wrought iron: see iron.

white iron pyrites: see marcasite.

sherardized iron: see galvanizing.

pig iron: see iron.

iron pyrites: see pyrite.

iron lung, device used to maintain artificial respiration over an extended period of time. Before the successful vaccination program against poliomyelitis, it was used mostly in treatment of that disease. Currently, its main usage is in cases where the respiration control center of the brain has been damaged (e.g. skull fractures, brain tumors and stroke) or where the diaphragm is paralyzed by spinal cord disease or injury. Invented (1928) by Philip Drinker, the iron lung is composed of a cylindrical steel drum, which encloses the entire body with only the head exposed. A rubber diaphragm makes the cylinder airtight without putting undue pressure on the neck. Pumps raise and lower the pressure within the chamber. A number of problems exist with the iron lung machine; food or vomit may be aspirated into the lungs, and serious skin ulcers may develop in a patient who is immobilized for long periods of time.

iron, metallic chemical element; symbol Fe [Lat. ferrum]; at. no. 26; at. wt. 55.845; m.p. about 1,535°C;; b.p. about 2,750°C;; sp. gr. 7.87 at 20°C;; valence +2, +3, +4, or +6. Iron is biologically significant. Because iron is a component of hemoglobin, a red oxygen-carrying pigment of the red blood cells of vertebrates, iron compounds are important in nutrition; one cause of anemia is iron deficiency. For the history of the use of iron, see Iron Age.

Properties

Iron is a lustrous, ductile, malleable, silver-gray metal found in Group 8 of the periodic table. It is known to exist in four distinct crystalline forms (see allotropy). The most common is the α-form, which is stable below about 770°C;, and has a body-centered cubic crystalline structure; it is often called ferrite. Iron is attracted by a magnet and is itself easily magnetized (see magnetism). It is a good conductor of heat and electricity. It displaces hydrogen from hydrochloric or dilute sulfuric acid, but becomes passive (loses its normal chemical activity) when treated with cold nitric acid.

Compounds

Iron forms such compounds as oxides, hydroxides, halides, acetates, carbonates, sulfides, nitrates, sulfates, and a number of complex ions. It is chemically active and forms two major series of chemical compounds, the bivalent iron (II), or ferrous, compounds and the trivalent iron (III), or ferric, compounds. Ferrous sulfate heptahydrate, FeSO₄·7H₂O, sometimes called green vitriol, is a compound formed by the reaction of dilute sulfuric acid (formerly called oil of vitriol) with metallic iron; it is used in the manufacture of ink, in dyeing, and as a disinfectant. Ferric chloride hexahydrate, FeCl₃·6H₂O, is a yellow-brown crystalline compound used as a mordant in dyeing and as an etching compound. Ferric oxide, Fe₂O₃, is a reddish-brown powder used as a paint pigment and in abrasive rouges. Prussian blue, KFe₂(CN)₆, is a pigment containing the ferrocyanide complex ion. Iron rusts readily in moist air, forming a complex mixture of compounds that is mostly a ferrous-ferric oxide with the composition Fe₃O₄.

Natural Occurrence

Iron is an abundant element in the universe; it is found in many stars, including the sun. Iron is the fourth most abundant element in the earth's crust, of which it constitutes about 5% by weight, and is believed to be the major component of the earth's core. Iron is found distributed in the soil in low concentrations and is found dissolved in groundwaters and the ocean to a limited extent. It is rarely found uncombined in nature except in meteorites, but iron ores and minerals are abundant and widely distributed.

The principal ores of iron are hematite (ferric oxide, Fe₂O₃) and limonite (ferric oxide trihydrate, Fe₂O₃·3H₂O). Other ores include siderite (ferrous carbonate, FeCO₃), taconite (an iron silicate), and magnetite (ferrous-ferric oxide, Fe₃O₄), which often occurs as a white sand. Iron pyrite (iron disulfide, FeS₂) is a crystalline gold-colored mineral known as fool's gold. Chromite is a chromium ore that contains iron. Lodestone is a form of magnetite that exhibits natural magnetic properties.

