be linked in a continuous chain in this
way. Moreover a given chain may have attached upon its sides or ends
one or more additional chains of elements or compounds and thus give
rise to an all but infinite number of substances with almost infinitely
varied properties.
READING REFERENCES.
Coal, and the Coal-mines of Pennsylvania.
=Harper’s= Magazine. xv, 451.
Diamonds.
=Scribner’s= Monthly. v, 529.
=Harper’s= Magazine. xix, 466; xxxii, 343.
Diamond Fields of South Africa.
=Harper’s= Magazine. xlvi, 321.
CHAPTER XXIV.
COMPOUNDS OF CARBON AND OXYGEN.
While compounds of carbon and _hydrogen_ are very numerous, those
already known being numbered by hundreds, the affinities of _oxygen_
and carbon give rise to a strikingly different result.
When combined with oxygen alone, carbon forms but two compounds. These
are expressed by the following names and formulas:
Carbon monoxide, CO.
Carbon dioxide, CO₂.
Carbon Monoxide (CO).
This gas is most familiarly known as that one which often plays upon
the surface of a hard coal fire and burns there with a dark blue,
feebly luminous, flame. Most of the phenomena of its production and
final burning may be presented as follows: When an ordinary coal
fire, burning in a stove, is amply supplied with air at the bottom,
the oxygen of the air burns the lower portions of carbon into carbon
dioxide. Next, this carbon dioxide is carried up, by the draft, between
any masses of fresh coal that may be upon the top of the fire. This
fresh coal has itself affinity for oxygen under the circumstances just
described as prevailing. As a result, each molecule of carbon dioxide
from the lower portion of the fire yields one of its atoms of oxygen to
an atom of carbon in the upper part.
The chemical change is represented by the following equation:
=CO₂= + =C= = =2CO.=
One molecule of One atom of Two molecules of
Carbon dioxide, Carbon, Carbon monoxide,
44 12 56
parts by weight. parts by weight. parts by weight.
\_____________________________________/ \_______________/
| |
56 56
As a result, therefore, carbon monoxide is formed and escapes as a
colorless gas from the top of the fuel; there, if the upper door of the
stove admits a sufficient amount of air, the carbon monoxide combines
with the oxygen of this air, and burns with the blue flame already
referred to, and so produces carbon dioxide again.
This chemical change is represented by the following equation:
=2CO= + =O₂= = =2CO₂=
Two molecules of One molecule of Two molecules of
Carbon monoxide, Oxygen, Carbon dioxide,
56 32 88
parts by weight. parts by weight. parts by weight.
\____________________________________/ \______________/
| |
88 88
The carbon monoxide is a very poisonous gas, far more injurious to
health than carbon dioxide.
Carbon Dioxide (CO₂).
This substance and its manner of production have been referred to more
than once in preceding chapters. A more extended notice of it, however,
is appropriate to this place.
It has already been stated that carbon dioxide exists ready-formed in
nature—notably in the atmospheric air. Its principal natural source
in the atmosphere is the combustion of fuel; for almost all fuel is
carbonaceous. Thus coal, wood, oil, illuminating gases, are all highly
carbonaceous substances, and one of the principal products of their
combustion is the gas now under consideration.
[Illustration: FIG. 90.—Machinery for filling bottles with artificial
mineral waters.]
As has already been described, the respiration of animals is closely
connected with a real combustion in the living being. It is true
that this sort of combustion is not attended by the evolution of
light; it is productive of heat, nevertheless, and the heat afforded
by respiration is an important factor in the sustenance of animal
existence. For this heat not only enables the living being to
endure the chilling effects of the winter’s cold; it also keeps the
temperature of the internal organs up to that point which is necessary
for the proper performance of certain animal functions—of which
digestion is a most important example. Now by this combustion carbon
dioxide is generated just as truly as would be the case if the flesh
of the living animal were consumed in a glowing fire. The product of
respiratory combustion is the same carbon dioxide as that recognized
in well-established burnings. The quantities of carbon dioxide evolved
by man and certain of the domestic animals, in each hour of their
existence, have been calculated. They are approximately stated in the
following table:
A man exhales 4 gallons carbon dioxide per hour.
