German refining forgeThe German refining forge.—Figs.601,602.represent one of the numerous refinery furnaces so common in the Hartz. The example is taken from theMandelholzworks, in the neighbourhood of Elbingerode.Fig.602.is an elevation of this forge.Dis the refinery hearth, provided with two pairs of bellows.Fig.601.is a vertical section, showing particularly the construction of the crucible or hearth in the refinery forgeD.Cis an overshot water-wheel, which gives an alternate impulsion to the two bellowsa bby means of the revolving shaftc, and the cams or tappetsd f e g.D, the hearth, is lined with cast-iron plates. Through the pipel, cold water may be introduced, under the bottom platem, in order to keep down, when necessary, the temperature of the crucible, and facilitate the solidification of theloupeor bloom. An orificen,figs.601,602., called thechio(floss hole), allows the melted slag or cinder to flow off from the surface of the melted metal. The copper pipe or nose piecep,fig.600., conducts the blast of both bellows into the hearth, as shown atb x,fig.602., andDg pfig.600.The substance subjected to this mode of refinery, is a gray carbonaceous cast iron, from the works of Rothehütte. The hearthD, being filled and heaped over with live charcoal, upon the side opposite to the tuyèrex,figs.601,602, long pigs of cast iron are laid with their ends sloping downwards, and are drawn forwards successively into the hearth by a hooked poker, so that the extremity of each may be plunged into the middle of the fire, at a distance of 6 or 8 inches from the mouth of the tuyère. The workman proceeds in this way, till he has melted enough of metal to form aloupe. The cast iron, on melting, falls down in drops to the bottom of the hearth; being covered by the fused slags, or vitreous matters more or less loaded with oxide of iron. After running them off by the orificen, he then works the cast iron by powerful stirring with an iron rake (ringard), till it is converted into a mass of a pasty consistence.During this operation, a portion of the carbon contained in the cast iron combines with the atmospherical oxygen supplied by the bellows, and passes off in the form of carbonic oxide and carbonic acid. When the lump is coagulated sufficiently, the workman turns it over in the hearth, then increases the heat so as to melt it afresh, meanwhile exposing it all round to the blast, in order to consume the remainder of the carbon, that is, till the iron has become ductile, or refined. If one fusion should prove inadequate to this effect, two are given. Before the conclusion, the workman runs off a second stratum of vitreous slag, but at a higher level, so that some of it may remain upon the metal.The weight of such aloupeorbloomis about 2 cwts., being the product of 2 cwts. and7⁄10of pig iron; the loss of weight is therefore about 26 per cent. 149 pounds of charcoal are consumed for every 100 pounds of bar iron obtained. The whole operation lasts about 5 hours. The bellows are stopped as soon as the bloom is ready; this is immediately transferred to a forge hammer, such as is representedfig.605.; the cast-iron head of which weighs 8 or 9 cwts. The bloom is greatly condensed thereby, and discharges a considerable quantity of semi-fluid cinder. The lump is then divided by the hammerand a chisel into 4 or 6 pieces, which are re-heated, one after another, in the same refinery fire, in order to be forged into bars, whilst another pig of cast iron is laid in its place, to prepare for the formation of a new bloom. The above process is called by the Germansklump-frischen, or lump-refining. It differs from thedurch-brech-frischen, because in the latter, the lump is not turned over in mass, but is broken, and exposed in separate pieces successively to the refining power of the blast near the tuyère. The French call thisaffinage par portions; it is much lighter work than the other.The quality of the iron is tried in various ways; as first, by raising a bar by one end, with the two hands over one’s head, and bringing it forcibly down to strike across a narrow anvil at its centre of percussion, or one-third from the other extremity of the bar; after which it may be bent backwards and forwards at the place of percussion several times; 2. a heavy bar may be laid obliquely over props near its end, and struck strongly with a hammer with a narrow pane, so as to curve it in opposite directions; or while heated to redness, they may be kneed backwards and forwards at the same spot, on the edge of the anvil. This is a severe trial, which the hoop L, Swedish iron, bears surprisingly, emitting as it is hammered, a phosphoric odour, peculiar to it and to the bar iron of Ulverstone, which also resembles it, in furnishing a good steel. The forging of a horseshoe is reckoned a good criterion of the quality of iron. Its freedom from flaws is detected by the above modes; and its linear strength may be determined by suspending a scale to the lower end of a hard-drawn wire, of a given size, and adding weights till the wire breaks. The treatises of Barlow and Tredgold may be consulted with advantage on the methods of proving the strength of different kinds of iron, in a great variety of circumstances.Steel of cementation, or blistered steel and cast steel, are treated under the articleSteel. But since in the conversion of cast iron into wrought iron, by a very slight difference in the manipulations, a species of steel may be produced callednatural steel, I shall describe this process here.Königdhütte worksFig.603.is a view of the celebrated steel iron works, called Königshütte (king’s-forge), in Upper Silesia, being one of the best arranged in Germany, for smelting iron ore by means of coke. The front shown here is about 400 English feet long.a aare two blast furnaces. A third blast furnace, all like the English, is situated to the left of one of the towersb.b bare the charging towers, into which the ore is raised by machinery from the level of the store-housesl l, up to the mouth of the furnacesa a;c cpoint to the positions of the boilers of the two steam engines, which drive two cylinder bellows atf.n n n nare arched cellars placed below the store-housesl l, for containing materials and tools necessary for the establishment.ForgeFigs.599.,604., are vertical sections of the forge of Königshütte, for making natural steel;fig.599.being drawn in the lineA Bof the plan,fig.600.ais the bottom of the hearth, consisting of a fire-proof gritstone;bis a space filled with small charcoal, damped with water, under which, atn, infig.604., is a bed of well rammed clay;dis a plate of cast iron, which lines the side of the hearth called rückstein (backstone) in German, and corrupted by the French intorustine;fis the plate of the counter-blast;gthe plate of the side of the tuyère: behind, upon the faced, the fire-place or hearth is only 51⁄2inches deep; in front as well as upon the lateral faces, it is 18 inches deep. By means of a mound made of dry charcoal, the posterior faced, is raised to the height of the facef.i,fig.600., is the floss-hole, by which the slags are run off from the hearth during the working, and through which, by removing some bricks, the lump of steel is taken out when finished.k l mare pieces of cast iron, for confining the fire in front, that is towards the side where the workman stands;ois the level of the floor of the works;pa copper tuyère; it is situated 41⁄2inches above the bottoma, slopes 5 degrees towards it, and advances 4 inches into the hearth or fire-place, where it presents an orifice, one half inch in horizontal length, and one inch up and down;qthe nose pipes of two bellows, like those representedinfig.602., and underSilver; the round orifice of each of them within the tuyère being one inch in diameter.ris the lintel or top arch of the tuyère, beneath which is seen the cross section of the pig of cast iron under operation.For the production of natural steel, a white cast iron is preferred, which contains little carbon, which does not flow thin, and which being cementedover or above the wind, falls down at once through the blast to the bottom of the hearth in the state of steel. With this view, a very flat fire is used; and should the metal run too fluid, some malleable lumps are introduced to give the mass a thicker pasty consistence.If the natural steel be supposed to contain too little carbon, which is a very rare case, the metal bath covered with its cinder slag, is diligently stirred with a wooden pole, or it may receive a little of the more highly carburetted iron. If it contains the right dose of carbon, the earthy and other foreign matters are made progressively to sweat out, into the supernatant slag. When the mass is found by the trial of a sample to be completely converted, and has acquired the requisite stiffness, it is lifted out of the furnace, by the opening in front, subjected to the forge hammer, and drawn into bars. In Sweden, the cast-iron pigs are heated to a cherry-red, and in this state broken to pieces under the hammer, before they are exposed in the steel furnace. These natural steels are much employed on the Continent in making agricultural implements, on account of their cheapness. The natural steel of Styria is regarded as a very good article.Wootz is a natural steel prepared from a black ore of iron in Hindostan, by a process analogous to that of the Catalan hearth, but still simpler. It seems to contain a minute portion of the combustible bases of alumina and silica, to which its peculiar hardness when tempered, may possibly be ascribed. It is remarkable for the property of assuming a damask surface, by the action of dilute sulphuric acid, after it has been forged and polished. SeeDamascusandSteel.Forge-hammerFig.605.is the German forge-hammer; to the left of 1, is the axis of the rotatory cam, 2, 3, consisting of 8 sides, each formed of a strong broad bar of cast iron, which are joined together to make the octagon wheel. 