of sulphur with a solution of a ferric salt. Potash, or brown iron ore; 3. Magnetic, or black iron ore; soda, and ammonia throw down a white hydrated 4. Ironstone, blackband, or clay iron ore; 5. Bog oxide from the former, and a brown hydrated iron ore, or phosphate of iron. peroxide from the latter. Ferrocyanide of potassium gives with ferrous salts a white precipitate, which soon becomes blue, while with ferric salts it at once produces a blue precipitate, even in a very dilute solution. Tincture of galls (tannic acid) produces no immediate change of colour with the ferrous, but a deep blackish-blue colour (ink) with the ferric salts. Sulphocyanide of potassium produces no change with the ferrous, but gives a deep blood-red tint with the ferric salts. Succinate and benzoate of ammonia produce no precipitate or change of colour with the former, while with the latter, if the solution is not too acid, they throw down pale reddish-brown precipitates. 2. Manufacture of Iron.-The increasing use of iron is a prominent characteristic of the present age. Every day sees some new application of it in the arts of life. Although the most useful of the metals, it was not the first known. The difficulty of reducing it from its ores would naturally make it a later acquisition than Gold, Silver, and Copper (q. v.). See also BRONZE, and BRONZE PERIOD. The reduction of the ore known as the black oxide of iron, however, has been carried on in India from the earliest times. In Europe, the rich specular and other ores of Spain and Elba were much used during the Roman period; in Greece, also, iron was known, though, as among the Romans, its use was subsequent to that of bronze. We are informed, too, by the Roman historians that this metal was employed by the ancient Britons for the manufacture of spears and lances. The Romans, during their occupation of Britain, manufactured iron to a considerable extent, as is evidenced by the cinder-heaps in the Forest of Dean and other places. The rude processes then in use left so much iron in the cinders, that those of Dean Forest furnished the chief supply of ore to twenty furnaces for between 200 and 300 years. In those early times, the iron ores were reduced in a simple conical furnace, called an air-bloomery, erected on the top of a hill, in order to obtain the greatest blast of wind. The furnaces were subsequently enlarged, and supplied with an artificial blast. Charcoal was the only fuel used in smelting till 1618, when Lord Dudley introduced coal for this purpose; but the iron-masters being unanimously opposed to the change, Dudley's improvement died with himself. It was not reintroduced till Abraham Derby, in 1713, employed it in his furnace at Coalbrook Dale. But as this method was not properly understood, the production of English iron declined with the change of fuel, till, in 1740, it was only threefourths of what it had formerly been. About ten years after this, however, the introduction of coke gave renewed vigour to the iron-trade, and then followed in rapid succession those great improvements in the manufacture which have given to the history of iron the interest of a romance. The introduction of Watt's steam-engine in 1770, the processes of puddling and rolling invented by Henry Cort in 1784, and the employment of the hot-blast by Neilson of Glasgow in 1830, have each been of inestimable service. So recently as 1856, Mr Henry Bessemer patented a process (see BESSEMER'S PROCESS) for the production of malleable iron and steel, which will probably ere long take its place as one of the greatest improvements ever introduced into the iron manufacture. The great supply of iron is derived from its numerous ores, which are abundantly distributed over the globe; the chief of which are-1. Hæmatite, specular, or red iron ore; 2. Brown hæmatite, The ore richest in the metal is the magnetic (see MAGNETISM), or black oxide of iron. When pure, it contains nothing but oxygen and iron, its chemical formula being Fe,O,, which gives 73 per cent. of iron by weight. It occurs in dark heavy masses or black crystals, and is found in the older primary rocks. Sweden is famous for this ore, and for the iron produced from it, which is esteemed the best in Europe. The celebrated mines of Dannemora, in that country, have been constantly worked since the 15th century. Russia, too, has great iron works in the Ural Mountains, which are supplied with this ore. So, also, have Canada and several of the American states, as Virginia, Pennsylvania, New Jersey, &c. The rock formations in which magnetic iron ore occurs contain no coal, hence it is almost always smelted with wood-charcoal, which, as it contains no sulphur, is one great cause of the superiority of the iron produced from it. The red oxide differs from the last only in containing proportionally a little more oxygen, its formula being Fe,O,, that is to say, 70 per cent. of iron by weight. There are several varieties of this ore, but only two need be referred to. The first of these, specular