indeed, and at temperatures under 40° 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° C. or thereabouts. Beyond this the jelly
should never be allowed to go, and to 50° only under exceptional
circumstances.

The tank in which the jelly is made is double-lined, in order to allow of
the passage of hot water between its inner and outer linings. A series of
such tanks are generally built in a wooden framework, and the double
linings are made to communicate, so that the hot water can flow from one
to the other consecutively. The temperature of the water should be about
60° C. if it is intended to gelatinise at 45° C., and about 80° if at
50° C.; but this point must, of course, be found by experiment for the
particular plant used. An arrangement should be made to enable the workman
to at once cut off the supply of hot water and pass cold water through the
tanks in case the explosive becomes too hot.

[Illustration: FIG. 31.--MR M'ROBERTS' MIXER FOR GELATINE EXPLOSIVES.]

The best way to keep the temperature of the water constant is to have a
large tank of water raised upon a platform, some 5 or 6 feet high, outside
the building, which is automatically supplied with water, and into which
steam is turned. A thermometer stuck through a piece of cork and floated
upon the surface of the tank will give the means of regulating the
temperature.