« PreviousContinue »
departure of the Romans, for the most part after the old methods. But about four hundred years since, the making of articles of cast iron was introduced into Sussex, afterwards celebrated for its cannon, which were exported in considerable quantities. As the manufacture extended, the Sussex woods became unable to meet the increasing demand upon them for fuel. To make a ton of pig-iron required four loads of timber converted into charcoal ; and to make a ton of bar-iron required three more loads of wood. The result was, that the voragious iron mills' shortly swallowed up everything that would burn, and the manufacture of iron in Sussex thus gradually fell into decay. The same circumstance tended to check the production of iron in other parts of England, and it was even proposed that all iron works should be put down, because of their devouring the woods, and threatening the community with the entire loss of fuel.
Under these circumstances, it was natural that the iron manufacturers should seek to employ some other fuel than charcoal of wood; and as coal abounded in the northern and midland counties, many attempts were made to employ it as a substitute. In 1611 a patent was granted to one Simon Sturtevant for the use of pit-coal in various metallurgical and other manufacturing operations, the extraction and working of iron being specifically mentioned. But Sturtevant failed in introducing his invention, as did his successor in the privilege, one John Rovenson. Other attempts were made to extract iron from the ore by means of pitcoal, but it was not until Dud Dudley's experiments were made * in the reign of Charles I. that any degree of success was achieved in this direction. He himself states that he smelted large quantities of firon by pit-coal, though he does not anywhere explain the process, which probably consisted in using coke instead of raw coal. Another attempt was subsequently made in Staffordshire, by Blewstun, a German, but his experiment ended in failure.
It was reserved for Abraham Darby,' says Dr. Percy, to solve the problem, with complete success, at the Colebrook Dale Ironworks, Shropshire, about the year 1735.'
The first Abraham Darby is known for his successful introduction into England of the manufacture of cast-iron pots (before exclusively manufactured abroad), for which he obtained a patent in 1708. Removing from Bristol to Coalbrookdale in 1709, he took the lease of a small furnace which had existed at that place for more than a century, and there he conducted the foundry business with great success until his death in 1717. To his son Abraham, who entered upon the management of the works about * See Quarterly Review,' vol. cix. p. 111.
1730, is due the successful introduction of pit-coal or coke, in lieu of charcoal, in the smelting of iron. The following is Dr. Percy's account:
* As the supply of charcoal was fast failing, Abraham Darby attempted to smelt with a mixture of raw coal and charcoal, but did not succeed. Between 1730 and 1735 he determined to treat pit-coal as his charcoal-burners treated wood. He built a fire-proof hearth in the open air, piled upon it a circular mound of coal, and covered it with clay and cinders, leaving access to just sufficient air to maintain slow combustion. Having thus made a good stock of coke, he proceeded to experiment upon it as a substitute for charcoal. He himself watched the filling of his furnace during six days and nights, having no regular sleep, and taking his meals at the furnace top. On the sixth evening, after many disappointments, the experiment succeeded, and the iron ran out well. He then fell asleep in the bridge house at the top of his old-fashioned furnace so soundly that his men could not wake him, and carried him sleeping to his house, a quarter of a mile distant. From that time his success was rapid. To increase the power of his water-wheels of twenty-four feet diameter, he set up a * fire-engine" (i. e., an old atmospheric steam-engine), to raise water from under the lowest and send it to the upper pond, which supplied water to the works, and put in motion the largest bellows that had been made. He obtained additional leases of valuable minerals, and erected seven furnaces, with five fire-engines. In 1754 the first furnace at Horsehay was blown in. In December, 1756, “Horsehay's work” was declared to be" at a top pinnacle of prosperity, twenty and twenty-two tons per week, and sold off as fast as made, at profit enough."
The substitution of pit-coal for charcoal in smelting the ore, involved the necessity of increasing the pressure of the blast, Hence powerful blowing machines were substituted for bellows, and Watt's steam-engine was eventually applied to work them. The invention of the steam-engine itself led to a rapid increase in the demand for iron, for the purpose of making the engines as well as the machinery of various kinds which they drove. Again, the employment of the steam-engine in mining operations facilitated the clearing of the pits of water and the raising of coal, the consumption of which steadily kept pace with the production of iron.
The first product of the blast-furnace is pig or cast iron—that is, iron in combination with carbon and silicon. To reduce this to the state of malleable iron, two methods are employed. One, the older, consists in the exposure of the melted pig-iron in a finery or hearth to the highly oxidising action of a blast of atmospheric air. The other, the modern practice, consists in stirring the melted pig-iron on the bed of a reverberatory furnace, so as to bring each portion of the whole mass successively up to
the surface, and allow the oxygen of the air to seize upon and combine with the carbon and silicon, which become separated from the iron in the form of cinder,' leaving as the product of the operation malleable or "wrought iron.' This last process is termed puddling,' the invention of which is usually ascribed to Henry Cort, as well as the method of producing bar-iron by means of grooved rolls instead of by the old process of beating it out by forge hammers.
As in the case of most inventions, Cort's claim has been disputed, and Dr. Percy shows that other inventors are at least entitled to share in the merit, more particularly the Craneges of Coalbrookdale, and Peter Onions of Merthyr Tydvil, both of whose patents preceded Cort's. The former, as early as 1766, converted pig-iron into malleable iron in the reverberatory furnace without the addition of anything more than common raw pit-coal; and the latter, in 1783, employed a puddlingfurnace, the fire of which was urged by a blast, in converting melted pig-iron into malleable, the workman stirring the metal during the process to separate the scoriæ, after which the lamp was taken from the furnace and forged by the hammer. But it does not appear that the inventions of either the Craneges or Onions were adopted by ironmakers to any large extent, and the merit unquestionably belongs to Henry Cort of practically introducing the method of puddling and manufacturing iron now generally followed, and which may be said to have established quite a new era in the history of the iron manufacture. When Cort took out his patents the quantity of pig-iron produced in England was about ninety thousand tons a year; now it is above four millions of tons; and it is said that there are not less than 8200 of Cort's furnaces in operation in Great Britain alone.
