w$ffi%ffl$& iwlwil Received. 2*<^ 187^ A TREATISE METALLURGY OF IRON; CONTAINING OUTLINES OF THE HISTORY OF IRON MANUFACTURE, METHODS OF ASSAY, AND ANALYSES OF IRON ORES, PROCESSES OF MANUFACTURE OF IRON AND STEEL, ETC., ETC. BY H. BAUERMAJST, F.GKS., Associate of the Royal School of Mines. foitjj nunurotts Wioab FROM DRAWINGS BY J. B. JORDAN. 1870 LONDON : ^ VIRTUE AND C0. r Stf^TTY LANE. NEW YORK : VIRTUE AND YORSTON. 1808. " Mir wiisse wie mo's Eisc macht Und wio's iin Sand zn Mixssle bacht ; Und wie me's drxif in d' Schmidto bringt Und Luppon untorm Hammer zwinj^t." HEBBL, PREFACE. THE importance of the subject has claimed for the Metallurgy of Iron much careful scientific investi- gation, both in this country and abroad ; but being con- fined, for the most part, to large and expensive works, or to the pages of scientific periodicals, it is scarcely available for the technical education of the great class to whom an accurate knowledge of the physical pro- perties of the ores, and the latest and most approved means of reducing them to a condition suited for the purposes of the manufacturer, has become an imperative necessity to enable us fully to meet foreign competition. To supply this want is the chief object the author has had in view in producing this volume, which he believes will furnish all the information that practical workers of iron, students, and owners of iron mines require. A work of this nature, as a matter of course, must IV PREFACE. in a great measure be a compilation "from the larger modern publications on the same subject. The author acknowledges his obligations to the following published abroad : BAEII. " Das Eisen," and the Swedish edition by Akerman. KARSTEN. " Eisenhuttenkunde." KERL. " Hiittenkunde," vol. iii. 2nd Edition. RITTINGER. " Erfahrungen." TUNNER. " Stabeisen und Stahlfabrikation." "Report on International Exhibition, 1862," in the Leoben Jahrbuch. WAGNER'S " Jahresbericht fiir technische Chemie." " Berg und liuttenmannische Zeitung of Freiberg." " Oesterreichische Bergwerks Zeitung." ANSIAUX AND MASSON. " Fabrication du Fer," &c. DE VATHAIRE. " Etudes sur les Hauts Fourneaux." GRUNER AND LAN. "Metallurgio du Fer en Angleterre," &c., published in the Annales des Mines. JORDAN. " Metallurgie du Fer au Pays de Siegen," published in De Kuyper's Revue Universelle. He has also perused with considerable advantage, especially in regard to our Iron Works Percy's " Metallurgy of Iron and Steel," Truran's " Iron Manufacture of Great Britain/ 7 ISToad's article " Iron " in " lire's Dictionary," and articles on Iron Works in ' Engineering." The illustrations, drawn by Mr. J. B. Jordan, have mostly been reduced from large-scale drawings, espe- cially those published by the Technical Institute of Berlin, under the title " Zeichnungen fiir die Hiitte." LONDON, March, 1838. CONTENTS. CHAPTER I. PAGE INTRODUCTORY AND HISTORICAL SKETCH ..... I CHAPTER II. OUTLINE OF THE CHEMISTRY OP IRON 12 CHAPTEE III. COMPOSITION AND DISTRIBUTION OP IRON ORES .... 48 CHAPTER IV. ASSAY AND ANALYSIS OP IRON ORES 79 CHAPTER V. PREPARATION OP IRON ORES 98 CHAPTER VI. ROASTING OR CALCINATION OP IRON ORES 106 CHAPTER VII. OP THE FLUXES USED IN IRON-SMELTING 120 CHAPTER VIII. OF THE BLAST FURNACE AND ITS ACCESSORIES . . . .135 CHAPTER IX. CAPACITY AND PRODUCTION OP BLAST FURNACES . 19G Tl fONTF.NTS. CHAPTER X. OF TUB CONSUMPTION OF FUEL AN TUB BLAST FTRNACK ........ -17 : I AFTER XI. ITIES AND COMPOSITION OF PIG IKON ..... CHAPTER XII. METHODS OF MAKING "WROUGHT IKON DIRECTLY FROM THE OKE . CHAPTER XIII. REFINING, OR CONVERSION OF GRSY rsro AVHITK CAST 1 Ma CHAPTER XIV. P*orcnox OF WROUGHT Isox ix OPEN FIRES .... CHAPTER XV. RBVRRRERATORT FIXERT OR PUDDLING PROCESS .... CHAPTER XVI. FORGE AX MILL MACHLSKSY CHAPTER XVII. KKHEATLXG AXD WELTIXG oil .PTER XVIII. METHODS OF PRODUCING Srzi^ CHAPTER XIX. AXAL--. - r AND WROUGHT LROX AND STEE T LIST OF ILLUSTRATIONS. 1. Gjere" calcining kfln. 2. a, Styrian kirn for pyritic ore* 4. 5. Plan w-m-Fiira 7. Froiitviewof hearth and dam of Hart t, 9. Dooble^cting blowing engine, Ttkal 10. Hot Hart itorc, with Up^ea. Dowkik 11. Hot Hart rtore, with piitol pipes. 12. WaMPMlfingeu rtore at ITcartadt 13. Cowper'i hot Hart rtore, ratieal aeetioii. 14. Plan of a pair of Cowper's tores. 15. AaaatgeaaA of bikiv ia Cowpo's rtore. 16. Water twT and blow pipe for hot Hart. 17. Furnace top, with cnp-and-ooe charger. Sooth Wales. 18. Furnace top, with Langen's charger. Eachwefld. 19. Hachette'0Hartfarnace,Tertacal 20. Hachette'f Hart funiace, plan timmgh 21. CompaniiTe section* of modem Hart 22. Catalan finery fire. 23. Vertical section of refinery. 24. Plan of refinery. 25. 2'. 27. Eastwood', mechanical p 28. 70-cwt ahinglmg helve. VI 11 LIST OF ILLUSTRATIONS. Fm. 29. Thwaites and Carbutt's steam hammer. 30. Ramsbottom's duplex steam hammer. 31. Double lever squeezer. Dowlais. 32. Rolling mill. 33. Rail mill roughing rolls. 34. Rail mill finishing rolls. 35. Universal rolling mill. 36. Cropping shears. Dowlais. 37. Reheating furnace. 38. Sections of piles for finished iron. 39. Siemens' gas furnace, vertical section. 40. Siemens' furnace, plan of flues. 41. Steel-converting furnace. 42. Steel melting furnace. 43. Siemens' steel melting furnace, vertical section. 44. Siemens' steel melting furnace, plan of flues. 45. Bessemer's steel converting apparatus, detailed section. 46. Bessemer's apparatus, general view, with casting apparatus. METALLURGY OF IRON. CHAPTER I. INTRODUCTORY ANJ) HISTORICAL SKETCH. THE subject of iron- smelt ing is the largest and most important in the whole domain of metallurgy, and, at first sight, presents a remarkable contrast to all other branches of the smelter's art. For in the case of most of the other metals employed as such in the arts, we have, as sources of supply, a numerous class of minerals varying greatly in richness and composition, and sus- ceptible of reduction to the metallic state by processes also differing greatly among each other ; while, in the case of iron 5 the few minerals that can be made useful as ores are restricted within much narrower workable limits, and form only one class of chemical compounds, namely, oxides, whose reduction can be effected practi- cally only by one agent that is, carbon or carbonic oxide. But as a very high temperature is necessary to effect the reduction, the metal almost always combines with a greater or less proportion of the reducing agent, as well as of other elementary substances, such as silicon, sulphur, and phosphorus, that may be present either in the ore, the fuel, or the flux, so that the ultimate result is never a pure metal, but a series of compounds, B 2 METALLURGY OF IRON. varying in proportion from great hardness to perfect malleability, and from ready fusibility to almost absolute infusibility. Practically speaking, absolutely pure iron may be said to have no commercial existence. But, on the other hand, extraordinarily small traces of foreign elements exert a very marked influence on the metal, and it is precisely these small and, in many cases, un- noticed differences of composition, that render so many points in the chemistry and practical working of iron obscure and difficult to be understood. When it is considered that the investigation of such problems calls for researches involving the utmost refinements of analytical chemistry, it is not remarkable that contra- dictory statements and opinions still abound on many points of the chemistry of iron-making. The mechanical considerations involved in this sub- ject are almost as important as the chemical ; for, unlike the smelter of other metals, who is able by fusion alone to bring his finished product to a merchantable state, the iron smelter has to deal with partly infusible masses, which require to be compacted and moulded by pressure by powerful machines, such as hammers, presses, rollers, &c., before they can be made available for consumption. In view, therefore, of the great magnitude of the subject, it may be as well to state, at starting, that the treatise now placed in the reader's hands is devised to furnish such information connected with the metallurgy of iron as may be necessary for the elucidation of the general principles upon which the processes used in the reduction of iron from its ores are based. While, there- fore, referring the student for the detailed discussion of INTRODUCTORY AND HISTORICAL SKETCH. 3 the various points to the larger works on the same sub- ject, such, for example, as the elaborate volume pub- lished by Percy, in this country, and those of Karsten, Flachat, Valerius, Julien, Tunner, and others on the Continent, we shall proceed to notice in as succinct a manner as possible, the principal facts and opinions current in the modern practice of iron-smelting under the following general headings : 1. Outline of the chemistry of iron from the metallur- gical point of view, noticing only such compounds as immediately interest the smelter. 2. Composition modes of occurrence and redistribution of the ores of iron. 3. Methods of assaying, mixing, and fluxing ores. 4. Description of processes whereby the ores are reduced to the metallic state. Before entering upon the consideration of the above subjects, it will be convenient to state broadly the nature of the finished products of the iron smelter's labour, and to glance rapidly at the historical part of the subject. Of the Products of Iron Smelting Cast Iron Malleable Iron Steel. Iron is employed in the arts i under three several states, whose variable properties are mainly due to dif- ferences in the quantity of carbon present, and in a lesser degree to that of other foreign matters. When alloyed with a maximum of the latter element, an amount which in ordinary smelting does not exceed 6 per cent., or fall below 2 per cent., the substance obtained is known as cast iron or pig metal. This METALLURGY OF IRON. is a hard and comparatively brittle substance, which can be readily fused at a high temperature, and is susceptible of being moulded into solid forms by cast- ing, but also in most modern iron works forms an intermediate product in the manufacture of the other classes. According as the metal may be most adapted for founders' or forge-masters' use, it is distinguished as forge or foundry pig. Wrought or Malleable Iron. This, the nearest approach to the chemically pure metal that can be obtained on the large scale, may be almost absolutely free from carbon, and never contains more than 0'25 per cent. It is a soft, malleable, and extremely tenacious sub- stance, infusible, except at the extreme temperatures obtainable in furnaces of special construction, but capable of being agglomerated by pressure, when at a white heat, to a compact state by the process of welding. When heated and suddenly cooled, it retains its soft- ness. It may be produced either directly from the ore or by the conversion of pig iron. The varieties of malleable iron are distinguished by many different names, but they have reference rather to form and destination than to differences of composition. Steel. Those varieties of iron in which the amount of carbon is above the maximum of malleable, and below the minimum of cast metal, are known as steel. The distinguishing property of this class of products is the power of being hardened or softened at pleasure, by sudden or rapid cooling, by the process known as tem- pering. Being intermediate in position between wrought and cast iron, steel is both fusible and malleable, but requires a higher temperature for fusion than the latter, and greater compressing power, owing to its lower INTRODUCTORY AND HISTORICAL SKETCH. O welding temperature, than the former. Those varieties that are richest in carbon are the hardest and most fusible, and are known as strong steels, while those that are nearer malleable iron in composition are distinguished as mild steels or steely irons. Steel may be obtained either direct from the ore at one operation, or indirectly by a variety of processes of greater or less complexity from either cast or wrought iron. Outline of the Progress of Iron Manufacture. The history of the production of iron is probably almost co- extensive with that of the human race ; at least, it goes back far beyond the periods of authentic history. According to the Pentateuch (Gen. iv. 22) the dis- covery of iron is attributed to Tubal Cain, who is said to have been sixth in descent from Adam. Pagan tradition assigns the discovery to Yulcan, placing it about the time of Deucalion's deluge. There can be little doubt that the discovery was made at a very early period, as the production of small masses of malleable iron is one of the simplest of all metallur- gical operations, requiring only a small furnace without blowing apparatus, such as can be made by digging a hole in the side of any bank exposed to the prevailing wind, a supply of easily reducible ore, and charcoal for fuel. Such processes as these have been described as in use in Africa by Mungo Park, and are still employed in Birmah ; and probably something of the same kind is indicated by the tradition which ascribes the discovery of iron in Scythia to the effects of forest fires in dis- tricts containing iron ores, when portions of the reduced metal are said to have been found among the ashes of the burnt trees. It may have been, however, that the masses of iron 6 METALLURGY OF IRON. referred to were meteorites, whose existence was first made apparent by the clearing of the ground. Homer refers several times to iron and steel. Thus in the twenty- third Iliad, Achilles, at the funeral games of Patroclus, gives a disc of iron as the prize ; and in the ninth Odyssey, the hissing of the burning stake that Ulysses plunges into the eye of Polyphemus is compared to the noise produced when steel is hardened by quenching it with water when at a red heat. Probably the first important improvement in the manufacture was the introduction of the artificial blast, which is of great antiquity. In Egyptian sculptures of the reign of Thothmes III. (1505 B.c.)smiths are repre- sented working at a forge, which is provided with two simple leather bellows, worked by the pressure of men's feet for the exhaust, and inflated by strings pulled by hand, in a manner exactly similar to that still employed in Birmah. Aristotle (B.C. 384-322) describes the process of making cast steel used in India, which is still produced under the name of wootz ; and also the manner in which the Chalybes of the Euxine procured iron. Pliny (A.D. 23- 79) mentions the great masses of iron ore still worked in Elba, Styria, and Spain, and describes the methods of making iron and steel, especially remarking that the quality of the latter depended upon the water used in quenching, and that small tools were tempered in oil. (" Natural History," bk. xxxiv. chap. 41.) Diodorus (B.C. 60-40), in describing the iron works of Elba, states the ore was reduced to small pieces and heated in furnaces ; the charge, when properly softened, was removed and divided into small masses, which had a spongy appearance (blooms), and were exported to the main land of Italy for conversion into tools. INTRODUCTORY AND HISTORICAL SKETCH. 7 Galen (A.D. 131) remarks that knives made of Indian iron (steel) were remarkable for their strength and hardness, but were often so brittle that the cutting edge splintered off, owing to their having been im- properly tempered. According to Franquoy, bellows with valves were in- troduced by the Romans into Gaul during the fourth century A.D. These, although single acting and made of leather, were a considerable advance upon the savage form, which required strings for their inflation. The wooden double bellows, which are still in use in some parts of the Continent, may be regarded as the pre- cursors of the cylinder blowing engine, and were intro- duced into the Harz about 1620, either from Franconia or Thuringia. During the middle ages the great improvement consisted in the gradually increasing height of the furnace, consequent on the use of ores of an infusible and difficultly reducible character. This necessitated a special means of withdrawing the reduced mass of iron (lump or bloom), which was effected through a lateral opening in the hearth, or lower part of the furnace, instead of being lifted out from above, as was done with the ordinary open fire. With tho increased length of the operation, the reduced metal being left for a considerable time in contact with the fuel, facility was given for a greater absorption of carbon, resulting in the formation of a larger quan- tity of molten pig iron, which was run out with the slag, than was the case with the open fires. The increased height of the furnace is well seen in Agricola ("De Re Metallica," lib. xii. edit. 1546), who 'describes two different methods of iron- working as common in 8 METALLURGY OF IRON. his time. The text is not very clear, but the engravings represent, in the first case, an ordinary bloomery, in which malleable iron is produced directly from the ore, together with a certain quantity of hard or pig iron ; while, in the second method described as in use with refractory ores, the furnace has a shaft of such a height that the furnace-man requires to ascend a short flight of steps to reach the throat, or charging-place. It is surprising that this author makes no mention of foundry work ; but as he states that the " hard iron " of the bloomery was useful for stamp heads, he was probably acquainted with the use of iron castings, but not with their mode of manufacture. The omission may also be accounted for by supposing that no foundries existed in Saxony, to which country most of Agricola's descriptions refer, until some time after their establishment in the Rhenish and Low Countries. The subject of iron-founding is noticed by Lazurus Ercker in his " Probierbuch," published in 1574. Kar- sten supposed that the Stiickofen, or high bloomery furnace above referred to, was of Eastern origin, and was first introduced into Styria, travelling thence westward to Burgundy and Alsace, subsequently re- turning eastward into Bohemia and Saxony ; and that the later forms of Blauofen and high furnace (the prototypes of the modern blast furnace) were invented in the Netherlands. The first indications of the latter are found in Lorraine and in the German Rhineland. Franquoy, who seeks with patriotic zeal to establish the priority of invention of the blast furnace to the Liege district, states that according to documentary evidence 'the hauts fourneaux at Yennes and Grivegnee in that country were established before A.D. 1400, and INTRODUCTORY AND HISTORICAL SKETCH. 9 also that the furnace at Marche les Dames was built by William, Count of ]STamur, A.D. 1340. Karsten, on the other hand, states that although the knowledge of pig iron dates from time immemorial, its use and systematic production for foundry purposes cannot be traced back with certainty to an earlier period than the end of the fifteenth century. In England, the blast furnace was probably in use at a very early period, as we have evidence, according to Lower, of ornamental castings being made in Sussex some time in the fourteenth century. The principal seats of the iron trade at that period in England were in the great forests of Sussex, Gloucestershire, and South Wales, where, under the older forms of bloomeries, iron works had existed since the days of the Romans. The gradual diminution of the forests of Sussex under the demands of the furnace, a process of destruction which may be seen going on at the present time with increased rapidity in Sweden, North America, and other countries producing charcoal iron, led to the passing of a stringent act in 1584 (27th Elizabeth) forbidding the further erection of iron works in the Weald of Sussex except under certain limitations. With the commencement of the seventeenth century came the first attempts at smelting with mineral fuel, the pioneer of this parti- cular improvement being Dud Dudley, who in 1619 produced both pig and wrought iron with coal in Wor- cestershire ; but the scheme was unsuccessful, owing to the opposition of the charcoal iron masters, so that after trials in several localities extending over upwards of thirty years, all of which ended unfortunately, the inventor finally abandoned the subject. A similar trial was made in Hainault by Octavius Strada, a native 10 METALLURGY OF IRON. of Bohemia, in 1625, who obtained a monopoly of the invention for twenty-five years, but it led to no prac- tical results. It was not till more than a century later, namely, in 1735, that the problem of smelting with coal , was successfully solved by Abraham Darby, of Cole- brookdale, who was the first to use coke in the blast furnace, an improvement which spread rapidly into all other iron-producing districts situated on or near the coal measures. The last furnace in the Weald of Sussex, at Ashburnham, was blown out \i 1829, and there are now only two or three scattered representa- tives of the ancient charcoal furnaces remaining in the whole of the United Kingdom. The century fol- lowing the success of Abraham Darby is marked by the introduction of the two great inventions which especially distinguish the modern period of iron manu- facture ; that is, the substitution of the reverberatory furnace for the open fire in the forge, and the use of heated air in the blast furnace. The former change effected by the puddling process, invented by Cort in 1784, has almost superseded all the older methods of making malleable iron ; and the latter, due to Neilson and Condie, -and first used at the Clyde Iron Works in 1828, has greatly increased the productive power of the blast furnace, with a diminution in the consumption of fuel. Since the introduction^ of the hot blast, the chief improvement in the blast furnace is that of intercepting the gases, which were formerly allowed to burn to waste at the throat, and leading them off by distri- buting pipes, to be usefully employed as fuel under steam boilers, hot blast stoves, &c. This was patented in France in 1811 by Aubertot, the gases being INTRODUCTORY AND HISTORICAL SKETCH. 11 employed for heating steel furnaces. In 1832 the waste gases were used for heating the blast at Wasser- alfingen, in Bavaria, and a similar apparatus was first erected in this country in 1848 by J. P. Budd, at Ystalyfera, in Glamorganshire, since which time various modifications of the same plan have been adopted to a considerable extent, especially in those furnaces thafc are obliged to draw their fuel from a distance, but in other districts, as for example in South Staffordshire and Scotland, the old flaming throats still prevail. Within the last few years, the chief inventions and improvements have been in steel manufacture, and many new processes have been introduced. Prominent among these is that named after its inventor, Henry Bessemer, which, although only of a few years' standing, has already effected important services by the produc- tion of a material admirably adapted for use in railway and other engineering work in place of wrought iron. Perhaps the problem of most immediate interest at present is that of the economical substitution of me- chanical for manual power in the process of puddling, so as to enable the forge-master to manipulate larger masses of malleable iron at a time, and thus to put him more nearly on an equality with the cast-steel maker than is the case at present. With the exception of the Weald of Sussex, very little change has taken place in the position of our principal iron- working centres from the earliest time down to the present day. Since the great expansion of railways several new and important localities have been brought into work, the ores being carried to the fuel or the reverse, according as might be most advantageous. In this way the great northern coal field of England, which 12 METALLURGY OF IRON. is almost absolutely without ironstone, gives rise to the largest production in the kingdom by feeding the Cleve- land district with coal and coke, and drawing iron- stone for its own fttrnaces in return. The prevalence of cheap ores in the oolitic districts has brought the blast furnace to within fifty miles of London in North- amptonshire, and the pastoral districts of Wiltshire have been invaded by the same visitor. It need not, therefore, be a matter of much surprise if at some future period the Wealden furnaces were to be re-lighted, as they could be easily supplied with fuel from the western coal fields should the supply of ore be sufficient to warrant the attempt, especially as on the opposite coast of France large furnaces have been established for smelting ores out of the same formation, and which are supplied with fuel from England. CHAPTER II OUTLINE OF THE CHEMISTRY OF IRON. THE chief chemical points involved in the metallurgy of iron will next be briefly noticed under this head, in the order adopted equally by Karsten in h?s classical " Eisenhiittenkunde," and also by Percy, commencing with the pure metal, and proceeding to notice the prin- cipal compounds with other elements, metallic and non- metallic, that are of importance from a metallurgical point of view. Metallic Iron. This may be obtained in a chemically pure condition by reducing peroxide of iron by hydro- OUTLINE OF THE CHEMISTRY OF IRON. 13 gen at a red heat, or by re-melting the purest varieties of malleable iron with an oxidising flux, in order to remove the last traces of combined carbon. It may also be deposited by electrolysis from a solution of pro- tochloride of iron, in the form of brilliant malleable films, a process that has been employed by engravers to protect the face of engraved copper plates from undue wear during printing, and is known as acierage, or steel facing. It does not appear to be quite certain, how- ever, from the contradictory statements made by differ- ent observers, that electro-deposited iron so obtained is absolutely free from nitrogen. The physical properties of the metal vary very con- siderably, according to the means adopted for its pro- duction. When obtained by reducing peroxide of iron by hydrogen at the lowest possible temperature at which the change can be effected (according to Magnus between 600 and 700 F.), it forms a dark grey powder, which combines energetically with oxygen, taking fire spontaneously when slightly heated and thrown into the air. When, however, the reduction takes place at a higher temperature, the metallic powder agglutinates to a sponge of a filamentous texture, a silvery grey colour, and metallic lustre, which is no longer pyrophoric. Larger and more compact masses may be obtained by removing the last traces of carbon and other foreign substances from the purest commercial wrought iron in the following manner : A small quantity, from 300 to 500 grains, of good wrought iron, such as pianoforte wire or Russian black plate, cut up into small pieces, and either rusted by exposure to steam or mixed with about 20 per cent, of pure peroxide of iron, is to be melted 14 METALLURGY OF IRON. under glass free from metallic oxides, in a refractory crucible, at a strong white heat, the operation requiring about an hour's full heat of a good wind furnace. The small quantity of carbon present in the metal is ex- pended in reducing a portion of the sesquioxide, the remainder passing into the slag; the result being a brilliant well-melted button of metal, which exhibits a decidedly crystalline structure, similar to that observed in meteorites when treated with an etching liquor, and is somewhat softer, but less tenacious, than the iron originally employed. The melting point of pure, or even ordinary, malleable iron has not been determined with certainty. According to Pouillet it lies between 1,500 and 1,600 centigrade, while Scheerer gives it as 2,100 of the same scale. The specific gravity varies from 7*7 to 7'9, the weight of a cubic foot at C. being about 486 Ibs. The linear dilatation by heat is B i- a between and 100, and ai 7 between and 300 C.* The specific gravity and tenacity vary with the method of treatment, and will be considered in connection with the strength of merchant ircn. Magnetism. Pure iron is susceptible of being mag- netised to a much higher degree than steel, but unlike the latter metal, it does not retain its magnetism when the exciting cause is removed. The so-called magnetic oxide, and some other compounds of iron, are also mag- netic, but in a less degree. The following determinations of the proportional magnetism of different compounds of iron are by Pliicker (Miiller's "Physik," vol. ii. p. 402) :- * In future, except where otherwise stated, the temperatures will be expressed in centigrade degrees. OUTLINE OF THE CHEMISTRY OF IRON. 15 Magnetic power. Metallic iron 100,000 ,, Magnetic oxide .... 40,227 ,, ISative peroxide .... 761 s , Precipitated peroxide . . 714 , , S olution, nitrate of peroxide 410 ,, ,, protochloride . . 490 . Hydrated peroxide ... 296 Specific Heat. 0-11379 according to Regnault, or O'llOO by Dulong and Petit. The conducting power for heat is 374, gold being taken as 1,000 (Despretz). The electrical resistance (as determined by Pouillet) is 5 '88 times that of a copper conductor of equal sectional area. The crystalline forms of iron are most probably to be referred to the cubical system, although there is some difference of opinion on this subject. Fuchs supposed them to be in part rhombohedral, and that the metal is dimorphous ; the balance of opinion is, however, in favour of the former view. The observed forms are the cube, octahedron, and tetrahedron. According to Peli- got, brilliant cubical crystals are occasionally obtained when protochloride of iron is reduced by hydrogen in a porcelain tube at a red heat. The equivalent or atomic weight of iron is 28 when hydrogen is taken as the unit of the scale, or 350 when oxygen is taken as 100 ; its symbol is Fe. Passivity of Iron. When a bright iron wire is im- mersed in fuming nitric acid, containing a certain amount of nitrous acid, it becomes passive ; that is, it is not dissolved, even if placed in acid of the ordinary strength, as long as no great increase of temperature takes place. If, however, the temperature be raised, or the metal be touched by a copper wire, it is immediately attacked and dissolved. 16 METALLURGY OF IRON. If the experiment be tried with ordinary nitric acid, a violent action is set up, and goes on until the wire is completely dissolved ; but by removing it from the liquid, and keeping it out until the adherent film of acid has become saturated, the face of the metal becomes of a dead white hue, and on re-immersion is found to have assumed the passive condition, which it retains until it is rubbed or polished. Steel wire, when similarly treated, gives rise to a violent ebullition for about twenty seconds, which suddenly ceases, and no further action takes place. This behaviour is characteristic of all varieties of steel, however they may have been pro- duced, and is a good method of distinguishing them from soft iron, which is rapidly dissolved under these conditions. By placing a bar of steel and another of iron in the same acid, and bringing their ends which project beyond the . liquid into contact, the latter is rendered passive, and remains so as long as the temperature of the liquid is not raised above 40. Steel which has been rendered passive in the cold may be digested for an indefinite period in boiling nitric acid, without under going any perceptible alteration. The cause of this peculiar property is not well made out ; it is, however, supposed that it may be due to the formation of a very thin, but closely adherent film of oxide, which in some way acts like a varnish and pro- tects the metal below from any further alteration. According to the recent researches of Ordway, the maximum temperature at which passivity may be in- duced in malleable iron varies with the strength of the acid used. Thus, with acid of specific gravity 1/38, iron is passive at 31, but is attacked at 32 ; with 1-42 OUTLINE OF THE CHEMISTRY OF IROX. 17 it is passive at 55, but is attacked at 56. With, red fuming acid of specific gravity 1*42 iron is passive at 82, but is attacked at 83. Compounds of Iron and Oxygen. Iron unites with oxygen in many different proportions, of which com- pounds three are simple oxides ; but these combine among themselves into more complex bodies. The following are the simple forms, with, their symbols, atomic weights, and percentage compositions : Symbols. Atomic Weight. Percentage Composition. Protoxide, or ferrous oxide .... Peroxide, sesqui-, or ferric oxide . . Ferric acid . . . FeO. Fe20 3 Fe0 3 Iron. 28 56 28 Oxygen. 8 24 24 Iron. 77-7 70-0 53-9 Oxygen. 