It has been shown (see tabulated list) that esters, either in large or small amounts, occur in all Eucalyptus oils, varying from 60 to 77 per cent, of geranyl acetate, in the oil of E. Macarthuri, to very minute quantities in such oils as E. dives, E. radiata, E. Smithii, etc. The amyl-ester of eudesmic acid occurs in some quantity in the oil of E. aggregata, and in the oil of E. carnea an acetic acid ester has been determined (see under that species). Butyl-butyrate is also a frequent ester in Eucalyptus oils of a certain class. The constituents of these four esters did not, however, explain the presence of a volatile acid resembling valeric acid, which constituent had often been detected in the oils of several species, and in those of E. saligna var. pallidivalvis, E. cinerea, E. gonio-calyx, E. Maideni, E. botryoides, etc, the presence of a considerable amount of ester had been determined. The product of E. saligna var. pallidivalvis appeared to be the best for the determination of this valeric acid ester, because the acid was so well demonstrated, and the amount of ester in the oil comparatively large. 200 c.c. of the oil of this species, collected at Lismore, New South Wales, in May, 1898, were boiled for some hours with aqueous potash, under a reflex condenser. The oil was afterwards separated, and the alkaline portion distilled; nothing came over below 100° C, so that alcohols boiling below that temperature were absent. The precipitate which had formed was filtered off and ignited; it was found to consist almost entirely of ferric oxide, which had evidently been derived from the iron digesters; and this acting on the phenols gave the deep red colour to the crude oil. The filtered solution, when evaporated to a small bulk, separated a dark substance which became semi-solid on cooling. On acidifying this with sulphuric acid, an acid was obtained which, on purification, gave crystals differing in no respect from eudesmic acid, previously obtained from the oil of E. aggregata. Amyl-eudesmate thus occurs in the oil of this species, and is probably a frequent constituent in Eucalyptus oils. The aqueous filtrate from the solid acid separated as above, was acidified with sulphuric acid, and repeatedly distilled until the whole of the volatile acids had been obtained. The distillate which had a strong odour of valeric acid, was neutralised with soda, and evaporated to dryness; the crystalline salt thus obtained, was decomposed with sulphuric acid, when an oily acid separated, having the objectionable odour of iso-valeric acid. The separated acids were recovered by agitating with ether and the ether removed. The product had the odour of, and gave the reaction for valeric acid, agreeing in this respect with those obtained with a sample of pure iso-valeric acid. The molecular value of the acid or acids thus obtained was determined in the ordinary way from the barium salt; 0.3328 gram. of the barium salt gave 0.2327 gram. of barium sulphate when ignited with sulphuric acid, equal to 69.92 per cent. BaSO4 or 41.08 per cent. of barium. Ba2C5H9O2 contains 40.45 per cent. of barium, and gives 68.73 per cent. of barium sulphate. It is thus apparent that the volatile acids occurring as an ester in some Eucalyptus oils, and particularly in the oil of E. saligna var, pallidavalvis is principally valeric acid, and most probably the iso-form.

The oil recovered after saponification with aqueous potash was then distilled, in order to determine, if possible, what alcohols were present. It was certain that one of these was amyl alcohol, derived from the ester of eudesmic acid, and on acetylating the portion distilling between 1300 C. and 1500 C. amyl acetate was readily obtained. Below 1300 C. only a few drops came over; but between 130° C. and 1500 C. 7 per cent. distilled, while between 155° C. and 1600 C. 66 per cent. distilled; this fraction was almost entirely dextropinene, and had specific gravity 0.868 at 150 C. The specific gravity of the fraction 1300 C. and 1500 C. was 0.850 at 150 C. What the alcohol is, if any, in the oil of this species besides amyl, we have not so far been able to determine, and further research is necessary to decide this question. Until this point is settled it would be difficult to calculate the actual percentage of ester in many Eucalyptus oils, particularly in cases when both the acetic acid ester and the valeric acid ester occur together. When the saponified oil was acetylated the saponification number was found to be 54.04, which, calculated as CH3COOC5H11 gives 12.55 per cent. The acetylated oil had a marked odour of amyl-acetate which was not masked by the terpenes present. That some free alcohol was also present in the oil of this species was shown by the saponification number of the original crude oil, including that of the free acid, being only 41.76.

It is, perhaps, worthy of remark that Eucalyptus oils which contain the valeric acid ester also show the presence of the corresponding aldehyde, and that crude cineol-pinene oils which have the most objectionable odour of volatile aldehydes, usually contain the valeric acid ester. From the results of these investigations it appears that the valeric acid in Eucalyptus oils occurs mostly as an ester and not in the free condition, because the free acid in Eucalyptus oils is acetic. (See the article dealing with the free volatile acid of Eucalyptus oils.)