A Manual of Pyrotechny; or, A Familiar System of Recreative Fire-works

by G. W. Mortimer

The operative parts of the mill consist of two stones placed vertically, and running on another placed horizontally, which is called the bed-stone, or trough. On this bed-stone, about forty or fifty pounds of the composition are spread out, and moistened with water till reduced to about the consistency of a very stiff paste: after the stone-runners have made the proper revolutions over it, which requires about eight hours continued action of the mill, which is worked sometimes by horses, and sometimes by water, it is then taken from the mill, and sent to the corning-house, to be corned or grained. Here it is formed into hard lumps, and these are put into circular sieves, with parchment bottoms, perforated with holes of different sizes, and fixed in a frame connected with a horizontal wheel. Each of these sieves is also furnished with a runner or spheroid of lignum vitæ, which, being set in motion by the action of the wheels, forces the paste through the holes of the parchment bottom, forming grains of different sizes. The grains are then separated from the dust by sieves and reels made for that purpose. The grains are next hardened, and the rougher edges are taken off by shaking them for some time in a close reel, moved in a circular direction with a proper velocity.

When the powder has been corned, dusted, and glazed, it is dried in the stove-house, where great care should be taken to avoid explosion. The stove-house is a square apartment, three sides of which are furnished with shelves or cases, on proper supports, arranged round the room; and the fourth contains a large cast-iron vessel, called a “gloom,” which projects into the room, and is heated from the outside, so that no part of the fuel may touch the powder. For greater security against sparks by accidental friction, the glooms are covered with sheet-copper, and are always cool when the powder is put in or taken out of the room.

Here the grains are thoroughly dried, losing in the process what remains of the water added to the mixture in the mill, for bringing it to a working stiffness. A method of drying powder, by steam-pipes running round and crossing the apartment, has been successfully tried; and thus the possibility of any injurious accident from over-heating is prevented. The temperature of the room, when heated in the common way by a gloom-stove, is always regulated by a thermometer hung in the door of the stoves.

If Gunpowder is injured by damp in a small degree, it may be recovered by again drying it in a stove; but if the ingredients are decomposed, the nitre must be extracted by boiling, filtering, evaporating, crystallizing, &c. and then, with fresh sulphur and charcoal, to be re-manufactured.

There are several methods of proving and trying the goodness and strength of Gunpowder. The following, as common methods, are frequently made use of. 1, By sight; for if it be too black, it is too moist, or has too much charcoal in it; so also if rubbed upon white paper, it blackens it more than good powder does. 2, By touch; for if in crushing with your finger-ends, the grains break easy, and turn into dust, without feeling hard, it has too much charcoal in it; or if in pressing under your fingers upon a smooth, hard board, some grains feel harder than the rest, or, as it were, dent your finger-ends, the sulphur is not well mixed with the nitre, and the powder is bad. And also by burning, in which method, little heaps of powder are laid on white paper three or four inches asunder, and one of them fired; which, if the flame ascend rapidly, and with a good report, leaving the paper free from white spots, and without burning holes in it, and if sparks fly off and set fire to the adjoining heaps, the quality of the powder may be safely relied on; but if otherwise, it is either badly made, or the ingredients are impure.

These are some from among the common methods made use of for this purpose; but for greater accuracy in determining the relative strength of Gunpowder, various machines have of late been invented by men connected with military affairs. That excellent mathematician and philosopher, C. Hutton, LL.D. F.R.S. and late Professor of Mathematics in the Royal Military Academy, Woolwich, has constructed a machine for this purpose, which, for convenience and accuracy, far surpasses any thing of the kind hitherto invented. It is called Eprouvette, or a Gunpowder Prover, (for plans and description see third vol. Hutton’s Tracts, page 153;) and from its possessing so many peculiar advantages, is now generally used. It consists of a small cannon, the bore of which is about one inch in diameter, suspended freely like a pendulum, with the axis in a horizontal direction. This being charged with the proper quantity of powder, which is usually about two ounces, and then fired, the gun swings or recoils backward, and the instrument itself shews the extent of the first or greatest vibration, which indicates the strength to the utmost nicety. The whole machine is so simple, easy, and expeditious in its use, that the weighing of the powder is the greatest part of the trouble; and it is also so uniform with itself, that the successive repetitions or firings with the same quantity of the same kind of powder, hardly ever yield a difference of the hundredth part from the first vibration.

Having thus given an account of almost every thing necessary to be known in regard to the process of making and ascertaining the relative strength of Gunpowder, we shall close this article with a few observations (which will be selected from the best authorities) on the physical causes of its inflammation and exploding. When the several ingredients of Gunpowder are properly prepared, mixed, and grained, in the manner already described, if the least spark be struck thereon from a steel and flint, the whole will be immediately inflamed, and burst out with extreme violence.

The effect is not hard to account for: the charcoal part of the grains whereon the spark falls, catching fire like tinder, the sulphur and nitre are ready melted, and the former also breaks into flame; and at the same time the contiguous grains undergo the same fate.—Now it is known that salt-petre, when ignited, rarefies to a prodigious degree. Sir Isaac Newton reasons thus on the subject: “the charcoal and sulphur in Gunpowder easily take fire, and kindle the nitre; and the spirit of the nitre, being thereby rarefied into vapour, rushes out with an explosion much after the manner that the vapour of water rushes out of an æolipils; the sulphur also, being volatile, is converted into vapour, and augments the explosion: add, that the acid vapour of the sulphur, namely, that which distils under a bell into oil of sulphur, entering violently into the fixed body of the nitre, lets loose the spirit of the nitre, and excites a greater fermentation, whereby the heat is farther augmented, and the fixed body of the nitre is also rarefied into fume; and the explosion is thereby made more vehement and quick.”

For if salt of tartar be mixed with Gunpowder, and that mixture be warmed till it take fire, the explosion will be greatly more violent and quick than that of Gunpowder alone, which cannot proceed from any other cause than the action of the vapour of Gunpowder upon the salt of tartar, whereby the salt is rarefied.

The explosion of Gunpowder arises, therefore, from the violent action whereby all the mixture being quickly and vehemently heated, is rarefied and converted into fume and vapour; which vapour, by the violence of that action, becomes so hot as to shine, and appear in the form of a flame.