22-2 30-0 46-1 The first and last of the above compounds are very unstable substances, and have never been isolated, or at any rate with sufficient certainty to allow of a deter- mination of their physical aad chemical characters. The peroxide, on the other hand, occurs abundantly in a nearly pure state, forming the hard and brilliant mineral known as hematite or iron glance. A lower oxide of the composition, Fe 4 0, is said to be formed when iron is burnt in oxygen, but this is doubtful. Protoxide of Iron. Although it has been generally stated that this oxide is too unstable a substance to be able to exist in an isolated state, yet according to Debray it is formed when mixtures of steam and hydrogen are passed over sesquioxide of iron at a red heat, provided that the proportion of the two gases to each other be not less than equal equivalents, or more than three c 13 METALLURGY OF IRON. of hydrogen to one of steam. With a greater propor- tion of hydrogen metallic iron is formed. The oxide so produced is said to be a non-magnetic black powder, which may be burnt in air, forming magnetic oxide. There are several known combinations of proto- and peroxide of iron. The most basic, and therefore the nearest approach to the pure protoxide, is found in the inner portion of the black magnetic scale which forms upon the surface of bar iron when heated to red- ness with access of air. The scale so formed, when of any thickness, is found to vary in composition from a nearly pure sesquioxide externally, to a sub- stance which, although probably not a definite chemi- cal compound, may be represented by the formula 6 FeO 4- Fe 2 3 on the inside in contact with the metal. When the two oxides are combined in equal equivalents, a substance is formed which occurs largely in nature as a definite mineral, known as magnetite or magnetic iron ore, which crystallises in the cubical system, and is, as its name implies, distinguished for its magnetic properties. It is a member of the group of minerals known as the Spinel group, all of which crystallise in the same form, and have the same general formula of RO + R 2 3 ; or, as it is sometimes con- tracted, R 3 4 ; thus FeO + Fe 2 3 =Fe 3 4 . Hydrated Protoxide of Iron may be produced by pre- cipitation from the solution of a protosalt by the addi- tion of potash or soda. It is a white flocculent powder, which almost immediately becomes green from the formation of hydrated magnetic oxide. When freshly prepared, however, the protoxide is soluble in 150,000 times its own weight of water, to which it gives an alkaline reaction. It is a strong base, and unites readily with OUTLINE OF THE CHEMISTRY OF IRON. 19 acids to form protosalts, which are mostly unstable compounds unless kept out of reach of the air, as they absorb oxygen with greater or less facility, and pass into the state of basic salts of the peroxide. The most important of these salts occurring in an anhydrous state is the carbonate, FeO. CO 2 , which is found abundantly in nature crystallised in a pure state as spathic iron ore, or siderite, in isomorphous combination with the carbonates of lime and magnesia as brown spar and pearl spar, or in an amorphous state associated with a greater or less proportion of carbonate of lime and clay, forming concretionary nodules, or septaria, of clay iron- stones and cement- stones in argillaceous strata of different geological periods. Protocarbonate of iron is sensibly soluble in water containing free carbonic acid, forming a bicarbonate, which is retained as such as long as the solution is pro- tected from the air, but is rapidly altered by absorption of oxygen into hydrated peroxide by exposure, as, for instance, when waters that hold iron in solution are exposed in ponds or swamps. This property has a most important bearing on the origin of ores, as it furnishes a means by which large masses of mineral may be elaborated from rocks comparatively poor in iron. When heated to redness with access of air, proto- carbonate of iron is decomposed, giving rise to the magnetic oxide, half of the acid being reduced to car- bonic oxide in order to supply the necessary oxygen : thus 2 FeO. CO 2 = (FeO + Fe 2 3 ) + CO + CO 3 . When iron-filings diffused through water which has 20 METALLURGY OF IRON. been thoroughly deprived of air are subjected to the action of carbonic acid gas, the water is partially decom- posed, hydrogen is evolved, and protocarbonate of iron is formed, which remains in solution until the excess of acid is removed. Peroxide or Sesquioxide of Iron (Fe 2 3 ). This oxide is largely met with in nature, both anhydrous, as hematite, iron glance, or red iron ore, a mineral having, when in its purest state, a bright metallic lustre, and crystallising in the rhombohedral system, and in com- bination with water forming various hydrates, among which are brown hematite, limonite, &c. It may be made artificially by calcining protosulphate of iron at a strong red heat, the salt, by its decomposition, giving rise to sulphuric and sulphurous acids, and a bright red pulverulent peroxide known as rouge, col- cot/iar, or croous, which is extensively used as a polishing material by glass and metal workers. The reactions in this process, which is employed commercially in the manufacture of fuming or Nordhausen sulphuric acid are as follows : 2 FeO. SO 3 = Fe' 2 3 + SO 2 + SO 3 . Pulverulent varieties of the same substance, but differing in colour and tenacity, may be obtained by the calcination of other salts of iron as follows : 1, from the pernitrate, which yields a nearly black product ; 2, from the persulphide, giving a rouge suitable for gold- smiths this requires a long- continued, and finally, rather a high heat ; and 3, from the neutral protoxalate, which gives a very finely divided product. A brilliant variety occurs in small steel- grey crys- tals in the hollows of lavas from Vesuvius and other OUTLINE OF THE CHEMISTRY OF IRON. 21 volcanoes. One of the finest examples of this kind, brought from Ascension, Island, is now in the Museum of Practical Geology. It may be artificially imitated by calcining protosulphate of iron at a strong red-heat with three times its weight of chloride of sodium. The latter salt is unaltered, and may be dissolved out with water ; the residue is peroxide of iron in brittle and crystalline scales of a dark violet or nearly black colour. These brilliant varieties are distinguished by mineralogists as specular iron, iron glance, or oligistic iron. Peroxide of iron is also found crystallised in regular octahedra in the mineral known as Martite, which be- longs to the cubical system ; it occurs in conjunction with the rhombohedral variety in lavas from Vesuvius and other localities, and also in the slaty hematites of Lake Superior. The true composition of this mineral is rather doubt- ful. It has been sometimes considered as a pseudo- morph of magnetite. E/ammelsberg found in octahedral crystals from the eruption of Vesuvius in 1855 as much as 15 per cent, of magnesia, and has described them as magnoferrite. He is not, however, prepared to regard this as necessarily a new definite member of the spinel or R 3 4 group, but considers it to be a dimorphous form of the peroxide, containing magnesia in isomorphous mixture, the peroxides and protoxides being capable of replacing each other without change of form. This view, if further extended, would make magnetite only a particular variety of octahedral hematite, in which the two isomorphous oxides are to each other in equivalent proportions, and would fairly explain the deviation in composition of nearly all magnetites from the theoretical 22 METALLURGY OF IRON. formula sometimes one and sometimes the other oxide being in excess of the required amount. Peroxide of iron forms a series of salts parallel to those of the protoxide, but it is difficult to obtain them of a neutral composition, as their solutions have a ten- dency to decompose into basic and acid salts, the former usually precipitating, while the latter remain in solution. At ordinary temperatures the peroxide is a very stable substance ; it may, however, be decomposed by heating it nearly to a white heat, when magnetic oxide is formed with evolution of oxygen ; thus 3Fe 2 3 = 2Fe 3 4 + 0; a reaction which explains why magnetic oxide is pro- duced when iron is burnt in oxygen, the temperature of the combustion being too great to allow of the exist- ence of the higher oxide. Hydrates of Peroxide of Iron. The hydrate produced by precipitation from the solution of a persalt of iron, or by spontaneous oxidation from the hydrated peroxide, consists of two equivalents of peroxide of iron combined with three of water, or 2 F 2 3 . 3 HO. It forms the base of a large class of minerals known as earthy brown hematite or limonite, and is the ultimate product of the alteration of any substance containing protoxide of iron when exposed to the action of atmospheric air and moisture. When boiled in water for seven or eight hours, the hydrated protoxide loses water, and is reduced to the form of Fe 2 3 . HO, which is a brick-red powder but slightly soluble in acids, and also occurs in nature beautifully crystallised in the minerals gothite, lepi- docrocite, &c. OUTLINE OF THE CHEMISTRY OF IROX. 23 The last equivalent of water may be removed, and anhydrous peroxide obtained, by heating the hydrate in a solution of chloride of calcium, or common salt, for several days, at a temperature of 160 to 180. Hydrated peroxide of iron is sensibly soluble in water containing carbonic acid, or any soluble organic salt of ammonia, such as are produced by the decomposition of vegetable matter. In the latter case the solution is attended with a reduction, and the formation of a proto- salt of the organic acid. Magnetic Oxide of Iron. This compound, one of the most important commercial sources of iron, is formed of equal equivalents of the per- and protoxide, or FeO + Fe 2 3 , or short Fo 3 4 . It is a black mineral of high lustre, crystallising in the regular system, the com- monest forms being either octahedra or dodecahedra, which may be artificially imitated by passing steam over iron wire at a red heat, when small brilliant black octahedra are formed on the surface of the metal. The natural mineral is always magnetic, often polar, and occasionally forms magnets capable of supporting con- siderable weights. The two latter conditions do not depend so much upon purity of composition as upon molecular structure, as they are best developed, not in the purest crystallised varieties, but rather in the com- pact slaty kinds, which often contain a considerable amount of foreign, especially earthy, matter. The other compounds of the two oxides of iron, which are formed by the oxidation of wrought iron when heated to redness in the air, have already been noticed under the head of Protoxide. Hydrated Magnetic Oxide of Iron. When freshly precipitated hydrate of protoxide of iron is boiled in 24 METALLURGY OF IRON. water, hydrogen is eTolved, and a hydrate of the mag- netic oxide is formed. According to Lefort, two different hydrates may be obtained by pouring solu- tions containing both proto- and persulphate of iron into boiling potash or soda in excess. When the salts of the two oxides are to each other in the pro- portion of equal equivalents, we obtain 2 (FeO + Fe 2 3 ) 3 HO, and in the second case, where the persalt is to the protosalt as 1 to 6, the resulting hydrate is of the composition 6 FeO -f Fe 2 3 + 4 HO. Similar results may be obtained with cold solutions by the use of am- monia as a precipitant. Magnetic Peroxide of Iron. Malaguti states that whenever carbonate or any organic salt of protoxide of iron is heated in the air until the acid is completely dissipated, a pure peroxide is obtained, which is always magnetic ; and also, that when the hydrated peroxides produced by the spontaneous action of the air upon hydrated protoxide, or iron rust, which processes are always accompanied by the formation of ammonia, are calcined at a gentle heat, similar magnetic varieties of the peroxide are produced ; while, on the other hand, the peroxide produced from the decomposition of a persalt is not in any degree magnetic, either before or after calcination. The above statements are disputed by De Luca, who supposes that probably the magnetic effect is due to a small quantity of protoxide, not altered by the low heat employed, as the property is lost when the oxide is subjected to a higher temperature. Probably these contradictory views may be reconciled by assuming that peroxide of iron is under certain conditions slightly magnetic, but that the property is fugitive and may be dissipated by heat. OUTLINE OF THE CHEMISTRY OF IRON. 25 It is not a little remarkable tliat the only chemist who has succeeded in obtaining protoxide of iron should describe it as non-magnetic. Rammelsberg found the octahedral peroxide from Vesuvius, contain- ing 15 per cent, of magnesia, to be magnetic. There is a large class of minerals analogous in con- position to magnetite, represented by the formula EG + K 2 3 , known as the Spinel group, in which the pro- toxides are those of magnesium, zinc, iron, or manganese, and the peroxides alumina and peroxide of iron. Some of these substances have been formed artificially, among them are, magnetite (FeO. Fe 2 3 ), black spinel (MgO. A1 2 3 ), franklinite (ZnO. MnO. Fe 2 3 ) ; and magno- ferrite (MgO. Fe 2 3 ). The latter substance, artificially produced by Deville, has been described by Rammels- berg as occurring in the products of the eruption of Yesuvius in 1855. Ferric Acid. This, the highest known oxide of iron, has the formula FeO 3 , and is very similar in its pro- perties to the corresponding oxide of manganese, MnO 3 , or manganic acid. It may be formed, among other methods, by fusing finely divided iron with four times its weight of nitre, or by passing a current of chlorine through a concentrated solution of caustic potash con- taining peroxide of iron in suspension. In the latter method the following reaction takes place : 3 Cl + 5 KO + Pe 2 3 = 3 KC1 + 2 KO. FeO 3 ; the ultimate products being chloride of potassium and ferrate of potash. The latter salt, being insoluble in excess of alkali, is slowly precipitated, if the solution of potash be sufficiently strong, as a black powder, which may be dried on unglazed porcelain, but is immediately decomposed when brought into contact 26 METALLURGY OF IRON. with filtering paper or any organic matter. It is soluble in water, giving a fine red solution, which, is slowly decomposed when evaporated, even in vacua, with the production of potash, peroxide of iron, and oxygen. No one has as yet succeeded in isolating ferric acid from its potash salt. Iron and Nitrogen. The effect of nitrogen upon iron, and more especially steel, has attracted the atten- tion of many chemists, and several elaborate memoirs have been published at different times on this subject. Unfortunately, however, the results obtained by dif- ferent chemists are so contradictory, that it is impossible at present to decide with any degree of certainty as to whether nitrogen plays an important part in deter- mining the good qualities of steel or not. All that will be attempted in this place will be to give a short analysis of the principal researches published up to the present time. According to Fremy, when iron wire is heated to dull redness for several hours in a current of ammonia- cal gas, it increases in weight from 12 to 13 per cent., and shows but little tendency to alteration when exposed to the action of the air. The nature of this change is not well understood, as it is not certain whether the product contains hydrogen or not. A similar substance is formed by acting on protochloride of iron with ammonia vapour at a red heat, the chloride being decomposed with the production of sal-ammoniac, peroxide of iron, and an amide salt, which in its turn is destroyed by the water present, forming ammonia and peroxide of iron. The residue of the operation is a fritted mass, partly fused, and often containing a greyish, brilliant, metallic-looking mass, which is nitride of iron. OUTLINE OF THE CHEMISTRY OF IRON. 27 This substance is less oxidisable than pure iron, and may be made permanently magnetic, although less perfectly than steel. By heating in a brasqued or carbon- lined crucible, it acquires the property of hardening when plunged into water at a red heat. Although it may be heated to redness in air without change, it is immediately decomposed when heated in an atmo- sphere of hydrogen, ammonia and pure iron being formed. The amount of nitrogen absorbed is said to be about 9J per cent., which corresponds in composi- tion to Fe 5 JN". According to Savart, however, the increase in weight of iron wire exposed to the action of ammonia vapour for nine hours is only yfo or about j? per cent. At the end of one or two hours the iron shows a finely granular fracture, and can be rendered sufficiently hard, by quenching in cold water, to give sparks when struck with a flint ; but when the process has con- tinued from eight to ten hours a more than ordinarily soft iron is obtained, no longer susceptible of temper- ing, and of a dark grey colour and graphitic appear- ance on a fractured surface. Dick obtained a similar small increase in weight, amounting to about TTTJ" when a spiral iron wire was heated to redness in a current of ammonia for one hour and a quarter, and only -g-oiF when a straight and thicker wire that is, one present- ing less surface was substituted. Bouis and Boussingault have determined the amount of nitrogen contained in various kinds of commercial iron, as well as in an artificial nitride prepared by Despretz; the latter contained about 2J per cent., while in the former the nitrogen varied from yi^r to $ per cent. 28 METALLURGY OF IRON. Iron and Phosphorus. Iron may be made to com- bine with phosphorus at a red heat, either directly or during the reduction of an oxide of iron in the pre- sence of an earthy phosphate and carbon, the latter condition being of very common occurrence in metal- lurgical practice. Percy, in a systematic account of the phosphides of iron, describes no less than seven, as follows : 1. Fe 12 P. Formed by dropping phosphorus on to red-hot iron. 2. Fe 6 P. heating Fe 2 P. 3. Fe*P. reducing protophosphate of iron with carbon. 4. Fe-P. exposing iron reduced by hydrogen to phos- phorus vapour at a low temperature. 5. Fe 8 P 3 . reducing sesquiphosphate of iron with hydro- gen at a white heat. 6. Fe 5 P 2 . acting on phosphuretted copper and iron with nitric acid. 7. Fe 3 P 2 . passing phoaphuretted hydrogen over iron pyrites at a low heat. Phosphate of Iron. Of the numerous class of salts formed by the oxides of iron and phosphoric acid, only one is of any great interest, namely, the natural mineral known as Vivianite, a product of alteration by partial oxidation of the tribasic phosphate of the pro- toxide, its composition being represented by the some- what complex formula, 6 (3 FeO. PO 5 ) -f (3 Fe 2 3 . 2 PO 5 ) -f 8 HO. It is very commonly formed in wet ground from decaying animal or vegetable matter con- taining phosphates, such as hard wood, or more especially bones and teeth of animals, when brought in contact with water containing a protosalt of iron in solution. Beech-trees growing in soils containing iron pyrites, which by decomposition yield protosulphate of iron, often deposit vivianite in their stems and roots OUTLINE OF THE CHEMISTRY OF IRON. 29 while still living, from the absorption of the sulphate which is decomposed by the phosphate of lime present in the plant, with the production of insoluble phos- phate of iron in the cells of the trunk. The wood becomes very hard by this addition, and when the tree is cut down the surface of the stump gradually assumes a greenish-blue colour by the absorption of oxygen from the air. The same mineral is also common in the bones and teeth of animals that have become imbedded in peat bogs, either as a dull blue incrustation or occasionally in small acicular crystals in the cavities, and occurs at times in the organic remains con- tained in impervious clays. An example of this is furnished by the fossils contained in the Oxford clay in Buckinghamshire, where the shells have at times entirely disappeared, leaving only a hollow cast in the stiif clay, the cavity being often lined with small tufts of vivianite and gypsum, derived from the mutual reaction of the products of decomposition of the soft parts of the animal and the mineral matter of the shell. Phosphorus is one of the most unwelcome ingre- dients in iron ores, from the ease with which it passes into the metal during the smelting process, producing the most injurious effects if present in more than a very small proportion. Wrought iron containing not more than TTT per cent, of phosphorus, is not sensibly affected in tenacity, but is only rendered somewhat harder ; with J per cent, it becomes somewhat cold short, or incapable of being wrought cold under the hammer without break- ing; with T S TF per cent, the cold shortness is very decided; and 1 per cent, makes the metal very brittle. 30 METALLURGY OF IRON. The tenacity of cast iron is also sensibly diminished by phosphorus, so that the metal made from the worst kinds of bog ores cannot be employed for castings requiring great strength ; but this is counterbalanced by the properties of acquiring great fluidity, and taking good impressions, which render it proper to be used for small and intricate ornamental castings. Arsenic and Iron readily unite, forming compounds which may be subjected to a high degree of heat without decomposition. These compounds are usually known by the German term, Speiss, and are of common occurrence in the smelting of arsenical silver and lead ores when the reduction of the sulphide of lead is effected by iron. They are found in thin layers of a columnar crystalline structure between the reduced lead and the supernatant regulus of copper and other sulphides when the molten contents of the furnace are allowed to settle in a basin after tapping. The ordi- nary composition of such a speiss is represented by the formula Fe 6 As. ; when nickel or cobalt is present in the ore it invariably passes into it. Although arsenic and iron are found in combina- tion in a great variety of minerals both as arsenides and arseniates, yet, as none of them are used as iron ores, nor do they as a rule occur in any quantity as acci- dental admixture with such ores, it is rarely that arsenic is found as an impurity in the metal. Two instances are, however, recorded of its presence in considerable amount in cast iron, both being in shot and shell of Turkish origin, those brought from Sinope containing 16 -2 per cent., while of others found in the arsenal at Algiers on the French occupation in 1830, the shells contained 9 and the shot 27 per cent. Such OUTLINE OF THE CHEMISTRY OF IRON. 31 metal is very brittle, white, with a brilliant radiated structure, and unfit for conversion into malleable iron by the puddling process, as it yields bars which are red short, or brittle at a red heat, although sufficiently tenacious to bear hammering when cold. A smaller amount of arsenic is, however, said to be beneficial when the metal is intended for chill casting ; that is, for castings whose surfaces are artificially hardened by the use of cold metal moulds. Sulphur and Iron. The compounds of sulphur and iron are of considerable importance to the iron smelter, as they are commonly present as impurities in many iron ores, and impart the defect of red shortness to the metal, even when only a very small proportion of sul- phur is taken. The protosulphide, FeS., corresponding in composition to the protoxide, is not found in nature, but may be readily formed by dropping sulphur on to heated scrap iron, or in the wet way by adding an alkaline sulphide to the solution of any protosalt of iron. When produced by the first method, it melts easily to a dark bronzy-black mass, with a metallic lustre, which combines readily with the sulphides of other metals, a property which is largely utilised in the smelting of copper and silver ores ; the so-called matte, coarse metal, or regulus, is an example, being a sulphide of iron con- taining more or less of the sulphides of the valuable metals, which is obtained in the first fusion, whereby the earthy matters in the ore are eliminated, and the metallic contents concentrated for further treat- ment. The protosulphide is but slightly affected when heated with ordinary reducing agents, such as carbon, or even hydrogen, but may be almost completely decom- 32 METALLURGY OF IROX. posod at a liigli temperature by oxidising substances, such as peroxide of iron or silica, or by the action of air at a red heat, the change in the latter case being accompanied by the formation of various sulphates of both protoxide and peroxide ; the ultimate product, however, being pure peroxide of iron. The persulphide Fe 2 S 3 may be formed artificially, but does not occur in nature in a free state, although it is found in combination with the sulphides of other metals, more especially those of copper. Magnetic Pyrites, or Pyrrhotine, 6 FeS + FeS 2 , the most basic of the native sulphides of iron, is a bright bronze- coloured mineral, crystallising in the rhombohe- dral system, and remarkable for its magnetic properties, which are, however, feebler than those of the magnetic oxide. It is occasionally found in association with iron ores, but more generally with those of copper and nickel, as well as with native gold, being more especially confined to crystalline rocks. Bisulphide of Iron, FeS 2 . This is the well-known substance which, under the name of iron pyrites, is found in greater or less quantity in every member of the geological series. Two principal varieties are dis- tinguishable, namely, ordinary iron pyrites, which is of a brassy-yellow colour, crystallising in the cubical system, and marcasite, or white iron pyrites, a rhombic mineral, of a lighter colour, softer, and more readily decomposed than the cubical kind. The percentage composition is, iron 48, sulphur 52. When heated in close vessels, iron pyrites is decom- posed with partial separation of sulphur, which sublimes, leaving a residue of proto- or perhaps magnetic sulphide. If, however, the operation is conducted with a free OUTLINE OF THE CHEMISTRY OF IRON. 33 access of air, the sulphur burns to sulphurous acid, caus- ing a great increase of temperature, and is ultimately wholly expelled, leaving peroxide of iron behind, which, if the pyrites employed be sufficiently pure, may be used as an iron ore. The residues obtained from pyrites in sulphuric acid manufacture are so employed in Cleveland, under the name of Blue Billy. When exposed to moist air, iron pyrites, especially the rhombic variety, is rapidly changed to protosulphate of iron, and con- versely, when the latter salt is brought into contact with decomposing organic matter in situations where air is excluded, pyrites is formed. It is probably in this way that the greater part of the pyrites existing in sedimentary rocks has been formed. Sulphate of Protoxide of Iron. This salt, well known by its commercial names of green vitriol or copperas, crystal- lises in the oblique system, forming pale green crystals having the composition FeO. SO 3 4' 7 HO. Like most other salts of the same base, it is very susceptible of oxidation, changing colour in the air even when crys- tallised, but more rapidly when in solution, by the absorption of oxygen and the formation of partly soluble and partly insoluble sulphates of the peroxide. These are very complex in composition, and are described at length in the larger chemical text-books. Among them are several minerals, such as coquimbite, copiapite, misy, and others. Iron and Chlorine. There are two chlorides of iron, corresponding in composition to the two lower oxides, or protochloride, FeCl^and perchloride, Fe 2 Clt? The former is produced wnen metallic iron is dissolved in hydrochloric acid, and may be obtained in a hydrated form by concentrating the solution, when green crystals 34 METALLURGY OF IRON. are deposited. These are doubly oblique in form, and have the composition FeCl r + 4 HO. When hydrochloric acid "gas is passed over iron wire heated to redness, anhydrous protochloride is formed, and condenses in the cooler portion of the tube in colourless cubical crystals. The hydrated perchloride may be prepared by boiling the protochloride with nitric acid, by dissolving peroxide of iron in hydrochloric acid, or by the action of aqua regia on metallic iron. The solution obtained by either of the above methods yields on evaporation, rhombohedral crystals, whose composi- tion is Fe 2 CJl + 6 HO. The anhydrous perchloride is formed when dry chlorine is passed in considerable quantity through a porcelain tube containing iron wire heated to redness. It crystallises in hexagonal scales, which deliquesce in moist air. When magnetic or other mixed ores, containing both per- and protoxide of iron, are dissolved in hydrochloric acid, both chlorides are formed in the solution, in the same proportion to each other as that of the two oxides in the substance operated upon. This property is of great value to the analytical chemist, as by it he is enabled to determine, in many cases, the state of oxida- tion in which iron exists in the ore. Iron and Silicon. According to Percy, chemically pure iron cannot be made to combine directly with silicon, unless carbon be present. Under the latter condition, however, by reducing an intimate mixture of peroxide of iron and sand with charcoal, a variety of cast iron may be obtained containing as much as 13 per cent, of silicon, which is very hard and brittle. Berzelius states that silicide of iron, yielding by analysis OUTLINE OF THE CHEMISTRY OF IRON. 35 19 per cent, of silica, which corresponds to 9 per cent, of silicon, is very soft, and can be hammered cold into thin plates. This result has not, however, been verified by subsequent observation. Protosilicate of Iron. Protoxide of iron combines readily with silica at the welding temperature of the metal. Familiar examples of this property are furnished by the use of sand in the smith's forge to remove the scale formed during the heating of the iron, and also by the so-called forge and mill cinders produced in the welding of malleable iron by the puddling and reheat- ing processes. The whole of the above substances are essentially tribasic silicates of protoxide of iron, represented by the formula 3 FeO. Si09- 1-27 2-98 1-35 6-00 3-20 Silica ) Organic matter 0-20 Water .... 0-43 100-40 100-45 99-79 100-14 100-67 No. I. Silurian limestone, Dudley. Used in South Staffordshire. II. Carboniferous limestone, Harmby, Durham. Used in Cleve- land. III. Permian limestone, Raisby Hill, Durham. Used in Cleveland. IV. Oolitic limestone, Wellingborough. Used in Northampton- shire. V. Chalk, after deducting 21 per cent, of water. Cleveland. Used in In the Lancashire and Cumberland hematite district, where the rich red ores of Ulverstone and Whitehaven are smelted alone, argillaceous fluxes are necessary in addition to limestone. For this purpose the shale of the coal measures is generally added ; but latterly a peculiar variety of brown hematite, remarkable for containing a large quantity of free alumina, has come into use in these districts, and also in South Wales. This substance is known as " Belfast Aluminous Ore." A somewhat similar mineral, called Bauxite, found at Baux, in the south of France, is now used to a con- siderable extent as an ore of aluminium. OF THE FLUXES USED IN IRON-SMELTING. 123 ANALYSES OF ALUMINOUS ORES AND FLUXES. I. II. in. IV. Silica . 61-91 9-75 9-87 2-8 Alumina 2173 27-95 34-57 57-4 Peroxide of iron 3.V91 27-93 25-5 Protoxide of iron 473 6-57 5-08 Lime . 0-09 0-60 0-91 0-2 Magnesia . 0-59 0-20 0-62 Potash 3-16 0-49 Soda . 0-25 Titanic acid __ 3-51 3-1 Volatile 7-43 18-60 19-36 11-0 99-89 100-12 101-85 100-0 No. I. Coal measure shale from the neighbourhood of Manchester. Frankland. II. Belfast aluminous ore. Tookey. III. Another sample of the same ore. IV. Bauxite, from Baux, in the south of France. Bell. Caustic lime is sometimes used instead of limestone, and produces a certain economy of fuel, as the local cooling, owing to the absorption of heat in the blast furnace consequent on the expulsion of the carbonic acid, is done away with. Comparative experiments on this point have been made at Ougree, in Belgium, and Konigshiitte, in Silesia. In the former case, 26 per cent, of lime replaced 40 of limestone, and the pro- duction of metal was increased 2'3 per cent., with a saving of 1/6 per cent, of coke. In the latter the saving was 2 '85 per cent., and the increase of produc- tion 3'1 per cent. It is of course necessary to use the lime as soon as possible after burning, in order to prevent it taking up moisture from the air. Forge and Mitt Cinders. It will be convenient to notice these substances, which play a very important part in the economy of modern iron works, before leaving the subject of iron ores, although, strictly speaking, they cannot be classified with them, but are 124 METALLURGY OF IRON. rather to be considered as waste products, winch are produced and regularly economised on a very large scale. When melted pig iron is exposed to the oxidising action of the air, its combined silicon is oxidised, with the formation of tribasic silicate of protoxide of iron, which is very fusible, and is capable of taldng up a further amount of iron, probably in the form of magnetic oxide. The same thing takes place when wrought iron is heated in contact with silica, at a welding temperature. It will subsequently be shown that the slags or cinders produced in the various opera- tions of refining, puddling, and reheating, performed in the conversion of cast into malleable iron, are of this composition. The amount of iron contained varies from 40 to 75 per cent., and in' this respect cinders might be considered as equal to the richest iron ores, were it not that practically the whole amount of phosphorus contained- in the pig iron operated upon is also taken up, as well as more or less sulphur, so that in reality their use in the blast furnace tends to de- teriorate the quality of the metal produced, when entering into the charge beyond a certain proportion. The chief reason, however, for the deterioration is to be found in the ready fusibility and comparatively difficult reducibility of the cinders, which, when added to the charge in the blast furnace, are apt to melt and run down into the hotter part of the furnace above the hearth, where the reduction of iron and silicon takes place simultaneously. Only a portion of the silicate, however, is so reduced : the remainder, passing into the blast-furnace slag, produces the so-called black or scouring cinder, which not only acts injuriously upon the siliceous matters of the hearth, but prevents the formation of cast iron at a maximum of carbonisa- OF THE FLUXES USED IN IRON- SMELTING. 