ON THE MANUFACTURE OF GUNPOWDER.

Composition of powder.

Gunpowder is an explosive propellant agent; a mechanical combination and intimate mixture of saltpetre, charcoal, and sulphur, in certain fixed proportions, the result of successive experiments.

To be effective, Gunpowder should,

Ought to keep without deterioration.

1st.—Preserve itself in a good state, whether in magazine or in carriage.

Leave no residue.

2nd.—Leave as little residue as possible after ignition.

Combine quickness and power.

3rd.—Should combine a certain quickness of combustion with great explosive force.

SALTPETRE, OR NITRE.

Nitre.

The principal ingredient in Gunpowder is an abundant production of Nature, and is a combination of nitric acid with the vegetable alkali. It is never found pure, being always contaminated with other salts and earthy matter. Where found.It is principally found in the East Indies, Ceylon, and South America, and is sometimes produced from decayed animal and vegetable matter. Unfit in natural state.It is totally unfit for Gunpowder until it has been refined; for, being combined with muriates of soda, lime, magnesia, and other salts, which absorb moisture, the close contact of the ingredients would be deranged by their presence, the strength of the powder weakened, and the power of resisting the action of the atmosphere greatly lessened. As for the efflorescent salts it may contain, they are noxious only inasmuch as, possessing no particular useful property, they interpose their atoms between the more combustible ingredients, and impede the rapidity of deflagration.

Two methods of refining.

There are two methods of refining saltpetre at Waltham Abbey:—1st, the Old Method, of re-crystallizing three times; and 2nd, the New Method, which has only just been adopted, both of which we shall here briefly describe.

OLD METHOD.

Old method.

About 35 cwt. of the grough saltpetre, as it is termed, viz., as it is imported in its impure state, is put into a copper capable of holding 500 gallons, with 270 gallons of water, in the proportion of about 1¹⁄₂lbs. of nitre to 1lb. of water, (which proportion varies with the quality of the saltpetre). This is allowed to boil, and the impurities are skimmed off as they appear on the surface. Cold water is occasionally thrown in to precipitate portions of the chloride, which otherwise would remain on the top by the action of boiling. After being allowed to boil from three and a half to four hours, the furnace doors are thrown open, when the chlorides and salts fall to the bottom. In about two hours, a copper pump is lowered into the liquor, which is pumped out into a wooden trough, having four or five brass cocks, under which are suspended canvas filtering bags in the shape of a V. The solution is then filtered, and run off into pans, containing about 36 gallons, and allowed to remain for twenty-four hours, to crystallize, when they are set up on edge, to drain off the liquor which remains uncrystallized, and which is called mother liquor. The saltpetre thus obtained is called once-refined, and undergoes the same process twice again, the only difference being that there is a greater proportion to the water each time, viz. 1³⁄₄lb. to 1lb. of water the second time, and 2lb. to 1lb. of water the third time: moreover, the third time, a small quantity of ground charcoal is put into the solution, and it passes through double filters, which brings it to a very fine pure white colour when melted. The mother water which remains in the pans after each crystallization is conveyed away by gutters to cisterns under the building; it is then evaporated in iron pots to one quarter of its original bulk, filtered, and allowed to crystallize. The saltpetre obtained from the first mother water is considered one stage inferior to grough; that from the second, equal to grough; that from the treble-refined, equal to once-refined saltpetre. The water left from every stage is treated in the same way, so that actually nothing is lost of the pure material. Saltpetre treble-refined by this process is perfectly pure, and fit for the manufacture of Gunpowder; and in order to free it from moisture, as well as for the convenience of storage and transport, it is melted in iron pots holding about 4 cwt., Saltpetre fuzes at 600°.by raising it to a temperature of 600° Fahrenheit, and cast into gun-metal circular moulds holding about 38lbs. each. It must be observed that it requires about two hours to bring the saltpetre into a liquid state, and that, after this, the furnace doors are thrown open, to lower the heat to the proper temperature for casting into the moulds. When the cakes are cold, they are packed away in barrels containing 1 cwt., 1 qr. each, and put into store. Care must be taken, in melting the saltpetre, not to raise it to too high a temperature, as this would reduce the quantity of oxygen, and form nitrite of potash, which would render it unfit as an ingredient in the composition of Gunpowder.

A neutral salt.

Saltpetre is a neutral salt, the constituents of which are 46.55 potash, and 53.45 nitric acid; the latter consisting of two volumes nitrogen and five of oxygen. It is white, and of a fresh, sharp, and slightly bitter taste. It crystallizes in six-sided prisms. Exposed to the air, it remains permanent unless impure, or that the atmosphere is very moist.

NEW METHOD.

New method.

