PRESIDENTS ADDRESS—SECTION B. 57 
dextro-rotatory, the other levo-rotatory, in its effect on polarised 
light. Thus he has found two pinenes, two phellandrenes, and 
two limonenes, the only difference between the two members 
of each pair being the effect on polarised light just referred to ; 
but each set of two is characterised by the formation of 
derivatives distinct from those of any other two, and also from 
those of other hydrocarbons belonging to the terpene group. In 
the case of the two limonenes, however, there is a_ special 
and most peculiar characteristic. When simply mixed in equal 
proportions these two hydrocarbons unite directly to form another 
hydrocarbon, called dipentene, which is very different from either 
of the originals. This reminds one, of course, of the relation- 
ships between dextro and levo tartaric and racemic acids. There 
is, however, this distinction, that dipentene differs much more 
widely from the limonenes than does racemic acid from the tartaric 
acids, and moreover, there seems to be at present no known means 
of regenerating the original hydrocarbons from the product. My 
object in referring to these researches, however, is to point out 
that the oil of Eucalyptus amygdalina has supplied one of the 
missing links in the chain of discovery, Wallach having found 
that it contains levo-rotatory phellandrene (this is at present 
the only source of this hydrocarbon), the dextro-rotatory variety 
occurring in the oil of Phellandrium aquaticum, and also in the 
oil of the bitter fennel in the south of France. The oil of 
Eucalyptus globulus, on the other hand, contains no phellandrene, 
but dextro-rotatory pinene, the two varieties of which are found in 
turpentines from different sources. The common constituent of 
both these oils is an oxygen containing liquid called cineol of 
formula CyoH,,0, and boiling point about 176° C, which is the 
chief constituent of oil of wormseed, oil of cajeput, and is also 
found in oil of rosemary and other essential oils. This substance 
is identical with the so-called ‘ Eucalyptol,” about the presence 
or absence of which in oils produced by different tirms there has, 
I understand, been a good deal of dispute. Wallach himself had 
at first some difficulty in isolating this substance from the oil of 
one of these (Eucalyptus amygdalina), apparently owing to the 
presence of some disturbing impurity. The fact that it appears 
to be more easily isolated from the oil of one variety than from 
that of the other may probably have caused the dispute referred 
to; at any rate there can be no doubt whatever of its presence 
in considerable quantities in the oils from both the varieties 
of eucalyptus I have named, and probably it exists in the 
oils from other species also. It is a very interesting fact, 
however, that there should be a considerable differenee 
between the constituents of the oils from these two trees, and 
there are indications of still wider differences between the 
oils from other species. The oil from Lucalyptus Staigeriana, 
for example, according to a report by Messrs. Schimmel and Co., 
