ACIDS AND ALKALIES HAVE EQUAL AND SIMILAR ACTIONS. 441 



alkali. A plate of clean platina was put into each cell and connected with a delicate 

 galvanometer, but no electric current could be observed. Hence the contact of acid 

 with one platina plate, and alkali with the other, was unable to produce a current ; 

 nor was the combination of the acid with the alkali more effectual (925.). 



939. When one of the platina plates was removed and a zinc plate substituted, 

 either amalgamated or not, a strong electric current was produced. But, whether 

 the zinc were in the acid whilst the platina was in the alkali, or whether the re- 

 verse order were chosen, the electric current was always from the zinc through the 

 electrolyte to the platina, and 'back through the galvanometer to the zinc, the cur- 

 rent seeming to be strongest when the zinc was in the alkali and the platina in the 

 acid. 



940. In these experiments, therefore, the acid seems to have no power over the 

 alkali, but to be rather inferior to it in force. Hence there is no reason to suppose 

 that the combination of the oxide formed with the acid around it has any direct in- 

 fluence in producing the electricity evolved, the whole of which appears to be due to 

 the oxidation of the metal (919.). 



941. The alkali, in fact, is superior to the acid in bringing a metal into what is 

 called the positive state ; for if plates of the same metal, as zinc, tin, lead, or copper, 

 be used both in the acid or alkali, the electric current is from tlie alkali across the 

 cell to the acid, and back through the galvanometer to the alkali, as Sir Humphry 

 Davy formerly stated*. This current is so powerful, that if amalgamated zinc, or tin, 

 or lead be used, the metal in the acid evolves hydrogen the moment it is placed in 

 communication with that in the alkali, not from any direct action of the acid upon 

 it, for if the contact be broken the action ceases, but because it is powerfully negative 

 with regard to the metal in the alkali. 



942. The superiority of alkali is further proved by this, that if zinc and tin be used, 

 or tin and lead, whichever metal is put into the alkali becomes positive, that in the 

 acid being negative. Whichever is in the alkali is oxidized, whilst that in the acid 

 remains in the metallic state, as far as the electric current is concerned. 



943. When sulphuretted solutions are used (930.) in illustration of the assertion, 

 that it is the chemical action of the metal and one of the ions of the associated elec- 

 trolyte that produces all the electricity of the voltaic circuit, the proofs are still the 

 same. Thus, as Sir Humphry Davy-^- has shown, if iron and copper be plunged into 

 dilute acid, the current is from the iron through the liquid to the copper ; in solution 

 of potassa it is in the same direction, but in solution of sulphuret of potassa it is re- 

 versed. In the two first cases it is oxygen which combines with the iron, in the latter 

 sulphur which combines with the copper, that produces the electric current ; but 

 both of these are irnis, existing as such in the electrolyte, which is at the same moment 

 suffering decomposition ; and, what is more, both of these are anions, for they leave 



* Elements of Chemical Philosophy, p. 149 ; or Philosophical Transactions, 1826, p. 403, 

 t Elements of Chemical Philosophy, p. 148. 



