is put upon the bar H, fig. 325, and fixed in the place of the rest, by the clamp, fig. 332, the distance from the centre n is adjusted by the screw h, which moves the slide, fig. 335, in the grooves i, figs. 331 and 334, with the whole apparatus upon it; by the screw m, figs. 331 and 335, as before described, the slide, fig. 336, may be moved in a direction perpendicular to the bar H, fig. 325, and its projections o o, acting against the slits pp, figs. 331 and 337, as inclined planes, will raise or lower the plate B, as is required.

The tool, which has been before fixed in the holders b b, can be set at the proper angle by loosening the screw e, as previously described; and, lastly, the tool with the holders and slider a, can be advanced or withdrawn by working the screw e. The nuts of the screws e and h, fig. 331, are not screwed fast to the sliding plates, but are held by two pins t, fig. 335, which fit into grooves u, fig. 334, in each side of the nut; by these means the sliding plate can at any time be taken out by only unscrewing one of the brass slides from the grooves i, without taking out the screw or nut. In order to make the grooves always fit their slides, the two pieces of brass yy, fig. 331, which compose the sides of the groove, have elliptic holes for their screws v, so as to admit, when the screws are slackened, of being pushed inwards by the screw w which works in a lump of metal cast with the part A A.

The large lathes which Mr. Maudslay uses in his manufactory, instead of being worked by the foot, as represented in fig. 325, are worked by hand; the wheel and fly-wheel which the men turn works by a strap on another wheel fixed to the ceiling directly over it; on the axis of this wheel is a larger one, which turns another small wheel or pulley fixed to the ceiling, directly over the mandrel of the lathe; and this last has on its axis a larger one which works the mandrel D, by a band of catgut. These latter wheels are fixed in a frame of cast-iron, movable on a joint; and this frame has always a strong tendency to rise up, in consequence of the action of a heavy weight, the rope from which, after passing over a pulley, is fastened to the frame; this weight not only operates to keep the mandrel-band tight, when applied to any of the grooves therein, but always makes the strap between the two wheels on the ceiling fit. As it is necessary that the workman should be able to stop his lathe, without the men stopping who are turning the great wheel, there are two pulleys or rollers (on the axis of the wheel over the lathe) for the strap coming from the other wheel on the ceiling; one of these pulleys, called the dead pulley, is fixed to the axis and turns with it, and the other, which slips round it, is called the live pulley; these pulleys are put close to each other, so that by slipping the strap upon the live pulley, it will not turn the axis; but if it is slipped on the other, it will turn with it; this is effected by a horizontal bar, with two upright pins in it, between which the strap passes. This bar is moved in such a direction as will throw the strap into the live pulley, by means of a strong bell-spring; and in a

contrary direction it is moved by a cord fastened to it, which passes over a pulley, and hangs down within reach of the workman's hand; to this cord is fastened a weight heavy enough to counteract the bell-spring, and bring the strap upon the dead pulley to turn the lathe; but when the weight is laid upon a little shelf, prepared for the purpose, the spring will act and stop it.

Mr. Maudslay has likewise some additional apparatus for cutting the teeth of wheels, in which the face of the mandrel D, fig. 325, has seventeen concentric circles upon it, each divided into a different number of equal parts, by small holes.

