AQUEOUS SOLUTIONS OF CERTAIN SALTS. 



17 



The suits which I usecl zinc sulphate (ZuSOj, magnesium sulphate (Mg-SO,), and 

 calcium chloride (CaCL) were bought as pure, repurified by crystallization, and dehyd- 

 rated by careful heating to the necessary temperature. 



In all cases, after the solution.* liad stood a while, a slight fluffy appearance presented 

 it.self in the bottles. The mass of the precipitated solid was, however, very small — so small 

 that it was hardly possible to weight it. Hence I considered that its effect on the result 

 might be neglected. It was probably due to the presence of some impurity in the water, 

 perhaps of ammonia. 



The following arc the results of the experiments : — 



Zinc Sulphate — ZuSO,. 



Vuluine of bottle to zero mark at VX'ô C. = 2ti87 c.c. 

 Jlass of water in bottle = 2683'1 grammes. 

 Mean section of tube ^ 0'40 sq. cm. 



In the above table, the first and fourth columns contain the results of observation; 

 the others are calculated from these. The third column shews the solutions examined to 

 have been of strengths varying from 0186 to 2'895 per cent, of salt in solution. The 

 fourth and fifth columns shew that even the weakest solution formed has a volume greater 

 than that of the water which it contains. 



The former rough measurements, alluded to above, which seemed to shew that weak 

 solutions of this salt had volumes less than the volumes of the water they contained, 

 were made with solutions, the weakest of which was of about 2.5 per cent, strength. It 

 appears therefore that zinc sulphate solutions do not exhibit this peculiarity. 



The relation between the mass of salt per unit mass of solution and the densitj'- of 

 weak solutions of this salt is shewn graphically in Plate I. The points determined by 

 taking the former as abscissae, the excess of the latter over unity as ordinates, are found to 



Sec. III., 1885. 3. 



