GUN-POWDER, a composition of saltpetre, sulphur, and charcoal, mixed together, and usually granulated; which easily takes fire, and, when fired, rarifies, or expands, with great vehemence, by means of its elastic force.
It is to this powder we owe all the action and effect of guns, ordnance, &c. so that the modern military art, fortification, &c. in a great measure depend thereon.
Method of making GUN POWDER. Dr Shaw's recipe for this purpose is as follows. Take four ounces of refined saltpetre, an ounce of brimstone, and six drams of small coal: reduce these to a fine powder, and continue beating them for some time in a stone mortar, with a wooden pestle, wetting the mixture between whiles with water, so as to form the whole into an uniform paste, which is reduced to grains, by passing it through a wire sieve fit for the purpose; and in this form being carefully dried, it becomes the common gun-powder.
For greater quantities, mills are usually provided, by means of which more work may be performed in one day, than a man can do in a hundred.
The nitre or saltpetre is refined thus: dissolve four pounds of rough nitre as it comes to us from the Indies, by boiling it in as much water as will commodiously suffice for that purpose: then let it shoot for two or three days in a covered vessel of earth, with sticks laid across for the crystals to adhere to. These crystals being taken out, are drained and dried in the open air.
In order to reduce this salt to powder, they dissolve
a large quantity of it in as small a proportion of water as possible; then keep it constantly stirring over the fire, till the water exhales, and a white dry powder is left behind.
In order to purify the brimstone employed, they dissolve it with a very gentle heat; then scum and pass it through a double strainer. If the brimstone should happen to take fire in the melting, they have an iron cover that fits on close to the melting vessel, and damps the flame. The brimstone is judged to be sufficiently refined if it melts, without yielding any fetid odour, between two hot iron plates, into a kind of red substance.
The coal for the making of gun-powder is either that of willow, or hazel, well charred in the usual manner, and reduced to powder. And thus the ingredients are prepared for making this commodity: but as these ingredients require to be intimately mixed, and as there would be danger of their firing if beat in a dry form, the method is to keep them continually moist, either with water, urine, or a solution of sal ammoniac: they continue thus stamping them together for twenty-four hours, after which the mass is fit for corning and drying in the sun, or otherwise, so as cautiously to prevent its firing.
Rationale of GUN-POWDER. The explosive force of gun-powder is now a thing commonly known, but the physical reason thereof may not perhaps be hitherto sufficiently understood. In order to explain it, Dr Shaw proposes the following observations: 1. That saltpetre of itself is not inflammable; and though it melts in the fire, and grows red hot, yet does not explode, unless it comes in contact with the coals. 2. That brimstone easily melts at the fire, and easily catches flame. 3. That powdered charcoal readily takes fire, even from the sparks yielded by a flint and steel. 4. That if nitre be mixed with powdered charcoal, and brought in contact with the fire, it burns and flames. 5. That if sulphur be mixed with powdered charcoal, and applied to the fire, part of the sulphur burns slowly away, but not much of the charcoal; and, 6. That if a lighted coal be applied to a mixture of nitre and sulphur, the sulphur presently takes fire with some degree of explosion; leaving part of the nitre behind, as we see in making the sal prunella, and sal polychrestum.
These experiments duly considered, adds the doctor, may give us the chemical cause of the strange explosive force of gun-powder. For each grain of this powder consisting of a certain proportion of sulphur, nitre, and coal, the coal presently takes 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 both a large proportion of air and water, which are now violently rarified 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.
Different kinds of GUN-POWDER. The three ingredients of gun-powder are mixed in various proportions according as the powder is intended for muskets, great guns, or mortars; though these proportions seem not to be perfectly adjusted or settled by competent experience.
Semienowitz, for mortars, directs an hundred pounds of saltpetre, twenty-five of sulphur, and as many of charcoal; for great guns, an hundred pounds of saltpetre, fifteen pound of sulphur, and eighteen pound of charcoal; for muskets and pistols, an hundred pound of saltpetre, eight pound of sulphur, and ten pound of charcoal. Miethius extols the proportion of one pound of saltpetre to three ounces of charcoal, and two, or two and a quarter of sulphur; than which he affirms, no gun-powder can possibly be stronger. He adds, that the usual practice of making the gun-powder weaker for mortars than guns, is without any foundation, and renders the expence needlessly much greater: for whereas to load a large mortar, twenty-four pound of common powder is required, and consequently, to load it ten times, two hundred and forty pound, he shews, by calculation, that the same effect would be had by one hundred and fifty pound of the strong powder.
