Fusel oil is of variable composition, depending upon the nature of the materials fermented, probably also on the kind of yeast, and on the method of distillation. Whilst the oil from grain spirit or potato spirit is largely composed of amyl alcohols, that from brandy-marcs contains a notable quantity of normal propyl alcohol, and sometimes normal butyl alcohol also; and much isobutyl alcohol is found in spirit distilled from beet sugar washes.

K. Windisch1 gives the following analyses of fusel oil from potatoes and from grain; the results are calculated upon the oils freed from ethyl alcohol and water: -

In the grain fusel oil Windisch also found terpenes, 0 033 per cent., and terpene hydrate, 0 048 per cent. Both these, even when highly diluted, had the characteristic aroma of grain spirit. The terpene resembled phellandrene,butwas not positively identified.

An old analysis of Rabuteau's2 shows 15 per cent. of isopropyl alcohol in fusel oil from potato spirit, but this has not been confirmed.

The acids and esters shown in Windisch's analyses were found to be chiefly capric and caprylic, with smaller amounts of caproic and pelargonic, a little acetic, and traces of butyric.

Dr. J. Bell3 gives the following as the composition of fusel oil obtained from patent-still distilleries producing (1) "grain " spirit and (2) "molasses " spirit: -

1 Arb. Kais. Gesund., 1892, 8, 228.

2 Compt. rend., 1878, 87, 500.

3 Select Committee on Spirits, 1891, Minutes, p. 93.

Ordonneau1 fractionated a large quantity of 25 year old cognac brandy, and obtained 344.5 grams of higher alcohols per hectolitre of brandy. This fusel oil portion had the following percentage composition: -

Similar treatment of commercial alcohols derived from maize, beetroot, and potatoes yielded Ordonneau no trace of n-butyl alcohol, but only propyl, isobutyl, and amyl alcohols. The n-butyl alcohol found in the brandy was attributed to the influence of elliptical yeast.

Claudon and Morin2 subsequently examined 250 grams of the oils obtained by Ordonneau. These were dehydrated with potassium carbonate and barium oxide, and fractionated: the composition of the fraction containing the higher alcohols was as follows: -

These investigators thus confirmed Ordonneau's observation that normal butyl alcohol was a constituent of the oils. It was identified by its vapour density and by conversion into the corresponding iodide. They were inclined, however, to attribute its presence in the brandy to the development of a bacillus - perhaps Bacillus bulylicus - in the wine from which the brandy was made, and not to the action of elliptical yeast. They adduced an experiment3 in which sugar was fermented by elliptical yeast, obtained from wine and purified by cultivation. Foreign micro-organisms were excluded. From 100 kilos, of sugar they obtained 545 grams of higher alcohols, but these did not include any normal butyl alcohol. The constituents and proportions were: -

The proportions of propyl and isobutyl alcohols are noted as being unusually low.

Subsequently, Morin4 distilled 92 litres of genuine cognac brandy and fractionated the products, obtaining therefrom 206 grams of higher alcohols, as follows: -

1 Compt. rend., 1886, 102, 217-219. 2 Ibid., 1887, 104, 1187.

3 Ibid., 1887, 104, 1109. 4 Ibid., 1887, 105, 1019.

Normal butyl alcohol was absent. It would therefore appear that this alcohol is not necessarily a constituent of the fusel oil obtained from brandy. Further investigations, however, are required.

An analysis of fusel oil from potato spirit, quoted by Herrick1 as due to Kruis and Raymann, shows 042 per cent. of amyl alcohol, and about 5 per cent. of ethyl alcohol, with isobutyl, propyl, and hexyl alcohols together totalling only about 05 per cent. This appears to be an abnormal sample; but in any case the other examples given above show that there is considerable variation in the composition of fusel oil - as indeed would be expected from the different conditions of production and collection under which different oils are obtained.

Fusel oil is soluble in ether, chloroform, carbon tetrachloride, carbon disulphide, benzene, and petroleum ether; but is dissolved by water to a small extent only. It absorbs chlorine with some avidity. Its chief application in the arts is for the manufacture of amyl acetate, which is employed in making flavouring essences and as a solvent for celluloid in the preparation of varnishes, leather substitutes, and similar articles. Fusel oil is also used as a source of higher alcohols, which are separated from it by fractional distillation. The special variety of fusel oil produced in Fernbaeh's process, which is said to contain about 65 per cent. of butyl alcohol, has been suggested for use in the manufacture of synthetic rubber.