The Chemistry of Powder and Explosives - Sciencemadness Dot Org

NITROGLYCERIN 209
the temperature rises greatly, or if local overheating occurs as by
burning in an iron pot, then an explosion ensues. The explosion
of nitroglycerin by heat is conveniently demonstrated by heating
a stout steel plate to dull redness, removing the source of heat,
and allowing the nitroglycerin to fall drop by drop slowly onto
the plate while it is cooling. At first the drops assume the spheroidal
condition when they strike the plate and deflagrate or burn
with a flash, but when the plate cools somewhat each drop yields
a violent explosion.
Nitroglycerin is very sensitive to shock, and its sensitivity is
greater if it is warm. A drop of the liquid on a steel anvil, or a
drop absorbed by filter paper and the paper placed upon the
anvil, is detonated by the blow of a steel hammer. The shock
of iron striking against stone, or of porcelain against porcelain,
also explodes nitroglyccrin, that of bronze against bronze less
readily, and of wood against wood much less so. Stettbacher 18
reports drop tests with a 2-kilogram weight: mercury fulminate
4.5 cm., lead azide 9 cm., nitroglycerin 10-12 cm., blasting gelatin
12-15 cm., and tetryl 30-35 cm. He also reports the observations
of Kast and Will and of Will that nitroglycerin at 90°
requires only half as much drop to explode it as nitroglyccrin at
ordinary temperature, while the frozen material requires about
three times as much.
Nitroglycerin and nitroglycerin explosives, like all other high
explosives, show different velocities of detonation under different
conditions of initiation and loading. They are sometimes described
as having low and high velocities of detonation. Berthelot
found for nitroglycerin a velocity of 1300 meters per second in
lead or tin tubes of 3 mm. internal diameter. Abel 10 found 1525
meters per second in lead pipe 30 mm. internal diameter, while
Mettegang :o found 2050 meters per second in iron pipes of the
same internal diameter. Comey and Holmes 21 working with pipes
of 25-37.5 mm. internal diameter found values varying from
1300-1500 to 8000-8500 meters per second, and, with especially
strong detonators, they regularly found velocities between 6700
18 Stettbacher, "Die Scliiess- und Sprengstoffe." Leipzig, 1919, p. 124.
i»Phil. Trans., 156, 269 (1866); 157, 181 (1867).
20 Internal. Congr., 2, 322 (1903).
21 Z. ges. Schiess- u. Sprengstoffw., 8, 306 (1913).