As a means of detecting isoamyl alcohol in spirits, A. Komarowsky in 1903 proposed treatment of the sample with salicylic aldehyde and sulphuric acid.1 When to 10 c.c. of the spirit are added 25 to 30 drops of a 1 per cent. alcoholic solution of salicylic aldehyde and 20 c.c. of strong sulphuric acid, the mixture develops a colour which is reddish by reflected light and yellow by transmitted light if isoamyl alcohol is present to an extent not greater than 0 01 per cent. With larger quantities of isoamyl alcohol, the colour appears garnet-red, however viewed.

T. von Fellenberg2 states that the red colour shows a yellow fluorescence, which becomes greater as the amount of salicylic reagent is increased. If, however, the mixture is diluted with 62 per cent. sulphuric acid, the yellow fluorescence disappears and a pure red is obtained. He applies the test to the colorimetric determination of the higher alcohols of cognac in the following manner. Ten c.c. of the hydrolysed distillate, diluted to a strength of 30 per cent. of alcohol by volume, are treated with 1 c.c. of a 1 per cent. alcoholic solution of salicylic aldehyde, and then carefully mixed with 20 c.c. of strong sulphuric acid. After the lapse of forty-five minutes the mixture is diluted with 50 c.c. of 62 per cent. sulphuric-acid. The colour obtained is then compared with those produced in standard mixtures treated in the same manner.

Other substances than the alcohols of fusel oil give the red colour, as, for example, aromatic alcohols, phenols, and all compounds which contain an ethylene group in their molecule. It is not given, however, by polyhydric alcohols, or by alcohols and phenols containing a carboxyl group.

1 Chem. Zeit, 1903, 27, 807. 2 Ibid., 1910, 34, 791.