4, 5, 6, are cast-iron binding rings or hoops; made fast by wooden wedges.b,b, are standards of the frame worke,l,m, in which the helve of the forge hammer has its fulcrum nearu.h, the sole part of the frame. Another cast-iron base or sole is seen atm.nis a strong stay, to strengthen the frame-work. Atrtwo parallel hammers are placed, with cast-iron heads and wooden helves.sis the anvil, a very massive piece of cast iron.tis the end of a vibrating beam, for throwing back the hammer from it forcibly by recoil.x yis the outline of the water-wheel which drives the whole. The cams or tappets are shown mounted upon the wheel 6,g, 6.Analysis of Irons.—Oxidized substances cannot exist in metallic iron, and the foreign substances it does contain are present in such small quantities, that it is somewhat difficult to determine their amount. The most intricate point is, the proportion of carbon. The free carbon, which is present only in gray cast iron, may, indeed, be determined nearly, for most of it remains after solution of the metal in acids. The combined charcoal, however, changes by the action of muriatic acid into gas and oil; sulphuric acid also occasions a great loss of carbon, and nitric acid dissipates it almost entirely. Either nitre or chloride of silver may be employed to ascertain the amount of carbon; but when the iron contains chromium and much phosphorus, the determination of the carbon is attended with many difficulties.The quantity of sulphur is always so small, that it can scarcely be ascertained by the weight of the precipitate of sulphate of barytes from the solution of the iron in nitro-muriatic acid. The iron should be dissolved in muriatic acid; and the hydrogen, as it escapes charged with the sulphur, should be passed through an acidulous solution of acetate of lead. The weight of the precipitated sulphuret shows the amount of sulphur, allowing 13·45 of the latter for 100 of the former. In this experiment the metal should be slowly acted upon by the acid. Cast iron takes from 10 to 15 days to dissolve, steel from 8 to 10, and malleable iron 4 days. The residuum of a black colour does not contain a trace of sulphur.Phosphorus and chromium are determined in the following way. The iron must be dissolved in nitro-muriatic acid, to oxygenate those two bodies. The solution must be evaporated cautiously to dryness in porcelain capsules, and the saline residuum heatedto redness. A little chloride of iron is volatilized, and the remainder resembles the red-brown oxide. This must be mixed with thrice its weight of carbonate of potash, and fused in a platinum crucible; the quantity of iron being from 40 to 50 grains at most.The mixture after being acted upon by boiling water, is to be left to settle, to allow the oxide to be deposited, for it is so fine as to pass through a filter. If the iron contained manganese, this would be foundat firstin the alkaline solution; but manganese spontaneously separates by exposure to the air. The alkaline liquor must be supersaturated with muriatic acid, and evaporated to dryness. The liquor acidulated, and deprived of its silica by filtration, is to be supersaturated with ammonia; when the alumina will precipitate in the state of a subphosphate. When the liquor is now supersaturated with acetic acid, and then treated with acetate of lead, a precipitate of phosphate of lead almost always falls. There is hardly a bit of iron to be found which does not contain phosphorus. The slightest trace of chrome is detected by the yellow colour of the lead precipitate; if this be white there is none of the colouring metal present.100 parts of the precipitated phosphate of lead contain, after calcination, 19·4 parts of phosphoric acid. The precipitate should be previously washed with acetic acid, and then with water. These 19·4 parts contain 8·525 parts of phosphorus.Cast iron sometimes contains calcium and barium, which may be detected by their well-known reagents, oxalate of ammonia, and sulphuric acid. In malleable iron they are seldom or never present.The charcoal found in the residuum of the nitro-muriatic solution is to be burned away under a muffle. The solution itself contains along with the oxide of iron, protoxide of manganese, and other oxides, as well as the earths, and the phosphoric and arsenic acids. Tartaric acid is to be added to it, till no precipitate be formed by supersaturation with caustic ammonia. The ammoniacal liquor must be treated with hydrosulphuret of ammonia as long as it is clouded, then thrown upon a filter. The precipitate is usually very voluminous, and must be well washed. The liquor which passes through is to be saturated with muriatic acid, to decompose all the sulphurets.The solution still contains all the earths and the oxide of titanium, besides the phosphoric acid. It is to be evaporated to dryness, whereby the ammonia is expelled, and the carbonaceous residuum must be burned under a muffle. If the iron contains much phosphorus, the ashes are strongly agglutinated. They are to be fused as already described along with carbonate of potash, and the mass is to be treated with boiling water. The residuum may be examined for silica, lime, barytes, and oxide of titanium. Muriatic acid being digested on it, then evaporated to dryness, and the residuum treated with water; will leave the silica. Caustic ammonia, poured into the solution, will separate the alumina, if any be present, and the oxide of titanium; but the former almost never occurs.Manganese is best sought for by a distinct operation. The iron must be dissolved at the heat of boiling water, in nitro-muriatic acid; and the solution, when very cold, is to be treated with small successive doses of solution of carbonate of ammonia. If the iron has been oxidized to a maximum, and if the liquor has been sufficiently acid, and diluted with water, it will retain the whole of the manganese. This process is as good as that by succinate of ammonia, which requires many precautions.The liquor is often tinged yellow by carbon, after it has ceased to contain a single trace of iron oxide. As soon as litmus paper begins to be blued by carbonate of ammonia, we should stop adding it; immediately throw the whole upon a filter, and wash continuously with cold water. What passes through is to be neutralized with muriatic acid, and concentrated by evaporation. It may contain besides manganese, some lime, or barytes. It should therefore be precipitated with hydrosulphuret of ammonia, the hydrosulphuret of manganese should be collected, dissolved in strong muriatic acid, filtered, and treated, at a boiling heat, with carbonate of potash. The precipitate, well washed and calcined, contains, in 100 parts, 72·75 parts of metallic manganese.The copper, arsenic, lead, tin, bismuth, antimony, or silver, are best separated by a stream of sulphuretted hydrogen gas passed through the solution in nitro-muriatic acid, after it is largely diluted with water. The precipitate must be cautiously roasted in a porcelain test, to burn away the large quantity of sulphur which is deposited in consequence of the conversion of the peroxide of iron into the protoxide. If nothing remains upon the test, none of these metals is present. If a residuum be obtained, it must be dissolved in nitro-muriatic acid, and subjected to examination. But, in fact, carbon, sulphur, phosphorus, silicon, and manganese, are the chief contaminators of iron.Chloride of silver affords the means of determining the proportion of carbon contained in iron, and of ascertaining the state in which that substance exists in the metal. Fusedchloride of a pale yellow colour must be employed. The operation is to be performed in close vessels, with the addition of a great deal of water, and a few drops of muriatic acid. The carbonaceous residuum is occasionally slightly acted