Forty cwt. of the grough saltpetre is put into a copper with 270 gallons of water, and treated in precisely the same way as we have before described for the first refining; it is then filtered and run off into large troughs, about 10 feet long by 6 feet wide, and 9 inches deep, lined with sheet copper; this liquor is then kept in a state of agitation by a wooden rake, until nearly cold. By this process a large quantity of very minute crystals are formed, which are collected as they form by a wooden hoe, and shovelled with a spade on to a framework covered with copper sieving resting on the opposite sides of the trough, and allowed to drain. These fine white crystals, which have exactly the appearance of snow, when they have drained sufficiently, are raked over in a washing cistern adjoining, which is about 6 feet long, 4 feet wide, and 3ft. 6in. deep, and fitted with a false wooden bottom that can be removed at pleasure. Cold water is allowed to run on to the saltpetre in this cistern till it is nearly level with the top. After remaining for an hour it is drained off, and filled again with fresh water, which is drained off after about another hour. The saltpetre thus obtained is perfectly pure, and equal in every respect to the treble-refined by the old method. The water remaining in the cisterns after agitation, is left till the next morning, when a quantity of larger crystals are formed on the bottom and sides; these are equal to once-refined by the old method, and are used with grough; the mother-liquor is then drained off, and evaporated in the usual way. The water from each washing is conveyed into cisterns, and used with grough saltpetre instead of water; but, as it contains a small portion of saltpetre in solution, a lesser quantity of grough is used to make the proportions correct.

Drying.

The saltpetre flour, however, contains a certain degree of moisture, which has to be dried off in the following way: two large copper trays, about 10 feet by 6 feet, with a 3-inch rim, are fixed over flues heated by a furnace, 4 inches of sand being between the flues and the bottom of the trays; the saltpetre is spread about 2 inches deep all over, and raked about till dry; it is then barrelled up for use. It takes about two hours to dry 5 cwt.

Comparison of the two methods.

On comparing the two systems, there cannot for one moment be a doubt as to the immense advantages of the latter over the former. As an example, in the refinery where this new process is carried on, the result (that is to say, pure saltpetre) is obtained in one day instead of six, with less than one half the amount of labour and coals.

Why new method best.

On reflection, the reason of the great gain of time by this process will suggest itself. In the former method, when allowed to remain quiet, the crystals formed are very large, and the spaces left in them always contain a certain amount of mother-water, which necessitates its being crystallized three times to perfectly free it from the liquor. In the latter, the crystals are so minute that there is practically no space for the mother-water to collect; consequently, by careful washing, the saltpetre is obtained perfectly pure.

CHARCOAL.

Charcoal.

Wood charcoal is the woody fibre that remains after the liquid and more volatile parts have been driven off by the fire in the process of charring. The temperature resulting from the combustion of charcoal is much higher than that from burning wood, in consequence of the absence of the large quantity of water which wood contains, amounting to between 50 and 60 per cent.; Object of charring.the object, therefore, of charring wood is the removal of moisture, and also, what is of great importance, the expulsion of those matters contained in it which become volatile before they are burned, thus rendering a large amount of heat latent. Best wood for charcoal.The woods generally used in this country in making charcoal for gunpowder are the alder, willow, and dogwood. There are about 60 acres of wood grown for charcoal at Waltham Abbey. The alder is cut every eight years, and the willow in six years. It is used after one year. Other woods are sometimes used by English and foreign manufacturers, but none produce a powder of such quality as obtained from the above. It is usually considered that better charcoal is distilled when the wood is allowed to season for a time; but recent experience has shown that wood only lately cut and peeled, after being desiccated in a hot chamber, will make equally good charcoal with that which has been seasoning for three or four years.

First process.

All the wood which is cut in the Government grounds or purchased from merchants, is stripped of the bark, on account of its being impregnated with salts and gummy substances, cut into lengths of 3 feet for the convenience of loading the iron slips, which are a little above this length, and stacked in the wood-yard.

Cylinder charcoal.

Cylindrical cases of the required size, fitted with lids, are filled with wood. These cases are made to fit easily, and slide horizontally into iron retorts built in the wall, which admit of the accurate regulation of heat (communicated to them by furnaces underneath) throughout the operation of charring. A great saving of time and heat is effected by their use, as when the wood has been properly charred the case or slip containing it may be easily withdrawn, and another containing a fresh charge at once introduced into the retort, without allowing the latter to cool down, as would otherwise be necessary. When it has been sufficiently charred (which is known by experience, in watching the burning of the gas that is produced and is conducted into the fire), the slip is withdrawn by tackling, and at once lowered down into iron coolers or cases, which are immediately covered up with close-fitting lids, and then allowed to remain until all fire is extinguished. The goodness of charcoal is an essential point in the manufacture of gunpowder. Quantity produced.About twenty-five to thirty per cent. is obtained; and one cord will produce about four cwt. of charcoal. Qualities.If properly charred, it should have a jet black appearance, and when powdered a lustre resembling velvet; it should be light and sonorous when gently dropped, and its fracture should exhibit the same appearance throughout; it should be so soft as not to scratch polished copper, and ought not to exhibit any alkali when treated with pure distilled water. Charcoal is very porous, and absorbs very greedily gases and moisture from the atmosphere; no large store therefore is ever kept, and particular care is taken to prepare it only in proportion as it is required for use. Kept dry.At all times it must be kept exceedingly dry; Absorbs.when whole it will absorb about eight per cent. its weight of moisture, and when in powder 15 per cent., so that the fresher the charcoal is the better for the powder.

