408 MR. F. E. SMITH ON THE NORMAL WESTOX CADMIUM CELL. 



cells are high in E.M.F. and approximately constant. In the normal cadmium 

 cells the appearance of the mercurous sulphate is the same as when freshly prepared. 

 An interesting question is whether the change in colour of the paste is the result of 

 association with the other ingredients of the standard cell or not, and whether 

 a charging or discharging current produces or accelerates the change. The first part 

 of this question may be answered so far as association with the cadmium amalgam is 

 concerned, for we have kept many samples of the paste together with saturated 

 cadmium sulphate solution and mercury in stock bottles. In two of these pastes 

 green patches have appeared and the dimensions of the patches are slowly increasing. 

 The change is therefore independent of the presence of free cadmium or cadmium 

 amalgam. The probable acceleration of the change due to a charging or discharging 

 current is discussed on pp. 413-415. 



A number of anomalous cells were closely examined in order to detect any other 

 peculiarities besides that of the coloration of the depolariser and crystals of cadmium 

 sulphate. In one of the cells a small bubble of air was imprisoned between the glass 

 and the paste, and the paste in contact with the bubble and to a depth of 1 millim. 

 from it was of a yellow tint, the remaining portion of the depolariser being normal in 

 colour. From these colour observations it appears probable that the change is of 

 the nature of a hydrolysis, but at present we have no reason to think that all the 

 pastes will, with time, similarly change, and that, as suggested by HULETT,* the 

 cathode leg of the cadmium cell is a system in unstable equilibrium. . Instead we are 

 inclined to believe that something abnormal occurred in the preparation of the 

 pastes. 



Two cells which were low in E.M.F. by O'OOOl volt, but very constant, were opened, 

 and the solution in them was found to be very slightly acid. We regard this as an 

 indication of insufficient washing of the mercurous sulphate. Cell No. 2 was 

 employed in a potentiometer circuit during the estimation of current in absolute 

 measure by the Ayrton-Joues Balance. It was used from October, 1905, to June, 

 1907, and could not have fallen by more than 1 part in 100,000 during this period. 

 Its low initial E.M.F. is probably due to the presence of acid. 



HULETT concludes that many of his cells have fallen 11 parts in 100,000 in a little 

 over two years, but that Clark cells have remained constant. In 1904 the author 

 pointed out that some cadmium cells made in 1902 had apparently fallen '00007 volt ; 

 these, however, were prepared in the old way with purchased mercurous sulphate 

 washed with water, and since 1904 there is every reason to believe that they have 

 remained constant. 



Drs. K. E. GTJTHE and C. L. v. ENDEt record the following results : Three 

 cadmium cells were prepared by them on Nov. 2, 1906 ; by the 17th of the same 

 month each had fallen about 50 microvolts below the normal value ; by Dec. 13, 1906, 



* G. A. HULETT, 'Phys. Rev.,' 23, pp. 166-183, August, 1906. 



t K. E. GUTHE and C. L. v. ENDE, ' Phys. Rev.,' 24, pp. 214-221, February, 1907. 



