If a current of electricity is passed through the wires and the electrodes, in the direction shown[p. 125] 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 free oxygen. By free oxygen is meant oxygen in the form of gas.
Composition of Water.—Now, water, in which harmful germs live, is one-third oxygen. Nevertheless, the germs thrive in water, because the oxygen is in a compound state, and, therefore, not[p. 126] an active agent. But if oxygen, in the form of gas, can be forced through water, it will attack the germs, and destroy them.
Common Air Not a Good Purifier.—Water may be purified, to a certain extent, by forcing common air through it, and the foulest water, if run over rocks, will be purified, in a measure, because air is intermingled with it. But common air is composed of four-fifths nitrogen, and only one-fifth oxygen, and, as nitrogen is the staple article of food for bacteria, the purifying method by air is not effectual.
Pure Oxygen.—When, however, oxygen is generated from water, by means of electrolysis, it is pure; hence is more active and is not tainted by a life-giving substance for germs, such as nitrogen.
The mechanism usually employed for purifying water is shown in Fig. [90].