ON FURNACES. 393 



working of the Cleveland blast furnace. Mr. Bell found that on passing 

 a slow current of CO 2 over ordinary Durham blast furnace coke, con- 

 tained in a glass tube, no CO was formed when the heat of the coke 

 did not exceed 550 to 650 C, and only traces even when the tem- 

 perature was raised to such a point that the combustion tube, of hard 

 German glass, began to soften.* 



In blast furnaces, no such saving as that above quoted is to be looked 

 for, by burning the gases in the upper part of the shaft ; as in these the 

 proportion that the fuel bears to the other materials of the charge is so 

 much greater than in a cupola, that the sensible heat, alone, of the gases 

 is more than sufficient to heat up the whole charge to their own tem- 

 perature ; and in addition to this there is, as Mr. Bell has shown, an 

 actual evolution of heat, in the upper part of the furnace, due to the 

 dissociation of a portion of the CO. In the case of the furnace, for 

 instance, eighty feet high, erected at the Clarence Works in 1866, the 

 total capacity for heat of the ore, coke, and limestone charged, is less 

 than half that of the gases ; so that, neglecting the absorption of 

 heat by chemical action, and its evolution by dissociation, the sensible 

 heat alone of these would be sufficient to heat up twice as much solid 

 material as is charged. 



The furnaces of the second group, or flame furnaces, are veiy varied 

 in form and character. In these, the useful effect is obtained by bring- 

 ing a flame, or current of highly heated and burning gas, into contact 

 with the matters to be acted on, instead of imbedding these in or 

 mixing them with the solid fuel. 



The ordinary reverberatory or flame furnace, with a fire grate, a 

 flame chamber or working chamber, and beyond that again a flue 

 leading to the chimney, is well known, and there is no need to go over 

 in detail the variations from the general type by which it is adapted to 

 different uses. 



The most important recent modification of this form of furnace is 

 the regenerative gas furnace of Messrs. Siemens, of which models and 

 a diagram are in the room. In this, which dates in its present form 

 from 1 86 1, the fuel is transformed, in a separate gas producer, into a 



* Proceedinss of the Institution of Mechanical Engineers, 1869, p. $$. 



B C 2 



