COMBINATION WITH THE ACID PRODUCES NO ELECTRICITY. 439 



being employed in the vessel v, fig. 5. in place of dilute sulphuric acid. All the effects 

 occurred as before : the galvanometer was deflected ; the decompositions of the solu- 

 tions of iodide of potassium, nitrate of silver, muriatic acid, and sulphate of soda 

 ensued at x ; and the places where the evolved principles appeared, as well as the 

 deflection of the galvanometer, indicated a current in the same direction as when acid 

 was in the vessel v, i. e. from the zinc through the solution to the platina, and back 

 by the galvanometer and decomposing agent to the zinc. 



932. The similarity in the action of either dilute sulphuric acid or potassa goes indeed 

 far beyond this, even to the proof of identity in quantity as well as in direction of the 

 electricity produced. If a plate of amalgamated zinc be put into a solution of potassa, 

 it is not sensibly acted upon ; but if touched in the solution by a plate of platina, hy- 

 drogen is evolved on the surface of the latter metal, and the zinc is oxidized exactly 

 as when immersed in dilute sulphuric acid (863.). I accordingly repeated the expe- 

 ment before described with weighed plates of zinc (864. &c.), using however solution 

 of potassa instead of dilute sulphuric acid. Although the time required was much 

 longer than when acid was used, amounting to three hours for the oxidizement of 

 7-55 grains of zinc, still I found that the hydrogen evolved at the platina plate was 

 the equivalent of the metal oxidized at the surface of the zinc. Hence the whole of 

 the reasoning which was applicable in the former instance applies also here, the cur- 

 rent being in the same direction, and its decomposing effect in the same degree, as if 

 acid instead of alkali had been used (868.). 



933. The proof, therefore, appears to me complete, that the combination of the acid 

 with the oxide, in the former experiment, had nothing to do with the production of 

 the electric current ; for the same current is here produced when the action of the 

 acid is absent, and the reverse action of an alkali is present. I think it cannot be 

 supposed for a moment, that the alkali acted chemically as an acid to the oxide 

 formed ; on the contrary, our general chemical knowledge leads to the conclusion, 

 that the ordinary metallic oxides act rather as acids to the alkalies : yet that kind of 

 action would tend to give a reverse current in the present case, if any were due to the 

 union of the oxide of the exciting metal with the body which combines with it. But 

 instead of any variation of this sort, the direction of the electricity was constant, and 

 its quantity also directly proportional to the water decomposed, or the zinc oxidized. 

 There are reasons for believing that acids and alkalies, when in contact with metals 

 upon which they cannot act directly, still have a power of influencing their attractions 

 for oxygen (941.); but all the effects in these experiments prove, I think, that it is the 

 oxidation of the metal necessarily dependent upon, and associated as it is with, the 

 electrolyzation of the water (921. 923.), that produces the current; and that the acid 

 or alkali merely act as solvents, and by removing the oxidized zinc, allow other 

 portions to decompose fresh water, and so continue the evolution or determination of 

 the current. 



934. The experiments were then varied by using solution of ammonia instead of 



3 l2 



