540 M. Poggendorff on Galvanic Circuits composed of 



the solution of chlorine acts more powerfully than hydrochloric 

 acid, m which, nevertheless, the chlorine is electrolytically com- 

 bined with hydrogen, and without doubt is more strongly re- 

 tained by the hydrogen than in the solution of chlorine by the 

 ivater. 



It might perhaps be replied, that the solution of chlorine is 

 not a mere solution of the chlorine, but a mixture of hydrochlo- 

 ric acid and the oxide of chlorine ; but setting aside that this 

 supposition is not proved, is not even very probable, and is 

 accompanied by a second supposition not more probable, that 

 this mixture or the oxide of chlorine is of more difficult decom- 

 position than hydrochloric acid, we need only call to mind the 

 other cases where non- electrolytes exert a sensible influence on 

 the development of the electromotive force, — the actions of sul- 

 phuric acid, of nitric acid, ammonia, water impregnated with oxy- 

 gen, of the peroxide of hydrogen^, of the gwm/o-sulphuret of 

 potassium {K S^) — to perceive that such a supposition is neither 

 required nor can be generahzed. 



The position, that those bodies which, brought between the 

 metallic plates of a voltaic pile, render it active, are all electro- 

 lytes {Exp. Res. § 858, 921), must therefore be thus altered, 

 that the fluids between the metallic plates must, it is true, be 

 electrolytes, i. e. decomposable bodies, since, at least with 

 aqueous fluids and with a certain intensity of current, no con- 

 duction can take place without decomposition; but that the 

 electromotive force which is developed on the contact of these 

 fluids with the metals is not in any necessary connexion with 

 the conductivity or decomposability, and can be increased or 

 diminished by bodies which are not electrolytes, i. e. not directly 

 decomposablef. I shall hereafter communicate another proof 

 on this point. 



Not less difficult for the disputed theory would be the cases 

 in which hydrochloric acid and sal-ammoniac, hydrochloric acid 

 and salt, or salt and sal-ammoniac are opposed to each other. In 

 each of them, according to it, only the chlorine could act on 

 both sides, and consequently no current arise. But I will pass 

 over the discussion of these cases and turn to the iodide of 

 potassium, from M'hich Faraday has derived the new argument 

 in favour of the chemical theory. 



In the preceding tables I have enumerated the action of the 

 iodide of potassium in 17 metallic combinations, both towards 



* Becquere], Ann. de Chun, et de Phys., vol. xxviii. p. 19. 



f De la Rive and other supporters of the oxidation-theory, admit also, as is 

 well known, that it is the oxidation of the zinc alone, no matter whether it be 

 caused by the oxygen of the atmosphere absorbed by the water or any other 

 action, which determines the current. 



