I907.] MAGIE— THEORY OF SOLUTIONS. 141 



from which water molecules are continually breaking off to be 

 replaced by others, and through which the ions of the solute mav 

 move without dragging with them a' load of water molecules. 

 Whether the effect of the molecules and ions of the solute is to 

 increase or diminish the heat capacity or the volume of the water 

 in these groups, or to leave these properties unchanged, is to be 

 determined from the values of the constants of the formulas found 

 for each particular solute. 



It should be stated that the solutions to which the formulas have 

 been applied are made up by dissolving one gram-molecule of the 

 solute in iY gram-molecules of water. The number of undisso- 

 ciated molecules and the number of the dissociated ions are then 

 expressed as fractions. They are obtained for each solution in the 

 usual manner from Kohlrausch's tables of molecular conductivities. 



The formula for the heat capacity formed on this hypothesis 

 reduces to the sum of three terms, of which the first represents the 

 heat capacity of the water used in making up the solution, the 

 second is a constant multiplied by the number of undissociated 

 molecules of the solute, the third, a constant multiplied by the num- 

 ber of dissociated molecules of the solute. The two constants repre- 

 sent the heat capacity of the molecules and ions of the solute re- 

 spectively, together with the changes which they produce in the 

 heat capacity of the groups of water molecules associated with them. 



The formula for the volume assumes the same form, and, inuta- 

 tts miitandis, the interpretation of the constants is the same as that 

 which has just been given. 



For solutions of non-electrolytes, in which there is no dissocia- 

 tion, the formula reduces in each case to the sum of two terms, one 

 of which represents the heat capacity or the volume of the water 

 used in making up the solution, and the other is a constant which 

 depends upon the particular solute employed. 



These formulas are abundantly verified by comparison with the 

 results of observation. With regard to the non-electrolytes it has 

 been shown^ that the heat capacity of their solutions, in most cases, 

 is the sum of the heat capacity of the water and of a constant 

 characteristic of the solute. This constant in general is not the 



' Magie, Phys. Rcviczv, Vols. IX., XIII. 



