6 Field Museum of Natural History 



in the model. These are large air-compressors driven 

 either by gas engines or by steam engines which take 

 their steam from gas-fired boilers. These engines or 

 boilers use the furnace gases which are drawn from the 

 top of the furnace through the down-comer and led 

 to the engine room by underground conduits. Other 

 conduits lead the compressed air for the blast from 

 the blowing engines to the STOVES where it is heated. 

 The stoves are the tall structures which appear at the 

 outer edges of the model. They are built of fire-brick 

 and cased with boiler iron. They are so designed that 

 the inside consists of numbers of narrow fire-brick 

 passages. Each furnace is provided with two or more 

 stoves although only one appears in the model. A pipe 

 connects the stove with gas ducts which are fed from 

 the down-comer of the furnace. Gas is burned in the 

 stove until all the fire-brick passageways become hot. 

 Then the gas is shut off and air from the blowing en- 

 gine enters at the top. This air becomes heated in the 

 passage and emerges below into underground ducts 

 which conduct it to the bustle pipe of the furnace. 

 Stoves are intermittent in operation, one supplies air 

 to the furnace while another is being heated. The out- 

 put of the furnace is pig iron, slag and gas. The gas 

 is consumed in the stoves and in operating the blowing 

 engines although there is sometimes a surplus which 

 may be used for other purposes. The slag is mostly 

 a waste product although some is used in the manu- 

 facture of Portland cement and in other ways. The 

 principal product is pig iron. This iron contains small 

 quantities of various impurities, which have an im- 

 portant effect in its properties. From long contact 

 with hot coke in the furnace it has absorbed a quantity 

 of carbon which has made it fusible and suited for 

 the manufacture of cast iron articles. Most pig iron 

 is refined to steel. Refining removes impurities and 



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