Free acids usually occur in Eucalyptus oils, and in some of them it is present in sufficient amount to attack the iron of the still when the leaves are undergoing the process of distillation. The reason why such a large number of crude Eucalyptus oils have a reddish colour when distilled from iron vessels is because the free acid has dissolved away a portion of the metallic fittings of the still, the iron thus removed reacting upon the phenol tasmanol present in the oil. That this is so, is demonstrated by the fact that the majority of these deeply coloured oils can be rendered almost colourless by agitating with a solution of aqueous potash or soda, and if the coloured precipitate thus obtained be tested it will be found to consist largely of ferric oxide, providing of course, that copper fittings had hot been used in the construction of the still, when the product would be tinted green. Under E. cinerea it has been shown that much copper was dissolved away during distillation, as copper still-heads had been employed. It has now become customary in Australia to discard copper fittings to the stills for Eucalyptus oil distillation.

The pinene-cineol oils usually contain the greatest amount of free acid, but with those of the more pronounced phellandrene-bearing species, like E. dives, E. Delegatensis, E. vitrea, etc, it is only present in comparatively small amount, consequently the crude oils of those species are usually but little coloured, although the phenol tasmanol also occurs in them to a small extent.

It was thought desirable to determine the free acid occurring in Eucalyptus oils, and for this purpose the following species were chosen, which may be considered as fairly representative of the several groups. From the study of these it was possible to form an opinion as to the general identity of the free volatile acid in Eucalyptus oils.

1. E. Smithii, a rich cineol-pinene oil, which contains but a small amount of esters, or free acid.

2. E. cinerea, a rich cineol oil, but which contains a comparatively large amount of both ester and free acid.

3. E. phellandra, representing an intermediate oil between those of the cineol-pinene group and the more pronounced phellandrene oils.

Through the kindness of the Australian Eucalyptus Oil Company, Sydney, we were supplied with a quantity of the water first obtained when rectifying the oils of these three species by direct distillation.

The water employed for the determination of the free acid in the oil of E. Smithii was derived from the rectification of 500 lb. of crude oil of that species. It was found that 20 gram. of the water required 0.058 gram, sodium hydrate, equal to 0.435 Per cent. calculated as acetic acid. The remaining water was neutralised, evaporated to a small bulk, dilute sulphuric acid added and distilled until the whole of the volatile acids had come over. The distillate was then exactly neutralised with barium hydrate solution, evaporated to dryness, and the combined acid determined in the usual way by changing the barium salt into barium sulphate. 0.4344 gram, gave 0.3967 gram, barium sulphate, equal to 91.32 per cent. Theory requires 91.37 per cent. BaSO4, so that it is evident that only acetic acid could have been present in the first distillate derived from the oil of this species.

The amount of free acid in the water obtained on rectifying the oil of E. cinerea by direct distillation was 2.1 per cent. considered as acetic (see under that species). The barium salt was prepared with the volatile acid similarly with that of E. Smithii. 0.9784 gram. of the barium salt on ignition with sulphuric acid gave 0.8930 gram. barium sulphate, equal to 91.27 per cent. Theory requires 91.37 per cent. barium sulphate, so that in this instance also, it seems probable that acetic acid could only have been present. It will be observed that the amount of free volatile acid in this case was about five times as much as in the distillate from E. Smithii.

In the water obtained on rectifying the oil of E. phellandra, 0.744 per cent. of free acid was present, calculated as acetic. The barium salt was prepared in the same manner as with the above two species. 0.5265 gram. of the barium salt when ignited with sulphuric acid gave 0.4804 gram. of barium sulphate, equal to 91.25 per cent., so that it is apparent that practically only free acetic acid could have been present as free acid in this oil also. The remainder of the acid distillate was neutralised with soda, and the soda salt crystallised out. Exhibits of pure sodium acetate in each instance were similarly prepared.

As concordant duplicate results were obtained in each case, it is evident that not more than mere traces of other volatile acids than acetic, could have been present in the oils tested, and as the species chosen were fairly representative of the whole genus, it is assumed that acetic is the free acid in the greater number of freshly distilled Eucalyptus oils.