246 



CHEMISTRY. 



the body of flame and heated air strongly against the arched 

 ceiling of the furnace, whence it rebounds, or is reverberated 

 down upon the iron which lies on the floor or hearth, d. 

 The openings, g and i, are for the introduction of the iron, 

 and at p is a damper by which the draught is regulated. 

 "When the "puddling" is finished the metal is taken out in 



the shape of a ball, and aft- 

 er being subjected to great 

 pressure by machinery, to 

 squeeze out the slag, it is 

 passed through a succes- 

 sion of rollers, each pair 

 having a smaller space be- 

 tween them than the pre- 

 ceding. The conclusion of 

 all this is the formation of 

 the soft bar-iron of com- 

 merce. Its qualities are the 

 Flg - 96 - very opposite of those of 



cast iron. It is soft, flexible, ductile, and malleable, while 

 cast iron is hard and brittle. When strongly heated it be- 

 comes only semifluid, and therefore can not be made to run 

 into moulds like cast iron. It is also different in its text- 

 ure. "While cast iron is granular, as you can see by ex- 

 amining a broken edge, the structure of wrought iron is 

 fibrous. It is a curious fact that long-continued jarring 

 will sometimes change the fibrous texture of wrought iron 

 into the granular arrangement peculiar to cast iron, show- 

 ing that it is not the mere absence of carbon that makes 

 wrought iron what it is. This has sometimes taken place 

 in the axles and wheels of railway cars, and the brittleness 

 induced has caused serious accidents. It is on account of 

 the peculiar structure of wrought iron that it can be 

 welded, which can not be done with cast iron. In welding 



