68 IRON AND STEEL. 



This process is still employed, and the product is variously known 

 as cement or blister steel, or, if the bars are rolled together to secure 

 homogeneity, as shear steel. Reaumur described this process in 

 1722 ; and it is not known how long before his time it was employed 

 or where, when or by whom it was introduced. About the middle of 

 last century Benjamin Huntsman, in England introduced the 

 modern method of making crucible cast steel substantially as it is 

 practiced to-day. 



Steel was also sometimes made by dipping bars of soft iron into 

 molten cast iron, from which they absorbed a portion of the carbon 

 and were converted into steel ; and sometimes malleable and cast 

 iron were fused together in a close chamber producing steel of an 

 inferior quality. 



Siemens-Martin steel is made by the decarbonization of cast iron 

 in a reverberatory furnace heated with gas, the flame of which assists 

 the reaction ; and the subsequent recarbonization of the bath by the 

 addition at the close of the process of white iron, spiegeleisen, or 

 ferro-manganese. The operation requires from four to eight hours. 



The Thomas-Gilchrist process is simply an improvement upon 

 the Bessemer or pneumatic process. A chemical lining is put into 

 the converter, which absorbs phosphorus and other objectionable 

 minerals from the melted metal, and permits the use of a lower 

 grade of iron than is possible in the Bessemer process. 



Puddled steel is made in much the same way as wrought iron is 

 made from cast iron. That is, the iron is melted in a reverberatory 

 furnace exposed to a strong draught of atmospheric air, and is kept 

 stirred or puddled until the oxygen of the air unites with the carbon in 

 the iron and burns it out. If steel is desired the metal is withdrawn 

 before all the carbon is consumed ; if iron is desired the process is 

 continued till the carbon is consumed, when the metal is brought to 

 a spongy, pasty condition, is rolled into balls or blooms, and is lifted 

 to the squeezer, where the slag and other impurities are squeezed 

 out. Puddled, or open hearth steel, as it is generally called is grow- 

 ing in favor, and in England its production is increasing more 

 rapidly than that of Bessemer or pneumatic steel. 



The most important metallurgical discovery of the age was that 

 of making steel from cast iron by the pneumatic process. This was 

 the invention of Sir Henry Bessemer, and was made about 30 years 



