of strength, according to their composition. Phosphorus, sulphur, and silicon appear to be highly injurious; whereas titanium, nickel, and perhaps manganese, exert a contrary action. Steel, besides possessing in a high degree the qualities of wrought-iron, when in a soft state, admits also of being raised to various degrees of hardness. The processes of hardening and tempering are very simple, and are thus conducted:-The steel to be hardened, having been raised to a red-heat, is plunged into water, or other cooling medium, whereby a very great state of hardness is obtained. The fracture is then crystalline. Steel in this condition is unfit for the generality of purposes, and therefore requires to be tempered previous to use; to effect this, it is gradually heated, becoming the softer the higher the temperature to which it is raised; the proper point of temper is ascertained by the color exhibited by a film of oxide, which forms on the exterior of the metal. This color is probably produced by the interference of light, which is caused by a ray of light striking the upper surface of the film, a part of it being immediately reflected, whilst another portion passes through the film with refraction, and is reflected from its lower surface, when, if the film be thin, it frequently happens that some of the component rays reflected from the lower surface interfere with and neutralize some of those previously reflected from the upper surface. Steel works for various purposes are thus with certainty prepared with the proper temper: for coach-springs and similar articles, it is tempered to a blue tint; for small springs, such as the spiral and blade springs made in the smaller machinery, the metal is raised to such a heat as will impart to it a pale-blue tint; for cutting-tools, the color is straw-yellow, varying in shade according to the manner in which the tool is to be used.

other materials Copper, as used

We must now offer a few remarks upon the with which, subsequently, we shall have to deal. in commerce, is prepared in a state of comparative purity; but the processes required for its reduction are exceedingly complicated, five or six operations in reverberatory furnaces being necessary for the reduction of sulphide of copper. The metal is ductile, but requires, when being worked, to be frequently annealed; it may be wrought under the hammer cold, but works better at a slight elevation of temperature. It has been found that the addition

of a small quantity of phosphorus materially improves the strength of copper; for although this element is so detrimental to iron, yet when it is combined with copper in the proportion of two to four per cent., it imparts to that metal considerable hardness and tenacity; its tensile resistance then becoming about four-fifths of that of ordinary iron, or two-thirds of that of the Low-Moor ironplates. Alloys of copper with aluminium have the advantage of homogeneity and tenacity; but from the fact that aluminium is powerfully affected by alkaline substances, its use is for many purposes precluded. Copper, when combined with about four per cent. of silicon, possesses the hardness of steel and the tenacity of wrought-iron, and if this alloy could be manufactured on a large scale with convenience, it would doubtless be found applicable to a great variety of purposes. It may be interesting here to mention the method of combining the phosphorus and copper, as advised by F. A. Abel, Esq., Director of the Chemical Establishment of the War Department. The phosphorus should be coated with copper by immersing the pieces in a solution of sulphate of copper; after which process they may be handled with perfect safety, and when they are thrown into the molten metal, the external film of copper will efficiently protect them from oxidation during the very short period required for combination. One of the most important alloys of copper is brass, though gun-metal is perhaps almost as extensive in its applications. The strength, however, of brass is not by any means equal to that of the phosphorus and copper alloy. The metals, tin, lead, and zinc, will also demand some consideration, but it is unnecessary here to comment farther upon them.

Having concluded our introductory remarks upon the earlier processes of metallurgy, we may proceed to mention the branch of manufacture of which we purpose next to treat. This includes the forging of metal both by hand and by steam-power; and also the various methods of reducing the materials to the required size and form. In this section we shall also refer to the formation of woodpatterns, as the models from which castings are usually made are called. In this part we shall most particularly explain the construction and method of using the tools and machinery with which the workmen must be provided, in order accurately to execute the manipulations with which they are engaged.

Our next subject will comprise the theory or principles upon

which the construction of the steam-engine generally is based, as also that of other machinery; but we shall not seek here to enter into very elaborate arguments or demonstrations, but rather to explain in the simplest and most succinct manner well-established facts, with which it is important for every practical man to be acquainted. We shall also include in this section simple rules for proportioning the various parts of machinery.