A dog ” 4½ ” ” ” ” ”
A horse ” 50 ” ” ” ” ”
An ox ” 70 ” ” ” ” ”
[Illustration: FIG. 89.—Production of carbon dioxide by combustion of a
diamond in oxygen gas.]
And M. Boussingault has calculated that the approximate amount
of carbon dioxide produced in the city of Paris during a single
twenty-four hours is as follows:
Amount produced by living animals, 55,000,000 cubic feet.
Amount produced by burning of various
kinds of fuel, 27,000,000 cubic feet.
——————————
Total CO₂ produced in twenty-four hours, 82,000,000 cubic feet.
There are certain other natural sources of carbon dioxide that are
worthy of passing mention. Thus in many parts of the world the gas
is continually evolved not only from active volcanoes but also from
extinct ones. Again, another interesting source—though not in the
aggregate a very important one—is found in natural mineral springs. In
these the water often comes to the surface highly charged with carbon
dioxide, and the gas, escaping into the air, imparts to the water its
well-known bubbling appearance.
Experiments with Carbon Dioxide.
For chemical purposes carbon dioxide is commonly produced by the action
of an acid upon some one of the salts known as carbonates. Accordingly
chlorohydric acid and calcic carbonate (that is, common marble) when
brought together produce carbon dioxide. This fact may be readily
shown by the performance of a simple but interesting experiment. The
operation may also serve for the display of some of the principal
properties of the gas.
The experiment in question may be conducted advantageously somewhat
as follows: Provide two convenient glass jars—such as candy jars or
preserve jars; also a short candle, a piece of copper wire, a bottle
of chlorohydric acid and some fragments of white marble. Now attach
the candle to the wire and after lighting the former let it down into
the jars, still burning. The combustion continues because the jars are
full of air and contain ample quantities of oxygen. Next withdraw the
candle and extinguish it for a moment. Now place in the bottom of the
larger jar some chlorohydric acid and into it gently drop some of the
fragments of marble. Effervescence immediately commences. A careful
examination of effervescence shows that in this, as in other cases, the
process consists in the evolution of a gas from a liquid. In the case
in question a colorless gas is plainly evolved, and this gas is carbon
dioxide.
The chemical change is represented by the following equation:
=CaCO₃= + =2HCl=
One molecule of Two molecules of
Calcic carbonate, Chlorohydric acid,
100 73
parts by weight. parts by weight.
\___________________________________/
|
173
= =CO₂= + =CaCl₂= + =H₂O=
One molecule of One molecule of One molecule of
Carbon dioxide, Calcic chloride, Water,
44 111 18
parts by weight. parts by weight. parts by weight.
\_______________________________________________________/
|
173
After allowing the effervescence to continue for five or ten minutes,
relight the candle and again lower it into the jar now containing
carbon dioxide. If a sufficient quantity of the gas is present,
the light will be promptly extinguished when the wick passes below
the surface of the gas. The experiment displays at this stage the
additional fact that the carbon dioxide is heavy, and in filling the
jar it does so from the bottom upward. Now relight the candle and
immerse it in the second jar; this is proved to contain air by the fact
that the candle continues to burn. While it is still quietly burning
there, pour gently upon it the carbon dioxide accumulated in the other
jar. If the amount of this gas is large enough, it will fill the jar
containing the lighted candle and so will readily extinguish the latter.
These experiments demonstrate simply and clearly, certain of the most
important properties of carbon dioxide. Its action in extinguishing
flame is to quench it, very much as water would. When the candle dips
beneath the surface of the carbon dioxide, the flame expires simply
from lack of that oxygen of the air which ordinarily supports the
combustion. And this leads very naturally to the additional statement
that, in similar fashion, living beings are drowned if immersed in
carbon dioxide. For just as water prevents the access of air to the
lungs, and then drowning ensues, so when the animal is beneath the
surface of carbon dioxide he dies from the similar deprivation of air.
