Crystallised eudesmol was first discovered by us in the oil of Eucalyptus piperita, and announced in a paper read before the Royal Society of New South Wales in August, 1897. Later, further work upon this substance was" submitted to the same society, by one of us, in a paper read August, 1899. The name eudesmol was derived from Eudesmia, which had been applied to the genus by Robert Brown.

When first isolated, eudesmol was thought to be an oxide related somewhat in constitution to cineol, but from the work carried out later by Semmler and E. Tobias (Ber. 46, 1913, 2026); and Semmler and F. Risse (Ber. 46, 1913, 2303); it was shown to be a bicyclic sesquiterpene alcohol, and to contain two rings and one double bond. The reaction with bromine in chloroform solution also shows it to be unsaturated.

During the last twenty years we have obtained much information concerning eudesmol and its peculiarities, and have isolated this interesting substance from the oils of numerous species of Eucalyptus.

There appears to be little doubt but that eudesmol occurs in Eucalyptus oils in both the liquid and crystallised conditions, although the line of demarcation separating these is evidently slight. It also appears that liquid eudesmol is the more stable form, because in nearly every case the tendency has been for the purified crystallised eudesmol to slowly change its character, until eventually it forms a thick liquid mass, and with one exception all our samples have remained in this condition after settling down. Although this tendency of the separated crystallised eudesmol to revert to the semi-liquid form is so pronounced, yet under some conditions - which at present are not clear - this change has not taken place, and we have in our possession one sample distilled from the oil of

Plate LXXXV.

Eudesmol the Bicyclic Sesquiterpene Alcohol of Euc 268

Illustrating the Unstable Nature of Eudesmol from Eucalyptus Oils, in Three Stages

(For description see page 376.)

E. camphora twenty years ago, and thus separated in the crude condition, which has remained in the crystallised form all that time. In other cases eudesmol prepared from the oil of this species has liquefied after a few months. We also possess one sample of eudesmol separated from the oil of E. Macarthuri, which has remained in the crystallised condition for two years, and at present shows but little signs of alteration, whilst other specimens from the oil of this species, distilled at varying times of the year, have liquefied after a few months, although they had been prepared in exactly the same manner. As shown later it is possible to partly change this liquefied eudesmol back to the crystallised form.

Under natural conditions crystallised eudesmol appears to occur more frequently, and in greater abundance, in the oils of species belonging to the more recent groups in the evolutionary sequence of the genus, as the " Peppermints,"

"Ashes," "Stringybarks," and some of the "Gums." whilst the liquid modification is more pronounced in those members belonging to the earlier groups, E. eximia for instance. It is also worthy of record that, so far, eudesmol has not been found to occur in the oils of species belonging to the typical "Box" group, E. hemiphloia, E. Woollsiana, etc, and with the exception of two species (E. elczophora and E. stricta) not in those of any species which contain one or more members of the cyclic aromatic aldehydes.

Plate lxxxv (page 375) illustrates very well the three different stages which may take place in the physical condition of eudesmol.

Originally the vessel was three parts full of pure crystallised eudesmol, melting at 79-800 C, which had been prepared from the oil of Eucalyptus camphora. After standing a few months the crystallised eudesmol had changed to the liquid condition, and had settled down to the layer shown at the bottom of the bottle. Some months after the formation of this condition, crystals began to grow from the thick liquid mass, and continued to increase until finally the whole assumed the appearance shown in the photograph. No further change has apparently taken place during the last seven -years. The crystals of the third stage which thus appear quite stable, are hair-like in character, quite flexible, semi-transparent, but do not polarise at all well, and in many cases exceed one inch in length. They melted at 79-800 and thus at the same temperature as the original eudesmol. Under the microscope the crystals are seen to be built up by the accumulation of longitudinal filiments, and when crushed can be separated into their component parts, thus showing how loosely they are combined. This is the only instance in which crystals of this character have formed naturally after the eudesmol had liquefied.

Plate LXXXVI.

Eudesmol the Bicyclic Sesquiterpene Alcohol of Euc 269

Eudesmol, recovered from the second stage, or liquid condition, into which the original crystallised eudesmol had passed on keeping.

As previously mentioned, this liquid eudesmol can be changed to the crystallised condition, and this result is well shown by the accompanying illustration. The crystals depicted were regenerated from the wholly liquefied form of eudesmol originally prepared from the oil of E. Macarthuri.

The liquefied eudesmol was dissolved in ether, and the resinous acid portion, which had formed during the alteration, shaken out by aqueous potassium hydrate. The amount of acid substances thus removed was equal to 8 per cent. The ether was then evaporated from the liquid eudesmol, which at this stage showed no signs of crystallisation, and the residue sublimed on the water bath. A considerable portion was thus obtained in the crystallised condition, as depicted in the illustration. Under the microscope these crystals were seen to be identical with those formed naturally, and although less stout, to have been built up in a similar manner.