upon. We may judge of this circumstance by the gases disengaged, as well as by the appearance of the charcoal.Ductile iron and soft steel, as well as white cast-iron which has been rendered gray by roasting, when decomposed by chloride of silver, afford a blackish-brown unmagnetic charcoal, and a plumbaginous substance perfectly similar to what is extracted from the same kinds of iron, by solution in acids. A portion of this plumbago is also converted into charcoal of a blackish brown colour, by the action of the chloride. Hence this agent does not afford the means of obtaining what has been called the poly-carburet, till it has produced a previous decomposition. But we obtain it, in this manner, purer and in greater quantity than we could by dissolving the metal in the acids. The only subject of regret is, that we possess no good criterion for judging of the progress of this analytical operation.Gray cast iron leaves, besides the polycarburet, a residuum of plumbago, and carbon which was not chemically combined with the iron; while tempered steel and white cast iron afford merely a blackish brown charcoal; but the operation is extremely slow with the latter two bodies, because a layer of charcoal forms upon the surface, which obstructs their oxidizement. For this reason the white cast iron ought to be previously changed into gray by fusion in a crucible lined with charcoal, before being subjected to the chloride of silver; if this process be employed for tempered steel, the combined carbon becomes merely a polycarburet. It would not be possible to operate upon more than 15 grains, which require from 60 to 80 times that quantity of the chloride, and a period of 15 days for the experiment.The residuum, which is separable from the silver only by mechanical means, should be dried a long time at the heat of boiling water. It contains almost always iron and silica. After its weight is ascertained, it is to be burned in a crucible of platinum till the ashes no longer change their colour, and are not attractable by the magnet. The difference between the weights of the dried and calcined residuum is the weight of the charcoal. The oxide of iron is afterwards separated from the silica by muriatic acid.In operating upon gray cast iron, we should ascertain separately the proportion of graphite or plumbago, and that of the combined charcoal. To determine the former, we dissolve a second quantity of the cast iron in nitric acid, with a little muriatic; the residuum, which is graphite, is separated from the silica and the combined carbon by the action of caustic potash. After being washed and dried, it must be weighed. The weight of the graphite obtained being deducted from the quantity of carbon resulting from the decomposition effected by the chloride of silver, the remainder is the amount of the chemically combined carbon.By employing muriatic acid, we could dissipate at once the combined carbon; but this method would be inexact, because the hydrogen disengaged would carry off a portion of the graphite.According to Karsten, Mushet’s table of the quantities of carbon contained in different steels and cast irons is altogether erroneous. It gives no explanation why, with equal proportions of charcoal, cast iron constitutes at one time a gray, soft, granular metal, and at another, a white, hard, brittle metal in lamellar facets. The incorrectness of Mushet’s statement becomes most manifest when we see the white lamellar cast iron melted in a crucible lined with charcoal, take no increase of weight, while the gray cast iron treated in the same way becomes considerably heavier.Analysis has never detected a trace of carbonunalteredor of graphite in white cast iron, if it did not proceed from small quantities of the gray mixed with it; while perfect gray cast iron affords always a much smaller quantity of carbon altered by combination, and a much greater quantity of graphite. Neither kind of cast iron, however, betrays the presence of any oxygen. Steel affords merely altered carbon, without graphite; the same thing holds true of malleable iron; while the iron obtained by fusion with 25 per cent. of scales of iron contains no carbon at all.The graphite of cast iron is obtained in scales of a metallic aspect, whereas the combined carbon is obtained in a fine powder. When the white cast iron has been roasted, and become gray, and is as malleable as the softest gray cast iron, it still affords no graphite as the latter does, though in appearance both are alike. Yet in their properties they are still essentially dissimilar.With 41⁄4per cent. of carbon, the white cast iron preserves its lamellar texture; but with less carbon, it becomes granular and of a gray colour, growing paler as the dose of carbon is diminished, while the metal after passing through an indefinite number of gradations, becomes steely cast iron, very hard steel, soft steel, and steely wrought iron.The steels of the forge and the cast steels examined by Karsten, afforded him from2·3 to 11⁄4per cent. of carbon; in the steel of cementation, (blistered steel) he never found above 13⁄4of carbon. Some wrought irons which ought to contain no charcoal, hold as much as1⁄2per cent. and they then approach to steel in nature. The softest and purest irons contain still 0·2 per cent. of carbon.The quantity of graphite which gray cast iron contains, varies, according to Karsten’s experiments, from 2·57 to 3·75 per cent.; but it contains besides, some carbon in a state of alteration. The total contents in carbon varied from 3·15 to 4·65 per cent. When the congelation of melted iron is very slow, the carbon separates, probably in consequence of its crystallizing force, so as to form a gray cast iron replete with plumbago. If the gray do not contain more charcoal than the white from which it has been formed, and if it contain the charcoal in the state of mechanical mixture, then it can have little or none in a state of combination, even much less than what some steels contain. Hence we can account for some of its peculiarities in reference to white cast iron; such as its granular texture, its moderate hardness, the length of time it requires to receive annealing colours, the modifications it experiences by contact of air at elevated temperatures, the high degree of heat requisite to fuse it, its liquidity, and finally its tendency to rust by porosity, much faster than the white cast iron.We thus see that carbon may combine with iron in several manners; that the gray cast iron is a mixture of steely iron and plumbago; that the white, rendered gray and soft by roasting, is a compound of steely iron and a carburet of iron, in which the carbon predominates; and that untempered steel is in the same predicament.For the following analyses of cast irons, we are indebted to MM. Gay Lussac and Wilson.Table.—In 100 parts.Cast iron.Iron.Carbon.Silica.Phos-phorus.Manganese.Remarks.White cast fromSiegen94·3382·6900·2300·1622·590By woodcharcoalDo.Coblentz94·6542·4410·2300·1852·490do.Do.a. d. Champ96·1332·3240·8400·703a tracedo.Do.Isère94·6872·6360·2600·2802·137do.GrayNivernais95·6732·2541·0301·043a tracedo.Do.Berry95·5732·3191·9200·188doMix. ofcoke & do.Do.a. d. Champ95·9712·1001·0600·869do.CharcoalDo.Creusot93·3852·0213·4900·604do.CokeDo.a. d. FrancheComté95·6892·8001·1600·351do.do.Do.Wales94·8421·6663·0000·492do.do.Do.Do.95·3102·5501·2000·440do.do.Do.Do.95·1502·4501·6200·780do.do.Karsten has given the following results as to carbon, in 100 parts of gray cast iron.Gray cast iron.Combinedcarbon.Freecarbon.Totalcarbon.Remarks.Siegen, from brown iron-stone0·893·714·60By wood charcoalSiegen (Widderstein), frombrown and sparry iron1·033·624·65do.Malapane, from spherosiderite0·753·153·90do.Königshütte, from brown ore0·582·573·15cokeDo. at a lower smelting heat0·952·703·65do.Cupola furnaceFig.607.represents in section, andfig.606.in plan, the famous cupola furnace for casting iron employed at the Royal Foundry in Berlin. It rests upon a foundationa, from 18 to 24 inches high, which supports the basement plate of cast iron, furnished with ledges, for binding the lower ends of the upright side plates or cylinder,e. Near the mouth there is a top-plated, made in several pieces, which serves to bind the sides at their upper end, as also to cover in the walls of the shaft. These plates are most readily secured in their places by screws and bolts. Within this iron case, at a little distance from it, the proper furnace-shafte, is built with fire-bricks, and the space between this and the iron is filled up with ashes. The sole of the hearthf, over the basement-plate, is composed of a mixture of fire-clay and quartz-sand firmly beat down to the thickness of 6 or 8 inches, with a slight slope towards the discharge-hole for running off themetal.gis theformor the tuyère (there are sometimes one on each side);hthe nose pipe; the discharge apertureiis 12 inches wide and 15 inches