IRON 



3060 



IRON 



purpose, especially to get rid of too much sul- takes its name from the Greek word for blood; 



phur. Calcination, a fourth process, differs 



from roasting in that air is not freely admitted. 



Hematite and magnetite are the names of 



it comprises over ninety per cent of the Ameri- 

 can ore. Both varieties are more fully de- 

 scribed in articles under their own names in 



the two principal varieties of ore. The first these volumes, in alphabetical order. 



Strength and Other Qualities of Iron 



Though iron sturdily resists most of the 

 varieties of strain described in the article 



absorb the carbon, so it is easy to see why 

 steel is stronger than either wrought iron, 



STRENGTH OF MATERIALS, the property in which which has little carbon, or cast iron, which con- 

 it exceeds all other materials is tensile strength, tains more than it can absorb, 

 or resistance to stretch. Pure iron will with- Iron and steel makers exercise great care 

 stand a pull of 40,000 pounds to the square and ingenuity in regulating the amount of 

 inch, and with the addition of proper amounts carbon and other impurities in their product 

 of carbon becomes much stronger. Special to suit the purpose for which it will be utilized, 

 piano wire has been made with a tensile The time of cooling must be controlled very 



United States 30,000,000 

 FIGURES REPRESENT GROSS TONS 



ANNUAL OUTPUT OF PIG IRON IN THE TEN LEADING IRON-PRODUCING COUNTRIES 



The figures given are for normal years, unaffected by war. To illustrate the usual method of 

 making pig iron, the hot molten iron is represented as flowing out of the blast furnace into trenches 

 in the sand. The amount of metal which has flowed into each trench is in proportion to the produc- 

 tion of the country whose name accompanies it. 



strength nearly twelve times as great, and the 

 usual strength of structural steel is from 50,000 

 to 70,000 pounds, and of .machine steel from 

 60,000 to 90,000 pounds per square inch. Wood, 

 which it seems strange to think of as pulling 

 apart, is seldom able to resist over 12,000 

 pounds. It is because of this property that 

 steel rods are embedded in concrete, for the 

 latter, though it cannot be easily crushed, is 

 pulled apart with comparative ease. 



The pictures accompanying this article show 

 why iron varies in endurance. Some forms 

 of the metal look white at a broken surface; 

 others, black or speckled. In the first case the 

 carbon has combined chemically with the iron; 

 in the second, part of it has remained free, in 

 the form of thin sheets of graphite between 

 the particles of iron, and any breaks which 

 occur are apt to be due to its presence. Be- 

 yond a certain point the iron is not able to 



carefully. If the metal is cooled rapidly the car- 

 bon does not have time to separate into graph- 

 ite. This fact explains why chilled plows are 

 superior to others and why steel is strength- 

 ened by being tempered, that is, by being 

 plunged into cold water or oil. It is said that 

 the famed sword makers of Toledo and Da- 

 mascus could temper a sword so thoroughly 

 that the point could be bent to touch the hilt. 

 Manganese and sulphur assist the carbon in 

 combining, while silicon and phosphorus have 

 an, opposite effect. When it is desired that 

 iron be soft, so that it can be drilled or cut, 

 silicon is included in large quantities, to assist 

 the formation of graphite. Phosphorus is in- 

 creased where intricate molds are to be used 

 for cast iron, because it assists the flow of the 

 metal. Too much sulphur is detrimental, for 

 it cools and contracts more slowly than the 

 rest of the materials and leaves small spaces. 



