 The per capita iron output rose sixfold between 806 and 1078, and by 1078 Song China was producing 127,000,000 kg (125,000 long tons; 127,000 t) in weight of iron per year. The historian Donald B. Wagner points out that this estimate was based upon the total number of government tax receipts on iron from the various iron-producing prefectures in the empire. In the smelting process of using huge bellows driven by hydraulics (i.e. large waterwheels), massive amounts of charcoal were used in the production process, leading to a wide range of deforestation in northern China. However, by the end of the 11th century the Chinese discovered that using bituminous coke could replace the role of charcoal, hence many acres of forested land and prime timber in northern China were spared by the steel and iron industry with this switch of resources to coal. This massive increase in output of the iron and steel industry in China was the result of the Song dynasty's needs for military expansion, private commercial demands for metal products such as cooking utensils found in the market and a wide variety of agricultural tools, and by new canals linking major centers of iron and steel production to the capital city's bustling market. The many uses for manufactured iron products in the Song period included iron for weapons, implements, coins, architectural elements, musical bells, artistic statues, and components for machinery such as the hydraulic-powered trip hammer, which had been known since the 1st century BCE during the ancient Han dynasty, and used extensively during the Song. Due to the enormous amount of production, the economic historian Robert Hartwell noted that Chinese iron and coal production in the following 12th century was equal to if not greater than England's iron and coal production in the early phase of the Industrial Revolution during the late 18th century. However, the Chinese of the Song period did not harness the energy potential of coal in ways that would generate power mechanically, as in the later Industrial Revolution that would originate in the West. There were certain administrative prefectures during the Song era where the Chinese iron industry was mostly concentrated. For example, the poet and statesman Su Shi wrote a memorial to the throne in 1078 that specified 36 ironwork smelters, each employing a work force of several hundred people, in the Liguo Industrial Prefecture (under his governance while he administered Xuzhou).
