Properties of Liquid Mixtures. 295 



identical with that of benzoic acid and water*, but the curve 

 brnnches of the diagram are of very different relative sizes to 

 those of the last-named mixtures. The features of the diagram 

 are as follows : — 



L. Freezing-point of water. 

 0. Freezing-point of phenol. 

 LS. Freezing-point of aqueous solutions of phenol. 

 ONFGHMS. Freezing-point of solutions of water in phenol. 

 S. Cryohydric point. 

 MC. Saturation of water with phenol. 

 NC. Saturation of (liquid) phenol with water. 

 C. Critical point of mixture. 

 The line LS is given by the thermodynamic equation 



0-02T 2 

 L 



where T is the absolute temperature of fusion of ice, L the 

 latent heat of fusion, and t the resulting molecular depression 

 of the freezing-point ; it accordingly starts with a slope of 

 o, 2 for one per cent, of phenol. The initial slope of ON is 

 given by a similar equation, and is 4°'15 for one per cent, of 

 water ; a direct observation gave as a point of the curve 



80*5 per cent, phenol, 

 melting-point + 5*0. 



This is marked with a dot in the figure, and lies to the right 

 of ON ; by continuing the curve through the point so found 

 until CN is met, we reach the point N where the phenol is 

 saturated with water ; on increasing the concentration a 

 second liquid layer appears, consisting of water saturated 

 with phenol. NFGHM is purely hypothetical, referring to 

 unstable mixtures ; actually any mixture of concentration 

 between 8 per cent, and 77 per cent, of phenol will separate 

 into two layers on cooling, and on further reduction of 

 temperature freeze at the constant temperature (about -f 1 0, 5) 

 represented by the horizontal straight line MN. The cryo- 

 hydric point lies to the left of the saturation curve CM, so 

 that it is actually attainable : its existence was shown by 

 making a solution containing 5 '25 per cent, of phenol, and 

 cooling it in a bath of ice and salt : it began to freeze with- 

 out previous separation into two layers, and the temperature 

 remained constant at — O- 9. About half of it was frozen, the 

 beaker removed from the freezing-mixture, and some of the 

 liquid remaining poured off for analysis ; it was found to 



* See van't Hoff, Vorlesungen ihber theoretische und physikalische 

 Chemie, Heft i. p. 48. (Braunschweig, 1898.) 



