Molecular Thermodynamics. 613 



while 



g = *o+R J log (1 + 2,,) + ^' [/.-&.J3 } • (25) 

 And similarly 



s2=* +BS *'S (26) 



g= ?0 ^%-[/;- 2ci | : ]. . . . (27) 



and again 



l^tfc+BStfc'^ (2S) 



g-,. + HS*'[/,-S*g].. . . (29) 



A few illustrations of application may now be given. 



We deal generally with two phases (whether naturally or 

 artificially separated) and we may expect the information to 

 be most clear and direct when we keep one phase (the second 

 or (a) phase) as simple as possible. 



We may place the experimental data under two heads : — 



(1) Concerning the dependence of —^ Upon the Concentra- 

 tions — Solvent-Separation-Data. v n 



Here we need only consider the common and preferable 

 case, where the second or (a) phase consists of pure "solvent" 

 though not necessarily in the same molecular condition as 

 in the first phase. The modifications required when this is 

 not so will be sufficiently obvious and need not be given in 

 these illustrations. 



(a) Cryoscopic,~Ebullioscopic, Vapour Pressure, and Freezing 

 Pressure* Data. Five important quantities characteristic of 

 the solvent are first accurately determined, viz. : — 



(i.j The two Latent Heats (L calories per gram) for the two 

 phase-changes of the solvent. 



Now L= k^ ~— 



for the change (8n -j-8n 0a ) in the limit when 2ci is zero 

 (pure solvent) — or since by (20), 



SM = m Bn + m Q 8n = 



we set L= — -"" — ), 



& \m 0a m o) 



being an absorption of heat on passing into the second phase. 



* This method has cot so far been used. Its possibilities are being 

 investigated. 



