should not subsequently exude when subjected to heat or damp. It is also
important that there should be no excess of nitro-glycerine, as this may
diminish instead of augment the strength, owing to a difference in the
mode of the propagation of the explosive wave in the liquid, and in the
mixture. Nitro-glycerine at its freezing point has a tendency to separate
from its absorbing material, in fact to exude. When frozen, too, it
requires a more powerful detonation to explode it, but it is less
sensitive to shock. The specific gravity of blasting gelatine is 1.5
(i.e., nearly equal to that of nitro-glycerol); that of gun-cotton (dry)
is 1.0.

Blasting gelatine burns in the air when unconfined without explosion, at
least in small quantities and when not previously heated, but it is rather
uncertain in this respect. It can be kept at a moderately high temperature
(70° C.) without decomposition. At higher temperatures the nitro-glycerine
will partially evaporate. When slowly heated, it explodes at 204° C. If,
however, it contains as much as 10 per cent. of camphor, it burns without
exploding. According to Berthelot,[A] gelatine composed of 91.6 per cent.
nitro-glycerine and 8.4 per cent. of nitro-cellulose, which are the
proportions corresponding to total combustion, produces by explosion
177CO_{2}+ 143H_{2}O + 8N_{2}.

[Footnote A: Berthelot, "Explosives and their Powers."]

He takes C_{24}H_{22}(NO_{3}H)_{9}O_{11} as the formula of the nitro-
cellulose, and 51C_{3}H_{2}(NO_{3}H)_{3} + C_{24}H_{22}(NO_{3}H)_{9}O_{11}
as the formula of the gelatine itself, its equivalent weight being 12,360
grms. The heat liberated by its explosion is equal to 19,381 calories, or
for 1 kilo. 1,535 calories. Volume of gases reduced temperature equals
8,950 litres. The relative value[A] of blasting gelatine to nitro-