Gunpowder is an explosive mixture of potassium nitrate, charcoal and sulphur in the proportions of 75, 15 and 10 - although alternative proportions are also used. The three ingredients must be very finely ground and mixed, and ordinary charcoal is not very suitable. Rather charcoal from dogwood, alder or willow is used. The wood is cut in spring and stored for between two and three years before being cut into small pieces and packed into thick iron containers with holes at one end to allow gases to escape, and heated for four hours.
The crude pottassium nitrate is dissolved in boiling water, filtered, and then allowed to cool and crystallize in a trough in order to purify it from nitrates of soda and lime, chlorides of potassium and sodium, etc, the liquid being continually agitated, so that the crystals may be formed small and pure. They are then washed and allowed to drain. The sulphur is purified and ground. The charcoal is obtained from alder or willow wood, or from dogwood for the finest powder. These ingredients are first roughly mixed, then sprinkled with water and incorporated under rollers in a mill, and formed into a cake termed 'mill cake'. This is broken up under grooved rollers, and brought by pressure into 'press cake'. After this it is granulated, by being passed between toothed rollers, and separated into classes by sieves of different sizes of mesh. Around the end of the 19th century a very large grain was adopted for the heaviest ordnance; this was termed pellet or pebble powder. 'Pellet' powder was made by filling the cylindrical holes in a thick gun-metal plate with mealed powder, and by means of pistons under a hydraulic press, forming them into short cylinders or 'pellets', with a small cavity at one end to catch a flame the more readily. 'Pebble' powder was made by cutting or pressing edges which divide the press cake into small cubes; these, like pebbles, have their corners rubbed off and rounded by friction. The largest pebble powder consisted of cubes of 1.5 inches.
There is also a gunpowder known as 'prismatic', the grains forming large hexagonal prisms with a hole through the centre. 'Cocoa' powders are made with other kinds of carbon than wood charcoal. The greatest precautions must be taken to prevent fire or water from coming into contact with gunpowder. Hence it was usually kept in magazines which were of great strength in defensive works, although lighter and well-ventilated buildings sufficed under other conditions. In the transportation of gunpowder, the casks should be dust-proof, and the carriages and vessels containing it should be water-tight. As iron vessels are dangerous, gunpowder was usually packed in copper-hooped barrels made with coppernails.
The explosive power of gunpowder is very great. It is, however, necessary to place it within a confined space, as, when it is heaped up in the open air, it explodes without report or much effect. As the result of experiments it appears that the weight of the gases produced by inflaming gunpowder is about three-fifths of that of the powder, and their volume 288 times its bulk, when they have attained an elasticity equal to that of the air. If the effect of heat evolved during the combustion be added, the elastic force is increased to 1000 atmospheres in round numbers, i.e. a pressure of about 6.5 tons to the square inch.
Gunpowder is thought to have been invented by the Chinese and Marcus Graecus, who lived about the 9th century, describes its composition, which was also known to Roger Bacon, who refers to it in 1267. It was also apparently known to the Arabs at an early period. In 1342 the Moors employed it in the siege of Algeciras. According to the common story the discovery of its propulsive power was due to the German monk Barthold Schwartz between 1290 and 1320.
Guns are said to have been employed by Edward III in 1327, on his invasion of Scotland. It is also asserted that gunpowder was employed in 1346 by the English at Crecy. It was not, however, until the 16th century that its use in warfare became general.
Abbreviations
Warfare
Research Gunpowder