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skin bellows until he produces his small lump of wootz, which is found in the hearth at the bottom of the furnace--produces a quality of iron that the most expert manufacturer in England cannot equal. Out of this wootz, afterwards carefully fused with carbonaceous matter, the finest Indian sword-blades are made, the wonderful temper of which, as of those of Damascus, is the despair of European cutlers. The iron made by the native Africans also, as we have already seen, is of the quality of steel, being a highly carbonized iron; and hence they refuse to use English iron, which they characterise as 'rotten' compared with their own.
The ancient metallurgists entertained the idea that by burying iron in the earth until the greater part of it was converted into rust, the remainder was capable of being forged into weapons, and particularly swords, with which bones, shields, and helmets, could be cut asunder. Beckman says, however improbable this may appear, it is nevertheless the process still used in Japan; and Swedenborg has introduced it among the different methods of making steel. There may possibly be some element in the Japanese soil to account for this extraordinary effect of burying iron in it until it rusts; but science can find no rationale for it, and remains incredulous. Certain, however, it is, that the old workers in metals believed that iron acquired a certain tenacity by burying it, and some of the old Sheffield cutlers, who were famous for turning out first-rate articles in their day, were in the habit of placing bundles of steel in the mud of some watercourse for a few weeks, by which they alleged it became greatly improved in quality. It has been stated that on the removal of old London Bridge, the wrought iron with which the piles were shod was found of such pure quality and so malleable, that Weiss, the celebrated cutler, contracted for some tons of it for conversion into steel the action of the moist clay, without exposure to the air, having had such an effect upon the metal as to render it almost equal to steel. So,' said one of the metropolitan journalists, we may one day mow our beards with a relic of old London Bridge.'*
The modern methods of producing steel are described by Dr. Percy under three general heads, viz., by the addition of carbon to malleable iron, the partial decarburization of cast iron, and the addition of malleable to cast iron. There are various processes for adding the carbon to the iron so as to produce the steel. One is the Catalan process, in which the ore is reduced by a charcoal fire, and the resulting metallic iron is afterwards carbonised on the hearth by contact with incandescent charcoal; but the objection to this process is that the result is not uniform, the
“Manufactures in Metal:" Cabinet Cyclopædia,' ii. 26.
lumps of metal consisting of irregular mixtures of iron and steel. Other methods have been proposed with the same object, such as melting rich ores in crucibles, mixed with carbonaceous matters ; but it has not been found possible to ensure uniform results, and they have not come into general use. The method most commonly employed, and one of the oldest, is the exposure of straight flat bars of iron in contact with ground charcoal, under a covering impervious to air, to the action of a glowing red heat in a converting furnace during a period varying from seven to ten days. The bars, when taken out, are found covered with blister-like protuberances, and are hence termed blister-steel.' method is that of fusing compact iron with carbonaceous matter, as practised by the Hindoos in making their wootz, and which has recently, with certain modifications, formed the subject of several patents, more particularly of Heath's and Mushet's. Of the latter Dr. Percy says, 'It is curious that Mushet's process, so far as relates to the use of malleable iron in the production of cast steel, should in principle, and I may add even in practice too, be identical with that by which the Hindoos have from ancient times prepared their wootz, I cannot discover any essential difference between the two.'
The next general head under which Dr. Percy describes the conversion of iron into steel is that of the partial decarburization of cast iron. This latter compound being surcharged with carbon, various methods have been contrived for getting rid of the surplus and reducing the carbon to the proportion in which it exists in steel. There are several contrivances for accomplishing this object
, which, though differing much in detail, lead to very nearly the same result. By the Siegen process, as well as by the Styrian, Corinthian, and others, described in great detail by Dr. Percy, the pig-iron is converted into steel by refining it in a hearth, with charcoal as the fuel. Another means employed for getting rid of the extra carbon in the cast iron is by admixture of oxide of iron, or other substances capable of yielding oxygen, to the metal while in a state of fusion. In Riepe's process, a little black oxide of manganese is also used, and the mass is puddled as in the making of malleable iron,--the result being puddled steel, a valuable metal applied to many important uses. . The art of making this article consists in a nice regulation of the temperature (which is lower than in puddling iron), and in arresting the process at the proper stage of decarburization. The same object is accomplished by melting malleable iron and cast iron together in suitable proportions, the proportion of carbon in the pig-iron, diffused through the increased mass, becoming reduced to the proportion necessary to form steel. In like manner, malleable
iron may be converted into steel by keeping it immersed in molten pig-iron-an old method necessarily uncertain in its results, and now disused.
Passing over the invention of cast steel by Benjamin Huntsman of Sheffield, of which the curious history is related by Dr. Percy, we arrive at the most important process of conversion of all,-one likely to lead to many important changes and improvements, as well as to a largely increased use of this valuable metal in the constructive arts, we mean the Bessemer process of decarburizing pig-iron while in the molten state, by blowing atmospheric air through it, and thereby producing steel. Although a patent was taken out by Martien, in 1855, for purifying iron from the blast furnace by blowing air or water through it, before being subjected to puddling, it is clear, from the terms of the specification, that he had no intention of thereby converting pig-iron either into steel or malleable iron. Mr. George Parry, of the Ebbw Vale Works, an indefatigable experimenter, was on the very track of the discovery of decarburizing pig-iron by blowing air through it, and was only defeated by an accident which occurred to the furnace in which he carried on his operations; in consequence of which, the manager of the works forbade further experiments, and the furnace was dismantled. Bessemer's discovery was itself in some measure accidental, like so many other discoveries in the arts. The remarkable thing is that, taking into consideration the attention paid to the chemistry of metallurgy of late years, the discovery was not made long ago; and that it should have been reserved for Bessemer to make it, who was neither a chemist nor an iron manufacturer.
