CHAPTER II. 



THE CHEMICAL AND PHYSICAL PROPERTIES OF 

 STRUCTURAL METAL. 



Wrought Iron. In attempting to discuss the physical and 

 chemical properties of the structural metals, investigation 

 leads by many stages from geological and metallurgical con- 

 ditions existing in Nature's great laboratory to those finished 

 products daily used in the mechanical arts. Each step in this 

 process of evolution has been given the devoted attention and 

 wisdom of learned scientists, who have contributed to the world 

 the results of their researches in many erudite and volumi- 

 nous works. It is not within the scope of this volume to do 

 more than attempt to explain certain pertinent features of 

 this complex subject. 



In general metallic reservoirs and their supports are con- 

 structed of riveted plates and members of iron or steel. 

 Until the last decade iron was almost universally employed, 

 but improved processes of manufacture, reducing at the same 

 time the cost of the product and eliminating the uncertainty 

 of the result, has produced a radical change in this practice, 

 until steel has attained first place as a suitable metal for struc- 

 tural purposes. 



In the production of wrought iron, the chemical process 

 is the conversion of crude or "pig" iron into a refined or 

 " merchantable " product by recarburization in a "puddling 

 furnace." For the manufacture of wrought iron, the lower 

 grades of smelted or "pig" iron are employed. The mechan- 

 ical process of ' * puddling ' ' is melting and stirring the pig iron, 



32 



