Molecular Thermodynamics. 619 



Now in " Solvent-Separation-data," we separate, in the 

 eases we are now considering, not one molecular species 

 but all those constituting the " solvent," and in the propor- 

 tions in which they occur. This applies also to the use of mixed 

 solvents — of which the molecular constitution may or may 

 not be known. 



We shall now obtain a general modification of the 

 method of the preceding sections, suitable for these special 

 <^ases, and which will show how far we can go with limited 

 knowledge of the molecular constitution of the solvent. 



We beoin bv referring the molecular concentrations to the 

 mass M of the solvent, which, incidentally, brings us into 

 closer touch with experimental practice. 



l 0i rii 



M ' Cl- M ' 





where m 0l m 02 . . . . are the molecular v eights (in grams) 

 of the various molecular species constituting the u solvent, 

 and 



The mean molecular weight ^— - or = — may be written ?~ . 



At first, let us assume that the molecular constitution of 

 the solvent is independent of the concentrations C\ c 2 . . - of 

 the solutes. Thea c 0l c . 2 . . .'can only depend on tempera- 

 ture and pressure, are not differentiate with respect to 

 cic 2 . . . ; and, in the general terms, can therefore be relegated 

 entirely to the parameters u\ u 2 . . . and v\ v 2 ' . . . . 



Taking now as " unit quantity of solution," the amount 

 containing one gram of solvent, we have 



U-2 V0l + Wi + RM>;/ z (^' 2 ....), . (48) 



Y = 2>w 0l + %n 1 v 1 + BM tv x %(c 1 c a . . . .). . (49) 



Whence clearly, as in preceding cases, 



^ = ^ 0l ^ 0l -Rlogg + Sn 1 (^-Rlog^) 



+ EM ^7,(M' 2 ,..) • • (50) 

 But 



%.c = 2<c 0l + 2 t c 1 = ==- +%Ci = -^ (l + m Sci), 



