melted in a reverberatory furnace and then poured into a vessel lined with refractory clay. This vessel, which is capable of holding from five tons and upwards, is called the converter. The converter is fixed on a pivot, and through the latter passes a tube leading from a powerful blowing apparatus. The air passing along the tube is blown into the converter through tuyeres or blow-holes fixed in the bottom of the vessel, and is thus forced to pass through the body or mass of the molten metal. In its passage through the metal the air burns off the carbon, as well as silicon and small quanti, ties of other bodies. At a certain point the blast of air is stopped, and the operation is finished, the whole process occupying about twenty minutes.

After the crude molten iron has been run into the converter, the blast is turned on, "when the process instantly commences, the jets of air rushing upwards, expanding in volume, and dividing into an infinite number of globules, which become dispersed throughout the fluid mass. The silicon is first attacked, neither the iron nor carbon being operated upon to any extent while any silicon remains. When the crude iron contains about one and a quarter per cent. of silicon, it requires about twelve minutes' blowing to remove it, during which time only a few sparks make their appearance; but as soon as the silicon is nearly all eliminated, the carbon and iron are more and more acted upon. At about this period, two minutes suffice to change entirely the outward indications of the process; for in that short space of time the bright sparks previously seen issuing from the vessel have almost wholly disappeared, and a voluminous flame rushes out of the mouth of the vessel, gradually passing from orange colour to a brilliant white. The light is so intense as to project shadows of every object on the wall of the building, even at midday. In about twenty-five minutes from the commencement of the process, the flame is observed to drop off suddenly, thus indicating the complete decarbonisation of the metal. Combustion can therefore no longer go on. The vessel is then immediately turned again into the horizontal position, and a small quantity of carburet of manganese, mixed with carburet of iron and silicon, added, when the vessel is again turned up, and the blast driven through it as before; the manganese almost wholly disappearing in a few seconds, whilst the carbon is retained. The steel may thus be carbonised to any desired extent, entirely depending on the known quantity of carbon thus added to the converted metal; while the carburet of manganese effects precisely the same chemical change as it does in the thousand other steel-pots in which it is daily employed in Sheffield—that is, it confers on it the property of welding and working more soundly under the hammer."

"By means of the various mechanical appliances which Mr. Bessemer has engrafted on his original process, the amount of labour and the exposure of the workmen to heat, when dealing with five tons of fluid steel, is found to be far less than has to be encountered in the manipulations of an 80-lb. puddle ball, or the removal from the furnace of a set of 30-lb. crucibles of cast-steel; but while the exposure of the workman to severe temperatures

has been diminished, and the reduction of manual labour, by a series of almost self-acting hydraulic apparatus, has been effected, improvements of equal importance have been made in the converting process, by which the degree of carburisation and toughness of the metal are put under the most perfect control of the workman, who, by weight and measure, can insure a thousand consecutive charges of precisely the same quality, or he can vary it by almost imperceptible gradations, from the hardest steel to the softest malleable iron.” *

In the manufacture of Bessemer steel Professor Roscoe has utilised the powers of the spectroscope, an instrument which is, beyond dispute, one of the most wonderful which the progress of science has bestowed upon mankind in recent times. This ingenious instrument has revealed the fact that bodies in an incandescent or burning state have definite spectra-a fact which has not only led to the discovery of a number of elementary substances whose existence on the earth had previously escaped the researches of chemists, but which has also enabled astronomical chemists to elucidate to a considerable extent the composition of the sun and the planets, and even that of nebulæ, comets, and fixed stars. In order to explain the use of the spectroscope in the Bessemer process, it is important to remember that steel differs from cast-iron in containing a smaller quantity of carbon, and that in the process of Mr. Bessemer, the carbon of cast-iron is burnt out of the molten white-hot metal by a blast of atmospheric air. The chemical changes occurring during the process are, speaking generally, as follows:-" In the first place, the graphite which is contained in the pigiron is converted into combined carbon; and in the second place, we find that the silicon begins to burn off, and that afterwards the combined carbon is oxidised." The oxygen of the air blown through the molten metal combines with the carbon and silicon contained in it--in other words, burns them off, and the burning gases issue in the form of a flame from the mouth of the converter. The appearance of this flame is changed in the course of the process; and to the success of the operation it is absolutely necessary that, at a certain stage, the blast of air should be stopped. If for ten seconds after this stage has been reached the blast is continued, or if it be stopped ten seconds before the proper point has arrived, then the operation will have failed, and Bessemer steel will not be produced. The metal contained in the converter is either too viscid to admit of being poured off, or it contains too much carbon, and will crumble up under the hammer like cast-iron. Experience had enabled those conducting the operation to tell, by the appearance of the flame, with tolerable accuracy, when the proper time had arrived for turning off the blast of air; but they naturally often made mistakes. Indeed, to an inexperienced eye no difference can be detected in the flame when the critical moment has arrived. By help of the spectrum analysis, the point can now be determined with the greatest certainty and accuracy; and that which formerly depended on the quickness of vision of a skilled eye has now become

