Page:The American Cyclopædia (1879) Volume IX.djvu/405

 IRON MANUFACTURE 391 in Styria and England are abundant. The method employed differed from that in use at present in India. Charcoal and ore were placed in a furnace consisting of a small hearth, generally rectangular, provided with a tuyere in the rear wall, and resembling a blacksmith's forge. This form of furnace has descended to the present day, and is still in use in many places. The Catalan forge, used mainly in the Pyrenees, and the American (a modified Ger- man) forge, now chiefly confined to Canada and northern New York, are the most promi- nent examples of this ancient method. (See BLOOMARY.) The nature of the process in low furnaces or hearths is extremely simple. The iron in the ore is reduced by the carbon and carbonic oxide, and, not being fusible at the temperature of the furnace, agglutinates or welds together to a pasty mass, which grad- ually sinks and accumulates in the bottom of the furnace. The completeness of the reduc- tion depends on the time of exposure and the amount of charcoal used. When reduction is incomplete, the unreduced ore fuses and min- gles with the iron. When silica is present in the ore, as is almost always the case, it unites with a portion of ferrous oxide and forms a basic ferrous silicate or fusible cinder, part of which flows off, while part remains incorpo- rated with the iron and is largely expelled in the subsequent working. Complete reduction is therefore never attainable in low furnaces, and the loss of iron is greater the more sili- cious the ore. Rich ores consequently are the only ones adapted to the process. The iron produced in low furnaces is generally of su- perior quality, because the impurities of the ore, not being reduced at the comparatively low temperature which prevails, pass off in the cinder. But the iron is apt to lack uniformity both in structure and in composition. The tendency to increase the height of the furnace, in order to increase the yield and thereby diminish the cost, was thwarted by the produc- tion of a fluid iron, which was probably for ages a waste product, since no method of util- izing it was known. The absorption of car- bon by iron and its conversion into steel or cast iron which is readily fusible depend main- ly on the heat of the furnace, and this in turn on the amount and pressure of blast. Increas- ing the height of a furnace necessitated a stronger blast to overcome the resistance of a higher column of material ; and carburization of the iron necessarily follows. The progress of development from the low furnaces and hearths to the modern high furnaces was there- fore slow ; and it was not until the art of ma- king castings and the method Of converting cast , ' into wrought iron were discovered, that mod- ern iron metallurgy took its rise. According to Verlit, cast iron was known in Holland in the 13th century, and stove plates were made from it in Alsace in 1400. Ancient ornament- al castings have been found in Sussex, England, which have been referred by Lower to the 14th century ; but Karsten says that the sys- tematic production of iron for foundery pur- poses cannot be traced with certainty to an earlier period than the end of the 15th century. According to Lower, the first cast-iron cannon made in England were cast by Ralph Hogge in 1543. Up to the year 1595 Thomas Johnson had made for the earl of Cumberland 42 can- non weighing three tons apiece. The method of converting cast into wrought iron, by expo- sing the fluid iron to a blast of air, was dis- covered very early. It is mentioned distinctly by Agricola, who died in 1555 ; but the regular manufacture of wrought iron by this method began some time later. In Styria, where the pure spathic ores have been regularly smelted since the year 712, there were in 1625 19 StucKfen or Wolfiifen (shaft furnaces 10 to 16 ft. high), producing mainly malleable iron, which was taken from the furnace in a mass (Stilck or Wolf). The process lasted about 18 hours, and "the weight of the mass often reached 1,300 to 1,400 Ibs. There was also produced at the same time more or less fluid carburized iron. The form of the furnace re- sembled two truncated cones placed base to base, a construction which has been retained to a great extent to the present day. In 1760 so-called Flossofen, 25 ft. high, were introduced, and white pig iron was regularly and continu- ously made. This iron was subsequently de- carburized and converted into wrought iron in charcoal hearths. From this time the Stilclc- ofen gradually disappeared. They lingered in some localities for a long time owing to the demand which still continued for Stuckofen iron, than which nothing could be purer ; but finally, during the early part of the present century, they had entirely ceased to exist. The Flossofen gradually enlarged into the Blauofen or Blcueofen, of which there were 34 in Styria in 1864. These furnaces are from 28 to 46 ft. high, and differ from the modern blast furnace mainly in having a closed breast with tapping openings for iron and cinder, while the blast furnace has an open fore hearth, originally de- signed doubtless to permit the dipping out of fluid iron for castings, and now generally re- tained on account of the facility of access it gives to the interior of the hearth of the fur- nace, in case obstructions or deposits have to be removed. Of late years the closed front has been adopted in many large blast furnaces with success; but the fore-hearth construction is still the prevalent one. Increasing the height of the furnace and the strength of the blast had for its immediate effect the more perfect ex- traction of the iron and a decided economy of fuel. The addition of lime as a flux to silicious ores likewise facilitated the complete extrac- tion of the iron. The cinder thus produced, instead of being rich in iron, as was previously the case, contained only the earthy ingredients of the ore with but a trace of iron. The cin- ders produced in low furnaces were for a long time successfully smelted in the Blauofen. In