THE SMITHSONIAN INSTITUTION. 40d 



We see here how much greater an electro-motive force the combina- 

 tion of atnalganiated zinc with hyper-oxide of lead indicates, tlian 

 amalgamated zinc and platinum, even if care is taken, as in No. ?>, 

 to prevent galvanic polarization from taking place at the negative 

 metal. 



The combination No. 3 is one of zinc and platinum corresponding 

 to Daniell's battery. Metallic platinum will be separated from the 

 solution of chloride and deposited upon the platinum plate by the 

 current, thus hindering galvanic polarization, as in Daniell's battery 

 by the dejwsition of copper. We can thus consider the numerical 

 value of No. 3 above, namely, 626, as the measure of the electrical 

 diiference between amalgamated zinc and platinum. 



Comparing the electro-motive force of No. 3 with that of Grove's 

 battery, we lind a considerable diiference, since the former is only 

 626, the latter 777, or according to my measurements 829, (section 18.) 



I think I can conclude from this difference that the nitric acid in 

 Grove's, as well as Bunsen's battery, not only prevents polarization 

 by the removal of oxygen, but that it acts as an electro-motor, also in the 

 manner of the hyper-oxide. A circumstance which renders this view 

 still more probable is this — that the electro-motive force of a combina- 

 tion of hyper-oxide of manganese with zinc, (No. 10,) is not sensibly 

 greater than that of Grove and Bunsen's battery. 



The above table also shows how considerably the electro-motive- 

 force can be augmented by replacing the electro-positive amalgam of 

 zinc, by the still more electro-positive amalgam of potassium ; the 

 expense of the latter amalgam, however, renders its practical ap- 

 plication in such batteries impossible. 



§ 43. Gi'ove's gas hattery. — Grove's battery can be understood from 

 Fig. 29, which represents a single element. 



Fig. 29. 



Fig. 30. 



