and tlie Western Normal Cell. 275 



consequence the cell is unstable for a very considerable 

 time — the E.M.F. rising. 



2. When the amalgam is at a temperature near to, but 

 below, the first transition point, the difference of concentra- 

 tion between the inner and outer parts of the amalgam need 

 be only small to enable the outer shell to be a two-phase 

 system. Owing to the small difference of cadmium concen- 

 tration throughout the mass the diffusion process will be slow 

 and the E.M.F. of the cell may remain constant for a very 

 long time. There is, however, in general, a small difference 

 in E.M.F. between such a cell and one containing a normal 

 two-phase system. 



3. Cadmium amalgams of such a composition that, if 

 homogeneous, they would be all liquid above certain 

 temperatures, may not in a standard cell have that E.M.F. 

 towards the solution corresponding to a homogeneous 

 amalgam. In such a case the E.M.F. of the cell is higher 

 than usual. The effect is due to the upper part of the 

 amalgam being a two-phase system and the lower part an all 

 liquid system of less cadmium concentration than the upper 

 part. Diffusion quickly equalises the concentration and the 

 E.M.F. falls to a normal value. 



-4. The 12^ per cent, cadmium amalgam at present used in 

 the Weston normal cell may be completely solid at tempera- 

 tures below 12°, and cells containing it may have a higher 

 E.M.F. than normal if used below that temperature. 

 Fortunately, even at temperatures such as 0° C. the amalgam 

 is comparatively near to its first transition point, and the 

 conditions are similar to those noted in (2). Inconsequence, 

 except in rare cases, cells containing the 12^ per cent, 

 amalgam will behave at 0° as though they contained an 

 amalgam which was always in a two-phase system at that 

 temperature. 



5. As a 10 per cent, amalgam at 0° is above its first 

 transition temperature this may be used in standard cells at 

 low temperatures. Such cells may also be used at tempera- 

 tures as high as 51°. We suggest that the 121- per cent. 

 amalgam in the Weston normal cell be replaced by a 10 per 

 cent, amalgam. 



INFERENCES. 



i. Dearlove. The Electrician, xxxi. p. 645, 1890. 



2. W. Jaegek. Wied. Ann., lxv. p. 10(5, 1898. 



3. E. Cohen. Zeitschr. f. physik. Cheniie, xxxiv. p. 69, 1900. 



4. Kerf and Bo-ettger. Zeitschr. f. anorir. Chem., xxv. p. 1, 1900. 



T2 