To increase the strength of powder, Dr Shaw thinks it proper to make the grains considerably large, and to have it well sifted from the small dust. We see that gun-powder, reduced to dust, has little explosive force; but when the grains are large, the flame of one grain has a ready passage to another, so that the whole parcel may thus take fire nearly at the same time, otherwise much force may be lost, or many of the grains go away as shot unfired.
It should also seem that there are other ways of increasing the strength of powder, particularly by the mixture of salt of tartar; but perhaps, adds the last-mentioned author, it were improper to divulge any thing of this kind, as gun-powder seems already sufficiently destructive.
Method of trying and examining GUN-POWDER. There are two general methods of examining gun-powder; one with regard to its purity, the other with regard to its strength. Its purity is known by laying two or three little heaps near each other upon white paper, and firing one of them: for if this takes fire readily, and the smoke rises upright, without leaving any dross or feculent matter behind, and without burning the paper, or firing the other heaps, it is esteemed a sign that the sulphur and nitre were well purified, that the coal was good, and that the three ingredients were thoroughly incorporated together: but if the other heaps also take fire at the same time, it is presumed, that either common salt was mixed with the nitre, or that the coal was not well ground, or the whole mass not well beat, and mixed together; and if either the nitre or sulphur be not well purified, the paper will be black or spotted.
In order to try the strength of gun-powder, there are two kinds of instruments in use; but neither of them
them appear more exact than the common method of trying to what distance a certain weight of powder will throw a ball from a musket.
There has been much talk of a white powder, which, if it answered the character given it, might be a dangerous composition; for they pretend that this white powder will throw a ball as far as the black, yet without making a report; but none of the white powder we have seen, says Dr Shaw, answers to this character; being, as we apprehend, commonly made either with touchwood or camphor, instead of coal.
Observations on the force of GUN-POWDER. Gun-powder, fired either in vacuum, or in air, produces, by its explosion, a permanent elastic fluid. For if a red-hot iron be included in a receiver, after being exhausted, and gun powder be let fall on the iron, the powder will take fire, and the mercurial gage will suddenly descend upon the explosion; and though it immediately ascends again, yet it will never rise to the height it first stood at, but will continue depressed by a space proportioned to the quantity of gun powder which was let fall on the iron.
The same production likewise takes place, when gun powder is fired in the air: for if a small quantity of powder be placed in the upper part of a glass tube, and the lower part of the tube be immersed in water, and the water be made to rise so near the top, that only a small portion of air is left in that part where the gun-powder is placed; if in this situation the communication of the upper part of the tube with the external air be closed, and the powder be fired, which will easily be done by a burning-glass, the water will in this experiment descend upon the explosion as the quicksilver did in the last; and will always continue depressed below the place at which it stood before the explosion; and the quantity of this depression will be greater, if the quantity of powder be increased, or the diameter of the tube be diminished. From whence it is proved, that as well in air as in a vacuum, the explosion of fired powder produces a permanent elastic fluid. It also appears from experiment, that the elasticity or pressure of the fluid produced by the firing of gun powder, is, ceteris paribus, directly as its density. This follows from hence, that if in the same receiver a double quantity of powder be let fall, the mercury will subside twice as much as in the firing of a single quantity.
To determine the elasticity and quantity of this elastic fluid, produced from the explosion of a given quantity of gun-powder, Mr Robins premises, that the elasticity of this fluid increases by heat, and diminishes by cold, in the same manner as that of the air; and that the density of this fluid, and consequently its weight, is the same with the weight of an equal bulk of air having the same elasticity, and the same temperature.
From these principles, and from his experiments, (for a detail of which we must refer the reader to his New Principles of Gunnery, in Scholium to prop. II.) he concludes, that the fluid produced by the firing of gun-powder will be of the weight of the gun pow-
der, and the ratio of the respective bulks of the powder, and the fluid produced from it, will be in round numbers 1 to 244.
Hence we are certain, that any quantity of powder fired in any confined space, which it adequately fills, exerts, at the instant of its explosion, against the sides of the vessels containing it, and the bodies it impels before it, a force at least 244 times greater than the elasticity of common air; or, which is the same thing, than the pressure of the atmosphere; and this without considering the great addition which this force will receive from the violent degree of heat with which it is endowed at that time, the quantity of which augmentation is the next head of Mr Robins's enquiry. He determines that the elasticity of the air is augmented when heated to the extremest heat of red hot iron, in the proportion of 796 to 194; and supposing that the flame of fired gun-powder is not less hot than red hot iron, and the elasticity of the air, and consequently of the fluid, generated by the explosion, being augmented by the extremity of this heat in the ratio of 796 to 194, it follows, that if 244 be augmented in this ratio, the resulting number, which is 999, will determine how many times the elasticity of the flame of fired powder exceeds the elasticity of common air, supposing it to be confined in the same space which the powder filled before it was fired.
