VOLTAIC BATTERY OF AMALGAMATED ZINC. 457 



the evolution of about 2400 cubic inches of hydrogen gas. This loss of power not 

 only takes place during the time the electrodes of the battery are in communication, 

 being then proportionate 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 con- 

 tain, 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 

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

 of these accidental metals. In the same proportion as they serve to discharge or con- 

 vey the electricity back to the zinc, do they diminish its power of producing an elec- 

 tric current which shall extend to a greater distance across the acid, and be discharged 

 only through the copper or platina plate which is associated with it for the purpose 

 of forming a voltaic apparatus. 



999. All these evils are removed by the employment of an amalgam of zinc in the 

 manner recommended by Mr. Kemp-}-, or the use of the amalgamated^zinc plates of 

 Mr. Sturgeon (863.), who has himself suggested and objected to their application in 

 galvanic batteries ; for he says, " Were it not on account of the brittleness and other 

 inconveniences occasioned by the incorporation of the mercury with the zinc, amal- 

 gamation of the zinc surfaces in galvanic batteries would become an important im- 

 provement ; for the metal would last much longer, and remain bright for a consider- 

 able time, even for several successive hours ; essential considerations in the employ- 

 ment of this apparatus %." 



1000. Zinc so prepared, even though impure, does not sensibly decompose the 

 water of dilute sulphuric acid, but still has such affinity for the oxygen, that the 

 moment a metal which, like copper or platina, has little or no affinity, touches it in 

 the acid, action ensues, and a powerful and abundant electric current is produced. 

 It is probable that the mercury acts by bringing the surface, in consequence of its 

 fluidity, into one uniform condition, and preventing those differences in character 

 between one spot and another which are necessary for the formation of the minute 

 voltaic circuits referred to (998.). If any difference does exist at the first moment, 

 with regard to the proportion of zinc and mercury, at one spot on the surface, as 

 compared with another, that spot having the least mercury is first acted on, and, by 

 solution of the zinc, is soon placed in the same condition as the other parts, and the 



* Quarterly Journal of Science, 1831, p. 388; or Bibliotheque Universelle, 1830, p. 391. 



\ Jameson's Edinburgh Journal, October 1828. 



X Recent Experimental Researches, p. 42, &c. Mr. Sturgeon is of course unaware of the definite produc- 

 tion of electricity by chemical action, and is in fact quoting the experiment as the strongest argument against 

 the chemical theory of galvanism. 



