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contact with the several particles of the iron and carbon, combining with the latter to form carbonic acid gas, which passed off by the throat of the vessel, through which the slag was also ejected, leaving as the product, when the combustion was complete, a mass of malleable iron, which was run off by the tap into the ingot moulds placed for its reception. Thus,' said he, *by a single process, requiring no manipulation or particular skill, and with only one workman, from three to five tons of crude iron pass into the condition of several piles of malleable iron, in from thirty to thirty-five minutes, with the expenditure of about one-third part of the blast now used in a fiery furnace with an equal charge of iron, and with the consumption of no other fuel than is contained in the crude iron.'
In the same paper, the inventor called attention to an important feature of the new process in the following words :- At the stage of the process immediately following the boil, the whole of the crude iron has passed into the condition of cast steel of ordinary quality. By the continuation of the process the steel so produced gradually loses its small remaining portion of carbon, and passes successively from hard to soft steel, and from softened steel to steely iron, and eventually to very soft iron i hence, at a certain point of the process, any quality may be obtained.'
It was, however, found in practice that this remarkable peculiarity of the Bessemer process constituted its principal defect. Thus it was extremely difficult
, if not impracticable, to determine with certainty when the decarburization had proceeded to the desired extent, and to the exact point at which the blast was to be stopped. If arrested too soon, no dependence could be placed on the result, as the metal might be only one-half or threefourths converted, according to chance; while if continued until the iron was quite decarburized, it would be burnt and comparatively worthless. The workmen could only judge by the appearance of the flame—first violet, then orange, then white-issuing from the throat of the vessel, when it was proper to interrupt the process. But the eyesight of the workmen was not to be depended on; and as the stoppage of the blast ten seconds before or ten seconds after the proper point had been attained, would produce an altogether different result, it began to be feared that on this account the Bessemer process, however ingenious, could never come into general use. Indeed, the early samples of Bessemer steel were found to exhibit considerable irregularity; the first steel tyres made of the metal, tried on some railways, were found unsafe, and their use was abandoned ; and the iron-masters generally, who were of course wedded to the established processes, declared the much-vaunted Bessemer process to be a total failure. It was regarded as a sort of meteor that had suddenly flitted across the scientific horizon, and gone out leaving the subject in more palpable darkness than before.
* Paper read before the British Association at Cheltenham, August, 1856.
Mr. Bessemer himself was by no means satisfied with the results of his first experiments. He was satisfied that he had hit upon the right principle; the question was, could he correct those serious defects in the process, which to practical men seemed to present an insuperable obstacle in the way of the the adoption of his invention. It was a case for persevering experiment, and experiment only. The inventor's patience and perseverance were found equal to the task. Assisted by Mr. Longsdon, he devoted himself for several years to the perfection of his process of conversion, in which he at length succeeded. We can only very briefly refer to the alterations and improvements in the mode of conducting it which he introduced. In the first place, he substituted for the fixed converting vessel a moveable vessel, mounted on trunnions, supported on stout pedestals, so that a semi-rotatory motion might be communicated to it at pleasure. It was found both dangerous and difficult, while the converting vessel was fixed, to tap the cupola furnace; for the blast had to be continued during the whole time the charge was running out of the vessel, in order to prevent the remaining portion from entering the twyers. By the adoption of the moveable converting vessel this source of difficulty was completely got rid of, while the charging of the vessel with the fluid metal, the interruption of the process at the precise moment, and the discharge of the metal when converted, were rendered comparatively easy. The position and action of the twyers were also improved, and the converting vessel was lined with 'ganister,' a silicious stone, capable of resisting the action of heat and slags, so as to last for nearly a hundred consecutive charges before becoming worn out, whereas the lining of fire-brick, originally used, was usually burnt out in two charges of twenty minutes each.
Another important modification in the process related to the kind of metal subjected to conversion, and its after treatment. In his earliest experiments Mr. Bessemer had by accident made use of a pure Blaenavon iron, but in his subsequent trials iron of an inferior quality had been subjected to conversion, and the results were much less satisfactory. It was found that the high temperature and copious supply of air blown through the metal had failed to remove the sulphur and phosphorus present in the original pig, and that the product was an inferior
metal. After a long course of experiments Mr. Bessemer at length found that the best results were obtained from Swedish, Whitehaven, Hæmatite, Nova Scotian, or any other comparatively pure iron, which was first melted in a reverberatory furnace, before subjecting it to conversion, in order to avoid contamination by the sulphur of the coal.
Finally, to avoid the risk of spoiling the metal while under conversion, by the workmen stopping the blast at the wrong time, Mr. Bessemer adopted the method of refining the whole contents of the vessel by burning off the carbon, and then introducing a quantity of fluid carburet of iron, containing the exact measure of carbon required for the iron or steel to be produced. To six tons of pig-iron decarburized in the converting vessel, he added four cwts, of molten carburet of iron, containing about four per cent. of carbon, and six per cent. of manganese. The result was a given quantity of steel ; and, according as the proportion of carburet was increased or decreased, so was the product a harder or milder steel. The important uses of carburet of manganese in the conversion of iron into steel had long been known. It formed the subject of the unfortunate Mr. Heath's patent of 1839, as well as of Mr. Mushet's patent of 1856, the form in which the latter gentleman proposed to employ it being that of spiegeleisen, or specular cast iron. But when the ores used in the Bessemer process are sufficiently rich, the use of the spiegeleisen is unnecessary; and in Sweden, where this is peculiarly the case, the fluid crude iron is carried direct from the blast furnace to the converting vessel, and reduced at once to the point of steel, as in the original programme.
