36 Dr. Faraday's Experimental Researches in Electricity, 



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 obstruction in the way of such experi- 

 ments ; but I remembered the easy decomposibility of the so- 

 lution of iodide of potassium (316.), and seeing no theoretical 

 reason, if metallic contact was not essential, why true electro- 

 decomposition should not be obtained 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 an- 

 gle, fig. 1. a. Plate I. 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 b. These two pieces 

 of metal were arranged together as delineated, but as yet with- 

 out the vessel c, and its contents, which consisted of dilute 

 sulphuric acid mingled with a little nitric acid. At x 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 x, the iodide being decomposed, and io- 

 dine appearing at the anode {66o.\ 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 current 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 cathode (663.) 

 against the zinc, in proportion to the evolution of iodine at the 

 anode. Hence the decomposition was perfectly polar, and 

 decidedly dependent upon a current of electricity passing from 

 the zinc through the acid to the platina in the vessel c, and 

 back from the platina through the solution to the zinc at the 

 paper x. 



882. That the decompostion at x was a true electrolytic ac- 

 tion, due to a current determined by the state of things in the 

 vessel c, and not dependent upon any mere direct chemical 

 action of the zinc and platina on the iodide, or even upon any 

 current which the solution of iodide might by its action on 

 those metals tend to form at x, was shown, in the first place, 

 by removing the vessel c and its acid from the plates, when 

 all decomposition at x ceased, and in the next by connecting 