SULPHUR.

Sulphur.

Sulphur is a simple, combustible, solid, non-metallic, elementary body. It is found generally in great quantities in the neighbourhood of volcanoes. It is also obtainable from metallic ores, and readily fuzes. At 170° Fahrenheit it begins to evaporate; at 185° to 190° it melts; at 220° it is perfectly fluid; and at 600° it sublimes. How purified.Sulphur is purified simply by melting: that which is supplied to Waltham Abbey has been once refined, and the following is a description of the apparatus and method for purifying and rendering it fit as an ingredient in Gunpowder. A large iron pot is set about three feet off the ground, or about the height that an ordinary boiling copper is placed, having a furnace underneath. This pot has a movable lid, which is fixed into the top of the pot with clay, and in which lid is an iron conical plug that can be removed at pleasure. From the pot lead two pipes, one to a large circular dome, and another to an iron retort, rather below its level. The last-mentioned pipe has a casing, or jacket, round it, which can be filled with cold water. The communication of these pipes with the melting pot can be shut off or opened, as occasion requires, by a mechanical arrangement. About 5¹⁄₂ to 6 cwt. of the once-refined sulphur is broken up into small pieces, placed in the iron melting pot, and subjected to the action of the furnace. The plug in the lid, and the pipe leading to the dome are now left open, but the pipe to the retort closed. After from two to three hours a pale yellow vapour rises, when the plug is put in, and the vapour conducted into the dome, where it condenses in the form of an impalpable powder, commonly called flowers of sulphur. A small pipe leads from the bottom of the dome, on the opposite side, into water, to allow the escape of the air, and sulphuric acid is taken up by this water. In about one and a half to two hours after, the vapour becomes of a deep iodine colour, when the communication with the dome is shut, and the one to the retort opened; at the same time, cold water from a tank above is allowed to pass into the jacket we have before mentioned, surrounding this pipe. The vapour then which distils over is condensed in the pipe, and runs into the retort below in the form of a thick yellow fluid. When nearly all has distilled, which can be known by the jacket getting cold, the communication is again closed with the retort, and the fluid sulphur left an hour, to get sufficiently cool to ladle out into moulds, the furnace door and the communication with the dome at the same time are again thrown open, that the rest of the vapour may pass into the latter. Flowers of sulphur unsuitable.The flowers of sulphur thus obtained are used for laboratory purposes, being unfit for the manufacture of Gunpowder, from the acid they contain, and the crystalline sulphur, after being allowed to cool in the moulds, is barrelled up and used as the third ingredient in Gunpowder.

PULVERIZING THE INGREDIENTS.

Grinding.

The three ingredients are now ground separately to a very fine powder. The mills (vide plate 1) which effect this, and incorporate, are so similar, that a description will be given under the head of “Incorporation.” Screening.After being ground in this way, the saltpetre is passed through a slope cylindrical reel, covered with copper sieving wire of 60 meshes to the inch, which, as it revolves, sifts it to the required fineness, being then received in a box or bin underneath. The charcoal and sulphur are likewise passed through similar reels of 32 and 60-mesh wire respectively, and that which remains without passing through, is ground again under the runners. A very excellent machine has been invented by Mr. Hall, the engineer, of Dartford, for grinding charcoal, which makes a most useful addition to the Gunpowder factory. It consists of a conical drum, working in a conical box, on the same principle as a coffee-grinding machine, the axis being vertical. The mill is fed with charcoal by a hopper, and, as it passes through in fine powder, falls into a revolving reel, which sifts it in the same manner as before described, the whole being covered in, to prevent the great annoyance of dust, which was felt until lately, from the old charcoal mill. The three ingredients having been pulverized, are now fit for the mixing process.

MIXING THE INGREDIENTS.

Mixing and proportions.

The ingredients are now weighed out very accurately, in the proportion of 75 nitre, 15 charcoal, and 10 sulphur, in 42lb. charges, viz., nitre, 31lbs. 8oz., charcoal, 6lbs. 4oz. 13drs., sulphur, 4lbs. 3oz. 3drs., and thoroughly mixed in a machine, which consists of a cylindrical gun-metal or copper drum, about two feet in diameter, with an axle passing through its centre, on which there are metal flyers, like forks. The machinery is so arranged that the flyers and drum revolve in opposite directions when in motion, at a rate of about one hundred revolutions per minute. Five minutes is sufficient for a thorough mixture. The composition is then drawn off by a slip into canvas bags the proper size to hold the 42lb. charges, which are tightly tied, and taken to small magazines. Green charges.These are called green charges, and are now ready for the next process, incorporation.

THE INCORPORATING MILL.

Incorporation.

