General Principles of Definite Electrolytic Action. 425 



posability, upon the nature of their elements only; for, of the 

 same two elements, bodies may be formed, of which one shall 

 belong to one class and another to the other class ; but pro- 

 bably on the proportions also (697.)- It is further remark- 

 able, that with very few, if any, exceptions (414*. 691.), these 

 decomposable bodies are exactly those governed by the re- 

 markable law of conduction I have before described (394.) ; 

 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 (664.)- 



824. Then, again, the substances into which these divide, 

 under the influence of the electric current, form an exceed- 

 ingly important general class. They are combining bodies; 

 are directly associated with the fundamental parts of the doc* 

 trine 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 parti- 

 cularly anions and cations, according as they appear at the 

 anode or cathode (665.); and the numbers representing the 

 proportions in which they are evolved electro-chemical equiva* 

 lents. Thus hydrogen, oxygen, chlorine, iodine, lead, tin, 

 are ions ; the three former are anions, the two metals are cat- 

 ions, and 1, 8, 36, 125, 104, 58, are their electro-chemical 

 equivalents nearly. 



825. A summary of certain points already ascertained re- 

 specting electrolytes, ions, and electro-chemical equivalents, may 

 be given in the following general form of propositions, with- 

 out, I hope, including any serious error. 



826. i. A single ion, i. e. one not in combination with an- 

 other, will have no tendency to pass to either of the elec- 

 trodes, 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 

 series of these Researches (518. &c). 



827. ii. If one ion be combined in right proportions (697.) 

 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 (530. 542.547.). 



828. iii. It', therefore, an ion pass towards one of the elec- 

 trodes, another ion must also be passing simultaneously to the 



* For references to the places in which the subjects of the several pre- 

 ceding series are noticed in our Magazine, see the number for September 

 last, present vol., pp. 161, 162, 165, 172. Edit. 



Third Series. Vol.5. No. 30. Dec. 1834. 3 I 



