as a Standard of Electromotive Force. 215 



the succeeding amalgams (with the exception of the 16 per 

 cent, amalgam which for some accidental * reason behaves 

 irregularly) is superficially weaker in Cd, in nearly the same 

 proportion (0*92 to 0*94; in each case, than the amalgam as 

 a whole. 



(ii.) At 20° C. (to which the cells were next heated) any 

 amalgam containing less than about 4*9 per cent. Cd should 

 be all-liquid, and any containing more than about 13'5 per 

 cent. Cd should be all-solid. The surface of the 11 per ceni. 

 amalgam is a mixture of these alloys, and as before the 

 surfaces of the 12 per cent, and 13 per cent, amalgams 

 appear to be solid and to contain slightly more than the 

 percentage of Cd (13*5 per cent.) in the richer constituent 

 of the two-phase amalgam. The surface of the 14 per cent, 

 amalgam contains about 13*6 per cent. Cd. 



It will be noticed that the surface concentrations of the 

 richer alloys (15 to 20 per cent ) as deduced by this method 

 are, as nearly as can be measured, the same at 20° as at 15°. 



(iii.) At 30° C, the equilibrium amalgams should (accord- 

 ing to Table VIII.) contain approximately 6*4 per cent, and 

 14*7 per cent. Cd. With certain limitations, discussed later 

 in § 9, (which apply equally to similar cases at the other 

 temperatures), the surface of the 11 per cent, amalgam is 

 now a mixture of these alloys. And we might expect that 

 the surfaces of the 12 to 16 per cent, amalgams would be 

 similarly constituted. But, as in (i.) and (ii.), the surface 

 film in these amalgams seems to be solid, since it contains a 

 slightly higher percentage of Cd than the solid component 

 of the two-phase system. 



From the results in column (ii.) we might expect the 

 surfaces of the 17 to 20 percent, alloys to remain unchanged. 

 It will be seen that this is true of the 19 and 20 per cent, 

 amalgams ; but the percentages of Cd in the surfaces of 

 the 17 and 18 per cent, amalgams are beginning to diminish 

 slightly and are exhibiting a time effect. 



The significance of these unlooked-for differences is 

 discussed in § 10 below. 



(iv.) At 40° C. the limiting alloys contain about 7'9 per 

 cent, and 15*9 per cent. Cd. As we might expect, the 

 surfaces of the 19 and 20 per cent, amalgams remain un- 

 changed. On the other hand, the percentage of Cd in the 



* It is obvious that irregularities of cooling and distribution must 

 sometimes occur. That sudden changes of the slopes of the curves, 

 between 15 and 20 per cent. Cd, are due to accidental irregularities is 

 shown by comparison of the present data with those for another series 

 (Table VI. /. c), in which similar changes of slope occur at other per- 

 centages. 