The Incorporating Mill consists of an iron or stone circular flat bed, about seven feet in diameter, fixed very firmly in the floor of the building which covers it, whereon two iron or stone cylindrical runners, from five to seven feet in diameter, fourteen to eighteen inches wide, and each weighing from 3 to 4¹⁄₂ tons, revolve. They have a common axle, and a vertical shaft passing through the centre of the bed is connected with this axle, and to machinery above or below, which communicates the motion. These runners are not equidistant from the centre, by which arrangement in their revolution every part of the composition on the bed is subjected to their action, which is threefold, viz., crushing, grinding, and mixing; crushing, from the weight of the cylinders; grinding, from the twisting motion which they are forced into from so large a diameter revolving in so small a circle; and mixing, from a combination of the two former motions. To prevent the powder from falling over the side of the bed, a wooden rim, about two feet in height, is placed at an angle of forty-five degrees with it, like the side of a funnel, and fitted closely all round its circumference. This is called the “curb;” and in the centre of the bed a gun-metal ring, or “cheese,” as it is termed, about two feet in diameter, and five inches high, concentric with the bed, prevents the powder working beyond in that direction. Moreover, two scrapers, or “ploughs,” connected by stays with the horizontal axle, revolve with the runners, one rubbing against the inner, and the other the outer circle. These ploughs are made of hard wood, shod with leather and felt, and their use is continually to disturb and rout about the composition, and keep it under the path of the runners, so that every part should get its share of incorporation. The houses or sheds which cover these buildings have hitherto been constructed of wood, with either corrugated iron or wooden roofing. The new incorporating mills in this factory, which are just completed, are built with three sides of strong three-foot brickwork, and the fourth side and roof of corrugated iron and glass. They are also placed in a line contiguous to each other, the alternate ones only facing the same way, so that an explosion from one would probably communicate no further, and the lighter parts of the building would blow away, leaving the rest entire. Most of the machinery in the factory is driven by water-wheels; the motive power of these mills is steam. A horizontal shaft, worked by the engine, passes underneath the entire length of the building in a cast-iron tank, and a bevel wheel on this shaft is geared into another one on the vertical shaft under the centre of each bed, which, communicating with the runners, gives the necessary motion.

Water-tanks to prevent explosions.

In order, as much as possible, to guard against any explosion spreading, above each bed, placed so as just to clear the runners, is suspended or balanced a copper tank, holding about forty gallons of water. On one side of the tank is fixed a small shaft, which communicates with similar cisterns over the beds of the mills on either side. The other end of the tank rests on a flat board, which is subjected to a great part of the force of an explosion. This consequently lifts, disengaging the support of the tank, the contents of which drench the bed which has just exploded, thereby putting out all fire, and cooling the machinery, besides having a similar effect on the mills right and left, preventing, by this means, any extension of fire.

INCORPORATING THE INGREDIENTS.

Incorporation.

The charge is spread pretty evenly over the surface of the bed, and moistened with from four to six pints of distilled water; the quantity varying according to the state of the atmosphere; the runners are then set in motion, and run from seven to eight revolutions per minute for three and a half hours, during which time the powder is often routed up by a copper-shod spud, and watered slightly with a fine rose watering pot, according to the experience of the millman; at the end of this time the mixture is thoroughly incorporated, possesses all the chemical properties of Gunpowder, and is taken off the bed in the form of a cake, varying from a quarter to half an inch in thickness, and of a blackish-grey colour. Mill cake.This is called “Mill Cake,” and when broken, the fracture should exhibit the same uniform appearance, without presenting any sparkling or yellow specks; should this, however, be the case, it is a sign of the ingredients not being sufficiently incorporated. Proof of mill cake.In this stage it undergoes certain proofs; samples of the cake are taken from every charge that is worked, dried in an oven, and granulated; half a drachm of this is fired in a vertical eprouvette, which it ought to raise 3.5 inches; and half an ounce is flashed on a glass plate. If very little residue or ash is left, it is an additional proof of its being well incorporated, and that the millman has done his work properly.

Importance of incorporation.

Incorporation is by far the most important process in the manufacture of Gunpowder; for, however carefully the other part of the fabrication is carried on, should there be a failing in this, the powder will be worth nothing.

Object of manufacture.

The great and ultimate object to be attained in the manufacture of Gunpowder is, to produce that which shall give equal results with equal charges; the greatest regularity should therefore be observed in this stage. The millman should have great experience; the runners and beds should be, as nearly as possible, the same size and weight, and driven at the same speed throughout the factory; at any rate, each charge should be worked to the same number of revolutions; the motion of the runners should also be as uniform as possible, which is very satisfactorily accomplished by each water-wheel being regulated by a governor.

BREAKING DOWN THE MILL CAKE.

Breaking down the mill cake.

