of Electrical and Chemical Changes. 103 



the zinc, and the alkali with the platinum, the effect will be 

 exceedino-ly feeble compared with that produced if the order 

 be reversed, and the zinc be in contact with the alkali, and 

 the platinum with the acid. 



The chemical changes taking place in combinations of this 

 kind ai-e always such as tend to restore the equilibrium ; the 

 hydrogen and the alkaline body always passing to the nega- 

 tive, and oxygen and the acid to the positive metal. < 

 There is no instance of continued electro-motion except in 

 cases where chemical changes can take place, for even De 

 Luc's or Zamboni's columns do not act when quite dry, and 

 the silver in combinations of this kind, when the negative 

 metal is wold, is uniformly found tarnished : for the exhibition 

 of electricities of tension, however, a very slight chemical ac- 

 tion is sufficient, as the quantity of electricity required to give 

 repulsion to light bodies is exceedingly small; but to form 

 electro-magnetic combinations the chemical agents must be 

 of an energetic kind. 



As most of the fluids which act powerfully in voltaic com- 

 binations contain water, or oxygen and hydrogen, it has been 

 suspected that these principles were essential to the effect: 

 this however does not seem to be the case, for I found zinc 

 and platinum formed powerful electro-motive circles in fused 

 litharo-e and fused oxy-chlorate of potassa, which are not 

 known to contain water ; and I have little doubt that similar 

 effects would be produced by other fused salts containing only- 

 acid and alkaline matter. 



It may elucidate this part of the subject, v,hich must at best 

 be obscure, to take a view of the changes occurring in one 

 of the simplest voltaic combinations, — that consisting of zinc, 

 platinum, and solution of sulphate of soda. It is a fact that 

 zinc and platinum become electrical by contact, the zinc posi- 

 tive, the platinum negative ; and the two kinds of electricity 

 are apparently most intense at the surfaces whei'e they are in 

 contact with the fluid, which is too imperfect a conductor to 

 allow them to neutralize or destroy each other : they conse- 

 quently exert their attractive and repellent powers upon the 

 elements of the menstruum ; acid and o.iygen ciiculate to the 

 surface of zinc, which in consequence is dissolved, and alkali 

 and hydrogen to the surface of platinum, ol' which the hydro- 

 gen is disengaged, and the equilibrium broken by the contact 

 of the metals is restored by the chemical changes ; so that a 

 constant circulation, or a current of electricity, takes jilace, 

 the power of the combination becoming feebler in proportion 

 as the solution is decomposed, and acid accumulated round 

 its positive, and alkali round its negative surface. 



In 



