dle and bruise, may melt and cool,
dissolve and crystallize, without explosion or change. It contains
conserved a force which represents the aggregate result of innumerable
minute actions, taking place among portions of matter which escape
our senses from their minuteness and excite our wonder by their
transformation. Closely similar are these actions to the agencies in
vegetation which build up the wood of the tree or the material of
the coal destined to serve for the production of fire in all the
applications of steam which we have briefly noticed in illustration.

In availing ourselves of the concentrated power accumulated in
saltpetre, we resort to bodies which easily kindle when fire is applied,
such as sulphur and finely powdered charcoal: these substances are
most intimately mixed with the saltpetre in a powdered state, and the
dampened mass subjected to great pressure is afterwards broken into
grains of varied size, constituting gunpowder.

The substances thus added to the saltpetre have both the disposition and
the power of burning with and decomposing the nitrous element of the
saltpetre, and in so doing they do not simply open the way for the
energetic action of the gases escaping, but, owing to the high
temperature produced, a new force is added.

If the gases escaped from combination simply, they would exert for every
cubic inch of saltpetre, as we have here considered it, the direct power
of 12,000 lbs.; but under the new conditions, the volume of escaping gas
has a temperature above 2,000 deg. Fahrenheit, and consequently its force
in overcoming resistance is more than four times as great, or at least
48,000 lbs.

Such, then, is the power which can be obtained from a cubic inch of
saltpetre, when it is so compounded as to form some of the kinds of
gunpowder; and the fact of greatest importance in this connection is the
control we have over the amount of the force exerted and the time in
which the energy can be expended, by variations in the proportions of
the eliminating agents employed.

We have used the well-known term Gunpowder to express the compound by
which we easily obtain the power latent in saltpetre; and the use of the
term suggests the employment of guns, which is secondary to the main
point we are illustrating. As the enormous consumption of power takes
place during peaceful times, so the consumption of saltpetre during a
state of war is much lessened, because the prosecution of public an