125 tion. The result is therefore an inferior description of white iron, usually known as cinder pig, together with the loss of a considerable quantity of iron in the slag, which sometimes contains nearly 20 per cent, of prot- oxide of iron. The purest class of cinders are those from the re- heating or welding furnace, being freer from sulphur and phosphorus than those obtained in puddling. Various methods have been suggested for overcoming the difficulties attendant on the smelting of cinders, such as subjecting them to a preliminary calcination, or combining them with lime and small coal in order to effect the reduction at a lower temperature. Of these methods only the former has been generally adopted. When silicate of protoxide of iron is roasted, either in heaps or kilns, with a free access of air it is decomposed, with a separation of silica : the protoxide of iron, absorbing oxygen, passes into the state of peroxide, or magnetic oxide, producing a very refractory sub- stance, which is employed, under the name of " bull- dog," for lining the hearths of puddling furnaces. Its infusibility is due to the fact that silica and peroxide of iron are both infusible, and do not combine together when exposed to a high temperature in an oxidising atmosphere. When the bulldog is produced from puddling-furnace cinders containing phosphorus in quantity a partial liquation takes place, and a fusible slag, known as bulldog slag, separates, carrying down with it a considerable portion of the phosphorus. Sulphur, when present, is almost entirely remoVed during the roasting, being converted into sulphate of iron, which forms a crust over the outer surface of the heap, and may be washed out with water, or decom- posed by further heating. It will readily be seen. 126 METALLURGY OF IRON. that when the iron is peroxidised it is in a much more favourable condition for treatment in the blast furnace, and the cinders may then be regarded as equivalent to a siliceous hematite. In Lang's method of preparing puddling and other forge cinders for the smelting furnace they are finely powdered, and mixed with milk of lime and coal slack, or charcoal dust, into a paste, which, when dry, forms a hard mass, and may be broken into lumps, having sufficient coherence to stand the pressure of the blast furnace without crushing. At Store, in Carniola, where this process was introduced in 1861, sixty- six parts of reheating furnace cinder, mixed with 22 parts of lime and 12 parts of charcoal dust, were smelted in a cupola without any addition of ore, and produced mottled pig iron of good quality. Several analyses of pig iron so produced have been published, but the composition of the cinder operated upon is not given. A somewhat similar process has been proposed by Minary and Soudry. The cinder, in a finely- divided state, is mixed with caking coal slack, and converted into coke in the ordinary way. According to the state- ments of the inventors, the protoxide of iron in the cinder is said to be reduced to the metallic state by the gases given off during the coking, at a temperature sufficiently low to be without effect upon the silica ; at the same time both phosphorus and sulphur are eliminated as phosphuretted and sulphuretted hydrogen. The coke produced is intended to be used in the blast furnace for smelting ores. In order to obtain it sufficiently coherent, it is necessary to keep the mixture of slack and cinders with certain proportions. The best results were obtained at Givors, with 40 of the OF THE FLUXES USED IN IRON- SMELTING. 127 latter to 60 of the former, which gave a coke containing from 20 to 25 per cent, of metallic iron ; but the propor- tions might be reversed without consuming any of the fixed carbon of the fuel in the reduction, which is effected entirely by the volatile products. The removal of the uncombined silica must, of course, be provided for by the addition of a proportionate quantity of limestone over and above that required by the ore in the blast furnace. The above statements are, to a certain extent, in opposition to the results obtained by Percy and Richardson, who found that the tribasic silicate of protoxide of iron could not be entirely reduced to the metallic state when heated with an excess of carbon, two atoms only of the protoxide being separated, leaving behind a monobasic silicate (FeO. SiO 3 .), which resisted further change. This result can only be obtained with chemically pure tribasic silicate, such as is prepared by fusing pure peroxide of iron with quartz sand, whereas the cinders produced in puddling or heating furnaces, always contain a sufficient proportion of earthy bases to allow the last atom of iron to be set free. The addition of fluxes in the blast furnace is regu- lated by several considerations. When the ores are of good quality, the chief point to be considered, is the production of the most fusible slag with the smallest addition of non-ferriferous matters ; this is more espe- cially the case with charcoal furnaces. When mineral fuel is used, however, it is necessary to form a slag that is capable of absorbing sulphur, which would otherwise be taken up by the iron, and for this purpose, a larger quantity of flux is used than that indicated by theory as giving the most fusible product. The fusibility of silicates depends chiefly upon their 128 METALLURGY OF IRON. composition, and, according to Plattner, increases with the increase of silica : thus for the same base the mono- basic (RO. SiO 3 ) and sesquibasic (3 RO. 2 SiO 3 ) forms are more fusible than the tribasic, containing 3 RO. SiO 3 , or the subsilicate, 6 RO. SiO 3 . For the same compo- sition, silicates containing one base are less fusible than those containing two or more. The following is the observed order of fusibility in the simple silicates : Silicate of Alumina .... melts at 2,400 C. ,, Magnesia .... ,, 2,200 2,250 Baryta 2,100 2,200 Lime 2,100 2,150 Protoxide of Iron \ 1 VftQ 1 RQQO Manganese ( Ij7fc ' l >* 62 Of double silicates of similar atomic composition, those containing both protoxide and sesquioxide bases are more fusible than those having both bases of the pro- toxide type, the order of fusibility being as follows : Silicate of Baryta and Lime melts at 2,100 C. ,, ,, ,, Alumina ,, 2,050 ,, Lime ,, Magnesia ,, 2,000 Alumina 1,918 1,950 The most fusible of the triple silicates likely to be produced in iron-smelting are those containing alumina, lime, and protoxide of iron, or manganese. Silicates of potash and soda, or of protoxide of lead, are among the most fusible ; but with these we are not at present con- cerned. The slags of blast furnaces may be regarded as silicates, whose composition ranges between the follow- ing limits : I. 3 CaO. 2 SiO 3 + APO 3 . 2 SiO 3 ; and II. 3 CaO. SiO 3 + APO 3 . SiO 3 . OF THE FLUXES USED IN IRON-SMELTING. 129 Those of charcoal furnaces are mixtures in indefinite proportions of both silicates, while those produced with coke or coal are more basic, and approach more nearly in composition to No. II. In the first of the above formulae the oxygen of the silica is double that of the bases taken together, corresponding to the composition 3 RO. 2 SiO 3 , or that of augite ; while in the second both bases and silica contain equal amounts of oxygen, giving the formula 3 RO. SiO 3 , or that of olivine. As a portion of the lime may be, and usually is, replaced by other protoxide bases, and also alumina may be partially substituted for silica, it is evident that these general expressions may be made to include substances differing widely in qualitative composition. The following are the maximum and minimum limits of the chief constituents of blast-furnace slags derived from the examination of a large number of analyses : Min. Max. Silica .... 20 . . 72 per cent. Alumina . . 30 n Lime .... . . 60 j > Protoxide of iron . . 26 ,, ,, manganese . . 34 11 Magnesia . . . 34 ,, Baryta . 8-2 Soda .... . . 11-3 ,, Potash . . 4-3 Bodemann gives the following formula for the most fusible silicate of lime and alumina : 4 (3 CaO. 2 SiO 3 ) + 3 (APO 3 . 2 SiO 3 ), containing, per cent., Silica, 56 ; Lime, 30 ; Alumina, 14. The following are a few examples of slags produced under different conditions of working. The composi- K 130 METALLURGY OF IRON. tion of the slags from furnaces in different localities, and under dissimilar conditions of working, is illustrated in the following table, as far as it can be done with such a small number of examples : ANALYSES OF BLAST FURNACE SLAGS. I. II. ill. IV. V. VI. VII. Silica 38-48 43-07 31-46 27-68 42-96 61-06 40-95 Alumina . . 15-13 14-85 8-50 22-28 20-20 5-38 8-70 Lime 32-82 28-92 52-00 40-12 10-19 19-81 30-36 Protoxide of iron 0-76 2-53 0-79 0-80 19-80 3-29 0-60 Protoxide of manganese . 1-62 1-37 2-38 0-20 1-53 2-63 2-18 Magnesia . 7-44 5-87 1-38 7-27 2-90 7-12 16-32 Sulphide of cal- cium 2-22 1-90 2-96 2-00 1-32 Sulphur. 0-34 Alkalies . 1-92 1-84 1-10 0-32 Phosphoric acid 0-15 o-io 100-54 100-35 99-47 100-35 100-00 99-29 99-87 No. I. From Dowlais, produced when making grey iron. Riley. II. produced with white iron. Riley. ,, III. Kirkless Hall, Wigan, produced with grey Bessemer iron, disintegrates in the air. IV. Clarence, Durham, from Cleveland ores. Bell. V. Cwn Celyn, South Wales, scouring cinder. Noad. VI. G-osberg, Sweden. Sjogren. VII. Neuberg, Styria, produced with grey iron. Kiippel- wieser. It occasionally, but rarely, happens in the smelting of spathic ores, that slags are produced entirely free from lime. The following are examples of this kind : I. II. III. Silica .... 49-57 48-39 37-80 Alumina ... 9-00 6-66 2-10 Protoxide of iron 0-04 0-06 21-50 Protoxide of manganese Magnesia .... 25-84 15-15 33-96 10-22 29-20 8-60 0-08 0-08 0'02 OF THE FLUXES USED IN IRON-SMELTING. 131 No. T. From Siegen, produced with grey iron. Karsten. II. ,, spiegeleisen. Karsten. ,, III. Styria, white iron. Von Mayrhofer. When the fusibility of a slag is reduced, by the addition of lime in excess, the iron will be highly carburetted, and the greater amount of sulphur will be taken up by the slag in the form of sulphide of cal- cium. Other things being equal, the iron will be grey if the slag is refractory, and white if it is very fusible. The reason of this is apparent when we consider that the iron may be reduced and carburetted, but cannot separate from the earthy matters till these have melted into slag ; if, therefore, the latter are very fusible, the metal which melts at a still lower temperature runs together, or falls through the region of the boshes and hearth, where the temperature is highest, without being exposed for any length of time to the energetic reducing agencies prevailing at and near the interior. If, on the other hand, the finely- divided particles of metal are kept from coalescing by the more refractory character of the slag, it will be subjected to a long- continued heating in a region favourable to the accu- mulation of carbon and silicon in the highest degree, and it is to the presence of the latter element that the greyness of pig iron is in part, at least, due. The power of taking up sulphur is also imparted to slags by protoxide of manganese, as well as lime, a property that receives an important application in the manufacture of spiegeleisen from manganesiferous spathic ores. Protoxide of iron increases the fusibility of slags, communicating at the same time a dark green or black colour, as is seen in the so-called scouring in black cinders which are produced when a furnace is working 132 METALLURGY OF IRON. with, a heavy burden, or increased charges of ore and fluxes in proportion to the fuel. These slags are accompanied by the production of white iron, from the reduction of a portion of the protoxide of iron in the molten silicate when brought into contact with the bath of cast iron in the hearth, at the expense of the carbon in the molten metal. With silicate of protoxide of manganese, however, this re- action does not take place, owing to the very high temperature required for the reduction of protoxide of manganese to the metallic state. The physical character of slags, such as colour, texture, fluidity, &c., varies with their composition and the working condition of the furnace, so that it is not possible from inspection alone to determine the charac- ter of the metal produced, except after considerable experience of the individual furnace ; and the relation between slag and metal in one district may be totally different in another. De Yathaire makes the following general observations on this point, which, of course, must be taken as applicable only within wide limits : Slags pro'duced from furnaces working hot i.e. with light burden when the reducing power is at a maxi- mum, and grey iron is made, are usually white or grey. Owing to the total amount of iron being re- duced, in the special case of the ores containing man- ganese, an amethystine tint is often observed under these conditions, especially in charcoal furnaces smelt- ing hematite or non-aluminous ores. Black slags, on the other hand, correspond to heavy burden, and a comparatively reduced temperature, when the furnace is said to be working cold, or with less fuel as compared with the weight of the charge smelted. The vitreous character and fluidity of slags increase OF THE FLUXES USED IN IRON-SMELTING. 133 in proportion to the amount of silica. A porcelanic or opalescent character is generally indicative of a con- siderable amount of alumina. Those produced in the smelting of coal-measure clay ironstones are often of this character, showing an alternation of light yellowish and dark green or blue bands and stripes. Slow cool- ing has a tendency to produce devitrification or crystal- lisation, so that it often happens that the same slag forms a perfect glass when suddenly solidified, but becomes opaque or porphyritic, with distinct crystals interspersed through a vitreous base, when cooled very gradually. When slags containing sulphides of calcium, barium, and manganese, such as are commonly produced when sulphur is present in the fuel, are allowed to flow over damp ground, in smelting with coke, steam is forced through the molten mass, which, in its passage, is decomposed by the sulphides and poly sulphides, with the production of sulphuretted hydrogen. This in its turn burns on coming in contact with the air, giving rise to sulphurous acid gas. If, however, water be thrown upon the surface of the slag, the sulphuretted hydrogen evolved is prevented from igniting, escapes unaltered, and may be recognised by its unpleasant odour. The reactions are as follows, according to whether a neutral or poly- sulphide of calcium be present : CaS + HO = CaO + US. CaS 5 + 3 HO = CaO + SO 2 + S 3 HS + S. In the latter case the decomposition is more complex, being attended with the formation of sulphurous acid, sulphuretted hydrogen, and free sulphur. Under ordinary conditions, however, the two latter products would unite and burn to sulphurous acid. This is pro- 134 METALLURGY OF IRON. bably the cause of the strong odour of this gas usually produced by the slags escaping from a coke furnace working very hot. When lime is present in large quantity, the fracture of the slag is usually of a dull stony character. Those of the Cleveland and Lancashire hematite furnaces are of this kind. A very large excess of this base causes the slag to fall to pieces when exposed to a moist atmosphere after cooling, in the same way as caustic lime, forming a powder which may be employed in making cement or mortar for building purposes. In many of the small iron works of Germany the slags are subjected to the processes of stamping and washing, in order to recover any entangled shots of metal, which are "afterwards returned to the furnace. As a general rule, steady and continuous flowing, a somewhat viscid fluidity, and a slow passage from the liquid to the solid state, are characteristic of the slags produced from furnaces working hot. Scouring slags, on the other hand, run as liquid as water, but solidify in crusts rapidly, without passing through the plastic state. Slags produced from manganesiferous hematites are of the usual manganese, violet, or amethystic tint in the vitreous portions, but when blown up by gases, the colour disappears, with the production of a pearly- white pumice-like body. "When the same furnaces are burdened for white iron the slags become dark green, and of an almost pasty consistency. In addition to the colours produced by metallic oxides, such as bottle-green or black by protoxide of iron, violet by protoxide of manganese, yellow or brownish green by protosulphide of manganese, ethers, especially shades of blue, are common in slags ; OF THE BLAST FURNACE AND ITS ACCESSORIES. 135 but it is not clearly made out what the colouring agent is in such cases. Thus a bright sky-blue tint, often seen in Swedish slags, has been variously attributed to vanadium, titanium, and sulphide of sodium (ultra- marine). Silicate of zinc is also stated to produce green and blue tints. CHAPTER VIII. OF THE BLAST FURNACE AND ITS ACCESSORIES. IT has already been stated that in the early days of iron- smelting the only merchantable product was bar or malleable iron obtained directly from the ore ; cast iron being a subsequent discovery, consequent upon the employment of larger furnaces and higher tempera- tures in the treatment of more refractory minerals. In process of time, it was found that the production of cast or pig metal, as an intermediate stage in the manufac- ture of malleable iron, was attended with advantages not possessed by the older method, so that at present it is followed exclusively ; the latter being confined almost entirely to a small and constantly diminishing area in Europe, besides being more extensively practised in Africa and India. The subject, therefore, naturally divides itself into two main heads : I. Direct method, or extraction of malleable iron from the ore, and II. Indirect method, or production of pig iron from the ore, and subsequent conversion into malleable iron by some form of finery process. The difference between the two processes is mainly 136 METALLURGY OF IRON. due to the height of the furnace. In the direct method, where a low charcoal hearth or forge is used, a portion of the ore is reduced to the metallic state at a com- paratively low temperature, while another part combines as protoxide with any silica that may be present, form- ing a highly fusible and basic slag, into which the reduced spongy mass sinks, any excess of carbon taken up being removed by the oxidising agency of the slag, aided by the blast which is introduced through an in- clined nozzle or twyer, so as to impinge directly upon the metallic bath. On the other hand, the furnace used for the produc- tion of cast iron is mainly distinguished by its height, and may be described in general terms as a conical hearth, whose walls are continued upwards into a chimney or stack of increasing but variable section ; the blast-nozzle being laid horizontally instead of in an inclined position. The height of the upper portion, i.e. above the twyer level, may be from ten to twenty times as great as that below, or hearth proper. When the furnace is at work, or, as it is technically termed, in blast, it is kept filled to the top or throat with alter- nate layers of fuel, ore, and flux, the latter being mixed in proper proportions to produce the most fusible com- binations of the earthy matters, a constant stream of air being maintained through the twyers, at a sufficient pressure to pass freely through the contents of the furnace. Part of the incandescent fuel subjected to the blast is completely consumed, burning to carbonic acid with a development of the maximum of heat, whereby the matters immediately adjacent are melted, and fall into the hearth, where they separate by liquation into metal and slag ; the latter, being specifically lighter, rises to the surface, and protects the former from the OF THE BLAST FURNACE AND ITS ACCESSORIES. 137 decarburising action of the blast. The carbonic acid formed in the first instance, encountering fresh fuel, is reduced to the state of carbonic oxide, a process that is attended with a great absorption of heat, so that the region in which a temperature sufficiently high for the fusion of metal and slag prevails does not extend more than a very short distance from the point of intro- duction of the air. The carbonic oxide so produced, and the unaltered nitrogen of the air, when brought in contact with an oxide of iron at a red heat, is again oxidised to carbonic acid, with the simultaneous pro- duction of metallic iron, which, becomes carburetted by further contact with carbonaceous matters in its descent towards the hearth. The alternate production of carbonic acid and carbonic oxide, by the reciprocal action of carbon and oxides of iron upon the gases, is continued in the upper part of the furnace as long as the temperature remains suffi- ciently high, the quantity of the former gas being augmented by the decomposition of the limestone flux generally used. Ultimately, however, a sufficient amount of carbonic oxide remains in the so-called waste gases, either to form a great body of flame at the throat of the furnace when the current is allowed to flow freely into the air, or a valuable fuel, yielding sufficient heat for all the accessory operations of the furnace, when collected and utilised. The shaft of the blast furnace may, therefore, be considered as combining within itself, and performing the functions of, several distinct furnaces ; thus the hearth is devoted entirely to fusion, while the middle region is essentially a concentration chamber, and the top parts, when raw fuel and flux are used, combine the functions of a limekiln with those of a coke oven. 138 METALLURGY OF IROX. Taken as a whole, therefore, the reactions in the manufacture of pig iron are more complex than those of the open-fire process of making malleable iron direct from the ore ; but, as the latter is only one out of many methods by which the same product is obtained, it will be more convenient to defer its consideration, and commence with a description of the former. Of Blast Furnaces. In its original, or what may be considered typical form, the blast furnace consists of a shaft or chamber formed of two truncated cones, joined by their bases. The upper and more acute of the two cones is placed upright, and is known as the stack, while the lower and more obtuse one is inverted : the line of junction forming the widest part of the furnace is called the boshes, possibly a corruption of the German bauch. Sometimes the lower cone is continued down to the level of the ground, but more generally the lower part of the furnace is enlarged, forming what is known as the hearth, in which the molten materials collect below the level of the twyers or pipes through which the blast is introduced. In France, the space between the twyers and the broadest part, or top, of the boshes is known as the laboratory or working place (ouvrage). The top, or throat, of the furnace is surrounded by a platform for the convenience of charging, and is in many cases covered by a short cylindrical chimney, which leads off the flame escaping at the throat ; this portion of the furnace is known as the tunnel head. In the newer forms of furnaces, the conical or spindle-shaped body and cylindrical hearth, with their sharply- contrasted divisions, are, for the most part, superseded by more flowing forms, the straight OF THE BLAST FURNACE AND ITS ACCESSORIES. 139 slopes of the sides being converted into curves, giving a more or less barrel- shaped outline to the stack. The same terms are, however, alike applied to the different parts, the boshes being taken as indicating the widest part of the stack, and the hearth that lying below the twyers. It will be beyond the province of an elementary sketch like the present to enter into elaborate details of the construction of blast furnaces ; only some of the leading points will be noticed in the following order : I. External form and construction. II. Details of the interior lining, or working parts. III. Construction of the hearth and furnace top. IV. Accessory apparatus, such as lifts, blast engines, and stoves. Y. Methods of collecting waste gases. The construction of blast furnaces varies very con- siderably in different localities, in regard to size and proportion of parts to each other, as well as material employed. In the early days of pig-iron manufac- ture, when a square horizontal section was in gene- ral use, the external form was usually that of a square base, pyramidal tower, tapering uniformly from the ground upwards, which became modified, on the introduction of the circular stacks, to a conical or cylin- drical form, the lower portions near the ground, and surrounding the hearth, still retaining the square base. Both of the above forms are characterised by extremely massive construction, the lower parts, or stack pillars, forming solid four-sided blocks of masonry, braced with iron rods, and united by cylindrical arches into the so-called twyer houses, a complete circular passage being usually formed through the mass of the pillars. When the whole furnace is of rectangular section it is 140 METALLURGY OF IRON. braced by a similar system of tie rods through the entire height, but in conical or cylindrical forms iron hoops, placed at short distances apart, are used for the same purpose. With every increase of size the massive character of the external casing of the blast furnace has diminished by the reduction of the mass of masonry, and the substitution of cast and wrought iron whenever it is possible to do so. Thus in many modern English furnaces the old stack pillars and twyer houses have Fig. 4. Swedish charcoal blast furnace, vertical section on line A B. Fig. 5. been replaced by cast-iron columns or standards, ar- ranged in a circle, whose entablature is a cast-iron ring, carrying the whole of the superstructure, or stack, so that the hearth casing, instead of being accessible OF THE BLAST FURNACE AND ITS ACCESSORIES. 141 only at the twyers, is now freely exposed all round. In like manner, the old solid stack casing of masonry and hooping has given place to a cylinder of wrought-iron plates riveted together. The latter class are known as cupola furnaces, from their resemblance to the common iron-founder's furnace of the same name. Examples of these different forms of construction may be seen in almost every iron-making district. The Fig. 5. Swedish charcoal blast furnace plan at E F, Fig. 4. oMer kinds, with massive stacks, are, as might be ex- pected, to be found chiefly in the older districts, such as South Wales, Staffordshire, and Scotland ; while in the newer furnaces of the north-eastern counties and Lancashire, the iron-jacketed cupola type is more com- monly seen. Figs. 4 and 5, which are the section and plan of a small charcoal blast furnace at Safveniis, in Lapland, may be taken as an example of the more massive con- struction, with square pillars and a round stack, while 142 METALLURGY OF IRON. Fig. 6 represents the cupola form of furnace, being the section of a large coke fur- nace, smelting hematite, at Barrow-in-Furness, Lanca- shire. The other points in the construction of both these furnaces will be referred to in the sequel. They are placed here merely as types of con- struction. In some of the furnaces of Sweden and Finland, which are of comparatively small dimensions, the outer casing is formed by a crib-work of wood, like a log hut, the in- termediate space between it and the interior furnace stack being filled in with earth. Construction of the working Parts of the Furnace. The shaft, or stack, of the fur- nace, i.e. the upper part above the boshes, is constructed at the same time as the casing. It is now invariably formed of fire-bricks, which are moulded to the proper curve of each ring. The thickness of the shaft or ring wall is about 15 or 18 inches, the joints being brought to a fine face and set in fire-clay. A second wall is, in the more massive class of furnaces, placed immediately outside the first ; this may be either of common or seconds fire-brick, and set in cement ; outside of all, comes the exterior casing, which, as has been already stated, may be either of iron, brick, or masonry. Fig. 6. Cupola blast furnace, Barrow-in-Furness. OF THE BLAST FURNACE AND ITS ACCESSORIES. 143 A small annular space, filled either with loose sand or small fragments of broken slag, is usually interposed between each successive lining, in order to allow for any alterations of form produced by the expansion of the inner one. In the outer casing a number of' square holes are often provided for the escape of moisture ; these are more especially used in furnaces which only remain in blast for a certain period of the year, as is the case in Sweden, but in those that work continuously, they are often omitted. The lower portion of the furnace, including the hearth and boshes, is built after the completion of the stack. The foundation of the hearth varies with the nature of the ground, and may sometimes require to be commenced, in concrete and rubble work, at a consider- able depth below the surface ; the hearth bottom consists of a thick layer of fire-brick, or sandstone, in blocks of as large a size as can be obtained, or in some cases both materials are used. The bricks for this purpose are laid in the form of an inverted flat arch, in order that they may not be forced up in the event of the molten metal finding its way through the joints. When a bed of masonry is used below the hearth bottom, it is generally built with a system of channels or flues inter- secting at right angles, through which air circulates, and prevents the access of moisture from the ground to the hearth. The arrangement of these flues is shown in Fig. 4. The sides of the hearth and boshes, up to their junc- tion with the stack, require to be made of refractory material, and also of considerable thickness, having to withstand a very high degree of heat, in addition to the common action of the molten slags. When the rectangular hearth was used, it was customary to build 144 METALLURGY OF 1ROX. these parts of sandstone similar to that employed for the hearth bottom, but for the circular form brick is generally adopted, and is in almost all cases to be pre- ferred. In Sweden and Germany the hearth and boshes are often formed of a mixture of finely-crushed quartz or ground fire-brick, and fire-clay, applied in a plastic state, and rammed tight between the casing walls and a wooden core or mould of the proper shape of the cavity required, which is afterwards removed. This kind of hearth, which is represented in the Swedish furnace, Figs. 4, 5, is found to answer well in practice for furnaces of small diameter, but requires to be very carefully dried before being heated, in order to prevent irregular shrinkage and cracking. A short distance above the ground level the passages for the introduction of the blast are perforated through the wall of the hearth. These are known as the twyer holes, and vary in number from two to six. On the front or working side of the hearth, a square or flat- arched opening extends from the hearth bottom to a little above the level of the twyer holes. The vertical sides of this opening are prolonged outwards for a short distance into a rectangular cavity, known as the fore-hearth, which is bounded in front by a wall of refractory material, called the dam. The arch covering the opening is called the tymp arch. The exterior of the hearth, and the faces of the nume- rous apertures pierced through it, are strengthened with cast-iron plates and wrought-iron bracings. The under side of the arch is, in large furnaces, usually protected by a cast-iron box or block, having a wrought-iron serpentine pipe inside, through which a current of water is kept flowing, in order to protect the OF THE BLAST FURNACE AND ITS ACCESSORIES. 