It will be remembered that, some ten years since, the minds of inventors were running, as they still are, in the direction of improved guns. It was believed that these might be made much stronger if some better material than cast iron were used ; and Bessemer, like many others, began a series of experiments to solve the problem if he could. He first tried a mixture of cast iron and cast steel, the result being a half decarbonised cast iron. Guns made of this metal were found to possess great strength, but as they were of comparatively small bore, 24-pounders, Bessemer resolved to make them on a larger scale, for the purpose of more conclusively testing the strength of the material. In the course of his experiments, the idea occurred to him, that if he could contrive to blow air through melted pigiron, he would be enabled to purify' it to an unusual extent. He thought that by thus bringing oxygen into contact with the fluid metal, the carbon with which it was surcharged would be removed, as well as the silicon, phosphorus, and sulphur which
it contained. This is exactly what is done, after another and very laborious method, in the process of puddling. He proposed to reverse this process, and so get rid of puddling altogether. Instead of bringing the particles of the iron in turn into contact with the oxygen of the air, his scheme was to force the air through the fluid mass into contact with the separated particles of the iron. Now that the thing is done, we see how simple, bow natural the first idea was. But it needs the quick intuition of genius to detect even simple things in practical science.
The only way of determining the matter was by putting the idea to the test of experiment. Accordingly, early in 1856, Bessemer ordered a stock of Blaenavon iron, and set up a blastengine and cupola at Baxter House, St. Pancras, where he then resided. The first apparatus which he used for conversion was a fixed cylindrical vessel three feet in diameter, and four feet high, somewhat like an ordinary cupola furnace, lined with fire-bricks; and at some two inches from the bottom he inserted five twyer pipes, with orifices about three-eighths of an inch in diameter. About halfway up was a hole for running in the molten metal, and on the opposite side at the bottom was the tap-hole, by which the metal was to be run off at the end of the process.
The first experiment was not made without occasioning considerable alarm. It was a most unusual process, and it looked dangerous, as indeed it proved to be. When the charge of pigiron was melted, the blast was turned on to prevent it running into the twyer holes, and then the fluid metal was poured in through the charging hole by the attending stoker. A tremendous commotion immediately took place within the vessel ; the molten iron bounded from side to side; a violent ebullition was heard going on within; while a vehement violet-coloured flame, accompanied with dazzling sparks, burst from the throat of the cupola, from which the slag was also ejected in large foam-like masses. A cast-iron plate, of the kind used to cover holes in the pavement, that had been suspended over the mouth of the vessel, dissolved in a gleaming mist, together with half a dozen yards of the chain by which it hung. The air-cock was so close to the vessel, that no one durst go near to turn it and stop the process. The flames shot higher and higher, threatening the destruction of the building, and the fire-engines were sent for in hot haste. Before they arrived, however, the fury of decarbonisation had expended itself, and the product was run off. The result was not quite satisfactory; the product was for the most part burnt' iron; but the experiment was sufficiently encouraging to induce Bessemer to make a second trial, and the product was found to be malleable iron. In the course of further experiments
it was found that by interrupting the process before the decarburization of the iron was complete, the product was unmistakeable steel, which was tried and found of good quality. Here was a discovery of immense importance. If malleable iron and steel could be thus made direct from pig-iron, by a process so rapid and so simple, it could not fail before long to effect an entire revolution in the iron trade..
The news of Bessemer's discovery soon flew abroad, and many distinguished metallurgists went to see the process. Among others, Dr. Percy went, and thus describes what he saw :
• Towards the end of 1856, I had the pleasure of seeing the process in operation at Baxter House, and I confess I never witnessed any metallurgical process more startling and impressive. After the blast was turned on, all proceeded quietly for a time, when a volcano-like eruption of flame and sparks suddenly occurred, and bright red-hot scoriæ or cinders were forcibly ejected, which would have inflicted serious injury on any unhappy bystanders whom they might perchance have struck. After a few minutes all was again tranquil, and the molten malleable iron was tapped off.'
Though the Doctor came away wondering, he was not convinced. He analysed a portion of the iron which he had seen produced, and when he found it to contain one per cent of phosphorus, he says his scepticism was rather confirmed than otherwise.
Among other visitors at Baxter House was the late George Rennie, the engineer, who, after witnessing the process, urged Bessemer to draw up an account of it for the meeting of the British Association at Cheltenham in the autumn of 1856. Το this the inventor assented, and the result was his paper · On the manufacture of iron and steel without fuel.'
On the morning of the day on which the paper was to be read, Bessemer was sitting at breakfast in his hotel, when an iron-master (to whom he was unknown) said, laughing, to a friend within his hearing, 'Do you know there is some one come down from London to read a paper on making steel from cast iron without fuel! Did you ever hear of such rubbish ?' The iron-master was, however, of a different opinion as to the new invention after he heard the paper read. Its title was certainly a misnomer, but the correctness of the principles on which the pigiron was converted into malleable iron, as explained by the inventor, was generally recognised, and there seemed to be good grounds for anticipating that the process would, before long, come into general use. The rationale of the method of conversion was intelligible and simple. Mr. Bessemer held that by forcing atmospheric air through the fluid metal, the oxygen was brought into