stake. Tin-plate requires an external layer of solder; spelter solder runs through the crevice, and need not project.

Fig. 223 is folded by means of the hatchet-stake, the two are then hammered together, but require a film of solder to prevent them from sliding asunder.

Fig. 224 is the folded angle-joint, used for fire-proof deed boxes, and other strong works in which solder would be inadmissible. It is common in tin and copper works, but less so in iron and zinc, which do not bend so readily.

Fig. 225 is a riveted joint, which is very commonly used in strong iron plate and copper works, as in boilers, etc.; generally a rivet is inserted at each end, then the other holes are punched through the two thicknesses with the punch 210, on a block of lead. The head of the rivet is put within, the metal is flattened around it, by placing the small hole of the riveting set 211 over the pin of the rivet, and giving a blow; the rivet is then clinched, and it is finished to a circular form by the concave hollow in another riveting set. When the works cannot be laid upon an anvil or stake, a heavy hammer is held against the head of the rivet to receive the blow; in larger works the holes are all punched before riveting, and the heads are left from the hammer.

Figs. 226 and 227; the plates a a, are punched with long mortises, then bb, are formed into tenons, which are inserted and riveted; but in 227 the tenons have transverse keys to enable the parts to be separated.

Fig. 228, the one plate makes a butt-joint with the other, and is fixed by L formed rivets or screw-bolts 8; the short ends are generally riveted to the one plate, even when screwed nuts are used. This mode is very common for cast-iron plates, as in stove work.

Fig. 229 is the mode universally adopted for very strong vessels, as for steam-boilers, in which the detached wrought-iron plates are connected by angle-iron, rolled expressly for the purpose, (see f, Fig. 27, p. 81). The rivet holes are punched in all the four edges, by powerful punching engines furnished with traveling stages and racks, which insure the holes being in line, and equidistant, so that the several parts when brought together may exactly correspond. The rivet r, which may be compared to a short stout nail is made red-hot, and handed by a boy to the man within the boiler, who drives it in the hole; he then holds a heavy hammer against its head, whilst two men quickly clench or burr it up from without: between the hammering, and the contracting of the metal in cooling, the edges are brought together into most intimate and powerful contact. Bolts and nuts b, may be used to allow the removal of any part, as the man-hole of the boiler.

For the curved parts of the boilers, the angle iron is bent into corresponding sweeps, and for the corners of square boilers, the angle iron is welded together to form the three tails for the respective angles or edges which constitute the solid corner: this when well done, is no mean specimen of welding.

. It frequently happens that several plates are required to be · joined together to extend their dimensions, or that the edges of one plate are united as in forming a tube; these joints are arranged in the figures 230 to 240, similarly to those for angles previously shown, from which they differ in several respects.

Fig. 230 is the lap-joint, employed with solder for tin plates, sheet lead, etc., and for tubes bent up in these materials.

Fig. 231, the butt-joint, is used for plates and small tubes of the various metals; united with the hard solders they are moderately strong, but with tin solder the junctions are very weak from the limited measures of the surfaces.

Figs. 230

231

232

233

234

235

236

237

238

239

240

Fig. 232 is the cramp-joint: the edges are thinned with the hammer, the one is left plain, the other is notched obliquely with shears, from one-eighth to threeeighths of an inch deep; each alternate cramp is bent up, the others down for the insertion of the plain edge; they are next hammered together and brazed, after which they may be made nearly flat by the hammer, and quite so by the file. The cramp-joint is used for thin works requiring strength, and amongst numerous others for the parts of musical instruments. Sometimes also 230 is feather-edged; this improves it, but it is still inferior to the cramp-joint in strength.

Fig. 233 is the lap-joint without solder, for tin, copper, iron, etc.; it is set down flat with a seam-set, Fig. 209, and used for smoke-pipes, and numerous works not required to be steam or watertight.

Fig. 234 is used for zinc works and others; it saves the double bend of 233. Fig. 235 is the roll-joint employed for lead roofs, the metal is folded over a wooden rib, and requires no solder; the water will not pass through this joint until it exceeds the elevation of the wood. The rolljoint is less bent when used for zinc, as that material is rather brittle; the laps merely extend up the straight sides of the wooden roll, and their edges are covered by a half-round strip of zinc nailed to the wood.

Fig. 236 is a hollow crease used for vessels and chambers for making sulphuric acid; the metal is scraped perfectly clean, filled with lead heated nearly to redness, and the whole are united by burning, with an iron heated also to redness. Solder which contains tin would be acted upon by the acid, whereas until the acid

is very concentrated, the lead is not injured; this method is however now superseded by the mode of autogenous soldering. The concentration of sulphuric acid and some other chemical preparations, is performed in vessels made of platinum.

Figs. 237 and 238 are very commonly employed either with rivets or screw-bolts; the latter joint is common in boilers, both of copper and iron, and also in tubes; copper works are frequently tinned all over the rivets and joints, to stop any minute fissures. Fig. 237 is the flange-joint for pipes.

Fig. 239, with rivets, is the common mode of uniting plates of marine boilers, and other works required to be flush externally.

