One gram of a standard mixture of higher alcohols (see below) is dissolved in 100 c.c. of pure 50 per cent. alcohol, and from this a standard solution is prepared containing 01 gram of the higher alcohols in 100 c.c.

To estimate the proportion of higher alcohols in a sample, 10 c.c. of the distillate, obtained as already described, are placed in a small flask of about 75 c.c. capacity, and in similar flasks are placed quantities 10 c.c. each of 50 per cent. alcohol containing from 05 c.c. upwards of the standard 01 per cent. solution. To these liquids is added 05 c.c. of a 1 per cent. solution of furfural in each case, and then 10 c.c. of concentrated sulphuric acid are slowly run in so that the acid forms a layer at the bottom of the flask. Each flask is placed in an ice-cold water-bath and the contents stirred by shaking gently during thirty seconds, after which it is allowed to stand for about an hour at the ordinary temperature of the room. In the presence of an appreciable quantity of higher alcohols, a reddish-violet colour develops, and the proportion of these alcohols in the sample can be estimated by comparison with the standards.

The standard mixture of higher alcohols used for comparison, and in terms of which the results of this test are expressed, contains: -

This mixture is some approximation to the average composition of the "fusel oil ' alcohols of pot-still spirits as determined by a number of experiments made in the Government Laboratory.

In exceptional cases it may be necessary to remove the esters and aldehydes before applying this process, but as a rule the colorations obtained with commercial spirits are very similar in tint to those given by the standard mixture, and with careful manipulation and similar conditions of working, comparable results can be obtained without much difficulty.

All the results are finally calculated to milligrams per 100 c.c. of absolute alcohol in the sample.