As considerable differences occur in the specific gravities of Eucalyptus oils at various temperatures, it was necessary that some standard be established whereby the several oils might be brought into uniformity. In Sydney the temperature during the summer months is usually high, and the ordinary temperature in the laboratory at that period is often 260 C. To reduce the oils to a standard temperature by artificial means was out of the question. It was decided, therefore, to determine the increase or decrease for varying degrees of temperature within ordinary working limits. A special pyknometer was constructed with a fine capillary, standardised at 150 C, and the specific gravity determined at the temperatures given below, the figures being restricted to four places of decimals. The following results were obtained, experimentally, with a Eucalyptus oil rich in cincol, and having a specific gravity 0.9156 at 150 C.: -

From these results it is seen that 0.00075 is practically the increase between 10° and 150 C, and that the same figures represent the decrease between 150 and 260 C. Taking the standard specific gravity at 150 C, and calculating either upwards or downwards, as the case may be, the following figures are obtained, and it is seen that they differ but little from those determined experimentally: -

For all practical purposes, therefore, 0.00075 may be taken as the increase or decrease, as the case may be, for Eucalyptus oils within the range of ordinary temperatures in the laboratory, and in this way the specific gravity at 150 C. may be calculated for any Eucalyptus oil, providing the apparatus had been standardised for 150 C. These figures have been repeatedly checked during this research, and have been found to agree very well for all those Eucalyptus oils so tested. It is thus easy to determine the specific gravity of a Eucalyptus oil for 150 C. If, for instance, the specific gravity was found to be 0.9095 and the temperature 210 C, then by adding 0.0045 we obtain 0.9140 as the corrected specific gravity for the particular sample at 150 C.

Taking advantage of the colder weather in June, determinations were made with two Eucalyptus oils belonging to different classes, in order to test the accuracy of the differences recorded above. A specific gravity bottle holding 50 grams of water was employed for the purpose, and the temperature of the oil increased to the desired degree by artificial means. The crude oil of E. Smithii 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: -

The oil from the " Narrow-leaf Peppermint " had a temperature of 160 C, and gave the following results: -

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 convenient 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 corrections for 15° C. could then readily be calculated as shown above.