iron, so called from its bright metallic lustre, occurs in large and beautiful crystalline masses in the island of Elba, where it has been worked for more than 2000 years, and is likewise found in many other parts of the world. It is of a steel gray colour, assuming a red tint in thin fragments and when scratched. The other variety is red hæmatite, an ore whose origin is still a curious problem, as its deposits occur sometimes in veins, and sometimes in apparently regular beds. Its characteristic form is in large kidney-shaped nodules, with a fine radiated structure. This shape, however, is only assumed in the cavities of massive deposits. Red hæmatite is sometimes called bloodstone. It is used for polishing metals, and yields a blood-red powder, used as a pigment. This valuable iron ore is found in many countries, but perhaps nowhere in greater abundance than at Whitehaven and. Ulverstone, in the north-west of England, where splendid masses of it occur, 15, 30, and even 60 feet in thickness. These two districts produced, in 1861, about 1,000,000 tons of hæmatite. Brown hæmatite is a hydrated peroxide of iron, and has the same composition as red hæmatite, except that it contains a certain proportion of water. It is generally found massive, more rarely crystalline, and a variety, occurring in small rounded nodules, is called pea iron ore. When mixed with earth or clay, it forms yellow ochre and brown umber, so largely used as pigments, but the latter also contains manganese. Brown hæmatite, though not much used in England, is an important ore on the continent, especially in France, Belgium, Prussia, and Austria. Bog iron ore is a mixture of brown hæmatite and phosphate of iron, occurring in marshy districts of recent formation." This ore is also extensively smelted in France. There is a sparry carbonate of iron, termed spathose iron ore, of considerable importance on the continent of Europe, especially in Prussia, where extensive deposits of it exist. It is of a yellowishgray colour, very much resembles the common mineral calc-spar, and yields from 40 to 50 per cent. of iron. It is much used for the manufacture of steel. Most of the ores of iron already described possess, either by their bright metallic surfaces, or the beauty of their crystalline forms, a certain attraction for CLAY IRONSTONE, CHIEFLY A CARBONATE OF IRON, BLACK-BED MINE, LOWMOOR, YORKShire. Protoxide of iron, Peroxide of iron, Protoxide of manganese, the cabinet of the mineralogist. But there remains the Memoirs of the Geological Survey, and the second to be noticed a dull, blackish or clay-coloured is by Dr Murray Thomson. mineral, possessing no beauty or symmetry, which Great Britain prizes as one of the greatest of her mineral treasures: this is the ironstone of the coalmeasures, which is variously named clay iron ore, clay carbonate of iron, and blackband. It is essentially a mixture of carbonate of iron with clay, containing also water, and in the case of blackband, coaly or bituminous matter. It is estimated that the coal-measures of Great Britain produce about nine-tenths of our iron; and it is a fortunate thing that, along with the ore, are found both the fuel and the limestone that are indispensable for its reduction. About ten years ago, the three great iron districts of Britain were South Staffordshire, South Wales, and Central Scotland, each producing nearly equal quantities, and together yielding about four-fifths of the total produce of the country. Now, however, the South Staffordshire field is being rapidly exhausted, its produce having diminished about a half, while that of the South Wales and Scottish districts have increased, and they are now yielding nearly a million tons each. North Staffordshire, Shropshire, Derbyshire, and the West Riding of Yorkshire are the principal remaining districts yielding ores of this class, but their total produce is not more than that of South Staffordshire, although the iron of the West Riding is the best in Britain as regards quality. Alumina, 36.14 0.61 1.38 0.52 2.70 2.05 26-57 0.34 trace 0-10 0.61 Phosphoric acid, Sulphuric acid, Bisulphide of iron, Water, hygroscopic, " combined, Organic matter, Metallic iron per cent. There is yet another great iron district, yielding an ore belonging to a more recent formation than It will be noticed that in the case of these ores the the carboniferous beds-namely, the lias. This impurities are rather numerous. Nevertheless, the deposit, which fifteen years ago was unknown, is modes of preparing and smelting them are somealready producing iron to the enormous amount what rude and simple, as the low price of iron will of 400,000 tons per annum. It is the ironstone not permit of its ores being treated with the same of the Cleveland Hills, in the north-east of York- care as the ores of lead, copper, tin, and some other shire, which, from its resemblance to common sand- metals. stone, passed unnoticed till 1847. About that time, isolated blocks of it, found on the sea-coast, were