broken up into its original
compounds. Thus, water is composed of two parts, by bulk, of hydrogen
and of oxygen, so that if two electrodes are placed in water, and a
current is sent through the electrodes in either direction, all the
water will finally disappear in the form of hydrogen and oxygen gases.

MAKING HYDROGEN AND OXYGEN.--During this electrical action, the hydrogen
is set free at the negative pole and the oxygen at the positive pole. A
simple apparatus, which any boy can make, to generate pure oxygen and
pure hydrogen, is shown in Fig. 89.

It is constructed of a glass or earthen jar (A), preferably square, to
which is fitted a wooden top (B), this top being provided with a
packing ring (C), so as to make it air-tight. Within is a vertical
partition (D), the edges of which, below the cap, fit tightly against
the inner walls of the jar. This partition extends down into the jar a
sufficient distance so it will terminate below the water level. A pipe
is fitted through the top on each side of the partition, and each pipe
has a valve. An electrode, of any convenient metal, is secured at its
upper end to the top of the cap, on each side of the partition. These
electrodes extend down to the bottom of the jar, and an electric wire
connects with each of them at the top.

[Illustration: _Fig. 89._ DEVICE FOR MAKING HYDROGEN AND OXYGEN]

If a current of electricity is passed through the wires and the
electrodes, in the direction shown by the darts, hydrogen will form at
the negative pole, and oxygen at the positive pole. These gases will
escape upwardly, so that they will be trapped in their respective
compartments, and may be drawn off by means of the pipes.

PURIFYING WATER.--Advantage is taken of this electrolytic action, to
purify water. Oxygen is the most wonderful chemical in nature. It is
called the acid-maker of the universe. The name is derived from two
words, _oxy_ and _gen_; one denoting oxydation, and the other that it
generates. In other words, it is the _generator of oxides_. It is the
element which, when united with any other element, produces an acid, an
alkali or a neutral compound.

RUST.--For instance, iron is largely composed of ferric acid. When
oxygen, in a free or gaseous state, comes into contact with iron, it
produces ferrous oxide, which is recognized as rust.

OXYGEN AS A PURIFIER.--But oxygen is also a purifier. All low forms of
animal life, like bacteria or germs in water, succumb to