Page:Encyclopædia Britannica, Ninth Edition, v. 11.djvu/340

320 U U N P W D E It years growth. The quality of the charcoal exercises the greatest influence upon the rate of combustion, so that both the description of wood used and the mode of burning are of the utmost importance. By a series of experiments first made by Proust, and since repeated by English chemists, it has been found that 12 grains of various charcoals, mixed with 60 grains of saltpetre, give the following average volumes of gas : Cubic inches. Dogwood (Rhamn us Franyula) 82 Willow (Salix alba) 77 Alder 74 Filbert 72 Fir, chestnut, hazel 66 Overheated willow charcoal 63 The production of the strongest powder does not depend alone upon the evolution of the largest volume of gas, but the above table is of interest since the three descriptions of wood which head the list have long been considered by universal consent as the best adapted for the manufacture of charcoal for gunpowder. Dogwood (so-called, but in reality it is alder-buckthorn, Rhamnus Frangula, the French bourdaine) is an underwood of slow growth, usually obtained from Sussex, Belgium, or Prussia ; it is cut about an inch in diameter, and packed in bundles 6 feet long. This wood is now used, both in England and on the Continent, for all military small-arm powders, as well as the best descriptions of sporting gunpowder. It has been found, moreover, that cannon powders mads from dogwood charcoal are, other things being equal, much more violent in action than those manufactured with willow or alder charcoal. Accidents with powder made from dogwood charcoal have usually proved more destructive than those made with any other description. Alder and willow charcoal is used for making gunpowders for field and heavy ordnance, as well as for the commoner kinds of commercial powders ; these woods are obtained from various parts of England, and should measure about 4 inches in diameter. The willow used is the Salix alba, one of the softest and lightest of English woods, white in colour, and of very rapid growth ; the pith is circular, and tolerably large. Alder is considerably harder and denser in texture, and of slower growth ; its colour is reddish -yellow, and the small pith triangular or bayonet- shaped in section. Dogwood has a very large pith in pro portion to its size, circular, and of a red colour, which is preserved even after the wood is converted into charcoal. The temperature at which the wood is charred exercises the most powerful influence upon the inflammability of the charcoal, and consequently upon the " explosiveness," or rate of combustion, of the gunpowder made from it. The higher the temperature the larger the proportion of hydrogen and oxygen expelled, and the nearer the approach of the charcoal to pure carbon ; at the same time, it becomes more dense and incombustible, and the gunpowder made from it is comparatively slow in action, and gives a low initial velocity Charcoal prepared at a low temperature is softer and more inflammable, and contains more volatile constituents ; it makes a quicker burning powder, giving a higher velocity to the projectile, but also producing more strain or pressure upon the metal of the gun. The chief defect, however, of this " slack-burnt " charcoal, or charbon roux, as it is called from its reddish-brown colour, is its property of absorbing moisture more readily than denser charcoal ; the powder manufactured from it is consequently more hygroscopic, and therefore more liable to deteriorate in strength from the effects of damp than that made with a more highly burnt charcoal. To show the great difference in inflammability caused by burning at low and high temperatures respect ively, it maybe stated that charcoal prepared at 500 Fahr. veadily ignites at about 640, while, if burnt at 1800 Fahr., nearly double the heat previously mentioned is required to inflame it. The following table exhibits con cisely the practical effects of different modes of preparing charcoal for gunpowder, the same kind of wood being used in each case ; it shows (a) the analysis of the charcoals, and (6) the comparative initial velocities and pressures given by powders made in a precisely similar manner from those charcoals. Xo. 1. Burnt 7 hours at a Xo. 2. Burnt 4 hours at a Xo. 3. Burnt 3 houis at low heat. heat. heat. f Carbon, percent. 78 23 81-23 87 55 Oxygen, and trace of 1 i -i nitrogen. . ... " 16-96 13-19 S-29 1 Hvdrocen. . 3 67 3 31 2 91 ~> (.Ash ,, 1-41 1"27 1-25 Initial velocity (feet per second).. Mean pressure in powder chain- / be.r (tons per square inch) ) 1417 16-83 1399 13-54 1353 8-85 For the manufacture of gunpowder, only the crystalline electro-negative variety of sulphur soluble in bisulphide of carbon (see CHEMISTRY, vol. v. p. 498) is used. Sublimed sulphur, commonly called "flowers of sulphur," which con sists of minute granules of insoluble sulphur enclosing the soluble variety,is considered unfit for gunpowder; the reason assigned has usually been that, from the mode of manufac ture, it is impregnated with sulphurous and sulphuric acids, but Prof essorBloxam points out that in all probability it is the fact of the sublimed sulphur consisting of the electro-positive insoluble variety, which exerts an injurious influence upon the gunpowder made from it. Sulphur performs the part of a second "combustible" in gunpowder; but there is no doubt that its chief value as an ingredient thereof arises from its great inflammability, owing to its tendency to combine with oxygen at a moderate temperature ; it inflames at about 560 Fahr., thus facilitating the ignition of the powder. Its oxidation by saltpetre appears also to produce a higher temperature than is obtained with charcoal, thus accelerat ing combustion, and increasing by expansion the volume of gas generated. An excess of sulphur would, however, be injurious by increasing the solid residue, in which the sulphur is found combined in various forms after the explosion. Some authorities have considered that, from its non-absorbent properties, sulphur renders gunpowder less hygroscopic, and more compact and durable. Powders made from exactly the same materials, mixed in the same proportions, yet differ greatly in " explosive- ness," which has been defined as the rate at which the powder burns or is converted into gas. This quality will depend chiefly upon the following properties : (a) extent of incorporation; (b) the density of the powder; (c) its hardness; (d) size of the grains or pieces; (<?) shape of the grains; (/) amount of glaze. Although not altogether synonymous with strength, we may consider "explosive- ness " as the quality upon which the value of gunpowder for any particular purpose chiefly depends. Next to the selection of the precise description of char- coal to be used, no point in the manufacture of gunpowder requires such care and attention as the thorough inter- mixture of the ingredients, the object being in fact to form out of the three components a new substance as nearly- homogeneous as possible. It is usually considered that there is a limit of time beyond which no advantage is gained by continuing the "milling" or incorporating process; but it is certain that nothing that can be done to the powder afterwards will add to its strength, although we may modify its explosiveness, and that the very best powders, especially for small-arms, are milled the longest time. This question will be further treated under the head of manufacture. Sulpl Exte: ofill(

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