high; across which the sole of the hearth is rammed down. During the melting operation, this opening is filled up with fire-clay; when it is completed, a small hole merely is pierced through it at the lowest point, for running off the liquid metal. The hollow shaft should be somewhat wider at bottom than at top. Its dimensions vary with the magnitude of the foundry. When 5 feet high, its width at the level of the tuyère or blast-hole may be from 20 to 22 inches. From 250 to 300 cubic feet of air per minute are required for the working of such a cupola. For running down 100 pounds of iron, after the furnace has been brought to its heat, 48 pounds of ordinary coke are used; but with the hot blast much less will suffice. The furnace requires feeding with alternate charges of coke and iron every 8 or 10 minutes. The waste of iron, by oxidization and slag, amounts in most foundries to fully 5 per cent. For carrying off the burnt air, a chimney-hood is commonly erected over the cupola. SeeFoundry.The double-arched air or wind-furnace used in the foundries of Staffordshire for melting cast iron, has been found advantageous in saving fuel, and preventing waste by slag. It requires fire-bricks of great size and the best composition.The main central key-stone is constructed of large fire-bricks made on purpose; against that key-stone the two arches press, having their abutments at the sides against the walls. The highest point of the roof is only 8 inches above the melted metal. The sole of the hearth is composed of a layer of sand 8 inches thick, resting upon a bed of iron or of brickwork. The edge of the fire-bridge is only 3 inches above the fluid iron.In from 2 to 4 hours from 1 to 3 tons of metal may be founded in such a furnace, according to its size; but it ought always to be heated to whiteness before the iron is introduced. 100 pounds of cast iron require from 1 to 11⁄2cubic foot of coal to melt them. The waste varies from 5 to 9 per cent.I shall conclude the subject of iron with a few miscellaneous observations and statistical tables. Previously to the discovery by Mr. Cort, in 1785, of the methods of puddling and rolling or shingling iron, this country imported 70,000 tons of this metal from Russia and Sweden; an enormous quantity for the time, if we consider that the cotton and other automatic manufactures, which now consume so vast a quantity of iron, were then in their infancy; and that two years ago, the whole of our importation from these countries did not exceed 40,000 tons. From the following table of the prices of bar iron in successive years, we may infer the successive rates of improvement and economy, with slight vicissitudes.Years.Per Ton.£s.£s.182490to1001825100—1401826810—100182780—901828710—801829510—70183055—60183155—510183250—5101833510—60183460—6101835510—70I have been informed upon good authority that the total production of iron in Great Britain, in the year 1836, was almost exactlyONE MILLION OF TONS!The export of iron that year, in bars, rods, pigs, castings, wire, anchors, hoops, nails, and old iron, amounted to 189,390 tons; in unwrought steel to 3,014, and in cutlery, to 21,072; in whole to 213,478: leaving apparently for internal consumption 776,522 tons, from which however one tenth probably should be deducted for waste, in the conversion of the bar iron. Hence 700,000 tons may be taken as the approximate quantity of iron made use of in the United Kingdom, in the year 1836.The years 1835 and 1836 being those of the railway mania over the world, produced a considerable temporary rise in the price of bar iron; but as this increased demand caused the construction of a great many more smelting and refining furnaces, it has tended eventually to lower the prices; an effect also to be ascribed to the more general use of the hot blast.The relative cost of making cast iron at Merthyr Tydvil in South Wales, and at Glasgow, was as follows, eight or nine years ago.At Merthyr.s.Tons.Cwts.Qrs.£s.d.Raw mineat10per ton,3701136Coalat621600166Limestone152014Other charges091Total Cost305At Glasgow.s.d.Tons.Cwts.£s.d.Raw mine at463100163Splint Coal at255150140Limestone at03014036Coals for the engine110030Other charges110Total cost2179The cost is still nearly the same at Merthyr, but it has been greatly decreased at Glasgow.The saving of fuel by the hot-blast is said to be in fact so great, that blowing cylinders, which were adequate merely to work three furnaces at the first period, were competent to work four furnaces at the last period. The saving of materials has moreover been accompanied by an increase of one-fourth in the quantity of iron, in the same time; as a furnace which turned out only 60 tons a week with the cold blast, now turns out no less than 80 tons. That the iron so made is no worse, but probably better, when judiciously smelted, would appear from the following statement. A considerable order was not long since given to four iron-work companies in England, to supply pipes to one of the London water companies. Three of these supplied pipes made from the cold-blast iron; the fourth, it is said, supplied pipes made with the hot-blast iron. On subjecting these several sets of pipes to the requisite trials by hydraulic pressure, the last lot was found to stand the proof far better than any of the former three.—That iron was made with raw coal.I have been since told by eminent iron-masters of Merthyr, that this statement stands in need of confirmation, or is probably altogether apocryphal, and that as they find the hot blast weakens the iron, they will not adopt it.Between the cast irons made in different parts of Great Britain, there are characteristic differences. The Staffordshire metal runs remarkably fluid, and makes fine sharp castings. The Welsh is strong, less fluent, but produces bar iron of superior quality. The Derbyshire iron also forms excellent castings, and may be worked with care into very good bar iron. The Scotch iron is very valuable for casting into hollow wares, as it affords a beautiful smooth skin from the moulds, so remarkable in the castings of the Carron company, in Stirlingshire, and of the Phœnix foundry, at Glasgow. The Shropshire iron resembles the Staffordshire in its good qualities.The average quantity of fine metal obtainable from the forge-pigs at Merthyr Tydvil, from the finery furnace, is one ton for 221⁄2cwt. of cast iron, with a consumption of about 91⁄2cwt. of coal per ton.Estimate of the average cost of erecting three blast furnaces.BUILDING EXPENSES.Foundations£480Masonry of hewn grit-stones600Common bricklayers’ work1200Lining of the furnace, hearth, &c., in fire-bricks1140Fire-clay for building80Lime and sand800CAST IRON.Cast-iron pieces, such as dam-plates, tymp-plates, beams, tuyère-plates, &c., weighing about 24 tons for each furnace;—in whole1140WROUGHT IRON.For the binding-hoops, keys, &c.; 5 tons for each300COST OF LABOUR.Bricklayers, masons, and labourers in building1080VARIOUS EXPENSES.Scaffolding48Tools160Shed in front of each furnace480Terracing, cost of ground, &c.2400Total cost of erecting the furnaces9908INCIDENTAL CHARGES.Blowing machinery, and steam engine of 80-horse power6400Inclined railway for mounting the charges120Gallery for charging160Steam engine house400Chimneys, boilers, &c.480Roasting kilns480Coke kilns800Dwelling-houses for workmen800Total cost of 3 furnaces complete£19,548Estimate from the Neath-Abbey Works in S. Wales, of the cost of machines requisite for a forge and shingling-mill, capable of turning out 120 tons of bar iron per week.1.Steam-engine upon Bolton and Watt’s construction; of 40 inches diameter in the cylinder, and 8-feet stroke; with boilers, pipes, grate, bars, fire-doors, &c. &c., complete£16002.System of great-geering for transmitting the crank-motion of the engine to the mill-work, with fly-wheel, &c.10903.A system of roughing rolls, with pinions, uprights, and every thing else necessary5254.Two pairs of finisher-rolls, with all their accessories5255.Two pairs of shear-machines, at 170l.apiece3406.One pair of rolls of 10 inches diameter, for making small bar iron, with all their accessories2307.Forge hammer, including the anvil, the cam-shafts, and all the other requisites1858.A complete turning lathe200£46959.To the above must be added, spare cylinders weighing about 60 tons96010.Duplicate articles for the steam-engine?11.150 tons of cast-iron plates, to cover the floor of the mill90012.Eight tons of cast-iron pieces for a reverberatory furnace5213.Tools of malleable iron; rakes, oars, &c.2814.Castings for mounting a cupola furnace5015.Blowing-machine for the cupola8016.Pieces of iron for a small forge, with two fires, two bellows, two anvils, iron tools faced with steel, and common iron tools, &c.10017.Eight tons of cast-iron pieces, and wrought-iron pieces for 14 puddling furnaces98318.Seven tons of cast-iron pieces, and wrought iron for 4 re-heating furnaces25219.Tools for the puddlers and other workmen1520.Iron mountings for two cranes, partly made of wood50Total cost of machines, and pieces of iron£8165To the above, the cost of the steam engine house is to be added, that of another forge hammer, and incidental expenses.In Staffordshire the following estimate has been given:A steam-engine of 60-horse power2016Rolls, with the iron work of the furnaces, &c., to make 120 tons of bar iron weekly2572£4588The Neath-Abbey estimate is greater, but that company has a high character for making substantial well-finished machinery.Bar iron made entirely from ore without admixture of cinder, or vitrified oxide, is always reckoned worth 10s.a ton more than the average iron in the market, which is frequently made by smelting 25 per cent. of cinder with 75 of ore ormine, as it is called.Importation of iron in bars or unwrought, for home consumption; and amount of duty, in1836.1837.1836.1837.18,978 tons 18 cwt.13,470 tons 4 cwt.