346 BULLETIN OF THE UNIVEKSITY OF WISCONSIN. 



The dissociation theory has led to Nemst's theory of the 

 E. M. F. of galvanic cells, which has already been referred to 

 above. This theory is an attempt to explain the difference of 

 potential between two electrolytes and to account for the differ- 

 ence of potential between an electrode and an electrolyte, and 

 this not only qualitatively but also quantitatively. Nernst's 

 theory assumes that metals have a certain tendency to pass into 

 the ionic condition, which tendency is termed the electrolytic 

 solution tension of the metal. That which operates against this 

 tendency is supposed to be the osmotic pressure of the ions of 

 the metal already present in the solution, and the difference of 

 potential between the metal and the electrolyte is the result of 

 the action of these two forces ; on the other hand, the difference 

 of potential between two electrolytes is ascribed to the different 

 rates with which the charged ions move. Nernst's formula 

 really involves the assumption that the law of mass action is ap- 

 plicable to electrolytes in the sense required by the dissociation 

 theory. That the law of mass action does not hold, however, in 

 the case of electrolytes par excellence, has already been men- 

 tioned. By maintaining the correctness of Kernst's formula 

 and thus assuming that the law of mass action does hold for such 

 electrolytes, Jahn has arrived at the conclusion (as clearly he 



must) that z^L does not correctly represent the degree of dis- 



Aoo 



sociation, and that the ionic velocities vary in dilute solutions. 

 The latter is not, in many cases at least, in harmony with the 

 facts. Arrhenius, on the other hand, stoutly defends his orig- 

 inal ul- which of course leads to a denial of the validity of 

 Aoo 



the mass law as applied to the electrolytes in question. Ost- 

 wald, too, in the new edition of his Grundriss (p. 406) clearly 



inclines toward maintaining the time honored — formula. 



The polemical discussion between Arrhenius and Jahn is still go- 

 ing on in the Zeit. phys. Chem., and recently Nernst has also 

 taken a hand in the debate. It seems at first rather deplorable 

 that so much valuable energy is being expended in trying to de- 



