Discoveries and Inventions of the Nineteenth Century

is not wrought iron or steel scrap that is mainly used to decarbonize the pig, but a pure oxide ore. This is thrown into the bath of molten metal in quantities of a few cwts. at a time, when a violent ebullition occurs. When samples of the metal and of the slag are found to be satisfactory, spiegeleisen or ferro-manganese is added, and the charge is cast. This process takes a rather longer time than the former, but gives steel of 71more uniform character. In both processes, phosphorus is oxidized at the high temperature attained and passes into the slag, which last floats of course on the molten metal and is from time to time tapped off as the action proceeds. Fig. 26a.—Rolling Mill. Fig. 26a shows a rolling mill with what is called a “two-high” train for finishing bars by passing them between the grooves cut in the rolls to give the required section. The rolls in the illustration turn in one direction only, and therefore the bars after emerging from the larger grooves have to be drawn back over the machine and set into a smaller pair from the same side. This inconvenience is avoided in the “three-high train,” on which three rolls revolve, and the bars can be passed through them from one side to the other alternately. The celerity with which a glowing steel ingot is without re-heating converted into a straight steel rail 60 or 100 feet long, by passing a few times backwards and forwards between the rolls, is very striking. These rolls are made of solid steel, and in some cases have a diameter of 26 inches or more. 72 IRON IN ARCHITECTURE. Everyone knows how much iron is used in those great engineering structures that mark the present age, and of which a few examples will be described in succeeding articles. One other feature of the nineteenth century is the use of iron in architecture. Some have, indeed, protested against the use of iron for this purpose, and would even deny the name of architecture to any structure obviously or chiefly formed of that material. Stone and wood, they say, are the only proper materials, because each part must be wrought by hand, and cannot be cast or moulded; and further, iron being liable to rust, suggests decay and want of permanence, and these are characters incompatible with noble building. All this can rest only on a relative degree of truth—as, for instance, machinery is used to dress and shape both wood and stone, and the permanence of even the latter is as much dependent on conditions as that of iron. Iron used in architecture is hideous when applied in shapes appropriate only to stone; but when it is disposed in the way suggested by its own properties, and receives ornament suitable to its own nature, the result is harmonious and graceful, and the structure may display beauties that could be attained by no other materials. Be that as it may, the great and lofty covered spaces that are required for our railway stations and for other purposes could have been obtained only by the free use of iron, and everyone can recall to mind instances of such structure not devoid of elegance, in spite of the absence—the proper absence—of the Classic “orders” or Gothic “styles.” The first notable instance of the application of iron on a large scale was the erection of the “Crystal Palace,” in Hyde Park, for the great Exhibition of 1851. It was taken down and re-erected at Sydenham, and there it has become so well known to everyone that any description of it is quite unnecessary in this place. As another conspicuous example of what may be done with iron, the Eiffel Tower at Paris may be briefly described. The idea of erecting a tower 1,000 feet high was not of itself new. It had been entertained in England as early as 1833, in America in 1874, and in Paris itself in 1881. It has been reserved for M. Gustave Eiffel, a native of Dijon, who commenced to practise as an engineer in 1855, to realize this ambitious project. He has long been occupied in the construction of great railway bridges and viaducts, and in these he has adopted a system peculiar to himself of braced wrought-iron piers without masonry or cast-iron columns. He also was the first French engineer to erect bridges of great span without scaffolding. In the Garabit viaduct he planned an arch of 541 feet, crossing the Truyère at a height of nearly 400 feet above it. One result of M. Eiffel’s studies in connection with these lofty piers was his proposal to erect the tower for the Paris Exhibition of 1889. This proposal met with great opposition on the part of many influential people in Paris—authors, painters, architects, and others protesting with great energy against the modern Tower of Babel, which was, as they said, to disfigure and profane the noble stone buildings of Paris by the monstrosities of a machine maker, etc. etc. The Eiffel Tower is now constructed, and no one has heard that it has dishonoured the monuments of Paris, for it has been instead a triumph of French skill, the glory of its designer, and the wonder of the Exhibition. 73 Fig. 26b.