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. 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