HYDROGEN GAS.
This element was discovered by Cavendish in 1766, and was called by him
inflammable air. The name hydrogen is derived from two Greek words, one
signifying “water” and the other “to generate,” on account of its
forming water when burnt. It occurs in its free state in the bases of
volcanoes, and by the aid of the spectroscope has been detected in the
sun and stars. It chiefly exists in combination with oxygen as water,
and is an important constituent of all vegetable and animal substances.
Hydrogen is obtained by the decomposition of water in various ways. On a
large scale, nearly pure hydrogen may be prepared by passing steam over
charcoal, or coke, heated to a dull redness. If the temperature be kept
sufficiently low hydrogen and carbon dioxide will be the sole products,
and the latter may be removed by causing it to traverse a vessel filled
with slaked lime, but if the temperature be allowed to rise too high, or
an excess of air be admitted, carbon monoxide is also produced, and
cannot be removed from the mixture.
Pure hydrogen is a colorless, odorless, transparent and tasteless gas,
and has never been liquefied. It is very slightly soluble in water. It
is the lightest of all known bodies and is not poisonous, although it
cannot support life, and if mixed with a certain proportion of oxygen it
can be breathed for a considerable length of time without inconvenience.
It is highly inflammable, and burns in the air with an almost colorless,
nonluminous flame, forming water. A burning taper is extinguished when
plunged into hydrogen, and all bodies which burn in the air are
incapable of burning in hydrogen.
Hydrogen does not spontaneously enter into reaction with any of the
elements, although it has a powerful affinity for several of them. Thus,
when hydrogen and oxygen are mixed nothing occurs, but if a lighted
splint is introduced a violent explosion ensues, water being produced.
Similarly chlorine and hydrogen are without action upon each other in
the dark, but if the mixture is exposed to a bright light, or if heated
by the passage of an electric spark, the gases are at once combined with
explosive violence, forming hydrochloric acid.
Hydrogen is usually prepared by the action of zinc or iron on a solution
of hydrochloric or sulphuric acid. All metals which decompose water when
heated readily furnish hydrogen, on treatment with hydrochloric or
sulphuric acid. Many other metals enter more or less readily (although
none so readily) into reaction with these acids. Also, many other acids
than sulphuric or hydrochloric acids may be used, but none acts so
quickly. In all cases the action consists of the displacement of the
hydrogen of the acid by the metal employed, and if the acid is not one
which can enter into reaction with the displaced hydrogen, the latter is
also evolved as gas.
If pure gas is required it is necessary to employ pure zinc or iron, as
the impurities in the ordinary metal communicate an extremely
disagreeable odor to the gas.
The pure gas is not absolutely essential for lead burning, and owing to
their being much cheaper, and also on account of their increased
quickness of action, the commercial qualities of sulphuric acid and zinc
are employed in the generator described.
The commercial zinc is known as spelter and is sold in pigs or blocks,
which are easily broken into fragments, like stove coal, with a heavy
hammer. The commercial sulphuric acid is known as oil of vitriol and is
sold by the pound. The acid cannot be employed in its pure state, but
must be reduced with water in the proportion of one part of acid to
seven parts of warm water. They must be mixed by adding the acid slowly
to the water; never the water to the acid. The combination of acid and
water enters at once into reaction and always generates heat, and the
result of adding water to acid would be small explosions. There would be
danger of the acid flying on one's clothes or into the eyes. The mixture
should never be stronger than six parts of water to one of acid.
The beginner will observe from the above that the generator cannot be
crowded by making the acid solution strong. Hydrogen is a peculiar gas
and also a dangerous one for one ignorant of its peculiarities to
experiment with, and in order to thoroughly understand it the following
experiments should be demonstrated, which can be done with little
expense. The beginner should note the result of each experiment as
demonstrated, and carefully commit the same to memory for future
reference.
Experiment 1.
_Test for Hydrogen._—Fill a small jar or wide mouthed bottle with
hydrogen. This is done by first filling the bottle with water, inserting
the end of the tube from the hydrogen generator, having first exhausted
the air in the tube, then quickly inverting the bottle and placing the
neck, Fig. 2, in a pan of water (A); the water will stay in the bottle.
Now turn on the hydrogen. The gas, being lighter than water, will rise
to the top of the bottle (B), drive out the water, and replace it with
pure hydrogen, which should be free from air. Remove the bottle from the
pan of water, keeping it inverted. Thrust a lighted splint into the
bottle. The gas will light and burn at the mouth of the bottle. If the
splint is thrust far into the bottle it will go out. Drops of water
collect in the bottle. Burning is a union with oxygen; therefore, the
burning of the hydrogen shows that it has an affinity for oxygen. The
splint goes out because the hydrogen does not support combustion. _If no
air is allowed to get into it the gas cannot burn or explode._
[Illustration:
_Fig. 2.—Experiment No. 1._
]
Experiment 2.
[Illustration:
_Fig. 3.—Experiment No. 2._
]
_Proving That Hydrogen is Lighter Than Air._—Bring an inverted bottle of
hydrogen close to an empty bottle, also inverted, Fig. 2. Gradually tip
the bottle containing hydrogen (A) until it is brought to an upright
position beneath the empty bottle. Test the bottles for hydrogen. The
hydrogen will be found in the bottle (B) that was at first empty,
proving that _hydrogen is lighter than air_, as it has risen in the
empty bottle, displacing the air that was in it. If the bottle of
hydrogen is left in an upright position without a cover for a few
moments the gas will entirely disappear.
Experiment 3.
[Illustration:
_Fig. 4.—Experiment No. 3._
]
_The Effect of Mixing Hydrogen and Air._—Half fill a bottle with water
and invert it in a pan of water, Fig. 3, leaving the upper half filled
with air. Displace the air in the bottle with hydrogen, then thrust a
lighted splint into the bottle, and the gas will light with an
explosion. When the bottle was half filled with water the other half was
air. The hydrogen took the place of the water, so that the bottle
contained equal quantities of hydrogen and air. When the hydrogen was
lighted it combined with the oxygen in the air. The union of the two
gases caused the explosion, proving that the combined gases are very
explosive.
Experiment 4.
_To Make Hydrogen From Water._—Drop a piece of potassium into a little
water and cover it. The potassium floats on the water and soon burns.
Potassium acts vigorously on cold water, setting free hydrogen, and
unites with parts of it to form “caustic potash.”