very plastic when heated towards 150° C., and tends to become very
sensitive to shock, and in large quantities might become explosive during
a fire, owing to the general heating of the mass, and the consequent
evaporation of the camphor. When kept in the air bath at 135° C.,
celluloid decomposes quickly. In an experiment (made by M. Berthelot) in a
closed vessel at 135° C., and the density of the charge being 0.4, it
ended in exploding, developing a pressure of 3,000 kilos. A large package
of celluloid combs also exploded in the guard's van on one of the German
railways a few years ago. Although it is not an explosive under ordinary
circumstances, or even with a powerful detonator, considerable care should
be exercised in its manufacture.

~The Manufacture of Gun-Cotton.~--The method used for the manufacture of
gun-cotton is that of Abel (Spec. No. 1102, 20. 4. 65). It was worked out
chiefly at Stowmarket[A] and Waltham Abbey,[B] but has in the course of
time undergone several alterations. These modifications have taken place,
however, chiefly upon the Continent, and relate more to the apparatus and
machinery used than to any alteration in the process itself. The form of
cellulose used is cotton-waste,[C] which consists of the clippings and
waste material from cotton mills. After it has been cleaned and purified
from grease, oil, and other fatty substances by treatment with alkaline
solutions, it is carefully picked over, and every piece of coloured cotton
rag or string carefully removed. The next operation to which it is
submitted has for its object the opening up of the material. For this
purpose it is put through a carding machine, and afterwards through a
cutting machine, whereby it is reduced to a state suitable for its
subsequent treatment with acids, that is, it has been cut into short
lengths, and the fibres opened up and separated from one another.

[Footnote A: The New Explosive Co. Works.]