Page:Elementary Text-book of Physics (Anthony, 1897).djvu/337



279. Electrolysis.—It has been already mentioned that, in certain cases, the existence of an electrical current in a circuit is accompanied by the decomposition into their constituents of chemical compounds forming part of the circuit. This process, called electrolysis, must now be considered more fully. It is one of those treated generally in § 277, in which work other than heating the circuit is done by the current. That work is done by the decomposition of a body the constituents of which, if left to themselves, tend to recombine, is evident from the fact that, if they be allowed to recombine, the combination is always attended with the evolution of heat or the appearance of some other form of energy. The amount of heat developed, or the energy gained, is, of course, the measure of the energy lost by combination or necessary to decomposition.

Those bodies which exhibit electrolysis are always such as have considerable freedom of motion among their molecules. Ordinarily, they are liquids or solids in solution or fused. The discharge through gases is also probably accompanied by electrolysis. Bodies which can be decomposed were called by Faraday, to whom the nomenclature of this subject is due, electrolytes. The current is usually introduced into the electrolyte by solid terminals called electrodes. The one at the higher potential is called the positive electrode or anode; the other, the negative electrode, or cathode. The two constituents into which the electrolyte is decomposed are