4 Field Museum OF Natural History 



eaten away by slag if they were not protected. Pro- 

 tection is afforded by water cooling. This is provided 

 by water which constantly runs through a number of 

 metal pipes imbedded in the masonry of the boshes. 



About five feet above the base of the furnace and 

 immediately below the boshes are six TUYERES. 

 These are metal nozzles through which a blast of hot 

 air continuously enters the furnace. The tuyeres 

 draw their supply of hot air from the BUSTLE PIPE, 

 a large brick-lined pipe which encircles the furnace 

 slightly above the tuyeres. Below the tuyeres is the 

 CRUCIBLE or HEARTH which is that part of the 

 furnace in which the molten iron accumulates until 

 there is sufficient to tap. The furnace is kept filled 

 with a carefully proportioned mixture of ore, coke and 

 limestone to a point near the top called the STOCK 

 LINE. The blast of hot air which enters through 

 the tuyeres burns the coke and in that part of the 

 furnace an intense heat is generated. The tall column 

 of charge which lies between this zone of combustion 

 and the stock line above rapidly absorbs heat from the 

 rising gases, so that the charge which is at an intense 

 white heat near the tuyeres is below a red heat at the 

 top. 



The section of the furnace shows the charge white 

 hot below, passing through the several stages of yellow, 

 orange and red heats to black at the top. When coke 

 or coal is burned in an ordinary stove combustion is 

 fairly complete and the principal product is an in- 

 combustible gas called carbon di-oxide. When a very 

 deep bed of fuel is burned, the combustion is not com- 

 plete and the product is a gas, carbon mon-oxide, which 

 can itself be burned. As the charge of the furnace 

 forms a bed over fifty feet deep the gas from burning 

 the coke of the charge in the hot blast of air at the 

 tuyeres is this combustible gas, carbon mon-oxide. 



[16] 



