cause of explosion, and such explosion may develop gases which are
non-supporters of combustion as well as those which are inflammable.
You throw table salt down a blazing chimney to set free the
flame-suppressing hydrochloric acid, you discharge a loaded gun up a
blazing chimney to put out the fire by another agency; still the salt,
with certain combinations, may be explosive, a resinous vapor may be
combustive in a hydrochloric atmosphere, and gunpowder isn't harmless
when thrown upon a blaze--in fact, our common fire-extinguisher, water,
has its explosive incidences as liquid as well as vapor.

Gases explosive in association may be set free by the temperature of
a burning building and get together. In respect to the old conundrum,
"Will saltpetre explode?" Mr. A. A. Hayes, Prof. Silliman, and Dr.
Hare's views were, as to the explosions in the New York fire of 1845,
that in a closed building having niter in one part and shellac or other
resinous material in another, the gaseous oxygen generated from the
niter and the carbureted hydrogen from the resins mingling by degrees
would at length constitute an explosive mixture. A brief consideration
of specific explosives uniting may serve to illustrate this phase of the
subject.

Though the explosion of gunpowder is the result of a chemical change
whereby carbonic acid gas at high tension is evolved (due to the
saltpeter and the charcoal), the effect and rapidity of action are
greatly promoted by the addition of sulphur. On the contrary, dynamite,
now so important, and various similar explosives, are but mixtures of
nitro-glycerine with earthy substances, in order to diminish and make
more manageable the development of the rending force of the base. The
explosive power of any substance is the pressure it exerts on all parts
of the space containing it at the instant of explosion, and is measured