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.’
The invention of the hot blast gave a new and mighty impulse to the production of iron. Though Mr. Scrivenor[[58]] mentions the remarkable fact that in the furnaces of Peru a contrivance has been noticed for letting the air pass over hot coals, and thus become heated in its passage to the fire, yet it was personal observation, and not archæological research, that, in 1829, suggested to Mr. Neilson, of the Clyde Iron Works, the possibility of economising fuel by substituting hot for cold air in blowing his furnaces. Before this important discovery more than eight tons of coke had been required to produce one ton of pig-iron; but on heating the blast, previously to its entering the smelting-oven, to a temperature of 300° F., it was found that a saving of two and a half tons of coal could be made on every ton of iron, and on raising it to the temperature of 600° F.—a heat somewhat more than sufficient to melt lead—a still more considerable saving of fuel was effected, while at the same time the important discovery was made that at this high temperature bituminous and even anthracitic coal might be used instead of coke. Another advantage was that the same steam power now sufficed for applying the blast to four furnaces which had formerly been required for three; and the total result of the improvement was a saving of 72 per cent. of fuel. Thus we have here another instance of the important results that may be gained from a single good idea when worked out by clever practical men, for the hot blast has most assuredly increased the wealth of England by many millions a year!
Another circumstance likewise tended considerably to increase the production of pig-iron. It was found that the hot blast not only had power sufficient to produce in the raw coal the requisite intensity of heat, but also to expel from it, to a certain extent, the sulphur, which injured the quality of the iron, and thus a great economy in labour as well as in the quantity of fuel was effected. Since then the black-band, an iron-stone found in great quantities in Scotland, and also, to a less extent, in Wales, but not readily convertible into iron by the old methods, and also the Northamptonshire and the Cleveland ores, discoveries of a later date and of an incalculable extent, have been made by the hot blast to yield their iron in great abundance.
The power of using the black-band alone in the furnace, and not, as before the introduction of the hot blast, in small quantities only, and combined with other ores, constituted a new era in the manufacture of iron, and gave to Scotland, till then an iron-making district of little importance,[[59]] the pre-eminence over all others for the production of soft fluid iron, best suited to ordinary founding purposes.
The Cleveland district, formerly unknown in metallurgy, is now the seat of a vast industry, keeping more than a hundred furnaces in blast.
The head-quarters of this new iron-country are established at Middlesborough, on whose site there existed but one house in 1829, but which in 1861 had grown into a town of 24,000 inhabitants, and still increases at the rate of 1,000 a year. Branch railways bring the stone here for smelting from all the neighbouring quarries, and the dense cloud of smoke that hangs over the place serves as a land-mark, not only from the high ground of Yorkshire, but even from some parts of Westmoreland.
But Middlesborough, ‘the youngest child of England’s enterprise’ as it has been called by Mr. Gladstone, is by no means one of the loveliest of her offspring. Scarcely a blade of grass and not a single tree relieves the dull monotony of its dreary streets of small houses, darkened by perpetual smoke, which, as the wind sways it, affords, at rare intervals, glimpses of distant hills or of the Tees, serving only to make the prison of a town more gloomy. Mines and furnaces have also been established in other parts of the district—in Rhosdale, at Grosmont near Whitby, and elsewhere—and not a year passes without the opening of new veins and the rising of new smoke-clouds amid the lovely dales of north-western Yorkshire. The iron which eventually finds its way to Middlesborough is sent thence to every part of the world. Its quality is essentially inferior to that derived from the coal-measures; but for ordinary purposes, and for mixing with the finer classes, it is of great value. Looking to the future, we cannot doubt that the Middlesborough district is destined to have no rival in any part of the world, for even now its works compete in magnitude with those of our old iron fields.
A material which had hitherto been thrown away was also, by the agency of the hot blast, made available for the purposes of the iron master. The ‘tap cinder,’ or refuse of the puddling furnace, which is not to be confounded with the cinder of the blast furnace, contains a considerable percentage of metal, and when thrown again into the furnace greatly increases the yield, though it proportionally deteriorates the quality of the iron. The results of all these successive discoveries and innovations, aided by the facilities of transport afforded by canals and railroads, are truly astonishing.
The make of iron which, on the introduction of steam, had suddenly risen to nearly 50,000 tons per annum, reached 125,000 in 1796, and in 1806 had advanced to nearly 260,000. In 1825 the make was nearly 600,000 tons; in 1840 it amounted to 1,300,000 tons; and in 1854 to 2,700,000 tons. In 1865 it reached the enormous figure of 4,819,254 tons—as much as the combined production of Continental Europe and the United States; and there is little doubt that the present yield does not fall much short of 6,000,000 tons! A similar colossal expansion is without a parallel in the annals of metallurgic industry.
The chief districts which furnish this incredible quantity of iron are situated in Yorkshire, South Wales, Staffordshire, Durham, Lancashire, Cumberland, Shropshire, Derbyshire, and the West of Scotland.