Faraday. 199 



tendency with which it can combine. It also explains why, in 

 numerous cases, the atoms of the evolved substances are not 

 retained by the terminals (an obvious difficulty in the way of 

 all theories which suppose the terminals to attract the atoms) : 

 for the evolved substances v are expelled from the liquid, not 

 drawn out by an attraction. 



Many of the perplexities which had harassed the older 

 theories were at once removed when the phenomena were re- 

 garded from Faraday's point of view. Thus, mere mixtures (as 

 opposed to chemical compounds) are not separated into their 

 constituents by the electric current ; although there would seem 

 to be no reason why the Grothuss-Davy polar attraction should 

 not operate as well on elements contained in mixtures as on 

 elements contained in compounds. 



In the latter part of the same year (1833) Faraday took up 

 the subject again.* It was at this time that he introduced the 

 terms which have ever since been generally used to describe 

 the phenomena of electro-chemical decomposition. To the 

 terminals by which the electric current passes into or out of the 

 decomposing body he gave the name electrodes. The electrode 

 of high potential, at which oxygen, chlorine, acids, &c., are 

 evolved, he called the anode, and the electrode of low potential, 

 at which metals, alkalis, and bases are evolved, the cathode. 

 Those bodies which are decomposed directly by the current 

 he named electrolytes ; the parts into which they are decomposed, 

 ions ; the acid ions, which travel to the anode, he named anions ; 

 and the metallic ions, which pass to the cathode, cations. 



Faraday now proceeded to test the truth of a supposition 

 which he had published rather more than a year previously ,f 

 and which indeed had apparently been suspected by Gay-Lussac 

 and ThenardJ so early as 1811; namely, that the rate at which 

 an electrolyte is decomposed depends solely on the intensity of 

 the electric current passing through it, and not at all on the 

 size of the electrodes or the strength of the solution. Having 



* Exp. Res., 661. f /*'*., 377 (Dec. 1832). 



Recherches physico-chimiqucs faites sur la pile ; Paris, 1811, p. 12. 



