GUNPOWDER, a well-known explosive mixture composed of sulphur, niter, and charcoal. Of use in several trades, its principal employment is in the discharge, for war or sport, Of projectiles from fire-arms, and iu the processes of blasting during big or quarrying. The history of gunpowder has been already given under fire-arms (q.v.), and it will therefore be only necessary now to consider the chemical am ion.which takes place when powder is ignited, and then to proceed to a short description of the manufacture.
Extreme care is requisite. in securing the. purity of the ingredients entering into the composition of gunpowder. The principal impurity of niter or saltpeter is chloride of sodium, or common salt, which, in consequence of its tendency to absorb moisture from the atmosphere, would have a very injurious action on gunpowder by weakening its power. The details of the process of purification of the niter would be out of place in this article. The sulphur may be purified either by fusion (when the heavier impuri ties sink, and the lighter ones may be removed by skimming) or by distillation. The preparation of the charcoal is a most important point. It should he light and porous, should yield a very small amount of ash, especially of carbonate of potash aud other deliquescent salts, and should contain little moisture. The.woods yielding the best charcoal for gunpowder are black alder, poplar, spindle-tree, willow, and dogwood, the last named giving off the largest volume of gas when ignited with a given weight of niter, and being on that account especially used for rifle powder.
A vast number of experiments have been made at different times, and by different nations, to discover the proportions of miter, sulphur, and charcoal best adapted for the production of different kinds of gunpowder; and upon the whole there has been great uniformity in the results, as may be seen from the following tablg of the percentage composition of the powder of different nations: The chemical processes which occur in the ignition of gunpowder are commonly described as follows: When the powder is ignited, the oxygen of the niter combines with the charcoal or carbon to form carbonic add, the potassium combines with the sulphur to form sulphide (or sulphuret) of potassium, and the nitrogen is liberated; the reaction being shown in the equation S +SC =3CO2 N+ KS. Powder
consisting of one equivalent each of niter and sulphur, and three equivalents of carbon, would contain 74.8 per cent of niter, 11.9 per cent of sulphur, and 13.3 per cent of car bon or charcoal, which approximates very closely to the Austrian powder in the above table. It is easily shown that one volume of such powder would yield 290 volumes of mixed carbonic acid and nitrogen gases, after the ordinary reduction for temperature and pressure, although from the intense beat developed at the momeLt of explosion the actual dilatation amounts to at least 1500 times the volume of the powder employed. The only solid residue, supposing the above equation to represent the true reaction, is sulphide of potassium (KS), and part of this is volatilized by the heat of the explosion, causing a whitish smoke by its combustion, while the part that is not burned gives the peculiar odor to the washings of the gun-barrel.
If a larger proportion of charcoal is added, more or less carbonic oxide gas is gen erated as a product of combustion. Blasting powder is so composed that, theoretically, it should yield on -explosion a mixture of carbonic oxide and carbonic acid gases, and leave a residue of bisuiphide of potassium; the reaction being expressed by the equation = 2C0+ N+ KS,. A powder composed accord ins. to this formula would contain 64.4 per cent of niter, 20.4 per cent of sulphur, and per cent of carbon; and the proportions actually employed are 65, 20, and 15, respectively.
Recent investigations of Bunsen and Schischkoff (Poggendorif's Annalen, Bd. 102, p. 321) show that in reality the chemical reactions are very far from being as simple as those given in the preceding paragraphs; the solid residue consisting of various com pounds of potassium (sulphate of potash being in greatest quantity), with portions of niter and carbon.