Production and Refining

Iron is produced in the United States chiefly from oxide ores. For many years rich hematite ores were produced by open-pit mining in the Mesabi Range near Lake Superior. However, these ores have been largely depleted, and iron is now produced from low-grade ores that are treated to improve their quality; this process is called beneficiation. Iron ores are refined in the blast furnace. The product of the blast furnace is called pig iron and contains about 4% carbon and small amounts of manganese, silicon, phosphorus, and sulfur. About 95% of this iron is processed further to make steel, often by the open-hearth process or the Bessemer process, but more recently in the United States and other countries by the basic oxygen process or by an electric arc furnace. The balance is cast in sand molds into blocks called pigs. It is further processed in iron foundries (see casting).

Cast Iron

Cast iron is made when pig iron is remelted in small cupola furnaces (similar to the blast furnace in design and operation) and poured into molds to make castings. It usually contains 2% to 6% carbon. Scrap iron or steel is often added to vary the composition. Cast iron is used extensively to make machine parts, engine cylinder blocks, stoves, pipes, steam radiators, and many other products. Gray cast iron, or gray iron, is produced when the iron in the mold is cooled slowly. Part of the carbon separates out in plates in the form of graphite but remains physically mixed in the iron. Gray iron is brittle but soft and easily machined. White cast iron, or white iron, which is harder and more brittle, is made by cooling the molten iron rapidly. The carbon remains distributed throughout the iron as cementite (iron carbide, Fe₃C). A malleable cast iron can be made by annealing white iron castings in a special furnace. Some of the carbon separates from the cementite; it is much more finely divided than in gray iron. A ductile iron may be prepared by adding magnesium to the molten pig iron; when the iron is cast the carbon forms tiny spherical nodules around the magnesium. Ductile iron is strong, shock resistant, and easily machined.

Wrought Iron

Wrought iron is commercially purified iron. In the Aston process, pig iron is refined in a Bessemer converter and then poured into molten iron silicate slag. The resulting semisolid mass is passed between rollers that squeeze out most of the slag. The wrought iron has a fibrous structure with threads of slag running through it; it is tough, malleable, ductile, corrosion resistant, and melts only at high temperatures. It is used to make rivets, bolts, pipes, chains, and anchors, and is also used for ornamental ironwork.

cast-iron architecture, a term used to designate buildings that incorporate cast iron for structural and/or decorative purposes. After 1800 cast-iron supports were exploited as an alternative to masonry, and with the introduction of wrought-iron beams at mid-century, an efficient, prefabricated method of skeletal construction was possible, of which the most notable example was Joseph Paxton's Crystal Palace (1851) in London. Iron and glass canopies were used to cover such diverse structures as shopping arcades, library reading rooms, and the vast new railway terminals. In the United States, James Bogardus pioneered the use of cast-iron commercial facades, which combined utility with the easy replication of attenuated classical orders in repeated bays.

cast iron: see iron.

bog iron ore: see limonite.

Saugus Iron Works National Historic Site: see National Parks and Monuments (table).

Atomic Number:	Atomic Number: 26
Atomic Symbol:	Atomic Symbol: Fe
	Name of Element: Iron
Atomic Weight:	Atomic Weight: 55.845
Electron Configuration:	Electron Configuration: 2 · 8 · 14 · 2

Iron, Ralph: see Schreiner, Olive.

Iron Guard, Romanian nationalistic, anti-Semitic, and antiparliamentary group, founded in 1924 by Corneliu Zelea Codreanu. Originally named the Legion of the Archangel Michael, it was organized on military lines and operated through terrorism. Its most notable victims were Premier Ion Duca, assassinated in 1933, and ex-Premier Nicolae Iorga, assassinated in 1940. Banned in 1933, the Iron Guard carried on as the All-for-the-Fatherland party. When King Carol II proclaimed his personal dictatorship in 1938, he had Codreanu and other leading Guardists imprisoned and eventually shot. Following the king's abduction in 1940, Marshall Ion Antonescu seized power with the help of the Iron Guard, but soon found himself in disagreement with it. He suppressed (1941) an Iron Guard rebellion, and Horia Sima, then leader of the Guard and vice premier, fled to Germany. With the collapse of the Axis Powers in World War II the Iron Guard disappeared from Romanian politics.

