PROPERTIES OF EXPLOSIVES

Definition
An explosive is a material, cither a pure single substance or
a mixture of substances, which is capable of producing an explosion
by its own energy.
It seems unnecessary to define an explosion, for everyone
knows what it is—a loud noise and the sudden going away of
things from the place where they have been. Sometimes it may
only be the air in the neighborhood of the material or the gas
from the explosion which goes away. Our simple definition makes
mention of the one single attribute which all explosives possess.
It will be necessary to add other ideas to it if we wish to describe
the explosive properties of any particular substance. For example,
it is not proper to define an explosive as a substance, or a
mixture of substances, which is capable of undergoing a sudden
transformation with the production of heat and gas. The production
of heat alone by the inherent energy of the substance
which produces it will be enough to constitute the substance an
explosive. Cuprous acetylide explodes by decomposing into copper
and carbon and heat, no gas whatever, but the sudden heat
causes a sudden expansion of the air in the neighborhood, and
the result is an unequivocal explosion. All explosive substances
produce heat; nearly all of them produce gas. The change is invariably
accompanied by the liberation of energy. The products

of the explosion represent a lower energy level than did the explosive

before it had produced the explosion. Explosives commonly
require some stimulus, like a blow or a spark, to provoke
them to liberate their energy, that is, to undergo the change

which produces the explosion, but the stimulus which "sets off1'

the explosive does not contribute to the energy of the explosion.
The various stimuli to which explosives respond and the mannci>
°i their responses in producing explosions provide a convenient
basis for the classification of these interesting materials.

Since we understand an explosive material to be one which is
capable of producing an explosion by its own energy, we have
opened the way to a consideration of diverse possibilities. An
explosive perfectly capable of producing an explosion may
liberate its energy without producing one. Black powder, for
example, may burn in the open air. An explosion may occur
without an explosive, that is, without any material which contains
intrinsically the energy needful to produce the explosion.
A steam boiler may explode because of the heat energy which
has been put into the water which it contains. But the energy is
not intrinsic to water, and water is not an explosive. Also, we
have explosives which do not themselves explode. The explosions
consist in the sudden ruptures of the containers which confine
them, as happens in a Chinese firecracker. Fire, traveling along
the fuse (note the spelling) reaches the black powder—mixture
of potassium nitrate, sulfur, and charcoal—which is wrapped
tightly within many layers of paper; the powder burns rapidly
and produces gas. It burns very rapidly, for the heat resulting
from the burning of the first portion cannot get away, but raises
the temperature of the next portion of powder, and a rise of temperature
of 10°C. more than doubles the velocity of a chemical
reaction. The temperature mounts rapidly; gas is produced
suddenly; an explosion ensues. The powder burns; the cracker
explodes. And in still other cases we have materials which themselves
explode. The molecules undergo such a sudden transformation
with the liberation of heat, or of heat and gas, that
the effect is an explosion.

source:the chemistry of powder and explosives