being thus very greatly diminished. The air required for combustion enters the fire-place in a state of compression, and is also previously heated by the waste heat of the furnace itself. Speaking from personal observation, it may be added that the furnace of Mr. Price has shewn itself quite capable of commanding a temperature sufficiently intense to melt steel with great facility. During the thirty-five years, or thereabouts, which followed the application of heated air to the smelting of iron, little or no improvement was effected in the construction of the necessary appliances. Ironmasters, amazed in many instances at the unexpected results of Neilson's invention, were probably satisfied that its then unexplained economy could not be further improved upon. It had, it is true, been demonstrated by philosophical research that the calorific power of the fuel was far from being exhausted by the work it had performed in the blast furnace. As far as concerns Great Britain, however, it must be admitted that in those days the voice of true science was rarely heard in our ironworks, and still more rarely was it listened to. Changes in the dimensions of the furnaces in use had, no doubt, been attempted; but the additional capacity was either insignificant, or the mechanical appliances were incommensurate with any great alteration in the general arrangement of the plant. Hence it happened that the several furnaces put down soon after 1851 in the new district now known as the Cleveland were, after due enquiry, erected on the old lines-i.e. they varied from 45 to 50 feet in height, with boshes having a diameter of from 14 to 16 feet. At that period, it may be said that the smelter on the Tees was satisfied, if he produced a ton of grey foundry iron with 35 cwts. of coke; while in Scotland, the other chief seat of the pig-iron trade, something like 50 cwts. of raw coal was the usual weight of fuel employed in the furnace. In both cases no fault was found with the furnace manager if the blast was hot enough to melt lead readily-indicating a temperature of about 650° F. (343° C.) In this rapid sketch of the progress of the iron trade, an Englishman may be permitted to observe with satisfaction that-with the exception, perhaps, of the gradual growth of the high from the low furnace, which is attributed, on no very sufficient grounds, to Germany -the different strides towards improvement have been exclusively of British parentage. The next, however, and a very important one it proved to be, is due to a Frenchman, M. Fabre Dufaur. He was the first to utilise the vast volume of flame which flashed from the throats of our older blast furnaces, lighting up the sky and the country for miles round the great centres of their operations. This French idea was first put into general practice in this country, for the purpose of raising steam and heating the blast, among the iron works of South Wales, where the apparatus connected with its use were simplified and improved by Mr. Parry at Ebbw Vale. The new furnaces, near Middlesbrough, were the next where it was applied, and so successfully that the direct saving in coals achieved by its means has amounted to not far short of a million and a-half tons per annum. This is, moreover, not the whole of the economy it has effected. The higher and more regular temperature maintained in the blast is the cause of a notable saving of coke in the furnace; and, in the matter of labour, it has been found that in an establishment of twelve furnaces it saves the work of thirty men or more, who were formerly engaged in coaling the fires of the blowing engine and hot air stoves. No marked economy having attended a moderate increase of the dimensions of blast furnaces, the new works at Middlesbrough were constructed similar to those which had obtained favour by many years' experience elsewhere-i.e. they did not exceed a capacity of 5,000 to 6,000 cubic feet. Messrs. Whitwell and Company departed from the practice hitherto observed by adopting a height of 60 feet, which, however, was not more than what had been already tried in Wales. A trifling reduction in the fuel consumed appeared to attend this change in form, but not more than that which had been already obtained in the 48 feet furnaces at Port Clarence, by the use of air heated to nearly 1,000° F. instead of 700° or 800°. The late Mr. John Vaughan, in the year 1864, erected a furnace of 75 feet, which was done chiefly, if not entirely, in the hope of increasing the weekly make; for this gentleman had not given any attention to the subject of the actual waste of heat in smelting iron. The experiment, however, was not only eminently successful in the direction in which he expected, but there was a most important saving in the consumption of fuel. Speedily other furnaces were erected somewhat higher-80 feet instead of 75—and of double the internal capacity of Mr. Vaughan's, with such beneficial results that before long all the small furnaces on the banks of the Tees were demolished, in order to make way for the colossal structures now universally employed in that district. Hitherto the limit to which the blast had been heated was that imposed by the power of the iron pipes to resist the action of the fire. This impediment was removed by Mr. E. A. Cowper's proposal to adopt the regenerative principle of Messrs. Siemens, in which brick-work was raised to a high temperature, and the heat thus stored up was then conveyed into the furnace by passing the air over the hot surface of the bricks. The ironmasters had thus placed at their disposal both larger furnaces and hotter blast-two very valuable modifications of the appliances they had been in the habit of using. Some among them were sanguine enough to believe that the margin of economy to be effected by one or both of these changes was very much larger than subsequent experience warranted. This, however, is a question that may be conveniently deferred until the action of the blast-furnace itself comes to be described. It will be useful at this place to glance at the effect produced by the various improvements in iron smelting referred to. For this purpose I have extracted from different sources an approximate statement of the weekly make of a blast furnace in 1835, 1845, 1855, and 1865; together with the quantity of coal, reckoned in its raw state, required to make a ton of iron. Coal Weekly per ton make. of iron. 1835. Height 40 to 50 ft., capacity 5,000 cub. ft., blast cold 1845. Ditto, ditto, 851 blast at 650° F. 120 1855.