Mix 5-10 c.c. of the alcoholic liquid with an equal volume of 50 per cent. sulphuric acid, and introduce it into a small flask containing 3 or 4 grams of powdered potassium dichromate and about 5 c.c. of water. Allow the mixture to stand a few minutes, and then distil off the aldehyde formed, collecting it in a little water. The acetaldehyde may be recognised: - (1). By its odour.

(2). By the production of reddish-violet colour, either immediately or after a few minutes, when treated with Setoff's reagent. (3). By the formation of aldehyde-resin, showing a yellow colour, on being allowed to stand some time in contact with a piece of caustic potash. (4). By the production of a silver mirror when heated with an ammoniacal solution of silver nitrate. Conversion into ethyl-m-dinitrobenzoate. - In special cases the following test described by Mulliken1 has been found useful by the writer. It is applicable only to a nearly pure alcohol containing not more than about 10 per cent. of water: two small pieces of porous tile. Place the powder in a dry 5- or 6-inch test-tube. Allow 4 drops of the alcohol to fall upon it, and then stopper the tube tightly without delay. Immerse the lower part of the test-tube in water having a temperature of 75-85°. Shake gently, and continue the heating for ten minutes.

Heat together gently in a 3-inch test-tube held over a small flame 0 15 gram of 3-5 dinitrobenzoic acid and 0 20 gram of phosphorus pentachloride. When signs of chemical action are seen, remove the heat for a few seconds. Then heat again, boiling the liquefied mixture very gently for one minute. Pour out on a very small watch glass and allow to solidify. As soon as solidification occurs remove the liquid phosphorus oxychloride with which the crystalline mass is impregnated by rubbing the latter between

1 "Identification of Pura Organic Compounds," I, 161.

To purify the ester produced in the reaction crush any hard lumps that may form when the mixture cools with a stirring-rod, and boil gently with 15 c.c. of methyl alcohol (2:1) until all is dissolved, or for a minute or two. Filter boiling hot if the solution is not clear. Cool. Shake and filter. Wash with 3 c.c. of cold methyl alcohol (2: 1). Recrystallise from 9 c.c. of boiling methyl alcohol (2: 1). Wash with 2 c.c. of the same solvent. Spread out the product on a piece of tile. Allow to become air-dry, and determine the melting point.

Ethyl 3: 5-dinitrobenzoate, the product in this test, crystallises in white needles melting at 92-93° (uncorr.).

This method is given by Winter Blyth1 for the definite proof of the presence of ethyl alcohol in toxicological cases.