Effervescing Beverages.
A large quantity of carbon dioxide taken into the _lungs_ is promptly
fatal to animal life, and even a small increase of that gas, in the
atmospheric air breathed, also produces a marked lowering of the
vitality. It is an interesting fact however that when this gas is taken
into the _stomach_, especially in its solution in water, it has a
wholesome and stimulating effect.
When carbon dioxide is dissolved in water it seems to produce a
true acid, though an unstable one. In accordance with the present
nomenclature, this acid is called carbonic acid and is represented by
the formula H₂CO₃. This substance is present as the main constituent,
or as a subordinate one, in certain natural mineral waters, and
in many simple effervescent beverages. Thus plain soda-water is
merely a solution of carbon dioxide in water. Such solutions are now
manufactured on a large scale, and by mechanical appliances are filled
into siphonlike bottles in such a way that small quantities of the
liquid may be withdrawn without loss of the principal stock of gas.
CHAPTER XXV.
ILLUMINATING GAS.
It has been stated more than once that the compounds of carbon are
very numerous; it might properly be added that their usefulness is
no less striking than their number. This portion of the subject is
so vast, however, that it is often discussed as an entirely separate
branch, called the chemistry of the carbon compounds, and often organic
chemistry. By organic chemistry is meant the chemistry of organic
substances; and by organic substances is meant materials derived from
those existences that possess organs. Now animals and plants, and
they alone, possess organs; whence organic chemistry is described as
the chemistry of animal and vegetable bodies. On some accounts, it is
better defined as the chemistry of the carbon compounds; for while it
was formerly thought that animal and vegetable beings involved in their
processes a chemistry peculiar to themselves, this notion has long
since been dispelled, and it is now clearly perceived that animal and
vegetable compounds are governed by the same chemical laws as others.
But not only is the number of these organic compounds very great;
the variety and importance of animal and vegetable matters give them
a high degree of interest. Thus they include animal and vegetable
juices, extracts, gums, resins, essences, remedial agents, bitter
principles, acids, oils, coloring matters; and of the members of each
one of these classes the name is legion. Moreover, the more any portion
of the subject is studied, the more it seems to reveal a continually
increasing complexity.
Most of the substances of the classes referred to are either compounds
of carbon and hydrogen, or of carbon, hydrogen and oxygen in varied
proportions, or they are compounds containing these elements and yet a
few others combined with them.
It is manifest, from what has been said, that in a book like the
present it is impossible to give any considerable discussion of the
vast field offered by the organic compounds of carbon. It seems better
to choose for description some important manufacturing operation that
involves these compounds and that is on other accounts specially
instructive. Accordingly the manufacture of illuminating gas is
selected for consideration here.
The Manufacture of Illuminating Gas.
The material on which this industry is based is bituminous coal.
This substance is clearly a vegetable product, though it is derived
from a vegetation which lived, flourished and decayed in a period of
prehistoric antiquity.
The manufacture of illuminating gas, although one of the most important
of the chemical industries of to-day, had its beginning but little
before the opening of the present century. A Scotchman named William
Murdoch is generally credited with the first introduction, into
considerable use, of burning gas made from coal. In 1798 he gained
the opportunity to introduce his method of illumination into the
engine works of Boulton & Watt, located at Soho, near Birmingham. From
that date the manufacture and use of illuminating gas from soft coal
has extended and expanded until it has reached its present enormous
development.
General Principles of the Process.
The general principle of the manufacture is exceedingly simple. But its
commercial growth has been assisted by the invention and application of
a multitude of delicate and ingenious appliances.
If any person will take a glass test-tube, place in it a few fragments
of starch, and will then heat the starch strongly over a lamp flame,
he will readily detect three important effects. The first is that a
mass of smoky gas or vapor pours out of the mouth of the test-tube. The
second is that an oily or tarry liquid condenses, on the inside of the
tube, and runs down in streams. The third is that at the close of the
operation a mass of carbon remains in the bottom of the tube where the
starch was. Now the various substances, that have been referred to as
produced by the heating process, are referable to the decomposition of
the molecules of starch.
