24 Proceeduigs of the Royal Irish Academy. 



molecular weight of the alcohol that may usefully be taken into account in 

 considering the relationship of the alcohols to water. 



It may, however, be noted that the boiling point of secondary butyl alcohol, 

 99-6", is only 2-4 degrees higher than that of normal propyl alcohol, but that 

 the butyl alcohol is only partially miseible with water, whilst the propyl 

 alcohol is infinitely miseible. 



Alcohols and, hydromrlons. — Consideriug next the relationship of the 

 alcohols to a hydrocarbon, sucli as noi-mal hexane, it will be obvious that 

 as the magnitude of the alkyl group increases, the influence of the hydroxyl 

 group must become relatively smaller, and the alcohol must approximate more 

 and more closely in its properties to the hydrocarbon. It is found, indeed, that 

 methyl alcohol is only partially miseible with normal hexane at ordinary 

 temperatures, whereas those of the higher alcohols which are liquid at ordinary 

 temperatui'es are miseible with this hydrocarbon in all proportions. It is 

 found also that several of the lower alcohols form azeotropic mixtures of 

 minimum boiling point with hexane, whilst the higher alcohols do not. Only 

 a few of the alcohols have, however, been distUled with hexane, and it is of 

 interest to consider which of the other alcohols are likely to form azeotropic 

 mixtures with this paraifin. 



The aromatic hydiocarbons, benzene and toluene, behave in a very similar 

 manner to hexane, but they are miseible in all proportions with methyl 

 alcohol, as well as with the higher liquid alcohols. 



Benzene. Uke hexane, forms azeotropic mixtures of minimum boiling point 

 with the lower alcohols, but not with the higher ones ; but here, again, there 

 are several alcohols which have not yet been investigated. 



Before considering the properties of mixtures of toluene with the alcohols 

 it may be well to point out that the normal relation between the boiling 

 points and the molecular composition of mixtures of two liquids is expressed 

 by a curve, and that the smaller the difference between the boiling points of 

 the two liquids the smaller is the curvature. If the two liquids had the same 

 boUing point, the relation would be expressed by a straight line ; and it is 

 obvious that, for such a pair of liquids, the slightest deviation from normality 

 would involve the existence of a mixture of minimum or maximum boiling 

 point. Conversely, since the normal c\u-vatiu-e is always slight, the greater 

 the difference between the boiling points of the two liquids the gieater must 

 be the deviation from normality for an azeotropic mixture to be capable of 

 formation. 



Kow, although the deviation from normality for toluene and methyl 

 alcohol is greater than for toluene and ethyl alcohol, yet the difference in boiling 

 point for the former pair, 45-9 degrees, is considerably greater than for the 



