324 PROPERTIES OF ELECTRICALLY CONDUCTING SYSTEMS 



preciable progress has been made in this direction. In dilute solutions of 

 weak electrolytes, the ionic theory has met with marked success and, 

 while it may be expected that here, too, the theory will have to be 

 materially modified when a final solution of the problem has been reached, 

 the mutual consistency of the results obtained indicates that a consider- 

 able measure of truth underlies the ionic theory as formulated. This 

 important fact should not be lost sight of in developing a more general 

 theory of electrolytic solutions. 



The inapplicability of the law of mass action in its simple form to 

 relatively dilute solutions of strong electrolytes has led to many contro- 

 versies relative to the nature of these solutions. On the one hand, it has 

 been suggested that such solutions are completely ionized at all concen- 

 trations ; * and, on the other, that they are not ionized at all. 2 Still other 

 theories attempt to relate these solutions with colloidal systems. 3 The 

 proposed theories may be grouped into three classes: (1) theories which 

 are derived by combining with thermodynamic principles auxiliary 

 assumptions, which, in part at least, are of an empirical nature; (2) 

 theories in which the interionic forces due to the charges are taken into 

 account; and (3) theories of a miscellaneous nature which as a rule are 

 of a qualitative character. 



2. Electrolytic Solutions from the Thermodynamic Point of View. 

 a. Scope of the Thermodynamic Method. If equilibria exist in solu- 

 tions of electrolytes, as we have reason to believe, then such solutions 

 must be subject to the thermodynamic principles governing equilibria. 

 That equilibria, in fact, exist in electrolytic systems is not to be doubted, 

 since in no other class of systems do reactions proceed so rapidly to a 

 definite condition. In most instances, it is not possible to measure the 

 speed with which reaction takes place in these solutions. The first 

 assumption which arises in the detailed application of the principles of 

 thermodynamics to equilibria in solutions of electrolytes is that of the 

 precise nature of the reaction involved. It is obvious that, before equi- 

 libria of the electrolytic type can be treated comprehensively, the nature 

 of the reactions involved must be definitely established. All considera- 

 tions in which these reactions are involved are necessarily subject to 

 uncertainty, since it has not been found possible to establish, definitely, 

 whether or not un-ionized molecules, as well as ions, exist in electrolytic 

 solutions. The nature of the reaction being assumed, the thermodynamic 

 treatment of electrolytic solutions is comparatively simple, so far as the 

 thermodynamic considerations themselves are concerned. When, how- 



1 Ghosh, Trans. Chem. Soc. UL3. 449 (1918). 

 *Snethlage, Ztschr. f. phys. Chem. 90, 1 (1915). 

 Georgievics, Ztschr. f. phys. Chem. 90, 341 (1915). 