-Height 40 to 50 ft., capacity 5,000 cub. ft., blast at 800° F'., and using the escaping gases for steam and hot air 220 62 1865.-Height 80 ft., capacity 20,000 cub. ft., blast at 1,000° F. 450 to 550 40 The saving consequent upon the introduction of heated air was very irregular in its amount. In South Wales it was stated to be something under one ton of coal per ton of iron, whereas no less than five tons was claimed in Scotland as having been economised by its use. The causes of this extraordinary discrepancy will be explained when the theory of the action of the hot blast is discussed. In all these examples the mineral under treatment is supposed to be ordinary clay ironstone, yielding about 42 per cent. of iron in its calcined state. When mineral of a richer description, and more quickly reduced, is employed, such as the magnetic ore of the United States, as much as 1,200 tons has been run in one week from furnaces containing only about 10,000 cubic feet. The last line of figures, in the table just given, contains a remarkable contrast with the particulars given by some1 French engineers of a works they visited in Wales about forty-five years ago. Then, in order to produce weekly almost exactly half the make of iron from one of the above furnaces, no less than five furnaces were required. These were worked by 309 men, women, and children; 257 of the number being men. It would be inconsistent with the object of the present work to attempt to do more than name, as occasion requires, the various furnaces or mechanical contrivances employed in the different processes referred to. A complete description of the whole of these is to be found in the admirable English work by Dr. Percy, as well as in those of many foreign writers, in France, Belgium, Germany, and Sweden. In 1796, or a few years earlier, pig iron had fallen sufficiently in price, and the art of the founder had made sufficient progress, to permit the construction of a bridge, at Sunderland, with large segments of cast iron. It was at the time considered a work of sufficient risk to render appropriate the affixing to the structure the mottoNil desperandum auspice Deo; and every traveller to the North of England considered himself bound to visit what then was regarded as a most daring example of metallic engineering. For a long time antecedent to Cort's use of grooved rollers, plates or sheets of iron had been spread out between plain cast iron cylinders. The last named invention is ascribed by Coxe, in his "Tour in Monmouthshire," to John Hanbury, whose family, in the early part of the eighteenth century, were lessees of coal and iron under the Earl of Abergavenny, in South Wales. The power of Hanbury's plate mills and those in use for above a hundred years after his time was such 166 Voyage Metallurgique en Angleterre," by MM. Dufrénoy, Elie de Beaumont, Coste, and Perdonnet. as to cause a piece of 400 lbs. to be held as one of unusual dimensions, and to be paid for accordingly. What a contrast this affords to the practice of the present time, in which are to be seen furnaces to heat, mechanical arrangements to move, and rolls to receive, masses of iron weighing nearly 40 tons, to be converted into armour plates for ships of war! In the early days of public railway construction, the only experience possessed by engineers to determine the strength required for their materials, was that obtained with the slow speed and light weights of the colliery lines, or wagon-ways, as they were styled, in the North of England. A rail weighing 50 lbs. per lineal yard was considered to afford ample margin for a considerable increase in velocity and tonnage; and these our rolling mills were not generally required to deliver in lengths exceeding 15 feet, or weighing, therefore, more than 250 lbs. when finished. Latterly, machinery has been constructed to roll 90 feet of finished rail, in one piece weighing 2,460 pounds; and this with not above half the men required to produce the old rail of 250 lbs. Such a mill, driven by the reversing engines designed by Mr. Ramsbottom (formerly of Crewe), has been known to turn out above 3,600 tons of rails in a single week. The machinery employed in hammering iron, which either from its shape or size could not be fashioned in the rolling mill, was formerly of the most insignificant dimensions; and this necessarily limited the weight of the work which could be undertaken. No hammer exceeded a few tons in weight, and of this only a very small portion was effective in giving the blow, the height of which never exceeded 3 or 4 feet. The peculiarity of construction of the Nasmyth hammer commands a blow due in some cases to the fall of a mass of 80 tons through a perpendicular height of 16 feet. Moreover the effective power of the impact is not limited to that produced by the mere falling weight, as in the old forges, but may be supplemented by steam pressure in the cylinder which works the hammer. The application of cast steel, particularly in France, to articles of very large dimensions has necessitated the employment of apparatus of corresponding capacity. At Creusot, in 1878, the members of the Iron and Steel Institute were permitted to witness the casting of armour |