[Footnote A:  G. M’Roberts, Jour.  Soc.  Chem.  Ind., 31st March 1890, p. 266.]

[Illustration:  FIG. 33.—­CARTRIDGE-MAKING MACHINE FOR GELATINE EXPLOSIVES.]

The issuing gelatine can of course be cut off at any length.  This is best done with a piece of hard wood planed down to a cutting edge, i.e., wedge-shaped.  Mr Trench has devised a kind of brass frame, into which the gelatine issuing from the nozzle of the cartridge machine is forced, finding its way along a series of grooves.  When the frame is full, a wooden frame, which is hinged to one end of the bottom frame, and fitted with a series of brass knives, is shut down, thereby cutting the gelatine up into lengths of about 4 inches.

It is essential that the cartridge machines should have no metallic contacts inside.  The bearing for the screw shaft must be fixed outside the cone containing the gelatine.  One of these machines can convert from 5 to 10 cwt. of gelatine into cartridges per diem, depending upon the diameter of the cartridges made.

After being cut up into lengths of about 3 inches, the gelatine is rolled up in cartridge paper.  Waterproof paper is generally used.  The cartridges are then packed away in cardboard boxes, which are again packed in deal boxes lined with indiarubber, and screwed down air tight, brass screws or zinc or brass nails being used for the purpose.  These boxes are sent to the magazines.  Before the boxes are fastened down a cartridge or so should be removed and tested by the heat test, the liquefaction test, and the test for liability to exudation. (Appendix, p. 6, Explosives Act, 1875.) A cartridge also should be stored in the magazine in case of any subsequent dispute after the bulk of the material has left the factory.

The object of the liquefaction test is to ensure that the gelatine shall be able to withstand a fairly high temperature (such as it might encounter in a ship’s hold) without melting or running together.  The test is carried out as follows:—­A cylinder of the gelatine dynamite is cut from the cartridge of a length equal to its diameter.  The edges must be sharp.  This cylinder is to be placed on end on a flat surface (such as paper), and secured by a pin through the centre, and exposed for 144 consecutive hours to a temperature of 85 deg. to 90 deg.  F., and during such time the cylinder should not diminish in height by more than one-fourth of an inch, and the cut edges should remain sharp.  There should also be no stain of nitroglycerine upon the paper.

The exudation test consists in freezing and thawing the gelatine three times in succession.  Under these conditions there should be no exudation of nitro-glycerine.  All the materials used in the manufacture of gelatine explosives should be subjected to analytical examination before use, as success largely depends upon the purity of the raw materials.  The wood-pulp, for instance, must be examined for acidity.