1888.] Development of Electricity by Atmospheric Oxidation, 199 



strength shaken up with powdered potassium permanganate to 

 saturation. 



B. Cells set up with 10H 2 SO 4 ,100H 2 O in contact with the aeration 

 plates opposed to platinum immersed in the same liquid after agitation 

 with chromic anhydride to saturation. 





A. Alkaline cells. 



B. Acid cells. 





Hydrogen. 



Coal-gas. 



Hydrogen. 



Coal-gas. 





1-525 



i-io 



1-02 



1-10 





0-865 



0-85- 



0-89 



0-895 





0-422 



0'425 









073 



0-78 













0-845 



0-85 



Gold foil 



0-72- 



0-75 



0-87 



0-90 



Palladium sponge .... 







1-37 



1-37 





0-87 



0-81 



0-89 



112 





0-845 



0-83 



0-85 



0-85 



In making these observations currents' were used, the density of 

 which in no case exceeded O02 micro-ampere per square centimetre of 

 aeration plate surface. 



Spongy platinum and palladium obviously are far more effective as 

 regards the E.M.F. set up than the other plates used; the chemical 

 action taking place may be regarded as the decomposition of alkaline 

 permanganate into hydrated manganese dioxide, caustic potash, and 

 oxygen (or of chromic anhydride and sulphuric acid into chromium 

 sulphate, water, and oxygen), and the combination of hydrogen with 

 the oxygen thus set free ; according to Thomsen's values, the heat 

 developed would accordingly be per 16 grams oxygen evolved — 



Alkaline cells. 



Decomposition of 



oxidising agent, . J x 28355 = 9452 

 Oxidation of hydrogen = 68360 



Acid cells. 



Corresponding with volts. 



77812 

 = 1-673 



| x 30407 



10136 



68360 



78496 

 1-688 



Hence, even with the most effective plates, the E.M.F. actually 

 generated falls distinctly short of that corresponding with the heat of 

 chemical change. On making the current passing larger by diminish- 

 ing the external resistance, the E.M.F. always fell rapidly; so that in 

 order to obtain a current capable of producing any considerable 



