VOLUME CHANGES IN THE PROCESS OF SOLUTION. 79 



There is a considerable amount of evidence now available 

 indicating the existence of solvates in solution. Further- 

 more Tver 1 has shown that in certain cases e.g., calcium 

 chloride in ethyl alcohol, in which there is little doubt that 

 the calcium chloride exists in solution as Oa01 2 , 4C 3 H 5 OH, 

 increasing concentration is accompanied by a marked 

 increase in the specific solution volume of the solute, due 

 to a decrease in the degree of solvation with increasing 

 concentration of solute. These results would indicate that 

 the variation of v s with concentration observed in aqueous 

 solutions even in the case of non-electrolytes is due also, 

 in part at least, to the formation of solvates. 



The solution volumes of many strong electrolytes in water 

 have been determined by various authors, and their results 

 show that the specific volume increases with concentration. 

 In certain cases, e.g., magnesium sulphate, if the value of 

 A be sufficiently reduced v s may even become negative, 

 indicating that the volume of the solution is less than that 

 of the water used. The effect of concentration varies con- 

 siderably with different electrolytes, being far more marked 

 for instance in the case of sodium chloride than with mag- 

 nesium sulphate. This decrease of v B with dilution has 

 been attributed to the effect of increasing dissociation of 

 the solute. The observed decrease in v s cannot be attri- 

 buted entirely to a decrease in the actual specific volume 

 of the solute. The fact that in certain cases a negative 

 value is obtained for v s indicates that in these cases the 

 water is appreciably contracted in the process of solution. 

 As Tyer has already pointed out, it is quite probable that 

 in aqueous solutions of electrolytes, the ions of the solute 

 cause a condensation in the volume of the water molecules. 

 But there is apparently no proportionality between the 

 degree of dissociation of an electrolyte and its specific 

 solution volume. 



1 J.C.S., 1911, 99, 87 L. 



