by considerably diminished, a matter of primary importance in such cases. the decomposition of such powder, a mixture of carbonic oxide and carbonic acid gases is evolved, and a higher sulphide of potassium produced. The comparative force exerted by a powder of this description is of course far less than that exerted by good fire-arm powder.

MANUFACTURE OF GUNPOWDER.-In the manufacture of gunpowder the minute state of division and intimate mixture of the ingredients is of equal importance with the proper proportions; hence considerable care must be bestowed upon the various processes through which the constituents and the powder itself have to pass. Different methods have been employed from time to time, for attaining the desired results. We shall confine ourselves chiefly to an outline of the manufacture of gunpowder, as conducted at the Waltham Abbey mills.

The Ingredients. The greatest care is taken in the preparation of pure ingredients for gunpowder.

The presence of any chloride in the nitre employed must be avoided, since the deliquescent nature of these salts would act very injuriously upon powder, causing it to absorb moisture, whereby its power is soon greatly weakened. Saltpetre containing more than of chlorides is rejected as unfit for use. By the method adopted at Waltham Abbey, of which an outline has already been given (§ 145), the nitre is obtained absolutely pure. In order to free it perfectly from moisture, it is always very carefully fused and cast into moulds. In this operation, the application of too high a temperature is guarded against with care, since the production of a small quantity of caustic potassa, by the decomposition of the nitre, would impart deliquescent properties to the latter.1

Carefully prepared flowers of sulphur are employed in the manufacture of gunpowder. The method of obtaining these at Waltham Abbey is similar to that described at § 103. When the walls of the chamber into which the sulphurvapors are conducted become too warm to effect their proper condensation to flowers, the communication between the chamber and the retort is closed, and another one opened, leading into a metal receiver; the sulphur is allowed to distil over into this, until the chamber has become sufficiently cool, and the flowers have been collected from its sides, when the vapors are once more allowed to pass into it.

Since, at the commencement of the distillation, when the retort and condensing-chamber still contain atmospheric air, the first portions of the sulphur-vapor must inflame, sulphurous acid being produced, the flowers will frequently possess a faint acid reaction when they are removed from the chamber. This is avoided by allowing the sulphur to condense upon damp cloths, or removed by allowing it to remain between such cloths for a short time previously to use.

The charcoal for powder is carefully prepared in retorts and slips, as described at § 121. The volatile products are conducted from the retorts, by pipes, into the fire by which the charring is effected, and there consumed. The species of wood exclusively employed by government for making powder-charcoal, are alder, dogwood, and willow. About twenty-five to thirty per cent. of charcoal are

The following is a delicate test for the over-fusion of nitre: a small quantity of the fused nitre is dissolved in water, and a few drops of a neutral solution of sulphate of copper added. The production of a bright-green tint indicates the presence of nitrous acid (nitrite of copper being produced), and shows that a portion of the nitre has at any rate undergone the first stage of decomposition (see Nitrate of Potassa); if, in addition, a flocculent blue precipitate (hydrated oxide of copper) is formed immediately upon the addition of the sulphate of copper, or is deposited after a short time, the presence of caustic potassa in the sample is indicated.

2 The massive (crystalline) sulphur thus obtained is employed by government in the manufacture of other laboratory compositions.

3 Dogwood charcoal is employed exclusively for rifle-powder.

generally obtained in successful operations. Good powder-charcoal should have a bluish-black appearance, and, when powdered, a lustre resembling that of velvet; it should be light, sonorous, firm, and slightly flexible. The wood used in the manufacture of powder-charcoal, as also the charcoal itself, must be carefully picked over, as directed at § 121 (Cylinder-charcoal).a

Pulverization and intimate mixture of the Ingredients.-The machine or mill by which the ingredients are first powdered, and afterwards intimately blended, or incorporated, as it is termed, consists of two upright mill-stones, or runners, of smoothly cut marble or limestone, or of iron (about 7 feet in diameter, and 12 inches thick, and weighing from 3 to 4 tons each), which turn upon one common horizontal axis, while this again turns upon a vertical axis, placed in the centre of a flat bed, of the same material as the runners that revolve upon it. The

The charge for a retort, at Waltham Abbey, is 14 cwt., which is burnt from three and a half to four hours; the charcoal obtained generally amounts to 40 lbs.

