Black powder was the oldest of explosives, more commonly known today as gunpowder though it was first used by the Chinese in firecrackers and to propel black-powder rockets (see Chinese fire-arrows) long before guns were invented. Its ingredients are saltpeter, or potassium nitrate (about 75%), charcoal (about 15%), and sulfur (about 10%). Knowledge of the explosive spread from China and other parts of the far East to the Arab world and then to Western Europe by the mid-thirteenth century. Its preparation was described, for example, by Roger Bacon and Albertus Magnus.