According to H. Agulhon,1 a reagent prepared by dissolving 0 5 gram

1 Ann. Chim. Anal., 1912, 17, 50.

Q of potassium dichromate in 100 c.c. of pure nitric acid, sp. gr. 1.310, gives a blue colour at once, in the cold, with alcohols and aldehydes, but doe3 not react with ketones until after some hours' contact. One c.c. of pure acetone with 3 c.c. of the reagent develops an olive-green colour only after three hours; a solution of acetone (1:5) requires twenty-four hours to form the colour. With solutions of alcohol, and of formaldehyde, a blue colour appears in one or two minutes at a dilution of 1 in 200; with double this dilution no colour appears. Approximate determinations of the alcohol or aldehyde can be made colorimetrically by means of the reagent.