1 72 Dr. Faraday's Experimental liesearc/ies in Electricity, 



cup, and served when the latter were tightened again to form 

 a porous division down the middle of the cup, sufficient to keep 

 any two fluids on opposite sides of the paper from mingling, 

 except very slowly, and yet allowing them to act freely as one 

 electrolyte. The two spaces thus produced I will call the 

 cells A and B, fig. 10. This instrument I have found of 

 most general application in the investigation of the relation of 

 fluids and metals amongst themselves and to each other. By 

 combining its use with that of the galvanometer, it is easy to 

 ascertain the relation of one metal with two fluids, or of two 

 metals with one fluid, or of two metals and two fluids upon 

 each other. 



938. Dilute sulphuric acid, sp. gr. 1*25, was put into the 

 cell A, and a strong solution of caustic potassa into the cell B; 

 they mingled slowly through the paper, and at last a thick crust 

 of sulphate of potassa formed on the side of the paper next 

 to the alkali. A plate of clean platina was put into each 

 cell and connected with a delicate galvanometer, but no elec- 

 tric current could be observed. Hence the contact of acid 

 with one platina plate, and [ofj alkali with the other, was un- 

 able 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 

 reverse 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 current 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 influ- 

 ence in producing the electricity evolved, the whole of which 

 appears to be due to the oxidation of the metal (919.). 



941. The alkali, in fiict, 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 the 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 



* Elements of Chemical Philosophy, p. 149; or Philosophical Transac- 

 tions, 1836, p. 403. [or Phil Mng. and Annals, N.S., vol. i. p. 101.] 