£28,450£20,065M. Virlet’s Statistical Table of the produce of Iron in Europe.Quintals.England (1827)7,098,000France (1834)2,200,000Russia (1834)1,150,000Austria (1829)850,000Sweden (1825)850,000Prussia800,000The Hartz Mountains600,000Holland and Belgium600,000Elba and Italy280,000Piedmont200,000Spain180,000Norway150,000Denmark135,000Bavaria130,000Saxony80,000Poland75,000Switzerland30,000Savoy25,000Total13,433,000(equal to about 672,000 tons.)For additional statistics of iron, seePitcoal,at the end.Bronzing of polished iron.—The barrels of fowling-pieces and rifles are occasionally bronzed and varnished, to relieve the eye of the sportsman from the glare of a polished metal, and to protect the surface from rusting. The liquid used for browning the barrels is made by mixing nitric acid of specific gravity 1·2, with its own weight of spirit of nitric ether, of alcohol, and tincture of muriate of iron; and adding to that mixture, a quantity of sulphate of copper equal in weight to the nitric acid and ethereous spirit taken together. The sulphate must be dissolved in water before being added; and the whole being diluted with about 10 times its weight of water, is to be bottled up for use. This liquid must be applied by friction with a rag to the clear barrel, which must then be rubbed with a hard brush; processes to be alternated two or three times. The barrel should be afterwards dipped in boiling water, rendered feebly alkaline with carbonate of potash or soda, well dried, burnished, and heated slightly for receiving several coats of tin-smith’s lacquer, consisting of a solution of shellac in alcohol, coloured with dragon’s blood.
German refining forge
The German refining forge.—Figs.601,602.represent one of the numerous refinery furnaces so common in the Hartz. The example is taken from theMandelholzworks, in the neighbourhood of Elbingerode.Fig.602.is an elevation of this forge.Dis the refinery hearth, provided with two pairs of bellows.Fig.601.is a vertical section, showing particularly the construction of the crucible or hearth in the refinery forgeD.Cis an overshot water-wheel, which gives an alternate impulsion to the two bellowsa bby means of the revolving shaftc, and the cams or tappetsd f e g.
D, the hearth, is lined with cast-iron plates. Through the pipel, cold water may be introduced, under the bottom platem, in order to keep down, when necessary, the temperature of the crucible, and facilitate the solidification of theloupeor bloom. An orificen,figs.601,602., called thechio(floss hole), allows the melted slag or cinder to flow off from the surface of the melted metal. The copper pipe or nose piecep,fig.600., conducts the blast of both bellows into the hearth, as shown atb x,fig.602., andDg pfig.600.
The substance subjected to this mode of refinery, is a gray carbonaceous cast iron, from the works of Rothehütte. The hearthD, being filled and heaped over with live charcoal, upon the side opposite to the tuyèrex,figs.601,602, long pigs of cast iron are laid with their ends sloping downwards, and are drawn forwards successively into the hearth by a hooked poker, so that the extremity of each may be plunged into the middle of the fire, at a distance of 6 or 8 inches from the mouth of the tuyère. The workman proceeds in this way, till he has melted enough of metal to form aloupe. The cast iron, on melting, falls down in drops to the bottom of the hearth; being covered by the fused slags, or vitreous matters more or less loaded with oxide of iron. After running them off by the orificen, he then works the cast iron by powerful stirring with an iron rake (ringard), till it is converted into a mass of a pasty consistence.
During this operation, a portion of the carbon contained in the cast iron combines with the atmospherical oxygen supplied by the bellows, and passes off in the form of carbonic oxide and carbonic acid. When the lump is coagulated sufficiently, the workman turns it over in the hearth, then increases the heat so as to melt it afresh, meanwhile exposing it all round to the blast, in order to consume the remainder of the carbon, that is, till the iron has become ductile, or refined. If one fusion should prove inadequate to this effect, two are given. Before the conclusion, the workman runs off a second stratum of vitreous slag, but at a higher level, so that some of it may remain upon the metal.
The weight of such aloupeorbloomis about 2 cwts., being the product of 2 cwts. and7⁄10of pig iron; the loss of weight is therefore about 26 per cent. 149 pounds of charcoal are consumed for every 100 pounds of bar iron obtained. The whole operation lasts about 5 hours. The bellows are stopped as soon as the bloom is ready; this is immediately transferred to a forge hammer, such as is representedfig.605.; the cast-iron head of which weighs 8 or 9 cwts. The bloom is greatly condensed thereby, and discharges a considerable quantity of semi-fluid cinder. The lump is then divided by the hammerand a chisel into 4 or 6 pieces, which are re-heated, one after another, in the same refinery fire, in order to be forged into bars, whilst another pig of cast iron is laid in its place, to prepare for the formation of a new bloom. The above process is called by the Germansklump-frischen, or lump-refining. It differs from thedurch-brech-frischen, because in the latter, the lump is not turned over in mass, but is broken, and exposed in separate pieces successively to the refining power of the blast near the tuyère. The French call thisaffinage par portions; it is much lighter work than the other.
The quality of the iron is tried in various ways; as first, by raising a bar by one end, with the two hands over one’s head, and bringing it forcibly down to strike across a narrow anvil at its centre of percussion, or one-third from the other extremity of the bar; after which it may be bent backwards and forwards at the place of percussion several times; 2. a heavy bar may be laid obliquely over props near its end, and struck strongly with a hammer with a narrow pane, so as to curve it in opposite directions; or while heated to redness, they may be kneed backwards and forwards at the same spot, on the edge of the anvil. This is a severe trial, which the hoop L, Swedish iron, bears surprisingly, emitting as it is hammered, a phosphoric odour, peculiar to it and to the bar iron of Ulverstone, which also resembles it, in furnishing a good steel. The forging of a horseshoe is reckoned a good criterion of the quality of iron. Its freedom from flaws is detected by the above modes; and its linear strength may be determined by suspending a scale to the lower end of a hard-drawn wire, of a given size, and adding weights till the wire breaks. The treatises of Barlow and Tredgold may be consulted with advantage on the methods of proving the strength of different kinds of iron, in a great variety of circumstances.
Steel of cementation, or blistered steel and cast steel, are treated under the articleSteel. But since in the conversion of cast iron into wrought iron, by a very slight difference in the manipulations, a species of steel may be produced callednatural steel, I shall describe this process here.
Königdhütte works
Fig.603.is a view of the celebrated steel iron works, called Königshütte (king’s-forge), in Upper Silesia, being one of the best arranged in Germany, for smelting iron ore by means of coke. The front shown here is about 400 English feet long.a aare two blast furnaces. A third blast furnace, all like the English, is situated to the left of one of the towersb.b bare the charging towers, into which the ore is raised by machinery from the level of the store-housesl l, up to the mouth of the furnacesa a;c cpoint to the positions of the boilers of the two steam engines, which drive two cylinder bellows atf.n n n nare arched cellars placed below the store-housesl l, for containing materials and tools necessary for the establishment.
