Two Fluids^ and of Two Metals not in Contact, 48? 
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 lawwith 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 
w^ondered 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 little impression, probably from their believing that no 
* Poggendorffs Amalm^ vol. xliv. p. 642, 