There is a thin stop x, fig. 325, which moves round on a screw fixed in the standard F; this stop is made of thin steel, and is so fixed, that when it is turned up, and its point inserted into any of the divisions of the mandrel, it will have a sufficient spring to keep it there; the wheel to be cut is fastened, by means of a chuck, to the screw n, and after it has been turned, and brought to the proper shape, the rest, j, is to be taken away, and the slide-tool substituted; a square bar is then put into the two holders bb, fig. 331; this bar has two branches for holding the ends of a spindle, near one end of which is a pulley, and at the other are four chisels fixed perpendicularly into the spindle for cutting out the teeth, (instead of the circular saw commonly used ;) the pulley is turned (with the intervention of several wheels to augment the velocity) by the same great wheel as the lathe, with 7300 revolutions per minute; the mandrel is then fixed by the stop a, fig. 325, and the cutter advanced towards the wheel, by the screw c, fig. 331. When it has cut that tooth, the cutter is withdrawn, and the mandrel turned to another division, and a tooth is cut again as before. At that part of the frame of the cutting-spindle where the bar which is fixed in the holders of the slide-tool connects with the two branches, there is a joint, by which the cutting-spindle can be set in an inclining position for cutting oblique teeth, like those which are to work with an endless-screw, The great velocity with which this spindle turns soon generates by friction and resistance a degree of heat sufficient to expand it very sensibly; but this ingenious mechanist, foreseeing such a circumstance, has judiciously compensated for it in his construction, by making the spindle so short as to play loosely in its sockets at the commencement of the motion; but after a few seconds the expansion is such as to cause the whole to fit together as it ought to do, and the work of cutting to proceed with accuracy and safety.

Mr. Smart, of the Ordnance-wharf, Westminster, has made some very useful improvements in the art of turning, and particularly has struck out a simple method of turning cylinders and cones in wood.

His turning machine is illustrated in figs. 339 and 340, where the legs or stiles L, the puppets A B, the cheeks o o, the pikes and screws M, N, R, with the handle D, are but slightly varied from the usual construction. Round the mandrel E passes a band F F, which also encompasses a large wheel, not shown in the figure; and when this large wheel is turned round with moderate swiftness, it communicates a rapid velocity to the mandrel E, and the long piece of wood G, which is proposed to be made cylindrical, This piece is previously hewn into an octagonal form. The cutting frame H contains a sharp iron tool, which is to answer the purpose of the common

turning gouge, and which is fitted into the frame so as to project a little beyond its inner part, after the manner of a carpenter's plane-iron for round or ogee work. Then, while the piece G is turning swiftly round by a man working at the great wheel, another man pushes the frame H gently on from L towards M, the lower part of that frame fitting between the cheeks o o, and sliding along between them. By this process, the piece G is reduced to a cylinder, moderately smooth; and, in order to render the smoothness as complete as need be, a second cutter, and its frame I, adapted to a rather smaller cylinder than the former, is pushed along in like manner from L to M. This operation may be performed with such speed, that a very accurate cylinder of six feet long, and four inches diameter, may be fixed to the lathe and turned in much less than a minute.

Mr. Smart turns a conical end to one of these cylinders with great facility, by means of a cutting-blade fixed in an iron hollow conical frame K, the smaller end of which admits the pike from the screw S, fig. 340, to which one end of the cylinder G is attached; as the cylinder turns rapidly round, the cutter K is conducted gently along it by means of the hollow frame, and soon gives the conical shape to the end of the cylinder, as required.

Some important directions for turning screws, ovals, cubes, rose-work, swath-work, &c. may be seen in Moxon's Mechanic Exercises: see also, 66 Tour pour faire sans Arbre toutes Sortes de Vis," par M. Grandjeau, in "Recueil des Machines et Inventions approuvées par l'Acad. Roy. des Sciences, tom. v.; and Mr. Healy's method of cutting screws in the common turning-lathe.

Previously to entering upon the several branches of our manufactures, where machinery will be found in its most complex state, it may, perhaps, be considered not altogether irrelevant, if we take a cursory view of the manner in which we have conducted the reader thus far. In the first place, we have taken up the subject by treating of the Mechanical Powers, and the attributes of matter, as if he were totally unacquainted with the science; and having given him every necessary information with respect to the fundamental principles, have then proceeded to demonstrate the Moving Powers; thus progressively leading him on to a perfect comprehension of the invariable laws of mechanics, before we have ventured to introduce to his notice certain simple machines acting, either separately or conjointly, as accessors to our manufactures. These we have now also portrayed, and so amply, that we feel satisfied he will, though totally destitute of the science at the commencement, be able fully to hend and appreciate the several excellencies of the various combinations which will now be unfolded to him.