When Mr. Bessemer, after great labour and expense, had brought his experiments to a satisfactory issue, and ascertained that he could produce steel of a quality and texture that could be relied on with as much certainty as any other kind of metal, he again brought the subject of his invention under the notice of the trade; but, strange to say, not the slightest interest was now manifested in it. The Bessemer process had been set down as a failure, and the iron and steel makers declined to have anything to do with it. The inventor accordingly found that either the invention must be abandoned, or he himself must become steel manufacturer. He adopted the latter alternative, and started his works in the very stronghold of steel making, at Sheffield, where he has for some years carried on his operations on an extensive scale, with marked success. He has not only turned out large quantities of steel of excellent quality, but his works have been a school for the instruction of numbers of steel-makers, who have carried the art with them into every iron making country in Europe, as well as to India and America.
Nothing, it is said, succeeds like success; and no sooner had Mr. Bessemer demonstrated the certainty, the celerity, and the cheapness of his process, as was abundantly proved by the article itself, and the price at which he sold it, than many of the great iron-manufacturers followed his example, and the production of Bessemer steel is now a large and rapidly increasing branch of English industry. In September last there were in actual operation in Great Britain seventeen extensive Bessemer steel works, and there were then erected, or in course of erection, no fewer than sixty converting vessels, capable of producing 6000 tons of steel weekly, or equal to fifteen times the entire production of cast steel in Great Britain before the introduction of the new process. The average price of the steel so manufactured being at least 201. less per ton than the previous average price of the metal, there is thus shown a saving of not less than 6,240,0001. per annum in this country alone, even in the present comparatively infant state of this important manufacture.
Bessemer steel is calculated to be of especial value in all engineering work where lightness and strength are required, such as the framing of marine engines, screw propellers, the cylinders of hydraulic presses, and all kinds of machinery. It is equally well calculated for light girder-bridges of large span, and for the plating of ships; much less weight of metal being required, at the same time that a greater degree of strength can be given to all parts subjected to heavy strains. One firm in Liverpool has already constructed 31,000 tons of shipping wholly or partially of Bessemer steel. But probably the most important uses of the metal consist in its application to railway purposes, where great strength is required to meet the tremendous strains arising from the high speeds at which railway traffic of all kinds is now conducted.
The first rails laid down between the pits and the coal staiths in the North were of wood. All that they were required to do was merely to bear the load of a chaldron waggon, drawn at slow speed by a horse ; and they were sufficient for the purpose. To protect them in a measure from the jolting occasioned by the irregularities in the road, as well as from the effects of increasing traffic and heavier loads, the wooden rails were in some cases tipped with thin plates of iron nailed along their upper surface. Cast-iron rails were next introduced, and continued in general use in the coal districts until the introduction of the locomotive engine. Even after the Killingworth locomotive had been at work for two years,
we find George Stephenson, in conjunction with William Losh, taking out a patent for an improved form of cast-iron rail; and when the Stockton and Darlington line was constructed and opened in 1825, half the rails laid down were of that sort. But the material was found altogether inadequate to bear the increasing weights and strains to which it was subjected. The locomotive, when running even at a moderate speed over the cast-iron rails, champed them up like so much pottery ware ; and the constant breakages and interruptions to the traffic which their failure occasioned shortly led to their total disuse, and the substitution of rails of malleable iron.
The first wrought-iron rails laid down were only 25 lbs. to the yard; but they were soon found too light for the loads they had to carry. When George Stephenson was examined by Mr. (afterwards Baron) Alderson, before the Committee on the Liverpool and Manchester Railway Bill, he was taken to task about the weakness of the Hetton road, and the danger of travelling by railway, on the assumption of trains being run at the dangerous, but then hypothetical, speed of twelve miles an hour. The witness was asked-Do not wrought-iron rails bend,--take Hetton colliery for instance?'— They are wrought iron, but they are weak rails.' Do you not know that those bend?'- Perhaps they may bend, not being made sufficiently strong.' 'And if they are made sufficiently strong, that will involve an additional expense?'— It will.' Then if you were to make them of adamant, that would be very expensive?'— It does not require a very great expense to make them strong enough for heavier work.'
That there might be no deficiency of strength in the fish-bellied rails first laid down upon the Liverpool and Manchester line, they were made of the unusual weight of 35 lbs. to the yard. But the extraordinary speed of the locomotive had not yet been discovered, and there is no doubt that the performances of the • Rocket' surpassed the expectations of even George Stephenson himself. Although the engine weighed only 41 tons, it proved too heavy—when running at high speeds—for the walleable rails; and as the traffic grew, and heavier engines were introduced on the line, the weight of the rails was increased from time to time, but not in like proportion to the weight of the locomotives. For while the malleable rails have been increased from 28 lbs. to 75 and even 86 lbs. to the yard, the locomotive has been increased from 41 tons, as in the • Rocket,' to 30 and 35 tons, the weight of first-class express engines. The disproportion between the weight and force of the engine and the resistance of the rail has been constantly increasing; until the point has at length been reached at which no additional weight in the rails will Vol. 120.-No. 239.