Iron Gate, Rom. Porţile de Fier, Serbian Gvozdena Vrata, gorge of the Danube River, c.2 mi (3.2 km) long and c.550 ft (170 m) wide, on the Serbia-Romania border between Orşova and Drobeta-Turnu Severin. There the river narrows and swiftly flows through a gap between the Carpathian and Balkan mts. Iron Gate, formerly an obstacle to shipping, was cleared of rock obstructions in the 1860s; the Sip Canal (opened 1896) permits large river craft to get past the gorge. Iron Gate is the site of one of Europe's largest hydroelectric power dams. The joint Serbian-Montenegrin-Romanian project (opened 1971) improved river navigation by impounding a large lake and has a substantial electricity generating capacity.

Iron Cross: see decorations, civil and military.

Iron Age, period in the development of industry that begins with the general use of iron and continues into modern times. In Asia, Egypt, and Europe it was preceded by the Bronze Age. It did not begin in the Americas until the coming of the Europeans. Iron beads were worn in Egypt as early as 4000 B.C., but these were of meteoric iron, evidently shaped by the rubbing process used in shaping implements of stone. The oldest known article of iron shaped by hammering is a dagger found in Egypt that was made before 1350 B.C. This dagger is believed not to have been made in Egypt but to be of Hittite workmanship. The use of smelted iron ornaments and ceremonial weapons became common during the period extending from 1900 to 1400 B.C. About this time, the invention of tempering (see forging) was made by the Chalybes of the Hittite empire. It is possible that the Hittite kings kept ironworking techniques secret and restricted export of iron weapons. After the downfall of the Hittite empire in 1200 B.C., the great waves of migrants spreading through S Europe and the Middle East insured the rapid transmission of iron technology. In Europe knowledge of iron smelting was acquired in Greece and the Balkans, and somewhat later in N Italy (see Etruscan civilization; Villanovan culture) and central Europe. The Early Iron Age in central Europe, dating from c.800 B.C. to c.500 B.C., is known as the Hallstatt period. Celtic migrations, beginning in the 5th cent. B.C., spread the use of iron into W Europe and to the British Isles. The Late Iron Age in Europe, which is dated from this period, is called La Tène. The casting of iron did not become technically useful until the Industrial Revolution. The people of the Iron Age developed the basic economic innovations of the Bronze Age and laid the foundations for feudal organization. They utilized the crops and domesticated animals introduced earlier from the Middle East. Ox-drawn plows and wheeled vehicles acquired a new importance and changed the agricultural patterns. For the first time humans were able to exploit efficiently the temperate forests. Villages were fortified, warfare was conducted on horseback and in horse-drawn chariots, and alphabetic writing based on the Phoenician script became widespread. Distinctive art styles in metal, pottery, and stone characterized many Iron Age cultures.

One of the two forms in which iron is obtained by smelting. Wrought iron is a soft, easily worked, fibrous metal. It usually contains less than 0.1percnt carbon and 1–2percnt slag. It is superior for most purposes to cast iron, which is hard and brittle because of its higher carbon content. In antiquity, iron was smelted directly by heating ore in a forge with charcoal, which served both as fuel and reducing agent. While still hot, the iron-and-slag mixture was removed as a lump and worked (wrought) with a hammer to expel most of the slag and weld the iron into a coherent mass. Wrought iron began to take the place of bronze (being far more available) in Asia Minor in the 2nd millennium BC; its use for tools and weapons was established in China, India, and the Mediterranean by the 3rd century BC. Later, in Europe, wrought iron was produced indirectly from cast iron (see puddling process). With the invention of the Bessemer process and open-hearth process, steel supplanted wrought iron for structural purposes, and its use in the 20th century has been principally decorative.

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Most common type of anemia, which may develop in times of high iron loss and depletion of iron stores (e.g., rapid growth, pregnancy, menstruation) or in settings of low dietary iron intake or inefficient iron uptake (e.g., starvation, intestinal parasites, gastrectomy). Much of the world's population is iron-deficient to some degree. Symptoms include low energy level and sometimes paleness, shortness of breath, cold extremities, sore tongue, or dry skin. In advanced cases, red blood cells are small, pale, and low in hemoglobin, blood iron levels are reduced, and body iron stores are depleted. Treatment with iron usually brings quick improvement.

