GUN MET′AL. An alloy containing 90·5% of copper and 9·5% of tin, used for casting pieces of ordnance (erroneously termed ‘brass guns’), also those parts of machinery which are subjected to considerable friction. See Alloys, Bronze, Stereo-metal, &c.
GUN′POWDER. This substance is a mechanical mixture of saltpetre, charcoal, and sulphur. It is seldom prepared on the small scale.
Prep. The saltpetre having been trebly refined, by boiling, skimming, filtering, and crystallising, is melted into cakes, which are then brushed to remove any adhering grit or dirt, broken into pieces with a mallet, ground to a fine powder in a mill, and sifted through a fine bolting sieve of brass wire. The charcoal is that of the alder or willow, and is carefully burnt, as already described, and is then reduced to powder. The sulphur is refined by distillation, and ground to the same fineness as the charcoal and saltpetre. The ingredients are weighed out in the proper proportions, and mixed together in a machine consisting of a wooden drum, having a shaft passing through its centre, to which numerous ‘flyers’ in the shape of knife-blades are attached, the drum and flyers revolving in a contrary direction. When mixed, the charge is carried to the ‘incorporating mill,’ where it is ground under vertical iron ‘mill-stones,’ with a small quantity of distilled water, until the ingredients are thoroughly incorporated. The product of this operation is then pressed into a hard cake, which is next broken into pieces, granulated by means of sieves, and after being ‘glazed’ by friction, and the dust separated, is dried, with proper precautions, in a stove heated to about 130° by steam pipes.
The proportions of saltpetre, charcoal, and sulphur, used for different kinds of powder, differ very slightly. In ‘sporting powders’ the proportion of saltpetre is generally from 1 to 3% greater than in the Government powders. In ‘miners’ powders’ it is about 10% less, an excess of sulphur being used. The following are the proportions adopted by European powers:
| Saltpetre. | Charcoal. | Sulphur. | |
| England | 75 | 15 | 10 |
| France | 75 | 12·5 | 12·5 |
| Austria | 75 | 15 | 10 |
| Prussia | 75 | 13·5 | 11·5 |
| Russia | 73·78 | 13·59 | 12·63 |
| Spain | 76·47 | 10·78 | 12·75 |
| Sweden | 76 | 15 | 9 |
| (Capt. Jervis-White Jervis.) | |||
Obs. The quality of gunpowder is best estimated by actual trial of its power and cleanliness in use. It should be dry, hard, and free from dust; the grains should be of a uniform size, and glossy, and the colour a dark-grey or brownish-grey, not perfectly black. A very little placed on a piece of paper and fired should instantly explode with a flash, and neither leave an appreciable residue on the paper nor burn it. Dried by the heat of boiling water, or in vacuo, it should not lose more than 1⁄2 to 1% of its weight. Damp powder rapidly ‘fouls’ the gun. Gunpowder, containing more than 7% of water, does not recover its strength by simply drying it. The sp. gr. ranges between 1·795 and 1·800.
Karolyi succeeded in analysing the gases of gunpowder which had been fired in conditions closely resembling those which occur in artillery practice. For this purpose he enclosed a charge of powder in an iron cylinder of such strength that it just burst when the powder was fired by means of the electric spark. This charged cylinder was suspended in a hollow spherical bomb, from which the air was exhausted before firing.
After the explosion had been produced, the gases and the solid residue of the powder were submitted to analysis. The results obtained were the following:[343]
[343] ‘Phil. Mag.,’ 1863.
1. Composition of the Powder used.