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IRON

(Anglo-Saxon, iron; L. ferrum)

Fe at. wt. 55.847
   at. no. 26
   m.p. 1535°C
   b.p. 2750°C
   sp.gr. 7.874 (20°C)
   valence 2, 3, 4, or 6. 

Iron use is prehistoric. Genesis mentions that Tubal-Cain, seven generations from Adam, was "an instructer of every artificer in brass and iron." Iron is a relatively abundant element in the universe. It is found in the sun and many types of stars in considerable quantity. Its nuclei are very stable. Iron is found native as a principal component of a class of meteorites known as siderites, and is a minor constitueny of the other two classes. The core of the earth, 2150 miles in radius, is thought to be largely composed of iron with about 10% occluded hydrogen. The metal is the fourth most abundant element, by weight, making up the crust of the earth. The most common ore is hematite (Fe2O3), from which the metal is obtained by reduction with carbon, Iron is found in other widely distributed minerals, such as magnetite which is frequently seen as black sands along beaches and banks of streams. Taconite is becoming increasingly important as a commercial ore. Common iron is a mixture of fout isot9pes. Six other isotopes are known to exist. Iron is a vital don- stituent of pl4nt and animal life, and appears in hemoglobin. The pure metal is not often encountered in commerce, but is usnally alloyed with carbon or other metals. The pure metal is very reactive chemically, and rapidly corrodes especially in moist air or at elevated temperatures. It has four allotropic forms, or ferrites, known as a, fi, y, and 6, with transition points at 7700, 9280, and 15300C. Thea form is magnetic but when transformed into the fi form, the magnetism disappears although the lattice remains un- changed. The relations of these forms are peculiar. Pig iron is an alloy containing about 3% carbon with varying amounts of S, Si, Mn, and P. It is hard, brittle, fairly fusible, and is used to produce other alloys, including steel. Wrought iron contains only a few tenths of per cent of carbon, is tough, malleable, less fusible, and has usually a "fibrous" structure. Carbon steel,is an alloy of iron with carbon, with small ampunts of Mn, 'S, P, and Si. Alloy steels are carbori steels with other additives, such as nickel, chromium, vanadium, etc. Iron is the cheapest and most abundant, useful, and important of all metals.

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