145 brickwork from destruction by the intense heat to which it is exposed, and the corrosive action of the molten slag which is constantly flowing through it. The dam in front of the hearth is formed of fire- brick, and is carried up to the twyer level. Externally it is supported by a cast-iron plate, called the dam plate. A semicircular furrow in the top edge, known as the cinder notch, forms a passage for the slag, which is now often moulded into large blocks by re- ceiving it in a shallow square-bodied railway truck, having movable sides of wrought iron. When the truck or cinder tub is full, it is removed, and the block of slag, weighing in some instances as much as 7 tons, is, as soon as it has cooled sufficiently to become solidi- fied, removed and thrown away. In charcoal and other small furnaces, the front of the dam is generally formed into a gently-sloping inclined plane or cinder fall, where the slag as it runs out solidifies in a compa- ratively thin layer, and may be broken up and re- moved by hand. In Staffordshire, the slag is allowed to collect in a shallow basin in the floor of the casting house, called the roughing hole, where it consolidates to an irregular disc- shaped lump, which is afterwards lifted out by a crane, and sent off on a truck to the slag bank or cinder tip. The tap-hole for withdrawing the molten iron from the hearth is a narrow vertical slit pierced through the dam, and extending from the hearth bottom about 12 or 15 inches upwards. During the time that the hearth is filling, it is stopped by a packing of sand rammed in tight, which can be easily perforated by a pointed bar, at the time of casting. The space between the top of the dam and the tymp arch is also stopped with sand or brick, a small passage being left for the 146 METALLURGY OF IRON. escape of slag. Sometimes the dam is raised above the level of the twyer, so that a greater depth of melted slag is retained in the furnace, and flows out continuously, the top of the fore-hearth not being stopped. In such cases the blast, instead of impinging directly upon the ignited fuel, first traverses the bath of melted slag. This method is known as blowing in the cinder. It is not quite clear what the exact effect of this operation is. It may act as a distributor for the blast, and also as a method of superheating. In order to prevent the escape of solid matters with the slag, it is necessary that the vertical distance between the crest of the dam and the underside of the tymp should be such as to allow of the accumulation of a column of molten material sufficient to exert a slightly greater pressure than that of the blast. At either side of the tymp there are often fixed to the hearth casing a series of cast-iron plates with ver- tical racks or notches, which form points of support or fulcra for the heavy tools used in clearing the hearth and other operations in the interior of the furnace ; these are known in France as gendarmes. Figs. 7 and 8, which are modified drawings of a South Staffordshire furnace, represent the general arrangement of the hearth of the blast furnace men- tioned in the preceding paragraph. Fig. 7 is a front view of the exterior of the hearth, and Fig. 8 a section on the line A B ; a is the dam in section, b the cast- iron dam-plate, c the tap-hole, d the water tymp in elevation in Fig. 7, and in section showing the water passages in Fig. 8 ; e is the blast main, and / a smaller pipe supplying water to the tymp and twyers. Details of the Top of the Furnace. The upper end OF THE BLAST FURNACE AND ITS ACCESSORIES. 147 of the stack, or throat of the furnace, is surrounded by a platform or charging plate sufficiently broad to give room for working the barrows used in filling ore, fuel, Fig. 7. Lower part of blast furnace, showing part of hearth and dam plate. and fluxes. In the older square-stacked furnaces, suffi- cient space for this purpose could usually be found Fig. 8. Lower pan of blast furnace, section through hearth and dam. between the ring wall and the external casing ; but in the more taper cylindrical or conical forms of modern 148 METALLURGY OF IRON. times, additional surface is necessary. This is provided by an overhanging gallery carried upon brackets, con- structed entirely of cast and wrought iron. When two or more furnaces are placed adjacent to each other, their galleries are united by bridges, which communi- cate with the lifts for bringing up materials to the furnace top. When the gases are allowed to burn at the throat, it is necessary to provide a chimney in order to carry the flame clear of the charging place. For this purpose a short cylinder of brickwork hooped with wrought iron, or even of cast iron, is used, known as the tunnel head. The charging holes are rectangular apertures, varying in number with the diameter of the throat, in the lower part of the tunnel head, through which the charges of ore, fluxes, and fuel are intro- duced. Except at the time of charging they are gene- rally closed by wrought-iron shutters. The arrangements of the head of the furnace when the gases are collected are somewhat more complicated, and will be described further on. Lifts. In hilly countries, where the valleys are deep, it often happens that blast furnaces can be placed below the general level of the ground, supplying the ores and fuel, so that all materials necessary for working may be delivered at the furnace top without any special appliances. In flat ground, on the other hand, such as prevails in most of the iron districts of England, it becomes necessary to resort to mechanical lifts for raising the charges. The following are some of the forms more generally employed. Inclined Planes. These are mostly to be found in old works, the more directly vertical lift being generally preferred at the present day. They are usually made OF THE BLAST FURNACE AND ITS ACCESSORIES. 149 with a double line of railway, or with a single line and crossings for the return trucks, carried on trestle work. The inclination is usually not more than 25 or 30 degrees. The most convenient form of truck is a triangular frame, with two pairs of wheels of unequal height, supporting a horizontal platform of sufficient size to carry four or more of the iron wheelbarrows used in charging, with their loads. The motive power is usually a steam engine of from 10 to 20 horse power, working a pair of winding drums. The load is drawn either by wire ropes, or in Staffordshire by flat-linked chains, such as are used in the same district for draw- ing in collieries. At the Barrow Iron Works, in Lancashire, two in- clined planes are used for the supply of seven furnaces. They are carried by bow and string girders of wrought iron, and extend from the ground to the top of the furnace, with only one intermediate support. The plat- form waggon, carrying the barrows, is received into a recess in the charging platform, and a similar one below, so that the barrows with the loads may be wheeled on and off on their arrival at either end. The motive power is a high-pressure steam engine placed behind the furnaces, working a wire-rope drum. About 4,000 tons of materials are lifted weekly by each plane. The most approved form of lift, where large quan- tities of material have to be raised to a considerable height, is a cage moving between vertical guides exactly similar to those used in collieries. As the load is com- paratively quickly raised, it is a useful precaution, where steam power is used, to have no self-acting valve gear, but to let the engine be entirely worked by hand, in order to prevent the chance of accidents from over- winding. 150 METALLURGY OF IRON. The water 'balance is an old and favourite form of lift for small furnaces. It consists of two cages moving vertically and guided, united by a rope or chain passing over a guide pulley ; below the floor of each cage is fixed a water-tight box, provided with a discharge valve in the bottom. When the empty cage is at the top of its stroke, water is allowed to flow into the box until the weight is sufficient to pull up the other cage with a fresh load, the speed being regulated by a brake on the guide pulley. As soon as the return cage reaches the ground, the projecting stalk of the discharge valve strikes against a catch, and is driven up, leaving a passage for the water, which runs out, and the cage is ready for another ascent when loaded. The chief merit about this plan is its extreme simplicity and the large useful effect got from the water, especially if a natural fall can be used, otherwise it must be pumped up by special machinery. The principal objection to it is the difficulty of keeping the water boxes tight, the lift houses being generally damp and sloppy from leak- ages. A more perfect kind of hydraulic lift is that con- structed upon Sir William Armstrong's system, where the lifting cage is connected to a water-pressure engine by means of a chain passing over a system of compound pulleys, so that when the engine makes a stroke of 6 or 8 feet the load is lifted through a height six or eight times greater, according to the multiplying pur- chase of the tackle. Pneumatic lifts are now used to a considerable extent in England, as the necessary power, compressed air, may be readily obtained from the main blast engines supplying the furnaces. The simplest form is a wrought- iron cylinder, open at the bottom and closed at the top, OF THE BLAST FURNACE AND ITS ACCESSORIES. 151 about 6 or 8 feet in diameter, and somewhat longer than the height of the furnace, suspended in a tank by counter-balance weights passing over pulleys in a manner exactly similar to an ordinary gasometer. A pipe for the admission of air at 3 or 4 Ibs. per square inch above the atmospheric pressure, is introduced through the tank. The waggon to be lifted is carried on the top of the bell, and as the whole of the moving parts of the apparatus are balanced, the amount of power required is only that necessary to raise the additional load. For the return stroke, the air within the bell is allowed to escape by opening a valve communicating with the atmosphere, the weight of the empty waggon being sufficient to lower the bell in the tank. In Gjers' pneumatic lift, which is much used in the newer Cleveland furnaces, the motive power, instead of being taken from the main blast engine, is furnished by a pair of double-acting air-pumps, the lift being effected by the pressure of the atmosphere acting against a vacuum, in a cylinder, while the empty waggons are returned by compressing air under the piston. The Jacob's ladder, or endless chain system of lift, usually described in older works, is probably no longer in use. Blowing Machines. The use of cast-iron cylinder blast engines has almost everywhere superseded the ruder contrivances of wooden chests with square pis- tons, bellows, &c. In Sweden, for small furnaces and forges, the single-acting form of engine is much used, being cheap and economical in working and main- tenance. Usually three inverted vertical cylinders are employed, of about 3J or 4 feet diameter and length of stroke, carried on cast-iron or wooden standards, and driven directly by a water-wheel. 152 METALLURGY OF IRON. The cylinder is provided with an air-tight piston, to which a reciprocating motion is imparted by appropriate mechanism. Two sets of valves are placed on the cylinder cover : the longer series open inwards as the piston recedes, giving a passage for the admission of the external air, and at the change of stroke are closed by the compressing force exerted by the piston on the included air ; and the second series, or discharge valves, which are in connection with the blast reservoir, open, and allow the compressed air to pass out. In the single-acting engine only one end of the cylinder is covered and provided with valves ; while in the double- acting form (represented in Fig. 9) both ends are similarly arranged, so that one side of the piston is drawing air through the intake valves, #, while the other is compressing the volume taken in at the pre- ceding stroke, and driving it over into the reservoir through the discharge valves, b. The valves employed are generally oblong rectangular plates, with their shorter sides placed vertically one of the long sides forming the hinge. In order to combine rigidity with lightness, it is usual to make them of a combination iir. 9. Cylinder blast engine. n .-, . n , .-! of thin sheet iron, with contact surfaces of felt, leather, or india-rubber. The hinge may be either of metal, accurately fitted, or merely a flexible leather flap. The seats or boxes to which they are affixed are usually rectangular tubes projecting from the outer face of the cylinder cover. In order that the OF THE BLAST FURNACE AND ITS ACCESSORIES. 153 valves may close by their own weight when relieved from the pressure of the air, it is usual to fix the beat- ing face of the seat in an inclined position, or counter- balance weights or springs of steel or india-rubber may be used for the same purpose. As the motion of the valves is similar to that of the pendulum, the time required for opening and shutting them is dependent on their vertical length, so that the piston cannot be driven beyond a certain speed, unless mechanical means, capable of being increased pari passu with the speed of the engine, be employed. This has been attempted in the so- called slide-blowing engines, where the flap valves are replaced by a slide similar to that used in steam engines, which travels at the same rate as the piston, and places the apertures at either end alter- nately in communication with the external air and the blast reservoir. The system of construction has been adopted at different times both in England and on the Continent. The best-known form is Slate's engine, where the slide is annular, and placed outside of the vertical blast cylinder, receiving motion by means of a pair of parallel rods connected with the rotary shaft of a steam engine below. The form of the slide is the solid of revolution produced by the rotation of an ordinary -/"\_ shaped slide valve about a vertical axis, formed by the centre line of the steam and blast pistons. In Thomas and Laurent's arrangement the cylinder is horizontal ; the air passages are of a rectangular form, and are, together with the slide, placed laterally in the same manner as the steam ports and slide valve in an ordinary horizontal steam engine. In Fossey's engine, which was exhibited in the Belgian department of the Exhibition of 1862, the 154 METALLURGY OF IRON. slide valves are replaced by discs with, radial perfora- tions, which are put in slow rotary motion by gearing from the fly-wheel shaft. A jacket is cast round the cylinder, with an interspace forming the passage from the cylinder to the reservoir. The apertures in the disc are sixteen in number, a corresponding series being formed in the cylinder ends, which are alter- nately opened and closed by the rotation of the disc in conformity with the motion of the piston. In the for- mer position the external air is admitted, while in the latter the volume enclosed is driven over into the jacket and reservoir. In practice the use of the slide blast engine has not been found to be advantageous, owing to the large amount of mechanical effect con- sumed by the friction of the slide against the rubbing face of the cylinder, which would be great in itself, on account of the high speed at which they require to be driven, but is materially increased, owing to the dusty state of the atmosphere almost unavoidable in iron works. In the ordinary form of engine with flap or clack valves it is necessary to provide as large an area of air ways as can be got out of the surface of the cylinder cover. The intake passages should be made, if possible, equal to one- half, and the outlet about one- eighth, of the area of the piston. As it is impossible in large engines to use single valves of these dimensions, on account of their weight, and consequent liability to give rise to injurious shocks in working, it is customary, therefore, to employ a number of small valves, whose united areas make up the required amount of surface. The question of the relative advantages of horizontal and vertical blast cylinders has been discussed at con- siderable length by engineers, both in this country OF THE BLAST FURNACE AND ITS ACCESSORIES. 155 and on the Continent. As in many other matters depending upon practical experience, there is much to be said on either side. For engines of small dimensions the horizontal form is cheaper, and may be worked with the least amount of clearance from the vertical position of the cylinder covers, which may be pierced through like a gridiron, giving a bearing for the valves, without any overhanging parts or valve boxes. The required foundations may also be less massive than in the vertical form, owing to the longer bearing of the framing, when a horizontal direct- acting steam engine is the motor ; this, of course, necessitates the comparatively larger surface for the engine-house. On the other hand, the difficulty of lubrication is increased, as the powdered graphite, which is generally used for this purpose, instead of being uniformly distributed round the pistons, is apt to fall to the bottom of the cylinder, while the upper side works dry, and the cylinder wall is worn irregularly, and becomes ovalised. The difficulty of keeping the weight of the piston off the bottom, and producing the same kind of unequal wear, is also urged against the use of large horizontal cylinders ; but this objection, which has also been applied in the case of horizontal steam engines, does not appear to be productive of any practical disadvantage in the larger modern engines used for screw propulsion, whose diameters are quite equal to those of the average of blast cylinders. In regard to vertical beam engines the chief disad- vantages are their great length and expensive character of construction, and the extra amount of clearance, equal to the volume of the valve boxes, rendered necessary by the horizontal position of the cylinder covers ; on the other, they have the great advantage of stability, and 156 METALLURGY OF IRON. may be made of any dimensions ; thus, in South Wales, engines are in use with blast cylinders up to 12 feet in diameter. In engines giving small volumes of blast at very high pressure, such as are used in Bessemer 's process, the valves require to be made extremely light: the construction employed in such cases is a plain ring or plate of india-rubber covering a perfo- rated plate, which opens and shuts by its own elasticity when exposed to, or relieved from, pressure. In Coulthard's blast engines the air passages are circular holes in the cylinder, similar to those used by Bessemer, but the valves are light wooden balls covered with india-rubber, which are arranged on inclined and grooved seats., sloping in a direction contrary to that of the current of air, so that when the pressure is suffi- cient to drive the balls up the incline the air way is opened ; but as soon as it is relieved, they roll down again, and stop the passage. The combination of the blast and steam cylinders, when steam power is used, is effected in various ways. The large vertical engines of modern date in this country are beam engines, the main bearing being supported either on the engine-house wall or on an entablature carried by cast-iron columns. The piston- rods are attached by the ordinary parallel motion. On the steam side, the beam is often continued beyond the point of articulation of the piston-rod, and turned up- ward into a short crane neck, to the end of which the connecting-rod working the fly-wheel is attached. This arrangement permits the use of a long light con- necting-rod, without unduly increasing the surface occupied by the engine. In Belgium, direct-acting engines with vertical cylinders are much used, the blast cylinder being placed OF THE BLAST FURNACE AND ITS ACCESSORIES. 157 uppermost. In an engine of this class built at Seraing, Evans's beam, with, an oscillating centre, is adopted, in order to keep the working parts within a comparatively small space, the length of the base of the engine- house being little more than the radius of the fly-wheel, or about 25 feet. The height, owing to the two cylinders being placed one above another, is consider- able, being not less than 40 feet. The steam cylinder is 41 J inches, and the blast cylinder 66 inches ; the length of stroke 88 inches. When working with steam of 30 Ibs. pressure, and blowing air at 4J Ibs. above the atmosphere in sufficient quantity for a large furnace burning coke, the work done is equal to between 80 and 100 horse power. In the newer kind of engines built at the same works, the vertical direct- acting form is preserved, but the piston-rods are guided by sliding blocks instead of the older and more complicated arrangement of Evans. In Austria a class of small direct- acting engines of the same character is used for charcoal furnaces, having the steam cylinder placed uppermost, which, together with the framing for the guides, is bolted on to the top flange of the blast cylinder. They are usually of small dimensions, averaging from 25 to 30 horse power, and delivers from 2,300 to 2,500 cubic feet of air per minute. In Siegen, and other parts of Rhenish Prussia, hori- zontal blast engines are preferred. The commonest pattern has both cylinders placed in the same line : the rod which carries the two pistons goes through both covers of the blast cylinder, and is guided on either side. Usually two engines are coupled together upon the same fly-wheel, but the construction is such that they may be disconnected if only the power of one engine is 158 METALLURGY OF IRON. wanted. For charcoal furnaces from 30 to 40 horse power is considered sufficient, but with the larger ones, working on coke, from 80 to 100 horse power is found to be necessary, as in other districts. The same kind of horizontal engine is generally adopted in new works in Sweden and Lapland, having only a single charcoal furnace. The working limits of blast pressure vary with the nature of the fuel employed, and the burden of the furnace, &c. Thus, in some of the small charcoal furnaces of Northern Europe, it does not exceed half or three-quarters of an inch of mercury above that of the atmosphere ; while in American anthracite fur- naces as much as 15 inches, or 7J Ibs., is used. In England from 2J to 3 Ibs. is used with cold blast and tender fuel, but 3J, 4, or 5 Ibs. is common with hard coke. In Bessemer' s process of steel-making, by forcing air through a column of molten pig iron, a pressure of from 15 to 20 Ibs. per square inch is used. The largest blast engines hitherto constructed are those at Dowlais and Ebbw Yale, in South Wales ; the former, which was erected by the late Mr. Truran, has a cylinder 144 inches in diameter, with the same length of stroke ; the area of the admission valves is 56 square feet, that of the discharge valves 16 square feet, the former being equal to half the surface of the piston. The steam cylinder is 55 inches in diameter, with a piston making a stroke of 13 feet, the motion being transmitted by an unequal- armed beam. Owing to the large area of the air ways a very high speed, as many as 20 strokes per minute, can be obtained. The volume of blast delivered is about 51,000 cubic feet, at a pressure of 3| Ibs., sufficient for the supply of six large OF THE BLAST FURNACE AND ITS ACCESSORIES. 159 furnaces and four refineries. The main blast pipe is 5 feet in diameter. The Ebbw Yale engine has a blowing cylinder of the same size, but the steam cylinder is 72 inches in diameter. The practice of blowing several furnaces by one engine of large size, though mechanically advantageous, is attended with considerable risk, as the safety of the furnaces may be endangered in the event of a break- down, unless there be a reserve of blowing power. It is therefore preferable to divide the work between two or more engines, according to the number of furnaces in blast. Where there is only a single furnace, as is usually the case in charcoal-smelting, two small engines coupled together, but capable of being worked indepen- dently of each other, may be used, for the same reason. Blast Regulators. The air or blast issues from the blowing cylinder in an irregular stream, owing to the variation in pressure at different points of the stroke, the supply being intermitted during the period of actual compression after the closing of the intake, and before the opening of the discharge valves. In order, therefore, to produce a steady current in the furnace, it is necessary to use some means of equalising the pressure. This may be done either by receiving the blast into a reservoir whose volume is several times that of the blowing cylinder, or by delivering it into a second cylinder containing a loaded piston, which rises when the supply of blast is greater than the amount required by the furnaces ; but when the quantity diminishes the piston falls, and exerts a compressing force, until the equilibrium is restored by increasing the speed of the engine. The same effect may be produced, with less loss from friction, by the use of a loaded bell, or gasometer, floating in a water tank. 160 METALLURGY OF IRON. The volume of these regulators may be from one and a half to twice that of the blast cylinder. Fixed reservoirs are usually made of wrought iron ; formerly a spherical, or balloon- shaped form was com- monly adopted, but they are now more generally made cylindrical, with flat ends like high-pressure steam boilers. The thickness of the plates, of course, depends upon the pressure and dimensions employed, as well as the form adopted : from one-twelfth to one-eighth of an inch may be taken as sizes commonly used. The volume of the regulator may be from twenty-five to fifty times as great as the amount of blast in cubic feet delivered by the engine per second, when it is placed near the furnace, but this may be considerably diminished when a long blast main is used. Indeed, it often happens that sufficient uniformity can be got in the latter case, especially when several engines are used, by blowing into the main direct, without the use of a special regulator. Regulators in masonry or brickwork are usually lined with cement in order to protect the air from taking up moisture. A regulator of this character, consisting of a chamber cut out in the solid rock, was applied at Devon Iron Works, in Scotland, as early as 1792. Blast Heating Apparatus. The use of heated air in the blast furnace, which was first introduced by Neil- son in 1828, has been found to be attended with a great economy of fuel, and at the same time the work- ing power of the furnace is increased. It is therefore employed at the present day in iron-making districts all over the world, almost to the exclusion of cold blast, the latter being retained only for certain special makes which command an extra price, and may there- OF THE BLAST FURNACE AND ITS ACCESSORIES. 161 fore be produced without the strict regard to econo- mical considerations which is necessary when working on an article of lower repute. The amount to which the temperature of the blast may be raised with advantage does not appear to have any practical limit, every fresh increase being attended with further saving of fuel ; thus, in the first instance, 100 were found to be an advantage over air at the ordinary temperature ; then came temperatures of 200 400, up to the melting-point of zinc ; and now it is actually used at a visible red heat, or about 700. Thus it was found that a saving was produced of 5 cwt. of coke per ton of iron made by using air heated to about 650, instead of the lower tempera- ture of 350 or 400, previously employed. The dif- ficulty of keeping the apparatus tight, and the rapid destruction of metal pipes when heated to redness in air, render a special construction necessary for the production of such extremely hot blast economically. The greater number of blast-heating apparatus in use at the present time, and known as hot blast ovens or stoves, consist essentially of a series of parallel, or spiral tubes, arranged in a chamber of fire-brick, and heated externally by a fire. The opposite ends of these tubes are connected with two mains intersecting them at right angles. One of these supplies cold air, while the other, or hot blast main, removes the heated air. In the older forms of stove, such as that originally adopted at Calder, in Lanarkshire, the fireplace is an oblong rectangle in plan. The two mains, which are placed parallel to the longer sides, are of a circular section, and cast with a number of circular sockets for the heating pipes. These are arched, horse-slioe / 162 METALLURGY OF IRON. siphon, or inverted U pipes, also circular in section, placed with the arched portion upright, and luted into the sockets on the mains. The fire-grate runs along the whole length of the bottom, and the flame, after playing on the un- der sides of the tubes, passes between and around them, by means of appro- priate flues, into the chim- ney, while the cold air, en- tering by the main on one side, flows continuously through the arched pipes, where it becomes heated, and passes off to the fur- nace by the opposite main. This arrangement is shown, in Fig. 10, in section across the shorter side of the stove : a is the cold blast main ; 5 the hot blast main ; c the arched heating pipe set in sockets on the two mains ; and d the fire- grate. To obviate the defects of this apparatus, many special modifications have been introduced. Thus, in order to get a greater amount of heating surface, the horse- shoe pipes are now usually made of flattened elliptical, or rectangular, instead of circular section. A smaller radius of curvature for the arch has been obtained by the use of inverted V pipes, and more uniformity in heating, by the introduction of stops at intervals in the entry main, so that the air is made to pass alternately backwards and forwards several times across the arch, instead of moving Fig. 10. Hot blast stove. Dowlais. (Truran). OF THE BLAST FUKNACE AND ITS ACCESSORIES. 163 only in one direction, as was the case in tae original, form. Whatever system of construction is used, the air should pass through the apparatus in the reverse direc- tion to the flame, entering cold, at the end farthest from the hottest point of the fire. Arch-headed pipes are very easily broken by irre- gular expansion at the crowns, if a certain freedom of motion is not allowed to the ends ; this is equally provided against by placing one of the mains loose on its bed, supporting it by spherical bearings, so that it may travel outwards to a slight extent as the pipes become heated. Round and oval ovens have been introduced to obtain a more uniform heat than can be got by the old rectangular form. These terms refer to the shape of the base, or fireplace. The mains are re- placed by a cast-iron box of a square or trapeziform section, divided by a central partition, one division cor- responding to the cold, and the other to the hot blast main. The vertical pipes, instead of being arched at the top, are united by a short horizontal one, the limbs being close together. This variety is much used in Staffordshire and Lancashire. A modification somewhat similar to the last, known as the pistol pipe, is used in Scotland, Cleveland, and other districts in this country, and is also rather in 'favour in France and Grermany. The two vertical pipes or limbs are replaced by a single one, divided by an internal partition reaching nearly to the top. It is closed at the upper end, and is either straight, slightly bulbed, or bent over into a half arch. One of the divisions is connected with the intake, and the other with the exit, so that the cold air rises on one side, and 164 METALLURGY OF IRON. passes through the bulbed chamber at the top, down the other, heated to -a the furnace. When the curved head is used, it is usual to place two series of pipes in opposite di- rections with the heads, meeting so as to form an arch for mutual support ; but, of course, the ques- tion of unequal expansion does not arise, as each half of the arch is inde- pendent of the other. The term pistol pipe is derived from the resem- blance of the curved head to a pistol stock, the straight portion corresponding to the barrel. This construction is represented in Fig. 11, the left-hand pipe being shown in section, and the right-hand one in elevation. All the preceding forms of stoves are characterised by the use of air ways presenting continual changes of form ; thus the blast passes from the main through the heating pipes alternately backwards and forwards. In what are known as spiral-pipe ovens, the heating is effected in tubes of uniform section, arranged similarly to the worm of a still. Among these may be mentioned the apparatus in use at Ebbw Yale, a horizontal coil of cast-iron pipes exposed to a fire running the whole length of the axis. The pipes are formed in segments corresponding to one-half of a complete turn of the screw, and are united by ordinary socket joints. Fig. 11. Pistol-pipe hot blast stove. Oberhausen. OF 1HE BLAST FURNACE AND ITS ACCESSORIES. 