As a rule, the detection of ethyl alcohol presents no difficulty, though occasionally, where minute quantities are being dealt with, or interfering substances are present, a definite proof may demand both skill and care. The first two tests described below will often suffice, but should be supplemented by one or more of the others if the circumstances require it.

Ethyl Acetate Reaction

Mix a little sodium acetate, or 2 or 3 drops of acetic acid, with 2 or 3 c.c. of the liquid to be tested, then add about an equal volume of concentrated sulphuric acid, and heat the mixture. The characteristic fruity odour of ethyl acetate is developed if ethyl alcohol is present.

Iodoform Reaction

A few drops of solution of iodine are added to about 2 c.c. of the alcoholic liquid, which is then heated to about 60°, and solution of sodium hydroxide or carbonate added drop by drop until the colour of the iodine is discharged. The characteristic odour of iodoform is produced even with very dilute solutions of alcohol; with stronger solutions a turbidity, or a definite yellowish, crystalline precipitate of iodoform, appears when the liquid cools.

The iodoform is produced in accordance with the equation:-

C2H5OH + 5I2 + 7NaOH = CHI3 + CO2 + 7NaI + 6H2O.

A similar reaction is given by acetone, hence the result should be confirmed by one or more of the other tests described.

Iodoform is also produced from acetone in the cold, but not by ethyl alcohol, except to a slight extent and on standing some time.

Ethyl Benzoate Reaction

Shake a few c.c. of the liquid with a little benzoyl chloride, allow to settle, pipette off the lower layer, and warm it with solution of potassium hydroxide. If ethyl alcohol is present, the odour of ethyl benzoate will be detected (Berthelot).

Guaiacum Reaction

Place a fragment or two of guaiacum resin, newly broken from a lump, in a test-tube, add the liquid to be tested, shake well, and filter into a Nessler glass. Do a similar experiment with distilled water, and then add to each glass a little dilute solution of hydrocyanic acid and one or two drops of a dilute solution of copper sulphate. If the sample contains alcohol a blue colour will be produced, much deeper than that given by the distilled water.