﻿On Molecular Thermodynamics. 611 



the treatment below will apply in full and without alteration 

 in such a cnse, if a lower solvate be regarded as a " negative" 

 solvate of a higher. 



The following alternative and more general statement of 

 the problem will make this clearer : — 



The molecular species present in the phase or solution 

 are the several solvent-molecular species which together 

 constitute the "free solvent"" and a number of solute- 

 molecular species. Now the latter can be grouped in such 

 a way that members of a group differ in composition only 

 in the amount of solvent per molecule, and can be regarded 

 as positive or negative solvates of one another. One member 

 of each group appears in the present discussion as a separable 

 or " experimental " solute — a component under the conditions 

 of experiment ; and the (positive or negative) quantities of 

 solvent by which the other members differ from this one 

 are, and are alone, regarded as " bound " solvent, which 

 together with the " free " comprises the " total solvent." 



In the " molecular " expression for i^, from which we 

 started in the previous paper, every molecular species 

 appears as a component. In the " experimental " expression 

 obtained in that paper the free solvent appears as one com- 

 ponent only, and in the present paper, starting from this 

 result, which we may refer to as our " original " expression 

 for yjr, we shall obtaia an expression in which the " total 

 solvent " and the " unsolvated solutes" are the components. 



It is clear that problems, such as dissociation and com- 

 bination of the solutes, excluded from present consideration, 

 •can be treated as further stages in this gradual reduction 

 of the components. 



Let M be the mass of free solvent considered, and M ' 

 that of the total solvent, the latter but not the former being 

 an experimental (known and controllable) quantity. 



Concentrations referred to the latter may be called 

 *' experimental " concentrations, 



t _ J^ r ,__l t n 1 _N_ 

 Cs ~ M " U - M ' - M " ' ' * * [l) 



while those referred to the former, 



e _ n > p _ Sn* _ N 



maybe called ''true" concentrations. The latter alone were 

 used in the consideration of " complex solvents." 



It will be a convenience making for clarity, to obtain 

 2R2 



