This section is from the book "A Treatise On Architecture And Building Construction Vol3: Stair Building, Ornamental Ironwork, Roofing, Sheet-Metal Work, Electric-Light Wiring And Bellwork", by The Colliery Engineer Co.. Also available from Amazon: A Treatise On Architecture And Building Construction.
29. "Wrought iron differs from cast iron principally in the characteristics that it is soft, malleable, and fibrous, while the latter is hard, brittle, and crystalline, as explained in Art. 2. This difference in character is due to the method of manufacture, as both kinds of material come originally from the same ore. Wrought iron is purer than cast iron, as the carbon, phosphorus, and sulphur are eliminated as far as possible, as well as other ingredients which abound in cast iron. It is the carbon which gives cast iron its hardness, and the phosphorus which makes it brittle, while the elimination of the sulphur renders wrought iron malleable and capable of being forged. While it is practically impossible to entirely eliminate these ingredients in the manufacture of wrought iron, they may be so reduced as to be harmless. The presence of too much phosphorus will render the iron what is termed cold short, that is, brittle, or liable to split or break when hammered or bent cold. Sulphur, however, does not so much affect the cold working of the iron, but if present in excess it tends to make it hot short, or brittle at a red heat, and unweldable at any temperature. The value of these characteristics will be better appreciated when the methods of working are described.