The mill cake, after it comes off the bed of the incorporating mill, is placed in wooden tubs, and taken to small-expense magazines, and from there, in about twelve hours, to the breaking-down house; Object of mealing.the object of the machine from which this takes its name, is to reduce the cake to a convenient size for the hydraulic-press box, and also that, by being crushed again to meal, it may get a more even pressure. It consists of a strong gun-metal framework, in which are fixed two pairs of fine-toothed or plain rollers, which revolve towards each other, working in spring collars, so that on any hard substance getting in by mistake, they would open, and allow it to pass through, thereby preventing the dangerous friction which would otherwise result. A hopper, or upright wooden funnel, capable of holding about 500 lbs. is fixed at one end of the machine, and an endless canvass band 2ft. 6in. wide, having strips of leather sewn across at intervals of four inches, passes over one roller at the bottom of the hopper, and one at the top of the machine. When set in motion, this conveys the cake from the hopper to the highest point of the band; it then falls through the first pair of rollers, and from thence through the second, passing in the form of meal into small wooden carriages underneath, which, as they are filled, move forward by a self-acting motion, making room for others. The mill cake thus broken down, is fit for the press.

PRESSING THE MEAL BY THE HYDRAULIC PRESS.

Hydraulic Pressure.

The meal is now subjected to very powerful pressure; and, in order to explain the way in which this is effected, a short description of the apparatus must be given. The principle of the hydraulic press is so familiar to most, that it will be unnecessary to do more than show how the power is applied (vide plate 2).

Description of box.

A very strong oak box, 2 feet 6 inches square, and 2 feet 9 inches deep, is constructed so that two of the sides of the lid will fall back on hinges, or form a compact solid box when screwed firmly together. Forty-six copper plates, 2 feet 5¹⁄₂ inches square, slide vertically into this box, and are kept five-eighths of an inch apart by two metal slips with corresponding grooves, which can be removed when necessary.

Quantity pressed.

About 800 lbs. of the meal is put into this box while the plates are in the position we have described. When full, the slips are withdrawn, the plates being then only separated by the powder between them: the lid is now firmly screwed down, and the box turned over by an arrangement of pulleys, so that the plates which were vertical will now be horizontal. The present upper side is then unscrewed, and a travelling crane, moving on a rail overhead, is lowered till the claws attached to it hook on to two trunnions fixed on the sides of the box; it is now hoisted by means of a handwheel windlass, and the box being suspended, is pushed easily by means of the rail, and deposited in this position on to the table of the ram under the press block. Amount of pressure.The pumps are now set in motion by a water-wheel, and are allowed to work up to the required pressure, which is about seventy tons to the square foot; it is then conveyed from under the block in the same manner, and very easily unloaded. The press cake is then taken out in layers between each plate, resembling dark pieces of slate, about half an inch in thickness. After a day or so, this hardens so much as to be difficult to break, and the appearance of the fracture resembles that of the finest earthenware. Many important advantages are gained by this pressure, of which the following are the principal:—

Reasons for pressure.

First, the density of the powder is increased, which prevents it falling to dust in transport, or by rough usage. Secondly, its keeping qualities are improved, for it withstands the action of the atmosphere, and absorbs less moisture than a porous light powder. Thirdly, it produces more grain in the manufacture than mill cake; and a less proportion, consequently, is lost in dust. Fourthly, a closer connection of the ingredients is obtained. Fifthly, a greater volume of inflammable gas is produced from a certain bulk, than from a corresponding bulk of lighter powder.

Disadvantages of pressure.

The range, however, is lessened, from a greater quantity being blown out of a gun unignited; but this small loss is more than counterbalanced by the former advantages, and actually it is only perceptible in newly-made powder; for a light, porous powder soon loses its superior range from its absorption of moisture, while that of the dense powder remains unaltered.

GRANULATING THE PRESS CAKE.

Mode of granulation.

The next process is granulation, or reducing this press cake into the proper sized grain for cannon, musket, or rifle powder. The machine which effects this is very beautifully contrived, and is entirely self-acting, obviating the necessity of any one being in the building while it is in motion. It resembles, in appearance and action, the breaking-down machine, except that it is larger, and is fitted with three pairs of toothed rollers, of different degrees of fineness, working in the same kind of collars already mentioned, so that, on any hard substance passing through, they would open accordingly, and thus prevent friction. At one end of the machine is a wooden hopper, or funnel, which is filled with the press cake. This is contrived so as to rise gradually by the motion of the machine, and constantly to supply an endless band, similar to the one described in the breaking-down house. When the cake arrives at the highest point of this band, it falls over, and is granulated between the first pair of gun-metal rollers. Screening.Under each pair is a screen, covered with 8-mesh wire. All that is not sufficiently small to pass through, is carried on to the next pair of rollers; and, in like manner, that which does not pass through the second screen is carried to the third pair. In addition to these screens, there are three oblong sieves covered with 8- and 16-mesh wire, and 56 cloth respectively, fixed under, and parallel to, each other, each being separated by about four inches of space, running at an incline just below the three pairs of rollers; these all lead to little wooden carriages placed on the opposite side of the machine, which are divided so as to collect the different sized grain as it passes down. To facilitate the separation and sifting of the powder, and to prevent masses of it forming and clogging up the wire, a shaking motion is imparted by a circular wheel attached to the framework of these sieves revolving against an octagonal one fixed to the machine. The grains which pass through each screen below the rollers fall on the upper one of these three last-mentioned sieves. That portion which passes through this, and is retained on the 16-mesh wire, is cannon powder; that passing through the 16-mesh sieve, and retained on the 56-cloth, is fine grain; and a board, running also parallel underneath, retains the dust that passes through the cloth.

