ON FURNA CES. 389 



obtained by an equal rise in temperature, from 620 C. to 760 C, is 

 not more, even according to the strongest advocates of highly-heated 

 blast, than two hundredweight per ton, or nine per cent. ; a reduction, 

 that is, in the amount of coke used to smelt ordinary Cleveland ores, 

 and in furnaces eighty feet high, from rather less than twenty-two 

 hundredweight per ton to twenty hundredweight.* 



Mr. Bell's investigationst show that the remarkable saving in fuel, 

 obtained by the use of highly heated blast, is due to the lower tem- 

 perature at which the gases escape from the furnace top, and the 

 smaller proportion of CO that they contain ; the ratio of the amount 

 of CO 2 to that of CO, in the gases, being the index of the more or less 

 advantageous manner in which the fuel is burned ; and he has pointed 

 out that the economy of large and high furnaces over smaller furnaces 

 is to be traced to the same causes ; the gases from a high furnace 

 carry off less sensible heat ; and up to a certain limit, which he 

 fixes, for the materials in use in the Cleveland district, at a height of 

 eighty or ninety feet, they are poorer in CO than those from lower 

 furnaces. 



Thus height of furnace and temperature of blast appear to be 

 capable in a great measure of replacing each other 'in their effect on 

 economy of working ; and the benefit to be derived from working 

 with very hot blast is likely to be greater in the case of furnaces 

 which, from the characters of the fuel and ore used, cannot be 

 made very high, than it is in the high furnaces in use in Cleveland. 

 As an instance of the similar effect, on the consumption of fuel, of the 

 use of hot blast and of an increase in height, Mr. Bell quotes the 

 working of the furnaces at Lillieshall. There, in furnaces fifty-three 

 feet high, the consumption of coke, with cold blast, was forty hundred- 

 weight per ton of iron made ; and this consumption was equally 

 reduced, to twenty-eight hundredweight per ton, in the case of one 

 furnace, by increasing the height to seventy-one feet ; and in another, 

 with the old height of fifty-three feet, by heating the blast. 



In the Glasgow district, the fuel generally used in the blast furnaces 

 is uncoked free burning coal ; and with this comparatively soft fuel it 



* C. Corhrane, Proceedings of the Institution of Mechanical Engineers, 1869, p. 21, and 

 1870, p. 62. 

 1 Blast Furnace Phenomena. 