A Similar Operation on a Large Scale.
In the manufacture of illuminating gas on a large scale there are
developed practically the same series of phenomena as those noted in
the experiment with starch just referred to.
[Illustration: FIG. 92.—Three views of a gas retort.]
In the manufacture of illuminating gas, instead of starch as just
described, soft coal or bituminous coal is used.
In place of a lamp, a large row of furnaces is employed to supply the
heat.
Instead of glass tubes, those of earthenware, ten or twelve feet in
length and between one and two feet in diameter, are used. These tubes,
called retorts, are placed in a horizontal position and so that the
flame of the fire in the furnace may sweep around them and raise them
to a cherry-red heat. At the front end of the retort is attached a
door to prevent the escape of the gases generated, and there is also a
suitable pipe to carry these gases forward to those other portions of
the works which serve to perform upon the crude gas certain necessary
purifications; these are: _First._ The condensation of condensable
vapors. _Second._ The removal of objectionable gases.
[Illustration: FIG. 93.—Section showing five retorts in place.]
The operations spoken of show that the gas must be carried from one
portion of the establishment to another. Now illuminating gas is made
up of material substances and although lighter than air yet they
distinctly possess weight. Gas will not move of itself; to carry it
from place to place the application of force by means of mechanical
appliances is requisite. In fact it is discovered that what is called
an _exhauster_ is necessary for use in gas-works. The exhauster is
simply a kind of rotary pump which pulls the gas from the retorts in
which it is first formed, and pushes it along through the various
purifiers, to the gas holder in which it is stored. If the exhauster
were not used, there would be a constant tendency to the creation of
pressure in the retort, by virtue of which the gas would penetrate the
earthenware into the fire, and so become a source of loss.
From what has been said it will be easily comprehended that the
essential parts of a gas-works are the following:
_First._ The furnace.
_Second._ The retorts, in which the coal is heated.
_Third._ The hydraulic main: a trough of water in which the gas is
cooled, and which also serves as a gate, through which the gas can pass
forward toward the purifiers but not backward toward the retort.
_Fourth._ The out-door condensers, in which the gas is cooled and some
of its vapors condense to tarry liquids.
_Fifth._ The scrubber, in which the gas is cleansed by a spray of water.
[Illustration: FIG. 91.—View in gas-works; drawing coke from the
retorts.]
[Illustration: FIG. 94.—Section to show the processes of the
manufacture of illuminating gas.]
_Sixth._ The purifiers, where sulphuretted hydrogen, and some other
objectionable gases are removed.
_Seventh._ The gas holder, in which the finished gas is collected and
stored prior to delivery to consumers.
The processes by which these various appliances are used in the
manufacture of illuminating gas may be briefly sketched as follows:
A suitable quantity of soft coal is placed in an even layer on the
bottom of the _retort_. Gas at once forms and streams out of the open
door. The door of the retort being now quickly closed by the workmen,
the gas passes out through an exit pipe—called the dip-pipe because it
dips into the water of the _hydraulic main_. The gas bubbles up from
the dip-pipe through the water. Once delivered in the hydraulic main,
the gas cannot go back to the retort.
Next, the gas passes through the _condensers_, a series of connected
up-and-down pipes. As these condensers stand in the open air they cool
the gas so that it deposits tarry liquids that, until this stage, have
been suspended in it in the form of vapor.
Next the gas flows to a large iron box, called the scrubber. In
different works the _scrubber_ varies considerably in outward shape
and internal arrangements. Its essential office however is to wash the
gas, and it does so by the use of water which is applied to the gas
either in sprays or thin films. Ammonia gas is the principal substance
absorbed by the water in the scrubber. Indeed the liquor thus produced
is the main commercial source, at the present day, of ammonia and its
compounds.
