904 



STEEL 



1909 



axes, at or near its centre of gravity. It is constructed of boiler-plates, and is lined 

 cither with fire-brick, road-drift, or ' ganister ' (a local name in Sheffield for a peculiar 

 kind of powdered stone), which resists the heat better than any other material yet 

 tried, and has also the advantage of cheapness. The vessel having been heated, is 

 brought into the position shown in fig. 1908, so that it may receive its charge of 

 melted metal, without either of the tuyeres being below the surface. No action can, 

 therefore, take place until the vessel is made to assume the position shown in Jiff. 1909. 

 The process is thus in an instant brought into full activity, and small though powerful 

 jets of air spring upward through the fluid mass. The air expanding in volume, 

 divides itself into globules, or bursts violently upwards, carrying with it some hundred- 

 weights of fluid metal, which again falls into the boiling mass below. Every part of 

 the apparatus trembles under the violent agitation thus produced, a roaring flame 

 rushes from the mouth of the vessel, and as the process advances, it changes its violet 

 colour to orange, and finally to a voluminous pure white flame. The sparks, which 

 at first were large, like those of ordinary foundry iron, change to small hissing points, 



and these gradually give way to soft floating 

 specks of bluish light, as the state of malle- 

 able iron is approached. There is no eruption 

 of cinder as in the early experiments, although 

 it. is formed during the process ; the improved 

 shape of the converter causes it to be retained, 

 and it not only acts beneficially on the metal, 

 but it helps to confine the heat, which during 

 the process, has rapidly risen from the com- 

 paratively low temperature of melted pig-iron, 

 to one vastly greater than the highest known 

 welding heats, by which malleable iron only 

 becomes sufficiently soft to be shaped by the 

 blows of the hammer; but here it becomes 

 perfectly fluid, and even rises so much above 

 the melting-point as to admit of its being 

 poured from the converter into a founder's 

 ladle, and from thence to ba transferred to 

 several successive moulds. The thin shell, or 

 skull of the ladle, shows the extreme fluidity 

 of the metal, and also how little of it is 

 solidified in the ladle during the time of cast- 

 ing. 



' The oxygen of the air appears, in this pro- 

 cess, first to oxidize the silicium, producing 

 silicic acid, and next to seize the carbon which 

 is eliminated, while the silicic acid, uniting 

 with the oxide of iron, obtained by the com- 

 bustion of a small quantity of metallic iron, 

 thus produces a fluid silicate of the oxide of 

 iron, or 'cinder,' which is retained in the vessel, 

 and assists in the purification of the metal. 



The increase of temperature which the metal undergoes, and which seems so dis- 

 proportionate to the quantity of carbon and iron consumed, is doubtless owing to 

 the favourable circumstances under which combustion takes place. There is no 

 intercepting material to absorb the heat generated, and to prevent its being taken 

 up by the metal ; for heat is evolved at thousands of points, distributed through- 

 out the fluid, and when the metal boils, the whole mass rises far above its natural 

 level, forming a sort of spongy froth, with an intensely vivid combustion going on 

 in every one of its numberless ever-changing cavities. Thus, by the mere action 

 of the blast, a temperature is obtained in the largest masses of metal, in ten or 

 twelve minutes, that whole days of exposure in the most powerful furnaces would fail 

 to produce.' 



The changes in the colour and volume of the flame, and the kind of sparks thrown 

 off, afford easy modes of judging of the state of the metal, since these are given off 

 exteriorly, and are not interfered with by the flamo of the fuel, as in the puddling 

 furnace. The sound which the metal produces in the suspended vessel affords also 

 n good indication to the workman. Indeed, few processes appeal so strongly to the 

 external senses. All mere judgment on this point has, however, been rendered un- 

 necessary, by the more certain indications, of an apparatus, which registers on a dial 

 the exact number of cubic feet of air passed through the metal, whereby tho precise 

 degree of hardness of the steel is regulated at pleasure ; its quality, in all cases, 



