Cast-iron is made only in blast-furnaces, of which Fig

2 shows a modern example. The furnace is an immense shaft 50 to 100 ft. high and 10 to 20 ft. inside diameter, cased outside with boiler iron and lined inside with fire-brick. The mixture of ore, fuel, and flux is charged in above, at the throat of the furnace (A), while heated air is blown in beneath from the blast-pipe D; the waste gases, leaving by the pipe F, deposit their dust in the box H, and are then burned in stoves to heat the blast. the body of the furnace, where reduction takes place: Care the boshes, where the charge is melted, slag formed and IMG:content-0809.jpg:[ocr errors] iron absorbs carbon and becomes fluid cast-iron. The slag and iron collect in the crucible G. The combustion of the fuel in the lower part of the furnace produces great heat and generates large quantities of carbonic oxide gas, which is a strong reducing agent and abstracts oxygen from the ore as it rises through the furnace. The impurities of the ore (silica, clay, etc.) unite with the flux (limestone) to produce a fluid slag; the reduced iron is hot enough to absorb carbon and melt freely; the slag and iron collect in the bottom of the furnace, the slag on top, and are tapped out at tap holes at different levels. The fuel used is charcoal, coke, or coal, the flux unburned or burned limestone. For producing one ton of pig-iron there is required one ton of charcoal or coke, or 14 of coal, with 14 to 24 tons of ore (according to its richne ), and to ton of flux (according to whether burned or unburned and the amount of impurities in the ore); meanwhile about 5 tons of air will be blown in and 6 tons of gases escape. The iron is run from the furnace on to the casting-bed, and there cast in sand into the bars called pig-iron, weighing ab. 100 lbs. each. Most modern furnaces have the blast heated by pa ing through hot-blast stoves; the gases coming from the furnace are utilized by being burned in these Pig-iron is used for three purposes: (1) For making castings; (2) for conversion into wrought iron; (3) for conversion into steel. stoves. For making castings, it is remelted in reverberatory or cupola furnaces (the latter being similar to a diminutive blast furnace). The melted iron is cast in molds, generally of sand, sometimes of iron.