salt with which gunpowder is made?

MRS. B.

Yes. Gunpowder is a mixture of five parts of nitre to one of sulphur,
and one of charcoal. --Nitre from its great proportion of oxygen, and
from the facility with which it yields it, is the basis of most
detonating compositions.

EMILY.

But what is the cause of the violent detonation of gunpowder when set
fire to?

MRS. B.

Detonation may proceed from two causes; the sudden formation or
destruction of an elastic fluid. In the first case, when either a solid
or liquid is instantaneously converted into an elastic fluid, the
prodigious and sudden expansion of the body strikes the air with great
violence, and this concussion produces the sound called detonation.

CAROLINE.

That I comprehend very well; but how can a similar effect be produced by
the destruction of a gas?

MRS. B.

A gas can be destroyed only by condensing it to a liquid or solid state;
when this takes place suddenly, the gas, in assuming a new and more
compact form, produces a vacuum, into which the surrounding air rushes
with great impetuosity; and it is by that rapid and violent motion that
the sound is produced. In all detonations, therefore, gases are either
suddenly formed, or destroyed. In that of gunpowder, can you tell me
which of these two circumstances takes place?

EMILY.

As gunpowder is a solid, it must, of course, produce the gases in its
detonation; but how, I cannot tell.

MRS. B.

The constituents of gunpowder, when heated to a certain degree, enter
into a number of new combinations, and are instantaneously converted
into a variety of gases, the sudden expansion of which gives rise to the
detonation.

CAROLINE.

And in what instance does the destruction or condensation of gases
produce detonation?

MRS. B.

I can give you one with which you are well acquainted; the sudden
combination of the oxygen and hydrogen gases.

CAROLINE.

True; I recollect perfectly that hydrogen detonates with oxygen when the
two gases are converted into water.

MRS. B.

But let us return to the nitrat of potash. --This salt is decomposed
when exposed to heat, and mixed with any combustible body, such as
carbon, sulphur, or metals, these substances oxydating rapidly at the
expense of the nitrat. I must show you an instance of this. --I expose
to the fire some of the salt in a small iron ladle, and, when it is
sufficiently heated, add to it some powdered charcoal; this will attract
the o