'270 Mr. F. E. Smith on Cadmium Amalgams 



chilled amalgam cell did not exceed 0*2 millivolt. Both 

 amalgams changed considerably on raising the temperature 

 to 50° C. and subsequent cooling, but although at 50° both 

 cells had nearly the same E.M.F., they differed very con- 

 siderably at 0°. In all cases cells containing amalgams in a 

 presumably solid state, whether chilled or not, could be 

 raised in temperature and subsequently cooled without 

 appreciable change in E.M.F., unless with increasing tem- 

 perature there was an abrupt change in the temperature 

 coefficient. In such a case the temperature coefficient 

 appears to diminish at first, but afterwards the E.M.F. of 

 the cell rapidly falls to a value which is nearly identical with 

 that of a cell containing a stable two-phase amalgam. In our 

 experiments the change usually occurred when the E.M. b\ 

 was from 0*4 to 2'b millivolts greater than that of a normal 

 cell. In all cases subsequent cooling showed that a change 

 in the amalgam had taken place as the new E.M.F. was less 

 than the previous value at the same temperature. 



At temperatures near to but below the first transition 

 temperature the diffusive processes in an unstable amalgam 

 .are no doubt accelerated, and the outer shell becomes richer 

 in cadmium with a corresponding increase in the E.M.F. of 

 the cell; even so the diffusion is very slow, and in general 

 before the first transition temperature is reached the outer 

 shell becomes partly liquid, and a two-phase system appears 

 at a lower temperature than would be the case if the amalgam 

 were homogeneous. On subsequent cooling a new outer shell, 

 with even less cadmium than before, is formed, but the inward 

 concentration gradient is greater than before, and hence the 

 cell is more unstable. The results given in Table IX. are 

 easiy explained on such an hypothesis. 



If a stable amalgam is taken in which the solid and liquid 

 phases are certainly present, increase of temperature will 

 diminish the solid and increase the liquid phase. When the 

 liquid phase alone is present the temp. coef. of a cell con- 

 taining the amalgam is very different from that of a cell with 

 a two phase system. This is evident from fig. 3. It was 

 surprising to find that even when the temperature of a cell 

 was maintained several degrees above the transition tempera- 

 ture (corresponding to the change to the all liquid phase), 

 several hours elapsed before the transformation was 

 complete. For example, the 8 per cent, amalgam appears to 

 be completely liquid at all temperatures above 41° C, yet 

 when a cell containing such an amalgam was kept at 45° for 

 four hours its E.M.F. was in exact agreement with that of a 

 cell containing a 10 per cent, amalgam, of which the transi- 

 tion point is about 51°. At the end of five hours the E.M.F. 



