The foregoing may be summarised as follows: -

1. That an accurate method for determining the amount of cineol in Eucalyptus oils under all conditions has yet to be discovered.

2. That no one present method is applicable in all cases.

3. That arsenic acid is less advantageous for the purpose than phosphoric acid.

4. That the use of petroleum ether in connection with phosphoric acid is an advantage if the process be carried out in the manner directed.

5. That the richest cineol Eucalyptus oils should be diluted with non-cineol containing terpenes, corrections being made for the dilution.

6. That the resorcinol method is only applicable with certain oils, such as those containing cineol in the greatest amount, or those in which it occurs in too small quantity to be determined with phosphoric acid. Constituents absorbable by resorcinol, other than cineol, are too abundant in Eucalyptus oils for this method to be of general application, although it has certain advantages for experimental work.

7. The process recommended for the purpose, in Australia particularly, is the rapid phosphoric acid method using petroleum ether in order to remove the non-cineol bodies before pressing.

Geraniol and its Acetic Acid Ester Occurring in Eucalyptus Oils.

The alcohol geraniol and its acetic acid ester are frequently occurring constituents in Australian plants, and in the oils of no less than three species does geranyl-acetate occur to the extent of 60 per cent. or over.

The coniferous tree Callitris Tasmanica, the "Oyster Bay Pine" of Tasmania, yields an oil of this character (Research on the Pines of Australia, Baker and Smith, Technical Education Series, N.S.W., No. 16, page 240), while the others belong to the Myrtaces. One of these is Darwinia fascicularis, a shrub growing around the shores of Port Jackson, New South Wales (Proc. Roy. Soc, N.S.W., December, 1899), while the other, Eucalyptus Macarthuri, is a fine foliaceous tree which grows plentifully in the Wingello and neighbouring districts of New South Wales (Proc. Roy. Soc, N.S.W., November, 1900). In lesser amounts this ester occurs in the oils of numerous species of Eucalyptus.

Geranyl-acetate is also the chief ester in the oils of the Angophoras, a genus closely related to Eucalyptus, and perhaps the older. If this is so then most likely the ester passed into Eucalyptus through Angophora, and as it occurs also in the oils of many of the "Peppermints" it probably runs through the whole genus Eucalyptus, although in some of the oils the amount is very small.

Eucalyptus Macarthuri, similarly with other species of Eucalyptus, shows a comparative constancy in oil products. That this is so has been well demonstrated from the results of much work carried out with this species during recent years. We have recorded some of this data under the species in this publication.

One distinguishing feature with the oil of Eucalyptus Macarthuri is the presence of crystallised eudesmol, a subtsance absent in the oils of both Darwinia and Callitris.

The following constants are those for a fair sample of the crude oil of Eucalyptus Macarthuri: -

In the course of these researches it was found that the acetic acid ester of geraniol was entirely saponified in the cold by two hours' contact with alcoholic potash, the reaction being of considerable quantitative value. In both the bark and leaf oils of Eucalyptus Macarthuri the naturally formed ester varies between 60 and 77 per cent., but this variation represents largely the oscillation between the ester and the free geraniol, consequently when the free alcohol is pronounced the ester is less, and when the ester is at a maximum the minimum amount of free geraniol is present. In no instance has less than 60 per cent. of geranyl-acetate been found in the oil of this species of Eucalyptus, although it sometimes reaches as high as 77 per cent. In one sample containing 74.9 per cent. ester, only 6 per cent. of free geraniol was present. Another sample gave 65.8 per cent. ester, and 11.5 per cent, free alcohol. Other determinations were in agreement, and in all the analyses we have so far been able to make with the oil of this Eucalypt the ratio combined geraniol/total geraniol ranged between 80-100 and 90-100.

With both the New South Wales and Tasmanian samples of the oil of Callitris Tasmanica, the combined geraniol/total geraniol was 78-100.

It has been found by Charabot and Hebert in their experiments "on the mechanism of esterification in plants," that the maximum ester content obtained with geraniol and acetic acid, by their methods of working, was reached when the combined geraniol/total geraniol equalled 67-100; but as shown above, this naturally formed ester in the oils of these two Australian plants does not fall below 78-100; and occasionally reaches 90-100. It is thus evident that the method whereby this large amount of geranyl-acetate is formed naturally, is not yet known.

The abnormal leaves which spring from the stumps of the felled trees of E. Macarthuri not only give a greater yield of oil, but the oil itself also contains a greater percentage of ester than does that from old leaves. A sample, distilled from such, collected at Paddy's River, New South Wales, in March, contained 77'5 Per cent, of ester saponified in the cold with two hours' contact.

The oil from seedlings has also a high ester content, exceeding, in some cases, 70 per cent., while in that from the very early shoots the ester was 75 per cent.

It is perhaps worthy of note that a predominance of this ester should be found in the oil from the youngest material, and that the trend of the mechanism of ester formation should show such activity so early in the life history of the plant.

It is characteristic, however, of the Eucalypts generally, for the perfumery products peculiar to the species to be formed very early in the plant, and in the very young seedling leaves the chief oil constituent of the species is in evidence.