[Proc. Rot. Soc. Victoria, 27 (N.S.), Part II., 1914]. 



Art. XU.— Studies iv the Physical Chemistri/ of Essential Oils. 



Part I. — The Physical Properties of mixtures oj two l^erjiene sub- 

 stances ill relation to those of the constituents. 



BY 



R. BARRY DREW, M.Sc, 



AND 



E. IVAN ROSEN BLUM, M.Sc. 



(Communicated by W. Hebei- Green). 

 [Read 9th July, 1914). 



It is of considerable interest to regard the mixture of organic 

 bodies which is presented to us by an essential oil from a physico- 

 chemical, as well as from the ordinary systematic point of view. 

 We have here a class of mixtures, easily obtainied in quantity, 

 whose constituents are mostly well-known, and of allied structure; 

 conditions v>^hich suggest a novel method of attacking the general 

 theory of solution, and should also give us valuable data, for judg- 

 ing the general composition of an oil from its physical constants 

 — a problem of interest, both from the commercial and from the 

 scientific standpoint. 



As sliowing the questions which meet us here we may cite as an 

 instance two eucalyptus oils from the same species, which yielded 

 the same percentage of phellandrene [a= — 69°] and contained no 

 other optically active substance, whose rotations were as far dis- 

 tinct as —2.30 and — 44o respectively. 



The major portion of an essential oil usually consists of one or 

 more terpenes. These may be considered as simple examples of 

 non-ionising, unassociated solvents, and it will be Avell, therefore, 

 to start our inquiry into essential oil equilibria by the study of 

 these simple substances, adding progressively more complex or more 

 reactive constituents, such as oxygenated derivatives, etc., and 

 essaying to evaluate the new solution factors as they occur. 



An ideal invest ig:at ion, then, would start from the simplest 

 case — a mixture of tw(j terpenes — proceed through increasing com- 

 plexity in the number and nature of the components, and finally 

 reach that complicated equilibrium presented by a natural essen- 

 tial oil, such as that of Eucalyptus globulus. 



