much larger castings, such as the propellers of screw steamers, the method is often adopted, especially in combination with " case hardening" or conversion of the outermost layer of all into steel by a subsequent process (vide infra). Although the process was described in 1722 by Réaumur, patents for it have been subsequently taken out, e.g., by Lucas in 1804 and Brown and Lennox some half century later. In order to carry out the conversion of cast iron into malleable iron in this way, the articles to be treated are packed in cast or wrought iron chests in iron oxide powder; the chests are then stacked one above another in a kind of reverberatory furnace, and gradually heated up to a red heat, which is maintained for the requisite time, after which they are annealed by slow cooling; with charcoal pig pretty free from silicon, sulphur, and phosphorus, and with fuel in the furnace free from any large quantity of sulphur, a soft but tough, tenacious, and readily malleable skin is produced; if, however, the heating is continued for some time after the whole of the carbon originally present has been removed, the articles become brittle, owing to the formation of oxide of iron disseminated through the mass, just as copper, bronze, and analogous substances are rendered brittle through a similar cause. This circumstance, together with the known character of the chemical actions of carbon dioxide on iron and carbon at a red heat, indicates the nature of the processes taking place during the decarbonization; the ferric oxide and the heated air in contact with it first oxidize the carbon in the outermost film to carbon dioxide; this then passes inwards by the process of "occlusion" (gradual solution of gases in solids), and reacts upon the carbon of the next layers in accordance with the equation CO2 + C = 2CO, one another in certain details: they may, however, be classified under two chief heads, viz., those in which the iron is more or less completely fluxed by heat in contact with the solid fuel used, by means of a blast of air on much the same principle as an ordinary smith's forge, and those in which the treatment of the iron is effected in a chamber separate from that in which the fuel is burnt when solid fuel is employed, or in which gaseous fuel is used in the first instance. Charcoal Finery.-Prior to the invention of puddling, the conversion of cast-into wrought iron was uniformly effected by a process which, though differing markedly in certain details in different countries, yet in all cases essentially consisted of exposure to an oxidizing atmosphere and agitation until practically all the carbon and silicon, etc., is removed. As the iron becomes purer its fusibility lessens, so that ultimately it collects into pasty semi-solid masses which when united together form a "ball," which is taken out and forged into a "bloom.” the carbon oxide thus formed first becoming dissolved in the iron, and subsequently when the iron is saturated therewith gradually diffusing outwards, becoming convert-propriately termed the Lancashire hearth, this differs slightly ed into carbon dioxide as soon as it comes in contact with either the ferric oxide of the packing or the partially oxidized iron of the outer film, which, when free from carbon, reacts on the carbon dioxide, thus Of the different kinds of finery in use some fourteen principal modifications have been enumerated by Tünner. divisible into the three classes of "Einmalschmelzerei" (single fusion process), "Wallonschmiede" (Walloon process), and "Aufbrechschmiede" or "Deutscheschmiede" (breaking up process, or German process). Of these most have been virtually out of date for years past; a few, however, are still in use, but like the puddling process are rapidly giving way to modern soft steel or ingot iron making processes, the use of malleable weld iron being on the whole rapidly decreasing, at least relatively to that of "steel" and fused iron. A single illustration of one of these processes (termed by Tünner the English Walloon process) will suffice: as carried out in Sweden in what is somewhat inapfrom the method as used in South Wales, the chief difference being that in the former case the pigs are melted down and the whole operation finished in the same furnace (saving that the rough blooms produced are reheated in a second furnace for further hammering), whilst in the latter the pig is melted in a separate hearth, in fact is passed through a sort of "running out" fire or refinery before it "brasqued" or lined with charcoal powder moistened and reaches the finery proper; the bed of this latter is rammed in, and so forcibly compressed. The tuyeres are directed downwards, so that the blast impinges more or less directly upon the fused metal. The effect of the blast upon the metal broken up and stirred amongst charcoal heaped over it is gradually to cause the formation of iron oxide and silica, with oxidation of the carbon and changed into two separate substances, viz., a pasty mass of other impurities, so that finally the metal used becomes spongy residual purified metal, and a bath of fluid cinder mainly composed of ferrous silicate; the former is ultimately removed as a ball and hammered into rough slabs, and finally after reheating forged into bars, etc.; in the production of "charcoal plates" (for tinplate making), the first rough forged slabs are cut into pieces termed termed