328 PROPERTIES OF ELECTRICALLY CONDUCTING SYSTEMS 



While Jahn's equation has not been tested in the case of non-aqueous 

 solutions, it is easy to see that it cannot hold generally. For example, 

 f or m = 1 in Equation 11, the function K' varies practically as a linear 

 function of the ion concentration. Such an equation will not reduce to 

 the form of that of Jahn. 



That Jahn's equation should not hold is in no wise surprising, since- 

 the assumptions underlying it are of an arbitrary nature. It is improb- 

 able that the free energy of electrolytic solutions may be determined as a 

 function of concentration without the aid of an equation of state. In 

 other words, the chance of finding the correct equation by mere accident 

 would appear to be vanishingly small. The method of Nernst does not 

 differ materially from that of Jahn and leads to a similar result. 



c. Comparison of the Thermodynamic Properties of Electrolytes. 

 Inconsistencies in the Older Ionic Theory. While the application of 

 thermodynamic principles yields no information relative to the mecha- 

 nism involved in electrolytic solutions, these principles when combined 

 with other hypotheses lead to consequences which admit of verification. 



The bearing of thermodynamics on the theory of electrolytic solutions 

 was long neglected and has often been misinterpreted. So, for example, 

 the correspondence between the ionization values as derived from con- 

 ductance and from osmotic measurements was looked upon as lending 

 support to the older ionic theory. As Nernst 10 pointed out, this apparent 

 confirmation of the ionic theory constitutes, in fact, one of the chief 

 obstacles in the path of its acceptance. 



Insofar as electrolytic solutions constitute systems in which equilibria 

 prevail, thermodynamic principles are applicable. It is evident, how- 

 ever, that the laws of dilute solutions are not applicable to these systems 

 at ordinary concentrations. Aside from a few very general relations, 

 the application of thermodynamic principles alone can furnish us very 

 little information relative to the nature of these solutions. The general 

 problem is to express the potentials of the various constituents in terms 

 of the independent variables of the system; that is, of the concentrations 

 of the various substances present. Since statistical and other methods 

 have not been developed to a point where they enable us to determine the 

 equation of state of these systems, the problem at the present time can 

 be attacked only by experimental methods. Fortunately, the potentials 

 of electrolytes in solution may be determined readily and with a rela- 

 tively high degree of precision. The values of the potentials as thus 

 determined may be treated by graphical or other empirical methods; and, 

 while the theoretical relation between the potentials and the concentra- 



Nernst, Ztschr. f. phys. Chem. 38 f 493 (1901) ; Jahn, iUd., 38, 125 (1901). 



