Page:Encyclopædia Britannica, Ninth Edition, v. 13.djvu/359

I B N 343 opening up the belly, the neck being furnished with a bamboo nozzle terminating in a clay tube, forming a rough tuyere. After the fire has been urged for some hours the contents of the furnace are removed by partially breaking down the front, in the form of a rough porous ball or bloom of partially melted metal, which is then cut into pieces and charged into a crucible (made of clay mixed with a small quantity of charred rice husks) together with the wood of Cassia auriculata, chopped into little fragments ; each crucible holds about a pound of metal, and is covered over with a few green leaves, preferably of Asclcpias giyantea or Convolvulus laurifolius, a clay cover being made by ramming in soft clay and drying gently. A number of these cru cibles (some twenty or twenty-four) are then piled up in a clay furnace furnished with a bellows something like the ori ginal smelting furnace, the interstices being filled with charcoal. After some two hours heating the steel is fused ; the crucibles are then removed and allowed to cool, and the melted cakes extracted by breaking away the clay. If the opera tion has been successful, the cakes are smooth-surfaced, with radiating striae ; such cakes when remelted in larger quan tities furnish an extremely line quality of steel ; when the conversion of the iron into highly carbonized steel is incom plete, the cakes are imperfectly melted down, and consist more or less largely of fritted lumps of metal not carbonized sufficiently to fuse ; such cakes yield only an inferior steel when remelted. In order to forge the steel the natives heat the calces in a charcoal bellows-forge for some- hours to a temperature short of fusion, and then hammer them out by hand into bars ; these are welded together by foT ging to wedge-heads, tying together with wire, sprinkling with borax, and quickly heat ing and hammering till united ; the long preliminary heating partially decarbonizes the steel, so as to make the final product less like a steely cast iron. When properly pre pared, the temper which this steel will take is magnificent ; it is said that sabres of such steel with an edge sharp enough to cut gossamer like a razor can be dashed with the full strength of a man s arm against a stone wall, or used to cut in two a bar of wrought iron, without having the cutting edge injured in the least degree if the swordsman be only sufficiently expert. According to analyses made by Faraday, wootz contains a small quantity of aluminium ; this probably existed as cinder dissemi nated through the mass, as subsequent analysts have entirely failed to detect aluminium in wootz free from slag ; thus Henry (Phil. Mag., 1852) and Rammelsberg (Berichte Deuf. Chem. Ges., 1870, p. 461) found the following mean numbers, the sulphur being probably overestimated in Henry s analysis : from the first crucible operation could be fused into one mass of somewhat less hard steel than that produced at first in the more successful operations. The possibility of producing steel by fusing together a malleable and a car bonized iron is evidently a simple deduction from the pro cesses whereby a steel is produced by the direct addition of carbon to malleable iron, e.g., those of Mushet and of Heath ( 35). Accordingly a few years after the latter patented the use of "carburet " of manganese, he proposed VIII. METHODS OF STEEL PRODUCTION ESSENTIALLY CONSISTING OF COMBINATIONS OF THE PRECEDING PROCESSES, MORE OR LESS PORE MALLEABLE IRON BEING PRODUCED IN ONE WAY, AND CARBONIZED [RON IX ANOTHER, AND THE TWO BEING BLENDED TO FORM STEEL. 36. The Bessemer-Musket Process and its Precursors. It has teen known since the beginning of the 18th century at least that steel could be prepared by fusing together in crucibles cast and wrought iron ; thus the operation was performed in 1722 by Reaumur employing the heat of an ordinary forge ; whilst in the production of wootz it must have been observed centuries ago that by continued heat ing the badly prepared cakes (consisting partly of fused steel and partially of unfused iron) frequently resulting Fig. 60. (1845) a method for making steel on a larger scale than crucible operations would permit, viz., by fusing in a cupola pig iron, running this into the bed of a steel-making furnace, into the upper part of which the malleable iron was intro duced in bars so as to be heated up by the waste heat and gradually pushed forward so as to dissolve, as it were, in the molten pig with formation of steel. This method is described by Siemens as being one which would doubtless hare led to complete success had the regenerative principle been known to Heath, BO as to enable him to obtain the requisite intensity of heat and absence of cutting draught essential to the proper combination together by fusion of the wrought and carbonized iron without oxidation ; it is substantially one of the forms of steel making by means of the open hearth or regenerative processes now in use, and known collectively as Siemens or Siemens-Martin processes (see 39). Other patents, amounting substan tially to. the same combination of wrought and cast iron by fusion so as to form steel, have been subsequently taken out by Price and Nicholson (1855), Gentle Brown, and Attwood (1862) ; a particular combination of this class patented by Mushet in 1855 (consisting of the addition to molten Bessemer blown decarbonized iron of fused spiegel- eisen) has proved of the highest practical value ( 27), notwithstanding that the non-removal of phosphorus and sulphur to any marked extent in the ordinary blowing process render it applicable to certain kinds of pig iron only; the recently invented "basic" process, however, bids fair to overcome this difficulty (see 37). The earliest form of converter patented by Bessemer, October 17, 1855, consisted of a rectangular furnace with firebars at the side instead of at thebottom, so that a number of crucibles could be heated therein, each furnished with a tapping hole at the bottom, and a pipe dipping to the bottom of the fused metal inside, through which air was to be blown, or a mixture of air and steam, the former causing the temperature to rise, the steam having a cooling effect. Two months later another patent was taken out, the use of a spherical or egg-shaped vessel of iron lined with firebrick and sup ported by axes being the main novelty. In May 1856 a fixed vertical cylindrical vessel, with blast pipes at the base and a tapping