3o 



ENERGY CHANGES INVOLVED IN DILUTION OF AMALGAMS. 



Electromotive Force of Standard Helmholts Cell. 



The average, X = 0.9925 -f- 0.00007 (* 2I ) international volts, is safe 

 to use on all measurements of zinc concentration cells. 



Eight months elapsed before the final determinations on cadmium concen- 

 tration cells were made. Standardizations against the Clark cell now gave 

 inconstant results, apparently due to the more rapid temperature changes of 

 the laboratory during the winter. The average of four determinations indi- 

 cated that X = 0.9931 volt at 19. It seemed unlikely that the Helmholtz 

 cell had changed as much as this ; but on the other hand, the Clark cell was 

 known to have fallen off considerably in six years, and may well have con- 

 tinued to do so since its standardization in June. Finally Mr. R. W. Kent, 

 of this laboratory, kindly lent two cadmium cells, carefully made up from 

 pure materials as recommended by Carhart and Hulett *" and at least a week 

 old. When opposed to the i-volt cell, they each gave very nearly 0.0261 

 of X, which was measured on the potentiometer like the electromotive force 

 of a concentration cell. Using the formula tt = 1.0186 -f- 0.00004 (20 t) 

 international volts, 00 a potential X = 0.9927 was established for the i-volt cell 

 at 19 . This value is practically the same as that observed in June. It 

 appeared more reliable than the slightly different verdict of the Clark cell, 

 and was adopted for all measurements on cadmium concentration cells, 



X = 0.9927 -f- .00007 (* I 9)- 



THE ELECTROMOTIVE FORCE BETWEEN ZINC AMALGAMS. 



The work on zinc amalgams is conveniently considered first. Before pre- 

 senting the quantitative data, a few more details must be reviewed. 



All the zinc amalgams were made by successive dilutions of two liquid 

 amalgams, No. 1 and No. 3, both of which were made from zinc and mercury. 

 There was some question as to the accuracy with which the pure zinc 

 described above could be weighed out ; hence the true concentration ratio of 

 No. 1 and No. 3 was not known with as much precision as could be attained 

 in the dilution of each separated. Direct evidence could have been secured 



49 American Electrochemical Society Trans., 5, 59 (1904). 

 u Ostwald-Luther, Hand- und Hulfsbuch, p. 362. 



