three times the effect of gunpowder. Its rapidity of combustion, however,
requires to be modified for use in firearms. Hence the lower nitrates are
generally used, or such compounds as nitro-lignose, nitrated wood, &c.,
are used.

The initial pressure produced by the explosion of gun-cotton is very
large, equal to 18,135 atmospheres, and 8,740 kilogrammes per square
centimetre for 1 kilo., the heat liberated being 1,075 calories (water
liquid), or 997.7 cals. (water gaseous), but the quantity of heat
liberated changes with the equation of decomposition. According to
Berthelot,[A] the heat of formation of collodion-cotton is 696 cals. for
1,053 grms., or 661 cals. for 1 kilo. The heat liberated in the total
combustion of gun-cotton by free oxygen at constant pressure is 2,633
cals. for 1,143 grms., or for 1 kilo. gun-cotton 2,302 cals. (water
liquid), or 2,177 cals. (water gaseous). The heat of decomposition of gun-
cotton in a closed vessel, found by experiment at a low density of charge
(0.023), amounts to 1,071 cals. for 1 kilo. of the substance, dry and free
from ash. To obtain the maximum effect of gun-cotton it must be used in a
compressed state, for the initial pressures are thereby increased. Wet
gun-cotton s much less sensitive to shock than dry. Paraffin also reduces
its liability to explode, so also does camphor.

[Footnote A: "Explosives and their Power," trans. by Hake and M'Nab.]

The substance known as celluloid, a variety of nitro-cellulose nearly
corresponding to the formula C_{24}H_{24}(NO_{3}H)_{8}O_{12}, to which
camphor and various inert substances are added, so as to render it
non-sensitive to shock, may be worked with tools, and turned in the lathe
in the same manner as ivory, instead of which material celluloid is now
largely used for such articles as knife handles, combs, &c. Celluloid is