Page:Elementary Text-book of Physics (Anthony, 1897).djvu/339

§ 280] special case in which the secondary reactions in the electrolyte exactly balance the work done by the current in decomposition, so that on the whole no chemical work is done.

280. Faraday's Laws.—The researches of Faraday in electrolysis developed two laws, which are of great importance in the theory of chemistry as well as in electricity:

(1) The amount of an electrolyte decomposed is directly proportional to the quantity of electricity which passes through it; or, the rate at which a body is electrolyzed is proportional to the current strength.

(2) If the same current be passed through different electrolytes, the quantity of each ion evolved is proportional to its chemical equivalent. The chemical equivalent is the weight of the radical of the ion in terms of the weight of the atom of hydrogen, divided by its valency.

If we define an electro-chemical equivalent as the quantity of any ion which is evolved by unit current in unit time, then the two laws may be summed up by saying:

The number of electro-chemical equivalents evolved in a given time by the passage of any current through any electrolyte is equal to the number of units of electricity which pass through the electrolyte in the given time. The electro-chemical equivalents of different ions are proportional to their chemical equivalents. Thus, if zinc sulphate, cupric sulphate, and argentic chloride be electrolyzed by the same current, zinc is deposited on the cathode in the first case, copper in the second, and silver in the third. The amounts by weight deposited are in proportion to the chemical equivalents, 32.6 parts of zinc, 31.7 parts of copper, and 108 parts of silver.

Faraday's laws may also be stated in another form, in which the word "ion" has a different meaning. The process of electrolysis consists in the separation of each molecule of the electrolyte into its constituent radicals. Each of these radicals is called an ion. If the valency of the radical be 1, the ion is called a univalent ion; if it be n, the ion is either called an n-valent ion or n-