THEORY OF GALVANISM. 151 



ingenious experiments and much valuable informa- 

 tion, we are presented with a new hypothesis, not 

 only of the action of the pile, but even of the 

 nature of the principle which produces the action. 

 Mr. Donovan examines at considerable length the 

 opinion of Volta, offering very much the same kind 

 of objections against it which I had previously 

 urged ;* and he likewise regards the hypothesis of 

 electric energies to be equally inapplicable to the 

 phenomena. He states the following fact, which 

 is assumed as the basis of his hypothesis. " If a 

 piece of zinc and a piece of copper be immersed 

 in dilute nitric acid, but not in contact, they 

 effervesce and dissolve rapidly ; and oxides of zinc 

 and copper are found in the solution. Hence 

 these two metals have an affinity for the oxygen 

 of nitrous acid. If the zinc and copper be 

 brought in contact, and immersed in the dilute 

 acid, both appear to effervesce, but the zinc alone 

 dissolves." f 



The conclusion which the author draws from 

 this fact is, that the copper has lost an affinity for 

 m'tric acid which it before possessed, which affinity 

 appears to be gained by the zinc ; for it must be 

 observed that the zinc dissolves more rapidly than 

 it did in the first instance, and therefore seems to 

 have acquired what the copper has lost. This 

 transfer of affinity from one metal to the other by 



* Ann. of Phil. iii. 32. 



t Essay on Galvanism, p. 274s 



