3 83 SECTION MECHANICS. 



way to make malleable iron, with the appliances then available, was 

 not, except in rare cases, to produce it directly from the ore, but to re- 

 duce the metal first to the state of cast iron, and to make malleable 

 metal from that by a second process. 



Among the further steps that have led up to the modern form of 

 blast furnace are the very general substitution of coke or coal for 

 charcoal as fuel, the use of hot blast, a very great increase in the size 

 of the furnaces, and the collection and use of the waste gases. 



The most recently erected furnaces in the Cleveland district are 

 eighty to ninety feet high, and from 26,000 to 30,000 cubic feet in 

 capacity.* The blast supplied to them is at a temperature of 500 C. 

 to 750 C., and the waste gases are collected, and so efficiently em- 

 ployed, to heat the blast and to raise steam for working the blowing 

 engines, that in many works no fuel, except the coke charged into the 

 furnaces, is used. 



The economies effected by the late increases in the height of blast 

 furnaces and in the temperature of the blast have been very great. 

 Thus, with blast at a temperature in each case of about 540 C., and 

 with other conditions the same, the consumption of coke which in 

 furnaces forty-eight feet high and of 6000 cubic feet capacity, built at 

 the Clarence Works in 1853, was twenty-nine hundredweight per ton of 

 iron made, is reduced, in more recently erected furnaces, by increasing 

 the height to eighty feet and the capacity to 12,000 cubic feet or more, 

 to twenty-two and a half hundredweight.f 



Again, in furnaces of the same size, each increase in the temperature 

 of the blast has been attended with a marked economy ; the extent of 

 which, however, diminishes, for equal increments of temperature, the 

 higher this is raised. When blast, for instance, heated from the tem- 

 perature of the air, which may be taken at 10 C., to 150 C., was first 

 introduced by Nielson, at the Clyde ironworks in 1830, the saving in 

 fuel effected by raising the temperature by 140 C. was equal to about 

 two tons of coke per ton of pig iron made, or thirty-six per cent, of the 

 whole consumption ;$ whereas, in modern practice, the further economy 



* J. Gjers, On Cleveland Blast Furnaces, Journal of the Iron and Steel Institute, 1871, 



p. 202. 



t Isaac Lowthian Bell, Blast Furnace Phenomena. Ibid., Proceedings of the Institution 

 of Mechanical Engineers, 1875, p. 364. 

 t J . Percy, op. cit, p. 391. 



