ON FURNA CES. 387 



the ores of iron, lead, and copper, and in fusing cast iron and other 

 substances. In all these, the fuel and the materials to be melted or 

 otherwise acted on are charged, together, into the upper end of a 

 vertical shaft ; and the combustion is maintained by air forced in 

 through one or more openings or tuyeres near the bottom. Of such 

 furnaces, those employed for the manufacture of cast iron are by far 

 the largest and most important, and may be taken as the type of the 

 class. 



The blast furnace for iron making has attained to its present con- 

 struction, and to its colossal size, by what may be described as a 

 process of natural selection ; a gradual advance and improvement, 

 and the survival of the fittest. Representatives of its earliest stages 

 are to be found in the small and simple furnaces that are described 

 as still in use, for the direct production of malleable iron, in the more 

 remote parts of Africa, India, and Borneo. Some of these are little 

 shafts of clay, hardly larger than a chimney-pot, and charged with a 

 mixture of rich iron ore and charcoal. A draught, to maintain the 

 combustion, is obtained either by placing the furnaces so that they are 

 exposed freely to the prevailing winds, or by forcing air in at the 

 bottom of the shaft by some simple form of hand-bellows. The 

 Osmund furnace of Sweden, with a shaft six feet high, and making 

 one and a half to two tons of malleable iron per week, and the 

 Stuckofen, ten to sixteen feet high, and yielding blooms of iron 

 weighing four to six hundredweight, were merely enlargements of 

 these primitive furnaces, and like them produced, not cast iron, 

 but malleable masses resembling puddled balls. The blast furnace, 

 yielding liquid cast iron, grew however directly from the Stuckofen ; 

 as, in a furnace of this height, cast iron was obtained at will, by 

 increasing the proportion of fuel and keeping the metal in the hearth 

 covered with slag ; and when the height was still further increased, 

 nothing but liquid metal was produced.* The possibility of obtaining 

 iron from the ore in a liquid form, that could be tapped out, greatly 

 cheapened its production, and permitted the use of still larger furnaces 

 and the smelting of poorer ores ; and it was found that the cheaper 



* Metallurgy, Iron and S J. Percy, 1864, pp. 325 et seqq. Ibid., J. A. Phillips, p. 170 