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IRON MANUFACTURE.

WORKS for the manufacture of iron, owing to the great sums necessary to be expended in their erection, have, till within these few years, been confined to a very limited scale; but the spirit of enterprise which has of late, and more especially since the French revolution, manifested itself in nearly the whole of our manufactures, conjoined to the immense capitals acquired by many individuals, and the difficulty of employing them to a better advantage, have given to the manufacture of this highly valuable metal a more decisive character.

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The ores from which the metal is extracted are, in this country, found, in general, to consist of iron united with oxygen and various proportions of earthy matter.

The earthy matter in a state of combination with the iron may be divided into two classes; the one called argillaceous, from abounding in excess of aluniine, or clay; the other calcareous, from abounding in lime. The former is by far the most common; indeed it is owing to the ore being so frequently met with in an argillaceous state, that iron-masters are so very inattentive to its quality, and that we sometimes see them use limestone as a flux when the ore already abounds with calcareous ingredients.

Both lime and clay, when separately subjected to the usual heat of the blast-furnace, are infusible; but on being mixed together in certain proportions, are too fusible even for the common purposes of brick-making. An alloy of two metals is also fusible at a temperature much less than the arithmetical mean of the metals themselves.

Such being the case, it is much to be regretted, that ironmasters, in general, are so very ignorant of, and inattentive to, the fusibility of the different combinations of the iron ores, which causes them so frequently to be at a loss what to add to the furnace in order to produce the most fusible cinder. An analysis of the ore, by which they might learn the relative proportions of its earthy constituents, and the quantity of limestone or clay to be added as a flux, would, in the end, prove much to their advantage.

In the usual process of smelting, the coke is always a fixed quantity, and the proportions of ore and limestone are varied according to the quantity of iron to be made, and the

working order of the furnace. In proportion to the quantity of lime and ore that is added to the standard quantity of the coke, the furnace is said to carry a greater or less burthen. Some furnaces carry so little burthen as not to produce more than 13 or 14 tons per week; whilst others, with the same sized furnace, will yield 60 and even 70 tons in an equal time. The burthen of the last-mentioned furnaces is very great, the ore to the coke being, in some cases, as 13 to 7. The quality of the iron is uniformly inferior.

The burthen of the furnace will vary according as the iron to be made is required to possess more or less carbon; for instance, in making No. 1, or the best iron, which contains the greatest portion of carbon, the burthen must be considerably less than that required to make less carburetted iron, or what is called white-iron, or forge-pig.

To afford a general idea of the proportions of the materials, we shall state the quantities, given by Mr. Mushett, as used at a blast-furnace, making good melting iron, which is of an intermediate quality between No, 1 and the forge-pig. The ore is argillaceous, containing on the average about 27 per cent. of iron; the coal rather soft, but not very bituminous, and contains a large proportion of carbonaceous matter; and the limestone, which is that abounding in shells, from Critch, in Derbyshire, is very good. It works with a bright tuyere, and receives from the blast about 2,500 cubic feet in a minute, through a circular aperture of 2 inches in diameter.

It is usual at this, and most other furnaces, to divide the men into two classes, one class to relieve the other every 12 hours; these periods are called shifts. The average

charges of coke per shift are 50 (each 2 cwt.) or about six tons. The quantity of calcined ore for the manufacture of good melting iron is upon a par with the coke; and for forge-pig, or the least carburetted variety, six of coke to seven of ore. The limestone unburnt, under the same circumstances, is to coke as 4 to 11; and for melting metal, retains a similar ratio. With the above charge per day, that is, for twelve hours, this furnace makes on the average about 40 tons melting iron per week.

After the ore is dug, it is drawn from the pit by the power of steam-engines; it is then, in order to extract the arsenic and sulphur, subjected to a process called roasting. This process consists in laying the ironstone in strata with refuse pit-coal, called in Staffordshire slack, and setting fire to it on the windward side, burning it in large heaps in the open air. When the ore has been roasted, it is taken to the smelting