274 Mr. F. E. Smith on Cadmium Amalgams 



identical. Probably, the upper limits are different because 

 the amalgams used by Bijl were not chilled. Bijl remarks 

 that the quite solid amalgams reached their final values within 

 a few days except in the case of those amalgams which lay in 

 the neighbourhood of the end of the nearly horizontal portion 

 of the curve (see fig. 2 of this communication), i. e. the 

 amalgams which were near the transition point. He states 

 also that on passing to lower temperatures these mixtures will 

 certainly become completely solid with a corresponding change 

 in the E.M.F. of the cell. He repeatedly noticed that in 

 such a case the E.M.F. attains its final value very slowly, and 

 ascribes this to the last quantity of liquid amalgam (the 

 surface being solid) requiring a long time to thoroughly mix 

 with the other portion. No observations on the electromotive 

 properties were made at 0°, but one or two observations on the 

 melting-points of the amalgams were made in the neighbour- 

 hood of 0°. From these latter observations we may infer (as 

 recently pointed out by Cohen 17 ) that the amalgams with 

 from 2*4 per cent, to about 9 per cent, of cadmium may be 

 usefully employed at 0°. Our own results fix the limits as 

 2'6 and 11 per cent. As one of the curves given by Bijl was 

 obtained by extrapolation below 8° the agreement may be 

 considered satisfactory. 



Cohen and Kruyt's 17 observations at 0° C. were made 

 with 10 and 12^ per cent, cadmium amalgams. At 0° the 

 maximum observed difference between cells containing the 

 amalgams was 0*25 millivolt. With chilled amalgams our 

 own observations show that the difference may be more than 

 10 times as great, the difference observed being 3*30 milli- 

 volt. Cohen also measured differences between two 10 per 

 cent, amalgams at 0° C, but the differences were sometimes 

 positive and at other times negative. 



Conclusions. 



1. Cadmium amalgams of such a composition that if 

 homogeneous * they would be completely solid below certain 

 temperatures, may not in a Weston normal cell have that 

 E.M.F. towards a cadmium sulphate solution corresponding 

 to such a solid. The general result is a lowering of the 

 E.M.F. of the cell and is due to lack of homogeneity of the 

 amalgam, the outer shell of which is of low cadmium con- 

 centration and the centre of the mass of high cadmium 

 concentration. Diffusion tends to restore uniformity, and in 



* The term is used in a relative sense. 