discovered to contain about 30 per cent. of iron. On further examination of the district, these were proved to be detached pieces of a massive bed, no less than 15 feet thick, which could be traced for many miles along the sides of the hills. Some idea of the value of this vast deposit of iron ore will be found in the fact, that the ironstone seams of the coal-measures seldom exceed 20, and are worked as low as 8 inches in thickness. Another mass of ironstone of great thickness, also belonging to the lias beds, has very recently been discovered in North Lincolnshire. In the oolite, too, beds of brown iron ore have been discovered in several counties, but chiefly in Northamptonshire, where it has been worked with so much spirit, that from 150,000 to 200,000 tons of ore per annum are now raised. To those remarkable discoveries may be added that by Mr Rogers of Abercarn, who, after examining the position of the pisolitic ore at the base of the carboniferous limestone in Belgium, searched the corresponding strata in South Wales, and curiously enough was rewarded with the discovery of a precisely similar bed at Cwm Noddi. The same gentleman, struck by the appearance of the sparry carbonates of iron in the Austrian and Prussian departments of the Exhibition of 1851, soon afterwards noticed veins of a like ore in the Devonian rocks of Somersetshire. In fact, the sources which have been discovered within the last fifteen years are already yielding a larger supply of iron than the total produce of any other European country except France. Before proceeding to describe the manufacture of iron, we give two analyses of British ores: the first is by Mr J. Spiller, taken from a series published in Iron ore is still reduced in the south of Europe by the old and imperfect process of the Catalan forge, not unlike a common smith's forge. In Great Britain, however, as well as in all other countries where iron is largely smelted, the blast-furnace is now universally employed, by means of which the metal is obtained in the state of crude or cast iron. For the finer kinds of iron, charcoal is the fuel employed, because, unlike coal or coke, it contains no sulphuret of iron or other injurious ingredients. The Russian and Swedish furnaces smelt with charcoal, and on this, as much as on their pure ores, depends the high reputation of their iron. A solitary charcoal-furnace at Ulverstone in England, and another at Lorn in Scotland, are still working-the only relics of times past, when this was the only fuel employed. As a preliminary process to the actual smelting in the blast-furnace, clay and blackband ironstones are generally roasted. This is accomplished by breaking the ore into small pieces, spreading it in open heaps on the ground, and mingling it more or less with small coal according to the nature of the ore. Black band commonly contains enough of carbonaceous matter to burn without the addition of coal. The pile, which may contain from one to several thousand tons of ore, is lighted at the windward end, and burns gradually along, aided by occasional fires in the sides, till the whole heap has undergone calcination, the time required for this purpose being generally about a month. Sometimes the operation of roasting is performed in close kilns, instead of open heaps, a mode by which the ore is considered to be more uniformly roasted, and with considerably less fuel. By calcination, clay ironstone loses from 25 to 30, and blackband from 40 to 50 per cent. of its weight, the loss consisting chiefly of carbonic acid and water. When roasted, the ore contains about 10 per cent. more of iron than it does in its raw state; and, moreover, it is reduced to the state of black oxide of iron and clay. It is now ready to be smelted. The blast-furnace is generally built in the form of a truncated cone, with a massive square base. Internally, it is either barrel-shaped or in the form of a double cone, like two flower-pots placed mouth to mouth. The inside requires to be built of the most refractory firebrick. The external portion is either of common brick or stone, secured with iron binders; without this, the great heat would soon displace the most substantial brickwork. A goodsized blast-furnace measures about 30 feet across the base, and is 50 or 60 feet in height. Three sides of the base have arched recesses for the pipes conveying the blast, and on the fourth there is a similar recess, in which are the openings for running off the metal and slag. Fig. 1 is a sectional view of a hot blast-furnace, with the blowing engine and other appliances, which is taken, with some modification, from Mr Fairbairn's work on Iron. It may be well to state here that one engine usually supplies the blast to several furnaces. A is the body of furnace; B, the hearth, above which are placed the tuyeres, C; D is the tunnel-head, around which there is a gangway, for the workmen to have access to the feeding-doors at E. The blowing-engine is shewn at F. Air is Row Libex Fig. 1.