combustion produced by the blast usually extends as far as the middle of the boshes, but its activity is there much reduced, as the greater part of the oxygen has been converted into carbonic acid before the ascending current reaches that point. The carbonic acid then combines with carbon to form carbonic oxide, which subsequently exercises a powerful reducing influence on the oxide of iron.

In the reverberatory furnace an oxidating influence may be obtained by the introduction of atmospheric air to the sole, or laboratory of the furnace, or the metal may be deoxidated in a manner similar to the action of a blast furnace; or it may be merely fused, by adjusting the admission of air so that its oxygen is almost entirely removed before passing the fire-bridge.

CHAPTER II.

ON FORGING IRON.

THE earliest process of forging which iron undergoes has for its purpose the forming of the blooms or balls of iron into bars or plates, in order that they may subsequently be applied by the mechanical engineer to the various purposes for which they are required. In this operation the blooms are frequently operated upon by hammers raised by a shaft furnished with cams, or projections, which act upon the tail of the hammer; but the most effective apparatus is the steam-hammer, of which various forms have from time to time been produced. We shall, however, here describe a fifty-cwt. steam-hammer on Nasmyth's plan.

An elevation of this steam-hammer, with a section of the foundation, is shown, Plate IV. The apparatus consists of a very strong cast-iron frame, supporting at the top a steam cylinder of the ordinary construction; within this cylinder is a piston, to which is attached a piston-rod, working steam-tight through the bottom cover of the cylinder; at the lower end of this piston-rod is a large mass of metal which constitutes the hammer-head; to the lower surface of this block the hammer-face is fixed by a dovetail joint, firmly wedged up. To the lower part of the steam cylinder the slide valve is attached, being surrounded by a jacket, as shown; it is worked by the action of the hammer-head upon a tappet, placed in front of the guides by which the hammer-head is retained in position during its fall, or by the hand-gear, shown. Beneath the hammer is an anvil, with a hard face dovetailed into it, and wedged up firm; the whole apparatus rests on foundations consisting of piles for the support of the anvil, and of cinders beaten down for the support of the hammer-frame. The action of the hammer is as follows: the steam being admitted beneath the piston, raises it, together with the hammer-head; when a sufficient elevation has been obtained, the steam is allowed to escape, and the

hammer-head falls upon the work to be wrought, the operation being repeated as often as may be desirable. The machine can be worked by those accustomed to its use with great accuracy, very delicate operations having been frequently performed, such as the corking of bottles, cracking of nuts without injuring the kernels, &c.

We may also include among the machinery used in forging iron, the rollers employed to reduce it to the form of bars; for this purpose, stout cylinders, with grooves turned upon them, are employed, the metal being passed through grooves gradually diminishing in size until the metal is reduced to the desired dimensions; the general form of this apparatus is shown in Fig. 6. For rolling plates true cylinders are required, and very great care must be employed

Fig. 6.

for the production of thin plates. We may now proceed to describe the smaller machinery of the forge; we must first, however, mention, that it is very important to select coals of a suitable nature as fuel for the forge; the best for the purpose is a strong, dense, durable coal, possessing a good body, dull and dirty in appearance. Bright, easily-broken coal is not good for this purpose, and such matters as tend to combine with the iron in the form of clinkers are very deleterious, sulphur being an element which should especially be avoided in forge-fuel. Tanfield coal, when unmixed with other varieties, is very convenient for the smith's work.

The first piece of apparatus of the smaller class which we have to describe is the forge-furnace, which is used when small portions of iron are being worked, larger masses being heated in a reverberatory furnace; these forges may be made eight or nine feet

square, and consist of a mass of brick-work as a foundation to support the fire; at the back of the fire is a tue-iron, through which a blast is supplied. This blast is frequently produced by a revolving the whole is surmounted by a hood and chimney, which serve to carry off the smoke and heated air. The iron is worked upon stout mass of iron, called an anvil (shown Fig. 7). It is rested

fan;

:

Fig. 7.

on a large block of wood, to raise it to a convenient height, and the metal is beaten by means of sledge-hammers and hand-hammers, swages or dies being used when requisite, to produce any particular form. The lower swage is fitted to an aperture in the anvil, the iron to be wrought placed upon it, and the upper swage laid on the iron, and struck with the hammer. The upper swage is held by means of a light hazel rod, which prevents the shock

of the hammer from producing any strain upon the hand of the operator. For ordinary forgings, two men are employed: the smith, who is responsible for the work, and receives a high salary, and the hammer-man, or striker, whose duty it is to wield the

sledge-hammer, and work the bellows, when such are used for the maintenance of the blast. Some forms of swages, and also a combined bottom swage, or swage-block, are shown at Fig. 8, as also a sledge and a hand-hammer.

For welding iron a flux is required, in order to prevent the oxidation of the surfaces to be joined. For this purpose fine white sand and common salt may be used. The iron is first heated, dipped in the flux, and the heating. continued, until the metal has attained a white heat. The flux is then fused over the surface, and has dissolved any oxide of iron which may have formed; the two surfaces to be joined are laid together and struck continuously, working towards the edges, in order to expel the flux and insure a perfect union of the metal. Cast-steel and wrought-iron scarcely admit of being welded together with facility; but shear-steel may thus be joined to wrought-iron; in which case, however, the steel is not raised to nearly so high a temperature as the iron.

For heavy forgings a crane is also required, but the form of this is too well known to require any special description. In large forgings each particular piece of metal requires different treatment, according to the use for which it is destined. Thus the heavy screw shaft, which is subject to torsion only, will require a different arrangement to that employed when a crank or cross-head is formed. The most ancient method of forging shafts consisted in piling together a certain number of slabs of iron, which were subsequently heated, welded, and hammered into the cylindrical form required. When, however, it became necessary to make larger shafts, this method was improved upon: a pile of slabs being taken as before, of which only a portion was drawn out to the circular form, a large mass being left at one extremity, on which to weld more slabs when required: after which the metal could be drawn out a little longer, the operations being continued as long as was needful. This method is still employed at many works in England, Scotland, and America, with considerable success, but it requires the utmost care, both with regard to workmanship and materials. A far superior plan consists in building up the shafts with a sufficient number of square bars; for if, in the slab method, any oxide of iron or dirt should intrude itself between the joints, the seams will run across the shaft; whereas in the bar method they will be longitudinal. It is, however, very important to avoid