The First Emperor's Gunpowder: I Am Waiting for the Flowers to Bloom in Xianyang

A modern engineering doctor traveled through time and became Qin Shihuang Yingzheng, retaining the emperor's memory and scientific and engineering knowledge. After discovering that Xu Fu's "elixir" formula actually contained saltpeter and sulfur, he decided to take advantage of the situation. In the name of longevity, he secretly established a laboratory and used ten years of planning to promote the thermal weapons revolution.