2 The superiority of a product of less complete carbonization of wood, called charbon roux (red charcoal), over the black charcoal, for the manufacture of gunpowder, has been maintained by some chemists, particularly in France. The subject still requires experimental investigation; we may however state, in a few words, what is known concerning it. A full red heat yields black charcoal containing about 90 per cent. of carbon, and 7 to 8 per cent. of hydrogen compounds. A temperature approaching red heat yields charbon roux, containing 70 to 72 per cent. of carbon, and 28 to 30 per cent. of hydrogen and oxygen. The latter appears to be charcoal containing the maximum amount of inflammable matter in wood.

Powder made with this kind of charcoal certainly appears to burn with greater energy than that made with black charcoal; this arises, probably, from the readier inflammability of the charcoal.

In charbon roux, there appear to exist about 28 per cent. of hydrogen and oxygen in the proportion to form water, besides about 2 per cent. of hydrogen over and above that amount. A larger proportion of charcoal must therefore be employed to effect the proper decomposition than if black charcoal were used, since the large percentage of hydrogen and oxygen above alluded to does not enter into the action; for in the combustion of organic substances, the heat is produced by the combustion of the carbon and of that amount of hydrogen present in the body, over and above the quantity required to produce water by the oxygen present in the substance. The produce thus obtained would be far less dense than ordinary powder, it would therefore occupy a greater bulk, and would be liable to dust very much, and also attract considerably more moisture than black charcoal powder. Moreover, the specific heat of aqueous vapor is very high, and a large amount of the heat generated in the explosion of the powder would consequently be absorbed in the conversion of the water into vapor; hence it is impossible that the expansion of the gases should be equal to that of the products obtained in the combustion of black charcoal gunpowder.

3 Other forms of machinery are employed in different parts of the Continent for pulverizing and mixing the ingredients. One of these consists of a drum or cylinder of wood or leather, strained over a frame, revolving on central axes. Projecting ridges of wood are fixed on the internal surface of the drum, at a short distance from each other. The coarsely-crushed ingredients are introduced into the drum through a flapdoor, together with a number of small balls (of bronze, or a harder alloy, copper to 1 tin). The barrel is then allowed to revolve with moderate rapidity, whereupon the balls are raised to a certain height, and then fall back from ridge to ridge, crushing the material with which they meet. This is termed the revolutionary process, having been adopted in France at the time of the first Revolution. In some parts of the Continent, the manufacture of powder is effected by stamping-mills, which consist of long rows of circular mortars of iron or of oak (with very hard wood inserted in the bottoms); long pestles, fitted with bronze shoes (weighing about 60 pounds), and provided. at the centre of the rod, with crosspieces, are lifted to a certain height (about 11⁄2 foot) by the projections of a long cog-wheel, and then allowed to fall upon the ingredients in the mortar. The pestle is lifted about sixty times in a minute: the mass to be pulverized or incorporated is moistened with water from time to time. The mortars being so formed as to contract gradually from the centre towards the opening, the mass, as it is forced up the sides of the mortar by the blows of the pestle, falls back again to the bottom; in this manner the mass becomes thoroughly mixed; to insure this result, it is, however, necessary to loosen, from time to time, the hard crust that will always form at the bottom of the mortar.

cylinders are not equidistant from the vertical axis; they do not consequently move over the same surface.1

The ingredients, having been reduced to a sufficiently fine state of division, are weighed out, for mixture, in the following invariable proportions :

which constitute what is termed a charge, or the quantity of material placed at one time upon the incorporating-mill. These quantities are then introduced into the mixing-machine, which consists of a wooden box, or cylinder, through which passes an octagonal shaft, provided with a number of fan-like arms. The cylinder is made to revolve round the shaft, which turns at the same time in the opposite direction. From five to ten minutes are allowed for effecting a thorough mixture of the ingredients; the powder is then removed from the cylinder and filled into bags, which are tied firmly, so as to prevent any separation of the ingredients from each other in their transport to the incorporating-mills."

