618 Mr. Bernard Cavanagh on 



f-r,'(g) ■ • • <«> 



**©-£♦(& *«> 



Now when we consider that, when the solvent is the 

 same in both phases, 



a|^=RA2^|^, . (46) 



&n s dc s K 



a|^=RA2v/|^-, . . . (47) 



cK * Be 



it immediately becomes clear that the measurement of E/T 

 and its temperature and pressure coefficients for concen- 

 tration cells in which the molecular concentrations are 

 known gives us precisely the same information as the 

 partition data already discussed. But (within its obvious 

 limitations) the E.M.F. method is much more easily and 

 widely applicable. 



IV.. Polymerized and Mixed Solvents. 



Hitherto, like Planck, we have assumed a complete 

 knowledge o£ the molecular constitution of the solution. 

 In the case of an absolutely non-associated solvent such as 

 a paraffin this will be readily obtainable, but many of our 

 best solvents consist of two or three different kinds of 

 molecules in proportions of which we have no more than 

 a rough idea. 



Concentrations referred to the " number of molecules of 

 solvent " as denominator, are obviously of no practical ii>e to 

 us in these cases, for indeed our definition of the "solvent" 

 as a particular molecular species has here to be altered to 

 u a particular group of molecular species, incompletely 

 specified." 



We have, therefore, to consider carefully how far both 

 Planck's treatment of extreme dilutions and the above 

 treatment o£ the general case can be made practically applic- 

 able — by suitable modification — in the face of this deficiency 

 of'data. 



