Page:Experimental researches in electricity.djvu/183

Rh one class and another to the other class; but probably on the proportions also (432). It is further remarkable, that with very few, if any, exceptions (150, 426), these decomposable bodies are exactly those governed by the remarkable law of conduction I have before described (130); for that law does not extend to the many compound fusible substances that are excluded from this class. I propose to call bodies of this, the decomposable class, Electrolytes (400).

559. Then, again, the substances into which these divide, under the influence of the electric current, form an exceedingly important general class. They are combining bodies; are directly associated with the fundamental parts of the doctrine of chemical affinity; and have each a definite proportion, in which they are always evolved during electrolytic action. I have proposed to call these bodies generally ions, or particularly anions and cations, according as they appear at the anode or cathode (401); and the numbers representing the proportions in which they are evolved electro-chemical equivalents. Thus hydrogen, oxygen, chlorine, iodine, lead, tin are ions; the three former are anions, the two metals are cations, and 1, 8, 36, 125, 104, 58, are their electro-chemical equivalents nearly.

560. A summary of certain points already ascertained respecting electrolytes, ions, and electro-chemical equivalents, may be given in the following general form of propositions, without, I hope, including any serious error.

561. i. A single ion, i.e. one not in combination with another, will have no tendency to pass to either of the electrodes, and will be perfectly indifferent to the passing current, unless it be itself a compound of more elementary ions, and so subject to actual decomposition. Upon this fact is founded much of the proof adduced in favour of the new theory of electro-chemical decomposition, which I put forth in a former part of these Researches (254, etc.).

562. ii. If one ion be combined in right proportions (432) with another strongly opposed to it in its ordinary chemical relations, i.e. if an anion be combined with a cation, then both will travel, the one to the anode, the other to the cathode, of the decomposing body (266, 278, 283).

563. iii. If, therefore, an ion pass towards one of the electrodes, another ion must also be passing simultaneously to the other electrode, although, from secondary action, it may not make its appearance (478).

564. iv. A body decomposable directly by the electric current,