[Footnote A:  Most of the wood-pulp used in England is obtained from pine-trees, but poplar, lime, birch, and beech wood are also used.  It is chiefly imported as wood-pulp.  The pulp is prepared as follows:—­The bark and roots are first removed, and the logs then sawn into boards, from which the knots are removed.  The pieces of wood are afterwards put through a machine which breaks them up into small pieces about an inch long, which are then crushed between rollers.  These fragments are finally boiled with a solution of sodium bisulphite, under a pressure of about 90 lbs. per square inch, the duration of the boiling being from ten to twelve hours.  Sulphurous acid has also been used.  Pine-wood yields about 45 per cent. and birch about 40 per cent. of pulp when treated by this process.  The pulp is afterwards bleached and washed, &c.

Birch.   Beech.   Lime.    Pine.    Poplar. 
Cellulose        55.52   45.47   53.09   56.99   62.77 per cent. 
Resin             1.14    0.41    3.93    0.97    1.37    "
Aqueous extract   2.65    2.47    3.56    1.26    2.88    "
Water            12.48   12.57   10.10   13.87   12.10    "
Lignine          28.21   39.14   29.32   26.91   20.88    “]

The following analysis of woods is by Dr H. Mueller:—­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.