Essential Oils oj Australian Myvtaceae. L53 



Part IT. — 77/'' Calculation of the Oil Content of Foliage from 

 Measurements <>/' the Number and Size of the Oil Glands. 



By A. E. DAWKINS, B.Sc. 



The collection and distillation of oil-containing materials is often 

 a matter involving much labour. Since therefore the oil is well 

 known to occur in the case of many species in small, well-defined 

 oil-dots or oil-glands, it was thought that it might be possible to 

 forecast the oil content of any particular species by making a few 

 measurements of the size and number of the oil-dots, weight of leaf, 

 etc. 



Let -^ be the average volume of the glands in c.c, 

 6 



n the number per sq. cm., 



i/ the specific gravity of the oil, 



w the weight of leaf per sq. cm., 



p the ratio of the weight of leaves to the total weight of leaves 



and stalks as usually taken for distillation. 



Then assuming that the oil glands are spherical the percentage yield 



of oil will be 



52Apd?ng 



w 



The measurement of the size and number of the oil-glands can 

 readily be accomplished microscopically, using an eye-piece pro- 

 vided with suitable micrometer scales. 1 



The specific gravity of the oil can of course only be determined 

 when a sample of the oil is available. For most oils, however, a 

 sufficient approximation will be attained by giving g the value 

 of 0.!). 



The value p is determined by stripping one or two typical branch- 

 lets, and weighing the leaves and the stalks separately. 



The accuracy of this method may be judged from the following 

 series of measurements on several species of oil-bearing plants which 

 we have recently had the opportunity of distilling. 



1 A convenient scale for counting the number of oil-dots can be easily made by ruling 

 of squares on a thin sheet of mica. 



