Page:Encyclopædia Britannica, Ninth Edition, v. 11.djvu/344

Rh 324 GUNPOWDER opening in the retort, through which, by means of pipes, the inflammable gases resulting from the charring of the wood are con ducted into the furnace and there burnt ; this saves a considerable amount of fuel. There are also pipes which receive and carry off the tar and pyroligneous acid produced. In the powder works of j Messrs Hall & Sou of Faversham, the retorts are disposed three on each side of the furnace, and the connecting pipes and dampers are so arranged that the gases from either set, or from any single cylinder, can be utilized for the charring of the wood contained in any of the others ; by this means it is claimed that little fuel is required beyond the quantity needed to warm the furnace and par tially char the first set of retorts. That the wood is sufficiently charred is shown by the blue colour of the gas flame, which indicates the formation of carbonic oxide; the door of the retort is then opened, and the slip is withdrawn by means of tackling, and placed in a large iron cooler having a close-fitting lid, where it is left a few hours till cool enough to be turned out and put into store. The charcoal is carefully picked over by hand, to en sure its being of uniform quality, and is kept from ten days to a fort night before being ground, to obviate the danger of spontaneous com bustion, to which it is liable if ground too soon after burning ; this arises from the heat generated by the very rapid absorption and con densation of oxygen from the air by the finely powdered charcoal, rac- Properly-made charcoal for gunpowder should be jet black in itics colour, and its fracture should show a clear velvet-like surface ; it ood should be light and sonorous when dropped on a hard substance, coal, and so soft as not to scratch polished copper. Slack-burnt charcoal, or that prepared at a very low temperarure, is at once known by its reddish-brown colour, especially when ground, and this peculiarity can be recognized in the powder made from it, when reduced to a fine state of division. Charcoal burnt at a very high temperature is known by its hardness, metallic ring, and greater density. In France, charcoal is prepared by injecting superheated steam into the retorts for a certain period. iding The charcoal mill in shape resembles an enlarged coffee mill ; a char- cone works within a cylinder, both being provided with diagonal teeth and ribs, wide apart at top, but gradually approaching one another below. The pulverized charcoal is thence conducted by a simple mechanical arrangement direct into a cylindrical frame or &quot;reel,&quot; about 8 feet by 3 feet, set at a slope and covered with copper wire cloth of about 32 meshes to the inch ; all that is fine enough to pass through the reel-covering falls into a bin which encases the reel, and the coarser particles pass on to a tub at the further end, in order that they may be ground over again, The ground charcoal store should always stand by itself, in case of spontaneous combustion taking place. ilmr The sulphur from Sicily known as &quot; Licara firsts&quot; is employed ing. for the best gunpowder ; it undergoes a rough purification before importation, leaving from 3 to 4 per cent, of earthy impurities. Formerly these were removed by simply melting the&quot;grough&quot; sulphur in an iron pot, and then ladling it into large wooden moulds or tubs, saturated with water to keep the sulphur out of the cracks ; when cool enough, these tubs were unhooped, and the top and bottom of each, mould of sulphur cut off. In the present day, however, the sulphur is refined by distillation in a simple apparatus. A large iron &quot; melting pot,&quot; or retort, is set in brick work, about 3 feet above the floor, with a furnace underneath ; this retort has a heavy movable lid, which is luted into the pot vith clay, and in the lid is also an opening, closed by an iron conical plug. From the melting pot lead two pipes at right angles to one another, one to a large circular &quot; dome,&quot; or subliming chamber, and a smaller pipe to an iron &quot;receiving pot&quot; placed on a lower level than the retort ; the latter pipe has an iron casing or &quot;jacket&quot; round it, through which cold water is allowed to circulate. The communica tion of these pipes with the retort can be shut off or opened as occa sion may require by means of valves worked from without. A charge of about 5J cvvt. of grough sulphur in small pieces being placed in the retort and the furnace lighted, the pipe leading to the dome is left open, as well as the plug-hole in the lid, but that leading to the receiving pot is closed ; after about two hours, a pale yellow vapour rises, when the plug in the lid is put in and the vapour allowed to pass into the dome, where it &quot; sublimes&quot; or con denses on the sides and floor in the form of a fine powder, known as &quot; flowers of sulphur.&quot; In about three hours from the commence ment, the vapour becomes of a deep iodine colour, when the pipe leading into the dome is closed, and that into the receiving pot opened, at the same time cold water from a tank overhead being allowed to circulate through the jacket ; the vapour is then con densed in the pipe, and runs into the receiving pot below in the form of a clear orange- coloured fluid. When the jacket commences to get cold, the receiving pipe is closed, and the communication with the dome is reopened, so that the rest of the vapour may pass into it, the furnace doors being at the same time thrown back ; the impurities remain at the bottom of the melting pot, and are thrown away. The flowers of sulphur thus obtained, being unfit for the nianufaoture of gunpowder, are placed in the melting pot as grough sulphur. A leaden pipe passes from the lid of the&quot; receiving pot into a small wooden chamber lined with lead, in which any vapom still remaining uncondensed may be deposited, as in the dome. The distilled sulphur is allowed to cool down to about 220 Fahr., when it is ladled into wooden moulds, as above described, and set aside to cool. The tests for refined sulphur are the following : (1) burn a small quantity on porcelain, when the amount of residuum should not exceed 25 per cent ; (2) boil a little with water, and test with blue litmus paper, which it should only very feebly redden. The sulphur from the moulds, being broken into pieces, is ground Pulver- nnder a pair of iron edge runners, similar to those of the incorporat- izing the ing mills, but of less size ; after this, it is passed through a reel sulphur, similar to that used for sifting the charcoal, but covered with even finer copper wire-cloth, having 44 meshes to the inch. MANUFACTURE OF GUNPOWDER. The following list will give a general idea of the chief Trocesse processes of manufacture, properly so-called, through which of maim* gunpowder passes, although it will be understood that more facture - or less variation takes place in some of the very different descriptions of powder now made : (1) mixing the ingredi ents ; (2) incorporation, or &quot; milling ; &quot; (3) breaking down the mill-cake ; (4) pressing ; (5) granulating, or cutting the press-cake ; (6) dusting ; (7) glazing ; (8) second dusting; (9) stoving, or drying; (10) finishing. The following is the most approved method of mixing. Mixing. The ingredients are carefully weighed out in the proper proportions for a 50 Ib mill-charge, with an extra amount of saltpetre according to the moisture found to be contained in it ; they are then placed in the mixing machine, which consists of a cylindrical gun-metal or copper drum, with an axle passing through its centre, upon which are disposed several rows of gun-metal fork-shaped arms, called &quot; flyers,&quot; the machinery being so arranged that the flyers and drum re volve in opposite directions, and at different rates of speed. After being mixed in this machine for about five minutes, the composition is passed through a hand-sieve over a hopper, falls into a bag placed below, and is tied up ready for the incorporating mill; it is now called a &quot;green&quot; charge. a~ Fig. 2. FlGS. 1 and 2. A, sectional elevation of incorporating mill, showing one runner and ploughs (p, p} ; 0, curb of bed ; M, machinery in tank, underground ; D, drenching apparatus ; 1. lever-board, or shutter ; t, tank ; /, /, floor line. The incorporating mill (see figs. 2 and 3) consists of a Incor- circular iron or stone bed, about 7 feet in diameter, firmly P oration -