The story of Henry Cort is well and impartially told by Dr. Percy. Cort was so unfortunate or so unwise as to become connected as partner with one Samuel Jellicoe, son of the DeputyPaymaster of Seamen's Wages. To enable the firm to carry on their business, the elder Jellicoe advanced to them large sums out of the public monies lodged in his hands, and when his accounts were investigated it was found that the Cort partnership owed to him, or rather to the public treasury, upwards of 27,0001. As Cort had assigned his patents to Jellicoe as security for the advances, these were at once taken possession of by the Crown; but although the processes which formed the subject of patents were very shortly adopted to a large extent by the Welsh and other ironmasters, the Government never levied any royalty for their use, and the whole benefit of the inventions was
thus made over to the public. Had Cort's estate been properly handled, there is every reason to believe that not only would the debt due by him to the Treasury have been paid, but that Cort himself would have realised a handsome fortune, As it was, the Government lost the money owing to the public treasury, while Cort was consigned to total ruin.
* This story,' says Dr. Percy, 'is one of the saddest in the annals of invention. Cort died in poverty, though he laid the foundation of the riches of many an ironmaster, and has largely contributed to the development of the resources and wealth of Great Britain. It is true that the value of the process of puddling has been greatly enhanced by subsequent improvements, especially two, viz., the application of iron bottoms to the puddling furnaces, and the boiling process. But this has been the course with many inventions, perfection only being arrived at by slow degrees; and merit is not the less because others subsequently appear who improve the methods of their predecessors.'
The next notable events in the history of the iron manufacture were the discovery of the Black-band ironstone in Scotland, and the invention of the Hot-blast. Before the commencement of the Carron Works, near Falkirk, in 1760, Scotland was almost entirely dependent on foreign countries for its supply of iron. In ancient times, raids were made across the Border as far south as Furness, for the purpose of obtaining iron plunder, which was carried back into Scotland and forged into tools and weapons. But in peaceful times the Scotch depended for the most part upon Sweden and Germany for their supply of the metal, down to about the middle of last century. Their yetlin (Dutch, gieten), or cast iron, was brought from Holland, mostly in the form of manufactured articles, such as cast-iron pots; while the cast-iron plates used for the backs of fireplaces were brought from Siegen, in Germany. Yet the soil of Scotland was full of iron-ore as well as coal, the value of which to the country has only quite recently been brought to light.
In the year 1801, as David Mushet, an enthusiastic analyst of iron ores, was crossing the Calder, in the parish of Old Monkland, near Glasgow, he picked up from the river-bed some pieces of dark-grey stone, which weighed unusually heavy in his hand. He took the specimens home with him, and, as was his practice, subjected them to the test of his crucible. He found, to his surprise, that the stone contained about 50 per cent. of protoxide of iron. Prosecuting his inquiries, he discovered extensive beds of the mineral distributed throughout the western counties of Scotland. It belonged to the upper part of the coal formation, and contained a variable proportion of coaly matter : hence he designated it Carboniferous Vol. 120.- No. 239.
Ironstone. When Mushet proposed to reduce the ore in the blast-furnace in the usual way, great was the outcry amongst the ironmasters and others for presuming to class the wild coals of the country (as Black-band was called) with ironstone fit and proper for the furnace. But the mineral having been smelted with success at the Calder Iron Works, in admixture with ores of the argillaceous class, other ironmasters followed the example, and the use of the material has steadily increased down to the present time, when not less than nineteen-twentieths of the pigiron produced in Scotland are made from the Black-band ironstone.
The rapid increase in the iron-trade of Scotland is, however, principally attributable to the invention of the Hot-blast by James Beaumont Neilson, in 1828. Scotch coals are, for the most part, unfit for coking, losing as much as 55 per cent. in the process ; but by using the hot-blast it was found that ordinary raw coal could be used in the furnace, as well as coal of an inferior quality. Besides, the coaly matter which the Black-band contained was not its least valuable ingredient; for when it existed in sufficient quantity, it became practicable, with the aid of the hot-blast, to smelt it almost without any addition of fuel.
Before the invention of the hot-blast, the ironmasters were under the impression that the best iron was made when the air blown into the furnace was at the coldest, and hence it was believed that the best was that produced in winter. The efforts of the ironmasters were accordingly directed to the cooling of the blast. The regulator was painted white, the air was passed over cold water, and in some cases the air-pipes were even surrounded with ice for the purpose of keeping the blast cold. Neilson's proposal to blow hot instead of cold air into the furnace, with the object at the same time of intensifying the heat and economising the fuel, was so entirely contrary to the received notions on the subject, that it was with the greatest difficulty that he could persuade any ironmaster to allow him to make the necessary experiments with blast furnaces actually in work. however, at length enabled to make a trial of his process at the Clyde Ironworks, and the results were so satisfactory, that the value of the process was at once recognised, and before long it became generally adopted by the trade.
Dr. Percy points out the remarkable saving effected in fuel by the new process; 8 tons 11 cwt. of coal being required at the Clyde Ironworks, in 1829, to produce a ton of pig-iron by the coldblast; while only 5 tons 31 cwts. were required to produce the same quantity by the hot-blast, or a saving of more than onethird. He further shows that the main cause of the saving in