﻿Molecular Thermodynamics. 233 



Van Laar we find "perfect solution" persisting up to very 

 high concentrations — sometimes over the whole range. 



The "general" terms of which (excepting the case of 

 electrolytes) little or nothing is yet known, have been touched 

 on only in so far as the treatment of the " linear " terms 

 involves (in general) a certain very slight alteration in the 

 division into u linear " and "general" terms, which may 

 sometimes have to be taken into account when dynamical 

 theory is employed. 



Experimental determination of the " general " terms for 

 comparison with theory must of course be preceded by 

 knowledge of the " linear " terms, — hence again the need 

 for rigorous and thorough treatment of the latter. 



III. Complex Solvents. 



The importance of this question of " complex" (polymer- 

 ized and mixed *) solvents is sufficiently obvious when it is 

 considered that of this type are most of our best solvents, 

 probably all our " ionizing " solvents, and, chief of all, water. 



We have to consider a solution consisting of the solute- 

 molecular species, m l3 m 2 , , m s , . . . . , in addition to the 



various species m 01 , m 02 , . . . . , which constitute the solvent. 



Concentrations being expressed in gram-molecules per gram 

 of solvent, the " molecular " expression for yjr is 



+ S» s (&-Rlog^-J^-) +-RM S4, x 'f x (e 01 ... ,....), (1) 

 which is of the form 



*-*"%+HWj- ■■ ■ > 2 > 



the several solvent-molecular species appearing as separate 



* Mixed solvents, while submitting to the same theoretical treatment 

 as the merely polymerized solvents, present certain peculiar difficulties 

 and some interesting possibilities with which it is hoped to deal at length 

 in a later paper. 



t A suffix outside a bracket is used to indicate, in less obvious cases, 

 independent variables which are held constant in a partial differentiation, 

 — a well-known usage. A single suffix may be used briefly for a whole 

 series, as n 0] here standing for w i, n 2, 



