398 



The Free Volatile Acid of Eucalyptus Oils, 



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 numter 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 not 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, &c., 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 Ib. 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 0-3567 

 gram, barium sulphate, equal to 91-32 per cent. Theory requires 91-37 per 

 cent. BaSO 4 , so that it is evident that only acetic acid could have been present 

 in the first distillate derived from the oil of this species. 



