Gunpowder
"There is a certain mixture that is made from three powders that dance and fly violently." Wei Boyang, a scholar from the Qin dynasty describes something that seems like gunpowder. Although gunpowder was used in the Tang dynasty it came from many dynasties of work which started from the Qin dynasty. They mixed sulfur, charcoal and potassium nitrate to create gunpowder. In 700 AD gunpowder was perfected and in use for fireworks. In 904 AD it was used as a weapon. They eventually created cannons by using gunpowder in a bronze tube and an iron ball. They were very weak compared to cannons now but they could still cause a lot of damage.