[Sidenote: Distribution and production of hydrogen]
HYDROGEN--Hydrogen is found in nature very widely distributed and
in large quantities. It forms one-ninth of the weight of water, and
is contained in all the principal substances which enter into the
composition of plants and animals. It may be obtained by decomposition
of water by means of the electric current, or by the action of
substances known as acids on metals. The latter method is more commonly
used in the laboratory. Acids contain hydrogen, give it off easily, and
take up other elements in its place. Among the common acids found in
every laboratory are hydrochloric, sulfuric, and nitric.
[Sidenote: Physical properties of hydrogen]
Pure hydrogen is a colorless, odorless, tasteless gas. It is not
poisonous, and may therefore be inhaled without harm. It is the lightest
known substance, being about 14.4 times lighter than air, 16 times
lighter than oxygen, and 11,000 times lighter than water.
[Sidenote: Chemical properties of hydrogen]
Hydrogen does not unite with oxygen at ordinary temperatures, but,
like wood and most other fuel substances, needs to be heated up to the
kindling temperature before it will burn. Hydrogen burns if a lighted
match be applied to it. The flame is colorless, or very slightly blue.
[Sidenote: Decomposition of water]
WATER--Water is a compound and not an element, as can be shown by
passing an electric current through it. If the ends of two wires, each
connected with an electric battery, be put a short distance apart, in
acidulated water, it will be noticed that bubbles of gas rise from each
wire. As these gases cannot come from, or through the wires, they must
be formed from the water. If they be analyzed, we will find that oxygen
gas comes from one wire and hydrogen from the other.
[Sidenote: Proportion of hydrogen and oxygen in water]
This experiment shows that when an electric current is passed through
water, hydrogen and oxygen are obtained, and also that there is obtained
twice as much hydrogen as oxygen by volume. This proves that water is
not an element, but a compound of two atoms of hydrogen and one of
oxygen. The chemist therefore writes the symbol for water H₂O.
We have just learned that with electricity we could decompose the
compound water into its elements, hydrogen and oxygen. Now we can
prove by another experiment that water contains these two elements. If
we burn hydrogen gas, or any substance containing hydrogen, water is
formed. This can be illustrated by inverting a cool, dry tumbler over a
gas flame, which is composed chiefly of hydrogen, and water vapor will
collect on the inside.
[Sidenote: Properties of water]
Though water is widely distributed over the earth, we never find it
absolutely pure in nature. All natural waters contain foreign substances
in solution. These substances are taken up from the air, or from the
earth. Pure water is colorless, tasteless, and odorless.
[Sidenote: Why ice floats]
On cooling, water contracts until it reaches the temperature of 4°
Centigrade (39° Fahrenheit). When cooled from 4° to 0° C. it expands,
and the specific gravity, or weight compared with the space occupied by
ice, is somewhat less than that of water; hence ice floats.
[Sidenote: Rain-water]
[Sidenote: Hard water]
[Sidenote: Mineral water]
The purest water found in nature is rain-water, particularly that which
falls after it has rained for some time; that which first falls always
contains impurities from the air. As soon as rain-water comes in contact
with the earth and begins its course toward the sea, it also begins to
take up various substances according to the character of the soil with
which it comes in contact. Mountain streams which flow over rocky beds,
particularly beds of sandstone, contain very pure water. Streams which
flow over limestone dissolve some of the stone, and the water becomes
"hard." The many varieties of mineral water from the various springs
throughout the country, take their properties from soluble substances
with which they come in contact.
[Sidenote: Salt water]
Common salt is deposited in large quantities in different parts of the
earth. Since salt is readily soluble in water, many streams pick up
large quantities of it, and as all water courses ultimately find their
way to the ocean, the latter becomes a repository for salt with which
the earth-water is laden.
[Sidenote: Effervescent waters]
Effervescent waters all contain some gas, usually carbonic acid gas in
solution, and they merely give up or set free a part of it when placed
in open vessels.
[Sidenote: Sulfur water]
Sulfur water contains a compound of hydrogen and sulfur, called hydrogen
sulfid or sulfureted hydrogen, which we will refer to in its order later
in this lesson.
[Sidenote: Distilled water]
Water may be purified by means of distillation. This consists in boiling
the water and condensing the vapor by passing it through a tube which is
kept cool by surrounding it with cold water. By means of distillation
most substances in solution in water can be eliminated. Substances,
however, which evaporate like water, will, of course, pass off with the
water vapor. Aboard ship salt water is distilled and thus made fit for
drinking. In chemical laboratories ordinary water is distilled in order
to purify it for chemical work.