METALLIC CONTACT NOT NECESSARY TO THE VOLTAIC CURRENT. 427 



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 cur- 

 rent 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 decomposition at x was a true electrolytic action, 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 miy 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 the metals, either 

 in or out of the acid, together, when decomposition of the iodide at x occurred, but 

 in a reverse order ; for now alkali appeared against the end of the platina wire, and 

 the iodine passed to the zinc, the current being the contrary of what it was in the 

 former instance, and produced directly by the difference of action of the solution in 

 the paper on the two metals. The iodine of course combined with the zinc. 



883. When this experiment was made with pieces of zinc amalgamated over the 

 whole surface (863.), the results were obtained with equal facility and in the same 

 direction, even when only dilute sulphuric acid was contained in the vessel c (fig. 1.). 

 Whichever end of the zinc was immersed in the acid, still the effects were the same : 

 so that if, for a moment, the mercury might be supposed to supply the metallic con- 

 tact, the reversion of the amalgamated piece destroys that objection. The use of 

 unamalgamabed zinc (880.) removes all possibility of doubt. 



884. When, in pursuance of other views (930.), the vessel c was made to contain a 

 solution of caustic potash in place of acid, still the same results occurred. Decom- 

 position of the iodide was effected freely, though there was no metallic contact of 

 dissimilar metals, and the current of electricity was in the same direction as when 

 acid was used. 



885. Even a solution of brine in the glass c could produce all these effects. 



886. Having made a galvanometer with platina wires, and introduced it into the 

 course of the current between the platina plate and the place of decomposition x, it 

 was affected, giving indication of currents in the same direction as those shown to 

 exist by the chemical action. 



887. If we consider these results generally, they lead to veiy important conclusions. 

 In the first place they prove, in the most decisive manner, that metallic contact is not 

 necessary for the production of the voltaic current. In the next place they show a most 

 extraordinary mutual relation of the chemical affinities of the fluid which excites the 

 current, and the fluid which is decomposed by it. 



888. For the purpose of simplifying the consideration, let us take the experiment 

 with amalgamated zinc. The metal so prepared exhibits no effect until the current 

 can pass : it at the same time introduces no new action, but merely removes an 

 influence which is extraneous to those belonging either to the production or the 