The remainder of the work will be occupied with descriptions of the various forms of steam-engines usually applied to manufacturing, marine, and locomotive purposes.

We will now conclude these brief introductory remarks, which may be regarded as an account of the branches of manipulative science which we purpose discussing, and proceed with the detailed consideration of the same.

CHAPTER I.

ON METALLURGY.

BEFORE proceeding with a description of the processes employed in the metallurgy of iron, it is necessary to enumerate the minerals from which it is usually obtained. Those which contain at least twenty per cent. of metal are usually considered ores, but if they contain less they are regarded as fluxes, the use of which in metallurgical operations will subsequently be indicated. Ores of iron are very widely disseminated, being found as beds in the sedimentary rocks, or as veins and massive deposits in the older formations, in which position the most valuable ores are obtained. They frequently occur beneath the coal-measures, which arrangement is exceedingly convenient, the fuel for the manufacture being found on the same spot with the ferruginous minerals. In some of the North American States, and in other places, magnetic iron-sand occurs in the drift at the foot of mountain-ranges, and bog-iron ores are also occasionally found in a similar position. In the cretaceous system, large deposits of ferruginous sand occur, but on account of their low yield they have never been extensively worked. Below the cretaceous system there are some extensive deposits of iron, which were formerly worked in Hampshire and Sussex, the metals being reduced by charcoal supplied from the neighboring forests; these are, however, at the present day neglected. In Northamptonshire and the Cleveland district of North Yorkshire are found beds of oolitic iron-ore, sometimes of a thickness of twenty feet, and affording in many instances thirty-three per cent. of metal. A few thin beds occurring in the lias formation have been partly worked in Lincolnshire and Yorkshire, but they are not rich in metal; in this formation, magnetic iron-sand and small portions of hematite also occur. The iron-works of this country, however, are supplied principally from the earthy carbonates of the coal-measures, from which excellent metal is obtained.

The coal-fields of South Wales, Staffordshire, Yorkshire, Scotland, North Wales, Shropshire, and Warwickshire, contain abundant deposits of this ore.

When the iron ores have been raised to the surface, the first operation consists in the cleansing of them. The earthy carbonates of the coal formations are placed in heaps, and left for several months, after which it will be found that the excess of adhering clay-shale has become separated by the action of the atmosphere, leaving the ores clean and fit for the furnace. The oolitic ores and the magnetic oxides and rich hematites of foreign countries are frequently cleansed by making use of the superior specific gravity of the ferruginous portion of the products; but in England the hematites undergo no other preparation than a partial hand-picking to separate large masses of refuse matter. We may now explain the theory of the reduction of iron. If an oxide of iron be highly heated in contact with carbon, the latter, having a greater affinity than the former for oxygen, takes it from the ferruginous oxide, thereby eliminating the metal. It is, however, necessary to provide some substance readily fusible, in order to dissolve certain impurities; such substances are called fluxes. They should be incapable of holding in solution any considerable quantity of iron. Chalk forms an excellent flux, but limestone is the cheapest material, and therefore most frequently employed. It may be interesting here to insert a list of the ores, fuels, and fluxes used in some of the principal works of Great Britain. At the Whitehaven foundry, hematite ore of a very pure character is employed, and is reduced by means of a mixture of Newcastle coke and coke manufactured at the works as fuel, with Whitehaven limestone and black shale, consisting of clay and carbonaceous matter, as fluxes. A sample of this ore when dried contained sixty-nine per cent. of metallic iron, generally pure, containing a large amount of silicon. At the South-Bank furnaces an earthy carbonate of iron with silicate is used containing thirty-five per cent. of metal, with a hard variety of coke as fuel, and dark-gray limestone for flux. At the Butterley works, blue-rake and brown-rake ores are used, the latter containing about thirty per cent. of metal; Brand's hard coal is the fuel, and Bullbridge or Crawford limestone the flux. At Lay's iron-works, a mixture of various ores is employed; the fuel is a mixture of Durham and Derbyshire Thickbone cokes, with Frog