Page:The fundamental laws of electrolytic conduction.djvu/63

 and recompositions in opposite directions, and finally causing their expulsion or exclusion at the boundaries of the body under decomposition, in the direction of the current, and that in larger or smaller quantities, according as the current is more or less powerful. I think, therefore, it would be more philosophical, and more directly expressive of the facts, to speak of such a body, in relation to the current passing through it, rather than to the poles, as they are usually called, in contact with it; and say that whilst under decomposition, oxygen, chlorine, iodine, acids, etc., are rendered at its negative extremity, and combustibles, metals, alkalies, bases, etc., at its positive extremity.

"The poles, § 556, are merely the surfaces or doors by which the electricity enters into or passes out of the substance suffering decomposition. They limit the extent of that substance in the course of the electric current, being its terminations in that direction; hence the elements evolved pass so far and no further."

In this way Faraday, for the first time, explains chemical decomposition with definiteness, as the conduction of the electric current through the electrolyte. He proves the important relation that "the sum of chemical decomposition is constant for every section taken across a decomposing conductor, uniform in its nature, at whatever distance the poles may be from each other or from the section; … provided the current of electricity be retained in constant quantity.…" Our conception even to-day of the process of electrolytic decomposition is embraced in these laws. In a later paper Faraday expressed the belief that they would need modification. The chemical theory of the galvanic cell, which he so energetically sought to defend, inclined him, primarily, to make this statement, as well as the fact that electrolytes often conduct weak currents without any decomposition being perceptible. Both points, however, have since been satisfactorily explained by science, without in any way affecting the postulated laws. On the contrary, every more exact investigation has only furnished a new confirmation of them.

We usually picture the process to ourselves by means of a row