During this research it has been demonstrated that both lævo- and dextrorotatory pinenes occur in Eucalyptus oils in varying quantities, from the small amount found in the richer cineol yielding species, to those oils consisting almost entirely of either dextro- or lævo-rotatory pinene. From the leaves of some species an excellent oil of turpentine can be obtained, corresponding to either the American or European varieties, and it thus becomes difficult to determine whether or not a Eucalyptus oil has been sophisticated by the addition of commercial oil of turpentine. If the presence of pinene in quantity were proved, there is still no reason why the oil might not have been derived entirely from Eucalyptus leaves, and we presume that such a product from such a source must be Eucalyptus oil, even if it consists almost entirely of pinene, like those of E. dextropinea, E. lævopinea, E. Wilkinsoniana, and others. As these pinene oils necessarily fail to meet the present requirements of the British or American Pharmacopoeias for Eucalyptus oils required for pharmaceutical purposes, they should be exploited in the direction of supplying commercial requirements for turpentine. Whether certain of the non-cineol-bearing Eucalyptus oils, or those containing but a small amount of that constituent, will eventually be used for medicinal purposes is a matter that has yet to be decided.

It has been shown in a previous article that the almost transverse parallel venation of Eucalyptus leaves, like those of E. calophylla, E. corymbosa, E. saligna, E. botryoides, etc, is an indication of the presence of a predominance of pinene in their oils, and it was the recognition of this constantly occurring constituent in this group that enabled this peculiarity in the oils of species with this leaf venation to be noted. In all Eucalyptus oils that are rich in cineol, pinene occurs, although in some of them it is present in only small amount. From oils of numerous species it has been isolated and its identity proved by chemical methods, as shown with the pinene which occurs in the oils of E. saligna, E. robusta, etc. From the results thus obtained it is apparent that the pinenes obtainable from the oils of the Genus Eucalyptus (N.O. Myrtaceae) are chemically identical with those obtainable from the Genus Pinus (N.O. Coniferae.). In the oils of Eucalyptus species that connect the large group of "Boxes" with the "Gums," as E. conica, E. Bosistoana, E. quadrangulata, E. propinqua, and others, the presence of pinene is pronounced, as might be expected from their closer proximity to the pinene group, and consequently these oils are on the border line which separates oils capable of passing the present standard, from those lower in this respect. The oils of the species belonging to this group all contain a fair amount of cineol, and the terpene phellandrene is entirely absent, or at the most only present in traces in rare instances. The predominant pinene in these oils is invariably the dextrorotatory one, and this is also true for oils belonging to the richer cineol class, but often the pinene of opposite rotation is present in such amount as to cause the oil to be almost inactive, and yet for it to be poor in cineol; for this reason the value of the test of optical rotation for Eucalyptus oils is limited in value, as it may be misleading. If the pinene found in Eucalyptus oils always rotated the ray in the same direction the test would be of greater value, but this is not the case, and in this respect the pinene differs from the phellandrene which appears always to be lævo-rotatory in Eucalyptus oils.

By the discovery of the pinene yielding oils, such as those of E. dextropinea and E. lævopinea, it has been possible to investigate somewhat completely the properties of the Eucalyptus pinenes. (See paper Proc. Roy. Soc, N.S.W. XXXII, 195) From this investigation it was possible to show the differences, chemically, between E. lævopinea and E. macrorhyncha, because the oil of the former does not contain eudesmol and other constituents which occur in the oil of E. macrorhyncha. These chemical differences are supported in another direction, as the leaves of E. lævopinea do not contain myrticolorin, which dye-material occurs in such abundance in the leaves of E. macrorhyncha. The lævo-rotatory pinene in the oil of E. phlebophylla is also sufficient to discriminate that species from E. coreacea, although morphologically these two species show great similarity. By similar means it is easy to determine the difference between E. dextropinea and E. pilularis, as the oil of the latter species is always strongly lævo-rotatory in its lower boiling portion, and also contains phellandrene, which terpene is absent in the oil of E. dextropinea.

The material for the original investigation was obtained from (1) Barber's Creek (now Tallong); (2) Currawang Creek (near Braidwood); and (3) Nullo Mountain (near Rylstone), all in New South Wales. The material from Barber's Creek, from which the dextro-rotatory pinene was obtained, was botanically identical with that of the species from Currawang Creek, and the results of the determinations of the oils from those localities (over 100 miles apart) indicate that the oils had been distilled from similar material, again emphasising the fact of the comparative constancy of chemical constituents in the oils of identical species. The Rylstone material was quite distinct, and gave an oil also consisting of pinene, but having even a greater rotation to the left than had the pinene of the other species to the right. It was a piece of good fortune to have obtained the material of E. dextropinea and E. lævopinea at the same time, so that their pinenes could be worked out together.

The presence of pinene in the oil from E. globulus was detected some time ago. M. Cloez, in 1870,* published the first detailed observations relative to the oil of E. globulus. This research is now of historic interest, from the fact that he obtained a hydrocarbon C10Hl6 boiling at 1650 C, by distilling his so-called eucalyptol with P2O5. This terpene he called eucalyptene. Afterwards Faust and Homeyerf gave the same name to a terpene from Eucalyptus oil, which, according to them, was a terebenthene, being readily polymerised by sulphuric acid. Later, Wallach and Gildemeister ‡ stated that the hydrocarbon, eucalyptene, from E. globulus, is identical with dextropinene.