give a short definition of its strange explosive force,
and cause of action, which, according to Dr. Shaw's opinion of the
chemical cause of the explosive force of gunpowder, is as
follows:--"Each grain of gunpowder consisting of a certain proportion
of sulphur, nitre, and coal, the coal presently taking fire, upon
contact of the smallest spark; at which time both the sulphur and the
nitre immediately melt, and by means of the coal interposed between
them, burst into flame; which spreading from grain to grain,
propagates the same effect almost instantaneously, whence the whole
mass of powder comes to be fired; and as nitre contains a large
proportion both of air and water, which are now violently rarefied by
the heat, a kind of fiery explosive blast is thus produced, wherein
the nitre seems, by its aqueous and aerial parts, to act as bellows to
the other inflammable bodies (sulphur and coal) to blow them into a
flame, and carry off their whole substance in smoke and vapour."

_How to meal Gunpowder, Brimstone, and Charcoal._

There have been many methods used to grind these ingredients to a
powder for fire-works, such as large mortars and pestles made of
ebony, and other hard woods; but none of these methods have proved so
effectual and speedy as the last invention, that of the mealing table.
This table is made of elm, with a rim round its edge four or five
inches high; and at the narrow end is a slider which runs in a groove
and forms part of the rim; so that when you have taken out of the
table as much powder as you conveniently can, with a copper shovel,
you may sweep all clean out at the slider. When you are going to meal
a quantity of powder, observe not to put too much on the table at
once; but when you have put in a good proportion, take a muller and
rub it therewith till all the grains are broken; sift it in a lawn
sieve, that has a receiver and top to it; and that which does not pass
through the sieve, return again to the table and grind it more, till
you have brought it all fine enough to go through the sieve. Brimstone
and charcoal are ground in the same manner as gunpowder, only the
muller must be made of ebony, for these ingredients being harder than
powder, would stick in the grain of the elm and be very difficult to
grind; and as the brimstone is apt to stick and clog to the table, it
would be best to keep one for that purpose only, by which means you
will always have your brimstone clean and well gro