But it is not the due proportion of the materials only, which is necessary to the making of good powder; another circum stance, not less essential, is the mixing them well together; if this be not effec tually done, some parts of the composition will have too much nitre in them, and others too little ; and in either case there will be a defect of strength in the powder. After the materials have been reduced to fine dust, they are mixed together, and moistened with water, or vinegar, or urine, or spirit of wine, &c. and then beaten to gether for twenty-four hours, either by 'hand or and afterwards pressed into a hard, firm, solid cake. When dry, it is grained or corned, which is done by breaking the cake of powder into small pieces, and so running it through a sieve: by which means the grains may have any size given them, according to the nature of the sieve employed, either finer or coarser; and thus also the dust is sepa rated from the grains, and again mixed with other manufacturing powder, or worked up into cakes again.
Powder is smoothed or glazed, as it is called, for small arms, by the following operation : a hollow cylinder or cask is mounted on an axis, turned by a wheel ; this cask is half filled with powder, and turned for six hours, and thus, by the mu tual friction of the grains of powder, it is smoothed or glazed. The fine mealy part, thus separated or worn off from the rest, is again granulated.
The velocity of expansion of the flame of gunpowder, when fired in a piece of artillery, without either bullet or other body before it, is prodigiously great, viz. seven thousand feet per second, or up wards, as appears from the experiments of Mr. Robins. But M. Bernoulli and M. Euler suspect it is still much greater; and Dr. Hutton supposes it may not be less, at the moment of explosion, than four times as much.
It is this prodigious celerity of expan sion of the flame of gunpowder which is its peculiar excellence, and the circum stance in which it so eminently surpasses all other inventions, either ancient or mo dern ; for as to the momentum of these projectiles only, many of the warlike ma chines of the ancients produced this in a degree far surpassing that of our heaviest cannon shot or shells; but the great ce lerity given to these bodies cannot be in the least approached by any other means but the flame of powder.
To prove gunpowder. There are several ways of doing this. 1. By sight; thus if it be too black, it is a sign that it is moist, or else that it has too much charcoal in it; so also, if rubbed upon white paper, it b ackens it more than good powder does; but if it be of a kind of azure colour, somewhat inclining to red, it is a sign of good powder. 2 By touching ; for if, in crushing it with the fingers' ends, the grains break easily and turn_ into dust, without feeling hard, it has too much coal in it ; or if, in pressing it under the fin gers upon a smooth hard board, some grains feel harder than the rest, it is a sign the sulphur is not well mixed with the nitre. Also, by thrusting the hand into the parcel of powder, and grasping it, as if to take out a handful, you will feel if it is dry and equal grained, by its evading the grasp and running mostly out of the hand. 3. By burning; and here the me
thod most commonly followed for this pur pose with us, says Mr. Robins, is, to fire a small heap of it on a clean board, and to attend nicely to the flame and smoke it produces, and to the marks it leaves be hind on the board; but besides this un. certain method, there are other contriv ances made use of, such as powder-triers, acting by a spring, commonly sold at the shops, and others again that move a great weight, throwing it upwards, which is a very bad sort of eprouvette.
The best eprouvette consists in a small cannon, the bore of which is about one inch in diameter, and is usually charged with two ounces of powder, and with powder only, as a ball is not necessary, and the strength of the powder is accu rately shewn by the are of the gun's re coil. The whole machine is so simple, easy, and expeditious, that, as Dr. Hutton observes, the weighing of the powder is the chief part of the trouble, and so accu rate and uniform, that the successive re petitions,or firings,with the same quantity of the same sort of powder, hardly ever yield a difference in the recoil of the one hundreth part of itself.
To recover damaged powder. The me thod of the powder merchants is this : they put part of the powder on a sail cloth, to which they add an equal weight of what is really good, then with a sho vel they mingle it well together, dry it in the sun, and barrel it up, keeping it in a dry and proper place.
Others again, if it be very bad, restore it by moistening it with vinegar, water, urine, or brandy ; then they beat it fine, sift it, and to every pound of powder add an ounce, or an ounce and a half, or two ounces (according as it is de cayed) of melted nitre, arid afterwards these ingredients are to be moistened and well mixed, so that nothing may be 'dis cerned in the composition, which may be known by cutting the mass, and then they granulate it is as usual. In case the pow der be quite spoiled, the only way is to extract the saltpetre with water, in the usual way, by boiling, filtrating, evapo rating, and crystallizing, and then with fresh sulphur and charcoal to make it up afresh.
On the subject of gunpowder, see also Euler on Robinsl Gunnery, Antoni Exa men de la Poudrd, Baume's Chemistry, and Thompson's Experiments in the Phi losophical Transactions for 1781.
Soon after the discovery of the oxyge nated-muriatic acid and its combination with potash, it was found that this oxy muriate produced a much more violent detonation with combustible bodies, than is afforded by nitre. It has been esti mated to possess more than double the force ; but on account of this extraordi nary power of gunpowder made with the new salt, and some fatal accidents by its exploding, in consequence of friction or percussion, to which it is liable, as well during the manufacture as afterwards, this modern compound has not been brought into use in military operations, but is likely to continue among the arti cles of scientific curiosity.