Gun-platform. See [Platform].
Gunpowder. A well-known explosive mixture, whose principal employment is in the discharge, for war or sport, of projectiles from fire-arms, and for mining purposes. The ingredients in gunpowder are saltpetre, charcoal, and sulphur. Slightly different proportions are employed in different countries. In the United States the proportions are 75 to 76 saltpetre, 14 to 15 charcoal, and 10 sulphur. Charcoal is the combustible ingredient; saltpetre furnishes the oxygen necessary to support a rapid combustion and to change the whole mass into gas, and sulphur adds consistency to the mixture and intensity to the flame, besides rendering the powder less liable to absorb moisture; increases the volume of gas by preventing the formation of a solid potassium carbonate, and by increasing the temperature.
In the manufacture of ordinary powder, the operations usually employed are [pulverizing] the ingredients, [incorporation], [compression], [granulation], [glazing], [drying], and [dusting].
The ingredients are pulverized by placing each separately in barrels which contain bronze or zinc balls, and which are revolved rapidly for several hours.
Incorporation or thorough mixing is effected partially by the use of a rolling barrel, and completed in the rolling-mill. This consists of two cast-iron cylinders rolling round a horizontal axis in a circular trough with a cast-iron bottom. The cylinders are very heavy, and give a grinding motion, which is very effective in bringing about a thorough mixture of the three ingredients. A wooden scraper follows the rollers and keeps the composition in the middle of the trough. The charge in the trough is moistened with 2 or 3 per cent. of water before the rollers are started. A little water is added from time to time as required. This is the most important operation in the manufacture of powder. The time required is about one hour for each 50 pounds of composition. When finished the composition is called [mill-cake].
Compressing.—This is next taken to the press-house, slightly moistened and arranged between brass plates, and then subjected to hydraulic pressure of about 70 tons (English tons) per square foot. Each layer is thus reduced to a hard cake.
Granulation.—The cake is broken up into grains by means of toothed rollers revolving in opposite directions, the cake being passed between them. The different-sized grains are separated by sieves between the different sets of rollers.
Glazing is effected by moistening the grains and revolving them in a rolling barrel.
Drying is done on sheets in a room heated to 140°-160°.
Dusting.—The dust is removed by revolving the powder in rolling barrels covered with coarse canvas. The dust is caught by an outside case.