36 TOWERS AND TANKS FOP WATER-WORKS. 



Physical Differences between Iron and Steel. The 



metamorphose of cast iron into steel is produced, as is the case 

 with the refinement of iron, by oxidation as the principal fac- 

 tor. Made from the same material, and transformed by sim- 

 ilar chemical agencies, it is not surprising that there is a great 

 similarity of the two finished products, one termed wrought 

 iron and the other structural steel. The difficulty of defining 

 steel and the narrow line separating it from iron is clearly put 

 in the "Manufacture and Properties of Structural Steel" as 

 follows : 



' * Prior to the development of the Bessemer and open-hearth 

 processes there was little room for disagreement as to the di- 

 viding line between iron and steel. If it would harden in 

 water it was steel; if not, it was wrought iron. When the 

 modern methods were introduced, a new metal came into the 

 world. In its composition and in its physical qualities it was 

 exactly like many steels of commerce, and naturally and right- 

 ly it was called steel. By degrees these processes widened 

 their field, and began to make a soft metal which possessed 

 many of the characteristics of ordinary wrought iron, and 

 which was not made by any radical changes in methods, but 

 simply by the use .of a rich ferro-manganese. Notwithstanding 

 this fact, some engineers claimed that the new metal was not 

 steel, but iron. The makers replied that it was made by the 

 same process as hard steel, and that it was impossible to draw a 

 line in the series of possible and actual grades of product which 

 they made." Mr. Howe, in his " Metallurgy of Steel ," says, 

 " The terms Iron and Steel are employed so ambiguously and 

 inconsistently that it is to-day impossible to arrange all varie- 

 ties under a simple and consistent classification." Continuing 

 to quote from the " Manufacture and Properties of Structural 

 Steel," "It is true, as argued by Mr. Howe, that many of 

 the common products of metallurgy and art shade impercept- 

 ibly into one another; but it is surely extraordinary when the 



