Acids and Alkalies have equal and similar Actions, 173 



powerful, that if amalgamated zinc, or tin, or lead be used, 

 the metal in the acid evolves hydrogen the moment it is placed 

 in communication with that in the alkali, — not from any direct 

 action of the acid upon it, for if the contact be broken the ac- 

 tion ceases, — but because it is powerfully negative with regard 

 to the metal in the alkali. 



942. The superiority of alkali is further proved by this, 

 that if zinc and tin be used, or tin and lead, whichever metal 

 is put into the alkali becomes positive, that in the acid being 

 negative. Whichever is in the alkali is oxidized, whilst that 

 in the acid remains in the metallic state, as far as the electric 

 current is concerned. 



943. When sulphuretted solutions are used (930.) in illus- 

 tration of the assertion, that it is the chemical action of the 

 metal and one of the ions of the associated electrolyte that 

 produces all the electricity of the voltaic circuit, the proofs 

 are still the same. Thus, as Sir Humphry Davy* has shown, 

 if iron and copper be plunged into dilute acid, the current is 

 from the iron through the liquid to the copper: in solution of 

 potassaitis in the same direction, but in solution of sulphuret 

 of potassa it is reversed. In the first two cases it is oxygen 

 which combines with the iron, in the latter sulphur which 

 combines with the copper, that produces the electric current; 

 but both of these are io?is, existing as such in the electrolyte, 

 which is at the same moment suffering decomposition ; and, 

 what is more, both of these are anions, for they leave the 

 electrolytes at their anodes, and act just as chlorine, iodine, 

 or any other anion would act which might have been previ- 

 ously chosen as that which should be used to throw the voltaic 

 circle into activity. 



944. The following experiments complete the series of proofs 

 of the origin of the electricity in the voltaic pile. A fluid 

 amalgam of potassium, containing not more than a hundredth 

 of that metal, was put into pure water, and connected through 

 the galvanometer with a plate of platina in the same water. 

 There was immediately an electric current from the amalgam 

 through the electrolyte to the platina. This must have been 

 due to the oxidation only of the metal, for there was neither 

 acid nor alkali to combine with, or in any way act on, the 

 body produced. 



945. Again, a plate of clean lead and a plate of platina were 

 put into inire water. There was immediately a powerful cur- 

 rent produced from the lead through the fluid to the platina : 

 it was even intense enough to decompose solution of the iodide 



• Elements of Chemical Philosophy, p. 148. 



