inium dish, consequently the horizontal ledge round
the top of the dish should be bent, so as to render it slightly untrue,
and leave a clearance of about 0.02 inch in some places. If these few
simple precautions be taken, the method will be found to be very accurate.
Duplicate determinations do not differ more than 0.01 per cent.[A]

[Footnote A: "Determination of Moisture in Nitro-glycerine Explosives," by
A. Marshall, _Jour. Soc. Chem. Ind._, Feb. 29, 1904, p. 154.]

~The Vaseline~ (C_{16}H_{34}), or petroleum jelly, used has a flash-point
of 400 deg. F. It must not contain more than 0.2 per cent. volatile matter
when heated for 12 hours on the water bath, and should have a specific
gravity of 0.87 at 100 deg. F., and a melting point of 86 deg. F. It is obtained
during the distillation of petroleum, and consists mainly of the portions
distilling above 200 deg. C. It boils at about 278 deg. C.

~Acetone~ (CH_{3}CO.CH_{3}), or dimethyl ketone, is formed when iso-propyl
alcohol is oxidised with potassium bichromate and sulphuric. It is also
produced in considerable quantities during the dry distillation of wood,
and many other organic compounds. Crude wood spirit, which has been freed
from acetic acid, consists in the main of a mixture of acetone and methyl-
alcohol. The two substances may be roughly separated by the addition of
calcium chloride, which combines with the methyl-alcohol. On subsequent
distillation crude acetone passes over, and may be purified by conversion
into the bisulphite compound.

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