The presence of aldehyde or acetone, which are difficult to remove, interferes with some of the ordinary tests for ethyl alcohol. According to A. Toninelli,1 the following reaction is not affected by the presence of these impurities, and when carried out as described is quite characteristic of ethyl alcohol.

The reagents required are (1) 1.5 grams of pure crystallised dinitrotoluene (m.p. 705°) dissolved in 200 c.c. of a mixture of

1 part of carbon disulphide and 2 parts of ether; (2) 12 grams of iodine dissolved in 100 c.c. of ether; and (3) 40 grams of potassium hydroxide dissolved in 100 c.c. of water.

In a 10 c.c. graduated stoppered tube are placed 2 c.c. of the liquid to be tested, and 2 c.c. of the iodine solution. After slinking and allowing to stand for two minutes, 4 c.c. of the potash solution are added, and the mixture shaken until it is decolorised. Finally,

2 c.c. of the dinitrotoluene reagent are added with vigorous shaking, after which the graduated tube is placed upon a white surface and the upper layer closely observed. If ethyl alcohol is present in quantity sufficient to react, an orange yellow colour is developed which passes through various shades, terminating in an intense garnet red. With as little as 3 per cent. of alcohol, the colour is a light rose.

Neither methyl alcohol nor pure acetone gives this reaction, and aldehyde diminishes the sensitiveness of the test only when present in large amount.

Some of the higher alcohols, however, give similar results to those obtained with ethyl alcohol. When it is necessary to eliminate them, 25 to 100 c.c. of the sample, according to its presumed content of ethyl alcohol, are placed in a separator, and treated with two volumes of a 5 per cent. solution of alum in water, shaking up several times after addition of a little benzene or petroleum ether. The aqueous layer, which contains nearly all the ethyl alcohol present, is drawn off and distilled, fractions of 2 c.c. being collected of the distillate passing over between 60° and 80°. The test is then applied to these.