While trying to discover a potion of immortality, Chinese alchemists of the Tang Dynasty accidentally discovered saltpeter, the main ingredient of gunpowder. Upon further experimentation, saltpeter was combined with charcoal and sulfur. While this combination did not grant everlasting life, it did have excellent flammable and explosive properties when ignited. Gunpowder was initially used by the Chinese for fireworks, however gunpowder was used for war as early as 904 A.D., marking the beginning of a long and deadly history of gunpowder. One of the first effective uses of gunpowder was against the Mongols during the Song Dynasty through "an arrow fixed with a tube of gunpowder that ignited and would propel itself across enemy lines" (Whipps). What was meant to be a potion of life would eventually become the main ingredient for death. 

Sources:

Whipps, Heather. “How Gunpowder Changed the World.” LiveScience, Purch, 6 Apr. 2008, www.livescience.com/7476-gunpowder-changed-world.html.