165 The union of the pipes and mains in stoves is always effected in the same manner, the latter being cast with sockets for receiving the ends or feet of the pipes, which are often made slightly conical, spigot fashion. The joint is made air-tight by rust cement. Stoves with straight or serpentine horizontal pipes are much in vogue in Germany, and are known after the name of the works at "Wasseralfingen, in Wurtemberg, where they were first introduced. In the original construction a number of straight pipes of circular bore, placed horizontally, extend from side to side of the walls of the fire chamber in a manner exactly similar to the tubes of a locomotive, and are united into a continuous serpentine coil by external arched bends not exposed to the fire. In this way the difficulty arising from the tendency of the pipes to break at the bends, owing to irregular expansion when heated, is avoided. The newer forms differ chiefly from the foregoing in the section of the pipes, which are now usually elliptical instead of circular. The position of the longer axis may be either horizontal or vertical ; the latter, being the most advantageous arrangement, is usually adopted. Fig. 1 2 is a section of a stove of this pattern at Neu- stadt, in Hanover. The coil consists of four pipes united by semicircular bends, four similar series being united by other bends placed horizontally, so that the whole appa- ratus contains sixteen pipes. The cold air enters at c, and passing downwards, issues in a heated state at d. The fuel employed is the waste gas from the blast furnace, which is supplied through the wrought-iron main, a, and jet-pipe, b. The latter is provided with a central tube for the admission of the air necessary for burning the gas. 166 METALLURGY OF IRON. Thomas and Laurent's stove, used in several of the newer French furnaces, consists of three vertical tubes of large diameter, united by external horse- shoe pieces placed externally, as in the Wasseralfingen apparatus. Fig. 12. Hot blast stove. Wasseralfhigen pattern. In order to obtain a larger heating surface, the inner side of the tube is studded with projecting radiating ribs about 3 inches high, the remaining interior space being filled with a cylindrical core of cast iron or fire-brick. These ribs are not continuous in the same place throughout the entire height of the tube, but are interrupted at diiferent levels, the series above and below being arranged so as to break joint with the central one. By this means the air is forced to travel in a somewhat deviating course through the passages enclosed between the core and the ribs. A very con- siderable heating effect is claimed for this arrange- ment, which is similar to that of the stoves known as "gill calorifiers," used for warming large rooms; but OF THE BLAST FURNACE AND ITS ACCESSORIES. 167 it is attended, owing to the irregular section of the air ways, with a notable loss of pressure from friction. In considering hot blast stoves, we have hitherto assumed that the heating of the air is to be effected by means of fuel burnt on a grate below the pipes. This is still done to a considerable extent, but the substitu- tion of the waste gases of the furnace is now almost equally common, especially in furnaces using fuel brought from a distance. For this purpose it is neces- sary to bring a branch pipe to the stove from the main gas conduit, which terminates either in a series of jets, or more commonly in a rectangular mouth-piece, a special aperture of a similar character, for the admission of air, being placed immediately above or below. It is generally advisable to have a grate with a small fire, which insures ignition of the gases ; with- out this, in case of the flame becoming extinguished, air would be liable to get back into the gas main, where it would most probably produce an explosion. Cowper's stove, for heating air to very high tempera- tures, is constructed on the so-called "regenerative" principle of Siemens. It consists, as shown in section, Fig. 13, of a cylindrical chamber, with a low-domed roof of fire-brick work, cased with wrought iron ; the discharging passage for the hot blast, made of similar materials, projects on one side, opposite to which is the stack for producing the necessary draught. In the interior of the chamber a vertical shaft, A, whose diameter is about one-third of the whole space between the walls, extends from the floor nearly to the roof, and communicates at the bottom with the passages, B, by which the inflammable gases and air are ad- mitted, and by a horizontal flue, c, with the hot blast exit passage. The annular space between the central 168 METALLURGY OF IRON. shaft and the walls of the chamber contains two parallel ring flues ; these serve alternately for the admission of cold blast, and the escape of spent flame to the chimney. Above these flues, which occupy about a quarter of the total height of the chamber, the whole of the re- Fig. 13. Cowper's hot blast stove. maining space, up to the springing of the dome, is filled with fire-bricks loosely stacked, so that a large number of small rectangular openings are left between them, forming the channels for the blast and gases to circulate. During the time of heating, the hot and cold blast valves, E and r, are shut, and the gas and air valves, G and H, below the central shaft, opened. The ignited gas then rises up the shaft, and passes downwards through the bricks and lower ring flues into the chimney, the draught being regulated by a special damper. The heat evolved by the burning gases is transferred to the bricks, the temperature of the layers being in- OF THE BLAST FURNACE AND ITS ACCESSORIES. 169 creased progressively from above downwards, until, in about two tours' time, the whole contents of the chamber are brought to a uniform strong red heat ; the air, gas, and chimney valves are then closed, and the cold blast is admitted by the valve, F, and passes through the chamber in the reverse direction to the heating current, upward through the bricks, abstract- ing their heat, and down the central shaft through the hot blast valve, E, to the furnace. The current of cold air is continued until the bricks, with the exception of a few of the upper layers, are no longer red-hot ; the blast is then stopped, and the heating is recommenced by admitting gas and air as before. It is of course necessary to have two stoves in order to keep up the blast continuously, one being heated while the other is cooling, and vice versa. By this system of stove the gaseous fuel is very perfectly economised, the tempera- ture of the current in chimney being not much above that of boiling water, 100 C to 120, while the blast is made visibly red-hot, and capable of melting antimony with ease, corresponding to a temperature of 700 to 800. In this stove all the parts brought into contact with the heated air are made of refractory brickwork, with the exception of the hot blast valve, which is of cast iron, with double walls, and cooled with water like an ordinary hot blast twyer. Fig. 14, taken from Tomlinson, shows the course of the air and gas in a pair of these stoves when at work. The right-hand one is being heated, while the. other is giving up its acquired heat to the blast. Fig. 15 shows the manner in which the bricks are stacked in the regenerators. A simple form of the stove last mentioned has been recently introduced by Whitwell. In it the cellular 170 METALLURGY OF IRON. piles of bricks are replaced by plain walls ; the former Fig. 14. Cowper's hot blast stove plan. C. Chimney. H.B. V. Hot blast valve. C. V. Chimney valve. A V. Air valve. G. V. Gas valve. d. V. Cold blast valve. 8. Shut. 0. Open. method of construction being objectionable when blast- furnace gas is used for heating, as the spaces between Jl Li I I Fig. 15. Cowper's hot blast stove. Details of arrangement of bricks the bricks are liable to become choked by the deposit of flue dust. The oven or heating chamber is enclosed by four upright walls, and divided by internal, up- right, parallel partitions into several narrow com- OF THE BLAST FURNACE AND ITS ACCESSORIES. 171 partments. Fire-brick, ganister, or any similar re- fractory material, may be employed in the construction of the oven. The interior partitions are constructed with openings placed alternately at the top and bottom, so that the burning gas, and also the blast, is made to pass through the entire height of the compart- ment, and over each face of the partition walls in succession. The top of the oven is flat, and provided with a series of holes over the tops of the alternate walls : these are ordinarily stopped with plugs of fire-brick, which can be easily removed when it becomes necessary to clean out the dust. There are similar holes in the side walls near the ground. In other respects, the ar- rangements for working in pairs alternately, and the valves for the admission of gas, air, and blast, are similar to those employed in Cowper's stove. The amount of heating surface in hot blast stoves with cast-iron pipes is usually about one square foot per cubic foot of blast passing through per minute when fired with coal. With gaseous fuel it is advisable to make them from 10 to 20 per cent, larger. Pressure Gauges. For low-pressure blast, such as is used in small charcoal furnaces, or for determining the tension of the waste gases, a water gauge is generally used, but for the more highly compressed air used in furnaces on mineral fuel, mercury gauges are necessary. When the blast is at a very high temperature, it is necessary to make the observations as quickly as possible, or to cool the air down by passing it through a tube placed in a current of water, before allowing it to come in contact with the mercury. By multiplying the indications of the mercurial gauge in inches by 13-59, the corresponding height measured in water is 172 METALLURGY OF IRONS'. obtained, and conversely, inches of water gauge may be reduced to mercurial inches by dividing by the same constants. When, as is usually the case, the height of the water gauge is expressed in feet and inches, it may be reduced to the corresponding pressure in inches and lines of mercury by multiplying by 0'882. The amount of blast passing through a twyer is found by multiplying the velocity of the current passing per minute or second, as deduced from the pressure, by its sectional area. The result must, of course, be corrected for temperature, atmospheric pressure, and moisture, and for the contraction of the jet at the point of efflux. The latter correction varies in amount with - the form of the nozzle, and is somewhat greater for cylindrical than conical pipes, and also increases with the pressure employed. As a general rule, the diminution of volume from this cause may be taken at about 8 per cent., and the real amount found by multiplying the theoretical quantity by 0*92. The determination of the amount of blast carried into the furnace, from the observations given above, may be approximately found by the following formula, given by Weisbach, as a simplification of the more exact one deduced by him from Poisson's law, checked by actual experiment : /T 1-018 Q= 1179F\/ y - / ! + Q003672? where Q = the number of cubic feet discharged per second, reduced to the temperature of 10 Centigrade, and 30 inches barometrical pressure, F = area of twyer, h = observed height of pressure gauge in inches of mercury, b = observed height of barometer. OF THE BLAST FURNACE AND ITS ACCESSORIES. 173 The second part gives the correction for the heat of the blast, when r = its temperature in Centigrade degrees. In the first part of the above formula, F is taken in square feet, by dividing by 144, or, putting F = 1 square inch, we obtain the following simple expression : = 8-2 (2) wnich gives the volume of blast per second per square inch of the sectional area of the twyer. The following table gives the value of Q for different values of the fraction - in formula (2) : k b a h b Q o-oi 0-82 0-30 4-49 02 1-16 35 4-85 05 1-83 40 5-19 10 2-59 45 5-50 15 3-18 50 5-80 20 3-67 55 6-08 25 | 4-10 60 6-35 These quantities require to be corrected for temperature when hot blast is used by the second part of formula (1). The quantity of air passing into a furnace may also be decided from the composition of the waste gases when the furnace works with a closed top, and the whole of the volatile products are collected. Determination of the Temperature of the Blast. Mer- curial thermometers cannot be used in determining temperatures much above 200 or 250 with accuracy, owing to the irregular expansion of the mercury when near its boiling-point. For measuring the high tern- 174 METALLURGY OF IRON. peratures prevailing in blast-furnace operations, me- tallic pyrometers of various kinds are employed, depending either on the expansion of a single metal, or a combination of two, such as iron and copper or platinum. These, although convenient, are liable to give inaccurate results after a time, from the metals becoming permanently expanded when repeatedly heated. In practice the temperature of the blast is generally determined by its power of fusing metals. This is done by exposing a thin rod of the metal to the current in the twyer, a hole being made for the purpose in the elbow of the branch pipe connecting the twyer with the blast main. The following are the reputed melting-points of the metals available for determining the temperatures of hot blast : Degrees. Tin 245 Bismuth 250 Lead ...... 330 Zinc . . . . . .410 Antimony ..... 512 In experiments on the temperature of the interior of the furnace, such as those made by Tunner in Styria, and Rinman and others in Sweden, alloys of gold and silver, and silver and platinum, are used, the increase of the melting-point being assumed as directly propor- tional to the increase in the amount of the more refractory metal. This method was also used by Plattner in determining the temperature of fusion of slags. The following table contains the melting-points OF THE BLAST FURNACE AND ITS ACCESSORIES. 175 of various alloys used for the above purposes by Tunner : Degrees. 9 Lead -f 1 Silver melts at 400 8 2 470 7 3 540 6 4 610 5 ,, 5 680 4 6 750 3 7 815 2 8 885 1 9 955 0-6,, 9-4 980 Degrees. 9-5 Silver -f 0'5 Gold melts at 1,030 7 3 1,050 4-5 5-5 1,070 2 8 ,, 1,090 Fine Gold ,, 1,100 9 Silver + 1 Platinum 1,175 8-5 1-5 ,', ,. 1,250 8 2 ,, ,, 1,325 7'5 2-5 ,, ,, 1,400 7 3 1,475 6-5 3-5 1,550 5 5 1,625 Pouillet's pyrometric method, which consists in ob- serving the increase of temperature produced in a weighed quantity of water by plunging into it a mass of metal, whose weight and specific heat are known, heated to the temperature to be measured, has also been applied to the construction of pyrometers for blast furnaces ; a ball of copper is used for medium, and platinum for higher temperatures. From the increase in the sensible heat of the water, the loss 176 METALLURGY OF IRON. experienced by the metal may be found by the follow- ing formula : ,, w t , t = - where w s w = weight of water, t = its increase of temperature, w = weight of metal ball, s = its specific heat. To this result must be added the observed temperature of the water in order to get at that of the furnace. Position of Hot Blast Stoves. It is in all cases de- sirable to place the stoves as near to the furnace as is consistent with the other requirements of the works, in order that the blast may lose as little of its acquired heat as possible, by not having to travel a long dis- tance through pipes exposed to the air. In some in- stances, especially in small charcoal furnaces, where the stoves are heated by waste gases, they are placed on a level with the furnace top, the gases being led in by a short flue in order to economise their sensible heat, as well as the much .greater quantity derived from their subsequent combustion. The hot blast main is then carried down vertically to the twyers. This practice is tolerably common in Swedish and German charcoal fur- naces, and appears to be very general in the United States, where the blast- engine boilers are often carried on the top of high-vaulted structures in the same manner. Much greater regularity of draught, and especially -freedom from choking by dust, can be ob- tained when the stoves are placed at the ground level, and the gases are brought down by a suitable conduit. Arrangement of the Twyers. The blast coming from the stoves passes through a ring main, which, in the old square- cased furnaces, is carried through the cir- cular passage traversing the stack pillars ; but in the OF THE BLAST FURNACE AND ITS ACCESSORIES. 177 newer forms is generally attached to the columns, surrounding the hearth at a certain distance above the ground. A vertical branch pipe, or goose neck, is led off opposite to each twyer hole, and at the proper level is turned over at right angles into a horizontal arm, to which the blast nozzle, or blowpipe, is attached. A throttle, or slide valve, for stopping or regulating the blast, is attached to each branch, as well as to the main near the stove. In cold blast furnaces the air is led through a conical copper nozzle, attached to a branch pipe by a flexible leather tube ; but with hot blast it is requisite to make all the fittings of metal, and the necessary means of adjustment are provided by interposing a sliding or tele- scopic tube and a ball-and-socket joint between the end of the branch pipe and the twyer. By the former the twyer is set to the proper length, while the latter allows the direction of the entering blast to be varied, so that it be made level, plunging or rising at pleasure. When hot blast is used, it is necessary to protect the walls of the hearth from the intense heat generated by the energetic combustion going on immediately in front of the twyers. This is done by the use of water twyers, which are hollow, conical, or tapering D-shaped tubes, with double walls, which are kept cool by a current of water circulating through the interspace. Fig. 16 represents a hot blast twyer as applied to a charcoal furnace at Rhonitz, in Hungary, a is the water twyer, formed of cast and wrought iron, with double walls, which are cooled by a current of water circulating through the intermediate space, b is the blowpipe, which is of sheet iron, and bears against a divergent conical orifice placed within the water twyer. The latter arrangement is not usual, the end of the N 178 METALLURGY OF IRON. blowpipe being generally inserted loose in the twver, and the intermediate space stopped with clay. The axis of the jet may be made horizontal, or to incline upwards or downwards by means of the ball-and- socket adjustment at c. The end of the twyer is ad- Fig. 16. Hot blast water twyer. Rhonitz, Hungary. vanced or withdrawn by the telescopic joint and setting screw at d. The flanged elbow-pipe fits on to the vertical branch pipe of the hot blast main. At e the elbow is perforated by a small hole, having a movable shutter, containing a plate of glass or mica, which gives a view of the interior of the hearth, or rather of the bright spot, or eye, immediately in front of the twyer. Through this aperture the fusible metals used in trying the temperature of the blast are introduced. Water twyers are made either entirely of cast or wrought iron alone, of a combination of both, or of copper or bronze. The water space is usually rectan- gular in section, but sometimes a spiral tube of wrought iron is used, either alone or set in a casing of cast iron. An advantage is claimed for bronze twyers of not being readily destroyed by "ironing," that is, of being melted by the imperfectly- fused masses of metallic iron which sometimes adhere to the end of the twyer when the furnace is not in good working order, and the reduced iron is imperfectly carburised. The removal of the adherent masses may be effected by raising the dam, and allowing the cinder to rise above the level of the twyers. Leaky water twyers are productive of great waste of fuel, owing to the large amount of heat OF THE BLAST FURNACE AND ITS ACCESSORIES. 179 absorbed in the decomposition of the steam produced in the hearth. The temperature in the region of fusion is consequently lowered, with the production of white iron of a low degree of carburisation. When the leak is considerable the consequences may become more serious, as the water, if it gets into the lower part of the hearth, is likely to produce an explosion. The number and arrangement of twyers vary very considerably. The smaller charcoal furnaces have often only two, placed on opposite sides of the hearth. Three is a more usual number, one being placed at the back ; i.e., opposite to the tymp, and the others at the sides of the hearth. When a larger number is used, they are generally placed at equal intervals all round tlie hearth. This method is usually adopted in cupola furnaces ; but in South Wales, where there are many large furnaces with only three twyer arches, they are sometimes arranged in series ; thus, two will be put through each of the side open- ings, and the same number at the back, or three at the sides, and one or two at the back, &c. This is done to avoid the use of twyers of an excessive diameter, and, by multiplying the points of contact with the fuel, to make the combustion more uniform over the entire area of the hearth. Sometimes a special twyer is added on the tymp side, for the purpose of removing irregu-, larities caused by local cooling, and is only used in case of the hearth becoming obstructed. Methods of Collecting Waste Gases. In small char- coal furnaces, working with an open throat, the gases are often taken off by wrought-iron pipes perforating the wall of the furnace about 10 or 12 feet below the top. This plan is commonly used in Sweden for sup- plying gases to mine kilns, hot blast stoves, &c., but 180 METALLURGY OF IRON. can only be practised on a small scale. The supply is apt to be somewhat irregular, from the stoppage of the holes by the descending charge. A more perfect method for the same purpose, is that of contracting the throat by the insertion of a cast or wrought- iron cylin- der of somewhat smaller diameter than the ring wall, so that an annular space at the top is kept clear from, the materials of the charge, and forms a collecting flue for the gases. In order to prevent the charges from blocking up the lower part, it is usual to increase the diameter of the shaft by the amount required to form the flue, and the tube restores the furnace to its original section. The application of this arrangement is shown in the charcoal furnace, Fig. 4. When it is desired to collect the whole of the gases given off at the top of the furnace, it is necessary to work with a closed throat. The most generally used, and, at the same time, one of the simplest contriv- ances for this purpose is that known as the cup and cone, Fig. 17. It consists Tig. 17.-Furnace top, with cup-and-cone f an ^Verted COnical Cast- char K er - iron funnel fixed to the top of the furnace, whose lower aperture is of about one-half of the diameter of the throat. An upright cast-iron cone is placed in the furnace below the cup ; it is suspended by a chain attached to its apex, so that it may be raised or lowered at pleasure ; in the former position it bears against the bottom of the cup, and forms an air-tight stopper, preventing the escape of any gas from the top of the furnace, which then finds its way out by proper passages through the OF THE BLAST FURNACE AND ITS ACCESSORIES. 181 wall of the furnace in the space above the charges enclosed by the cup ; but when lowered it allows the charges in the cup to be dropped into the furnace, and at the same time acts as a distributer. Only the small amount of gas that is lost during the time of charging is allowed to escape, and as this operation is very quickly performed, the current through the mains is kept up with great regularity. The cone is suspended by an arch-headed lever, carrying a counterbalance at the end of the opposite arm. The raising or lowering is effected by a pinion, moved by a hand- wheel gearing into a segmental rack attached to the counterbalance weight. The gas passes through a lateral flue into a square wrought-iron main pipe, or conduit, which dis- tributes it to the various pipes feeding the boiler fires and hot blast stoves. A modification of the cup and cone is in use in Cleveland, where the cone is replaced by an external cylindrical stopper, which is lifted during the charging time, and lowered when the throat is stopped, the object being to allow the charges to occupy the space which is necessarily kept empty for working the cone on the old system. It was found, however, that the working of the furnace was injured from the want of a proper distributer for the charges, on account of the absence of the cone : when this was supplied by suspending a conical ring by three chains to the bottom of the plug, regularity in charging was restored. In the above methods, the gas is collected chiefly from the sides of the furnace, a practice which, as will be shown further on, is not in all cases to be recom- mended. The alternative plan is to collect from the centre ; this is usually done by inserting an iron tube a short distance down the centre of the furnace, the lower end being supported on ribs of brickwork, while the 182 METALLURGY OF IRON. upper part is turned over in the form of a siphon, as, for example, in the furnace, Fig. 6, at p. 142. The annular opening between the tube and the ring wall forms the space for charging, an arrangement exactly the reverse of that noticed at p. 179. Only a part of the gases are collected by this method. The draught is in some cases aided by an exhausting fan. Coingt's apparatus, in use in France, is a combination of the central tube with the cup and cone. Lan gen's apparatus, Fig 18, differs from those hitherto considered, in being placed above the furnace, which may therefore be kept filled to the throat in the same manner as one with- out any means of collecting gases. The Fig. 18._Furnace top, W ith Langen's charger. cnarg i ng portion is a conical ring, whose smallest diameter is equal to that of the throat, into which the charges are filled in the usual way. The gas tube is also slightly conical, diminishing upwards ; the lower end, which is about 5 feet above the top of the column of materials in the shaft, is turned over into a gutter or water trough. The gases rising from the furnace are collected in a bell- shaped tube, whose lower end rests in the conical cup at the top of the furnace, while the upper part is turned over into a lip, which dips into the water trough on the gas tube, forming a perfectly air-tight stopper. At the time of charging, the bell, which is suspended by chains to a lever, is lifted, the upper end sliding on the out- side of the gas tube, which forms a kind of telescopic OF THE BLAST FURNACE AND ITS ACCESSORIES. 183 joint. The charges in the cup then fall into the fur- nace. In order to keep the water joint tight, it is necessary to make good the waste caused by evapora- tion from time to time, owing to the high temperature of the gases. To prevent the chance of an explosion, a safety-valve is placed on the top of the gas tube at a, and another on the lateral tube at b. Even in furnaces where the gases are not collected, the use of a conical charger is attended with consider- able advantage. "Where the diameter of the throat is large, it is customary to fix charging plates inclining inwards, immediately within the charging holes, which distribute the charges in a similar manner. In the charcoal furnaces of Lake Superior and Styria, a charging barrow is used, which is constructed exactly in the same manner as the cup and cone. The body of the barrow is an inverted eight-sided pyramidal cup, the bottom being an upright cone, which, when dropped by a lever attached to its summit, leaves an annular space for the materials to pass out into the furnace, at the same time they are directed towards the circum- ference of the throat, in sliding over the surface of the cone. At Hhonitz, in Hungary, charging barrows are used having sliding cylindrical sides in addition to the dropping conical bottom, so that the charging takes place in a ring towards the sides of the furnace as well as at the centre. Form of the Interior of the Blast Furnace. In laying out new works at the present time it is usual to build the furnaces of a more or less skittle or tub- shaped section, all sharply-contrasted slopes being avoided, the diameter increasing continuously from the throat to the boshes, and then being contracted in a similar manner down to the hearth bottom, without having a cylindrical hearth. The form of the body of such a 184 METALLURGY OF IRON. furnace is well represented by a common soda-water bottle, supposing the neck and the pointed bottom to be removed. In Scotland the same kind of section is used, with the addition of a broad cylindrical hearth. In Cleveland slightly- curved stacks, with conical boshes and cylindrical hearths, are the rule. In South Wales the latter conditions are often reversed, the lower part, up to the top of the boshes, being made conical, while the stack, which is for a certain distance cylindrical, is terminated by a strongly- curved dome. In all cases of the above, however, the hearths are of considerable breadth. In French, Belgian, and German furnaces curved sections are less common than in this country. A more especial characteristic is, however, the small diameter of hearth generally adopted, the sides being brought in from the boshes in a strongly-curved convex sweep. This type, which is usually combined with an extremely massive construction of hearth, is very similar in form to an inverted claret bottle, having the bottom and the greater part of the neck removed ; the body, which increases from the bottom upwards with a slight taper, representing the stack, the shoulder the sweep of the boshes, and the narrow neck the hearth. Swedish charcoal furnaces are generally of considerable height when compared with their diameter ; the hearth and boshes form part of the same cone, usually very acute. The stack is either wholly or in part cylindrical. In Styria the charcoal furnaces used for smelting spathic ores resemble those of Sweden by their considerable height, as compared with the breadth and the steep slope of the conical parts, but are specially distinguished by their extremely narrow throats, which in some in- stances do not exceed 2J feet. The height and other dimensions of blast furnaces OF THE BLAST FURNACE AND ITS ACCESSORIES. 185 vary very considerably in different localities with the nature of the ores and fuel. No special rules can be laid down as to the form best suited for a particular class of ore, experience having shown that the require- ments of each class are to be met by special arrange- ments. The most useful guide in the construction of new furnaces is furnished by the condition of those that have been blown out after working upon the same kind of ore. It was by comparisons of this kind that the modern barrel-shaped furnace was elaborated by Gibbons, in South Staffordshire, from the older conical form, the section of the newer furnace being modified wherever the action of the fire was found to be strongest : thus square hearths were burnt out to a circular form, and the sharp angle at the joining of the hearth and boshes was also removed. It was therefore apparent that, by altering these parts in con- formity with the indications, a double advantage was attained, a certain amount of materials being saved, while the furnace was sooner brought to its best work- ing condition than was the case when it had first to be cut into shape by the heat. If we consider the nature of the work done in the blast furnace with reference to the amount of iron pro- duced in a given time, it will be evident that an increase of such production can only be obtained from the same ores by passing a larger number of charges through in the same time ; this, however, depends upon the facili- ties possessed for withdrawing them by fusion at the bottom ; for, however great the cubic contents may. be, it is clear that new materials can only be supplied in proportion to the speed with which those charged before them are removed. The power of fusion is, however, to be measured bv the space offered for combustion of fuel by the blast, 186 METALLURGY OF IRON. and as in the best condition of work, this space should be confined as much as possible to the plane of the twyers, it follows that increase of space for more active combustion is to be got mainly by augmenting the width of the hearth. The amount of such an increase is to be determined by the power of the blast, which must be of sufficient tension to penetrate to the centre of the hearth. Greater height may be given to a furnace, either to increase its capacity, or to intercept more completely the enormous quantity of heat carried upward by the gaseous products of combustion. Strictly speaking, there should be no combustion of fuel, except in the region of fusion, and the space immediately adjoining, where the carbonic acid produced at the twyers is con- verted into carbonic oxide. The latter gas, and the nitrogen of the air consumed, are charged with the reduction of the oxides of iron in the ore to the metallic state, and the progressive heating of the materials in the upper region of the furnace. The greater the dis- tance, therefore, of the upper end of the column of materials from the level of most active combustion, the more perfectly will the heat be abstracted from the gases; therefore, we might expect that the greatest economy of fuel would be found in the tallest furnaces, and this is practically the case, as exemplified in the newer furnaces in Cleveland, which have been succes- sively increased from a height of 50 or 60 feet to 70 feet and upwards, in one instance attaining as much as 96 feet, with an increased saving of fuel in each case. Of course only the sensible heat is abstracted from the gases, an amount that is quite independent of the further and much larger quantity that may be got by burning them in air. OF THE BLAST FURNACE AND ITS ACCESSORIES. 