140 MAGIE— THEORY OF SOLUTIONS. [April ,9, 



Jones^ and his fellow workers have been led by their observa- 

 tions of abnormally great freezing point depressions in concen- 

 trated solutions to adopt the view that the solute interacts with the 

 water to form groups of molecules which are so closely bound 

 together that they move as one body in the solution. Jones calls 

 these combinations hydrates. He explains the abnormality of the 

 freezing point depressions by the hypothesis that the molecules of 

 water which combine to form the hydrates are removed from the 

 solvent so that it contains fewer free molecules or becomes more 

 concentrated than would be inferred from the way in which the 

 solution is made up. By following out this hypothesis he reaches 

 the conclusion that the extent of hydration is a function of the con- 

 centration, being generally greater as the concentration increases, 

 at least up to a certain limit. 



According to our ordinary conception of the range of molecu- 

 lar force, we should not expect such a variable hydration as is 

 assumed by Jones. We should expect, rather, a practically uniform 

 action of the molecules and ions of the solute, forming groups of 

 water molecules which are constantly the same for all concentra- 

 tions ; at least for those in which the groups do not frequently inter- 

 penetrate each other. 



In constructing the formulas to represent the heat capacity and 

 the volumes of solutions, I have adopted the simple conception 

 which has just been stated. I assume that each undissooiated 

 m.olecule of the solute and each ion of the dissociated molecules 

 interacts with the water around it in such a way as to change its 

 heat capacity and its volume ; these changes being the same for all 

 concentrations to which the formulas apply. The solution, then, is 

 considered as a mass of free and unaffected water, in which are 

 suspended groups of water molecules, surrounding the molecules 

 and ions of the solute, and with their properties modified by the 

 action of the solute. It is not necessary to consider these groups 

 as stable. Indeed it is almost necessary, if we are to account for 

 the laws of electrolytic conduction in harmony with this hypothesis, 

 to consider them as extremely loose and unstable aggregations, 



^ Zcitschrift fi'ir phys. Chcm., XLVL, p. 244, 1903; XLIX., 385, 1904. 