Chucks regranulated.

The “chucks,” as they are called, or those grains that are too large to pass through these different sieves, are collected in the same way as the grain, and undergo the process of granulation again.

DUSTING LARGE-GRAIN POWDER.

Object of dusting.

The keeping qualities of powder are very much improved by removing the dust, which quickly absorbs moisture from the atmosphere. How performed for large-grain.This operation, for large-grain, is performed by cylindrical reels, about 8ft. 6in. long, and 3ft. 8in. in diameter, clothed with 28-mesh canvas, which revolve at the rate of thirty-eight times per minute. Those for large-grain are called horizontal reels, in contradistinction to those for fine-grain, that are called slope reels. Each is enclosed by a wooden case, to prevent the dust flying about the house. When the powder has run its time, one end of the reel is lowered. It then runs out into barrels placed to receive it. Glazed at same time.This entirely separates the dust, and imparts a fine black gloss, which is sufficient glazing for the large-grained powder.

DUSTING FINE-GRAIN POWDER.

Dusting fine-grain.

The fine-grain powder has a much greater proportion of dust when it leaves the granulating house than the large-grain, and it is found necessary, on this account, to use a different kind of reel. They resemble those for the former powder, except that they are covered with 44-mesh canvas instead of 28, and are placed at an incline which prevents their being choked up with the quantity of dust; each end is also open, and a continuous stream of powder, fed by a hopper, passes through while they revolve, and pours out at the lower end into barrels. This process is repeated a second time, which sufficiently frees it from dust.

GLAZING FINE-GRAIN POWDER.

Glazing fine-grain.

The fine-grain powder thus dusted, is then glazed for three hours in barrels capable of holding 300lbs. which are 3ft. 6-in. in length, and 2ft. 8-in. in diameter, revolving at the rate of thirty two times in a minute. By the mere friction of the grains against each other and the inside of the barrel, a glaze is imparted, presenting a fine polished surface to the grain.

Object of glazing.

Powder glazed in this way withstands the action of moisture to a far greater extent than unglazed powder, and in transport very little dust is formed.

STOVING OR DRYING POWDER.

Drying.

A drying-room, heated by steam pipes, is fitted with open framework shelves, on which rests small wooden trays about 3ft. long, 1ft. 6-in. in breadth, and 2¹⁄₂in. deep, having canvas bottoms; on each is spread 8lbs. of powder. This room holds about 40 barrels, or 4,000lbs., which remains in it for twenty four hours, and is subjected to a heat of 130° Fahrenheit for sixteen hours, communicated by steam passing through pipes arranged horizontally on the floor of the room. The temperature is raised and lowered gradually, otherwise the too sudden change would be likely to destroy the texture of the grain. The ceiling and roof are fitted with ventilators, through which all the moisture escapes, so that there is a constant current of hot air circulating through the room. It is of the greatest importance that the vapour should be carried off; for, if this is not effectually done, on the decrease of temperature, it would return to its liquid state, and form again on the powder.

FINISHING DUSTING.

Final dusting.

The action of heat however produces a small portion of dust; both these powders, therefore, when they leave the stove, are reeled in horizontal reels, clothed with 28 and 44-mesh canvas respectively, for one hour and a half. This perfectly separates any remaining dust, and gives the finishing glaze to the large-grain powder. Barrelling.This is the final process, and the powder thus finished is taken to the barrelling-up house; weighed out into barrels holding 100lbs. each; marked L. G. (large-grain), and F. G. (fine-grain), as the case may be; and stored in magazines.

EXAMINATION AND PROOF OF GUNPOWDER.

Desired properties of gunpowder.

The great and ultimate object to be attained in the manufacture of Gunpowder is, not so much to produce that which ranges the highest, as one that shall be durable in its texture, not easily deteriorated by atmospheric influence or transport, and one with which equal charges shall produce equal effects. It should present uniformity in the appearance of its grains, which should be angular, crisp and sharp to the touch, not easily reduced to dust by pressure between the fingers, or dusty in handling; Specific gravity.its specific gravity should not be under 55lbs. to the cubic foot, (that of Waltham Abbey is generally 58lbs.) taking water at 1000ozs.; Strength.its strength is tested by firing three rounds from an 8 inch mortar, throwing a 68-pounder solid shot with a charge of 2oz. this should give a range of from 270 to 300 feet. The distance however, varies considerably, according to the state of the atmosphere, and the density of the powder: for, the greater the density, the less the range in small charges. Purity.Half an ounce flashed on a glass plate should leave little or no residuum; should white beads or globules appear, it is a sign of imperfect incorporation.

