Most readers are aware[57] that the flaming towers which give such an unearthly effect at night to what is called the Black Country, round Wolverhampton, are iron furnaces, and that the projecting circular galleries which surround their tops are contrived for pouring down their capacious throats, by apertures placed at equal distances, an equable and regular supply of the materials with which they are fed. Besides the iron-stone and the fuel, there is needed a third substance, which is called ‘a flux,’ because it forms a fusible compound with the earthy matter of the mineral. When we are acquainted with the foreign matter in combination with the ore, chemistry tells us what substance we ought to add for the purpose of eliminating the metal. Among the wonderful provisions of nature for the convenience of man, none is more remarkable than that by which many substances are fusible in conjunction at a temperature which either could resist separately. The British ores are for the most part argillaceous, that is to say, they are combined with what, in its general character and appearance, resembles clay. To all such limestone in due proportion must be added; but if the earthy matter consists of lime, clay is the proper flux. In either case the foreign matter and the flux are fused into one substance. The liberated iron sinks downwards, and having now itself become fusible by the combination of carbon, with which it has been impregnated by the fuel, it melts as it reaches the point of fusion, and settles down in the lowest part of the furnace, otherwise called the hearth. It is followed by the scoria, slag, or ‘cinder’ (as it is always called in the trade), composed of the flux, the foreign matter of the ores, and the ashes of the fuel, which are now in a vitrified state; and this artificial lava, being of much less specific gravity, rests on the surface of the iron and protects it from the action of the blast. The furnace is ‘continued in blast,’ that is to say, in full operation, and must be fed equably and constantly night and day, till the manufacturer thinks fit to blow it out, either for the purpose of repairing it, or of reducing his make of iron. At certain intervals, generally twice in the twenty-four hours, the furnace is tapped; that is to say, the stoppage of sand which closes an orifice at the bottom is knocked away, the liquefied metal rushes out, and is guided successively into moulds of sand in the form of short thick bars, which, by a rude metaphor, as old as the invention of casting, are called ‘pigs,’ while the main channel down which the red-hot torrent flows is called the ‘sow.’ Footnote 57: ‘Quarterly Review,’ vol. cix. p. 114.