2U 



Scientific Proceedings, Royal Dublin Socieii). 



Table V. 



The values of K in Table V have been calculated from figures given by 

 Vrevsky.^ The value of K, and consequently all the distillation values, 

 are dependent on the concentration of the solution — the greater the concen- 

 tration the smaller the distillation coefficient. For aqueous solutions of the 

 soluble alcohols of concentration less than that of the constant boiling point 

 mixture the distillation figure increases -with increasing dilution, reaching a 

 maximum value in dilute solution. In very dilute solutions the values for 

 the different alcohols are of the order of those recorded in Tables I and II. 

 A comparison of these coefficients with vapour pressures at 100° of the 

 various alcohols shows that there is no apparent agreement between the 

 rates of distillation in aqueous solutions and the volatility of the alcohols. 



Although these substances are associated in the pure state, it is improbable 

 that the molecular complexes are not dissociated in very dilute solution. 

 The lack of agreement between the rates of distillation of the aqueous 

 alcohol mixtures and the volatility of the pure alcohol cannot be due to the 

 presence of molecular association of the solute. 



There is the possibility that soluble alcohols become associated in part 

 with some of the solvent when dissolved in water ; and, if it be assumed that 

 only the free solute is volatile, the concentration in the vapour phase will be 

 proportional to the concentration of the free substance in the liquid phase. 



The evidence in favour of the associating theory is, however, very small 

 in these cases. Against the hypothesis that there is any kind of combination 

 or association of the alcohol with water, we have the fact that when the 

 azeotropic mixture of 7i-propyl alcohol and water is cooled in a freezing 

 mixture pure ice separates out. In addition, the formation of an azeotropic 



I Zeit. phys. chem., 1912, 81, 1. 