Forge
Figs.599.,604., are vertical sections of the forge of Königshütte, for making natural steel;fig.599.being drawn in the lineA Bof the plan,fig.600.ais the bottom of the hearth, consisting of a fire-proof gritstone;bis a space filled with small charcoal, damped with water, under which, atn, infig.604., is a bed of well rammed clay;dis a plate of cast iron, which lines the side of the hearth called rückstein (backstone) in German, and corrupted by the French intorustine;fis the plate of the counter-blast;gthe plate of the side of the tuyère: behind, upon the faced, the fire-place or hearth is only 51⁄2inches deep; in front as well as upon the lateral faces, it is 18 inches deep. By means of a mound made of dry charcoal, the posterior faced, is raised to the height of the facef.i,fig.600., is the floss-hole, by which the slags are run off from the hearth during the working, and through which, by removing some bricks, the lump of steel is taken out when finished.
k l mare pieces of cast iron, for confining the fire in front, that is towards the side where the workman stands;ois the level of the floor of the works;pa copper tuyère; it is situated 41⁄2inches above the bottoma, slopes 5 degrees towards it, and advances 4 inches into the hearth or fire-place, where it presents an orifice, one half inch in horizontal length, and one inch up and down;qthe nose pipes of two bellows, like those representedinfig.602., and underSilver; the round orifice of each of them within the tuyère being one inch in diameter.ris the lintel or top arch of the tuyère, beneath which is seen the cross section of the pig of cast iron under operation.
For the production of natural steel, a white cast iron is preferred, which contains little carbon, which does not flow thin, and which being cementedover or above the wind, falls down at once through the blast to the bottom of the hearth in the state of steel. With this view, a very flat fire is used; and should the metal run too fluid, some malleable lumps are introduced to give the mass a thicker pasty consistence.
If the natural steel be supposed to contain too little carbon, which is a very rare case, the metal bath covered with its cinder slag, is diligently stirred with a wooden pole, or it may receive a little of the more highly carburetted iron. If it contains the right dose of carbon, the earthy and other foreign matters are made progressively to sweat out, into the supernatant slag. When the mass is found by the trial of a sample to be completely converted, and has acquired the requisite stiffness, it is lifted out of the furnace, by the opening in front, subjected to the forge hammer, and drawn into bars. In Sweden, the cast-iron pigs are heated to a cherry-red, and in this state broken to pieces under the hammer, before they are exposed in the steel furnace. These natural steels are much employed on the Continent in making agricultural implements, on account of their cheapness. The natural steel of Styria is regarded as a very good article.
Wootz is a natural steel prepared from a black ore of iron in Hindostan, by a process analogous to that of the Catalan hearth, but still simpler. It seems to contain a minute portion of the combustible bases of alumina and silica, to which its peculiar hardness when tempered, may possibly be ascribed. It is remarkable for the property of assuming a damask surface, by the action of dilute sulphuric acid, after it has been forged and polished. SeeDamascusandSteel.
Forge-hammer
Fig.605.is the German forge-hammer; to the left of 1, is the axis of the rotatory cam, 2, 3, consisting of 8 sides, each formed of a strong broad bar of cast iron, which are joined together to make the octagon wheel. 4, 5, 6, are cast-iron binding rings or hoops; made fast by wooden wedges.b,b, are standards of the frame worke,l,m, in which the helve of the forge hammer has its fulcrum nearu.h, the sole part of the frame. Another cast-iron base or sole is seen atm.nis a strong stay, to strengthen the frame-work. Atrtwo parallel hammers are placed, with cast-iron heads and wooden helves.sis the anvil, a very massive piece of cast iron.tis the end of a vibrating beam, for throwing back the hammer from it forcibly by recoil.x yis the outline of the water-wheel which drives the whole. The cams or tappets are shown mounted upon the wheel 6,g, 6.
Analysis of Irons.—Oxidized substances cannot exist in metallic iron, and the foreign substances it does contain are present in such small quantities, that it is somewhat difficult to determine their amount. The most intricate point is, the proportion of carbon. The free carbon, which is present only in gray cast iron, may, indeed, be determined nearly, for most of it remains after solution of the metal in acids. The combined charcoal, however, changes by the action of muriatic acid into gas and oil; sulphuric acid also occasions a great loss of carbon, and nitric acid dissipates it almost entirely. Either nitre or chloride of silver may be employed to ascertain the amount of carbon; but when the iron contains chromium and much phosphorus, the determination of the carbon is attended with many difficulties.
The quantity of sulphur is always so small, that it can scarcely be ascertained by the weight of the precipitate of sulphate of barytes from the solution of the iron in nitro-muriatic acid. The iron should be dissolved in muriatic acid; and the hydrogen, as it escapes charged with the sulphur, should be passed through an acidulous solution of acetate of lead. The weight of the precipitated sulphuret shows the amount of sulphur, allowing 13·45 of the latter for 100 of the former. In this experiment the metal should be slowly acted upon by the acid. Cast iron takes from 10 to 15 days to dissolve, steel from 8 to 10, and malleable iron 4 days. The residuum of a black colour does not contain a trace of sulphur.
Phosphorus and chromium are determined in the following way. The iron must be dissolved in nitro-muriatic acid, to oxygenate those two bodies. The solution must be evaporated cautiously to dryness in porcelain capsules, and the saline residuum heatedto redness. A little chloride of iron is volatilized, and the remainder resembles the red-brown oxide. This must be mixed with thrice its weight of carbonate of potash, and fused in a platinum crucible; the quantity of iron being from 40 to 50 grains at most.
The mixture after being acted upon by boiling water, is to be left to settle, to allow the oxide to be deposited, for it is so fine as to pass through a filter. If the iron contained manganese, this would be foundat firstin the alkaline solution; but manganese spontaneously separates by exposure to the air. The alkaline liquor must be supersaturated with muriatic acid, and evaporated to dryness. The liquor acidulated, and deprived of its silica by filtration, is to be supersaturated with ammonia; when the alumina will precipitate in the state of a subphosphate. When the liquor is now supersaturated with acetic acid, and then treated with acetate of lead, a precipitate of phosphate of lead almost always falls. There is hardly a bit of iron to be found which does not contain phosphorus. The slightest trace of chrome is detected by the yellow colour of the lead precipitate; if this be white there is none of the colouring metal present.
100 parts of the precipitated phosphate of lead contain, after calcination, 19·4 parts of phosphoric acid. The precipitate should be previously washed with acetic acid, and then with water. These 19·4 parts contain 8·525 parts of phosphorus.
Cast iron sometimes contains calcium and barium, which may be detected by their well-known reagents, oxalate of ammonia, and sulphuric acid. In malleable iron they are seldom or never present.
The charcoal found in the residuum of the nitro-muriatic solution is to be burned away under a muffle. The solution itself contains along with the oxide of iron, protoxide of manganese, and other oxides, as well as the earths, and the phosphoric and arsenic acids. Tartaric acid is to be added to it, till no precipitate be formed by supersaturation with caustic ammonia. The ammoniacal liquor must be treated with hydrosulphuret of ammonia as long as it is clouded, then thrown upon a filter. The precipitate is usually very voluminous, and must be well washed. The liquor which passes through is to be saturated with muriatic acid, to decompose all the sulphurets.
The solution still contains all the earths and the oxide of titanium, besides the phosphoric acid. It is to be evaporated to dryness, whereby the ammonia is expelled, and the carbonaceous residuum must be burned under a muffle. If the iron contains much phosphorus, the ashes are strongly agglutinated. They are to be fused as already described along with carbonate of potash, and the mass is to be treated with boiling water. The residuum may be examined for silica, lime, barytes, and oxide of titanium. Muriatic acid being digested on it, then evaporated to dryness, and the residuum treated with water; will leave the silica. Caustic ammonia, poured into the solution, will separate the alumina, if any be present, and the oxide of titanium; but the former almost never occurs.
