240 RELATION OF PHYSICAL PROPERTIES OF AQUEOUS SOLUTIONS 



gravities of very dilute solutions is clearly shewn in the results 

 of Kohlrausch and Hallwachs's observations^ 



So far as Sodium and Potassium Chlorides are concerned, 

 Bender found that in respect to their density at 15 0.; 



For n = 1-0 20 3'0 



( P 1-P 2 )/ = >0 2 43 '2 49 '2 51 



The value of I k for NaCl is +0'01424 and for KC1 +0-01316, 

 while a glance at the first table (p. 221) shows that the ionisa- 

 tion coefficient of solutions of the former salt falls oft' with the 

 concentration somewhat more rapidly than, indeed for some 

 concentrations, about twice as rapidly as, in the case of the 

 latter. There cannot, therefore, be a close approximation to 

 constancy in the absolute values of (P l P 2 )/n, but as these 

 values are comparatively large, the percentage difference between 

 them is comparatively small. 



For the thermal expansion of these salts we have from 

 Bender's observations, 



For n = 1 1-5 2 2'5 



(Pi-P 2 )M = '0 3 108 -0 4 85 -0 4 815 -0 4 78 



The value otl-k in this case for NaCl is + 0'0 3 9i, and for KC1 

 + 0'0 2 13. There is thus a closer approximation to equality in 

 the values of (I k) A /&n for the two salts, for thermal 

 expansion than for density. Accordingly the absolute differ- 

 ences in the values of (P x P 2 ) /n are smaller than in the case 

 of density. But as the values themselves are much smaller, the 

 differences between the values when expressed as percentages 

 of any one of the values are greater. And thus the approxima- 

 tion to constancy, of (P l P 2 ) /n, in the case of thermal 

 expansion is not so great as in the case of density, when 

 judged in this way. 



For viscosity I k for NaCl is 0'0022 and for KC1 



-0-0028. The values of (l k)*a/*n will thus be less 



nearly equal than in the case of the thermal expansion and the 



Wied. Ann., liii, (1894), p. 14. 





