Where the proportion is not too small, an approximate determination of the alcohol can be made by converting it into ethyl iodide and measuring the volume of this. The following process can be used for mixtures of alcohol and acetone containing 10 per cent, and upwards of alcohol. If more than a small proportion of water is present - about 5 per cent. say - the mixture should first be dehydrated with lime or potassium carbonate.

Where the proportion of alcohol is likely to be low - not more than 20 to 40 per cent. by volume, say - 20 c.c. of the mixture are taken, and added to 20 grams of iodine in a small flask, together with 5 c.c. of water: the latter helps to regulate the reaction. Two grams of amorphous phosphorus are then added, the flask attached to a small reflux condenser, and the action allowed to proceed for about ten minutes. If the action becomes too violent, the flask must be cooled a little.

When the reaction is over and the flask has cooled down, the condenser is reversed and the mixture distilled. The ethyl iodide is collected under 15 c.c. of water contained in a graduated 25 c.c. cylinder, surrounded by a bath of cold water; and the distillation is continued as far as practicable in order to obtain the whole of the ethyl iodide. The delivery-tube should dip under the surface of the water in the cylinder; and it should preferably be a bulbed tube, to guard against liability to back-suction due to absorption of hydriodic acid gas by the water. When the iodide is all collected it should be allowed to settle for some hours, and the volume read off. Each c.c. of iodide = 0573 gram of ethyl alcohol.

With higher proportions of alcohol 15 c.c. or 10 c.c. of the acetone-alcohol mixture should be taken, and treated in the same manner, but using 30 grams of iodine and 3 grams of amorphous phosphorus, instead of the preceding quantities. Where nothing is known as to the probable proportion of alcohol, or indicated by the specific gravity and refraction of the dehydrated sample, a preliminary experiment should be made, using 10 c.c, and the larger quantities of iodine and phosphorus, and the experiment repeated with any necessary modification.