Properties of Liquid Mixtures. 293 



solution in it of the maximum quantity of water. We get 

 the following results at 100° : — ■ 



Vapour-pressure of water = 760 millim. 



Solubility of aniline = 6*5 per cent. = 1*32 molecular 

 per cent. 



Partial pressure of water = 98*68 per cent, of 760 

 = 7499 millim. 



Vapour-pressure of aniline = 46 millim.* 



Solubility of water in aniline = 8*7 per cent. = 33 mole- 

 cular per cent. (Alexejew). 



Partial pressure of aniline = 30'8. 



Total pressure = 749*9 + 30*8 = 780*7. 



Observed pressure = 784*6 millim. 



The vapour-pressure of the saturated mixture is therefore 

 given fairly well by the above rule. The rule cannot be 

 applied to phenol mixtures, as below the critical point the 

 vapour-pressure of phenol is too low to determine with 

 accuracy. Konowalow's measurements of the vapour-pressure 

 of isobutyl alcohol-water mixtures, combined with Alexejew's 

 measurements of solubility, give the following results. At 

 90°:— 



Vapour-pressure of water = 525 millim. 



Solubility of isobutyl alcohol = 7 per cent. = 1*8 mole- 

 cular per cent. 



Partial pressure of water-vapour = 98*2 per cent, of 

 525 = 515-5. 



Vapour-pressure of isobutyl alcohol = 378 millim. 



Solubility of water = 25 per cent. = 57*8 molecular per 

 cent. 



Partial pressure of isobutyl alcohol = 159*5. 



Sum = 675*1. 



Observed pressure =767. 



In this case the alcohol saturated with water contains more 

 molecules of water than of alcohol, and it is not to be expected 

 that the normal depression of the vapour-pressure should 

 hold over so wide a range as 57*8 per cent. The numbers 

 in fact show that the partial pressure of isobutyl alcohol 

 must be very much greater — about 250 millim. The curve 

 of partial pressures is therefore comparable with that for 

 ethyl alcohol in benzene and toluene (see Part II. tables 

 p. 53). 



* Kahlbaura, Zeitsch. f. phys. Chem. xxvi. p. 604. 



