Dr. J. Henderson on Cadmium Standard Cells. 153 



being determined by balancing it against the fall of potential 

 down a standard resistance carrying a current which was 

 accurately measured on a Kelvin current-balance. The value 

 obtained was 1/0190 volt at 21°*5 C. The comparisons of 

 E.M.F. were made on a specially constructed manganin 

 potentiometer which was carefully calibrated before the expe- 

 riments were made. 



Three sets of cadmium cells were set up altogether, Sets I. 

 and II. being crystal cells, whilst those in Set 111. were made 

 up in H-shaped glass vessels, with a saturated solution of 

 CdS0 4 in place of crystals. 



Paraffin- wax. 



CdS0 4 crystals (moist). 



Mercury. 



Cadmium Crystal Cell. 



Solde 



-*" Platinum wire. 



Enlarged View of Contact-wire. 



The results obtained from Set III. were, however, very 

 unsatisfactory, in one case a variation of as much as 027 per 

 cent, being found to exist between two of the cells at the 

 same temperature. 



The accompanying diagrams give an idea of the method of 

 construction of the crystal cells in Sets I. and II. 



