154 Dr. J. Henderson on Cadmium Standard Cells. 



In Set I. six cells were set up, the chemicals employed 

 being purchased as pure at an ordinary chemical store. On 

 testing the sulphates both the CdS0 4 and Hg 2 S0 4 were found 

 to be strongly acid. The paste used in all the cells consisted 

 of a mixture of CdS0 4 , Hg 3 S0 4 , distilled water, and mercury, 

 whilst the cadmium amalgam had the composition 6 Hg to 

 1 Cd by weight. 



In Set II. six cells were also made up, but the chemicals 

 employed were specially purified, and were obtained from 

 Messrs. Kahlbaum of Berlin ; careful tests showed that both 

 the CdS0 4 and Hg 2 S0 4 were perfectly neutral. The compo- 

 sitions of paste and amalgam were the same as in Set I. One 

 cell in each set, however, was specially acidified by making 

 up the paste and moistening the OdS0 4 crystals with a 

 20-per-cent. mixture of H 2 S0 4 and water, instead of distilled 

 water, in order to examine the effect of added acid. 



The results of over two hundred observations of E.M.F. at 

 different temperatures have been summarized in the following 

 tables ; the numbers, however, do not include the results 

 obtained from the specially acidified cells. 



Set I. 





10°-15° C. 



15°-20° C. 



20°-30° O. 





E.M.F. (volts) 



10186 



1-0187 



1-0180 





Maximum variation 1 

 from mean (volts) J 



•0002 



•0001 



•0002 



Set II. 



Temp 



10°-15° C. 



15°-20° C. 





E.M.F. (volts) 



1-0188 



1-0187 



Maximum variation "1 

 from mean (volts) J 



•0001 



•0001 



It will be noticed that the cells in both sets agree very 

 closely amongst themselves. 



The results obtained from the specially acidified cells show 

 higher values for the E.M.F. (about l'Orjl), and they do not 

 agree so well anions themselves. 



