matter in the explosive exceeds 0.5 per cent., the sifted material should
be dried at a temperature not exceeding 140° F, until the proportion does
not exceed 0.5 per cent. After each sample has been ground, the mill must
be taken to pieces and carefully cleaned. The sieves used consist of a
nest of two sieves with holes drilled in sheet copper. The holes in the
top sieve have a diameter = 14 B.W.G., those in the second = 21 B.W.G.

If too hard for the mill, the cordite may be softened by exposure to the
vapour of acetone,[A] or reduced, to the necessary degree of subdivision
by means of a sharp moderately-coarse rasp. Should it have become too soft
in the acetone vapour for the mill, it should be cut up into small pieces,
which may be brought to any desired degree of hardness by simple exposure
to air. Explosives which consist partly of gelatinised collodion-cotton,
and partly of ungelatinised gun-cotton, are best reduced to powder by a
rasp, or softened by exposure to mixed ether and alcohol vapour at a
temperature of 40° F. to 100° F.

[Footnote A: Mr W. Cullen _(Jour. Soc. Chem. Ind._, Jan. 31, 1901) says:--
"Undoubtedly the advent of the horny smokeless powders of modern times has
made it a little difficult to give the test the same scope as it had when
first introduced." As a rule a simple explanation can be found for every
apparently abnormal result, and in the accidental retention of a portion
of the solvent used in the manufacture, will frequently be found an
explanation of the trouble experienced.]

~Ballistite.~--In the case of ballistite the treatment is the same, except
that when it is in a very finely granulated condition it need not be cut
up.

~Guttmann's Heat Test.~--This test was proposed by Mr Oscar Guttmann in a