Liu Bowen (1311–1375) also describes naval mines used at sea or on rivers and lakes; made of wrought iron and enclosed in an ox bladder, it was a timed device in that a burning joss sticks floating above the mine determined when the fuse was to be ignited; the text explicitly mentions that without air and doused in water the fuse would not burn, so the fuse was protected by a long waterproof tube made out of goat's intestine; a later model shown in Ming Chinese scientist and encyclopedist Song Yingxing's (1587–1666) encyclopedia of 1637 shows the ox bladder replaced with a lacquered leather bag while the mine is ignited by a rip cord pulled from the shore to rotate a flint-and-steel firing mechanism. Nickel silver: Nickel silver was first known and used in China during the modern Manchu-led Qing dynasty. During the Qing Dynasty, it was "smuggled into various parts of the East Indies", despite a government ban on the export of nickel silver. O Open-spandrel segmental arch bridge: The earliest known fully stone open-spandrel segmental arch bridge is the Zhaozhou Bridge in southern Hebei province, China, completed in 605 by the Sui Dynasty (581–618) engineer Li Chun. The bridge span is 37.5 m (123 ft) and the structure relatively light in weight due to the four semi-circular arch spandrels which allow for additional flood waters to pass through. Other Chinese bridges would be influenced by this design, such as the open-spandrel Yongtong Bridge of Zhao County, Hebei built in 1130, and the simple segmental arch Lugou Bridge built in 1698 (originally in 1189). The latter, located just west of Beijing and features eleven segmental arches. Oil refining: The Chinese were among the first civilizations to refine oil. During 512 A.D. and 518 A.D., in the late Northern Wei Dynasty, the Chinese geographer, politician, and writer Li Daoyuan introduced the process of refining oil intro various lubricants in his famous work Commentary on the Water Classic. During the first century AD, the Chinese were among the first peoples to refine oil for use as an energy source. During the Northern Song Dynasty, a workshop called the "Fierce Oil Workshop", was established in the city of Kaifeng to produce refined oil for the Song military as a weapon. The troops would then fill the iron cans with refined oil and threw them toward the enemy troops, causing a fire –