Sir W. Fairbairn: "Iron Manufacture."

a matter of exact scientific observation. "By a simultaneous comparison of the lines in the Bessemer spectrum with those of well-known substances," writes Professor Roscoe,* ‚*“I was able, in the year 1863, to detect the following substances in the Bessemer flame-sodium, potassium, lithium, iron, carbon, hydrogen, and nitrogen. At a certain stage of the operation I found that all at once the lines supposed to be due to carbon disappeared, and we got a continuous spectrum. The workmen, by experience, had learned that this is the moment at which the air must be shut off; but it is only by means of the spectroscope that this point can be exactly determined."

In the Bessemer process the molten metal attains a temperature or heat far more intense than had ever before been attained in metallurgical operations, and this it does without the addition of a particle of fuel, but simply from the combustion of the carbon in the crude iron by the blast of air forced through the molten metal. The metal thus decarbonised retains its fluidity long enough to admit of its being cast in ingots, capable of extension by being passed through rollers or under the hammer.

The iron and steel produced by this process are not only obtained at a very great economy of time and expense, but they possess the further advantage of being of better quality than iron or steel produced by the old methods. This has been conclusively established by numerous experiments. The tensile strength of Bessemer unhammered cast-iron is more than twice as great as that of common cast-iron, and about twenty per cent. greater than the Swedish, which is the best of all the old varieties of cast-iron. The weight required to break a rod of ordinary cast-iron, of a square inch, was found to be 18,500 lbs.; for Swedish cast-iron it is 33,000 lbs. ; while in the case of Bessemer cast-iron it is 41,000 lbs. The breaking weight of Yorkshire wrought-iron plates, the best of all English wrought-iron, is 59,500 lbs. per square inch; while that of Bessemer wrought-iron plates is, for soft iron, 68,000 lbs., and that for Bessemer soft cast-steel is 110,000 lbs. per square inch. The breaking weight of the best Sheffield cast-steel is 130,000 lbs. to the square inch, while that of the best Bessemer cast-steel is 152,000 lbs. to the square inch.

A practical illustration of the strength and powers of endurance of Bessemer steel was given in 1862, when one of the earliest experiments with steel rails was made. Near the bridge at the Chalk Farm station on the London and North-Western Railway-a point where it was believed that there was more traffic than on any other rails in the world-two new rails of Bessemer steel were laid down, and opposite to them two new rails of iron, so that no engine or carriage which passed over the one could fail to go over the other also. As soon as the iron rails were too much worn to be safe any longer they were, as usual, reversed, and the other surface exposed to the traffic. When worn out, the iron rails were taken up, and ano her pair laid down in their place. These, also, after a time, had to be reversed, and afterwards to give place to a third pair. This process went on until eight pairs of

"Lectures on Spectrum Analysis."

605

iron rails, or sixteen faces, had been worn out, while the steel rails had not yet even been reversed. When the steel rails were taken up for examination, the ninth pair of iron rails had already been worn out on their upper surface. The steel rails were found to have been worn much thinner, but it was the opinion of the platelayers that their first surfaces would still have worn as long as six more surfaces of iron rails, showing that the strength or endurance of the steel rail was equal to that of twentytwo or twenty-three iron rails. The success of the experiment led to the rapid adoption of steel rails, particularly for those parts of railway lines where the traffic is greater than the average. On an average, 8,000 goods trucks passed daily over the steel rails at Chalk Farm station; and it is estimated that between the time of their being laid down and their examination in September, 1864, no fewer than 7,000,000 wagons had passed over them. The earliest trial with rails of Bessemer steel, however, was at the railway station at Crewe, where the traffic is also very great. In November, 1864, or three years after the rails had been laid down, they had not even been reversed, and the upper face still showed very little of the effects of wear and tear.

