492 



SMITH S INTERMEDIATE CHEMISTRY 



checkerwork of brick. When this has become hot, the valves 

 are reversed, the gas and air now enter through the hot brickwork 

 and pass out through the checkerwork on the opposite side, raising 

 its temperature. The direction of the gases is changed every 

 twenty minutes or so, and the whole operation lasts 8 to 12 hours. 



FIG. 114 



Towards^he end some ajum^miumjs added to combine with 

 oxygen (present as CO), and give sounder ingots. Recently, iron 

 Containing 10 to 15 per cent of titanium has been added instead, 

 titanium combines witkJboiyb^jriitrogen and oxygen, and 

 passes into the slag. Rails made of steel purified with this 

 element are less liable to breakage and are 40 per cent more dur- 

 able than ordinary open-hearth rails. 



The advantage of this process over that of Bessemer is that 

 it is not hurried and is therefore under better control. The 

 material can be tested by sample at intervals, and defects cor- 

 rected. The product is of better and more uniform quality. 



As in the Bessemer process, phosphorus and sulphur are re- 

 moved by using a basic lining. 



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