The mixture is then spread upon the bed of the incorporating-mill, moistened with distilled water to such an extent as to make the particles cohere firmly,3 and once more submitted to the action of the mill. The runners are not allowed to revolve so rapidly as in the first instance, when the ingredients are merely ground, in order that the particles may be uniformly submitted to the crushing action and pressure of the rollers for a longer period. Great care must be taken that no hard or gritty particles fall upon the bed of the mill, and the mass must be retained in a sufficiently moist state throughout the incorporation, which lasts from three to four hours. A can with a very fine rose is employed for moistening the powder; any particles that are pushed by the rollers beyond their track, are carried back by scrapers, which are appropriately fixed, and travel round with the rollers. Towards the close of the operation, the latter are allowed to revolve only very slowly.

The mass that is removed from these mills after incorporation, is now possessed of all the chemical properties of powder, the particles having become most uniformly and intimately mixed. It soon hardens, forming cakes of about inch thick, which should have a dark grayish-black appearance, and be perfectly homogeneous, exhibiting no specks whatever. In this state the powder is called

mill-cake.

These cakes, before they are thoroughly dry, are reduced to coarse powder, in what is called the breaking-down mill (which consists of two sets of metal rollers, furnished with teeth, between which the powder passes); this is then placed in layers of a certain thickness between copper plates, and packed in very stout boxes, in which it is submitted to a pressure of 122 tons on the square foot, by means of a powerful hydraulic press. When the powder is removed from between the plates, it presents very much the appearance of slate, being in very

Any portions of the ground substance adhering to the rollers is removed, as they revolve, by scrapers of wood, tipped with iron, which are fixed within sufficiently close proximity to the surface of the roller.

2 If a mixture of this description, or a gunpowder that has not been subjected to sufficient pressure, be but loosely packed, the comparative densities of the ingredients being very different, they will gradually separate to a great extent, if subject to any concussion in their transport; the light charcoal-powder will collect on the upper surface, and much will escape, as dust, through the fissures in a box, or between the interstices of a sack.

The quantity of water required for this purpose varies considerably with the temperature and state of the atmosphere.

dense blackish cakes, about inch thick (called press-cake). By subjecting the powder to this powerful pressure, several important results are attained. The density of the powder is very greatly increased, and consequently a certain bulk of the pressed powder will yield, upon combustion, a far greater volume of gas than an equal bulk of powder that has only been subjected to the pressure of the incorporating-mill. Moreover, the hardness of the powder is naturally increased in a similar proportion, whereby it is better enabled to withstand the action of the atmosphere, and is also far less liable to loss from dusting, in its transport. Granulation of the Powder.-By this process the powder is obtained in grains of the various sizes and forms required for fire-arms of different descriptions, or for other purposes (e. g. in blasting operations), the fineness of the powder determining to a great extent the rapidity of combustion, which requires modification according to circumstances.

A very ingenious piece of machinery is employed at Waltham Abbey for granulating the powder, and separating it into the different kinds, known as large grain (or L. G.), fine grain (or F. G.), and meal-powder, or dust. It does not come within our province to give more than a sketch of the principle of this machine.

A continuous supply of the coarsely-crushed press-cake is allowed to fall upon a pair of revolving metal rollers, provided with large teeth, whereby it is partly reduced to grains of different sizes; the powder, as it passes from these rollers, is received by a set of three long, sloping screens, or sieves, of different fineness, fitted one upon the other, and working continually backwards and forwards, with a trough, running their whole length at the bottom. The powder is thus subjected to the usual sifting motion; those portions that are retained by the first sieve, as they work their way down its surface, are made to fall between a second pair of rollers with finer teeth, the powder granulated by these again falls upon the upper screen, where it is once more sifted; any portions that may still be too coarse to pass through, are reduced by a third, still lower, set of rollers with very fine teeth. The powder, on passing through the first screen falls upon the second, where the large-grain powder is retained, being separated from the fine grains and dust by the sifting motion to which it is subjected; the third sieve retains the fine-grain powder, while the dust or meal-powder falls through into the trough beneath. Each kind of powder, as it travels down to the bottom of the screens, is collected at the opening in boxes, running on wheels and rails. Various additional contrivances are applied to this piece of machinery, to obviate the necessity of the presence of workmen, during the granulation of the powder, in case of an accidental explosion.1