PROOF OF MERCHANT’S POWDER.

The following are the different proofs merchant’s powder is subjected to:—

Lots of 100 barrels are sent in, marked with the number of the lot and the maker’s name on the head of each barrel. 25 per cent. of these are unheaded in the examining house; the Proof Officer then—

If dusty.

First, takes a bowl out of each barrel, and holding it about three feet above, pours it out quickly; should there be a good deal of dust, it is satisfactorily shown by this means.

Firmness.

Secondly, it is handled and pressed between the fingers, to test the firmness of its grain; Size of grain.and should there appear to be any great difference in the proportions of different sizes to that laid down as a standard, it is sifted and compared accordingly, being rejected should the quantities fall short or exceed the sample in any great degree.

Density.

Thirdly, a barrel or two are selected, and the powder poured into a hopper, under which is placed a box very carefully constructed, so as to hold exactly a cubic foot. A slide is now withdrawn at the bottom of the hopper, and the powder allowed to run into the box in a continuous even stream until it is piled up; the hopper is then removed, and the powder struck off with a straight edge, level with the top of the box. The weight is now carefully taken, that of the latter being subtracted; should this not amount to 55lbs. it is rejected, as not being of sufficient density.

Strength by range.

Fourthly, samples are taken from every barrel, and lot for the firing proof.

Firing Proof.—An average of nine rounds of sample Waltham Abbey powder is taken, three rounds being respectively fired at the beginning, middle, and end of the proof, from the same kind of mortar before mentioned, with a charge of 2oz. An average of three rounds of each lot of the merchant’s powder is also taken; should it fall short by more than 1 in 20, it is rejected.

Purity by flashing.

Fifthly, to ascertain if any residuum or ash is left after ignition, about half an ounce is burned on a clean glass plate, and fired with a hot iron. The explosion should be sharp, and produce a sudden concussion in the air; and the force and power of this concussion should be judged by that of known good quality. Few sparks should fly off, nor should white beads or globules appear, as it would be a sure indication, as we have before explained, of insufficient incorporation. It is also subjected to a second proof.

Purity by weight after exposure to damp.

Second proof.—A sample of 1lb. from each lot, carefully weighed up, and a similar sample of the comparison powder, is exposed for three weeks in a box perforated with holes (called a damp chest), to the action of the atmosphere. This box is placed under cover, so that it is sheltered from the wet, but that the moisture can get to it. If, at the end of this time, there is a greater proportion of difference in range between them than one-twentieth, it is rejected. The pounds are also very carefully weighed up again, to ascertain the comparative absorption of moisture. This is called the hygrometric test.

REMARKS ON THE PROOF OF POWDER BY THE EPROUVETTES.

By eprouvettes or pendulum.

By comparing the results of the proofs by the eprouvettes with those furnished by the cannon pendulum (vide plate 1, fig. 2 and 3), it will appear that the eprouvettes are entirely useless as instruments for testing the relative projectile force of different kinds of powder, when employed in large charges in a cannon. Powders of little density, or of fine grain, which burn most rapidly, give the highest proof with the eprouvettes, whilst the reverse is nearly true with the cannon.

Real use of eprouvettes.

The only real use of these eprouvettes is to check and verify the uniformity of a current manufacture of powder, where a certain course of operations is intended to be regularly pursued, and where the strength, tested by means of any instrument, should therefore be uniform.

Best proof, by service charges.

The only reliable mode of proving the strength of Gunpowder is, to test it with service charges in the arms for which it is designed; for which purpose the balistic pendulums (vide plate 3), are perfectly adapted.

Best proof for small arms.

For the proof of powder for small arms, the small balistic pendulum is a simple, convenient, and accurate instrument.

Common eprouvette.

The common eprouvettes are of no value as instruments for determining the relative force of different kinds of Gunpowder.

OF THE SIZE OF GRAIN FOR GUNPOWDER.

On size of grain.

With regard to the particular size of grain for Gunpowder, I am confident great improvements might be made, both in obtaining greater regularity of effect and propelling force, by the adoption of a more uniform even grain. There are at present half-a-dozen different sizes in our cannon and musket powder; and I think it stands to reason, that the more equal the size, the more uniform will be the ignition of all the grains, and consequently the effect of the same charges will be much more regular.

OBSERVATIONS ON THE MANUFACTURE OF GUNPOWDER ON THE CONTINENT AND AMERICA.

It may not be uninteresting to have a slight knowledge of the method employed on the Continent, &c., for the production of Gunpowder.

Proportion of the ingredients.

The proportions of the three ingredients vary slightly all over the Continent and America, being as follows:—

SALTPETRE. CHARCOAL. SULPHUR.

France - 75 12.5 12.5

Belgium

Russia 73.78 13.59 12.63

Prussia 75 13.5 11.5

Austria 75.5 13.2 11.3

Spain 76.47 10.78 12.75

United States 76 14 10

PRODUCTION AND PURIFICATION OF THE INGREDIENTS.