The gas next goes to the _purifiers_. These are large iron boxes
supplied with a multitude of shelves upon which, in most works, dry
quicklime is spread. The quicklime absorbs sulphuretted hydrogen and
some other acid gases. From these purifiers the gas is carried on to
the _gas holder_.
The Distillation of Coal, Chemically Considered.
Under the influence of the high temperature of the gas furnace, the
soft coal in the retorts undergoes decomposition. As has before been
intimated, three distinct classes of substances are produced: Solids,
which are left in the retorts; liquids, which are condensed in the
various coolers; gases, which pass on the gas holder.
_First._ _The solids._ These are principally two kinds of carbon. One
is coke,—the principal solid matter found in the retorts as a residue
from the soft coal after the latter has ceased to evolve gas. It is
merely a form of carbon, somewhat spongy in its structure. It is sold
for use as fuel. Beside this the retorts accumulate a sort of scale of
a very different form of carbon called gas carbon. It is extremely hard
and almost non-combustible, being even very difficult to remove from
the retorts. It is at present somewhat used in the manufacture of the
carbon pencils employed in electric lights of the arc variety. Prior to
this use it found scarcely any commercial outlet.
_Second._ _The liquids._ The first condensation of liquids takes
place in the hydraulic main where tarry and oily matters condense and
accumulate, and are drawn off from time to time into the tar well.
Again in the condensers there is a still further deposition of liquids,
also tarry and oily in their nature.
These liquids consist of very complicated mixtures of carbon compounds,
but they are of the most interesting character. In the earlier stages
of the manufacture of coal-gas they were regarded as mere nuisances.
Little by little however chemists have learned to separate the
intermingled products, and have thus been able to obtain a number of
substances of striking interest and usefulness in the arts. Among the
multitudes of substances that go to make up the liquid called coal-tar,
some are as yet hardly classified others are distinctly recognized and
have uses of great commercial importance. Of these latter, two will be
mentioned here. These are anthracene and benzole.
The substance called _anthracene_, a compound of carbon and hydrogen
(C₁₄H₁₀), has within the last ten years sprung into the highest
commercial importance. This is referable to the fact that it has been
found to be a suitable material from which, by chemical processes,
there may be manufactured a substance known as alizarine, besides other
equally valuable and interesting compounds. Alizarine was previously
recognized as the coloring matter of chief value in madder root, a
substance that has been used as a dye-stuff for above a thousand years.
The alizarine, whether of madder or from anthracene, is a coloring
matter of the highest value and usefulness. It affords turkey-red
and other colors that are very important because they are extremely
brilliant and extremely fast. Its _artificial_ manufacture, from the
anthracene of the filthy and offensive coal-tar, is one of the greatest
triumphs of this or any age.
Another substance found in the coal-tar is _benzole_, a compound of
carbon and hydrogen having the formula C₆H₆. This is the principal
material from which, by a variety of well understood though complicated
chemical processes, the well-known aniline colors have been produced.
While these colors may well command the admiration of all, on account
of their unsurpassed beauty and brilliancy, they are of especial
interest to the scientist by reason of the chemical laws they
illustrate. The preparation of these colors, as a group, ranks second
only as a chemical achievement to that of artificial alizarine.
_Third._ _The Gaseous Products._ The gases generated in the process
of the coal-gas manufacture are extremely numerous; some of them are
of high illuminating power, of which that called ethylene (C₂H₄) is
an excellent example. Again there are some that are combustible, but
yet are of slight illuminating power. Substances of this class are
present in the finished product. Hydrogen and carbon monoxide (CO) may
serve as examples. There are always present also gases that are either
injurious to the illuminating power or are otherwise objectionable.
For example, nitrogen is always present, and it is not practicable to
remove it from the gas. It contributes nothing to the value of the
product. Again certain sulphur compounds, like sulphuretted hydrogen,
are usually present. These indeed burn, but they give rise to offensive
and unwholesome oxides of sulphur.
