Page:Encyclopædia Britannica, Ninth Edition, v. 11.djvu/348

328 GUNPOWDER Finish- ins. portion of the "chucks " or larger pieces, waicli are after wards sifted out. The glazing process causes a great alteration in the appearance of the grain, especially in that made from dogwood; the dull brownish hue is replaced after a few hours by a fine black colour with more or less polish. Some powders are glazed from 10 to 12 hours, a considerable amount of heat being generated by the friction. Fine-grain powders are again passed through the slope reel after glazing. All kinds of gunpowder are dried in the same manner. The " stove," or drying room, is fitted with open framework shelves or racks, the heat being produced by steam pipes underneath. The powder is spread upon either copper trays or wooden frames with canvas bottoms, each capable of holding about 12 ft, which are then placed upon the racks. Not more that 50 cwt. may be dried at one time. The length of time required for stoving depends upon the nature of the powder, and the proportion of moisture it contains ; it varies from about twelve hours for fine-grain up to three or four days for the very large cannon powders; the heat ranges from 120 to 145 Fahr., the temperature being gradually raised or lowered. It is most important that a stove should be well ventilated, so that a constant current of hot dry air may be supplied, and the air charged with vapour carried off; if this be not done effect ually, the moisture would be recondensed upon the powder as the temperature was lowered. The drying process produces a small portion of dust which it is necessary to remove ; but the finishing process has, especially upon the fine-grain powder, a much more considerable effect than the mere removal of dust. It is usually finished by being run from two to three hours in a horizontal reel (see fig. 9), the charge being 300 ft, and acquires a very glossy appearance, if the quality be good, even without the addition of graphite, which is very com monly added to sporting gunpowder. Large cannon powder, such as "pebble" and "cubical," is finished in large skeleton wooden reels, shaped like barrels, and enclosed in cases ; after being run for about three quarters of an hour, c ,1- Tfl 11 tnni r L| I | B FlO. 9. Horizontal Dusting Reel (longitudinal section). A, cylindrical reel ; B, reel case ; 0, apparatus for lowering one end for unloading; D, hopper for loading; E, opening in reel for loading ; F, barrel for unloading into. a small portion of the purest graphite (2 oz. to 400 ft of powder) is introduced in muslin bags, and the powder is run for a short time longer. This skeleton reel will hold a whole "glazing," as the contents of four glazing barrels is termed, being about 16 barrels of 100 ft each, and advantage is taken of this finishing process to mix together a number of glazings, so as to get a batch of 50 or 100 barrels giving uniform results at proof. These batches are afterwards " blended " together in four-way hoppers, with others of opposite character, should they not in all respects be up to specification, and any quantity of gunpowder so finished or blended as to give identical results at proof is termed a brand, and receives a distinctive number. Upon the introduction of very heavy ordnance, large charges, it was found that the ordinary (L.G. o R.L.G.) cannon powder was too sudden in its action, owing rovik- to the whole charge being consumed before the projectile for vei had sensibly moved from its seat in the bore, thus causing heav > r a most violent strain to the metal of the gun. To obviate guns- this defect, the grains or pieces were made much larger, so as to diminish the total surface of combustion, and, con sequently, the volume of gas evolved at the first instant of explosion; the powder was also given a considerably higher density, which retarded its combustion. These changes resulted in the adoption of the pebble and cubical powders, already mentioned, in England, and in America, of "Mammoth" powder, consisting of large, irregular-shaped Ameii grains (k, fig. 10) from 0" G to 0" 9 in size ; an improvement mam- has since been made in this powder by pressing it in uni- oi] form-sized pieces, of the shape shown in i, fig. 10, being the pov frusta of two hexagonal pyramids, separated by a pris matic space left rough. Fig. 10. The figures a to k show the relative sizes and shapes ol grain now commonly employed for military purposes iu Europe and America, except that the three largest powders pebble (?), prismatic (f, g], and cubical (//) are figured half the real size to save space, whereas the remainder indicate the actual dimensions of the grains. Powder for small-arms is represented in a ; all the other descriptions are intended for cannon of various sizes. The improvements above described materially lessen the initial strain, at the expense of requiring a longer gun to burn the powder completely, but it still remains true that, even with a charge composed of large, dense pieces, the evolution of gas is greatest at the commencement of com bustion, and decreases as the grains burn away, although Rodms

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