$o Conductivity of Aqueous Solutions. Part II. 



senting the conductances of sodium and potassium chloride at 18 in 

 the still more dilute solutions investigated by Kohlrausch and Maltby. 

 These deviations are 0.53 and 0.42 per cent, respectively, in case of 

 the 0.0001 normal solutions, and 0.36 and 0.25 per cent, respectively, 

 in that of the 0.0002 normal solutions. Thus this function does not satis- 

 factorily represent the results at very low concentrations, and seems there- 

 fore unsuitable for obtaining the value (A ) at zero concentration. 

 Moreover, this function, as well as that of Barmwater, does not seem to 

 admit of any theoretical interpretations, since it does not even correspond 

 to any functional relation between the concentrations of the ions and 

 un-ionized molecules. 



The fact that the van't Hoff equation does not satisfactorily express 

 the results with many salts* at 18 and 25 has led to the suggestion 

 by Storch and later by Bancroft that a general expression of the form 

 A A = KA. n C n - x be employed, the exponent n being varied as required 

 by the results with different salts. An equation of this general form has 

 the advantage that it does express the concentrations of the ions and 

 un-ionized substance as a function of each other. This becomes obvious 

 when the function is written in the form C(A A) = K (AC)", which 

 is equivalent to C(l y) = const. X (Cy) n , where y is the conductance 

 ratio (A/A ) or the fraction of the salt ionized. That such an expres- 

 sion with three arbitrary constants (assuming that A is to be deter- 

 mined with the help of the function itself) can be made to express the 

 conductivity fairly accurately through a considerable range of concen- 

 tration is obvious. It is nevertheless of interest to determine what values 

 of the exponent n must be used for different salts and for the same salts 

 at different temperatures. For this purpose it is best to write the equation 

 in the form 



A A 



and to plot the values of against those of (CA)" _1 , the exponent being 



given successively different values (in the neighborhood of 0.5) until 

 the points fall as nearly as possible on a straight line. We have done this 

 with the final values for sodium and potassium chloride given in table 9. 

 The values of the exponent n so found at various temperatures are 

 given in table 11. It was usually possible to determine them within 0.02. 

 It will be seen that the exponent varies but little with the temperature, 

 and that the results do not correspond at all closely at any temperature 

 with the mass-action law, which requires the exponent 2. 



*See Kohlrausch and Maltby, loc. cit, p. 222. 