-Hot Blast-furnace. forced into the furnace by means of the blowing cylinder, G, from which it passes into the receiver, H, and thence along a pipe into the heating-oven, I. Here a large surface of pipe is exposed, in archshaped rows, to the fire, which heats the enclosed air to 600° F. and upwards-a heat sufficient to melt lead. At this temperature, it enters the lower part of the furnace by means of the tuyeres, C. From 5000 to 10,000 cubic feet of air is discharged into the furnace per minute. The operation of smelting is thus performed: the roasted ore, coal, and lime (flux) are either hoisted, or, if the nature of the ground permits, moved along a platform or gangway to the gallery near the top of the furnace, and fed into it at intervals through the openings in the side. We may here state that the furnace is kept continually burning except when under repair. The materials are of course raised to a very high heat, and gradually fuse into a softened mass. The clay of the ironstone then unites with the lime to form a coarse glass, or slag; the oxide of iron at the same time gives up its oxygen to the fuel, and allows the metal itself to collect on the hearth at the bottom of the furnace, united with about 5 per cent. of carbon, which it takes from the fuel, forming the variety called cast iron. Every twelve, and sometimes every eight hours, the metal is run off from the furnace, by means of a tap-hole at the bottom of the hearth, into rows of parallel moulds, called pigs, which are formed in sand, hence the name 'pig iron.' The slag which floats on the melted iron is run off by an opening at the top of the hearth. If the furnace is working well, the slag should be of a light-gray colour; a dark-brown or black colour shews that too much iron is passing into it. The quantity of materials necessary to yield a ton of pig iron may be taken roundly as follows: 2 tons of calcined ironstone; 2 tons of coal, of which about 8 cwts. are required for the blowing-engine and hot-air pipes; and from 12 to 16 cwts. of broken limestone. The weekly produce of a single blast-furnace varies extremely-50, 100, and even the enormous quantity of 600 tons, is now occasionally obtained. The last amount, however, can only be procured from hæmatite ore. There are about six varieties of cast iron, but it will be sufficient to describe three of them. No. 1 has a large and clear grain, is of a dark-gray colour, and contains its carbon for the most part mechanic. ally diffused through its substance. It brings the highest price, is very fusible, and therefore largely used for castings, especially for those of a fine description. No. 4 has a much closer grain, is of a light, though dull gray colour, and contains its carbon partly diffused through it and partly in chemical combination. It is generally employed for conversion into malleable iron. No. 6 is called white or silvery iron, and has all its carbon chemically combined with the metal. It is not in much request, being usually produced when the furnaces are working badly. The qualities of the intermediate numbers differ only in degree from those described; thus, No. 2 is rather less gray, crystalline, and fusible than No. 1, and so on. The hot-blast process which has been described 635 above, was introduced, in 1830, by Mr James B. Neilson, of Glasgow, and has been productive of very remarkable effects on the iron trade. The whole invention consists in simply heating the air blown into the furnace, and yet the saving of fuel by this is about one half, and the production of iron, since it came into use, has increased at least fourfold. The cold blast' is still, however, to a limited extent employed, and produces the strongest iron, though necessarily at a much higher cost. The difference in quality appears to be caused by the greater heat in the case of the hot blast facilitating the passage of impurities into the iron. We pass now to the consideration of malleable or wrought iron. It differs from cast iron in containing no carbon. The great object in the processes adopted for the conversion of cast into malleable iron, accordingly, is to deprive the former of its carbon. But it is also very desirable to get rid of deleterious ingredients, such as sulphur and phosphorus, which are generally present in minute quantities in the cast iron. The ordinary processes for the manufacture of malleable iron are refining, puddling, shingling or hammering, and rolling. The refinery is shewn in section in fig. 2. It consists of a flat hearth, A, covered with sand or loam, and surrounded with metal troughs, B, through which a stream of water is constantly flowing, to keep the Fig. 2.