The origin of the invention of gunpowder is a question upon which the learned are by no means agreed; some attributing it to Schwartz, a German monk, in 1320, others to Roger Bacon, who lived nearly a hundred years prior to that date; whilst other writers again contend, and with every appearance of probability, that the invention had its rise in the East, and that it has been known to the Indians and Chinese for thousands of years. The most improved proportions for the composition of gunpowder are 75 parts by weight of nitre, to 16 of charcoal, and 9 of sulphur, which being separately reduced to a fine powder, are intimately blended together with a small quantity of water. This operation was formerly performed in wooden mortars, with wooden pestles; in the large way by means of a mill, wherein the mortars were disposed in rows, and in each of the mortars a pestle was moved by the arbor of a water wheel. The heat, however, produced by the blows of the pestle, occasioned such frequent explosions, that an Act of Parliament was passed in the 12th of Geo.

III. prohibiting their use, and limiting the licenses to mills similar in principle to the one which we shall describe towards the close of this article.

The mixture is, from time to time, moistened with water which serves to prevent its being dissipated in the pulverulent form, and likewise obviates the danger of explosion. When the process of blending the materials together in this manner is complete, (which requires several hours,) the gunpowder is in fact made, and only requires to be dried, to render it fit for use. The granulation of gunpowder is effected by placing the mass, while in the form of a stiff paste, in a wire sieve, covering it with a board, and agitating the whole; by the pressure of the board, it is thus cut into small grains or parts. The powder is smoothed or glazed, as it is called, for small arms, by the following operation: a hollow cylinder or cask is mounted on an axis, and turned by means of a water-wheel or other power; this cask is half filled with powder, and turned for six hours, and thus by the mutual friction of the grains of powder, it is smoothed or glazed. The fine mealy part thus separated from the rest is again granulated. The granulation causes it to take fire more readily, as the inflammation is more speedily propagated through the interstices of the grains.

The variations in the strength of different samples of gunpowder are generally owing to the more or less minute division and intimate mixture of the parts; the reason of this may be easily deduced from the consideration, that nitre does not detonate until in contact with inflammable matter, consequently the whole detonation will be the more speedy the more numerous the points of contact. For this reason also the ingredients should be very pure, as the mixture of any foreign matter not only diminishes the quantity of effective ingredients, but prevents their contact by its interposition. The elastic product obtained by the detonation of gunpowder was found by Berthollet to consist of two parts of nitrogen gas, and one part of carbonic acid gas. The sudden extrication and expansion of these gases are the cause of the effects of gunpowder.

We shall now proceed to describe an improved gunpowder mill invented by Mr. James Monk, the manager at the gunpowder mills of Messrs. Burton, Children, and Burton, near Tunbridge. Some few years ago a model and description of it was presented to the Society of Arts, who voted to Mr. Monk their silver medal and twenty guineas, as a mark of their sense of its merits, a a Fig. 1, on the following page, is a compound lever, formed of two iron bars, the extremities of which terminate above the bedstones of the pair of mills, A B; these levers are connected at their other extremities by a bolt at b, forming a joint, and permitting the levers to move so as to form a very obtuse angle, when a power from below upwards is applied to either of the ends of the levers a a as shown by the dotted lines, c c are two oblong holes in the lever bars, through which two screws are put, which, being screwed into the two uprights, constitute the two fixed fulcrums of the levers; d d are two uprights, with an eye or loop in each to receive and steady the ends of the lever, which are made long enough to allow the bars to take the position indicated by the dotted lines; e e are two blowers, made of thin sheet iron, in the form of hollow three-sided pyramids, and are suspended by two iron rods to the ends of the levers a a.

These blowers are placed as near as possible to the tops of the upright stone shafts, and as close to the wheels as the timber will allow; f f are two copper chains attached by one end to the lever bars, and by the other supporting two copper valves, which are not seen in Fig. 1, being inside the tubs; but one of them is shown at g in the section of a tub, Fig. 2. h h are two oval tubs capable of holding six gallons of water, and having a circular hole at the bottom; surrounding this hole is a grooved block having a cylindrical channel all round it, into which the bottom edges of the cylindrical valves fit, shown in section at Fig. 2. i i are two small spring catches fastened to the two uprights. The lever bars are laid on the top of these catches, so that when the ends of the levers rise, that part of the lever which is on the catch moves downwards, as shown by the dotted lines, till it slips over the end of the catch, and thus the lever is prevented from resuming its horizontal position till released from the catch.

In order to fit that part of the apparatus above described for action, bring the lever to a horizontal position, place the valve g in the circular channel at the bottom of the tub so as to cover the hole; fill the channel with mercury, and then fill the tub with water; hence it is evident that the water is prevented by the mercury from escaping out of the tub so long as the valve remains in its place. Now, if an explosion happen in either of the mills, the blower e hanging over the bedstone will be thrown up, and the lever will, in consequence, be brought into the position indicated by the dotted line, and will be retained there by the spring catches i i; at the same time the valves g will be drawn up out of the mercury, and the water in both tubs will pour down on their respective bedstones, extinguishing in one the inflamed powder, and in the other preventing it from taking fire. In a certain stage of the grinding the materials are apt to clot and adhere to the runners; parts of the bedstones are thus left bare, and the runner and bedstone coming in contact, an accidental spark may be elicited, and an explosion ensue. To prevent this most usual cause of accidents, Mr. Monk fixes to the axles of the wheel a scraper formed of a curved piece of wood k shod with copper, which, being placed behind and almost touching each of the runners, scrapes off the powder as it collects, and thus keeps each of the bedstones always covered. l is the greater water-wheel, which gives motion to the rest; m m are two vertical beveled wheels, fixed on the axis of the great wheel; n n two horizontal bevel wheels working in m m, and turning the vertical shafts, upon the upper part of which are also fixed two horizontal wheels oo, which drive the wheels p p. To the shafts of these latter wheels are fixed the runners q q, which traverse on the bedstones uu; vv are the curbs surrounding the bedstone to keep the powder from falling off. The mill A presents a view, and the mill B a section of the bedstone and curb. Fig. 2 shows the position of the apparatus after an explosion has taken place; the valve being raised up out of the channel, and the water pouring down on the bedstone.

Fig. 1.