187 The conditions limiting the height of the furnace are mainly due to the character of the ores and fuel, as regards their power of resisting crushing when exposed to the pressure of a tall column of materials, and the initial velocity of the blast. The favourable results given above, as obtained in Cleveland, are due to the extremely hard character of the coke employed, which, according to Bell, is capable of resisting a crushing strain of 5 cwt. per square inch. Very tall furnaces, therefore, can scarcely be used with tender fuel, such as soft charcoal, or coal, and pulverulent ores. Much of the anthracite of South Wales is in the same condition, as it decrepitates, and is apt to choke up the furnace, if not removed by an extra-powerful blast. The furnaces, therefore, worked with this fuel, though of large diameter, and provided with a great number of twyers, are usually of small height. The time occupied in the descent of the materials from the throat to the hearth is chiefly dependent upon the capacity of the furnace. It is of the greatest im- portance that this should be so regulated as to insure an early commencement of the reduction of the ore to the metallic state at a low temperature, otherwise, in the event of protoxide of iron and silica coming in con- tact with each other in a more highly-heated atmo- sphere, a silicate is formed, which is easily fusible, but difficultly reducible, and, running down into the hearth, forms what is known as a scouring or black cinder, at the same time giving rise to white iron. The harder a furnace is driven, therefore, the greater is the tendency to deterioration in the quantity of the metal produced, owing to the quicker descent of the charges ; and it will, therefore, be apparent that when an increased make is desired, larger furnaces should be used. 188 METALLURGY OF IRON. The difficulty of insuring uniformity of temperature in circular hearths of large character has led to the proposal of a more elongated form, such as an ellipse or oblong rectangle ; the latter being adopted in Rachette's furnace, which was introduced in Russia a few years back, and has been tried experimentally in other parts of Europe. It is represented in plan and section in Figs. 19 and 20. The oblong hearth is combined with a shaft, increas- ing regularly in diameter upwards, the section at the Racliette's blast furnac 1 . Fi. 19. Vertical section. Fig. 20. Plan at twyer level. throat being from two and a half to three and a half times as large as that measured at the level of the twyers. The object of this arrangement, which gives a furnace similar in form to a calcining kiln, is to pro- duce a more prolonged contact between the gases and the materials of the charge, by reducing the velocity of the upward current. The use of drying flues is another new feature in Rachette's furnace ; these are a series of ramifying rectangular passages, traversing the outer casing of the stack at different levels, which are in connection with a OF THE BLAST FURNACE AND ITS ACCESSORIES. 189 similar chamber placed below the hearth. Before blowing in, a fire, placed in the chamber, warms up the whole of the masonry uniformly, and more quickly than can be done on the old system ; afterwards the flues may be used for the reverse purpose of cooling the masonry by the circulation of cold air. The twyers, from twelve to sixteen in number, are arranged in two rows, breaking joint with each other, on the opposite long sides of the hearth ; a dam and tapping place are provided on each of the short sides, so that the removal of slag and iron may be effected from either end. In order to obtain greater regularity in the distribu- tion of the blast, the large number of twyers may be replaced by a single mouth-piece, with a long, narrow, rectangular aperture, which delivers the air in a thin stream uniformly along the entire length of the hearth. This system of twyer, together with the elliptical form of hearth, has been adopted in the construction of cupolas for smelting slags in the Lake Superior copper works. In the original furnaces of this class in the IJral, the breadth of the hearth at the twyers is 3 feet, at the throat 7 feet, height 30 feet, cubic capacity 1,950 feet, and the daily production, when working on rich magnetic ore (67 per cent.), with charcoal and cold blast, about 30 tons of grey pig iron. The mode of charging has an important influence upon the working of blast furnaces : this becomes evi- dent when we consider that, in order to obtain regularity of action, the descending materials ought to be heated uniformly by the upward current of hot gases. This, however, is by no means the case, owing to the essential differences in the character of the two motions, the gases following the sides of the furnace close to the wall, the flow at the centre being almost imperceptible. 190 METALLURGY OF IRON. Thus, in an open-topped furnace, a wooden pole may be plunged into the centre of the charge to a depth of 2 or 3 yards, without being carbonised, while the materials adjoining the wall, at the same level, are at a red heat. The descent of the charges, however, takes place under precisely opposite conditions, the velocity being greater at the centre than at the sides, where the fragments are retarded by friction against the wall. It therefore appears that the central portion of the column of materials is likely to be imperfectly heated in its passage downward, and to arrive in the region of fusion in an unprepared state. When the charges are of ore and fuel, deposited uni- formly in the throat of the furnace in parallel layers, the increased velocity of descent at the centre causes the middle of an upper layer to overtake the sides of that preceding it, so that at a certain depth below the mouth the contents of the furnace are more or less completely mixed. But for this circumstance, it would be impos- sible to maintain a uniform heat in the hearth, which would become alternately hot and cold, according to whether fuel or burden happened to be in front of the twyers. In large furnaces, where it is necessary to drop the charges from a certain height into the throat, the dis- tribution of the materials becomes complicated by the nature of the upper surface of the column in the shaft, which may be either a cone raised in the centre, an inverted or conical funnel depressed in the middle, or a combination of both, such as a conical ring, according to the method of charging employed. The charges, therefore, instead of being deposited in parallel layers, have to accommodate themselves to the inclined surface of the preceding one. OF THE BLAST FURNACE AND ITS ACCESSORIES. 191 In the simplest of the above cases the charge is dropped into the centre of the throat, and forms a conical heap, sloping outwards to the circumference at an angle varying, with the nature of the materials, from about 35 to 40, the latter being the maximum inclination of the talus formed by coke. Owing to differences of form and density, the fragments of ore and fuel take up different positions in the furnace, the former usually remaining in the place where they first strike the surface of the column, while the lighter and more voluminous masses of fuel roll down the slope until they have established a talus at the proper angle of repose. It will easily be seen, there- fore, that this is the worst possible combination, the fuel being mainly distributed towards the circumference, where there is a comparatively free passage for the gases, while the ore remains in a dense column, impenetrable at the centre, and descends without being properly heated. When coke is used, the friction of the frag- ments against the wall is so great as to increase the tendency to form obstructions, or scaffolds, and their attendant evil, known as slips, when the charge falls, owing to the removal of the obstruction, by gradually increasing pressure from above, and the removal of supports below. The ore in the centre, by its greater velocity of descent, passes through the fuel charged before it, producing an inversion of charge, so that the slags change irregularly from white to black, according to the preponderance of ore or fuel at the twyers. When the charges are thrown in close to the circum- ference of the throat, the surface of the column of materials forms a conical cup, the lighter fragments rolling inwards towards the centre, while the ore re- mains at the outside. The tendency is, therefore, for 192 METALLURGY OF IRON. the fuel and larger masses of ore to collect in the middle, where it forms a column, which, on account of its ready permeability as compared with the more densely -packed ore at the sides, gives a more equable draught over the entire horizontal section of the shaft, at the same time that the bulk of the ore descends slowly through the region of maximum heating by the gases, both conditions tending to uniformity of working and economy of fuel. When the throat is very wide, however, and the furnace low, the draught at the centre may become too strong, leading to an unneces- sary consumption of fuel by diverting the gases from the sides. The continual contact of metallic oxides has also an injurious effect upon the lining of the furnace, as the silica of the bricks is liable to combine with protoxide of iron, forming a fusible silicate, by which they are rapidly destroyed. When a conical funnel or charging plates are used, the surface of the column in the furnace presents an annular ridge, sloping both towards the centre and the circumference, the ores occupying the crest of the ring, while the fuel and larger blocks are intermixed at either side. This is by far the most favourable condition for uniform working, as the charge and fuel are more per- fectly mixed than by either of the preceding methods. The use of the movable cones below the funnel, as in the ordinary cup-and-cone arrangements, corrects the tendency to accumulations at the centre, which is ex- perienced when the charging funnel is too much con- tracted at its lower end. In Sweden, charcoal furnaces with narrow throats are charged by hand, the richer magnetic ores broken into small pieces are placed in a ring close to the wall, while the more siliceous hematites and specular ores, as OF THE BLAST FURNACE AND ITS ACCESSORIES. 193 well as the limestone flux, are spread uniformly over the surface. The charges are weighed in a large wrought- iron scoop with a long wooden handle, which is sus- pended by a chain above the top of the furnace. Tapping. The molten metal accumulating in the hearth of the furnace is removed at regular intervals by tapping, or piercing a hole through the lower part of the dam, and allowing the metal to flow into sand or cast-iron moulds placed in front of the furnace. Before tapping, the blast is shut off, and the tymp stopping removed. The tap-hole is opened by driving in the point of a wrought- iron bar, which is held by one man, while another strikes the end with a sledge hammer if necessary. The moulds, or pig beds, usually consist of a series of furrows in the sand of the casting floor, moulded by wooden cores of a D-shaped section. The curved side is placed downwards, and usually has the name or mark (brand) of the works attached to it. The moulds are arranged in parallel series on either side of a central feeder, known as a sow ; and as soon as one series is filled, the current is allowed to flow into the next, and so on until the cast is completed. In Sweden cast-iron moulds are generally used instead of sand. When the ores contain lead, a certain quantity may be obtained in the metallic state by tapping the hearth at the lowest possible point, or by making a hole below the hearth bottom, and collecting the metal which finds its way through the joints of the stones. In the latter case a small fire is kept burning in the hole to prevent the lead from solidifying, and it is then allowed to accumulate until a sufiicient quantity has been obtained for a cast. Blowing in. When a furnace is quite new, the whole of the masonry must be very carefully dried before it o 194 METALLURGY OF IRON. can be lighted. This may require several weeks, ac- cording to the state of the atmosphere and the nature of the materials employed. When perfectly dry the hearth is filled with wood, and the upper part of the furnace, to the top of the boshes, with coke, which is then lighted from below. As soon as the fire has burnt through to the surface a light charge of ore is given, which is repeated when the fire reappears at the top. Twelve hours after lighting, a grating of bars, carried by an external bearer laid across the rack plates of the hearth, is placed within the furnace, a little below the level of the tymp ; the column of materials being thus supported, the cinders and ashes of the coke filling the hearth are then removed, and the air passing through the grate bars, revives the combustion in the upper part of the furnace. When the lower part of the mass is glowing, the bars are withdrawn, and the ignited materials are allowed to fall into the hearth. The fire is then slackened by stopping up the fore-hearth as before. The same process is repeated at the end of every twelve hours, or if it is desired to get the furnace in blast quicker, every six hours. As soon as the first charge gets down to the hearth the dam and twyers are fixed in position, and the blast is turned on, cold air, and nozzles of a reduced diameter, being adopted at first. The furnace is then filled to the throat, as if in regular work ; but the weight of the charges, as well as the temperature of blast and diameter of twyers, must be gradually increased, so as to get to the proper burden in about seven or eight days. "W hen several kinds of ore are at hand it is well to commence with the poorest, as for the same volume of charge the burden will be lighter. The above is the old method of scaffolding, which is OF THE BLAST FURNACE AND ITS ACCESSORIES. 195 still used in France. In England a more rapid plan is adopted. The top of the wood in the hearth is covered by a considerable quantity of coke, followed by alternate layers of coke and limestone, the latter for fluxing the ash of the fuel, until the furnace is one-third full. When the fire is well started, small charges of ore are added, and the blowing is commenced with twyers of a reduced area. If properly managed, grey iron and clean cinders may be obtained from the beginning ; but for this purpose it is essential not to increase the burden too rapidly, or to drive too hard at first. Blowing out. When a furnace is to be put out of blast, it is advisable to reduce the charges as much as possible for a short time before, in order to get the hearth as hot as possible, so as to remove any metallic obstructions. The gas tubes, and all metal fittings of the throat, are then removed, and the charging being stopped, the contents of the furnace are entirely lique- fied by the last charge of fuel. The last tapping must be made from as low a point as possible. The sides and bottom of the hearth are often found to be covered with masses of imperfectly- agglomerated malleable iron, the so-called bears, wolves, or sows, and isolated crystals, or even large masses of a copper- red compound, formerly supposed to be metallic titanium, but which has been shown by Wohler to be a cyano- nitride having the composition Ti C 2 N + 3 Ti 3 N. Stoppage of Furnace. It may sometimes happen, through failure of the blast engine, or a deficiency of materials, that a furnace must be stopped for some time. This is done by closing up the throat and all the twyer holes hermetically with sand or clay. If the charges have been previously diminished to a certain extent, so as to keep a good body of fuel in the furnace, 196 METALLURGY OF IRON. it may be stopped for about a week without serious inconvenience ; but if the blast be interrupted for a longer period, the cooling takes place to such an extent that the furnace becomes blocked up, and would pro- bably be obliged to be abandoned. CHAPTER IX. CAPACITY AND PRODUCTION OF BLAST FURNACES. THE greatly-increased production of modern, as com- pared with older furnaces, is due partly to their much larger size, and partly to more rapid driving, produced by giving more blast. No general rule can be laid down as to the time necessary for complete reduction of the ores previous to their actual fusion and the separation of metal and slag by liquation, as it is obviously dependent upon many variable elements, such as the greater or less density of the ores and fuel, the richness of the former, whether they are readily reducible, or have a tendency to scorification, &c. This point must, therefore, be determined by actual expe- riment for each particular furnace, by varying the amount of blast and the burden of ore and fluxes, until the particular result required, either in respect to quality or quantity of produce, is obtained. Other things being equal, the time of reduction will be lessened the more perfectly the materials are exposed to the action of the upward gaseous current. It there- fore becomes of the greatest importance to render the flow of gases as uniform as possible throughout the mass, by the use of proper charging and gas-collecting appliances. Especial care must be, taken that no CAPACITY AND PRODUCTION OF BLAST FURNACES. 197 hindrance is offered to the free efflux of the current at the top of the furnace. For this reason, these methods, based upon the collection of the gases above, or in the centre of the charge, are to be preferred to such as employ lateral flues, penetrating the wall below the level of the throat, whereby the current is diverted, without being allowed to give up its heat to the upper part of the column of materials above the flues. An increase in the volume of blast, keeping the pressure constant, has a tendency to put the furnace on white iron. By increasing both pressure and tem- perature, on the other hand, especially with refractory ores, greyer or more highly-carburised iron is likely to be produced. In the table on page 199 the cubic contents and daily make of a series of furnaces are shown, together with the effective volumes required to produce one ton daily in each case. The quantities in the last column but one cannot be fairly paralleled with each other, without taking into account the differences in the nature of the materials employed. Thus, in Nos. 1, 2, and 4, the ores are treated almost without fluxes, so that the production of slag is reduced to a minimum, whereas in the largest English and Welsh furnaces, working with a mixed burden, the weight of slag considerably exceeds that of the iron made. The descent of the charge is quickest in the Styrian furnaces, where rich and easily-reducible spathic ores pass through the furnace in four and a half or five hours. In Wales, on the other hand, in some instances, the charges do not arrive in the hearth until forty-two hours after the time of charging. In Cleve- land the time of descent is about thirty- six hours; while, Fig. 21. Comparative sections of blast furnaces CAPACITY AND PRODUCTION OF BLAST FURNACES. 199 05 Oi rf>> CO tO I OCOOO -~J Oi Ol ^ CO tO >- Sit it o o o o o g g? S"^s~o g- g" Q cg.Q Lsf 1 ^p-p ^ p- R Pi p oo o o Cubic contents, feet. tO 05 Daily make, tons. co > 'i 'to ' co to " ' ' to O5O- . . 2 ,, 100 CONSUMPTION OF FUEL AND DISTRIBUTION OF HEAT. 217 CHAPTER X. OF THE CONSUMPTION OF FUEL AND DISTRIBUTION OF HEAT IN THE BLAST FURNACE. THE theoretical distribution of the heat given out by the fuel in the blast furnace is found by comparing the sensible temperature and weight of the matters dis- charged, multiplied by their specific calorific capaci- ties, with the heat produced by the combustion of the fuel and from other sources, according to the known laws of heat. The following example of a calculation of this kind, made on a French furnace, and exhibiting the results in the form of a debtor and creditor account, is taken from an excellent treatise by De Yathaire, recently published ("Etudes sur les Hauts Fourneaux," chap. vi. 72). I. Calculation of the Quantity of Heat absorbed in the different Operations of the Blast Furnace. The carbon burnt in the furnace is employed for three different purposes. These are : 1. Heating of fixed and volatile matters. 2. Reduction of metallic oxides. 3. Restitution of heat absorbed during the re- duction. Let us select as an example a furnace working upon grey iron (No. 3), whose charges yield 40 per cent, of pig iron, with a consumption of coke 14 per cent, of ash, at the rate of 1,350 kilogrs. per ton (1,000 kilogrs.) of pig iron ; the blast being heated to 300. The mean composition of the charge, including the ash of the fuel, is as follows : 218 METALLURGY OP IRON. Peroxide of iron 1,344 equal to 950 iron, or 1,000 cast iron. Silica . . 256 \ Lime . . 266 ( 649 of slag. Alumina . . 127 ) Carbonic acid . 257 Water 250 2,500 kilogrs. weight of charge per ton of metal. Quantity of Heat carried out of the Furnace by the liquid Products. The number of units of heat con- tained in the products of fusion was found, by the calorimetric method of melting ice, to be 330 per kilogr. of grey cast iron, and 550 ,, ,, slag. The total quantity absorbed, therefore, per 1,000 kilogrs. of metal and 643 kilogrs. of slag, is 1,000 x 330 = 330,000 units of heat. 649 X 550 = 354,750 Making together 684,750 Quantity of Heat carried off by the Waste Gases. Out of the total amount of 1,350 kilogrs. of coke, 50 are taken up by the iron, and the remaining 1,300 (representing 1,118 of pure carbon) is volatilised, and passes out at the throat. To this must be added 70*1 kilogrs. derived from the carbonic acid of the flux, making a total of 1,188 kilogrs. of carbon volatilised per ton of pig iron. The composition of the waste gases by weight was found to be as follows : CONSUMPTION OF FUEL AND DISTRIBUTION OF HEAT. 219 Carbonic acid 12*80 containing 3 '491 carbon. Carbonic oxide 25-53 ,, 12'215 Hydrogen . 0'07 Nitrogen . 61 -60 15-706 ,, 100-00 The amount of carbon in the gases being 15-707 per cent., the above quantity of 1,188 kilogrs. represents a total of 7,556 kilogrs., which, being discharged at a mean temperature of 200, carry with them the follow- ing amounts of heat. This temperature is considerably lower than that usually observed in English close- topped furnaces. At Clarence, in Durham, Bell found it to be between 500 and 600. Weight. Specific heat. Sensible heat. Total units of heat. 7566 Carbonic a rid . 12 80 X 221 X 200 X Too" : 42-810 Carbonic oxide 25 53 X 288 X do. X do. = 111-270 Hydrogen . 07 X 903 X do. X do. = 958 Nitrogen . 61 60 X 275 X do. X do. = 256-370 Water . 250 kilogrs. X 1 00 X 750 = 187-500 598-908 The quantity 750 in the last line is made up of the sen- sible heat, 200 plus 550, rendered latent by conversion of the water into steam. Quantity of Heat absorbed in the Reduction of Oxides of Iron. The amount of carbon required for the reduc- tion of an iron ore is proportional to the number of equivalents of oxygen contained, or taking into account the difference of atomic weights, is equal to three- quarters of the total weight of oxygen, the equivalents of carbon and oxygen being to each other as 6 to 8. Therefore 220 METALLURGY OF IRON. Protoxide of iron cntg. 77*72 iron and 22-22 oxygen requires 21*42 carbon Magnetic oxide 72-41 27*59 28*66 Peroxide . . 70 -00 30*00 321-75 per ton of iron reduced. The reduction of the oxide in the furnace is entirely performed by carbonic oxide ; but as the carbonic acid so produced is, by the secondary action of ignited car- bon, immediately re- con verted into carbonic oxide, the result is much the same as if it had been effected directly by solid carbon, as it is only near the top of the furnace, where the temperature is comparatively low and the current rapid, that any carbonic acid can exist as such. The production of carbonic oxide by the action of carbon upon oxide of iron is attended with a consider- able absorption of heat. Iron, when burnt in oxygen, evolves 6,216 units of heat for each litre of oxygen consumed (1*436 grammes). The inverse phenomenon of reduction, therefore, renders the same amount of heat latent. But 1 litre of oxygen (1*436 grs.), combining with 1 litre of carbon vapour (1*677 grs.) to form two litres of carbonic oxide, only gives out 1,598 units of heat, which, deducted from the 6,216 rendered latent, leaves 4,618 as representing the cooling effect produced for each litre of oxygen displaced from the iron, and converted into carbonic oxide by a consumption of 1*077 grs. of carbon. The consumption of carbon per ton of iron reduced, and the heat absorbed, is therefore with Kilogrs. Peroxide of iron . 321*75 of carbon and 1,368,550 units of heat. Magnetic oxide . 285'6 1,270,227 ,, Protoxide of iron . 214*2 870,704 In order to simplify the calculation, the amount of CONSUMPTION OF FUEL AND DISTRIBUTION OF HEAT. 221 heat given out on combustion by the carbon employed in reduction will be for the moment neglected, and only the absorption of heat by the separation of the iron and oxygen brought into account. This is for the different oxides as follows : Oxides. Kilogrs. Units. Kilogrs. Units. Kilogrs. Units. Fe^O 3 1,000 1,298,610 1,429 1,855,700 1,341 1,744,358 Fe 3 O 4 1,194,300 1,381 1,649,300 1,282 1,550,342 Fe 961,840 1,285 1,236,000 1,208 1,161,840 The third column in the above table shows the quan- tity of heat absorbed in the reduction of a ton of each oxide ; the fifth, the amount corresponding to the quantities of each oxide required to make a ton of iron ; in the seventh, a similar series of quantities calculated to the ton of pig iron, supposing it contains 94 per cent, of iron and 6 of foreign matters. Heat absorbed by the Reduction of Vapour of Water. The hydrogen contained in the gases of the furnace is derived from the decomposition of steam introduced with the blast. The quantity, '07 per cent, corresponds to 47,666 kilogrs. of steam per ton of metal produced, or 00786 of the weight of the air injected, a result corre- sponding fairly with the hygrometrical condition of the atmosphere at the time. The amount of heat absorbed by the separation of 4 '59 6 kilogrs. of hydrogen per ton of metal is 4-596 X 31,742 = 159,681 units of heat: 34,742 being the calorific power of hydrogen burning to water. II. Calculation of Heat developed in the Furnace. This is derived from two principal sources, namely, 1. Heat produced by the combustion of fuel ; and, 2. Heat brought into the furnace by the hot blast. 222 METALLURGY OF IRON. The heat produced by the combustion of 1,118 kilogrs. of carbon is made up of two quantities, part being derived from the formation of carbonic acid, while the remainder results from the imperfect combustion of the larger portion of the fuel to carbonic oxide. In addition to the above quantity of 1,118 kilogrs., 70 kilogrs. of carbon contained in the gases are derived from the carbonates of the charge, making a total of 1,188 kilogrs., distributed as follows in the gases : As carbonic acid 3-491 percent, or in 1,188 kilogrs. 264 kilogrs. carbon. carbonic-oxide 12-216 924 15,707 1,188 From this amount, however, must be deducted the 70 kilogrs. contained in the carbonic acid of the carbonates which has been volatilised as such, and is not derived from combustion of carbon in the furnace. The total amount disposable for heating purposes therefore be- comes 194 kilogrs. burnt to carbonic acid. 924 ,, carbonic oxide. Multiplying these by their respective calorific powers, we obtain 194 x 7,170 = 1,390,980 924 x 1,386 = 1,280,664 2,671, 644 units of heat as the total amount of heat given out by the fuel under the conditions of the experiment. Heat introduced by the Blast. The quantity of air blown into the furnace is to be calculated from the pro- portion of nitrogen found in the waste gases. The amount of nitrogen in the gases is found to be CONSUMPTION OF FUEL AND DISTRIBUTION OF HEAT. 223 61*6 per cent., air containing 76 - 9 per cent. The amount corresponding to 7,556 kilogrs. of gases evolved in the production of a ton of metal is therefore 7,556 x 0-616 . 769 = 6060-6 kilogrs. of air. Supposing this to be heated to the temperature of 300, the extra amount of heat from this source, the calorific capacity of air being 0-2669, 6060-6 X 0-2669 X 300 = 485,272 units of heat. The small amount of hydrogen contained in the gases is derived from the decomposition of steam contained in the air by ignited carbon. As the amount of heat absorbed in this decomposition has been deducted, the quantity brought in by the heated water vapour must be taken into account as follows : 5*2962 kilogrs. of hydrogen contained in the gases corre- spond to 47,666 kilogrs. of water, containing 300 of sensible and 550 of latent heat ; or, in all, 47,666 X (300 + 550) = 41,506 units of heat; which, when added to 485,272 ,, , gives a total of 526,778 ,, ,, as the contribution of the hot blast to the heat of the furnace ; or about 20 per cent, of the whole amount of heat ex- pended, a theoretical determination which fairly corre- sponds with the saving of 20 to 30 per cent, of fuel, obtained in practice by the use of hot blast. On comparing the two sides of the account, we obtain the following balance sheet of heat developed and ex- pended per ton of metal. 224 METALLURGY OF IRON. CK. CAUSES OF ABSORPTION OF HEAT. Units. Heat carried out of furnace by 1,000 kilog. of molten metal 330,000 649 slag. 354,760 the waste gases . . 598,908 rendered latent by reduction of 1,343 kilog. of peroxide of iron . 1,744,358 4,596 hydrogen 159,681 Total amount of heat expended . . .3,187,697 DR. SOURCES OF HEAT. Heat given out by combustion of carbon .... 2,671,644 introduced by the hot blast air . . . . 526,778 Total amount of heat employed . . .3,198,422 leaving a balance of 10,725 units unaccounted for a quantity far within the probable limits of error in the computation. A few minor sources and causes of ab- sorption of heat have been neglected, from the want of numerical data for their calculation. These are : 1. Heat absorbed by the reduction of silica, the calorific power of silicon being undetermined. If it be the same or nearly that of carbon, the reduction of from 15 to 20 kilogrs. of silicon per ton of metal will require from 100,000 to 150,000 units of heat. 2. Latent heat of volatilisation of carbonic acid upon the decomposition of the carbonates. This is probably trifling in amount, judging from the small quantity of fuel consumed in lime-burning. 3. The cooling caused by the dilatation of the blast, from the pressure of 9 or 10 centimetres of mercury to that of the atmosphere. A source of heat not taken into account is that given out by the combination of silica with earthy bases in the formation of the slag. Supposing now the blast to be heated to 600 instead CONSUMPTION OF FUEL AND DISTRIBUTION OF HEAT. 225 of 300, the total available amount of heat becomes 3,725,220 an increase of about 16 per cent, on the former quantity. A saving of from 17 to 18 per cent, of fuel was effected by the introduction of Cowper's stoves, producing a similar increase of temperature. If, therefore, the products of combustion remained un- altered, the saving of fuel would appear to be directly proportional to the extra heat introduced by the blast ; but this is by no means certain, and it is probable thp\ a part of the economy is due to more perfect combus- tion. The heating up the large quantity of inert nitro- gen, which in weight considerably exceeds the whole amount of solid materials, fuel and fluxes taken to- gether, before introducing it into the furnace, must ob- viously prevent a great waste of heat in the hearth ; and this saving would be proportionately greater the less per- fect the combustion and the smaller the amount of heat developed by the fuel, supposing the temperature of the blast to be constant. In the particular case before us, it will be seen that only about 17 per cent, of the whole quantity of fuel burnt is converted into carbonic acid, with the product of a maximum of heat, the remaining 83 per cent, giving rise to less than one-half of the total amount evolved. Supposing the combustion to have been com- plete, 8,016,060 units would have been evolved, so that, by the imperfect combustion, two-thirds of the total heating power of the fuel is undeveloped. The production of carbonic oxide in considerable quantity is, however, a necessary condition to the proper working of the furnace ; the entire conversion of the fuel into carbonic acid could not be allowed, even were it possible, as the maintenance of a reducing atmosphere is of primary importance. The utmost that can be done Q 226 METALLURGY OF IRON. is to increase the relative amount of carbonic acid by the use of compact fuel in. large masses, a fine state of division being favourable to the production of carbonic oxide, on account of the larger surface and increased resistance offered to the passage of the gas. The effective heating power of the gases may be computed from the analyses given above. The calorific power of carbonic oxide being 2,478 units, and of hydrogen 34,742 units per kilogramme, the total amount obtainable from the gases evolved, per ton of coke burnt in the furnace, is 3,808,492 units of heat, or as much as would be produced from the combustion of 616 kilogrs. of coke. It therefore appears that 61 per cent, of the fuel charged in the furnace remains available in the gases. If now the consumption of coke be 30 tons per day, the gases, if applied to steam boilers, will by their combustion raise steam for an engine of 257 horse power. As, however, not more than 80 horse power is required for working the blast engine, there will evi- dently be a sufficiency remaining for heating the stoves and other accessory operations. Composition of the Gases of the Furnace at different Heights. This subject has been investigated at different times by Bunsen, Ebelmen, Scheerer, Playfair, Einman, Tunner, and others, both in coke, charcoal, and coal- fed furnaces. The results arrived at are generally similar, allowance being made in the first instance for the products of distillation where raw mineral fuel ores or fluxes are used. The ultimate products include the whole of the carbon contained in the fuel, less the amount required for carburising the metal produced, as carbonic oxide and carbonic acid in combination, with the oxygen of the air blown in at the twyers, and that CONSUMPTION OF FUEL AND DISTRIBUTION OF HEAT. 227 set free by the reduction of the ores, the nitrogen of the air, and small quantities of hydrogen and hydro- carbons, arising from the decomposition of water vapour introduced by the blast. ANALYSES OE WASTE GASES FHOM THE TOPS OE BLAST FURNACES. PERCENTAGE 15Y VOLUME. I. II. in. IV. Nitrogen 55-35 55-62 57-79 57-06 Carbonic acid 7-77 12-59 12-88 11-39 Carbonic oxide 25-97 25-24 23-51 28-61 Marsh gas . 