238 PROPERTIES OF ELECTRICALLY CONDUCTING SYSTEMS 



tions in electrolytic systems will fail at concentrations below this value. 

 Furthermore, in the case of salts of higher type, it is not improbable that 

 intermediate ions are formed, as a result of which a divergence will arise 

 between the results as determined by conductance and by osmotic 

 methods. 



Nernst 7 has called attention to the fact that, since the law of mass- 

 action in its simple form does not hold for solutions of strong electrolytes, 

 the laws of dilute solutions cannot be applied to these mixtures. As a 

 consequence, if the ionization is correctly determined by, the conductance 

 method, the ionization as determined by osmotic methods, assuming the 

 laws of dilute solutions to hold, should differ from that determined by 

 conductance measurements. It appears, however, that in the case of 

 certain electrolytes, such as potassium chloride, osmotic methods and 

 conductance methods lead to the same value of the ionization, and, in 

 the case of other electrolytes, the two methods lead to very nearly the 

 same value at concentrations approaching 10~ 3 normal. Yet, in the 

 neighborhood of 10~ 3 normal, strong electrolytes do not conform to the 

 simple law of mass-action. Those who would use the results of osmotic 

 methods to substantiate the correctness of the results of conductance 

 methods thus find themselves in a dilemma, for, if the two methods lead 

 to identical values of the ionization, then, if the results of osmotic meas- 

 urements are looked upon as correct, the interpretation of conductance 

 measurements must be in error, while, if the results of conductance meas- 

 urements are accepted in their usual sense, the laws of dilute solutions 

 are inapplicable. That the concordance of the ionization values deter- 

 mined by conductance and osmotic methods at low concentrations is an 

 accidental one is very improbable. It appears, rather, that this agree- 

 ment is the expression of a fundamental property of such solutions. The 

 significance of this agreement, however, remains uncertain. This ques- 

 tion will be discussed further in the next chapter. 



The molecular weight of electrolytes in aqueous solutions has like- 

 wise been determined from the measurement of the elevation of the boil- 

 ing point. The precision of such measurements is necessarily much 

 lower than that of the freezing point depression and need not be discussed 

 in detail here. The molecular weight of electrolytes in aqueous solutions 

 has also been determined from vapor pressure measurements. 8 The 

 experimental difficulties attending the use of this method are very great 

 and it is doubtful if the precision of such determinations equals that of 



T Nernst, Ztschr. f. pJiys. Chem. 38, 494 (1901). 



"Lovelace, Frazer and Sease, J. Am, Chem. SQC. $3, 102 (1921). 



