Two Fluids, and of Two Metals not in Contact. 487 



a property of all electric currents to decompose on their passage 

 through a series of different fluids equivalent quantities of each, 

 then a priori, every consequent conclusion from the law with re- 

 spect to the origin of voltaic electricity is impossible. That the 

 latter is then actually the case, that in fact the electrolytic law is 

 common to all electric currents, that consequently the identity 

 of electricities of various origin (manifoldly proved by Faraday 

 himself in other respects) is established with reference to this 

 law also, the simple experiment, published by me last year, on 

 the simultaneous decomposition of two portions of water by 

 the same magneto-electric current, can leave not the least room 

 for doubt*. 



Of the arguments advanced in favour of the chemical theory, 

 there is now left in force for the present only the third. 



The experiment upon which this is mainly founded consists 

 in the fact, that two strips, one of zinc and the other of platina, 

 are separated at their extremities, on the one side by sulphuric 

 acid, on the other by a solution of the iodide of potassium. An 

 electric current then occurs in a direction which indicates the 

 preponderance of the sulphuric acid circuit over that of the 

 iodide of potassium. The iodide of potassium, which, in case 

 the two metallic slips are in direct contact at their other end, is 

 decomposed in such manner, that its electro-negative constituent, 

 the iodine, passes over to the zinc, gives it to the platina as 

 soon as metallic contact is suspended at those ends and sulphu- 

 ric acid inserted there. 



Faraday places this experiment at the head of his researches 

 on the origin of voltaic electricity. He regards it, as it were, as 

 a scale for weighing two chemical affinities, that of the oxygen 

 and that of the iodine for the zinc. Both endeavour, according 

 to him, to excite an electric current ; but that of the oxygen 

 being the strongest, sets more electricity in movement than that 

 of the iodine ; the latter is therefore overpowered, and a current 

 thus originates in the direction of the affinity of the oxygen, 

 which, at the same time, since the two metals do not touch, 

 affords another proof of the non-necessity of metallic contact to 

 excite voltaic electricity. 



The experiment is so remarkable, and the explanation given 

 has in appearance so much plausibility, that it is not to be 

 wondered at if the supporters of the chemical theory of gal- 

 vanism have regarded it as a main prop of their opinion. 

 Upon the defenders of the contact theory it made, however, 

 but httle impression, probably from their beUeving that no 



* PoggendorflTs Annalen, vol. xliv. p. G42. 



