Gunpowder, the oldest known explosive, was probably discovered in China during the tenth century, though some sources cite a much earlier date. It consists of a mixture of saltpeter (potassium nitrate), sulphur, and charcoal, in variable proportions. Saltpeter is formed from the oxidation of organic matter containing nitrogen, and the process of making and purifying it was probably discovered in either India or China. A Chinese recipe for explosive powder dates to about 1000 A.D., and this was probably used to make incendiary bombs, fireworks, or terrifying explosions. It was probably not used to launch a projectile out of a gun or cannon until about 1304, the year in which the Arabs are said to have constructed the first gun, a crude device made of hollowed bamboo and reinforced with iron that was used to fire arrows. English and Italian manuscripts dating from around 1326 show the existence of guns...