STRINGYBARK TREES AND THEIR ESSENTIAL OILS. 117 



because its specific gravity is only 0*9035 at 18° 0. • (Another re- 

 distillation gave an oil having a specific gravity of 0-9058 at 14° 0.) 

 Although the rectified portion of this oil (E. macrorhyncha) , might 

 be rejected because of its low specific gravity, the crude oil being 

 of high specific gravity, 0-927, might be accepted as indicating an 

 excellent oil. 1 The reason is, that besides the usual residue, this 

 oil contains a large percentage of eudesmol (the stearoptene found 

 in Eucalyptus oil, and discovered by us last year), 2 the fraction 

 distilling between 268° and 289° C, representing 27 per cent, of 

 the original oil having a specific gravity of 0'954 at 18° C. We 

 showed in our paper on the Grey Gum (E. punctata) that the 

 specific gravity of an oil was no criterion as to the amount of 

 eucalyptol contained therein, and we are enabled in this research 

 to further emphasise that fact. It is evident that if the specific 

 gravity 0*910 — 0*930 be insisted upon, some excellent oils 

 would be made to appear of inferior quality while inferior oils 

 would pass the test. We suggest that fixing the test as high as 

 0'910 is both unnecessary and unsatisfactory, and that if it were 

 insisted upon that the oils should contain 50 per cent, of eucalyptol 

 then the specific gravity test might be reduced to 0*90 - 0*925. 

 Another instance of the unreliability of the specific gravity of an 

 Eucalyptus oil to indicate the eucalyptol content, is that the frac- 

 tion of the oil of E. macrorhyncha distilling between 185° and 

 195° C. had a specific gravity of 0911 and contained only 43 per 

 cent, of eucalyptol, much less than in the previous fractions of the 

 same oil, and which had a lower specific gravity. ' 



We have taken this opportunity of drawing attention to the 

 matter of specific gravity of Eucalyptus oils because of its im- 

 portance. We have had our attention directed to this feature, 

 i.e., of specific gravity, during these researches, and it would be a 

 mistake to consider an important oil like that of E. macrorhyncha 

 of inferior quality because it does not come up to requirements 



1 The colour is no objection, as being of an acid character it is readily 

 removed by agitating with potash. 



2 Proc. Roy. Soc. N.S.W. loc. cit. 



