give a more familiar idea of the invention, three penny pieces, mounted on an axis, with a little distance between them, form, to all intents and purposes, the disc-propeller. It seems strange that a paddle-wheel without paddles should be able to propel at all; but Mr. Ashton has proved that not only does it propel, but that it propels nearly, if not altogether, as quickly as if floats were attached. It was claimed, moreover, to be much more economical than a paddle, driving, with a given speed, the vessel with a smaller consumption of coal; producing no vibration; and, what is of no small importance in canal navigation, not the slightest swell.

Iron Fabrication. — In illustrations of iron fabrications the Exhibition was exceedingly rich. The Butterley Iron Company, of England, exhibited a rolled boiler-plate twelve feet nine inches long, seven feet six inches wide, and one and a half inch thick. Krupp, the celebrated steel manufacturer, of Essen, Germany, has recently proposed to construct rolls not less than seventeen feet in width, and to manufacture therewith a boiler-plate sufficiently large to form of itself an entire boiler; and from the great success which Mr. Krupp has already achieved in working iron, there can be little doubt but that he will eventually accomplish his object.

Of sheet-iron there were numerous fine illustrations. Fine sheets from Belgium were especially characterized by a smooth and darkbluish-gray, glossy surface. The color here was obviously due to a thin and firmly adherent skin of oxide of iron, which has been detached here and there near the edges of several of the sheets, clearly revealing the color of the subjacent iron. The London Times, in noticing these specimens, stated that they could not as yet be produced in England. Russia, however, still continues without a competitor in the production of a peculiar description of sheet-iron, which has long been highly esteemed in commerce. The quality of the iron, which is both smelted and worked with charcoal throughout, is excellent, and the dark polish on the surface is remarkable. The process of manufacture is not known, and mythical stories are current as to the precautions taken with a view to secrecy, and the lamentable fate of those who have gained unlawful access to the works in order to possess themselves of the mystery. The manufacture of this description of sheet-iron in other parts of the world is a great desideratum, and the man who succeeds in introducing it will probably not have cause to repent. The Russians are said to anneal their sheets with charcoal-dust interposed, and finally to hammer them in packets. They are not all obtained equally good, and a selection is accordingly made.

No metallurgical illustrations in the Exhibition were more interesting at the present time than the rolled armor-plates for ships. We give the dimensions of two manufactured by the Atlas Works of Sheffield: :- (No. 1.) Length 21 feet 8 inches, width 4 feet 2 inches, thickness 6 inches, weight 10 tons 12 cwt. (No. 2.) Length 24 feet, width 3 feet 8 inches, thickness 5 inches, weight 7 tons 17 cwt. A few years ago the rolling of such enormous masses of iron would have seemed incredible. In the Great Exhibition of 1851, Messrs. Bagnall, of South Staffordshire, England, presented a rolled round bar, which was considered extraordinary on account of its size, but

it weighed only 1 ton. In the Paris Exhibition, in 1855, there were much larger bars, but still nothing that could compare in weight with the gigantic bars above mentioned. As the public mind is at the present time so much interested in everything relating to armorplates, we present a description of the process by which the two great plates above referred to were manufactured. The metal consisted of "best new scrap," obtained from a mixture of Swedish, Shropshire, and Derbyshire refined iron. It was balled under a four-ton steam hammer, piled under a six-ton, and rolled into bar, re-rolled into slabs, all crossed, then rolled into "moulds," and lastly rolled into the finished plates. There were 360 layers in the 6-inch plate. The expense of manipulating such enormous masses of iron as these armor-plates is necessarily very great; and the present cost of them ranges between $175 and $225 per ton. The display of bars, rails, and girders, in the Exhibition, was very fine and extensive; and in no branch of iron fabrication has greater progress been made within the last few years. The mill-power required to produce some of these articles must be enormous, but we are probably far from having reached the maximum limit. Among the curiosities in this department-shown, probably, as evidences of what could be done-were a rail 117 feet long and 54 inches deep, and a tension bar for girders 83 feet long, 1 foot wide, and 1 inch thick; both sent by the Butterley (English) Company. Another company exhibited two rails of the following dimensions:- One 53 feet 6 inches long, 42 inches across the head, and 10 inches deep; the other 31 feet 6 inches long, 5} inches across the head, and 15 inches deep. The Austrian Society of State Railways exhibited specimens of rails, some with the head of granular and the foot of fibrous iron, and others of puddled steel. This is a great manufacturing company, established in 1855, with the view of producing everything required for the use of railways. They not only smelt and manufacture iron, but meddle with copper, lead, gold, silver, paraffine, etc. How far this system is founded on correct economical principles the future will decide.

