Molecular Thermodynamics. 617 



If, however, A ^- etc. can be reproduced (whether known 

 or not) at different temperatures and pressures, then since 



*>y (8) 



T'lj^^^.'A^, • • • (37) 



and by (7) 



-T|-S^A^=^A^ ; , . • • (38) 



OP OCs OCs 



we can thus determine tg x 'A ^ and %v x 'A~? and by 



OCs OCs' 



extrapolation to zero concentration %q x ' ^r^ an d ^vj— . It 



OCs OCs 



^— etc. or A^— 1 etc. be determinable on theoretical 

 dc s OCs 



grounds we thus obtain q{ v/ <pi etc. at once. Generally, 

 however, it will be possible to determine them by empirical 

 methods given an adequate set of data as to the variation of 



%(j) x '~ with concentrations, temperature, and pressure. 

 (jc s 



Cs 



In Solubility Methods of course log - — ^ — vanishes. 



l + ^ia 

 The modification when the molecular weight of the solute is 

 not the same in the two phases is obvious (cp. (33; above) . 



(b) E.M.F. Data in the special case of Electrolytes. — This 

 gives essentially the same information as the partition 

 data, but is more widely and easily applicable. A virtual 

 transference of the solute is effected by means of electrodes, 

 and for this 



-T^ = Eoe, (39) 



where he units of electricity are involved in the transference of 

 the Sni gm.-mols. of electrolyte or (say) vSni equivalents of 

 electrolvte, so that 



8e = Fv8n l9 (40) 



F units being one faraday. 



Thus if A signify the (finite) difference between two 

 phases, (39) and (40) give 



-Ta(|±W=ES £ 



=EFvBm, . . . (41) 



