234 Scientific Proceedings, Royal Dublin Society. 



In the case of some of the higher alcohols obtained by fermentation, such as 

 MO-butyl and *so-aniyl alcohols, only partly miscible mixtures are obtained 

 with water, and it is more convenient to classify these as partly miscible, 

 not-closely -related, mixtures. 



Investigations on the distillation of homogeneous mixtures were first 

 carried out by G-ay-Lussac,' and subsequently by Magnus,' Eegnault,' 

 Berthelot,^ and others. This early work was correlated by Duclaux, who 

 used it as the basis of experimental work, which led to the establishment of 

 a relation between the composition of the liquid to be distilled and the 

 distillate. He states' that ethyl alcohol distils from aqueous solution more 

 slowly than amyl or iso- butyl alcohols. 



One of the processes adopted for the purification of ethyl alcohol on a 

 technical scale consists in the distillation of a dilute aqueous solution of 

 the " raw spirit."^ Under these conditions the fusel oil, various esters, 

 and other impurities are removed more readily than the ethyl alcohol, and in 

 consequence are collected in the first running. The dilute solution of ethyl 

 alcohol collected in the subsequent fractions is then concentrated. The 

 process depends on the fact that the higher alcohols distil from dilute 

 aqueous solution at a more rapid rate than does ethyl alcohol. 



Duclaux studied the rate of distillation of the alcohols with diminishing 

 volume. He took a certain volume of aqueous alcohol and distilled it, 

 collecting the distillate in several fractions. By expressing the volume of the 

 alcohol as a percentage of the total amount distilled he obtained a series of 

 constants for each alcohol which served to identify the particular alcohol. 



As the original method outlined by Duclaux does not give concordant 

 results with different workers, a large amount of experimental work has been 

 carried out to remedy the discrepancies observed. It has been shown that the 

 loss of heat from the exposed flask and still-head, by convection currents and 

 radiation, leads to irregular results. Various arrangements for preventing 

 this have been used. It is not, however, advisable to keep the exposed flask at 

 a higher temperature than that of the vapour, otherwise errors will be 

 introduced by splashing and by complete evaporation of drops of solution. 

 The best conditions for preventing condensation are obtained by surrounding 

 the flask with a steam jacket. 



The original formula of Duclaux may be expressed thus : — 



da a 



= c ■ 



db a + b' 



' Ann. de Phj'sique et de Chimie, 1815. - Ann, de Physique et de Chimie, 1836. 



3 Phil, Mag,, 1855, 9, 4. i Comptes rendus, 18G3, 57, 430, 985. 



5 Ann, inst, Past,, 1895, is, 575, » E. Guillaume, E,P,, 5194, 1902, 



