Physical Chemistry of Essential Oils. 151 



terpreling the equations so obtained, makes this rather a waste 

 of labour, it suffices at present, where properties are atomic (e.g., 

 Refractivity) to use the first of these equations, while for those 

 where the molecular influence is introduced (e.g., Density) the 

 second formula, giving what is known as the Molar Fraction, 

 serves as some correction. 



Hence, these two methods of calculation are all that have been 

 employed in the present research. 



7'/(e System l-pinene — d-pinene. 



In considering the purity of the terpenes mentioned, it must be 

 remembered that where suitable solid derivatives, from which a 

 terpene may be regenerated in quantity, are wanting, the only 

 means of purification is repeatedly to distil under diminished pres- 

 sure. The product, of course, may be parti)- racemised, or may 

 contain some of its optical isomers. For tliis reason the physical 

 properties of two optical isomers, such as d- and l-pinene, are not 

 numerically identical, a point which is of little significance in the 

 present research, since these well-fractionated terpenes are " pure" 

 from the practical point of view. Indeed, the l-pinene of rotation 

 — 390 is almost free from I'acemate, while the + 25° rotation of 

 the d-pinene is quite as high as other workers have usually, ob- 

 tained. In the mixture of these two isomers, from our stand- 

 point, the simplest case, we should anticipate no constitutive ef- 

 fects, and indeed, the observed properties of the mixtures a<gree 

 excellently with those calculated by (1), the simple mixture for- 

 mula, and the slight deviations whicli occur n\ay be taken as indi- 

 cative of the magnitude of the exijerimental error in the other 

 systems as well. 



The pineries were obtained from oils from Eucalyptus dextro 

 pinea and E. laevopinea, which were generously given us by Mr. 

 Smith, of the Sydney Technological Museum. He has w-orked out 

 their composition, and his results we have confirmed, and by dis- 

 tilling iii a rod and disk apparatus at 10 mm. pressure we have 

 obtained pinene fractions with the following properties : — 



At25°C. d-Pinene. 1-Pinene. 



Rotation ... +25.40° -39.64° 



Refractive Index L4640 1.4639 



Density ... .8604 .8646 



