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° C.; 
Roe = 1:0 20 30 
(P,-P,)/n = 0,43 0,49 0,51 
The value of 1—k for NaCl is +0:01424 and for KCl +0-01316, 
while a glance at the first table (p. 221) shows that the ionisa- 
tion coefficient of solutions of the former salt falls off 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,;—P,)/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, 
Kor 4, = 1 15 2 2°5 
(P,-P,)/n = 0,108 0,85 0,815 0,78 
4 
The value of /—k in this case for NaClis + 0:0,91, and for KCl 
+0:0,13. There is thus a closer approximation to equality in 
the values of (1 —k)4a/an for the two salts, for thermal 
expansion than for density. Accordingly the absolute differ- 
ences in the values of (P,—P,)/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,—P,)/n, in the case of thermal 
expansion is not so great as in the case of density, when 
judged in this way. 
For viscosity 1—k for NaCl is —0-0022 and for KCl 
—00028. The values of (J—k) 4a/An will thus be less 
nearly equal than in the ease of the thermal expansion and the 
§ Wied. Anm., lili, (1894), p. 14. 
