1 32 Dr. Faraday's Experimental Researches in 'Electricity, 



in the solution by a plate of platina, hydrogen is evolved on 

 the surface of the latter metal, and the zinc is oxidized exactly 

 as when immersed in dilute sulphuric acid (863.). I accord- 

 ingly repeated the experiment 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 equiva- 

 lent 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 current being in the same di- 

 rection, and its decomposing effect in the same degree, as if 

 acid instead of alkali had been used (8^38.). 



933. The proof, therefore, appears to me complete, that 

 the combination of the acid with the oxide, in the former ex- 

 periment, had nothing to do with the production of the elec- 

 tric 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 quan- 

 tity 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, 1 think, that it is the oxidation of the metal necessarily 

 dependent upon, and associated as it is with, the electrolyza- 

 tion 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 solution of potassa; and as it, when 

 pure, is a bad conductor, like water {^^b^.), it was occasion- 

 ally improved in that power by adding sulphate of ammonia 

 to it. But in all the cases the effects were the same as before; 

 decompositions of the same kind were effected? and the electric 



