Three days later they arrive at the Valley of Sorrows. Li Kao tells the story of Prince Liu Sheng, younger brother of Emperor Wu-ti. He was appointed as lord of Dragon Head Valley. He had the peasants plant gourds, and used the seeds to burn in horn lamps to light a salt mine. He used the brine and an area of shale that seeped an odorless, easily ignited gas to dry the salt. When the salt ran out, he had work started on mining a vein of iron ore. He set up an Iron Works that used a combination of acids to produce a less brittle form of iron. The suffering of the peasants sent him into gales of laughter. At that time he became known as The Laughing Prince.