The largest works for the manufacture of Bessemer steel are situated at Barrow-in-Furness. This town, situated in the north of Lancashire, is, indeed, itself the most striking practical illustration of the rapidity with which British industry and commerce have progressed in the second half of the nineteenth century. In 1861 Barrow-in-Furness was still so insignificant, that it was not noticed as a separate place in the report of the census of that year. It is only from local chronicles that we learn that in 1850 Barrow was a small hamlet consisting "of three or four farmhouses, eight or ten low-roofed cottages, and two public-houses." Its population in 1861 numbered but a few hundreds; but in 1871 the census showed that the hamlet had grown into a borough of more than 18,000 inhabitants, enjoying the dignity of self-government under a mayor and corporation. Railways radiate from it in all directions on the land side, while wharves and quays and docks are constantly extending along the shores. The principal cause of this sudden growth of Barrow is to be found in the development of the iron manufacture. "To the north and east it is surrounded by rich deposits of hematite ores, which in ancient times had been worked by charcoal, the wood having been obtained from adjoining forests. Even as late as 1840 charcoal iron was made from hæmatite ores, and some of the oldest ironmasters of that part of the country still continue to manufacture it." In the year 1859, however, new works were erected, where more modern processes were adopted. The blast-furnaces, commenced in 1859 at Hindpool, and the steel-works established in the neighbourhood by Mr. Ramsden in 1864, were in 1866 amalgamated under the Barrow Hæmatite Iron and Steel Company, and from this time forth the progress of the town was most rapid. The company in question produce nearly a quarter of a million tons of pig-iron annually. The mines of iron ore in the neigh bourhood are of great richness. About one hundred and

twenty thousand tons of ore are annually shipped for South Wales and Staffordshire, while of four hundred and eighty thousand tons more, part is sent to other districts by rail, and the remainder is smelted on the spot. In 1868 it was estimated that the eleven blast-furnaces at Hindpool would yield 55,000 tons of railway iron weekly, or 286,000 tons annually, which, at only £4 a ton, would be worth £1,444,806. The steel-works, when in full operation, could convert weekly about a thousand tons of pig-iron into Bessemer steel;" and the 52,000 tons of Bessemer steel thus annually produced, selling at £12 to

66

town and district up to between fifty and sixty thousand souls.

Another town which has been recently called into existence by the development of the iron manufactures is Middlesborough, in the North Riding of Yorkshire. The enormous iron trade of the Cleveland district dates only from the year 1851-that is, about ten years earlier than that of Barrow. In 1829 there was but a single farmhouse where Middlesborough now stands. A shipping trade sprang up after that date, and by 1851 the town had a population of between seven and eight thousand (7,431)

£14 per ton, would be worth more than three-quarters of a million sterling. The quantity of pig-iron manufactured by the Barrow company was only 22,592 tons in 1860. It was 167,584 tons in 1867, and was, as above stated, estimated at 286,000 tons in 1868. It was considered that at that time the firm, if not already, would soon become the largest iron-manufacturing company in

the world.

Such was the description given, as it were but yesterday, of this youngest of the more notable manufacturing towns of England. But so rapid is its progress, that every day makes the description more and more inadequate. On a recent occasion, Sir John Ramsden, to whose intelligence, energy, and enterprise the town is greatly indebted for its marvellous growth and prosperity, stated that the works in process of erection would, in the course of a few years, bring the population of the

Then commenced the new industry; and in the course of the next twenty years the population had multiplied itself fivefold, the inhabitants in 1871 numbering no fewer than 39,563. The discovery of iron ore in the Cleveland district, of which Middlesborough is the centre, took place a little before 1851, in which year the first blastIn 1871 there were furnace was erected in the district. seventy blast-furnaces within four miles of the centre of Middlesborough, some of them producing each from four to five hundred tons of pig-iron weekly. The Cleveland district, in fact, in 1871 produced nearly as much pig. iron as all Scotland or the whole of South Wales; the produce in each case being more than a million tons per

four and a half million tons annually, and the actual produce of that year was only 3,218,154 tons. The value of the latter was £8,045,385, while the value of the pig-iron produced in 1871 was £16,667,947 sterling. The quantity produced had, therefore, increased in the sixteen years by 3,409,025 tons, and the value by £8,622,562 sterling. Our total exports of all classes of iron and iron manufactures was not more than 919,479 tons in 1851; the value of which was less than eight millions sterling. In 1871 our iron exports were not less than 3,169,219

in 1796 to 1,512,000 tons in 1839, or to rather more than twelve times the quantity in this interval of fortythree years. In 1871 the quantity produced was 6,627,179 tons, or more than four times as much as in 1839.

The great establishments of English mechanical engineers and workers in iron are among the modern wonders of the world. Here, to use the words of Mr. Sime, the spectator may see iron blocks squeezed between rollers or compressed in the jaws of an iron alligator,-two or three welded into one, or formed into