BANCROFT. — POTENTIAL OF METALS. 



117 



One other point remains to be considered, whether the potential dif- 

 ference at the surface of a reversible electrode is a function of the con- 

 centration at all. The only direct measurements are those of Neumann,* 

 which confirm the Nernst theory in every detail. In addition, there 

 are many determinations on two-liquid cells made chiefly by Ostwald's 

 pupils, and in all these instances there is a most satisfactory agree- 

 ment between the theory and the facts. On the other hand, there are 

 a few observations by different people which are not so easily recon- 

 ciled with the theory. In Table XVII. I give some measurements of 

 Paschen's f on cells having zinc and mercury electrodes and solutions 

 of ZnSOi and MgS04 of varying concentrations as electrolyte. The 

 first column gives the nature of the cell ; the second, the specific 

 gravity of the electrolyte ; the third, the concentration in grams per 

 hundred grams of the solution ; the fourth, the electromotive force 

 observed. The values for the concentrations are only approximate, 

 because they were not determined by Paschen directly, and I have 

 taken them from Landolt and Bornstein's tables. 



TABLE XVII. 



These figures lose a good deal of their value owing to the consider- 

 able variation in the determinations for the same solutions, and because 



* Zeitschr. f. ph. Ch., XIV. 225, 1894. t Wied. Ann., XLIII. 570, 1891. 



