'V^'*"'*" '"'^;,, 



[ 131 ] ( MAR' 5 1921 



^^*l»a«l jg-os *■" 



XII. 



NOTES ON SOME APPLICATIONS OF THE METHOD OF 

 DISTILLATION IN STEAM. 



By JOSEPH EEILLY, M.A., D.Sc, F.E.C.Sc.L, 



AND 



WILFEED J. HIGKINBOTTOM, B.Sc. 



[COMMONICATED BY DU. F. E. HACKETT, jM.A.] 

 [Read Apeii, 2G. Published Ootobeu 11, 1920.] 



Synopsis. — Distillation of dilute solutions; Applications. The limitations and 

 possibilities of the distillation method for determining molecular structure are dis- 

 cussed. A consideration of the distillation constants of a number of compounds 

 shows that, although tlie molecular structure may be inferred in certain cases, this 

 method cannot be applied generally without the support of further evidence. 



Determination of changes in state of molecular ac/gregation. The distillation 

 constant is deduced from Nernst's law of distribution ; consequently any alteration 

 in the state of molecular aggregation during distillation will alter the distillation 

 constant. A scheme has been proposed by which it is possible to follow any change 

 in the solute occurring in solutions the concentrations of which difler widely. 



A method has also been devised to dift'erentiate butter-fat from other fats 

 containing a comparatively high proportion of volatile acids. It is based on the 

 presence of butyric acid in butter-fat, while this acid does not occur in appreciable 

 amounts in other fats of the types examined. 



The distillation constants of the lower fatty acids containing a normal chain 

 rise in an approximately regular manner with increasing molecular weight. 

 With acids in which a branched chain occurs the distillation constants are 

 higher than those containing a normal chain. They correspond approximately 

 with the distillation constants of the next higher member in the series of 

 normal compounds.^ These facts suggest that the regularity may be general. 

 The determinations of the distillation constants of the lower alipliatie alcohols 

 showed that in this series there was also a parallel between the distillation 

 constant and the molecular weight. Furthermore, the distillation constants 

 of isomers were higher if the chain of carbon atoms was not a normal one. 



It appears, therefore, in the homologous series of saturated aliphatic 

 alcohols and acids that the distillation constant of the substance may be 

 deduced if the molecular configuration of the acid and its molecular weight 

 are known. 



' Reilly and Hickinbottom, Proc. Royal Dub. Sec, xv, 37, 51.3. 



SCIENT. PROC. R.D.S., VOL. XVI., NO. XII. S 



