For estimating the aldehydes, a standard solution of aldehyde in 50 per cent. alcohol, containing 0 01 gram of aldehyde per 100 c.c, is required; this is prepared as described later on.

Ten c.c. of the distillate under examination are placed in a small Nessler tube, and in similar tubes 10 c.c. each of 50 per cent. alcohol containing from 05 c.c. upwards of the 001 per cent. standard aldehyde solution. To each tube is added 1 c.c. of Gayon and Schiff's reagent.

After shaking, the tubes are allowed to stand for thirty minutes, when the violet colours which develop are compared.