Text-book of medical and pharmaceutical chemistry . oal; higher up, carbonmonoxide is produced, which actsupon the oxide of iron, reducing itto the metallic state. As the reduced iron sinks, it comes intocontact with the coal, takes up a small quantity of carbon, andforms cast-iron, which, on further sinking, fuses, and is drawnoff into moulds made in sand, to form pig iron. The earthyimpurities of the ores, remaining in the furnace, unite with thefluxes, fu;ie in the intense heat, and are drawn off as slag. Thepig iron is then subjected to the puddling process, by whichit is more completely f
Text-book of medical and pharmaceutical chemistry . oal; higher up, carbonmonoxide is produced, which actsupon the oxide of iron, reducing itto the metallic state. As the reduced iron sinks, it comes intocontact with the coal, takes up a small quantity of carbon, andforms cast-iron, which, on further sinking, fuses, and is drawnoff into moulds made in sand, to form pig iron. The earthyimpurities of the ores, remaining in the furnace, unite with thefluxes, fu;ie in the intense heat, and are drawn off as slag. Thepig iron is then subjected to the puddling process, by whichit is more completely freed from carbon and slag, and wroughtiron results. This process is usually carried on in reverberatoryfurnaces with a free supply of air, while the molten mass is beingthoroughly stirred. The greater part of the carbon is in thisway burned into carbon monoxide, and the silicon, sulphur,and phosphorus oxidized. Steel was formerly prepared fromwrought iron only, by cementation, or heating wroughtiron, packed in leather shavings or with charcoal. At. BLAST FURNACE. IRON. 287 present it is chiefly prepared directly from cast or pig iron by themethod invented by Bessemer in 1850. This process consists inblowing air, under high pressure, into a mass of molten cast-iron,until the carbon has been burned out, when spiegeleisen, contain-ing a known quantity of carbon, is added, to give the properamount for steel. Pure iron is obtained by heating ferricoxide in a current of hydrogen ; this is the ferrum redactumof the U. S. P. Fe,03 + 3H,-= 3H,0 + Fe,. 485. Properties.—Pure iron is soft, fuses at about 1600° C.(2912° F.), and has a specific gravity of to Iron isnot affected by dry air at ordmary temperatures; in moist air, itcovers itself with a thin layer of ferric hydroxide, known asrust. Heated strongly in the air, it becomes coated with alayer of ferrous-ferric oxide (FesO^), which is readily loosened,forming the blacksmiths scales. At a red heat, it decomposeswater, wi
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