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 solutions 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 C., but with 

 solutions as dilute as those which I used, the difference could 

 hardly affect the third significant figure. f I have therefore 

 regarded the concentrations at the two temperatures as the same. 



As the method of calculation 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 Pycnometer. They might be in 

 error by about 5 in the fifth decimal place. No change of volume 



*Trans. N. S. Inst. Sci., 9, 291, (1897-8). 



tFrom Kerch'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., (1), 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 

 solutions examined, and in the case of these only to the extent of 1 or 2 units. 

 J. G. M. 



