ELECTROLYSIS. With respect to their ability to conduct electricity, all substances are divided into the two general classes, conductors and non-conductors; there is, however, no hard and fast boundary line between the two, but a more or less gradual merging from one into the other. The conductors are again divided into two classes, those which conduct the cur rent without any apparent decomposition and those in which the conduction is invariably ac companied by decomposition. In this latter class, the conduction of the current with con comitant decomposition is called electrolysis, and the liquid subjected to decomposition is termed the electrolyte. These are the names originally proposed by Faraday. True electrol ysis is almost entirely confined to liquids. Evi dences of electrolysis have been found, how ever, in a few cases in solids and similar phe nomena have been observed in connection with high-tension discharges through gases. large number of liquids, particularly of organic na ture, fall in the class of non-conductors. Water, and a number of other liquids of inor ganic origin are also non-conductors when care fully purified. Liquids that conduct without de composition are limited to liquid metals. Liquids that conduct with decomposition — that is, electrolytes, may be a pure liquid, a fused salt, or a solution, either aqueous or non-aqueous. In the case of solutions the conductivity is not necessarily dependent on the conductivity of the constituents of the solution, but may be a prop erty of the solution itself. A solution of one
non-conductor in another may give a solution of good conductivity.
Also, in the case of a solution, the decom position caused by the electrolysis may affect the solvent or the solute or both, and may vary with the conditions of electrolysis.. If the con stituents of the solute are obtained directly at the anode and cathode, the reaction is said to be a primary one; but if for any reason, these constituents react on either the electrodes or the solution, the reaction is said to be secondary. (See ELECTROCHEMISTRY). Primary reactions are dependent only on the amount of current acting, and are not subject to modification by physical conditions (see FARADAY'S LAWS), but secondary reactions may be modified by tem perature, concentration, current density and other physical conditions and in this type of reaction with its various modifications lie many of the possibilities in the field of industrial electrochemistry. (See ELECTROCHEMICAL IN DUSTRIES). The problem of the mechanism of electrolysis is one that has attracted more at tention than any other in the field of electro chemistry. A brief discussion of the early his tory and the present status of this problem will be found in the article on ELECTROCHEMISTRY. This question is also closely related to, and to a certain extent dependent on, the problem of the nature of solutions, and a further discus sion of the principles involved will be found in the article on SOLUTIONS.