a "hollow fire" on a mass of the same kind of 'stamps," which are then reheated in a reheating furnace metal forged into a shovel shape, the blades of the shovel and the mass of stamps piled on it being then forged into a slab which is virtually a much bigger blade; this is doubled upon itself to ensure equality of the two sides, welded, cut off from the shank, and rolled into bars and plates, etc. Sweden the metal is usually forged by hammering throughout and not rolled at all. For inferior iron plates this process has been used with the substitution of coke for charcoal and of less pure pig for the better qualities used for the finer plates; but puddled iron has for the most part long superseded that made in a coke-fired finery for general purposes. The following anaylses illustrate the character of Swedish irons produced in the charcoal finery : 46 In the outermost layers, accordingly, there is always a tendency to the formation of iron oxide in virtue of this reaction, and simultaneously a tendency to the reduction of this oxide by the agency of the carbon oxide which is being formed in the interior layers and travelling outwards; as long as this latter action keeps the former in check, the accumulation of iron oxide in the outer layers does not take place to such an extent as to deteriorate materially the tenacity of the malleable iron skin; but, when the carbon of the core has been so completely removed that the supply of carbon oxide from the interior almost ceases, the formation and accumulation of iron oxide in the outer layers goes on, rendering them more or less brittle. In the inner layers the removal of carbon by the penetration of the dissolved carbon dioxide and its reaction on the carbon is continually progressing, the decarbonization gradually creeping inwards, as it were, until finally the innermost central part becomes decarbonized also. The non-removal of silicon, sulphur, and phosphorus during the process is due simply to the fact that these elements are not acted upon by the occluded carbon dioxide as the carbon is, and consequently not being oxidized cannot be eliminated. The iron oxide used becomes partially reduced during the operation; in order to make it fit for use over again, it is moistened with a solution of sal-ammoniac and exposed to the air, in order to rust and so reoxidize it. The whole process is in effect an exact inversion of the chemical changes taking place during the manufacture of blister steel from malleable iron by the process of cementation (see 232), and differs from the ordinary puddling method for the purification of cast iron in this salient respect that in the latter case the formation of oxide of iron by the effect of heated air, and its direct addition in the form of "fettling," give rise to the production of a fluxed mass, in which is incorporated a notably larger amount of oxide of iron, which reacts on the carbon, sulphur, silicon, and phosphorus, oxidizing them Analyst... and converting them into products which are either gaseous and escape (carbon and sulphur dioxides, or are non-metallic and fusible, and hence separate from the iron as a fused slag or cinder. Brand. Iron In Carbon (total)... 23. Refining, Fining, and Puddling of Cast Iron.In order to convert large masses of pig iron into Manganese. wrought iron, a large variety of methods have been and to some extent are still employed, differing from Refinery. The term "refining," although in strictness applicable to all methods by which impure iron is purified, is in practice restricted to one particular operation practised as a preliminary stage in the puddling process, viz., melting pig iron on a hearth such as that shown in figs 30, 31 (taken from Bolley's Technology), on which the fuel (coke or charcoal) is piled, the combustion being urged by a blast of air, which also partially oxidizes the iron, both as it melts and subsequent FIG. 30.-Refinery-Elevation. ly; the molten mass when the operation is complete is either run out into moulds, chilled by throwing water on to it (the solidified upper surface being removed as a rough cake), or tapped into a separate similar open furnace or into a puddling furnace, in which the conversion into malleable iron is finished." The effect of this first treatment is materially to reduce the percentage of total carbon, and almost entirely to remove the silicon present, the latter forming a slag with the oxidized iron together with more or less of FIG. 31.-Plan of fig. 30. the ash of the fuel; when the metal from the refinery is cast, it solidifies as "white iron" destitute or nearly so of graphitoidal carbon. Sometimes the removal of carbon and silicon is accelerated by adding to the fluxing pig mill scales or other tolerably pure readily fusible iron oxide; lime is also sometimes added, with the intention of either partially removing sulphur present in the pig or preventing its further absorption from the fuel. A modification of the refinery has been introduced by Parry specially applicable to the direct treatment of the molten metal from the blast furnace; the molten pig being tapped straight into the refinery hearth, a jet of superheated steam is made to play upon its surface (the temperature being maintained by an air blast in addition); the oxidation of the iron is then rapidly effected, with evolution of hydrogen from the decomposition of the steam; in this way a