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).
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.