A collection of architectural irons from France indicated, what is generally believed to be the fact, that iron is much more extensively used in that country for building purposes than in England. Of forged iron, two objects were preeminently worthy of notice, both by the Mersey Steel and Iron Company, of England. One of these was a monster engine-shaft, weighing about twenty-five tons; the other was an armor-plate bearing the following inscription:— "This armorplate, 21 feet 3 inches long, 6 feet 3 inches wide, 53 inches thick, having a superficial area of 133 feet, weighing upwards of 13 tons, was forged at the Mersey Steel and Iron Works, Liverpool, and has been neither smithed nor tooled since it left the steam-hammer. plate would have been made 15 feet to 20 feet longer if space could have been obtained." The same company also exhibited a monster wrought-iron muzzle-loading gun, called the Prince Alfred, and forged hollow by a process patented by the superintendent of the works, Mr. W. Clay. This gun is 12 feet long, 35 inches in diameter at the breech, 18 inches at the muzzle, 104-inch bore, and weighs 10 tons. The rifling consists of twelve shallow grooves, making one turn in 30 feet. Before being rifled it was fired with a 140-pound

This

ball, and 30 pounds of powder, against a target of 4-inch iron plates, backed with timber and sand. The plate was indented six inches, but not actually penetrated, and was exhibited along with the gun. During the process of forging it was necessary to move these heavy masses with ease and rapidity, just as a blacksmith handles his iron; and, in order to effect this, most powerful mechanical appliances and the exercise of great skill must have been indispensable.

The Exhibition contained many very interesting illustrations of welding under difficult conditions, and of these we will notice a few, without attempting, for want of space, any description of the processes employed. The Butterley Company, above referred to, showed a girder in the form of a double T, twelve inches across each end, and three feet deep, welded longitudinally. A large, stamped, solid wrought-iron wheel was shown in the English department, as an example of combined strength and cheapness. Illustrations of the successful welding of iron and steel in railway tire bars were shown by the Monkbridge (English) Company. In these the melted steel was cast round an iron tire, the latter being first heated to redness and dusted over with borax powder. The union of the two metals in the specimens exhibited seemed perfect, and even where the combination was hammered out into thin plate there was no sign of any separation. This process is the invention of a Frenchman, and promises to be very valuable. The French, indeed, have recently made such progress in the manufacture of iron, that bars of beam-iron are now constantly exported to England from France as an article of commerce. Another curious fact, bearing upon the vexed questions of tariff and free-trade, brought out during the past summer in a published correspondence in the London Times, was, that Belgium, which for years past (and at the present time) has maintained a prohibitory duty on the importation of foreign iron, not only undersells British rolled and bar iron in foreign markets, but even largely exports the same products into Great Britain.

Among the curiosities in this department were two bars of malleable iron one, which had been tested by the admiralty to 64 tons per square inch, the standard strain being 59 tons, and which broke the admiralty chains instead of yielding; the second, which had been tested with a strain of 511⁄2 tons, by Mr. W. Fairbairn. There were also several pieces of crystalline iron, polished like silver, and suspended by silken cords, which, when struck, emit a note as clear as a bell, showing the perfect homogeneous character of the metal. Chain Cables. - The prize medal for the best chain cable was awarded for a patent plan invented by Sisco and Sinibaldi. The links of this chain are oval in shape, made from hoop iron, galvanized and brazed. The hoop is wound on a reel by a machine, the invention of the patentees, till the thickness required is secured. It is then passed through a furnace of molten metal, and afterwards rounded off for the completion of the latter operation of brazing. Between the links there is a stay as in the ordinary chains. The principle may be understood by taking a long slip of paper, or tape, and rolling it round the hand, lay upon lay, till the necessary thickness of a chain is gained, then placing a stay across the inner part of the oval thus formed, and a good idea is obtained of Sisco and Sinibaldi's

