355 

 OIL OF E. POLYBRACTIiA. 



At 22-5 C. = 1-4572"! n/r 



Mean alteration for each 

 30-0 C. = 1-4537 J 



*- i \J tJ / J 



42-0 C. = 1-4481 , 



40-0 C. = 1-4491 f degree, approximately 



(c) OIL OF . DIVES. 

 At 20-0 C. 1-4793") 



39-0 C. = 1-4706 Mean alteration for each 



37-0 C. = 1-4713 \- degree, approximately 

 34-0 C. 1-4727 j 0-00047. 

 31-0 C. 1-4741 J 



The above results indicate that 0-00047 ls the mean alteration in refractive 

 index for each degree of temperature for ordinary Eucalyptus oils, and this 

 correction has been employed in this work for standardising the oils at 20 C. 



Eucalyptus Oils and their Constituents. 



THE constituents detected in Eucalyptus oils now number about forty. 

 Many of them, however, are identical with similar substances occurring in 

 other essential oils, and are thus obtainable from other sources, although, with 

 several of them, much less advantageously. 



The following list includes practically all the constituents so far deter- 

 mined, many of which have been brought to light during these researches. They 

 are found in the oils of the different Eucalypts in varying quantity, occurring 

 more abundantly in some species than in others. It is now known, however, 

 from which investigated species the desired constituents can be most readily 

 obtained, and in the greatest quantity, particularly as those characteristic of 

 specific oils are comparatively constant. 



Although the main constituents in the several oils have been determined, 

 yet, in many cases, it is difficult to say with certainty that all have been 

 detected, and it is possible that some do occur in small amounts in the oils of 

 species in which they have not, so far, been found. 



During the last twenty-five years, however, much work has been done 

 upon the products of the Eucalypts, and our knowledge concerning the 

 constitution of their oils is now such that it has been possible to evolve some 

 order with the several members of this extensive genus. 



EARLIER INVESTIGATIONS. 



The first investigation of a Eucalyptus oil was undertaken by M. Cloez 

 (Compt. Rend., 1870, p. 687) upon the oil of E. globulus. Trees of this species of 

 Eucalyptus had for some years previously been successfully cultivated in many 

 parts of Europe, although the young shoots of the trees grown at Paris did not 

 withstand the frost, and it was due to this circumstance that Cloez was led 

 to investigate the essential oil obtainable from the leaves. It was from this 