3-75 0-20 Olefiant gus . 0-43 Hydrogen , 6-73 6-55 5-82 2-74 ]So. I. Alfreton, Derbyshire, charge containing calcined argilla- ceous ore, limestone flux, and raw coal. II. Audincourt, France, charge containing brown hematite and forge cinders, limestone flux, -vrood, and charcoal. ,, HI. Clerval, France, charge containing brown hematite, lime- stone, and charcoal. IV. Seraing, Belgium, charge containing brown hematite, mill cinders, limestone, and coke. It will be seen that the principal component of these gases is nitrogen, which is brought in by the blast, ana passes through the column of materials without taking part in the chemical changes involved in the reduction of the ore and the combustion of the fuel. The propor- tion is, however, considerably less than in atmospheric air, and as practically none is absorbed, it follows that the considerable increase observed in the amount of oxygen from 12 to 18 per cent, in volume must be derived from the solid materials of the charge. The principal source of this increase is to be found in. the decomposition of the oxides of iron in the ore, while a further but much smaller quantity may be derived from the reduction of silica to silicon in hot blast furnaces working on quartzose ores. The pro- 228 METALLURGY OF IRON. portion of carbonic acid to carbonic oxide diminishes progressively in the gases taken at lower levels, until, in the upper part of the hearth, they are found to consist almost entirely of nitrogen and carbonic oxide. According to Tunner, the temperature prevailing in the Styrian furnaces at a point about 3 inches above the twyer level was only 1,450 when making white iron, and 1,750 with grey iron. At the twyers wrought iron melted easily, but not platinum, so that the temperature was assumed as being higher than 1,900, and less than 2,500, or about 2,200. The furnace at Eisenerz, upon which these experi- ments were made, the zone of maximum temperature was approximately spheroidal, extending inwards and upwards for about 6 or 7 inches in front of each twyer. It is only within these small spaces that carbonic acid is produced by the complete combustion of the fuel. The amount of carbonic oxide evolved by combustion is greatest with light, easily combustible fuel, such as soft-wood charcoal, and a low temperature and pressure of blast. In the same way the transformation of car- bonic acid into carbonic oxide is more readily effected under similar conditions than with harder fuel, such as coke or anthracite. In charcoal furnaces, therefore, carbonic oxide prevails even at the lowest level, while at a very small height above the twyer carbonic acid is almost entirely absent. Higher up the quantity of the latter gas increases, because in the less highly heated parts of the furnace the oxidation of carbonic oxide by the oxygen of the ore goes on more energeti- cally than the converse reduction of carbonic acid to carbonic oxide by carbon. The temperature at which the reduction of the ore commences is, in the case of CONSUMPTION OF FUEL AND DISTRIBUTION OF HEAT. 229 spathic ores, stated to be from 600 to 700. Reduction and carburisation of the metal are more easily effected, and with a less consumption of fuel, when charcoal is used than is the case with coke, as, although with the latter a more intense heat may be obtained in the lower part of the furnace, the production of reducing gases will be diminished ; for the more compact the fuel, and the denser and hotter the blast, the greater will be the amount of carbonic acid produced at the twyers, and consequently the higher the temperature in the hearth. But as the carbonic acid so produced is less easily con- verted into carbonic oxide by coke than by charcoal, there is likely to be a smaller production of reducing The manufacture of pig iron, therefore, is attended with a larger expenditure of fuel when coke is used than is the case with charcoal, but when only heat is involved, as in remelting pig iron for founding, the same weight of iron can be melted with a smaller weight of coke than of charcoal. In furnaces worked with raw coal, the gases, in ad- dition to the products of combustion, contain small quantities of condensible vapours, especially tarry matters and ammonia, which it has been proposed to collect and utilise in a similar manner to the waste products of gas works. Bunsen and Playfair suggested that the ammonia might be collected as sal-ammoniac by passing the gases through a chamber containing hydrochloric acid. More recently D. Price has proposed the injection of finely-divided water into the main gas conduit, as well as the use of hydraulic mains, such as are employed in gas works for the same purpose. The gases of blast furnaces usually carry over n con- siderable quantity of finely-divided solid matter in the 230 METALLURGY OF IRON. form of dust, which deposits in the throat flues and gas culverts, and requires to be removed from time to time. The following is the composition of the dust from two different localities : Dowlais, South. Clarence, Clev< Wales (Kiley). land (Bell). Silica . . . 30-33 .... 34-82 Alumina . 8-43 . 16-00 Peroxide of iron . 47-05 . 8-20 Peroxide of manganese Lime .... 1-77 2-30 . 12-15 Magnesia . Protoxide of zinc 1-13 . 0-57 . 4-60 Potash 1-80 . 0-40 Soda .... 0-36 . 6-85 Water 0-93 . . . . 5-60 Sulphate of lime . Phosphate of lime 4-42 0-75 Sulphuric acid 8-80 Chlorine 1-56 99-27 99-55 AttheConcordia furnace, nearAix-la-Chapelle, where brown iron ores containing a considerable quantity of oxide of zinc are .smelted, the gases are simply washed by passing them through a pipe of large section, kept about half filled with water, by which means a portion of the zinc fume is deposited; sufficient is, however, kept in suspension to render it necessary to clear out all the flues at very short intervals. When the main gas pipe at the throat is obstructed, the furnace is allowed to go down until the top of the column of materials is about 9 feet below the charging plate. The surface is then cooled with water and covered with iron plates, forming a platform for the workmen who are employed in clearing out the deposit. The oxide of zinc recovered is sold to the neighbouring zinc works. VARIETIES AND COMPOSITION OF PIG IRON. 231 The presence of dust in the waste gases interferes considerably with their use as a fuel in certain cases. Thus in the earlier application of Siemen's regenerator to hot blast stoves, it was found that the apertures be- tween the bricks became rapidly choked when the heating was effected by means of blast furnace gases. Cowper's method of removing the dust consists in interposing a chamber of large area between the furnace top and the place where the gases are to be burnt, containing numerous shallow trays of wrought iron fixed at short vertical distances from each other by means of appropriate pillars. The velocity of the gas passing through the chamber is sufficiently reduced to allow the deposit of the suspended dust in the trays, which are placed with a slight inclination forward, so that they may be cleaned by washing through with a jet of water when necessary. CHAPTER XI. VARIETIES AND COMPOSITION OF PIG IRON. THE produce of the blast furnace is divisible into seve- ral different qualities, which, for practical purposes, are determined by the appearances presented by a freshly- fractured surface, a certain number of pigs taken from each cast being broken for the purpose. The numerous gradations in the scale are mainly dependent upon colour or degree of greyness, texture or size, of the crystalline plates, and their uniformity and lustre. The largest- grained brilliant and graphitic dark grey metal is known as No. 1 pig, while the smaller- grained va- rieties with diminishing lustre and colour are dis- tinguished by the higher numbers as far as No. 4. 232 METALLURGY OF IRON. Beyond this point, when the metal ceases to be grey, the numerical scale is not used, the remaining quali- ties being known as mottled, with a further division in some instances into weak and strong mottled, and white, the last being the lowest. This classification is subjected to slight variations in different districts, as in the following examples of scales used in differents parts of England : Cleveland .... Xos. 1.2.3.4.4 Forge. Mottled. White. Lancashire hematite 1 . 2 . 3 . 4 . V. Mottled. White. The grey numbers as far as No. 3 are also called foundry or melting pigs, the lower qualities, which are only adapted for conversion into malleable iron, coming into the class of forge pigs. In Lancashire and Cum- berland two extra classes are made, known as Bessemer iron Is os. 1 and 2. These command higher prices than the same numbers in the ordinary scale. The relative greyness or whiteness of pig iron fur- nishes no real standard of quality as compared with the produce of other districts, but is rather an indica- tion of the working conditions of the furnace. Other things being equal, white cast iron can be more readily and cheaply produced than grey, as the same amount of fuel is made to carry a larger burden of ore, and the charges are driven more rapidly. As, however, it can only be used for forge purposes, while the more expen- sive grey metal is available for making either castings or malleable iron, it is usually sought to diminish its production as much as possible, except in special cases, where quantity of make or an extreme economy of fuel is desired. White cast iron melts at a lower temperature than grey, but becomes less perfectly fluid : in cooling it passes through the pasty or semi-fluid condition, and contracts VARIETIES AND COMPOSITION OF PIG IRON. 233 very considerably on solidification. Grey cast iron, on the other hand, expands in becoming solid, so as to be capable of filling up the smallest cavities and depres- sions of a mould. When both kinds of metal are con- tained in the hearth of a blast furnace at the same time, the whitest being the heaviest, goes to the bottom, and will be found in the first pigs obtained at the next cast. The method of flowing is also indica- tive of the quality of the molten metals to an expe- rienced eye. White iron flows in a sluggish stream, throwing out brilliant sparks, while the grey foundry qualities run perfectly fluid and without sparks. In Sweden, and other countries where the practice of casting in metal moulds is adopted, the fractured surface of the metal, even when perfectly grey, is whitened by the chill to a considerable depth. Another class of metal often obtained under similar circum- stances consists of about equal parts of white columnar and fine dark grey iron in alternating stripes, or the latter may be interspersed in ragged patches, stars, or spots through a white ground. These varieties are in great request for conversion into malleable iron, as they approximate in character to the mixtures of grey pig iron with refined metal that are found to be most advantageous for such purposes. The so-called steel iron or white columnar pig of Siegen, and the flowery pig iron of Styria (blumige floss), are of this character. Common white iron, made with a heavy burden of cinders, is dull in colour, and presents a rough, honey- combed appearance on the upper surface of the pig ; it usually contains a considerable amount of phos- phorus and sulphur, and though very hard, may be easily broken. In the United States, the white pig iron produced in New Jersey from the residues obtained in the treatment 234 METALLURGY OF IRON. 6 * CO T 1 1 O CO o 3 ! 1 1 - M <:-> 1 H M ^ .8 3,8 i l.^ 8 BI o5 .- S)3" E^S ,4*3 5,-a GC OQ Bu F cO VARIETIES AND COMPOSITION OF PIG IRON. 235 M co '0 cc- 1 2 | X .7) CO CO CO O) CM M I CO CO 1 co 1 o cc ,_, CM O5 n t> H 1 CO <* o ? 1 o 1 1 1 n CM o> , 1 | CM "H o o | 1 C^ a> CM ^s J^ o 1 o ! i 1 1 s o co CO cc I CM CM CI o I 1 1 2 CO , f ^ "~ GO ^-N CO CO CO T< CO r CM OC CO iH CM | i 1 CO M O CO o o ^ 1 O CO M CO o o cc $ 1 CO CO CO CO I ^ LJ o 00 O-l T-t O ^ s- 05 . CO o ^r 1C O o *^ C^l O .-H CO CO MO ^1 CO CO 1-53 .j Pi 1 o ! as 2 S o s s Carbon s i fcc n ^ 1 g H A K ."S ! j* j ^3P 11 b 236 METALLURGY OF IRON. of franklinite after the oxide of zinc has been removed enjoys a very high reputation for use in the manufac- ture of chilled articles, especially crushing and forge rolls and stamp heads. In foundries where the re- melting is performed in reverberatory furnaces, dark grey iron can be used to advantage, and the quality of the metal may be greatly improved by the addition of a proportion of malleable scrap iron. The following are the appearances to be noted on the fractures of different classes of foundry iron according to Guettier : A moderately large grain of slight lustre, mottled with fine patches having a tendency to whiteness, indi- cates the highest degree of resistance. A smaller grain, but similarly dull, with a mottled grey base, marks the quality of metal best suited to resist tractive strains. A somewhat fibrous grain, terminating in fine jagged pyramidal points on the fractured surface, with a close regular grey base, is a mark of great transverse strength A fine-grained grey metal, bordering upon mottled, when the fracture is small-grained and even, and not in flat broad plates, is the best for resisting compression. The varieties presenting the least resistance are those that are full of graphite of a blackish-grey colour and large brilliant grain, or of an irregular grain upon a shining base, and the mottled white kinds in which there is no granular structure apparent. Guettier found that No. 1 Scotch pig reached its maximum strength after the eighth melting. Fairbairn found that the same point was reached with No. 3 pig (Eglinton) after twelve meltings. Those varieties of cast iron that are smelted from spathic ores containing manganese in considerable quantity are also white and intensely hard, the frac- MAKING WROUGHT IRON DIRECTLY FROM THE ORE. 237 tured surface presenting an aggregate of bright lamel- lar crystals, sometimes nearly an inch across, forming the so-called specular pig (spiegeleisen). Unlike ordinary white iron, it contains a very large amount of carbon, all of which is in chemical combination. The circumstances favouring its production have been noticed at p. 203. Manganese is always present, but the amount may vary very considerably without affecting the large lamellar crystalline structure. The chemical composition of pig iron is subject to considerable variation, as will be seen by the preceding table, which comprises analyses from the principal British and foreign iron-smelting districts. CHAPTER XII. METHODS OF MAKING WROUGHT IRON DIRECTLY FROM THE ORE. THE chief modern representative of the bloomeries or hearths by which iron was produced from the earliest ages down to the introduction of the blast furnace is the so-called Catalan or Corsican forge, which still sur- vives in the Pyrenees, and a few other isolated localities in the South of Europe. As it is of comparatively small importance in the economy of modern iron-making, a very brief notice will suffice. The hearth, or furnace, employed in this process is represented in longitudinal section in Fig. 22. The bottom of the hearth is of refractory sandstone, and before using, is lined or brasqued with a coating of charcoal dust or breeze. The front wall, or face, fl, is curved outwards so as to increase the capacity of the hearth at the top. The opposite side is 238 METALLURGY OF IRON. "Fig. 22. Catalan Finery. provided with a twyer made of sheet copper, in- clined at an angle of from 30 to 40 degrees. The tapping hole for removing the slag is placed in one of the side walls, which is also covered with an iron plate, forming a point of support for the tool used in working the contents of the hearth, and removing the spongy mass or ball of iron produced. The blast is usually produced either by a trompe, or a wooden engine with a square piston: its pressure never exceeds Ij to If inches of mercury. The method of conducting the operation is as follows: After repairing the lining of the hearth bottom, a pile of ore, usually a rich and easily-reducible brown hematite, occupying from one- third to one-half of the total contents of the hearth, is placed at b y parallel to the curved wall, the remaining portion, to the twyer wall, being filled with charcoal. The whole is then covered with char- coal dust and small ore (greillade) moistened with water. At first only a gentle blast is used, and as soon as flame appears at the surface, it is damped by a fresh application of greillade in order to prevent too rapid combustion, and the falling in of the heap before the reduction of the oxide of iron to the metallic state is effected. The preliminary stage lasts about two hours, after which the blast is turned full on, and the slags are tapped off. The workman then pushes the heap of ore further into the hearth by means of an MAKING WROUGHT IRON DIRECTLY FROM THE ORE. 239 iron bar introduced between it and the front wall. The reduction commences at the bottom of the heap with the formation of spongy masses of iron, which, as they appear, are pushed forward by the workman towards the twyer, in order to facilitate the separation of the metal from the slag by the liquation of the latter. The progress of the work is chiefly guided by the character of the slags, which are very liquid when highly charged with protoxide of iron, and stiff or pasty when deficient in bases. In the latter case the necessary fluidity is imparted by the addition of finely-divided ore in small quantities, which is allowed to dissolve in the slag without being reduced to the metallic state. This is, in fact, one of the essen- tial points of the process, a portion of the ore being intentionally expended in fluxing the silica, in addition to the earthy bases associated with the peroxide of iron, in order to obtain an easily -fusible slag, which in its turn reacts upon the reduced masses of spongy metal, and prevents the assimilation of carbon and the for- mation of cast iron. Perfect liquidity of the slag is also desirable in order to facilitate its removal during the subsequent forging. When the whole of the charge has been reduced, the blast is stopped, and the spongy masses in the hearth are worked together into a lump, or ball, which is lifted out and carried to the hammer, where it is forged, or shingled, to a rough bar, or bloom. During the first period of the process, while the ore is being re- duced, the bloom obtained from the preceding charge, after having been cut up into several pieces, is re- heated in the upper part of the hearth, and drawn out into bars under the hammer. The iron produced in the Catalan forge is usually 240 METALLURGY OF IRON. more or less hard and steely, though this depends in great part on the manipulation. By increasing the angle of inclination of the twyer, and keeping a large amount of slag in the hearth, the decarburisation of the spongjr mass is facilitated, and a softer iron is obtained than is the case when the ore is allowed to be reduced slowly, and to remain in prolonged contact with the fuel; these conditions being favourable for the production of what is known as steely iron, or natural steel. The slags produced in this process consist essentially of tribasic protoxide silicates, the principal base being protoxide of iron ; but lime, magnesia, and protoxide of manganese are generally present in, greater or less quantity. The silica usually exists in the ore in a free state as quartz. Although the presence of several bases is advan- tageous as tending to produce a fluid slag, it is espe- cially necessary that the amount of the earthy bases, lime and magnesia, should be small, as their silicates are too refractory to be properly melted at the tempera- ture obtained in the hearth. The conditions governing the formation of slags in the Catalan forge are therefore exactly the reverse of those sought to be obtained in the blast furnace, where the scorification of protoxide of iron is prevented by the use of a large amount of lime as a flux for the silica in the charge. It will be shown subsequently that the same considerations are involved in all processes for the conversion of cast into malleable iron. Whenever silica or silicon is present, it is always eliminated as a silicate at the expense of a portion of the metal, and, at the same time, the highly basic silicate so formed, when brought into contact with molten cast iron, acts upon the combined carbon of the MAKING WROUGHT IRON DIRECTLY FROM THE ORE. 241 latter, with the production of carbonic oxide and metallic iron. It will be remembered that the nearest approach to this reaction observed in the blast furnace is when the cinder is black and scouring, correspond- ing to the production of white iron poor in carbon. The weight of ore treated in a hearth of the largest size in one operation lasting six hours is about 9 J cwt., containing 45 to 48 per cent, of iron, the fuel con- sumed about lOf cwt., and the produce of finished bar iron about 3 cwt. The average consumption of mate- rials per 100 Ibs. of bar iron is, of ore 312 Ibs., and charcoal 340 Ibs., or 100 Ibs. of ore in good work should yield '31 Ibs. of bar iron, and 41 Ibs. of slags contain- ing 30 per ceat. ($f iron. Of the total contents of the ore, therefore, 71 per cent, is reduced to the metallic state, while the remaining 29 per cent, is expended in the slag. The ore in question contains about 14 per cent, of silica. The dimensions of the hearth vary in different districts ; the smallest, or Catalan fire, in use in the central and eastern parts of the Pyrenees, is 20 inches in length and breadth, 16 inches total depth, 9 inches measured from the twyer to the hearth bottom, and takes a charge of 3 to 4 cwt. of ore. The Navarrese hearth, employed in French and Spanish Navarre and Gfuipuscoa, is 30 inches long, 24 inches broad, and 16 inches deep from the twyer to the bottom ; the charge weighs from 5 to 6 cwt. The largest, or Biscayan hearth, is 40 inches long, 30 to 32 inches broad, and 24 to 27 inches in total depth, or from 14 to 15 inches below the twyer. The charges are from 7 to 9 cwt., as given above. Various processes for the direct production of wrought iron from the ore have been proposed, differ- ing from the Catalan forge, in the use of a closed vessel, 242 METALLURGY OF IRON. such, as a gas retort or fire-brick chamber, for the reduction, which, is effected at as low a temperature as possible, either by the direct contact of finely-divided carbon, or in a current of reducing gases produced by the passage of air over red-hot coal in a special gas generator. The spongy masses of iron, after removal and cooling under a covering of charcoal, are welded in open hearths or reheating furnaces, with or without pre- viously undergoing a mechanical separation from the earthy matters by crushing and treatment with electro- magnetic apparatus. As these methods are only appli- cable to the treatment of easily- reducible ores, and are essentially slow in work, giving only a small pro- duction from a plant of considerable extent, as compared with the old open fire, they have not as yet been found to possess sufficient advantages to be generally adopted on the large scale. At Santa Ana de Bolueta, in Biscay, Gurlt's process of reducing the rich brown hematite of Sommorosteo, containing 68 per cent, of iron, by means of carbonic oxide, has been tried with the -following results. The furnace has a shaft like an ordinary blast furnace, communicating with a series of gas generators near the bottom. When three charges were made daily, 72 cwt. of ore and 18| cwt. of charcoal yielded 23*8 cwt. of spongy metallic iron, which was removed while still hot in iron barrows, and allowed to- cool under a cover- ing of charcoal dust. The subsequent welding of the sponges or balls was effected in an ordinary Catalan fire, the waste being about 50 per cent, by weight, and the consumption of charcoal equal to the weight of the finished bars produced. The total consumption was, therefore, per 100 Ibs. of bars made, 174 Ibs. of charcoal aud 285 Ibs. of ore ; the loss of iron, amounting to nearly CONVERSION OF GREY INTO WHITE CAST IRON. 243 one-half, was larger than in the ordinary Catalan pro- cess, but a considerable saving of fuel was effected. In India wrought iron is made directly from the ore, either in shallow hearths with an artificial blast, or in furnaces with shafts, which may be worked with a blast, or by a natural draught, the former resembling the Catalan forge, while the latter may be compared to the lump or wolf furnaces which prevailed in Europe before the introduction of the flowing or modern blast furnace. In either case the dimensions are small, as are also the blooms produced, which vary from 20 Ibs. to 2 cwt. In the Burmese furnaces, which depend upon natural draught, the shaft is excavated in the face of a bank exposed to the prevailing wind, from 10 to 15 feet high, a number of conical pipes or nozzles being inserted in an opening at the lower part, corre- sponding in position to the tymp in an ordinary blast furnace. This primitive system of construction is said to have been used by the ancient Celtic inhabi- tants of the Rhenish hill countries, heaps of slags being found in Nassau, on the tops of bare swelling downs far away from water- courses, under ' circum- stances which indicate the probability of their having been produced in furnaces of this class. CHAPTER XIII. REFINING, OR CONVERSION OF GREY INTO WHITE CAST IRON. WHEN grey cast iron is melted in an oxidising atmosphere, the silicon in combination is oxidised to silica, and separates as a silicate of protoxide of iron, a portion of the iron being oxidised at the same time. 244 METALLURGY OF IKON. If the metal be run into moulds and suddenly cooled, the whole of the carbon enters into combination, with the production of a peculiar silvery- white metal, which is analogous in composition to that smelted from pure ores at a low temperature with a high burden of materials. The same result may be obtained by strip- ping thin plates or discs from the bath of molten metal by throwing water on to its surface, and sub- jecting them to a red heat in contact with air for several hours, a process followed in parts of Germany, and known as roasting (braten). The more usual method, however, consists in melting the metal with coke or charcoal in a small hearth of rectangular section, with one or more inclined twyers, through which cold blast air is made to impinge upon the surface of the melted metal. This process is known as refining, and the furnace, or hearth, as the refinery. The object of the operation is to reduce the fluidity of the melted metal, as well as to diminish the amount of silicon, or slag- making material, whereby the subsequent treatment in the puddling furnace is facilitated. The term " running out fire," which applies to the refinery, has reference to the use of a long cast-iron trough, forming a chill-mould for the metal, which is run out of the hearth as soon as the refining has been carried to the proper point. The general arrangements of a refinery fire are shown in Figs. 23, 24, which, together with the accompanying description, have been taken from Tomlinson's " Cyclo- paedia." The hearth H, Figs. 23, 24, is 2J feet wide, and 3J feet long. It is formed by the junction of four cast- iron troughs, i, through which a stream of cold water is made to circulate, to prevent them from being fused by the heat. The bottom of the crucible is of grit- stone or argillaceous sand, and is slightly inclined in CONVERSION OF GREY INTO WHITE CAST IRON. 245 the direction of the tapping-hole, o. The air, which is usually supplied by the same engine that blows the Fig. 23. The refinery. blast furnaces, enters the hearth through the six twyers, Fig. 24. Plan of refinery. t, which are inclined at an angle of from 25 to 30, and so arranged that the blast from each may be 246 METALLURGY OF IRON. directed towards the face of the opposite side of the furnace, not in opposition to the opposite twyer. The twyers are furnished with double casings, through which cold water is constantly running. A supply of water is brought by a pipe p into the reservoirs e y whence it passes to the twyers, through the pipes/, and escapes through the tubes c 1 into the tanks w, into which the water from the iron troughs flows by the syphon tubes c. A furnace of this kind consumes about 400 cubic feet of air per minute. This is sup- plied by the pipes T, which are furnished with screw- valves at s for regulating the supply. Above the hearth is a chimney 16 to 18 feet high, supported by four cast-iron columns, so as to allow free access to the fire on all sides. The tapping hole o is placed in one of the shorter sides of the hearth, and by it the melted metal and the slag flow out into the mould c, where the metal is cooled by quenching with water. In Wales the hearth of the refinery is about 4 feet square, and from 15 to 18 inches deep, with two or three twyers on either side. In Yorkshire the twyers usually alternate with each other on opposite sides, two being placed on one side and three on the other. The hearth bottom is made of sandstone or fire-brick. Sometimes the metal is run in directly from the blast furnace, but more usually the charge of selected pigs is melted down with coke in the hearth. In the latter case, the metal in the form of pigs and scrap is placed in alternate layers with coke, upon a bed of ignited fuel, at the bottom of the hearth, and the blast is supplied at a pressure of from 1J to 2J Ibs., according to the combustibility of the coke. In from two to two and a half hours' time, the charge, weighing two tons, is CONVERSION OF GREY INTO WHITE CAST IRON. 247 melted. Fresh fuel is then added, and the blowing is continued for half an hour, until the metal is sufficiently decarburised. The fluid contents of the hearth, metal and slag, are then tapped off together into shallow cast-iron troughs placed in front, which are kept cool with water. The usual dimensions of the moulds are about 10 feet long, 3J feet broad, and 6 or 8 inches deep. The separation of the slag is facilitated by throwing water upon the surface. When the metal is run directly from the refinery into the puddling furnace, the slag must first be removed. When freshly-fractured fine metal is of a silvery- white colour, the lower part is compact, with a radiated or parallel columnar structure, the top being dull and cellular. The usual thickness of the plate of metal is about 3 inches to a depth of 1 inch or Ij inch. From three to four hours are necessary to work off one charge, according to whether the iron is grey or white, the former taking the longer time. The con- sumption of coke is about 2J cwt. per ton of pig iron operated upon. When taken directly from the blast furnace, 22 '3 cwt. of common forge, or 22*1 cwt. of good grey cast iron, are required to produce one ton of fine metal. In the melting finery the quanti- ties are about 20 per cent. more. The slag produced amounts to about 3 cwt., and contains from 50 to 60 per cent, of iron. The loss of weight in refining hot blast pig iron, from its being more highly charged with foreign matters, is greater than is experienced in the treat- ment of that smelted by cold blast. The metal pro- duced from blackband is especially difficult of treat- ment, owing to its comparatively ready fusibility, which renders it necessary to continue the blowing for 248 METALLURGY OF IRON. a long time, with a corresponding increase of waste, 24 cwt. being required to make a ton of fine metal. The twyers are usually inclined at an angle of 38 , and from 1J to If inches in diameter : 94,000 cubic feet of blast are given per ton when the metal is run in from the blast furnace, but when melted in the hearth 136,000 feet are required with white, and 153,000 feet with grey cast iron. The weekly production of a refinery is from 150 to 160 tons in the former, and from 80 to 100 tons in the latter case. About 16- horse power is required to furnish the blast. In France and Belgium, the consumption of coke is about 30 per cent, by weight of that of the pig iron refined. A hearth with six twyers produces 130 tons, and one with four twyers only 90 tons of fine metal per week. The process of refining may be accelerated in the same manner as is usual in all methods of making malleable from cast iron, namely, by the addition of solid oxygen in the form of rich basic silicates of pro- toxide of iron, such as the slags from reheating fur- naces, or forge scale, which consists chiefly of magnetic oxide of iron. By the use of these fluxes the action of the blast is supplemented, and the carbon of the cast iron is employed in the reduction of a portion of the oxides of iron to the metallic state, with a diminution of the loss of iron. The saving is, however, more apparent than real, as the essential point of the pro- cess is the removal of combined silicon, and this can only be effected by its oxidation to silica, with the simultaneous production of tribasic silicate of protoxide of iron ; and whether this be done at the expense of the metal under treatment, or of the iron reduced by the secondary reaction from the rich slags added, is of very little consequence, as the latter owe their origin to CONVERSION OF GREY INTO WHITE CAST IRON. 249 exactly the same kind of destructive action upon metal previously operated upon. Lime may be beneficially employed as a flux for the removal of sulphur, especially that contained in the fuel, but its use is restricted by the fact of its giving a pasty and comparatively infusible slag, except when present in very moderate quantity. Manganese works in a similar manner, but more efficaciously, and, as has been already stated in considering its action in the blast furnace, increases the fluidity of the slag. In Silesia, the conversion of grey into white cast iron is performed in the reverberatory furnace, heated by gas instead of solid fuel. The construction is very similar to that of the ordinary founder's reverberatory furnace. The bed is made of sand set in an iron frame with hollow sides, which is kept cool by a current of air passing through it. The fireplace is replaced by a vertical shaft of rectangular section, about 5 feet high, which is filled with coal. Air at a pressure of about 4 Ibs. per square inch is admitted through a passage close to the level of the floor, and is distributed to the fuel through a number of small parallel jets attached to a wrought-iron pipe. The gas produced by the imperfect combustion of the coal is burnt at the top of the shaft, which corresponds in position to the fire- bridge of an ordinary furnace, by a fresh supply of air introduced through a long narrow mouth-piece, extending across the entire breadth of the hearth, and inclined at an angle of about 30, so that the flame is urged downwards in a thin sheet upon the surface of the metal. The charge, weighing two tons, takes about three hours to run down, during which time the draught is regulated by the stack alone. A small quantity of limestone is then added, in order 250 METALLURGY OF IRON. to convert the infusible dross on the surface of the metal into slag, after which the blowing proper commences, by means of a further supply of air from two twyers placed on opposite sides of the hearth, which impinge obliquely on the molten metal, producing a movement of rapid rotation. The duration of the operation varies from two and a half to five hours, according to the quality of metal required, the longer time giving a perfectly white iron. The loss is only about 5 per cent., owing to the use of limestone flux. According to Abel, the change is chiefly confined to the elimina- tion of carbon and silicon, as in the common refinery, sulphur and phosphorus, when present in the pig iron, being but slightly affected. The following are the rela- tive proportions of these elements before and after refining : Pig iron. Refined iron. Silicon . . . 