76 ODOROGRAPHIA. 
Its boiling-point varies from 183° to 195°. This oil is syste- 
matically adulterated on a large scale, and is rarely sent into the 
market pure. The adulterants are oil of turpentine, petroleum, 
essential oil obtained from the leaves, an inferior oil distilled 
from the residue of the fruit which has passed through the 
écuelle process, oil of sweet orange, and oil of lemon. 
The admixture of oil of orange and of oil of lemon at once 
lowers the sp. gr., and augments the optical activity, as will be 
seen by the following figures :— 
Average sp. gr. Optical rotation in 
at 15° C. 100 mm. tube. 
Pure oil of Bergamot, expressed. 0°881 to0°888 
ti ee ariel GbE } Melisa oe 
Pureoil of Sweet Orange,distilled 0°849to0°855 +97°-4to +97°°32 
Pure oil of Lemon, expressed . 0°857t00°863 +40°1to +62° 
55 ss distilled. . 0°856 +66°°2 
One part of pure oil of bergamot forms a clear solution at 20° C. 
with half a part of 90 per cent. (vol.) alcohol, and is not rendered 
turbid by the further addition of alcohol of the same strength ; 
whereas the oils of sweet orange and lemon do not form clear 
solutions under those conditions. The addition of turpentine 
would of course decrease the solubility in alcohol. Additions of 
alcohol or petroleum would lower the sp. gr. 
Additions of fatty oils are recognized by the higher sp. gr. of 
the specimens, and by the residue which they leave when volatilized 
at 100° C. If about half a drachm of oil of bergamot is warmed 
on a watch-glass to 100° C., until the odour has completely dis- 
appeared, there is left behind a green homogeneous residue of 
ointment-like consistency, which in genuine oil amounts to about 
6 per cent. In the presence of fatty oil the residue on volatilization 
is increased, and has a different consistency ; it presents the ap- 
pearance of a green thick layer on the inner surface of the glass 
with a supernatant oily yellow liquid. Upon the data of these 
experiments, the sp. gr. of oil of bergamot should not be under 
0°873, and the optical rotation (in 100 mm.) not over +20. The 
oil must be clearly soluble in 4 part 90 °/, (vol.) alcohol, and the 
solution should not become turbid on the further addition of 
alcohol of equal strength. The residue on volatilization should be 