Production and purification of the ingredients.

The nitre is purified in a similar way to the new method employed at Waltham Abbey, though it is seldom obtained with so faint a trace of chlorides, owing probably to its being of an inferior quality, and of higher refraction when it is imported.

The sulphur is supplied to the manufactories in France in the form of roll sulphur, from Marseilles and Bordeaux, where there are very large refineries.

The charcoal is prepared from dogwood, alder, willow, hazel, and poplar, sometimes in pits, and occasionally in cylinders, as at Waltham Abbey. At Wetteren, and in some parts of France, it is distilled by the action of steam. The “charbon roux” taking its name from its brownish-red tinge, from being only partially burned, was used formerly more than now, as the powder made from it was found to injure and exert very pernicious effects upon fire-arms.

PULVERIZING AND MIXING THE INGREDIENTS.

Pulverizing and mixing the ingredients.

The ingredients are generally pulverized in copper drums, capable of holding 224 kilogrammes. Part of the charcoal is mixed with the sulphur, and part of the sulphur with the saltpetre. They are then put into separate drums, which revolve about twenty-five times per minute for three hours, and in which are about 500 gun-metal or bronze balls, the size of good large marbles. The ingredients are brought to the most minute state of division by these means, and are then mixed all together, for one hour, in similar drums covered with leather, containing wooden balls.

INCORPORATING PROCESS.

Incorporation.

The fine powder thus obtained is sometimes merely moistened, so as to form a stiff paste, and passed through rollers, the cake formed, being dried and granulated. The incorporating cylinders are used occasionally, but the more usual plan adopted on the Continent to effect this operation is the stamping-mill, which requires a short description. It is nothing more nor less than the pestle-and-mortar principle, each mill consisting of from six to twelve bronze or wooden mortars bedded in the floor of the building; they are the shape of the frustum of a cone, the mouth being much narrower than the base; the pestles, or stampers as they are called, are made of wood, shod with either very hard wood or bronze, on which project wooden teeth about twelve inches long; a vertical movement is imparted to them by a shaft worked by the water-wheel having similar teeth attached; in its revolution it raises the stamper about eighteen inches, which falls again as the projection is disengaged, twenty five times in a minute. This operation is carried on for twelve hours, during which period the charge (about 15lbs.) is moistened at intervals, and routed up with a copper-shod spud; at the end of this time the cake is taken out, and left to dry and harden; it seldom receives any pressure—although, in some manufactories, presses are being erected.

GRANULATING.

Granulation.

The cake is then granulated in sets of sieves fitting one into the other, having perforated zinc bottoms of different degrees of fineness, which are suspended from the ceiling of the room by ropes, an ash spring being attached to each box holding the sieves, the cake is put into the uppermost one with some gun-metal balls, and shaken backwards and forwards, which motion the spring facilitates; it is thus broken up into different sized grains, which are separated by passing through the several meshes.

The grain formed is then dusted in bags or shaking-frames covered with canvas, and then glazed in barrels.

STOVING OR DRYING.

Drying.

In summer the process of drying is often performed in the sun, and in winter by the steam stove, in the following way. The powder is spread about three or four inches thick on a large canvas tray, under which is an arrangement of pipes, which convey the hot air forced by a fan through a cylinder heated by steam: it is considered to be sufficiently dried in from three to four hours, during which time it is occasionally raked about. In some manufactories it undergoes a further operation of being dusted, and is then barrelled up for use. Generally the great failure in the foreign manufacture is the neglect of the principal stage of the fabrication, viz. incorporation; with the old stamping-mill, it is quite impossible that the process can be carried out to the necessary extent. Comparative merits of foreign and English gunpowder.The Continental powder is usually very soft in its grain, dusty, and quickly absorbs moisture from the atmosphere; its density is below the English powder, on account of its never being subjected to pressure; consequently it is not so durable, and forms a good deal of dust in transport; a great amount of residue is generally left in the gun, and its strength, as a propelling agent, is far inferior to our powders. On being flashed on a glass plate, instead of producing a sudden concussion, like the sharp rap of a hammer, it burns more like composition, throwing off a quantity of sparks.

NEW RIFLE POWDER.

The following mode of manufacturing rifle powder, appeared in Garrison Orders at Woolwich, 31st December, 1859:

Composition in 100 parts:—

Saltpetre 75

Charcoal 15

Sulphur 10

100

The charcoal to be prepared from dogwood, burned slowly in cylinders three hours. The composition to be worked under the runners for five and a half hours, and submitted to a pressure of about 50 tons to the square foot. The size of the grain to be that collected between sieves of 16 and 24 meshes. The grain to be glazed for five hours.

Note.—The foregoing, on the manufacture of gunpowder, is principally taken from an article in the Aide Memoire (1860), by Major Baddeley, Royal Artillery; Captain Instructor, Waltham Abbey.