rolled hoop link. The advantages of this make are the doing away with welding, and increased strength. In a common chain one bad link destroys the security on which a ship is held, and unless a chain is severely tested, a flaw or imperfect weld may send a vessel and crew to destruction. Sisco and Sinibaldi overcome this defect in welding, which makes the iron brittle, by making rolled hoops homogeneous. They coil the hoops cold, and the dipping the chain into molten metal, by heating every part equally, consolidates the layers into one mass, and constitutes a really strong chain. In rolling hoop iron in this manner, there is danger of fracture at the bend; but where there are so many consecutive layers, the fracture of one is of no serious consequence, for its weakness is counteracted by the liquid metal which enters and brazes it to the hoops on either side. The strength of this hoop chain must be comparatively great, for every layer has a skin, and each link is made of sixteen layers, so that the chain is never likely to snap. If one skin is broken, the other fifteen may be intact, and the breakage of one skin will give warning to the crew, whereas, by the existing chain, there is no premonition, and the snapping is sudden. In this respect the patented chain of Sisco and Sinibaldi partakes of the character of a rope, whose strands give before it breaks. The links of a good iron cable will be elongated before it parts, but bad iron snaps without distending. The admiralty strain for a 2-inch chain is 72 tons. A chain this same size, made from rolled hoop iron, was tested at her Majesty's yard at Woolwich. It was attached to a testing chain of 2 inches in diameter, and on the . hydraulic power being applied, one of the links was lengthened § of an inch, and the other of an inch, when it reached a strain of 110 tons; and the 24 inch testing chain broke off in two places when the strain reached 114 tons. The hoop iron chain had some openings in one of the links, which had been imperfectly brazed, but it did not appear to have been made otherwise defective. One link of the same dimensions, 2 inches thick and 2 inches broad, was afterward placed in the testing frame, and when a strain of 70 tons was applied it had lengthened of an inch; with 80 tons, of an inch; with 100 tons, of an inch; with 110 tons, of an inch; with 115 tons,

of an inch, and when it reached 120 tons' strain it was considered advisable not to continue the strain, as it was so great as to loosen the stone frame on which the machine rested, and liable to damage other parts of the iron frame of the machine. The strain applied on this occasion was one ton more than had ever been previously applied, and the hoop chain was only slightly opened on one side.

Steel Manufacture. Never before has so complete, and, in some respects, so marvellous a series of specimens illustrating the manufacture of steel been witnessed as was shown in the Exhibition building. In order to make clear to the general reader the nature of the various steels here brought together, we propose to state first, as concisely as possible, the properties of steel; and, secondly, to explain the principles of the various processes by which it is made. In the first place, then, steel may be said to be, essentially, iron containing carbon within certain limits, which cannot be exactly assigned, but which may be taken, approximately, as a half to one-and-a-half per cent. Steel is much more fusible than wrought iron, and may be melted in

ordinary furnaces, when it is termed cast steel. Steel may be welded to steel, or to wrought iron, under suitable conditions as to quality of metal and temperature. The fracture of steel is peculiar, and varies with the proportion of carbon and the treatment which the metal may have previously received. It is more or less finely granular, and when produced in the brittle state of the metal may be conchoidal or shell-like, such as is presented by the broken surface of a lump of glass.

The processes now in operation for producing steel are founded on two opposite principles, namely, putting carbon into wrought iron, and taking carbon out of pig iron, which last, it will be borne in mind, contains more carbon than steel.

Carbon is put into iron in the following ways: 1. By melting wrought iron with carbon. This is the ancient Hindoo method of preparing the famous "wootz." The principle has recently been revived in making the so-called homogeneous steel or metal. Numerous specimens of wootz, sent from India, were exhibited in the Exhibition, in the form of little conical ingots; but there was nothing peculiar about them to demand special notice. Not so with regard to the so-called homogeneous metal, which has excited much attention of late. It is extremely malleable and tough, and may be placed midway between wrought iron and ordinary steel; it may be regarded as steel containing a low percentage of carbon. This is the metal of which the celebrated English engineer, Whitworth, has constructed his largest rifled ordnance. It is no doubt extremely valuable for many purposes, but it is, thus far, difficult to produce it uniform in quality. Examples of tubing made of this metal were shown, flattened down vertically, and at first glance might be mistaken for Indiarubber. The metal, in this instance, we were informed, was produced by melting pieces of Swedish iron and carbonaceous matter. specification of a recent English patent granted for manufacturing homogeneous metal, it is stated that scale, which falls off from steel or iron during the process of hammering or rolling, is employed in addition to the ingredients in common use for cast steel.

In the

2. Another process of introducing carbon into iron is known as "cementation," and consists essentially in exposing flat bars of iron imbedded in charcoal to about the temperature of melted copper during many days. Carbon thus travels into the very centre of the bars; but how this takes place has not yet been clearly explained. This process of preparing steel is an English one; the furnaces are termed "converting furnaces," and the bars of steel produced are called "blister-steel," from their being studded here and there with blister-like protuberances.

A great number of examples of steel produced by the cementation process were shown in almost every department of the Exhibition; but there was nothing about them which requires from us any particular comment. Until recently, all the steel at Sheffield, England, was made by this process, and Swedish iron has been largely consumed for the purpose. Different varieties of iron are known to yield different qualities of steel, but the knowledge respecting these differences is generally regarded as a trade secret. The prices of Swedish iron in the English market vary considerably, i. e., from $160