e enough, should be sifted
through a brass sieve, and packed away ready for use in zinc air-tight
cases, or in indiarubber bags. The various gelatine compounds, gelignite,
gelatine dynamite, and blasting gelatine, are manufactured in exactly the
same way. The forms known as gelatine dynamite differ from blasting
gelatine in containing certain proportions of wood-pulp and potassium
nitrate, &c. The following are analyses of some typical samples of the
three compounds:--

Gelatine Blasting
Gelignite. Dynamite. Gelatine.

Nitro-glycerine 60.514 71.128 92.94 per cent.
Nitro-cellulose 4.888 7.632 7.06 "
Wood-pulp 7.178 4.259 ... "
Potassium nitrate 27.420 16.720 ... "
Water ... 0.261 ... "

The gelignite and gelatine dynamites consist, therefore, of blasting
gelatine, thickened up with a mixture of absorbing materials. Although the
blasting gelatine is weight for weight more powerful, it is more difficult
to make than either of the other two compounds, it being somewhat
difficult to make it stand the exudation and melting tests. The higher
percentage of nitro-cotton, too, makes it expensive.

When the dry nitro-cotton, which has been carefully weighed out in the
proportions necessary either for blasting gelatine or any of the other
gelatine explosives, is brought to the gelatine making house, it is placed
in a lead-lined trough, and the necessary quantity of pure dry nitro-
glycerine poured upon it. The whole is then well stirred up, and kept at a
temperature of from 40 deg. to 45 deg. C. It should not be allowed to go much
above 40 deg. C.; but higher temperatures may be used if the nitro-cotton is
very obstinate,[A] and will not dissolve. Great caution must, however, be
observed in this case. The mixture should be constantly worked about by
the workman with a wooden paddle for at least half an hour. At a
temperature of 40 deg. to 45 deg. the nitro-glycerine acts upon the nitro-cotton
and forms a jelly. Without heat the gelatinisation is very imperfect
indeed, and at temperatures under 40 deg. C. takes place very slowly.

[Footnote A: Generally due to the nitro-cotton being damp.]

[Illustration: FIG. 30.--WERNER, PFLEIDERER, & PERKINS' MIXING MACHINE.]

The limit of temperature is 50 deg. C. or thereabouts. Beyond this the jelly
should never be allowed to go