I intend to repeat these experiments upon a
larger scale, by which I shall procure more accurate precision in their
results; the following, however, is the process I have hitherto
employed. I would very earnestly advise such as intend to repeat some of
these experiments, to be very much upon their guard in operating upon
any mixture which contains nitre, charcoal, and sulphur, and more
especially with those in which oxygenated muriat of potash is mixed with
these two materials.

I make use of pistol barrels, about six inches long, and of five or six
lines diameter, having the touch-hole spiked up with an iron nail
strongly driven in, and broken in the hole, and a little tin-smith's
solder run in to prevent any possible issue for the air. These are
charged with a mixture of known quantities of nitre and charcoal, or any
other mixture capable of deflagration, reduced to an impalpable powder,
and formed into a paste with a moderate quantity of water. Every portion
of the materials introduced must be rammed down with a rammer nearly of
the same caliber with the barrel, four or five lines at the muzzle must
be left empty, and about two inches of quick match are added at the end
of the charge. The only difficulty in this experiment, especially when
sulphur is contained in the mixture, is to discover the proper degree of
moistening; for, if the paste be too much wetted, it will not take fire,
and if too dry, the deflagration is apt to become too rapid, and even
dangerous.

When the experiment is not intended to be rigorously exact, we set fire
to the match, and, when it is just about to communicate with the charge,
we plunge the pistol below a large bell-glass full of water, in the
pneumato chemical apparatus. The deflagration begins, and continues in
the water, and gas is disengaged with less or more rapidity, in
proportion as the mixture is more or less dry. So long as the
deflagration continues, the muzzle of the pistol must be kept somewhat
inclined downwards, to prevent the water from getting into its barrel.
In this manner I have sometimes collected the gas produced from the
deflagration of an ounce and half, or two ounces, of nitre.

In this manner of operating it is impossible to determine the quantity
of carbonic acid gas disengaged, because a part of it is absorbed by the
water while passing through it; but, when the carbonic acid is absorbed,
the azotic gas remains; and, if it be agitated for a few minutes in
ca