—The Eiffel Tower in course of construction. The tower rests on four independent foundations, each at the angle of a square of about 330 feet in the side, and it may be noted that the two foundations near the Seine had to be differently treated from the other two, where a bed of gravel 18 feet thick was found at 23 feet below the 74surface, and where a bed of concrete, 7 feet thick, gave a good foundation. The foundations next the river had to be sunk 50 feet below the surface to obtain perfectly good foundations. Underlying the whole is a deep stratum of clay; but this is separated from the foundations by a layer of gravel of sufficient thickness. Above this are beds of concrete, covering an area of 60 square metres, and on the concrete rests a pile of masonry. Each of the four piles is bound together by two great iron bars, 25 feet long and 4 inches diameter, uniting the masonry by means of iron cramps, and anchoring the support of the structure, although its stability is already secured by its mere weight. The tower is of curved pyramidal form, so designed that it shall be capable of resisting wind pressure, without requiring the four corner structures to be connected by diagonal bracing. The four curved supports are, in fact, connected with each other only by girders at the platforms on the several stages, until at a considerable length they are sufficiently near to each other to admit the use of the ordinary diagonals. The work was begun at the end of January, 1887, and M. Eiffel notes how the imagination of the workmen was impressed by the notion of the vast height of the intended structure. Not steel, but iron is the material used throughout, and the weight of it is about 7,300 tons, without reckoning what is used in the foundations, and in the machinery connected with the lifts, etc. It has long ago been found that stone would be an unsuitable material for a structure of this kind, and it is obvious that only iron could possibly have been used to build a tower of so vast a height and within so short a space of time, for it was completed in April, 1889. A comparison of heights with the loftiest stone edifices may not be without interest. The highest building in Paris is the dome of the Invalides, 344 feet; Strasburg Cathedral rises to 466 feet; the Great Pyramid to 479 feet; the apex of the spire in the recently completed Cathedral at Cologne to 522 feet. These are overtopped by the lofty stone obelisk the Americans have erected at Washington, which attains a height of more than 550 feet. Such spires and towers have been erected only at the cost of immense labour. But iron, which can be so readily joined by riveting, lends itself invitingly to the skill of the constructor, more particularly by reason of the wonderful tensile strength it possesses. It is scarcely possible to convey any adequate idea of the great complicated network of bracings by which in the Eiffel Tower each standard of the columns is united to the rest to form one rigid pile. The horizontal girders unite the four piers in forming the supports of the first storey some 170 feet above the base. The arches which spring from the ground and rise nearly to the level of these girders are not so much intended to add to the strength of the structure as to increase its architectural effect. The first storey stands about 180 feet above the ground, and is provided with arcades, from which fine views of Paris may be obtained. Here there are spacious restaurants of four different nationalities. And in the centre of the second storey (380 feet high) is a station where passengers change from the inclined lifts to enter other elevators that ascend vertically to the higher stages of the tower. On the third storey, 900 feet above the ground, there is a saloon more than 50 feet square, completely shut in by glass, whence a vast panorama may be contemplated. Above this again are laboratories and scientific observatories, and, crowning all, is the lighthouse, provided with a system of optical apparatus for projecting the rays from a powerful electric light. This 76light has been seen from the Cathedral at Orléans, a distance of about 70 miles. Fig. 26c.—The Eiffel Tower. The buildings of the Paris Exhibition of 1889 are themselves splendid examples, not only of engineering skill, but of good taste and elegant design in iron structures and their decorations. The vast Salle des Machines (machinery hall) exceeds in dimensions anything of the kind in existence, for it is nearly a quarter of a mile long, and its roof covers at one span its width of 380 feet, rising to a height of 150 feet in the centre. This great hall is to remain permanently, as well as the other principal galleries with their graceful domes. The Eiffel Tower having proved one of the most striking features of the great Paris Exhibition, and of itself a novelty sufficient to attract visitors to the spot, and having, long before the Exhibition closed, completely defrayed the expense of its construction, with a handsome profit besides, its success has naturally provoked similar enterprises,—as, for instance, at Blackpool, a seaside resort in Lancashire, there has been erected an openwork metal tower, resembling the Paris structure, but of far less altitude. Tall Buildings in American Cities. In several of the great cities of the United States, the last few years have witnessed a novel and characteristic development of the use of iron in architecture. In many structures on the older continent, this material has been frankly and effectively employed, forming the obvious framework of the erection, even when the leading motive was quite other than a display of engineering skill. The Crystal Palace at Sydenham and other erections have been referred to, in which iron has taken its place as the main component of structures designed more or less to fulfil æsthetic requirements: the guiding principle in “tall office buildings” in the cities of the Western continent is, on the contrary, avowedly utilitarian. Iron has, of course, long been used in the form of pillars, beams, etc., in ordinary buildings, and it is only the extraordinary extension of this employment of it, after the lift or elevator had been perfected, and the ground-space in great commercial centres was daily becoming more valuable, that has led to the erection of structures of the “sky-scraper” class in American cities. For a given plot at a stated rent, a building of many stories, let throughout as offices, will obviously bring to its owner a greater return than one of few stories. The elevators now make a tenth story practically as accessible as a third storey, and the tall