The following analysis of woods is by Dr H. Müller:—These mixing machines can either be turned by hand, or a shaft can be brought into the house and the machine worked by means of a belt at twenty to thirty revolutions per minute. The bearings should be kept constantly greased and examined, and the explosive mixture carefully excluded. When the gelatine mixture has been thoroughly incorporated, and neither particles of nitrate or wood meal can be detected in the mass, it should be transferred to wooden boxes and carried away to the cartridge-making machines to be worked up into cartridges.
[Illustration: FIG. 32.—PLAN OF THE BOX CONTAINING THE EXPLOSIVE, IN
M'ROBERTS' MACHINE.]
The application of heat in the manufacture of the jelly from collodion- cotton and nitro-glycerine is absolutely necessary, unless some other solvent is used besides the nitro-glycerine, such as acetone, acetic ether, methyl, or ethyl-alcohol. (They are all too expensive, with the exception of acetone and methyl-alcohol, for use upon the large scale.) These liquids not only dissolve the nitro-cellulose in the cold, but render the resulting gelatine compound less sensitive to concussion, and reduce its quickness of explosion (as in cordite). They also lower the temperature at which the nitro-glycerine becomes congealed, i.e., they lower the freezing point[A] of the resulting gelatine.
[Footnote A: It has been proposed to mix dynamite with amyl alcohol for this purpose. Di-nitro-mono-chlorhydrine has also been proposed.]
The finished gelatine paste, upon entering the cartridge huts, is at once transferred to the cartridge-making machine, which is very like an ordinary sausage-making machine[A] (Fig. 33). The whole thing must be made of gun-metal or brass, and it consists of a conical case containing a shaft and screw. The revolutions of the shaft cause the thread of the screw to push forward the gelatine introduced by the hopper on the top to the nozzle, the apex of the cone-shaped case, from whence the gelatine issues as a continuous rope. The nozzle is of course of a diameter according to the size of cartridge required.
[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.