Manganese is best sought for by a distinct operation. The iron must be dissolved at the heat of boiling water, in nitro-muriatic acid; and the solution, when very cold, is to be treated with small successive doses of solution of carbonate of ammonia. If the iron has been oxidized to a maximum, and if the liquor has been sufficiently acid, and diluted with water, it will retain the whole of the manganese. This process is as good as that by succinate of ammonia, which requires many precautions.
The liquor is often tinged yellow by carbon, after it has ceased to contain a single trace of iron oxide. As soon as litmus paper begins to be blued by carbonate of ammonia, we should stop adding it; immediately throw the whole upon a filter, and wash continuously with cold water. What passes through is to be neutralized with muriatic acid, and concentrated by evaporation. It may contain besides manganese, some lime, or barytes. It should therefore be precipitated with hydrosulphuret of ammonia, the hydrosulphuret of manganese should be collected, dissolved in strong muriatic acid, filtered, and treated, at a boiling heat, with carbonate of potash. The precipitate, well washed and calcined, contains, in 100 parts, 72·75 parts of metallic manganese.
The copper, arsenic, lead, tin, bismuth, antimony, or silver, are best separated by a stream of sulphuretted hydrogen gas passed through the solution in nitro-muriatic acid, after it is largely diluted with water. The precipitate must be cautiously roasted in a porcelain test, to burn away the large quantity of sulphur which is deposited in consequence of the conversion of the peroxide of iron into the protoxide. If nothing remains upon the test, none of these metals is present. If a residuum be obtained, it must be dissolved in nitro-muriatic acid, and subjected to examination. But, in fact, carbon, sulphur, phosphorus, silicon, and manganese, are the chief contaminators of iron.
Chloride of silver affords the means of determining the proportion of carbon contained in iron, and of ascertaining the state in which that substance exists in the metal. Fusedchloride of a pale yellow colour must be employed. The operation is to be performed in close vessels, with the addition of a great deal of water, and a few drops of muriatic acid. The carbonaceous residuum is occasionally slightly acted upon. We may judge of this circumstance by the gases disengaged, as well as by the appearance of the charcoal.
Ductile iron and soft steel, as well as white cast-iron which has been rendered gray by roasting, when decomposed by chloride of silver, afford a blackish-brown unmagnetic charcoal, and a plumbaginous substance perfectly similar to what is extracted from the same kinds of iron, by solution in acids. A portion of this plumbago is also converted into charcoal of a blackish brown colour, by the action of the chloride. Hence this agent does not afford the means of obtaining what has been called the poly-carburet, till it has produced a previous decomposition. But we obtain it, in this manner, purer and in greater quantity than we could by dissolving the metal in the acids. The only subject of regret is, that we possess no good criterion for judging of the progress of this analytical operation.
Gray cast iron leaves, besides the polycarburet, a residuum of plumbago, and carbon which was not chemically combined with the iron; while tempered steel and white cast iron afford merely a blackish brown charcoal; but the operation is extremely slow with the latter two bodies, because a layer of charcoal forms upon the surface, which obstructs their oxidizement. For this reason the white cast iron ought to be previously changed into gray by fusion in a crucible lined with charcoal, before being subjected to the chloride of silver; if this process be employed for tempered steel, the combined carbon becomes merely a polycarburet. It would not be possible to operate upon more than 15 grains, which require from 60 to 80 times that quantity of the chloride, and a period of 15 days for the experiment.
The residuum, which is separable from the silver only by mechanical means, should be dried a long time at the heat of boiling water. It contains almost always iron and silica. After its weight is ascertained, it is to be burned in a crucible of platinum till the ashes no longer change their colour, and are not attractable by the magnet. The difference between the weights of the dried and calcined residuum is the weight of the charcoal. The oxide of iron is afterwards separated from the silica by muriatic acid.
In operating upon gray cast iron, we should ascertain separately the proportion of graphite or plumbago, and that of the combined charcoal. To determine the former, we dissolve a second quantity of the cast iron in nitric acid, with a little muriatic; the residuum, which is graphite, is separated from the silica and the combined carbon by the action of caustic potash. After being washed and dried, it must be weighed. The weight of the graphite obtained being deducted from the quantity of carbon resulting from the decomposition effected by the chloride of silver, the remainder is the amount of the chemically combined carbon.
By employing muriatic acid, we could dissipate at once the combined carbon; but this method would be inexact, because the hydrogen disengaged would carry off a portion of the graphite.
According to Karsten, Mushet’s table of the quantities of carbon contained in different steels and cast irons is altogether erroneous. It gives no explanation why, with equal proportions of charcoal, cast iron constitutes at one time a gray, soft, granular metal, and at another, a white, hard, brittle metal in lamellar facets. The incorrectness of Mushet’s statement becomes most manifest when we see the white lamellar cast iron melted in a crucible lined with charcoal, take no increase of weight, while the gray cast iron treated in the same way becomes considerably heavier.
Analysis has never detected a trace of carbonunalteredor of graphite in white cast iron, if it did not proceed from small quantities of the gray mixed with it; while perfect gray cast iron affords always a much smaller quantity of carbon altered by combination, and a much greater quantity of graphite. Neither kind of cast iron, however, betrays the presence of any oxygen. Steel affords merely altered carbon, without graphite; the same thing holds true of malleable iron; while the iron obtained by fusion with 25 per cent. of scales of iron contains no carbon at all.
The graphite of cast iron is obtained in scales of a metallic aspect, whereas the combined carbon is obtained in a fine powder. When the white cast iron has been roasted, and become gray, and is as malleable as the softest gray cast iron, it still affords no graphite as the latter does, though in appearance both are alike. Yet in their properties they are still essentially dissimilar.
With 41⁄4per cent. of carbon, the white cast iron preserves its lamellar texture; but with less carbon, it becomes granular and of a gray colour, growing paler as the dose of carbon is diminished, while the metal after passing through an indefinite number of gradations, becomes steely cast iron, very hard steel, soft steel, and steely wrought iron.
The steels of the forge and the cast steels examined by Karsten, afforded him from2·3 to 11⁄4per cent. of carbon; in the steel of cementation, (blistered steel) he never found above 13⁄4of carbon. Some wrought irons which ought to contain no charcoal, hold as much as1⁄2per cent. and they then approach to steel in nature. The softest and purest irons contain still 0·2 per cent. of carbon.
The quantity of graphite which gray cast iron contains, varies, according to Karsten’s experiments, from 2·57 to 3·75 per cent.; but it contains besides, some carbon in a state of alteration. The total contents in carbon varied from 3·15 to 4·65 per cent. When the congelation of melted iron is very slow, the carbon separates, probably in consequence of its crystallizing force, so as to form a gray cast iron replete with plumbago. If the gray do not contain more charcoal than the white from which it has been formed, and if it contain the charcoal in the state of mechanical mixture, then it can have little or none in a state of combination, even much less than what some steels contain. Hence we can account for some of its peculiarities in reference to white cast iron; such as its granular texture, its moderate hardness, the length of time it requires to receive annealing colours, the modifications it experiences by contact of air at elevated temperatures, the high degree of heat requisite to fuse it, its liquidity, and finally its tendency to rust by porosity, much faster than the white cast iron.
We thus see that carbon may combine with iron in several manners; that the gray cast iron is a mixture of steely iron and plumbago; that the white, rendered gray and soft by roasting, is a compound of steely iron and a carburet of iron, in which the carbon predominates; and that untempered steel is in the same predicament.
For the following analyses of cast irons, we are indebted to MM. Gay Lussac and Wilson.
Table.—In 100 parts.
Karsten has given the following results as to carbon, in 100 parts of gray cast iron.
