Gunpowder is a mixture of potassium nitrate (saltpeter), sulfur and charcoal. The sulfur and charcoal act as fuels, and the potassium nitrate acts as an oxidizer. When the fuel and oxidizer are combined, they create an explosive reaction that produces hot gases. The gases expand very quickly, producing a lot of pressure. That pressure pushes the bullet out of the barrel of the gun at high speed.
The first recipe for gunpowder was written in China around 900 A.D., but it was not until around 1250 A.D. that it was used in weapons [source: Britannica]. The Chinese used it to launch rockets and fire arrows from bamboo tubes called "eruptors." They also used it to propel rockets into the air during celebrations [source: Britannica].
In Europe, gunpowder was used in cannons and guns beginning in the 13th century [source: Britannica]. In fact, when Europeans first encountered Chinese fireworks during trade missions to China, they were so impressed by their power that they brought them back to Europe as well as their recipe for making them [source: Britannica].
The word "gunpowder" comes from the Chinese words "huo yao," which means "fire drug" or "fire medicine" [source: Britannica]. It is also known as black powder or gun powder because it is made from three ingredients -- saltpeter (potassium nitrate), sulfur and charcoal -- that are ground together into a fine powder before being mixed together into a paste-like substance that can be molded into sticks or balls for storage or transport [sources: Britannica; NRA].
Gunpowder has been used in weapons for hundreds of years because it is powerful and easy to store and transport compared to other explosives like dynamite or TNT [source: NRA]. It's also relatively safe compared to other explosives -- if you're careful when handling it -- because it requires a source of heat or flame to ignite it [sources: NRA; UPI].