id the Weston Normal Cell. 



271 



began to fall, and at the end of: two more hours it became 

 constant but 1^ millivolt lower than previously. This liquid 

 amalgam cell was now perfectly stable and could >e raised 

 in temperature to 05° or lowered to 41° without any 

 permanent change such as was observed with the solid 

 amalgams (see also data, following Table L, with regard to 

 a 6 per cent, amalgam). Probably the reason of this 

 behaviour lies in a difference of concentration of cadmium 

 in the amalgam in the upper and lower parts, such as was 

 indicated on p. 26?). In a two-phase system, since the solid 

 crystals are lighter than the mother liquor they naturally 

 rise to the upper part of the amalgam, and it is this part 

 which is in contact with the cadmium sulphate solution. 

 When the transition temperature corresponding to the 

 amalgam is reached, the lower half will be unsaturated with 

 cadmium and therefore completely liquid, while the upper 

 part will contain an excess of cadmium and be part solid and 

 part liquid. If the temperature is raised the E.M.F. of the 

 cell will correspond to one with a two-phase system until the 

 upper part of the amalgam is completely liquid. 



We will now fix certain limits of temperature, between 

 which various amalgams may be most usefully employed in 

 the standard cell. Fig. 3 (PL III.) gives the desired infor- 

 mation and the results are tabulated below. 



Table X. 





Limits of Temperature for use 





in Weston Normal Cell. 



Percentage of Cadmium 





in the Amalgam. 





Lower Limit. 



Upper Limit. 



3 



below 0° C. 



about 3°-4 



4 



,, 



„ 12°-7 



5 



>) 



„ 21° 1 



6 



ii 



„ 27° 7 



7 



»» 



„ 34°-6 



8 



J> 



„ 41°0 









„ 46°-0 



10 



51 



„ 51° 



11 



about 0° C. 



„ 56° 



12 



8°-7 



,, 00°0 



125 



12°-1 



above 00° 



13 



16° 1 



i> 



14 



24°0 





15 



32° -5 





16 



39°-7 





17 



45° 3 





18 



52°6 



5) 



J'.) 



57 -i> 





20 



C2°l 



" 



