This is given with sufficient accuracy for most requirements by the hydrometer, or by the specific gravity taken direct with the pyknometer, without distillation or preliminary purification of the sample. If it is desired to remove the mineral naphtha, together with the bulk of the acetone and the smaller impurities, the diluted sample is saturated with common salt, extracted with petroleum ether, and distilled as directed on p. 170 (Thorpe and Holmes's method).

Methyl Alcohol

This is conveniently determined by the modification of Deniges's method described on p. 183. The sample, purified if necessary, is diluted with water until it contains 10 per cent. of total alcohols by volume, and then further diluted twenty-fold with ethyl alcohol of 10 per cent. strength. Five c.c. of this diluted liquid are then oxidised with potassium permanganate as described (loc. cit.), employing standards for comparison which contain from 00015 to 0002 gram of methyl alcohol.