340 THE CHEMISTKY OF ESSENTIAL OILS
that of Cocking.^1 It is based on the formation of a compound of ortho-
cresol and eucalyptol, which was first obtained by Bellucci and Grassi.
2
This compound melts, according to Cocking, at 55
- 2°, and he attempts
to determine eucalyptol by noting the freezing-point of a mixture of $
grams of the oil and 2
1 grams of ortho-cresol. His experiments were
carried out with a mixture of pure eucalyptol and terebene, and with a
mixture of pure eucalyptol and oil of copaiba. But as eucalyptus oil
contains various other bodies, and further, since ortho-cresol freezes at
about 30° so that a varying mixture of the compound (cresineol), melting
at 55
2°, and ortho-cresol melting at 30°, is under consideration, it is-
obvious that such an empirical method cannot be relied on. Bennett
and Salamon
3
have examined this method, and consider that it is only
useful as a rapid method in a works for grading eucalyptus oils all
derived from the same variety of Eucalyptus.
Eucalyptus oil is produced principally in Australia and Tasmania,
which practically supply the world's requirements. Small amounts
are distilled elsewhere, as in Algeria, the South of France, Italy, Por-
tugal, the Transvaal, Mexico, etc., etc., but commercially they are of
little importance.
The systematic examination of the Eucalyptus oils of Australasia i&
almost entirely due to E. T. Baker and H. G. Smith, of the Technological
Museum, Sydney, N.S.W., and the greater part of the details here re-
corded is acknowledged to their numerous valuable publications.
From the purely commercial point of view the following notes 4 will
indicate the direction in which distillation of the oil for the markets is.
tending:—
Economically the industry is becoming of some importance to
Australia. Most of the old species which used to do duty for oil pro-
duction have been replaced by others economically better in every way,
and the oil of Eucalyptus globulus only remains largely as a name, its.
pride of place being taken by the products of other species. Eucalyptus
dumosa, Eucalyptus oleosa, etc., have also fallen back as oil-producing
plants. The species now mostly worked for pharmaceutical oils in New
South Wales and Victoria are Eucalyptus polybractea, the " Silver-leaf
Mallee" of Victoria and the "Blue Mallee" of New South Wales;
Eucalyptus Smithii, which is a good yielding species and perhaps the
best of all eucalyptus oils for pharmaceutical purposes; and a recent
species, Eucalyptus Australians, which produces an excellent oil, and
no doubt will be much heard of in the future. This oil gave 79*5 per
cent, eucalyptol by the resorcinol method. It does not contain objection-
able volatile aldehydes except in traces, nor does it contain aromadendral.
In Research on the Eucalypts this species is referred to under Euca-
lyptus amygdalina, and it was there shown that if fractionally separated
during the original distillation the first-hour oil was richer in eucalyptol.
This discovery remained unused for over twelve years, but is now being
employed commercially in the Nerrigundah and Yourie districts of New
South Wales, where the phellandrene has been replaced by eucalyptol.
There are a few compounds which have been described as occurring in
eucalyptus oils, which are, so far as is known, not found in other oils.
]
P. and E.O.R., 1920, 282.
2
3 Gazz. Chim. ItaL, 43, II., 712.
4 P. and E.O.R., 1920, 302.
Private communication from Mr. H. G. Smith to the author.