The sketch thus given, while it but imperfectly describes the wonderful
industry in question, with its various well contrived and delicate
appliances, serves however to give some idea of the importance of
the operation, from a chemical point of view, and the mine of rich
materials its carbon compounds offer to chemical students.
CLOSING CHAPTER.
CHAPTER XXVI.
SILICON.
Silicon may well be considered important on account of its _quantity_
in the earth, if on no other. In an earlier chapter it has been shown
that oxygen exists in our globe—including its atmosphere and its
oceans—in an amount equal to about one-half of the weight of the whole.
Now silicon exists in a quantity equal to about one-fourth of this
entire weight. In the earth however, neither of these substances exists
in the uncombined form. These facts seem to involve as a necessary
consequence that they exist in the earth, to a large extent, combined
with each other; indeed this is found to be the case. The principal
earthy matter of our planet is the compound of silicon and oxygen,
existing either alone in the form of sand, quartz crystal and similar
minerals, or else in combination with other well-known abundant earth
materials, such as oxides of calcium, magnesium and aluminum. It has
already been stated that carbon is the characteristic element of
animal and vegetable matters; so silicon is the characteristic element
of mineral matters. Thus granite and similar archaic rocks contain
approximately twenty-five per cent of silicon.
In nature, silicon performs its important office as a constituent of
rock material, with a fitness that is referable largely to the high
degree of stability possessed by most of its compounds. The permanence
of the materials of the earth’s surface under the influence of heat,
and water, and frost, and similar agencies is an illustration of this
principle.
_Silicic oxide_ (SiO₂), occurs on our globe in many different forms of
which diatomaceous earth and rock crystal may be mentioned.
Diatomaceous earth is a powdery material found in abundant deposits in
many parts of the world. Its characteristic structure, when examined
under the microscope, reveals its nature; then it is seen to be made
up of the shells of minute vegetable organisms called diatoms. These
assume a great many beautiful forms, and some of them are checkered
all over with markings of such extreme fineness that they have been
used as test objects for trying the resolving power of the objectives
of microscopes. This kind of earth is employed, as has already been
stated, in the preparation of dynamite.
[Illustration: FIG. 95.—Diatomaceous earth as seen through the
microscope.]
Quartz sometimes occurs in colorless transparent masses of great beauty
and clearness called rock crystal. The amethyst is the same substance
slightly colored by compounds of the metal manganese, while quartz
exists of a variety of other shades, in some of which it is prized as
a gem. Quartz generally assumes forms of a hexagonal tendency: they
are often hexagonal prisms terminated by hexagonal pyramids.
[Illustration: FIG. 96.—Mass of natural quartz crystals.]
Quartz and the finer and purer varieties of sand are used largely in
the manufacture of glass. The silicic oxide here displays what may be
expressed as its acid tendencies; for in the manufacture of glass it is
fused with sodic carbonate, and then the silicic oxide displaces the
carbon dioxide from the sodic carbonate; as a result there is formed
what must be regarded as a true salt, or a mixture of salts, that in
the simplest kind of glass may be termed _sodic silicate_.
* * * * *
_Closing Words._ The course laid out in the preface is now terminated
with silicon, as there planned. From scientific considerations, this
is a natural ending; it seems to be appropriate on another account
also. After the reader has been carried, in thought, among the various
gaseous elements, that make up atmosphere and oceans, it seems suitable
that we should say farewell to him upon the discussion of that element
that may be called the characteristic material of our solid earth.
INDEX.
