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.