Young — Note on Azeotropic Mixtures. 23 



afterwards obtained and examined by Miss Fortey and the author; later, 

 several such mixtures were obtained in the Trinity College laboratory, and 

 recently the number of known mixtures has been greatly increased by the 

 researches of Lecat. 



No ternary azeotropic mixture of maximum boiling point has yet been 

 discovered. 



The question whether any two or three given liquids are likely to form a 

 binary or ternary azeotropic mixture, respectively, is of interest, and in a few 

 instances it now seems possible to answer the question with a fair degree of 

 confidence. 



Alcohols and vxcter. — The higher monhydric aliphatic alcohols are either 

 partially miscible or non-miscible with water ; and, adopting Lecat's term 

 "heterogeneous mixtures" for pairs of partially miscible or non-miscible 

 mixtures, it may be stated at once that all the higher alcohols of this series 

 form binary (heterogeneous) azeotropic mixtures of minimum boiling point 

 with water. The behaviour of the lower homologues with water has been 

 investigated, and it is certain that methyl alcohol is the only one that does 

 not form an azeotropic mixture with water. 



Since the alcohols of the methyl alcohol series may be regarded as com- 

 pounds of alkyl radicals, C„Ha«+i) with hydroxyl, OH, it follows that the 

 smaller the alkyl group the greater must be the relative influence of the 

 hydroxyl group on the properties of the compound, and the closer must be 

 the relationship to water ; and this conclusion is confirmed by the decreasing 

 miscibility of the alcohols with water as the molecular weight increases, and 

 in many other ways. Thus methyl alcohol, ethyl alcohol, and the two propyl 

 alcohols are miscible with water in all proportions, whereas only one of the 

 four isomeric butyl alcohols is infinitely miscible, and all the amyl alcohols 

 are only partially miscible with water. 



It is, however, not only the molecular weight, but also the constitution of 

 the alcohol that has to be considered ; thus, of the four butyl alcoJiols, the 

 primary alcohol derived from normal butane has the highest boiling point, 

 116'9 , and it is this alcohol which is the least soluble in water. On the other 

 hand, the boiling point of the tertiary alcohol, derived from isobutaue, is the 

 lowest, 82'55°, and it is this alcohol which is miscible with water in all propor- 

 tions. 



The boiling point of the tertiary alcohol is only a few degrees higher than 

 that of ethyl alcohol, 78-3°, and is much lower than that of normal propyl 

 alcohol, 972°, and in many of its properties tertiary butyl alcohol resembles 

 ethyl alcohol more closely than the isomeric butyl alcoliols. It may, in fact, 

 be concluded that, for many purposes, it is rather the boiling point than the 