notable saving in fuel is said to be effected. In South Wales a coke refinery has been largely employed to partially purify the iron subsequently finished in an ordinary puddling furnace; this refinery or running out fire is a rectangular hearth with two or more tuyeres delivering blast slanting-wise downwards upon the surface of the fused metal, which is simply introduced as pig piled up on the hearth alternately with layers of coke, melted down, and kept fused with the blast playing on its surface for some time. Owing to the partial removal of silicon, etc., in this previous treatment, the subsequent puddling develops less cinder, and accordingly is sometimes distinguished as dry puddling; whilst puddling proper (consisting of the fusion in a more or less modified Cort's furnace of the pig, and its complete treatment therein at one operation) is spoken of as pigboiling, the term "boiling" being derived from the rapid effervescent evolution of carbon oxide from the fused mass at a certain stage, when the iron oxide reacts vigorously on the dissolved carbon. The following analyses by Rocholl illustrate the charges produced during the refining of Bowling cold blast pig: Iron Carbon (total)......... 94-461 95-324 95.240 95.521 95.768 96-013 3.686 3.510 3.707 3.644 3.544 3-342 Silicon 1.255 0.575 0:478 0-273 0-154 0-130 Sulphur... 0.033 0:034 0.038 0.032 0-025 0-025 Phosphorus. 0-565 0:557 0.537 0.530 0.509 0-490 100-000 100000 100000 100-000 100-000 100-000 Puddling.-In the "dry puddling" process (which, as compared with the "pigboiling process, is so little used that the generic term "puddling" is much more frequently employed to indicate the latter operation than the former), the iron which has passed through the refinery is placed on the bed of a reverberatory furnace together with a certain amount of mill cinder or other fettling, and melted down in a somewhat oxidizing atmosphere, the result of which is the formation of a fluxed mixture of pig iron and iron oxide; this is well stirred, whilst the flame keeps it fluid, so that the iron oxide gradually reacts on the carbon, silicon, phosphorus, and sulphur present, oxidizing them and converting them either into gases which escape, or oxides which by uniting with ferrous oxide form a readily fusible slag. As this process goes on, just as in the charcoal finery, the consistency of the mass alters, the whole thickening firstly to a porridge-like substance and finally to a mixture of pasty solid lumps partly of coherent spongy malleable iron and partly of fluxed slag, mechanically adherent thereto, and dripping from the spongy mass when this is lifted. When the proper consistency is reached the iron is said to " come to nature;" the spongy mass is then raked together with the iron rabble or stirring rod employed, and formed into a rough loosely coherent "ball," which is worked as described in 25. The use of the refinery conjoined with the dry puddling process has almost ceased in England; certain brands of Yorkshire iron, however, of high reputation, are still prepared in this way. The superiority of the metal is largely due to the carefulness with which the plates and bars finally prepared are made; the puddled bars are broken into fragments, and each piece carefully examined as to its fracture, the crystalline portions being worked up separately from the fibroid portions which yield the better plates; by piling, reheating, and rolling, etc., the fragments are worked into bars, which are again piled and rolled into plates. Cold blast pig is preferred for certain of these brands. In the "pigboiling" process, or puddling par excellence as now understood, the main differences as comin the first instance instead of refined pig, so that the pared with the preceding are that raw pig iron is used purification takes longer owing to the greater amount of impurity to be removed, and, in consequence of this and of the larger amount of fettling used, a much larger amount of slag or "tap cinder is formed; in other respects the operation is much the same. The furnace is usually lined in the first instance by melting down and partially oxidizing scrap iron on the bed so as to make a firm foundation: "bull dog" or roasted tap cinder, mainly consisting of ferric oxide and silica, also forms a material largely used, the upper surface being finished off with a layer of a smooth unctuous variety of hæmatite or with "blue billy" (25) or some other variety of ferric oxide. In order to facilitate the removal of phosphorus and sulphur in the puddling forge, numerous chemicals reagents have been employed incorporated with the mass by stirring. Thus common salt and manganese dioxide have been recommended by Schafhäutl, chlorides of phosphorus, arsenic, and sulphur being said to be formed and volatilized, whilst manganese is communicated to the iron, and by its oxidizing action whilst becoming oxidized itself promotes the purification; moreover it renders the slag more fusible. Henderson employs a mixture of titaniferous iron ore and fluor spar, whereby fluorides of phosphorus, silicon, etc., are said to be evolved. Good results are said to be produced by the employment of fluorides (cryolite or fluor spar) as a flux in puddling. Sherman recommends iodide of potassium; according to Siemens, who carefully tried the Sherman process at the Landore works, no appreciable diminution is produced in the amount of sulphur and phosphorus by the addition of the iodide even in some considerable quantity both during the ordinary process of puddling and in a steel converting furnace, and the same kind of negative result has also been testified to by others, notably Snelus (Journal I. and S. Inst., 1871, ii. 181), and also by Euverte after full trial at Terre Noire. On the other hand, trials of the Henderson process appear to indicate that it causes a more rapid purification than ordinary puddling; thus in experiments made at Blochairn Works, Glasgow, the following percentages of phosphorus were obtained:Original pig iron........... .1.14 per cent. Partly refined iron 30 minutes after fusion.0.23 Final wrought iron........ The resulting cinder contained considerably less phosphorus than that in the pig employed, so that apparently some notable amount was volatilized. Parry has proposed after puddling in the ordinary way to recarbonize the iron by melting it along with coke and a little lime, etc. (to avoid sulphuration as much as possible), in a cupola furnace, and then to puddle a second time; the phosphorus being considered by him to be reduced in each puddling operation to about one-fifth of the original amount, the double puddling would convert even a moderately phosphorized pig into a tolerably pure bar iron. Very good iron has thus been made from highly phosphorized pig on a moderately large scale (some 80 tons). Appliances for Puddling. The Puddling Forge.The puddling furnace introduced by Cort in 1784 differs from those in use at the present day only in one essential particular, viz., that whereas Cort used. a bed of sand on which to run the metal fused previously in a runningout fireplace, the modern furnace as improved by Rogers some half century ago has a bed of iron plates cooled by air spaces underneath and covered with roasted scrap iron or with "bulldog," on to which the metal is heaped, having been previously refined or not according as the dry puddling or pigboiling process is used. The substitution of iron bottoms and a firm bed for the loose sand effects a great saving in iron through the formation of much less silicious cinder, and a great saving in time on account of repairs to the bed being much less frequently required; moreover, a much greater degree of purification from phosphorus is at the same time brought about. FIG. 33. Siemens Regenerative Puddling Furnace. Fig. 32 represents the general arrangement of a puddling furnace; a is the charging door for the fuel, d the bridge with an air course to cool it, c the bed supported on iron plates with air courses under them, f the exit flue leading to the chimney stack, which is surmounted with a damper k worked by a chain i from within the shed in which the forge is placed; b is the ashpit, g the slag-hole, and e the working door suspended by a chain from a lever with a counterpoise attached h, resting on the front side of the furnace roof. A large number of patterns of puddling furnaces differing one from the other in details have been constructed by various inventors; the limits of the present article as to length forbid that these should be minutely discussed. Instead of using solid coal or coke as fuel for the puddling forge, gas is equally applicable, i.e., such as is described in 10. In order to apply at will an oxidizing or a reducing atmosphere, it is only requisite to regulate the supply of air (usually hot blast) to the reverberatory furnace in which the gas is used. In Silesia gas puddling furnaces have been long in use, consisting of producers in which coal is burnt by means of a number of small jets of air forced in at the base of a square brick chamber some 5 feet in height, the top of the chamber being level with the bridge of an ordinary reverberatory furnace, the producer taking the place of the firegrate. In this way a mixture of nitrogen and i carbon oxide with more or less hydrogen and carburetted hydrogens from the distillation of the coal results, the combustion of which in the reverberatory is effected by blowing a series of jets of heated air from a row of tuyeres arranged horizontally, or from a long narrow horizon tal slit-shaped tuyere, across the issuing gases so as to form something like a gigantic blow-pipe, or series of par allel blow-pipe flames, which are somewhat inclined down ward so as to impinge on the substances in the bed of the furnace. Similar arrangements have been adopted elsewhere; thus in Carinthia gas-fired puddling fur naces are in use where wood is the fuel, the producer and furnace proper adjoining one another, and the combustion of the gas being completed in the furnace by a jet of blast from a tuyere inclining somewhat downwards; the blast is moderately heated by being made to circulate through flues under the furnace bed, thus also cooling the brickwork; the pigs to be puddled are previously heated up to near' their fusing point by the waste gases from a previous operation, being placed in a chamber just beyond the hearth. The waste gases have also been employed to heat the air blast by placing a pistol-pipe or other equivalent kind of stove between the furnace and the chimney. Several furnaces for thus utilizing the waste heat have been introduced, in England in particular; J. Head describes under the name of the "Newport Furnace" a somewhat analogous arrangement, a dry steam jet being used in connection with the air blast; a great diminution in consumption of fuel is thus said to be produced (Journal I. and S. Inst., 1872, p. 220). The Siemens regenerative furnace as applied to puddling consists essentially of a furnace fired by the gases from a Siemens gas producer heated (along with the air requisite to burn them) by means of Siemens regenerators (? 