Acetone is usually prepared, however, by the dry distillation of crude calcium or barium acetate.

(CH_{3}.COO)_{2}Ca = CH_{3}.CO.CH_{3} + CaCO_{3}.

The distillate is fractionated, and the portion, boiling between 50 deg. and 60 deg.  C., mixed with strong solution of sodium bisulphite.  The crystalline cake of acetone sodium bisulphite, which separates on standing, is well pressed, to free it from impurities, decomposed by distillation with dilute sodium carbonate, and the aqueous distillate of pure acetone dehydrated over calcium chloride.  Acetone is a colourless, mobile liquid of sp. gr. .792 at 20 deg.  C., it boils at 56.5 deg.  C., has a peculiar, pleasant, ethereal odour, and is mixible with water, alcohol, and ether in all proportions.

The acetone used in the manufacture of cordite should conform to the following specification:—­

SPECIFICATION FOR ACETONE.

1.  The acetone to be not more than 0.802 specific gravity at 60 deg.  F. When mixed with distilled water it must show no turbidity, and must leave no residue on evaporation at 212 deg.  F. On distillation, four-fifths by volume of the quantity taken must distil over at a temperature not exceeding 138 deg.  F. The residual matter left after this distillation must not contain, besides acetone, any ingredient that is not a bye-product incidental to the manufacture of acetone.

2.  One c.c. of 0.10 per cent. solution in distilled water of pure permanganate of potash, added to 100 c.c. of the acetone, must retain its distinctive colour for not less than 30 minutes.  This test should be made at a temperature of 60 deg.  F.

3.  The acetone tested by the following method must not show more than 0.005 per cent. of acid, calculated to acetic acid:—­

To 50 c.c. of the sample diluted with 50 c.c. of distilled water, with 2 c.c. of phenol-phthalein solution (1 gramme to 1,000 c.c. of 50 per cent. alcohol) added as an indicator, add from a burette N/100 sodium hydrate solution (1 c.c. 0.0006 gramme acetic acid), and calculate to acetic acid in the usual manner.

The water used for the dilution of the acetone must be carefully tested for acidity, and the pipettes used for measuring should not be blown out, as it would be possible thus to neutralise nearly 2 c.c. of the soda solution.

The presence of water in a sample of acetone may be detected by Schweitzer and Lungwitz’s method (Chem.  Zeit., 1895, xix., p. 1384), which consists in shaking together equal volumes of acetone and petroleum ether (boiling point, 40 deg. to 60 deg.  C.), when if present a separation of the liquid in layers will take place.

Estimation of Acetone.—­Kebler (Jour.  Amer.  Chem.  Soc., 1897, 19, 316- 320) has improved Squibb’s modification of Robineau and Rollins’ method.  The following solutions are required:—­

(1.) A 6 per cent. solution of hydrochloric acid.