258 Mr. J. Prideaux on the Theory of Voltaic Action. 



When of two similar plates, one is withdrawn from the action 

 of the acid, the other remaining subject to it, the latter will 

 give off positive electricity to the liquor, which the former, on 

 reentering, must take up and convey back through the wire, 

 as copper does. 



So in a voltaic pair, when acid is brought by electrical at- 

 traction or otherwise into contact with zinc, the metal is at- 

 tacked ; the acid or water being decomposed on the one hand, 

 and the zinc dissolved on the other. The positive electricity 

 passes from the zinc into the liquid (40) in the direction of 

 the galvanic current (and assuming the theory of two elec- 

 tricities, the negative passes from the acid to the zinc, also in 

 the direction of the current). Thus the chemical action com- 

 pensates, or surpasses, the neutralizing effect of the negative 

 liquid particles on the zinc, in proportion to its facility of 

 decomposition, and to the electrical character of its residual 

 ingredients ; whilst the copper is negatively excited by the acid 

 to the highest degree (23). 



43. Sulphuric acid decomposes the water, as does probably 

 the muriatic ; hydrogen gas being given off in both cases, and 

 carrying with it # some of the positive electricity generated. 

 But nitric acid gives rise to no gas (in moderate charges) ; and 

 there being no waste of electricity, its action should be the 

 greater, as is known to be the fact. 



44. These three acids, employed in atomic proportions, in 

 equal quantities of water, placed in three cells of the trough 

 (30) ; one of the calorimotors being moved from one to the 

 other and back again alternately, so as to give all the acids 

 equal opportunity for action, gave the following deflections. 



Why the muriatic acted so much more powerfully than the 

 sulphuric acid is not evident, as the acids were pure. Possibly 

 the muriatic acid may be itself decomposed, and the chlorine 

 combine directly with the metal. No evidence occurred to me, 

 when employing atomic proportions, of the less durability of 

 nitric acid, as stated by Singer ; but my experience is not to 

 be set in competition with his. 



45. An experiment quoted by Berzelius^:, and which I do 



* Pouillet, Ann. de Chim. et de Phys. September 1827. 

 f This figure was not recorded, through oversight. 

 X Tr. de Chim. torn. i. p. 152. 