-Refinery. sides from melting. C are the tuyeres in connection with the blowing-engine. The cast iron is melted with coke on the hearth, and a blast of air kept blowing over it, which causes its carbon to unite with the oxygen of the air, and pass off as carbonic oxide gas. Oxygen also unites with silicon to form silica, and with iron to form the oxide. The silica of the sand uniting with oxide of iron, produces a slag of silicate of iron. The refined metal is finally run out in cakes on a bed of cast iron, kept cool by a stream of water. Being only partially decarbonised by this process, it is next broken up for the puddling furnace. About 10 per cent. of iron is lost in the refinery. Fig. 3 shews a puddling furnace in longitudinal section. A represents the hearth; F, the grate or fireplace; and C, the chimney, which has a damper at the summit, to regulate the draught. The grate is separated from the hearth by means of a bridge, D, which prevents the direct contact of the fuel with the iron. In the operation of puddling, about four cwts. of refined iron are placed on the hearth, and the heat raised till it is melted; the metal is then thoroughly stirred with an iron rod, so as to expose fresh surfaces to the oxygen of the air which a spongy, granular mass. The whole charge of the furnace is now divided and formed into balls,' weighing from 80 to 110 lbs. each, which are then raised to a welding heat, and taken singly to be shingled. Instead of being both refined and puddled, pig iron is now largely decarbonised by means of the single process of boiling.' By this method, which is very similar to puddling, gray pig iron is deprived of nearly the whole of its carbon in the puddling furnace. In this way the metal requires to be raised to a higher heat and more frequently stirred than in ordinary puddling, so as to expedite the escape of the larger amount of carbon; which has the effect of causing the metal to boil or bubble as the gases become disengaged. The boiling process requires about 24 cwts. of pig to produce a ton of bar iron, while the two processes of refining and puddling require 26 cwts. or thereby for a ton of similar bar iron. There is therefore least loss when the single operation of boiling is adopted, but, on the other hand, with it there is more tear and wear of the furnaces, and also more manual labour required. The process immediately following the puddling or boiling is called 'shingling,' and consists in hammering the puddled balls with either the helve or steam-hammer, or in passing them through a squeezer till they are sufficiently consolidated, and the greater part of the cinders forced out. Fig. 4 represents Mr Nasmyth's steam-hammer (see HAMMER), which is now largely used in shingling as well as in heavy forgings. Puddled balls which have undergone shingling are called slabs or blooms. These are next passed through heavy rollers termed 'forge' or 'puddle-bar rolls,' and reduced to the form of a flat bar. For all the better kinds of iron, the bars thus treated are cut into short lengths, piled together, reheated in a furnace, and again passed through the forge rolls. Once more the iron is cut, piled, and heated, and then passed through the mill-train,' consisting of what are termed the bolting' or 'rough rolls,' and finally through the 'finishing rolls.' Both these sets of rolls in the case of plates and sheets are plain, but in the case of bars are grooved, so as to form them into the required shape, such as flat, square, round, octagonal, or T-shaped iron. Fig. 5 indicates the arrangement and appearance of the 'rough' and 'finishing rolls' of a bar mill-train. There is still another important variety of iron, viz., Steel, the manufacture of which remains to be described. Steel is essentially iron containing from to 1 per cent. of carbon. Remembering that cast iron contains some 5 per cent. of carbon, the uninitiated reader will be a little astonished to learn that, in this country at least, most of the steel is made from malleable iron, seeing that, at some stage of the conversion of cast into wrought iron, the metal must have passed into the condition of steel. ing malleable iron into steel is called cementation. There are other modes of manufacturing steel, such as by the partial decarbonisation of cast iron on a charcoal hearth, a method largely prac tised on the continent. Bessemer's method of producing malleable iron directly from crude pig iron is described elsewhere. See BESSEMER'S PROCESS. Malleable iron made by Mr Bessemer's process is apt to be cellular and unsound, defects which the inventor has had great trouble in overcoming, if even now he has thoroughly succeeded. According to the same process, steel is made by introducing into the Nevertheless, our manufacturers have hitherto melted iron a given quantity of spiegeleisen (a peculiar thought it best to take the whole of the carbon out kind of cast iron), containing a known percentage of the cast iron, and then restore a certain portion of carbon; and so steel may be produced with any by heating with charcoal. This process of convert-required proportion of carbon. The spiegeleisen Fig. 5.-Rough and Finishing Rolls. dissolves in the iron like sugar in water, rendering | tunately, when pig iron containing phosphorus is the metal more fusible and very liquid. Unfor- operated on in this way, this injurious element is |