as a Standard of Electromotive Force. 



20 ( .» 



fig. 2, which exhibits (diagrammatical ly) how, at a constant 

 temperature, the E.M.F. of a Weston cell alters with the 



Via. 2. 



/ 3 £/?CE/vT/iG.£ or Cadmium. 



percentage o£ Cd in the amalgam. In one set of experi- 

 ments, represented by the curve ABCD, the amalgam was 

 cooled suddenly (as above) to —50° C. and then allowed to 

 rise in temperature to 0° C. before the cell of which it formed 

 part was constructed. In the other set, represented by ABEF, 

 the amalgam was cooled " slowly " (i. e. from the liquid state 

 to 0° C. in several hours) before being used. 



On the scale of representation, the curves are identical 

 from A to C, and BCE is a horizontal straight line. The 

 observed time effects and variations in the horizontal parts 

 of the curves are discussed later. 



It is easy to anticipate from fig. 1 that the curve for 

 measurements like those of fig. 2 will consist of two branches 

 joined by an intermediate horizontal portion. For at a given 

 temperature 0, any amalgam containing less than x per cent. 

 Cd would be all-liquid, and any amalgam containing more 

 than y per cent. Cd might be all-solid ; while intermediate 

 amalgams could consist of mixtures in different proportions 

 of x per cent, liquid and y per cent, solid respectively. 



In all-liquid and all-solid amalgams the electromotive force 

 would, it is natural to suppose, vary continuously with the 

 percentage of Cd. In mixtures consisting of the same two 

 constituents (in different proportions) it might similarly be 

 expected that the electromotive effect would remain constant. 



Phil May. S. 6. Vol. 20. No. 115. Jidy 1910. P 



