iSU.] On the Hypotheses of Galvanism. §5 



Article II. 



Remarks oh the Hypotheses of Galvanism. By J. Bostock, 

 M.D. M.G.S. &c. &c. 



(Continued from y. 42.) 



The electrical hypothesis being not adequate to account for tlie 

 |)hcnomena of the Galvanic pile, we must substitute for it the 

 chemical hypothesis, wliich supposes that the fir'it step of the 

 process consists in the action of the fluid upon one of the metals, 

 and that the electrical phenomena depend upon this action. This 

 action essentially consists in the oxidation of the surface of one of 

 the metals, while the opposite surface of the other metal is not 

 oxidated. The positions upon wliich the chemical hypothesis rests 

 are the following:— I. That a metal (the zinc, for example,) is 

 oxidated, the oxidated pait has its capacity for electricity dimi- 

 nished, and electricity is consequently evolved. 2. This electricity 

 is received by the contiguous fluid, and is transmitted by it to the 

 other metallic surface, the copper, which is not oxidated, and is 

 therefore disposed to receive it ; and the whole of the copper plate 

 hence becomes positive. 3. The remaining part of the zinc, which 

 is not oxidated, remains in its natural state ; and therefore, as it 

 relates to the copper, is negative. 4. The elements of the pile, 

 which, according to the electrical hypothesis, are supposed to be in 

 the order of copper, zinc, fluid ; are, according to the chemical 

 hypothesis, zinc, fluid, copper; the electricity passing from the 

 first zinc plate, across the fluid, to the copper plate. 5. The 

 action takes place, not between the metals, but between the 

 oxidated surface and the fluid ; no change would therefore be pro- 

 duced by placing a copper plate beyond the first zinc plate, or a 

 zinc plate beyond the last copper plate. Strictly speaking, it is the 

 icinc end of the apparatus which is negative; and the copper, 

 positive. * 



The chemical hypothesis accounts for all the efl^ects of the Gal- 

 vanic pile, and appears to be consistent with itself in all its parts. 

 It explains satisfactorily why the action of the pile is always in 

 proportion to the oxidation of the metals, a fact pointed out and 

 insisted upon by Dr. Wollaston. f The progressive increase in the 

 action of the different parts of the apparatus is easily explained. 

 The fiist copper plate, in consequence of the electricity which it 

 lias acfiuired from the oxidated part of the zinc, becomes positive ; 

 or, to use the numerical illustration, is brought to the state of 1 10°. 

 This state it communicates to the contiguous, or second zinc plate, 

 which also becomes liU°. The fluid oxidates the surface of the 

 metal acre, as in the former case ; but a larger quantity of electri- 



• See Erman, Lcliot, De Luc, fcc. i Pliil. Tram. 1801. 



