354 



was taken to represent an oil rich in cineol, and a commercial sample of the 

 " Narrow-leaf Peppermint " to represent an oil containing much terpene, and only 

 about 30 per cent, of cineol. The laboratory temperature of the crude oil of 

 E. Smithii was 15-5 C., and the determinations made with it gave the following 

 results : 



At 15-5 C. specific gravity = 0-9197 



18-0 C. ,, - 0-9177 theory requires 0-91783 



21-0 C. = 0-9154 0-91558 



25-0 C. = 0-9125 0-91258 



28-5 C. = 0-9097 0-90995 



The oil from the "Narrow-leaf Peppermint " had a temperature of 16 C., 

 and gave the following results : 



At 16-0 C. specific gravity = 0-8960. 



18-0 C. ,, = 0-8943 -- theory requires 0-8945 



20-0 C. ,, = 0-8929 ,, 0-8930 



22-0 C. , = 0-8911 ,, 0-8915 



27-5 C. = 0-8874 0-8874 



It is thus seen that the difference 0-00075 for each degree of temperature 

 may be safely used for corrections of specific gravity for all Eucalyptus oils under 

 ordinary conditions, and it has been used for the needed corrections in this work. 

 If a standard for specific gravity of Eucalyptus oil be insisted upon, it is necessary 

 that it be stated at a uniform temperature, and 15 C. has been chosen as probably 

 the most useful for the purpose, although, as can be readily seen, any other con- 

 venient temperature would suit just as well. 



For the purposes of the distiller, or those dealing in Eucalyptus oils, a 

 hydrometer standardised for liquids lighter than water might be employed, the 

 temperatures being taken with a centigrade thermometer. The necessary correc- 

 tions for 15 C. could then readily be calculated as shown above. 



The Alteration in the Refractive Index of Ordinary 



Eucalyptus Oils under the Influence of 



Changes of Temperature. 



THE apparatus employed was a Zeiss-Abbe Refractometer with heatable 

 prisms, and water at the stated temperatures was run through the machine for one 

 half hour before final reading. The three species chosen may be considered as 

 representative of the main groups of commercial oils. 



(a) OIL OF E. AUSTRALIAN A. (First hour oil.) 

 At 22-5 C. = 1-4610 \ 



oo!x r' I Mean alteration for each 



2-0 C 1-4566 } degree, approximately 



** " **-} r\*r\f~\r\ A <*7 



31-0 C. = 1-4571 47 ' 

 30-0 C. = 1-4575 / 



