426 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 



in it, and revealing more clearly that which is true, is as useful in his place, and 

 as necessary to the general progress of the science, as he who first broke into the 

 intellectual darkness, and opened a path into knowledge before unknown to man. 



877. The identity of the force constituting the voltaic current or electrolytic 

 agent, with that which holds the elements of electrolytes together (855.), or in other 

 words with chemical affinity, seemed to indicate that the electricity of the pile itself 

 was merely a mode of exertion, or exhibition, or existence of true chemical action, or 

 rather of its cause ; and I have consequently already said that I agree with those 

 who believe that the supply of electricity is due to chemical powers (857.)- 



878. But the great question of whether it is originally due to metallic contact or 

 to chemical action, i. e. whether it is the first or the second which originates and 

 determines the current, was to me still doubtful ; and the beautiful and simple 

 experiment with amalgamated zinc and platina, which I have described minutely as 

 to its results (863, &c.), did not decide the point ; for in that experiment the che- 

 mical action does not take place without the contact of the metals, and the metallic 

 contact is inefficient without the chemical action. Hence either might be looked 

 upon as the determining cause of the current. 



879. I thought it essential to decide this question by the simplest possible forms 

 of apparatus and experiment, that no fallacy might be inadvertently admitted. The 

 well known difficulty of effecting decomposition by a single pair of plates, except in 

 the fluid exciting them into action (863.), seemed to throw insurmountable obstruc- 

 tion in the way of such experiments ; but I remembered the easy decomposibility of 

 the solution of iodide of potassium (316.), and seeing no theoretical reason, if me- 

 tallic contact was not essential, why true electro- decomposition should not be ob- 

 tained without it, even in a single circuit, I persevered and succeeded. 



880. A plate of zinc, about eight inches long and half an inch wide, was cleaned 

 and bent in the middle to a right angle, fig. 1 a, Plate XVIII. A plate of platina, about 

 three inches long and half an inch wide, was fastened to a platina wire, and the 

 latter bent as in the figure h. These two pieces of metal were arranged together as 

 delineated, but as yet without the vessel c, and its contents, which consisted of di- 

 lute sulphuric acid mingled with a little nitric acid. At o^ a piece of folded bibulous 

 paper, moistened in a solution of iodide of potassium, was placed on the zinc, and 

 was pressed upon by the end of the platina wire. When under these circumstances 

 the plates were dipped into the acid of the vessel c, there was an immediate effect at a?, 

 the iodide being decomposed, and iodine appearing at the anode (663.), i. e. against 

 the end of the platina wire. 



881. As long as the lower ends of the plates remained in the acid the electric cur- 

 rent continued, and the decomposition proceeded at x. On removing the end of the 

 wire from place to place on the paper, the effect was evidently very powerful ; and 

 on placing a piece of turmeric paper between the white paper and zinc, both papers 

 being moistened with the solution of iodide of potassium, alkali was evolved at the 



