The Subterranean World

by G. Hartwig

The iron weapons found in the lacustrine dwellings of Switzerland likewise point to a very ancient use of iron in Central Europe, no less than the fact mentioned by Cæsar, that during the siege of Avaricum (Bourges) the works erected by the Romans for taking the town were repeatedly destroyed by the subterranean galleries of the besieged, who, as the conqueror relates, were accustomed to such underground labour from their habitually working in iron-mines, an industry which, to judge from this passage, must even then have been of ancient date in Gaul.

For many ages the uses of iron remained chiefly confined to the instruments of agriculture and of war—to the ploughshare and the sword. With the progress of civilisation its employment extended to many purposes unknown before; and in our times the construction of ships and buildings, of railroads and bridges, absorbs quantities which would have appeared incredible almost within the memory of living man. Hence the manufacture of iron has made more rapid progress since the beginning of the present century than in any former period of the world’s history, and even the present immense production scarcely keeps pace with a demand to which it is not easy to assign a limit.

Among the iron-producing countries of the globe Great Britain occupies by far the first rank, and there is every reason to believe that it will long continue to maintain it. The British ores, indeed, are generally poor, as clay, silica, phosphorus, and a variety of impurities which are with difficulty separated from the metal, enter into the composition of those which supply the greatest part of our iron; but this deficiency is more than counterbalanced by many advantages. Most of the British iron mines are situated in those districts where coal is cheapest, the ore being often even raised from the same pit as that from which the coal is extracted. Limestone, the necessary flux, is at hand, while fire-clay, no unimportant article in the building of the furnaces, on whose long-continued working so much depends, is found in the same ground as the ore itself. The largest and most complete manufactories have long been established in the most convenient places. With an almost unlimited amount of capital, the most perfect and the cheapest communication by water is open to all parts of the world; and the further processes which the metal has to undergo are performed at once on the spot in the best manner and at the smallest possible expense. No other land can boast of equal or greater facilities for the production of an unlimited quantity of cheap iron, so that, even with the assistance of heavy protective duties, most of the iron-producing countries of Europe find it difficult to compete in their own markets with the produce of Great Britain.

The art of making iron in this country is of very ancient though of unascertained date. It was probably found by the Romans in a far advanced state. It certainly was carried on by them subsequently to a great extent—a fact proved by the immense beds of iron cinders discovered in the Forest of Dean; nor has it ever been discontinued by the other races who in succession have held sway in the island. But, though of such ancient origin, and enjoying so many natural advantages, our iron manufacture remained confined within very narrow limits so long as the ore was exclusively smelted by means of charcoal made from wood. The manufacture was even for some time partially prohibited in England, the consumption of wood-charcoal in the process of smelting being so great as to create apprehensions that, if care were not taken of the remaining forests, enough timber would not be left to supply the wants of the navy. It seems almost incredible in our days that Acts were passed in the reigns of Elizabeth and James forbidding the felling of timber for the smelting of iron, except in certain districts of Kent, Sussex, and Surrey, then the principal seats of the manufacture, and even there the erection of new works was expressly forbidden.

Attention was then directed to the smelting of ironstone by means of pit coal. Amongst others, Lord Dudley gallantly struggled to establish a manufactory in the neighbourhood of Stourbridge, and partially succeeded; but what with riots among the ironworkers, who destroyed his works, and the wars of the Great Rebellion, which ruined his fortune, he reaped no advantage from his enterprise. Nothing contributed to arrest the decline in this branch of trade, and towards the middle of last century the number of furnaces, which in the reign of James I. had amounted to 300, fell off to 59, the total make of which amounted to not more than 17,350 tons, being an average of 294 tons per annum for each furnace, a quantity very little exceeding that sometimes made in a single week in some of the huge furnaces in Wales in the present day. The partial use of pit coal in the process of smelting was revived in Coalbrookdale, in Shropshire, about 1713. The chief difficulty was to keep the coal in a state of combustion sufficiently intense for the purpose of smelting the ore; the hand-worked bellows, or the more powerful water movement, which produced blast enough for charcoal, having comparatively little effect upon coal.

This obstacle was finally overcome through the perseverance and enterprise of Dr. John Roebuck (a physician in Birmingham, and grandfather of the late distinguished member for Sheffield), who, seeking for more economical methods of smelting iron ore than those then in use, founded in 1759 the now celebrated Carron Works, where John Smeaton, the illustrious architect of the Eddystone lighthouse, first introduced (1760) a new contrivance for throwing a powerful and constant blast into the furnace. By means of a forcing pump, a large column of air, of triple or quadruple density to that which had been previously obtained, could now be poured into the furnace; and effects equivalent to this great improvement followed. The same smelting oven that formerly yielded ten or twelve tons weekly now sometimes produced forty tons in the same period; and such was the impulse given to the trade by this unexpected success of a powerful blast with pit coal that in 1788 the manufacture of pig-iron in England, Wales, and Scotland amounted to 68,300 tons, being an increase of 50,950 tons on the quantity manufactured previous to the introduction of pit coal.

In 1782 Mr. Cort, after many years of experiments, discovered the means of converting cast or pig-iron into malleable iron by a process which was at once sure, rapid, and economical. The iron is remelted in a puddling furnace, as it is called, which is heated with raw coal, and there, by a series of operations, the object of which is to give the iron malleability and toughness by expelling the carbon, it is manipulated until it acquires the consistency of a solid white-hot ball. In this shape it is subjected to the action of an enormous hammer, by which the coarser parts are beaten from it, and it is formed into the shape of thick short bars, called blooms or slabs. While still red-hot it is passed through a series of grooved rollers, till it is drawn out into a long bar, the exact dimensions of which are regulated by the requirements of the manufacture for which it is destined. The bars thus made are technically called puddled bars, and considered as half-manufactured iron. To refine them into merchant-iron, they are again submitted to the action of fire, and, when hot enough, are welded together and formed into the various denominations of bars, rods, hoops, sheets, or plates. Mr. Cort’s discovery, though of immense importance, would yet have proved of comparatively small value without the aid of the double-power steam-engine, which was about the same time invented by James Watt, and supplied the power which was needed to give our iron-works their full development.

Hitherto the ‘top measures’ only of the mineral had been worked, and generally on ‘the rise of the mine,’ where the water would not lie, or those strata favourably situated on the side of a hill where levels could be driven in and the water released. Water was the great enemy in the pits, and even in shallow workings it often accumulated faster than a gin turned by horse-power could bring it to the surface. By the new agency of steam the deepest pits were drained, and materials were drawn up from the bowels of the earth in a quantity and with a rapidity and security hitherto unknown. By the same means that prodigious blast was obtained for the furnaces to which all subsequent improvements of the manufacture owe their origin. Instead of the rude machinery of waterwheels and bellows, huge engines of enormous power forced an immense volume of air through several small tuyeres or tubes so disposed at the lower part of the furnaces that in each portion of the ignited mass an equally diffused blast might raise an equal intensity of heat. Furnaces of greater height and much larger capacity than any hitherto known were erected, and in its general aspect the iron manufacture assumed very much the appearance which it maintains at the present day.

BLAST FURNACE.
a. Tuyeres.