Abel, F. A., 182
Acid, Boric, 157
——— Nitric, 35, 168
——— Sulphuric, 35, 37, 152
——— Chlorohydric, 33, 190
——— Phosphoric, 192
Affinity, Chemical, 44, 46-52
Alizarine, 226
Alkali Trade, 94, 106
Allotropism, 190
Amethyst, 229
Ammonia, 166, 174, 225
Anhydride, 151
Anhydrite, 146
Anthracene, 226
Antimony, Sulphide of, 148
Apatite, 188, 189
Arsenic, Sulphide of, 148
Atom, 41, 42
Atomic Theory, 52
Atmosphere, 170
Bacon, Roger, 178
Balard, 100
Balloons, 74
Barilla, 107
Benzole, 227
Berthollet, 94
Berzelius, 24
Beverages, effervescing, 219
Binary Compounds, 32
Biot, 80
Black, Joseph, 61, 63, 76
Bleaching-Powder, 93
Blende, 146
Blowpipe, Compound, 129
Bone-Ash, 187
Borax, 157
Boron, 157
Boussingault, 217
Brandt, 187
Bromine, 100
Carbon, 197
——— Dioxide, 173, 216
——— Monoxide, 215
Cavendish, Henry, 60
Charcoal, 197
Chemistry, Scope of, 7, 9
Chlorine, 85
Cinnabar, 146
Coal, 201
Coal-tar, 226
Coke, 226
Compounds, 32
——— Number of, 8, 9
——— Organic, 221
Copper, Sulphate of, 51
Cotton, 181
Courtois, 108
Current, Galvanic, 64
Daguerre, 103
Dalton, John, 52, 56
Davy, Humphry, 60, 86, 108
De Rozier, 78
Diamond, 203
Diatoms, 185, 228
Diffusion, 69
Döbereiner, 70
Dynamite, 183, 185
Earth’s Crust, Composition of, 15
Elements, Chemical, 9, 12, 14, 28
——— Names and Symbols of, 19, 23
Equivalence, 48, 72
Ethylene, 227
Explosives, 177
Fertilizers, 188
Fluorine, 112
Fireworks, 180
Fulminates, 181
Galena, 146
Gas, 63
—— Illuminating, 221
Gas-Carbon, 226
Gay-Lussac, 80
Glaisher and Coxwell, 81
Glass, 229
Glycerine, 184
Granite, 228
Graphite, 201
Gun-Cotton, 181
Gunpowder, 177
Haüy, 15
Heat, unit of, 71
Hydrogen, 58
Iodine, 105
Iron, Sulphide of, 146
Janssen, 83
Kelp, 107
Lamp-Black, 200
Larderel, 160
Lavoisier, 19, 21, 118
Lead, 34
——— Sulphide of, 146, 148
Leblanc Process, 94
Liebig, 101
Light, Calcium, 131
——— Electric, 211, 226
Limestone, 209
Lithium, 30
Marble, 209
Mass, 39
Matches, 192
Mayow, 121, 163
Metals, 28, 29
——— Names of, 16, 20
Mercury, 30
——— Sulphide of, 146
Moisture in the Air, 173
Molecule, 40
Montgolfier, 74
Murdoch, 222
Nobel, 185
Nitrogen, 162
Nitroglycerine, 184
Nomenclature, Chemical, 19, 20, 32, 33, 37
Non-metal, 30
Oxide, Ferroso-ferric, 66
Oxygen, 117
——— Abundance of in the earth, 14, 16
Palladium, 70
Pelletier, 89
Petroleum, 209
Photography, 93
Phosphorus, 187
Phosphorus Necrosis, 189
Phosphuretted Hydrogen, 191
Potassic Chlorate, 123
Priestley, Joseph, 64, 118, 163
Puymaurin, 115
Pyrites, 146
Quartz, 228
Roe, 89
References, Reading, 10, 17, 24, 27, 31, 38, 45, 56,
73, 84, 98, 111, 116, 133, 156,
161, 186, 196, 214
Rutherford, 163
Scheele, 85, 114, 118, 162, 187
Silicon, 228
——— Abundance of, 16
Sodium, 67
Sugar, 41
Sulphur, 142
——— Dioxide, 33, 149
——— Trioxide, 33, 151
Sulphuretted Hydrogen, 147
Ternary Compounds, 34
Van Helmont, 63
Varech, 107
Vitriol, Oil of, 152
Water, 127, 134
Weight, Atomic, 17
Zinc, 68
—— Sulphide of, 146, 149
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