or Early Five Dynasties), in Ji Le Pian by Zhuang Jisu (Southern Song Dynasty), in the Book of Tree Planting by Yu Zhen Mu (Ming Dynasty), in the book Guangdong Xing Yu (17th century), Lingnan by Wu Zhen Fang (Qing Dynasty), in Nanyue Miscellanies by Li Diao Yuan, and others. Blast furnace: Although cast iron tools and weapons have been found in China dating to the 5th century BC, the earliest discovered Chinese blast furnaces, which produced pig iron that could be remelted and refined as cast iron in the cupola furnace, date to the 3rd and 2nd centuries BC, while the vast majority of early blast furnace sites discovered date to the Han Dynasty (202 BC – 220 AD) period immediately following 117 BC with the establishment of state monopolies over the salt and iron industries during the reign of Emperor Wu of Han (r. 141 – 87 BC); most ironwork sites discovered dating before 117 BC acted merely as foundries which made castings for iron that had been smelted in blast furnaces elsewhere in remote areas far from population centres. Bomb: The first accounts of bombs made of cast iron shells packed with explosive gunpowder—as opposed to earlier types of casings—were written in the 13th century in China. The term was coined for this bomb (i.e. "thunder-crash bomb") during a Jin Dynasty (1115–1234) naval battle of 1231 against the Mongols. The History of Jin (compiled by 1345) states that in 1232, as the Mongol general Subutai (1176–1248) descended on the Jin stronghold of Kaifeng, the defenders had a "thunder-crash bomb" which "consisted of gunpowder put into an iron container ... then when the fuse was lit (and the projectile shot off) there was a great explosion the noise whereof was like thunder, audible for more than a hundred li, and the vegetation was scorched and blasted by the heat over an area of more than half a mou. When hit, even iron armour was quite pierced through." The Song Dynasty (960–1279) official Li Zengbo wrote in 1257 that arsenals should have several hundred thousand iron bomb shells available and that when he was in Jingzhou, about one to two thousand were produced each month for dispatch of ten to twenty thousand at a time to Xiangyang and Yingzhou. The significance of this, as British sinologist, scientist, and historian Joseph Needham states, is that a "high-nitrate gunpowder mixture had