Cupola furnace
Fig.607.represents in section, andfig.606.in plan, the famous cupola furnace for casting iron employed at the Royal Foundry in Berlin. It rests upon a foundationa, from 18 to 24 inches high, which supports the basement plate of cast iron, furnished with ledges, for binding the lower ends of the upright side plates or cylinder,e. Near the mouth there is a top-plated, made in several pieces, which serves to bind the sides at their upper end, as also to cover in the walls of the shaft. These plates are most readily secured in their places by screws and bolts. Within this iron case, at a little distance from it, the proper furnace-shafte, is built with fire-bricks, and the space between this and the iron is filled up with ashes. The sole of the hearthf, over the basement-plate, is composed of a mixture of fire-clay and quartz-sand firmly beat down to the thickness of 6 or 8 inches, with a slight slope towards the discharge-hole for running off themetal.gis theformor the tuyère (there are sometimes one on each side);hthe nose pipe; the discharge apertureiis 12 inches wide and 15 inches high; across which the sole of the hearth is rammed down. During the melting operation, this opening is filled up with fire-clay; when it is completed, a small hole merely is pierced through it at the lowest point, for running off the liquid metal. The hollow shaft should be somewhat wider at bottom than at top. Its dimensions vary with the magnitude of the foundry. When 5 feet high, its width at the level of the tuyère or blast-hole may be from 20 to 22 inches. From 250 to 300 cubic feet of air per minute are required for the working of such a cupola. For running down 100 pounds of iron, after the furnace has been brought to its heat, 48 pounds of ordinary coke are used; but with the hot blast much less will suffice. The furnace requires feeding with alternate charges of coke and iron every 8 or 10 minutes. The waste of iron, by oxidization and slag, amounts in most foundries to fully 5 per cent. For carrying off the burnt air, a chimney-hood is commonly erected over the cupola. SeeFoundry.
The double-arched air or wind-furnace used in the foundries of Staffordshire for melting cast iron, has been found advantageous in saving fuel, and preventing waste by slag. It requires fire-bricks of great size and the best composition.
The main central key-stone is constructed of large fire-bricks made on purpose; against that key-stone the two arches press, having their abutments at the sides against the walls. The highest point of the roof is only 8 inches above the melted metal. The sole of the hearth is composed of a layer of sand 8 inches thick, resting upon a bed of iron or of brickwork. The edge of the fire-bridge is only 3 inches above the fluid iron.
In from 2 to 4 hours from 1 to 3 tons of metal may be founded in such a furnace, according to its size; but it ought always to be heated to whiteness before the iron is introduced. 100 pounds of cast iron require from 1 to 11⁄2cubic foot of coal to melt them. The waste varies from 5 to 9 per cent.
I shall conclude the subject of iron with a few miscellaneous observations and statistical tables. Previously to the discovery by Mr. Cort, in 1785, of the methods of puddling and rolling or shingling iron, this country imported 70,000 tons of this metal from Russia and Sweden; an enormous quantity for the time, if we consider that the cotton and other automatic manufactures, which now consume so vast a quantity of iron, were then in their infancy; and that two years ago, the whole of our importation from these countries did not exceed 40,000 tons. From the following table of the prices of bar iron in successive years, we may infer the successive rates of improvement and economy, with slight vicissitudes.
I have been informed upon good authority that the total production of iron in Great Britain, in the year 1836, was almost exactlyONE MILLION OF TONS!
The export of iron that year, in bars, rods, pigs, castings, wire, anchors, hoops, nails, and old iron, amounted to 189,390 tons; in unwrought steel to 3,014, and in cutlery, to 21,072; in whole to 213,478: leaving apparently for internal consumption 776,522 tons, from which however one tenth probably should be deducted for waste, in the conversion of the bar iron. Hence 700,000 tons may be taken as the approximate quantity of iron made use of in the United Kingdom, in the year 1836.
The years 1835 and 1836 being those of the railway mania over the world, produced a considerable temporary rise in the price of bar iron; but as this increased demand caused the construction of a great many more smelting and refining furnaces, it has tended eventually to lower the prices; an effect also to be ascribed to the more general use of the hot blast.
The relative cost of making cast iron at Merthyr Tydvil in South Wales, and at Glasgow, was as follows, eight or nine years ago.
The cost is still nearly the same at Merthyr, but it has been greatly decreased at Glasgow.
The saving of fuel by the hot-blast is said to be in fact so great, that blowing cylinders, which were adequate merely to work three furnaces at the first period, were competent to work four furnaces at the last period. The saving of materials has moreover been accompanied by an increase of one-fourth in the quantity of iron, in the same time; as a furnace which turned out only 60 tons a week with the cold blast, now turns out no less than 80 tons. That the iron so made is no worse, but probably better, when judiciously smelted, would appear from the following statement. A considerable order was not long since given to four iron-work companies in England, to supply pipes to one of the London water companies. Three of these supplied pipes made from the cold-blast iron; the fourth, it is said, supplied pipes made with the hot-blast iron. On subjecting these several sets of pipes to the requisite trials by hydraulic pressure, the last lot was found to stand the proof far better than any of the former three.—That iron was made with raw coal.
I have been since told by eminent iron-masters of Merthyr, that this statement stands in need of confirmation, or is probably altogether apocryphal, and that as they find the hot blast weakens the iron, they will not adopt it.
Between the cast irons made in different parts of Great Britain, there are characteristic differences. The Staffordshire metal runs remarkably fluid, and makes fine sharp castings. The Welsh is strong, less fluent, but produces bar iron of superior quality. The Derbyshire iron also forms excellent castings, and may be worked with care into very good bar iron. The Scotch iron is very valuable for casting into hollow wares, as it affords a beautiful smooth skin from the moulds, so remarkable in the castings of the Carron company, in Stirlingshire, and of the Phœnix foundry, at Glasgow. The Shropshire iron resembles the Staffordshire in its good qualities.
The average quantity of fine metal obtainable from the forge-pigs at Merthyr Tydvil, from the finery furnace, is one ton for 221⁄2cwt. of cast iron, with a consumption of about 91⁄2cwt. of coal per ton.
Estimate of the average cost of erecting three blast furnaces.
Estimate from the Neath-Abbey Works in S. Wales, of the cost of machines requisite for a forge and shingling-mill, capable of turning out 120 tons of bar iron per week.
In Staffordshire the following estimate has been given:
The Neath-Abbey estimate is greater, but that company has a high character for making substantial well-finished machinery.
Bar iron made entirely from ore without admixture of cinder, or vitrified oxide, is always reckoned worth 10s.a ton more than the average iron in the market, which is frequently made by smelting 25 per cent. of cinder with 75 of ore ormine, as it is called.
Importation of iron in bars or unwrought, for home consumption; and amount of duty, in
M. Virlet’s Statistical Table of the produce of Iron in Europe.
For additional statistics of iron, seePitcoal,at the end.
Bronzing of polished iron.—The barrels of fowling-pieces and rifles are occasionally bronzed and varnished, to relieve the eye of the sportsman from the glare of a polished metal, and to protect the surface from rusting. The liquid used for browning the barrels is made by mixing nitric acid of specific gravity 1·2, with its own weight of spirit of nitric ether, of alcohol, and tincture of muriate of iron; and adding to that mixture, a quantity of sulphate of copper equal in weight to the nitric acid and ethereous spirit taken together. The sulphate must be dissolved in water before being added; and the whole being diluted with about 10 times its weight of water, is to be bottled up for use. This liquid must be applied by friction with a rag to the clear barrel, which must then be rubbed with a hard brush; processes to be alternated two or three times. The barrel should be afterwards dipped in boiling water, rendered feebly alkaline with carbonate of potash or soda, well dried, burnished, and heated slightly for receiving several coats of tin-smith’s lacquer, consisting of a solution of shellac in alcohol, coloured with dragon’s blood.