GUNPOWDER 319 for five centuries, and its rapid development in very recent years, are facts which support this presumption. Even about 1410 the proportions were still but 3 saltpetre, 2 sulphur, and 2 charcoal. The relative amount of saltpetre was gradually increased, and Tartaglia (Qucsiti e Inventioni diversi, Venice, 1546) mentions twenty-three various com positions as having been used at different times ; the gun powders of his days were Saltpetre. Charcoal. Sulphur. Cannon powder 4 1 1 Musket , .... 48 8 7 or 18 3 2 It is remarkable that Robins states the above proportions to have been very nearly those of his own day (1742), for there is a great deficiency of saltpetre in the cannon powder, and a considerable excess in that for muskets, com pared with the relative quantities now employed in England. For a long period of time it was the custom for the fine grain or musket powder to contain a larger proportion of saltpetre than that for cannon ; and, again, the amount of nitre was relatively reduced as the piece of ordnance became heavier, doubtless with the view of obtaining a slower burn ing powder for large charges. However, we find that by the latter part of the last century, what was called " com mon war powder " was almost universally composed of 6 saltpetre, 1 charcoal, and 1 sulphur, and these are the pro portions still in use by many Continental nations (D Antoni On Gunpowder, translated by Capt. Thompson, R.A., Lon don, 1787). So far back as the 16th century, Baptista Porta is said to have arrived at the proportions now used in France, which, however, were certainly not adopted until a comparatively recent period. Exhaustive experiments have also been carried out in that country by Beaumo, the Committee of Public Safety, Chaptal, and Proust, who fixed upon per centages of saltpetre varying from 76 to 80, of charcoal from 13 to 16, and sulphur from 5 to 9. These may seem to give rather a wide margin, but this will surprise no one who is acquainted with the great differences in results given by comparatively slight variations in the conditions of ex periment, with powder of the same composition. In the British Government service but one scale of proportions has been employed for many years, and the very extensive trials of the " Committee on explosives " have shown that there is no good reason to depart from that scale ; for they have conclusively demonstrated that the variations in the mechanical and physical properties of gunpowder, produced by the processes of manufacture, exert even more influence upon its action than a comparatively considerable difference in composition ; this does not, however, apply to the small charges used in firearms. It will be seen, moreover, that one of the three ingredients charcoal can be so varied in quality as very materially to affect the results. The following table gives the percentage composition of gunpowder as now made in different countries for military purposes : Saltpetre. Charcoal. Sulphur. England, Royal Gunpowder Factory, France 75 75 15 12-5 10 12 5 Germany 76 14 10 Austria 76 14 10 Russia 75 15 10 Belgium 75 12 5 12 5
- -. Cannonpowder...
75 15 10 ( Rifle ,, 75 12 5 12 5 United States 75 12 - 5 12 5 The proportions of the ingredients in English commercial vdcrs. gunpowders vary considerably according to the market for which they are intended. The best sporting powders have about the same composition as those made by Government. Wherever cheapness is the chief object in view, the quantity of nitre is diminished, and the other two components relatively increased. Some of the powder for the African trade, commonly called " nigger powder," does not contain much more than 50 per cent, of saltpetre, while other kinds are nearly as bad. Blasting powder contains a low proportion of saltpetre, from 60 to 62 per cent. ; but, although this reduction may originally have been made in order to manufacture a cheaper article, yet it is also the most effective for the object desired in many cases, which is to remove large masses of earth or soft rock, and this can best be done by using a comparatively weak or slow-burning powder. The element of time is here of great importance; a very quick-burning or violent explosive would not displace such large masses of a soft material, although the local effect would be more destructive (see BLASTIXG and EXPLOSIVES). Before proceeding further, it will be as well briefly to consider the properties of the three ingredients of which gunpowder is composed, and the part played by each. Saltpetre, or nitrate of potash (KNO 3 ), occurs as a Saltpe natural production on or near the surface of the earth in several warm climates, especially the plains of India and China. When it arrives in England, it has only been partially separated from the earthy and foreign saline matters with which it was combined when found, and is quite unfit for the manufacture of gunpowder; the salts of sodium especially, from their property of absorbing mois ture, are most injurious. In this state the saltpetre is known as "grough " nitre, the impurities commonly present being the chlorides of potassium and sodium, and the sulphates of potash, soda, and lime, together with sand and organic matter; they do not usually exceed 5 Ib per cwt., the exact proportion of impurities in any sample being termed the " refraction " of the saltpetre, and allowed for in the price. The nitrate of soda, called " cubical nitre " or Chili saltpetre, which is found abundantly in South America, although chemically adapted to supply the place of potassium nitrate, cannot be employed in the manufac ture of gunpowder, owing to its very deliquescent properties. This salt is, however, largely converted into saltpetre by the action of chloride of potassium. In France and Germany, also, nitre is produced artificially (see SALTPETRE). Saltpetre, which is a compound of 54 parts of nitric acid and 46 of potash, acts as a magazine of oxygen in a solid form, one volume of saltpetre containing as much oxygen as about 3000 volumes of atmospheric air. This oxygen, with which it readily parts when raised to a certain temperature, combines violently with the carbon to form carbonic acid and a proportion of carbonic oxide ; these with free nitrogen constitute the chief gaseous products of com bustion. The potassium is found combined in the solid residue. Wood charcoal is the charred woody fibre or residue Char- which remains after the liquid and more volatile parts have coal - been driven off by destructive distillation. The object of charring wood is the removal of moisture, and, which is of great importance, the expulsion of those matters which become volatile before they are burned, and which would absorb a large amount of heat. It may be charred in the ordinary way in pits ; but the usual mode of preparing charcoal for gunpowder is by heating it in large iron cylinders or retorts, as hereafter described. By this latter method, the operation is performed with more uniformity and economy, and the charcoal kept more free from par ticles of grit or earthy matter. Charcoal is best fitted for the manufacture of gunpowder when prepared from light spongy wood, containing a very small proportion of mineral sub
stances ; it should be sound, and of not much more than ten