PROPERTIES OF STRUCTURAL METALS. 35 



heat and rolled into the required shape. The effect of scrap 

 steel or of impure metal within the mass of this pile is to de- 

 stroy the homogeneity and produce segregation. 



Whilst it is true that sometimes carelessness is responsible 

 for such process of manufacture, more frequently it is the di- 

 rect result of determined effort upon the part of the manufac- 

 turer to cheapen his product by utilizing cheap, miscellaneous 

 scrap metal. When nicked and broken across, or when rup- 

 tured under tension, the appearance of this iron, instead of 

 the long, fibrous arrangement of the molecules, indicative of 

 tough, strong material, is crystalline, and the fracture shows 

 a decided brittleness. 



According to Prof. J. B. Johnson, there are three well- 

 recognized causes of this crystalline structure, indicative of 

 inferior material. 



" First, the so-called wrought iron may have been rolled 

 from fagotted scrap, some of which was probably high-carbon 

 steel, and this portion would show a crystalline fracture. 



" Second, the puddle-ball may have been formed under too 

 great a heat (a common fault), so that a portion of it had 

 been actually melted, thus forming of this portion ingot metal 

 or steel, which part would, when cold, be wholly crystal- 

 line. 



" Third, the puddling process may have been incomplete, 

 when, with a low fire, some of the unreduced pig iron would 

 be removed from the ball, and this would form a coarsely 

 crystalline portion of the final rolled bar." 



Steel manufactured for constructive purposes is at present 

 produced by one of two processes: either the "Bessemer" 

 or converter, or by the " open-hearth " or furnace method. 

 From the character of the lining of the converter or furnace 

 being either acid or basic, a further distinctive technical term 

 of " acid" or "basic Bessemer," or " acid " or "basic open- 

 hearth steel " is commercially used. 