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or iron pyrite or fool's gold

Naturally occurring, gold-coloured iron disulfide mineral. Pyrite has frequently fooled prospectors into thinking they had discovered gold. Pure pyrite (FeS₂) contains 47percnt iron and 53percnt sulfur, by weight. Pyrite is used commercially as a source of sulfur, particularly for the production of sulfuric acid. Because there are much better sources of iron, it is not generally used as an iron ore. For many years Spain was the largest producer; other countries include Japan, the U.S., Canada, Italy, Norway, Portugal, and Slovakia.

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Metallic chemical element, one of the transition elements, chemical symbol Fe, atomic number 26. Iron is the most used and cheapest metal, the second most abundant metal and fourth most abundant element in Earth's crust. It occurs rarely as a free metal, occasionally in natural alloys (especially in meteorites), and in hundreds of minerals and ores, including hematite, magnetite, limonite, and siderite. The human body contains about one-sixth of an ounce (4.5 g) of iron, mostly in hemoglobin and its precursors; iron in the diet is essential to health. Iron is ferromagnetic (see ferromagnetism) at ordinary temperatures and is the only metal that can be tempered (see tempering). Its uses in steels of various types, as well as in cast and wrought iron (collectively, “ferrous metals”), are numerous. Alteration of its properties by impurities, especially carbon, is the basis of steelmaking. Iron in compounds usually has valence 2 (ferrous) or 3 (ferric). Ferrous and ferric oxides (FeO and Fe₂O₃, respectively) are used as pigments and the latter as jewelers' rouge. Rust is ferric oxide containing water; ferric oxide is widely used as a magnetic recording material in computer data-storage devices and magnetic tapes. Ferrous and ferric sulfates and chlorides are all of industrial importance as mordants, reducing agents, flocculating agents, or raw materials and in inks and fertilizers.

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Alloy of iron that contains 2–4percnt carbon, along with silicon, manganese, and impurities. It is made by reducing iron ore in a blast furnace (cast iron is chemically the same as blast-furnace iron) and casting the liquid iron into ingots called pigs. Pig iron is remelted, along with scrap and alloying elements, in cupola furnaces and recast into molds for a variety of products. In the 18th–19th centuries, cast iron was a cheaper engineering material than wrought iron (not requiring intensive refining and hammering). It is more brittle and lacks tensile strength. Its compressive (load-bearing) strength made it the first important structural metal. In the 20th century, steel replaced it as a construction material, but cast iron still has industrial applications in automobile engine blocks, agricultural and machine parts, pipes, hollowware, stoves, and furnaces. Most cast iron is either so-called gray iron or white iron, the colours shown by fracture; gray iron contains more silicon and is less hard and more machinable than white iron. Both are brittle, but malleable cast iron (produced by prolonged heat-treating), first made in 18th-century France, was developed into an industrial product in the U.S. Cast iron that is ductile as cast was invented in 1948. The latter now constitutes a major family of metals, widely used for gears, dies, automobile crankshafts, and many other machine parts.

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(born March 24, 1855, Wittebergen, Cape Colony—died Dec. 11, 1920, Cape Town, S.Af.) South African writer. She had no formal education but read widely, developing a powerful intellect and militantly feminist and liberal views. After working as a governess she published (as Ralph Iron) the semiautobiographical The Story of an African Farm (1883). The first great South African novel, it concerns a girl living on an isolated farm in the veld who struggles to attain independence in the face of rigid Boer social conventions. Her later works include Trooper Peter Halkett of Mashonaland (1897), attacking Cecil Rhodes, and Woman and Labour (1911), an acclaimed bible of the women's movement.

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Final technological and cultural stage in the Stone–Bronze–Iron-Age sequence (or Three-Age System) in which iron largely replaced bronze in implements and weapons. The start of the Iron Age varied geographically, beginning in the Middle East and southeastern Europe circa 1200 BC but in China not until circa 600 BC. Though the large-scale production of iron implements brought new patterns of more permanent settlement, use of iron for weapons put arms in the hands of the masses for the first time and set off a series of large-scale movements and conquests that did not end for 2,000 years and that changed the face of Europe and Asia. Seealso Bronze Age.

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