After granulation, the powder is freed from dust by allowing it to run gradually through sloping reels, inclosed in boxes and covered with canvas, or with silk of about fifty-six meshes to the inch, according to the size of the grains introduced. The finest-grained powder is afterwards rounded and polished by what is termed the glazing process. This consists in subjecting the powder, in a sufficiently moist state, to a rotary motion in barrels or drums, containing arms

1 On the Continent, the powder is chiefly granulated in drum-sieves of different fineness, fitting one in the other, to which an alternating rotary motion is imparted. On the upper of these is placed, together with the crushed powder, a lenticular disk of heavy wood (sometimes loaded with lead). By the motion of the drum, this disk is made to travel over the surface of the upper sieve, crushing the particles of the powder with which it meets until they are all sufficiently fine to pass through the first sieve.

The so-called Champy, or Swiss globular powder, is obtained by allowing minute drops of distilled water to fall from a very finely perforated tube upon meal-powder, which is made to revolve in a drum, such as has been already described as used sometimes for powdering and mixing the ingredients. Each drop of water thus collects, in a globular form, a certain quantity of the powder; the grains thus formed are afterwards separated from the dust by means of sieves.

similar to the mixing-drums already described, the velocity of the motion being only sufficient to allow the grains to roll over each other and become polished by attrition. Powder thus glazed is less liable to dust in its transport, and is rendered more impervious to the action of atmospheric moisture. Very coarsegrained powder (blasting-powder) is sometimes glazed with graphite.

The last operation which the powder has to undergo, is that of desiccation. It is requisite during all the processes enumerated to retain the powder in a more or less moist state; it is, however, necessary when the manufacture is completed to expel the moisture. For this purpose the powder is exposed for some time to a temperature of 134° F. in a chamber heated by steam, and so constructed that there shall be a continual change of atmosphere, the moist air escaping as dry air enters.

The greatest precautions are adopted to prevent accidents during the manufacture of powder, or at any rate to prevent a fire in one part of the factory extending to any other portion. Each process is conducted, if possible, in detached premises at some distance one from the other, and in some cases these are flanked by high buttresses of brick or stone, of great thickness. All kinds of grit are most carefully excluded from the various buildings, the floors of which are frequently covered with leather, and into which no person is permitted to enter in shoes that have been worn out of doors. Nevertheless, terrible accidents occur at times, the affinities between the constituents of powder being balanced with such nicety that trifling causes, such as comparatively slight friction, are sometimes sufficient to impart to it the impulse necessary for its decomposition. Properties of Gunpowder.-Good powder should exhibit perfect uniformity of texture; light specks or glittering points indicate an incomplete mixture. The grains should be sufficiently hard not to be easily crushed between the fingers, and not to soil these or a piece of paper by mere contact. Gunpowder should burn rapidly, leaving a very slight residue. If inflamed upon white paper, it should blacken the latter but slightly, and should on no account set light to it. Powder is inflamed by any burning substance, by an electric spark, or redhot metal, or by violent concussion. It does not, however, ignite if exposed to a temperature below a red heat. If it be exposed in a glass vessel, containing an atmosphere of hydrogen or carbonic acid, to a gradually increasing temperature, the sulphur may be completely separated, subliming upon the cool portion of the vessel.

It has been proved that powder may be inflamed not only by the powerful concussion of iron against a hard substance, but by the concussion of comparatively soft bodies, provided it be sufficiently powerful. Experiment has shown that powder placed upon lead, or even wood, may be ignited by the concussion

of a leaden bullet fired at it.

The inflammability of powder is greatly influenced by its physical nature, as has been already stated. A fine-grain powder will burn more rapidly than largegrain powder; the greater the density of a powder, the more gradual its combustion.

Angular powder will burn more rapidly than round-grained powder; glazing also decreases the inflammability of powder. The presence of moisture naturally retards the inflammability of powder considerably.

Powder in which the theoretical proportions are exact, and in the manufacture of which a very inflammable charcoal has been used, the ingredients having been mixed without the application of very great pressure, will undergo, when ignited, an almost instantaneous decomposition; such a powder resembles the fulminates in many respects, the strain which it exerts upon the fire-arm is far too powerful, hence it is not so generally applicable as powder which undergoes a more gra dual decomposition.

Gunpowder always attracts moisture, more or less, since charcoal, however