Gunpowder (or gun powder) is a mix of chemical substances (75% saltpeter, 15% charcoal and 10% sulfur). It is used primarily in firearms, burns very quickly, and creates gases. Those gases use up more space than the gunpowder they come from, so they push outward. If the gunpowder is in a small space, the gases will push on the walls of the space, building up pressure. In a gun, the pressure pushes against a bullet, causing it to fly out at high speeds. If the pressure became too high, it could destroy the gun barrel.
Gunpowder was invented by the Chinese. The first references of black powder, the original form of gunpowder, date to the 9th century. According to legend, Chinese alchemists were looking for a formula to create the elixir of life, or the mythical potion that causes whoever drinks it to become immortal, when they accidentally created gunpowder. Because the powder was highly flammable, or burned very easily, they decided to call it "fire medicine" (Simplified Chinese: 火药 / Traditional Chinese: 火藥). The Chinese soon weaponized the substance, or made weapons out of it. In later centuries they made many weapons using gunpowder, including rockets, bombs, flamethrowers, and land mines, before making cannons and guns. The oldest weapon that uses gunpowder dates back to a bronze handheld cannon made in northeastern China in 1288. The first mention in Europe was in the 13th century when Roger Bacon described the formula of black powder. Gunpowder was extremely valuable to the Chinese civilization, in fact so valuable that sometimes it was traded for gold.
- Gunpowder -Citizendium