Waste of Electric Power hy the Use of ordinary Zinc. 337 



the electric current ; and that this obstruction should be over- 

 come more or less readily, in proportion to the greater or less 

 intensity of the decomposing current, is in perfect consistency 

 with all our notions of the electric agent. 



996. I have elsewhere (947.) distinguished the chemical 

 action of zinc and dilute sulphuric acid into two portions; that 

 which, acting effectually on the zinc, evolves hydrogen at once 

 upon its surface, and that which, producing an arrangement 

 of the chemical forces throughout the electrolyte present, (in 

 this case water,) tends to take oxygen from it, but cannot do 

 so unless the electric current consequent thereon can have 

 free passage, and the hydrogen be delivered elsewhere than 

 against the zinc. The electric current depends altogether 

 upon the second of these ; but when the current can pass, by 

 favouring the electrolytic action it tends to diminish the former 

 and increase the latter portion. 



997. It is evident, therefore, that when ordinary zinc is 

 used in a voltaic arrangement, there is an enormous waste of 

 that power which it is the object to throw into the form of an 

 electric current; a consequence which is put in its strongest 

 point of view when it is considered that three ounces and a 

 half of zinc, properly oxidized, can circulate enough electri- 

 city to decompose nearly one ounce of water, and cause the 

 evolution of about 2400 cubic inches of hydrogen gas. This 

 loss of power not only takes place during the time the elec- 

 trodes of the battery are in communication, being then pro- 

 portionate to the quantity of hydrogen evolved against the 

 surface of any one of the zinc plates, but includes also all the 

 chemical action which goes on when the extremities of the pile 

 are not in communication. 



998. This loss is far greater with ordinary zinc than with 

 the pure metal, as M. de la Rive has shown *. The cause 

 is, that when ordinary zinc is acted upon by dilute sulphuric 

 acid, portions of copper, lead, cadmium, or other metals which 

 it may contain, are set free upon its surface ; and these, being 

 in contact with the zinc, form small but very active voltaic 

 circles, which cause, great destruction of the zinc and evolu- 

 tion of hydrogen, apparently upon the zinc surface, but really 

 upon the surface of these accidental metals. In the same pro- 

 portion as they serve to discharge or convey the electricity 

 back to the zinc, do they diminish its power of producing an 

 electric current which shall extend to a greater distance across 

 the acid, and be discharged only through the copper or pla- 



• Quarterly Journal of Science, 1831, p. 388; ov BibliothequeUniver seller 

 1830, p. 391.' [Also Phil. Mag. and Annals, N.S., vol. viii. p. 298.~Edit.] 



Third Series. Vol. 6. No. 35. May 1835. \ 2 X 



