COMPLEX SOLUTIONS.—ARCHIBALD. 35 
Preparation and Analyses of Solutions. 
The potassium sulphate solutions were prepared by adding 
to water a known weight of anhydrous salt which had been 
dried to constant weight in an air bath, so as to form a known 
volume of solution at 18°C. In the case of the sodium sulphate, 
a solution was prepared, and analysed by gravimetric determina- 
tion of the sulphuric acid present in a known volume of solution. 
Several soiutions of both salts of different concentrations were 
prepared in the above manner, and others were prepared from 
these by addition of water, their concentrations being calculated. 
Check analyses were made whenever any portion had gone 
through two or three dilutions, and if found necessary the 
calculated concentrations were corrected from these results. 
The complex solutions were prepared by mixing equal 
volumes of the constituent solutions at 18° C., the same pre- 
cautions being observed for securing equality of volume of the 
constituents as are described in a former paper communicated 
to the Institute on the conductivity of these salts.* 
The concentrations of the solutions at 18° C. would, of course, 
be slightly less than their concentrations at 0° C., but with 
solutions as dilute as those which I used, the difference could 
hardly affect the third significant figuret I have therefore 
regarded the concentrations at the two temperatures as the same. 
As the method of ecaleulation required a knowledge of any 
appreciable change of volume which might occur on mixing, 
simple solutions of each of the salts were prepared, and density 
determinations were made of such solutions before and after 
mixing. These measurements were carried out at 18° C. with 
Ostwald’s form of Sprengel’s Pyenometer. They might be in 
error by about 5 in the fifth decimal place. Nochange of volume 
*Trans. N.S. Inst. Sci., 9, 291, (1897-8). 
7From Forch’s observations on the thermal expansion of solutions of potassium 
sulphate (Wied. Ann., 55, 100 (1895)), and Marignac’s on sodium sulphate (Ann. Chim., 
Phys., (4), 22, 385, (1871) ), I find that the difference of temperature referred to would 
affect the third significant figure of the concentrations only in the case of the stronger 
Beene examined, and in the case of these only to the extent of 1 or2 units.— 