10). The chief difference between this form of furnace, represented by fig. 33, and the Carinthian gas furnaces is that the flame does not enter at one end and issue at the other, but leaves the furnace at the same end as that at which it enters, circulating in the furnace, and thereby leaving the other end free for access by means of au ordinary door. According to Siemens the loss of weight between pig and puddled bar did not exceed 2 per cent. on an average of six months' continuous working, whilst the consumption of coal (including the reheating furnace) was 30 cwts. 3 qrs. 8 lb. per ton of finished wire rod (3 cwts. of ordinary fettling being used per ton of iron). Modifications of the Siemens furnace have been adopted in various iron-works differing more or less in detail, but not greatly in general principle; thus the Ponsard furnace (240) and the Swindell furnace mainly differ in having the producer placed close to the furnace so that the gases are used directly without passing through the regenerators, which are only used to heat the air. The total fuel used in a Swindell puddling furnace in a large American works on a four months' average was 2024 lb of slack per ton of yield in iron (2240 b), or 0904 per unit of iron; the furnace, however, was not at work at night, so that a greater consumption of fuel was occasioned than would have been with double shifts of workmen. Kosmann has made a careful comparison (Preussicher Zeitschr. f. Berg-, Hütten-, und Salinenwesen, 1870, 145) between the effects and relative economy of puddling in the ordinary manner and in a Siemens regenerative gas puddling furnace, arriving at the conclusion that the latter is preferable in all cases where an extremely high heat is required, and where the fuel is of bad quality and unsuited for use in the ordinary way, or when a fixed temperature and particular constant quality of flame are required for any length of time. If, however, these conditions are not required, there is little advantage in the Siemens furnace over the ordinary one, whilst the latter admits of waste heat being utilized for heating boilers, etc. The waste of iron is nearly equal in the two cases, the ordinary furnace being slightly at a disadvantage; thus the cinder contained 24. Machinery for Saving Labor in Puddling.-In | machine rabble applied to a double puddling furnace. order to diminish the amount of laborious and exhausting work performed by the puddler, various mechanical contrivances have been introduced from time to time, mostly consisting of an ordinary rabble or some similar stirrer to which motion is communicated by machinery, in such a way as to move it (with some amount of guidance on the part of a workman) more or less in the same way as the puddler would use it. Fig. 34 represents one of this class of mechanical rabbles known as Witham's Dormoy's rabble (figs. 35, 36) differs from others of this class in being worked by rotation like a hair-brushing machine; the tool being made to revolve very rapidly (300 to 500 turns per minute for white iron and 800 to 1000 for gray pig) gives the metal such an impulse that it gyrates horizontally round the bed, continually renewing the surface in contact with the atmosphere; this is further aided by making the end of the rabble to carry a disk, which is replaced by a short twisted point when the metal comes to nature; only for the final balling is a hand-worked rabble requisite. According to Paget (Journal I. and S. Inst., 1872, 338) one fettling serves for forty charges worked in this way; an increase of 30 per cent. in the yield is effected, with an expenditure of only 0.552 parts of coal per unit of wrought iron made (114 cwts. per ton); the puddler is but little fatigued, although charges are worked off much more rapidly, whilst sulphur and phosphorus are so well eliminated that inferior brands of pig produce iron equal to good charcoal iron. Numerous other mechanical rabbles and analogous appliances have been FIG. 35.-Dormoy's Rabble-Transverse Section. introduced by various inventors; reports on the working of several of these (Witham's, Griffith's, Stoker's, Wilson's, etc.), and on the construction and performance of several kinds of puddling furnace, are given by the Puddling Committee of the Iron and Steel Institute in the Journal, 1872; also of the Carron-Dormoy furnace and mechanical rabble, ibid., 1876, 109. Many attempts were made prior to 1869, chiefly by Walker and Warren, Maudsley, Yates, Tooth, and Menelaus, to effect puddling by a revolving furnace rotated by machinery so as to cause the requisite intermixture of pig, fettling, and slag mechanically; Bessemer pro FIG. 36.