llulose, which may
be in the form of paper, cotton, or linen, is twice nitrated--first in the
acid mixture employed in a previous operation; and secondly, in a fresh
mixture of 3 parts sulphuric acid of 1.83 specific gravity, and 2 parts
concentrated nitric acid containing nitrous acid. After each nitration the
mass is subjected to pressure, and is then carefully washed with water, to
which, at the last, a small quantity of ammonia or caustic soda is added
to remove the final traces of acid. The impregnation of the pyroxyline
with the camphor is effected in a variety of ways.

The usual proportion of the constituents is 2 parts pyroxyline and 1 part
camphor. In Trebouillet and De Besancele's process, 100 parts of
pyroxyline are intimately mixed with from 40 to 50 parts camphor, and
moulded together by strong pressure in a hot press, and afterwards dried
by exposure to air, desiccated by calcium chloride or sulphuric acid. The
usual method is, however, to dissolve the camphor in the least possible
quantity of alcohol, and sprinkle the solution over the dry pyroxyline,
which is then covered with a second layer of pyroxyline, and the whole
again treated with the camphor solution, the addition of pyroxyline and
camphor solution being repeated alternately until the requisite amount of
celluloid mixture is obtained.

The mass, which sinks together in transparent lumps, is worked for about
an hour between cold iron rollers, and then for the same period between
rollers which can be gently heated by steam. The layer of celluloid
surrounding the rollers is then cut away and again pressed, the resulting
cake, which is now about 1 cm. thick, being cut into plates of about 70
cm. long and 30 cm. broad. These are placed one above the other, and
strongly pressed together by hydraulic pressure at a temperature of about
70 deg. for twenty-four hours. The thick cakes are once more cut into plates
of the desired thickness, and placed in a chamber heated from 30 deg. to 40 deg.
for eight to fourteen days, whereby they become thoroughly dry, and are
readily made into various articles either by being moulded while warm
under pressure, cut, or turned. Occasionally other liquids, e.g., ether
and wood spirit, are used in place of alcohol as solvents for the camphor.

Celluloid readily colours, and can be marbled for manufacturing purposes,
&c. It is highly inflammable and not explosive even under pressure, and
may be worked under the hammer or