MR. F. E. SMITH ON THE NuKMAL WESTON CADMIUM CELL. 401 



DISCUSSION OF THE RESULTS. 



I '"' ' "f Various Amalgams. 



The E. M.F.'s of the cells set up with amalgams prepared at different times agree 

 under otherwise equal conditions within 1 part in 100,000. The amalgam prepared 

 by the electrodeposition of cadmium in mercury is perhaps preferable for the cells of 

 standardising institutions, but our observations do not show any certain difference 

 between it and that prepared by the fusion of cadmium and mercury, when the latter 

 amalgam is freed from dross. 



Effect of the Cadmium Sulphate. 



We have obtained our cadmium sulphate from various sources, but after one 

 crystallisation and thorough washing of the crystals with water no certain difference 

 in the behaviour of the solutions has been detected. 



Effect of the Depolarizer. 



The mean value of the cells set up with the electrolytic mercurous sulphate is 

 T01828 volts ; that of the cells containing the salt prepared by chemical precipitation 

 (Method II.) is 1*01830 volts ; when mercurous sulphate was employed which had 

 been precipitated from hot strong sulphuric acid, TO 1832 volts is the mean ; and the 

 salt prepared with fuming sulphuric acid gives 1 '01831 volts. 



We conclude that the mode of manufacture of the mercurous sulphate is immaterial, 

 provided that certain conditions are observed, and our guiding principle in the 

 manufacture of the salt and the preparation of the paste is to prevent hydrolysis 

 by keeping the salt in contact with dilute sulphuric acid (1 to 6), or with saturated 

 cadmium sulphate solution. This is in accordance with HULETT'S investigations. 



CARHART and HULETT* have examined Weston cadmium cells containing electro- 

 lytic and chemically prepared sulphate (Method II.), and conclude that there is no 

 appreciable difference in E.M.F. Later, HuLErrt constructed two other cells 

 containing the chemical sulphate, and found- them about O'OOOIS volt higher than 

 cells containing the electrolytic salt. He concludes that the electrolytic sulphate is 

 the most reliable preparation. Dr. F. A. WOLFF and C. E. WATERS^ have examined 

 many more specimens, and conclude that the four methods dealt with in this 

 communication give practically identical results. They have also examined samples 

 of mercurous sulphate prepared by the action of sulphuric acid containing a small 

 percentage of nitric acid on mercury (Lunge reaction) ; by the reduction of mercuric 

 sulphate by mercury, and by digesting commercially pure samples of mercurous 



* H. S. CARHART and U. A. HULETT, ' Amer. Electrochem. Soc. Trans.,' 6, pp. 109-126, 1904. 

 t G. A. HULETT, 'Phys. Rev.,' 22, pp. 321-338, June, 1906. 



F. A. WOLFF and C. E. WATERS, 'Electrical World,' 49, pp. 100, 101, January 12, 1907. 

 VOL. COVII. A. 3 F 