-Dormoy's Rabble-Details of Puddling Tool. posed to employ an ovoid oscillating chamber fired by flame passing in through a hollow trunnion on one side and escaping similarly on the other side, whilst Oestlund (of Sweden) invented a rotating globular vessel into which the flame was directed from the front. Practically none of these machines ever came much into use. A considerable measure of success, however, has attended the improved form of rotary puddling furnace invented by Danks of Cincinnati, and represented in fig. 37. The fuel is burnt in an ordinary fireplace, a blast B being admitted under the bars and another over them A, level with the firing hole, so that by regulating the two streams of air the atmosphere can be kept reducing or oxidizing at will. tion rollers and arranged so that its axis is about level with the top of the bridge; at the other end is a movable terminal shaped like the frustum of a cone D, supported by chains or rods from a crane so that it can be swung on one side if required, thus serving as a door; this is connected by a lateral tube with the flue; a small orifice E closed by a stopper allows the interior of the furnace to be viewed when at blast turned off, the pigs are introduced at the end, and the work. The movable end being swung on one side and the terminal replaced; on turning on the blast and causing the drum to rotate slowly the pig is melted and incorporated with the fettling, etc., by the rotation; motion is communicated by means of a large external cog wheel F gearing into a pinion. Through a small cinder hole G the fluid slag is drawn off. The main difficulty experienced by previous inventors was to obtain a furnace lining that would last for any length of time, silicious bricks and analogous substances being used by them; this difficulty was overcome by Danks in the following way. The iron external drum is cased inside with firebrick, or preferably a cement composed of crushed ore and lime; a fusible iron ore such as hammer slag or mill scale is then introduced and melted down, the drum being slowly rotated; the rotation being stopped, the melted mass collects as a pool at the lowest level; large irregular lumps of an infusible ore (American iron mountain ore in preference, or Marbella lumps when this is not attainable) are then thrown into the pool; the cooling effect of these soon sets the liquid mass, which then acts as a cement, binding the lumps to the lining. This operation is repeated several times, so that finally the whole inside is lined, the pool being formed in a new place each time. The performance of the Danks puddler was very fully investigated a few years ago by a special commission of the Iron and Steel Institute, whose various reports are given in the Journal of the I. and S. Inst. for 1872 (see also ibid., 1871, i. 258); the general results of the experiments being that the production from the rotator is several times that from a hand furnace using the same pig, and that a larger yield of iron is obtained, more being in fact taken out of the furnace than is put in as pig, the surplus arising from the reduction of the fettling; moreover, with suitable fettling the quality of iron produced is always at least equal to that yielded by the hand furnace, and is usually much superior owing to the more complete elimination of phosphorus due to the less "acid" nature of the slag; the consumption of fuel per ton of iron made is much about the same, but usually somewhat less with the rotator than with the hand furnace; thus whilst something like 214 cwts. of pig were required to give a ton of wrought iron by the hand process, slightly less than 183 sufficed with the Danks furnace; i.e., 100 parts of wrought iron were obtained from 1075 and from 93'6 parts of pig in the two processes respectively. It is to be noticed, however, that further practical experience has not altogether confirmed the results of the commission, and that so far as England is concerned the advantages derived from mechanical puddling by the Danks machine (and also by others subsequently introduced) have not proved as great in actual practice as the success of the machine in America at first seemed to indicate would be the case in other countries. A circular chamber or drum C is supported on massive fric In order to avoid the damage done to the lining by introducing solid pigs, Wood proposes to granulate the iron by means of a machine somewhat analogous to his slag granulator (17), whilst fusion of the pigs in a separate furnace or cupola has also been often employed, the molten metal being then tapped into the rotary puddler. A large number of modifications of Danks's furnace and many other more or less analogous rotating arrangements for puddling have been subsequently constructed by various inventors; thus Williams (Pittsburg, United States) makes the rotating chamber of the Danks furnace to be separated from the combustion chamber a little way, the flame being led in through a movable flue analogous to that at the chimney end, so that access to both ends of the rotator is possible.1 Amongst other rotating puddling furnaces may be noticed the following. Seller's Furnace.-In this arrangement the flame does not pass through the chamber to the chimney, but turns back on itself as in the Siemens puddling furnace (fig. 33). The far end is cooled by water or steam; the fuel employed is gaseous, the generator being immediately in front of the furnace; mechanical arrangements of special character are also applied for the purpose of charging and discharging the furnaces. The rotating chamber rests on friction wheels which are made to turn by an engine instead of having an external cog wheel affixed to the drum itself as in Danks's 1See Iron, vol. x. p. 456, 1877, from the Metallurgical Review. |