ALCOHOLS AND ESTERS. 505 



Fermentation amyl alcohol, or isoamyl alcohol constitutes the 

 bulk of fusel oil. It occurs as ordinary, optically inactive alcohol, 

 (CH 3 ) a .CH.CH 2 .CH 2 (OH), but, according to MABOKWALD (I.), is 

 invariably accompanied by the active alcohol 



which rotates the plane of polarised light towards the left. Le 

 Bel states that it is converted into the dextro-rotatory modifica- 

 tion under the influence of mould fungi. The name, amyl alcohol, 

 was bestowed by CAHOURS (I.) because the alcohol is formed from 

 materials containing starch. The ainyl alcohols are found in all 

 technical fusel oils, and to a smaller extent in cognac as well ; 

 compare also PEDLER (I.), KRUTSCH (I. and II.), BALARD (I.), and 

 HALENKE and KURTZ (I.). 



Various hypotheses have been advanced to account for the 

 formation of the fusel oils. According to BREEELD (XVIII.), 

 by-products are formed as soon as the materials requisite for the 

 continued growth of the yeast are exhausted, the yeast dying and 

 decomposition setting in as fermentation progresses. If the higher 

 alcohols originate in normal fermentation, the amount so formed 

 must, pace LINDET (IV.), bear a constant relation to the quantity 

 of ethyl alcohol during the various stages. This, however, is not 

 the case, the amount of fusel oils formed during the first fourteen 

 hours being 0.36 part per 100 of alcohol, but 14.07 parts in twenty- 

 four hours. This increase is apparently due to micro-organisms 

 which do not come into action to their full extent until fermenta- 

 tion has terminated. The higher alcohols are products of a 

 secondary fermentation, and are also formed, to a smaller extent, 

 when the fermentation is accelerated by increasing the quantity 

 of pitching yeast, or by adding sterile beer wort. 



PEUDUIX (I.) established the fact that bacteria are able to 

 produce fusel oils, this worker having isolated from Seine water 

 a bacterium that furnished amyl alcohol. PEREIRE and GUIGNARD 

 (I.) found a similar bacillus in calcareous waters, and thought of 

 utilising it technically ; and PRINGSHEIM (I.) described an amylic 

 bacillus, isolated from American potatoes. Perdrix's bacillus, how- 

 ever, produces such a small quantity of this alcohol that it cannot 

 be regarded as the sole agent in the formation of fusel oils. The 

 experiments of LINDET (IV.), which showed that the amount of 

 higher alcohols formed remained nearly constant, despite modifi- 

 cations in the conditions, might be explained by bacterial activity, 

 although, as a matter of fact, it is not quite clear why the action 

 of the bacteria was not influenced by the modifications in question. 

 Stronger proof of bacterial agency in this connection is afforded 

 by the experiments of GAYON and DUPETIT (I.). The quantity of 

 the fusel oil formed can be considerably lessened by the addi- 

 tion of bactericidal substances or by powerful aeration, which 