Fig. 240 is a similar mode, used of late years for constructing the - largest iron steam-ships; the ribs of the vessels are made of T iron, varying from about four to eight inches wide, which is bent to the curve by the employment of very large surface-plates cast full of holes, upon which the wood model of the rib is laid down, and a chalk mark is made around its edge. Dogs or pins are wedged at short intervals in all those holes which intersect the curve; the rib, heated to redness in a reverberatory furnace, is wedged fast at one end, and bent round the pins by sets and sledge-hammers, and as it grows or yields to the curve, every part is secured by wedges until the whole is completed.

The following method of constructing metallic boats, invented by Mr. Francis, of the Novelty Works, New York, is taken from Harper's New Monthly Magazine.

In many cases of distress and disaster befalling ships on the coast, it is not necessary to use the car, the state of the sea being such that it is possible to go out in a boat, to furnish the necessary succor. The boats, however, which are destined to this service must be of a peculiar construction, for no ordinary boat can live a moment in the surf which rolls in, in storms, upon shelving or rocky shores. A great many different modes have been adopted for the construction of surf-boats, each liable to its own peculiar objections. The principle on which Mr. Francis relies in his life and surf-boats, is to give them an extreme lightness and buoyancy, so as to keep them always upon the top of the sea. Formerly it was expected that a boat in such a service, must necessarily take in great quantities of water, and the object of all the contrivances for securing its safety, was to expel the water after it was admitted. In the plan now adopted the design is to exclude the water altogether, by making the structure so light and forming it on such a model that it shall always rise above the wave, and thus glide safely over it. This result is obtained partly by means of the model of the boat, and partly by the lightness of the material of which it is composed. The reader may perhaps be surprised to hear, after this, that the material is iron.

Iron-or copper, which in this respect possesses the same properties as iron-though absolutely heavier than wood, is, in fact, much lighter as a material for the construction of receptacles of all kinds.

on account of its great strength and tenacity, which allows of its being used in plates so thin that the quantity of the material employed is diminished much more than the specific gravity is increased by using the metal. There has been, however, hitherto a great practical difficulty in the way of using iron for such a purpose, namely, that of giving to these metal plates a sufficient stiffness. A sheet of tin, for example, though stronger than a board, that is, requiring a greater force to break or rupture it, is still very flexible, while the board is stiff. In other words, in the case of a thin plate of metal, the parts yield readily to any slight force, so far as to bend under the pressure, but it requires a very great force to separate them entirely; whereas in the case of wood, the slight force is at first resisted, but on a moderate increase of it, the structure breaks down altogether. The great thing to be desired therefore, in a material for the construction of boats, is to secure the stiffness of wood in conjunction with the thinness and tenacity of iron. This object is attained in the manufacture of Mr. Francis's boats by plaiting or corrugating the sheets of metal of which the sides of the boat are to be made. A familiar illustration of the principle on which this stiffening is effected is furnished by the common table waiter, which is made usually, of a thin plate of tinned iron, stiffened by being turned up at the edges all around-the upturned part serving also at the same time the purpose of forming a margin.

The platings or corrugations of the metal in these iron boats pass along the sheets, in lines, instead of being, as in the case of the waiter, confined to the margin. The idea of thus corrugating or

plaiting the metal was a very simple one; the main difficulty in the invention came, after getting the idea, in devising the ways and means by which such a corrugation could be made. It is a curious circumstance in the history of modern inventions that it often requires much more ingenuity and effort to contrive a way to make the article when invented, than it did to invent the article itself. It was, for instance, much easier, doubtless, to invent pins, than to invent the machinery for making pins.

The machine for making the corrugations in the sides of these metallic boats consists of a hydraulic press and a set of enormous dies. These dies are grooved to fit each other, and shut together; and the plate of iron which is to be corrugated being placed between them, is pressed into the requisite form, with all the force of the hydraulic piston-the greatest force, altogether, that is ever employed in the service of man.

The machinery referred to will be easily understood by the above engraving. On the left are the pumps, worked, as represented in the engraving, by two men, though four or more are often required. By alternately raising and depressing the break or handle, they work two small but very solid pistons which play within cylinders of corresponding bore, in the manner of any common forcing-pump.

By means of these pistons the water is driven in small quantities, but with prodigious force, along through the horizontal tube seen passing across, in the middle of the picture, from the forcing-pump to the great cylinders on the right hand. Here the water presses upward upon the under surface of pistons working within the great cylinders, with a force proportional to the ratio of those pistons compared with that of one of the pistons in the pump. Now the piston in the force-pump is about one inch in diameter. Those in the great cylinders are about twelve inches in diameter, and as there are four of the great cylinders the ratio is as 1 to 576. Areas being as the squares of homologous lines, the ratio would be, mathematically expressed, 13: 4 x 12'-1: 4 x 144-1: 576. This is a great multiplication, and it is found that the force which the men can exert upon the piston within the small cylinder, by the aid of the long lever with which they work it, is so great, that when multiplied by 576, as it is by being expanded over the surface of the large pistons, an upward pressure results of about eight hundred tons. This is a force ten times as great in intensity as that exerted by steam in the most powerful sea-going engines. It would be sufficient to lift a block of granite five or six feet square at the base, and as high as the Bunker Hill Monument.

Superior, however, as this force is, in one point of view, to that of steam, it is very inferior to it in other respects. It is great, so to speak, in intensity, but it is very small in extent and amount. It is capable indeed of lifting a very great weight, but it can raise it only an exceedingly little way. Were the force of such an engine to be brought into action beneath such a block of granite as we have described, the enormous burden would rise, but it would rise