Hence then, the absolute quantity of the pressure exerted by gun-powder at the moment of its explosion may be assigned: for since the fluid then generated has an elasticity of 999, or, in round numbers, 1000 times greater than common air; and since common air, by its elasticity, exerts a pressure on any given surface equal to the weight of the incumbent atmosphere with which it is in equilibrium, the pressure exerted by fired powder, before it has dilated itself, is 1000 times greater than the pressure of the atmosphere; and consequently the quantity of this force on a surface of an inch square amounts to above six tun weight, which force however diminishes as the fluid dilates itself. The variations of the density of the atmosphere does not any way alter the action of powder by any experiment that can be made. But the moisture of the air has a very great influence on the force of it: for that quantity which in a dry season would communicate to a bullet a velocity of 1700 feet in one second, will not in damp weather communicate a velocity of more than 12 or 1300 feet in a second, or even less, if the powder be bad and negligently kept.
The velocity of expansion of the flame of gun-powder, when fired in a piece of artillery, without either bullet, or any other body before it, is prodigious. By the experiments of Mr Robins, it seems this velocity cannot be much less than 7000 feet in a second. This, however, must be understood of the most active part of the flame. For, as was observed before, the elastic fluid, in which the activity of gun-powder consists, is only of the substance of the powder, the remaining will in the explosion be mixed with the elastic part, and will by its weight retard
ard the activity of the explosion; and yet they will be so completely united, as to move with uncommon motion; but the unelastic part will be less accelerated than the rest, and some of it will not even be carried out of the barrel, as appears by the considerable quantity of unctuous matter, which adheres to the inside of all fire-arms, after they have been used. These inequalities in the expansive motion of the flame render it impracticable to determine its velocity, otherwise than from experiments.
To recover damaged Gun powder. The method of the powder-merchants is, to put part of the powder on a sail-cloth, to which they add an equal weight of what is really good; and with a shovel 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, scarce it, and to every pound of powder add an ounce, an ounce and a half, or two ounces, according as it is decayed, of melted salt petre. Afterwards these ingredients are to be moistened and mixed well, so that nothing can be discerned in the composition, which may be known by cutting the mass; and then they granulate it as aforesaid. In case the powder be in a manner quite spoiled, the only way is to extract the salt-petre with water, according to the usual manner, by boiling, filtering, evaporating, and crystallizing; and then with fresh sulphur and charcoal to make it up a new again. In regard to the medical virtues of gun-powder, Boerhaave informs us, that the flame of it affords a very healthy fume in the height of the plague: because the explosive acid vapour of nitre and sulphur corrects the air; and that the same vapour, if received in a small close pent up place, kills insects.
It is enacted by 5 and 11 of Geo. I. and 5 Geo. II. c. 20. that gun-powder be carried to any place in a covered cartage; the barrels being close jointed; or in cases and bags of leather, &c. And persons keeping more than 200 pounds weight of gun-powder at one time, within the cities of London and Westminster, or the suburbs, &c. are liable to forfeitures if it be not removed; and justices of peace may issue warrants to search for, seize, and remove the same.
The invention of gun-powder is ascribed by Polydore Virgil to a chemist, who having accidentally put some of the ingredients in this composition in a mortar, and covered it over with a stone, it happened to take fire, and blew up the stone. Thevet says, the person here spoken of was a monk of Friburg, named Constantine Anelzen; but Belleforest and others hold it to be Bartholdus Schwartz, or the black; at least it is affirmed, that he first taught the use of it to the Venetians, in the year 1380, during the war with the Genoese. But what contradicts this account, and shews gun-powder to be of an older date, is, that Peter Mexia, in his Variae Lectiones, relates, that Alphonso XI. king of Castile, used mortars against the Moors in a siege in 1343. Ducange adds, that there is mention made of this powder in the registers of the chambers of accounts in France, as early as the year
1338; and frier Bacon, our countryman, mentions the composition in express terms, in his treatise De nullitate magie, published at Oxford, in the year 1216.