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 renresentative of the main groups of commercial oils.

(a) Oil Of E. Australiana. (First hour oil.)

At 22.5° C.

=

1.4610

Mean alteration for each degree, approximately 0.00047.

35.5° C.

=

1.4550

33.0° C.

=

1.4561

32.0° C.

=

1.4566

31.0° C.

=

1.4571

30.0° C.

=

1.4575

(b) Oil Of E. Polybractea

At 22.5° C.

=

1.4572

Mean alteration for each degree, approximately 0.00047.

42.0° C.

=

1.4481

40.0° C.

=

1.4491

30.0° C.

=

1.4537

(c) Oil Of E. Dives

At 20.0° C.

=

1.4793

Mean alteration for each degree, approximately 0.00047.

39.0° C.

=

1.4706

37.0° C.

=

1.47I3

34.0° C.

=

1.4727

31.0° C.

=

1.4741

The above results indicate that 0.00047 is the mean alteration in refractive index for each degree of temperature for ordinary Eucalyptus oils, and this correction has been employed in this work for standardising the oils at 200 C.