THE MISCIBILITY TEST FOR EUCALYPTUS OILS. 109 
THK MISOIBILITY THST FOR KUCALYPTUS OILS. 
By CHARLES EK. FAWSITT, D.Sc., Ph.D., and 
CHRISTIAN H. FISCHER. 
[Read before the Royal Society of N. S. Wales, August 2, 1922. | 
THE technique of Eucalyptus oil testing has been well 
developed by H. G..Smith.' Among the tests for these 
oils the miscibility test has been found useful. The method 
hitherto used consists in a direct measurement of the 
amount of aqueous alcohol required to give a clear solution 
with a given volume of oil. It is possible, however, to: 
carry out the test in a different way, and it occurred to us 
that these oils might be suitably tested in the same manner 
as the fixed oils and fats. In this method the oil (A) is 
mixed in definite proportions witha suitable liquid (B), say 
an aqueous alcohol, giving two layers of liquid at the 
ordinary temperature. The critical solution temperature 
is then determined by heating until only one layer is formed, 
and then allowing to cool until a cloudiness develops. The 
critical solution temperature(C.S.T.) has been found to alter 
considerably with slight changes in the composition of the 
oil, and so this method of testing the miscibility gives a more: 
sensitive test than the other method in which the volume 
of aqueous alcohol required for complete solution of one 
volume of the oil is determined. 
A method which is too sensitive may have disadvantages. 
however. We have noticed that the changes in composition 
which Eucalyptus oils undergo say by exposure to the air 
or by distillation are liable to cause very marked changes in 

* Baker and Smith, “ Eucalypts and their Essential Oils,’ 2nd Hdition. 
Sydney, 1920. 