4-66 . . 0'62 Phosphorus . . 0'56 . . 0'50 Sulphur . . 0-04 . . 0-03 The amount of silicon remaining is considerable ; but this is probably due to the use of limestone instead of fluxes containing oxides of iron, the object being merely the production of refined iron for foundry mixtures, and not for conversion into malleable iron. In Parry's method of refining, the cast iron operated upon is run directly from the blast furnace into the hearth of a reverberatory furnace, heated by a coal fire in the usual way. The blowing is effected partly by air and partly by a jet of steam, introduced through a twyer inclined at an angle of 45. The weight of the charge is 35 cwt. of pig iron, and about 7 cwt. of forge cinders. A ton of grey iron may be refined by steam in half an hour. The jet is three-eighths of an CONVERSION OF GREY INTO WHITE CAST IRON. 251 inch in diameter, with a pressure of from 30 to 40 Ibs., and superheated to 300 350, by keeping the orifice about 2 or 3 inches above the surface of the iron. Of course, water twyers must be used, as in the case of the hot blast furnace. The consumption of coal is said to be at the rate of 2 cwt. per ton of re- fined metal produced. This is chiefly expended in replacing the heat absorbed by the decomposition of the steam, which produces great local cooling, so that, if the supply be too great, as compared with that of the air blast, the iron may be cooled below its melting point. The chief advantage of this process is the removal of sulphur from the iron, and partly of phosphorus, which are evolved as sulphuretted and phosphuretted hydro- gen respectively. The effect is much more marked upon the slag than the metal. Silicon is also removed by the formation of silicate of protoxide of iron in the usual way. The following analyses of metal and slags, obtained in this process at Ebbw Yale, in South Wales, are by Noad : Pig iron used. Refined metal. Carbon, graphitic . 2'40 . . 0'30 Silicon . . . 2-68 . . 0-32 Slag . . . 0-68 . . Sulphur . . 0-22 . . 0'18 Phosphorus . . 0'13 . . 0*09 Manganese . . 0'36 . . 0'24 Forge cinder added. Cinder run out. Sulphur . . 1-34 . .0-16 Phosphoric acid . 2-06 . . 0-13 The slags obtained are therefore as pure, in respect to sulphur and phosphorus, as the ordinary run of Welsh iron ores. 252 METALLURGY OF IRON. CHAPTER XIV. PRODUCTION OF WROUGHT IRON IN OPEN FIRES. THE numerous processes employed in the production of malleable from cast iron are divisible into two classes, according to the nature of the furnaces employed, namely, open-fire or hearth fineries, where the pig iron is melted and decarburised in a shallow hearth before the blast of an inclined twyer, and reverberatory or puddling fineries, where the same operation is performed on the bed of a reverberatory furnace. The reactions going on during the process are similar in either case. The carbon, if it exist originally as graphite, first passes into the combined state, and is then converted into carbonic oxide either by the oxygen of the blast, directly, or indirectly by the action of protoxide, peroxide, or magnetic oxide of iron dissolved in the slag. These oxidising agents may be derived from the pig iron under treatment, which is always oxidised to a certain extent under the influence of the blast during the melting, or they may be added in the form of red hematite, forge scale, or slags containing protoxide of iron in large quantity, such as are produced towards the end of the finery process itself. When these latter substances are used, it is necessary to bring them into intimute contact with the metal by mixing them well together when the charge is in a semi-fluid con- dition. White cast iron is more suitable for conversion into malleable iron than grey, as it does not, when raised to a high temperature, pass immediately from the solid to the liquid state, but assumes, when near its melting PRODUCTION OF WROUGHT IRON IN OPEN FIRES. 253 point, an intermediate or pasty condition, favourable to the more effectual action of the air or other agents employed in the removal of the combined carbon. Grey metal, on the other hand, though requiring a higher temperature for fusion, becomes very liquid, and in a deep hearth sinks below the level of the blast, and becoming covered with a coating of slag, is com- pletely protected against the action of the air, unless it is brought under the influence of the blast by stirring or lifting with an iron bar, an operation which in- volves great labour, and delays the fining. This gives rise to an increased expenditure of fuel and waste of iron. No sensible amount of decarburisation takes place until the whole of the graphitic carbon has entered into combination with the iron, or what amounts to the same thing, until the metal has passed from the grey to the white state : this conversion is an essential preliminary in all finery processes where the air is introduced above the surface of the melted metal. In Bessemer' s process, which consists essentially in forcing air through molten pig iron from below, exactly the reverse conditions prevail, grey pig iron being exclusively used on account of its fluidity, and probably from the uncombined carbon being readily consumed, owing to the extremely high temperature at command. As the removal of the carbon is effected by air alone, the plastic quality of white iron is not requisite, and would interfere with the free passage of the blast. This process, although of great importance in steel manufacture, is not directly used in the pro- duction of malleable iron ; it will not, therefore, be necessary to consider it further in this place, it being only mentioned to show the great practical differences in the action of a blast of air upon molten cast iron, 254 METALLUKGY OF IRON. according to whether it be made to act from above or below the metal. Grey pig iron is often subjected, as a first step in the process of making malleable iron, to a preliminary oxidising fusion in the refinery or running- out fire, which is a rectangular hearth with one or more strongly-inclined twyers. The molten metal, after a certain amount of blowing, which deprives it of its graphitic carbon and silicon, is converted into fine or refined metal) and may either be run directly into the finery furnace or hearth, cast in chilled moulds, or stripped in thin flat discs by throwing water upon its surface when melted. The product is a white brittle metal, resembling the cellular or flowery white pig iron obtained in charcoal furnaces from a heavy burden of rich ores ; it differs from common or white cinder pig iron in being almost free from silicon. The application of the terms finery and refinery is somewhat contradictory : the latter, though apparently of larger signification than the former, refers only to a single step in the process of making malleable iron, namely, the conversion of grey into white cast iron. In Germany, this operation is distinguished as whiten- ing (weiss inacheii), and the finery or conversion proper of cast into malleable iron as freshening (frischen). The same term is applied to the reduction of metallic lead from litharge, an operation known in England as reviving. In former times hearth fineries were usually called bloomeries a term having refer- ence to the form of the product, which was called a bloom or lump. The reheating or welding fires were called chafcries. The methods of making malleable iron depending upon the use of open fires or hearth fineries, though of PRODUCTION OF WROUGHT IRON IN OPEN FIRES. 255 great interest from their antiquity and comparative simplicity, are gradually diminishing in importance, owing to the more general use of the reverberatory or puddling process, which can be advantageously em- ployed with fuel and materials of a lower quality, and also requires less skill in manipulation, owing to the more extensive use of machinery in the elaboration of the finished product. In a general way, the working of a hearth finery may be described as follows : the charge of pig iron, usually in the form of broad thin slabs, is introduced into a shallow rectangular hearth, whose sides and bottom are formed of cast-iron plates, which are pro- tected against the action of the fire by a lining or brasque of charcoal dust. The fuel employed is char- coal, the fire being urged by a blast of cold, or some- times heated, air, introduced through an inclined twyer placed on one of the sides close to the top of the hearth. The fusion of the metal is allowed to take place very gradually, so that it may be exposed as fully as possible to the oxidising influence of the blast by falling in single drops through the entire height or depth of the hearth. By this means the silicon is converted into silica, and together with any sand adhering to the surface of the pig, combines with protoxide of iron, produced at the same time, forming a fusible silicate of protoxide of iron or slag, which, being specifically lighter than the molten metal, swims above it. As t'he oxidation of the iron continues, the slag becomes more basic by the addition of magnetic oxide in indefinite proportions, which, when the whole mass is well liquefied, reacts upon the carbon of the metal, producing malleable iron and carbonic oxide. Owing to the intensely oxidising atmosphere prevail- 256 METALLURGY OF IRON. ing in the hearth, the production of the silicate goes on much more rapidly than its reduction by combined carbon, so that the volume of slag increases to such an extent as to form a coating sufficient to protect the metal from the action of the blast. It therefore be- comes necessary to break up the iron, that is, to lift the imperfectly- refined masses from the bottom of the hearth to the twyer, in order to subject them afresh to the joint influences of the blast and slag as often as may be necessary, until the carbon is almost entirely removed. With the progressive decarburisation, the fusibility of the mass diminishes, and ultimately a spongy, slightly coherent mass or ball of malleable iron is obtained, which, when removed from the hearth, is at a strong white heat, and therefore susceptible of being welded, and is immediately reduced to a rough, prismatic lump, called a bloom, or a slab, by the blows of a heavy hammer moved by steam or water power. The bloom is drawn out into a finished bar under the same or a lighter hammer, after reheating either on the same hearth during the melting down of the next charge, or in a fire or furnace of special construction. The simple operation sketched out in the preceding paragraph is susceptible of numerous modifications. More than a dozen so-called finery methods have been described by Tunner as in use at the present day : they are for the most part confined to the continent of Europe. As may be imagined, the differences between them are in many cases extremely small, and turn rather upon details of manipulation than actual diversity in principle or construction of apparatus. The most remarkable point in connection with this subject is the great diversity of terms used in different districts, almost every locality having a complete set of its own, PRODUCTION OF WROUGHT IRON IN OPEN FIRES. 257 which, as a general rule, are only current within a limited area. The reason of this becomes apparent, when we consider that iron-making in the olden times was carried on in remote districts, where wood and water power could be easily obtained, as, for instance, in the valleys on the flanks of great mountain ranges of Central Europe, the small size and weight of the finished bars, &c., requiring only the simplest means for conveyance to market, such as could be found in pack animals, without even the necessity for roads passable for wheeled carriages. In this way each district may have developed its own process without knowledge of what was doing in the same matter else- where ; and the local experience would be incorporated as a technical language, whose use would be confined to a small class of workmen on the spot. The introduction of the puddling furnace, and the necessity of good roads for the economic transport of materials to and from the forge, have had the effect of bringing iron manufacture from the seclusion of the valley to the high road, and as a consequence of the change, an almost exact uniformity of language has been introduced, all the terms connected with the puddling furnace and rolling mill originating in Eng- land having been adopted in foreign countries, in many cases even without alteration, or at most have been literally translated. The gradually-increasing scarcity and consequent rise in the price of wood, together with the increase of facilities for conveyance of coal to works at a dis- tance, have led to the abandonment of the open-fire method of finery in many districts, as, for instance, in the Eifel and Walloon countries ; and even in Scandinavia, although carried to a high degree of perfection, it is 258 METALLURGY OF IRON. giving way before the puddling and other modern processes, which are susceptible of greater economy in working. The numerous methods of hearth finery which have been alluded to above may be classified under three heads, according to the number of times that the metal requires to be broken up or lifted, from the melting down of the charge to the preparation of the ball for hammering; that is, as single, double, or manifold running-down processes (einmal, zweimal, or mehrmal schmeherci) . The distinction between these is in great part due to the number of furnaces employed. Thus in the last, of which the old German or Walloon forge may be taken as the type, the three operations of refin- ing, or conversion of grey into white metal, lifting and fining proper, or breaking up, and the final balling, are performed in the same hearth ; in the second, or double process, the metal is run into the finery or blooming hearth from a melting finery or running- out fire ; and in the first, or single process, which is used in Styria with white pig iron approximating in composition to refined metal, the removal of the combined carbon is effected chiefly by special oxidising agents without much working before the twyer : the product is a steely iron, whose excess of carbon is afterwards removed by subjecting the bloom to several welding heats. A further distinction of these processes is founded upon the method adopted in working the iron as it fines, or, as is said in English, comes to nature. Thus, with metal of a good quality, the whole charge may be allowed to come up together by lifting and working it in one mass before the twyer, whereas with a lower quality the particles of iron, instead of being allowed to coalesce as they form, are broken up into several masses, which, after having being refined separately, are worked into PRODUCTION OF WROUGHT IRON IN OPEN FIRES. 259 one ball as before, or each one may be forged alone into a bloom of smaller size. The slags produced in the earlier part of the pro- cess, as well as those of the refinery, as a rule approxi- mate in composition to tribasic silicates of protoxide of iron, with variable quantities of manganese and earthy bases, according to the character of the pig iron under treatment. Towards the end they become more basic, and at last a difficultly-fusible substance, contain- ing from 75 to 85 per cent, of protoxide of iron, remains in the hearth. This, together with the more fluid, but also basic slag expressed from the ball by hammering, is employed as a decarburising agent. The construction of hearth fineries is subject to a certain amount of modification in different localities. In the simplest, or old German forge, already alluded to, the top of the hearth is near the ground level, and the flame escapes directly into an open hood, like that of an ordinary smithy fire ; but in the more improved forms adopted in the Franche Comte and Lancashire forges used in Sweden, the hearth proper is covered with a cylindrical roof, and communicates by a lateral flue with a brick chimney. A portion of the waste heat of the flame is economised by causing it to pass over the pig iron forming the next charge, which is placed in the flue, and is raised to a strong heat, and partly oxidised. It is found that this preliminary heating causes a considerable saving, both of fuel and time, in the subsequent process of fining, being somewhat similar in effect to the refinery. The flame is* also used in heating the blast, for which purpose a coil of cast-iron pipes is placed, either above the hearth, or between it and the base of the chimney stack. The Bergamask forge process, used in the neigh- bourhood of Bergamo, Brescia, and Lecco, in Northern 260 METALLURGY OF Italy, differs from those already noticed by the large use made of oxidising substances, and may be regarded as bearing the same relation to them that the modern or boiling system of puddling does to the original or dry process. The charge of pig iron, when melted and cleared from the supernatant cinder, is mixed with rich forge slag, which reduces it to a pasty consistency, re- moved from the hearth, and cooled with water. The partially- refined product is then exposed in small por- tions in the same hearth, after making up the fire, to a low heat, sufficient to agglutinate the iron and cinder into a cake, which is again taken out and cooled. In the third stage, each of these cakes, or cotizzi, is refined in the ordinary way, but with the addition of a further quantity of rich slag or cinder. Owing to the intermittent nature of the process, the hearth having to be twice heated and cooled in each operation, the consumption of fuel is considerable, being nearly two and a half times the weight of the finished bars. The loss of iron estimated on the pig is 4| per cent., or, taking into account that contained in the cinder added, from 18 to 19 per cent. The charge weighs 5 cwt., and produces in one operation, lasting eighteen hours, about eighteen finished bars, weighing from 25 to 30 Ibs. each. The pig iron employed is smelted from mangane- siferous spathic ores occurring in the triassic rocks near the lake of Como, in stratified masses, of which five are known, the greatest individual thickness of 27 feet being observed in the bed of La Manina, in the valley of Dezzo. In South Wales, a superior quality of iron, adapted for rolling into thin sheets for use in the manufacture of tin plates, is made in the charcoal finery. The PRODUCTION OF WROUGHT IRON IN OPEN FIRES. 261 metal treated is usually of a good class, such as that smelted with anthracite or coke ; in the latter case, with cold blast from Welsh mine or hematite pig. The charge, weighing generally from 5 to 6 cwt., is first healed in a small coke refinery about 18 inches square, with two twyers, and, after the requisite amount of blowing, is run off by an inclined gutter into the charcoal fineries, of which there are two, placed in front of and a little below the running-out fire. These hearths are made of cast-iron plates ; the bottoms are hollow, and cooled by a current of air. Three of the sides are vertical; the fourth, or working side, is slightly inclined upwards and outwards. The charge of fine metal is equally divided between the two hearths, which are each blown by a single twyer. Although cold blast is used, the nozzle is protected by water twyers, both in the refinery and charcoal hearths. The fining appears to be done dry, that is, without the addition of slag or scale, by continual breaking up and raising the iron with a pointed bar ; the slag, or cinder, is tapped off two or three times during the operation which lasts from one hour to one and a quarter. The whole of the charge is worked into a single ball, weighing somewhat less than 2 cwt., which is shingled and drawn under a lever hammer to a long bar, about 1^ or 2 inches thick, and then broken into pieces, called stamps, weighing about J cwt. each, by nicking the bar half through, and striking the weakened part with a sledge hammer. This method of breaking up the bar affords a ready means of selecting the iron by the appearance of the fracture, only such por- tions as present a fine uniform crystalline grain being lised in the formation of the pile from which the finished sheet is made. A similar process of stamping 262 METALLURGY OF IRON. and selection of rough bars is in use in those forges of the West Riding of Yorkshire that are noted for the high quality of their malleable iron. The reheating or welding of the stamps is effected in a special furnace, known as the hollow fire, interme- diate in character between the old chafery and the modern reheating furnace. It consists of a deep rect- angular hearth roofed over at the top. The upper part forms a chamber, in which the piles are reheated. The lower part of the hearth is filled with coke, which is burnt by a blast of air introduced by an inclined twyer, near the top of the fuel, in the ordinary way. The piles consist of fragments of the broken bars, or stamps, obtained in the preceding operation, and are supported on a flat plate or staff in the upper part of the fire, clear of the top of the fuel, but fully exposed to the flame. If the blast is introduced at a lower point, so that the air has to traverse a certain thickness of ignited fuel, the conditions of combustion become similar to those of a gas generator, and the furnace approximates to a gas reheating furnace with the top blast omitted. A portion of the waste flame is economised by the use of a second heating chamber, where the pile receives a preliminary heating before it is brought up to the welding temperature. In Sweden, three principal methods of charcoal finery are in use : the German, or rather Walloon, the Franche Comte, and the Lancashire processes. The first of these is confined to those forges tliat produce the Dannemora steel irons. The hearth is not covered, and the fining, which takes place in a bath of slag, is much accelerated by almost continuous breaking up and stirring of the molten metal. The bloom is of small size, weighing only about 100 Ibs., and is pro- PRODUCTION OF WROUGHT IRON IN OPEN FIRES. 263 duced in from twenty-five to thirty minutes. The pig iron of a white or strongly-mottled character is not charged and melted down in one quantity, but is used in the form of slabs or bars from 15 to 18 feet long. Only the fore-end of the slab is exposed to the fire, so that the metal melts and runs down in drops before the blast like sealing-wax in the flame of a candle, the end, as it wastes, being kept in the same position by pushing forward. The bloom obtained from the previous heat is reheated for the first time in the fore- part of the hearth during the period of melting, being held with tongs in an inclined position : the subsequent heats, to the number of six or seven, required in drawing it out into a bar under the hammer, are effected in a separate fire. The consumption of char- coal is very large, being three times the weight of the bar iron produced ; the loss of weight, or difference between the latter and the pig iron used, is from 20 to 25 per cent. The Franche Comte and Lancashire processes are conducted in covered hearths with flues for heating up the charge of pig iron previous to melting, and stoves for the blast, which is raised to a temperature of about 100 ; the pressure is from 1 Ib. to 1 Ib. The princi- pal difference between them is that in the former the reheating of the bloom, which is cut into two pieces after shingling, is effected in the same fire, while in the Lancashire forge either a second hearth, or what is now more usually the case, a gas- welding furnace, is used for this purpose. The proportional yield is about the same in both cases, the weight of bar iron produced being about 15 per cent, less than that of the pig iron used. The consumption of charcoal is, under the most favourable conditions, about the same in either pro- 264 METALLURGY OF IRON. cess, being one and a half times the weight of the finished bars, or only half as much as in the Wal- loon forge. CHAPTER XY. REVERBERATORY FINERY OR PUDDLING PROCESS. THE use of the reverberatory furnace, instead of the open fire or hearth, in the conversion of cast into malleable iron, was introduced by Cort in 1784, and has now almost entirely superseded the older processes in those localities that are chiefly dependent upon mineral fuel. Even in wooded districts its use is becoming general, more especially since the introduction of gas furnaces, which are capable of being worked with fuel of inferior quality and heating power such as wood, brown coal, peat, &c. when converted into carbonic oxide, such substances being unfit for use in fineries where the heat is produced by combustion of the fuel in contact with the iron. The reactions going on during the operation of puddling are substantially the same as those observed in hearth fineries, the decarburisation of the pig iron being effected by the joint action of a current of air produced by the draught of a chimney, instead of being blown in under pressure from a twyer, and oxidising fluxes, such as hematite, magnetic oxide of iron, forge scale, or the molten slag, a highly basic silicate of protoxide of iron. According to the relative importance of the parts played by these agents, the process is divided into dry and wet puddling, the former being dependent mainly REVERBERATORY FINERY OR PUDDLING PROCESS. 265 on the exposure of the metal to the action of the air, while in the latter, which is more generally known as the pig-boiling process, the slag and oxide of iron added are the most important oxidising agents. As the charge of melted pig presents a larger surface for the same weight in the puddling furnace than is the case in the open fire, it forms a thinner layer, and therefore can be more readily brought into contact with the air ; the operation of fining is more quickly performed ; and the labour of lifting, &c., although very severe, is less so than in the hearth finery, especially in the treatment of grey iron. The conversion of the latter into white metal by a preliminary fusion in the refinery is, however, equally advantageous in either case. The general details of the construction of the pud- dling furnace, are shown in the four figures (Fig. 25), A, B, c, and D. The fireplace is of rectangular form, built of fire-bricks, and divided from the hearth by a low wall or fire-bridge. The roof of the furnace is curved to a flat arch, and is generally made to slope at a small angle towards the flue. The whole of the brickwork is cased with side plates of cast iron, united by flanges and bolts, and bound together with wrought-iron tie-rods across the top. The bottom of the bed is formed of plates of cast iron, united by tenon joints, and supported upon dwarf pillars or standards of the same metal. The sides of the bed may be variously constructed, the differences being due to variations in the methods of artificial cooling adopted. In the furnace in question they are formed of hollow iron castings, united into a rectangular tube, through which a current of air circulates for the purpose of protecting the metal against the intense heat of the 266 METALLURGY OF IRON. furnace. The bed is terminated at either end by a straight wall or bridge : that nearest the fireplace is called the fire-bridge, and the opposite one the flue- bridge ; both are built of fire-brick, overlapping the top Fig. 25. Puddling furnace. A. Vertical section through the centre. B. Plan at level of bed. D. End elevation of fireplace. c. Side elevation. of the side frame, so as to form a recess for the recep- tion of the refractory material used in lining or fettling the sides. The fire grate presents no peculiar features ; it is made of plain wrought- iron bars placed horizontally, and carried at either end by transverse bearers. The depth of the fireplace varies with the nature of the REVERBERATORY FINERY OR PUDDLING PROCESS. 267 fuel employed, being greatest with the least bituminous kinds of coal, in such cases, especially, where anthra- cite is burnt. A. forced draught, produced by blowing air in below the grate, may be sometimes used to ad- vantage. With peat, brown coal, or slack, inclined or step- grates are used, and by the combination of these accessories the indirect or gas furnace is produced. The best fuel for furnaces with ordinary grates is coal of a dry, non-caking quality, burning with a long flame, as free from sulphur as possible. The surface of the grate should be between one-half and one-third of that of the bed, which, taking the latter at 20 square feet, would give from 7 to 8 square feet. The amount of coal burnt is from 1^ to 2 cwt. per hour. The charging or fire-hole is 10 inches above the grate ; it has no door, but is stopped with lumps of coal when the fire is lighted. The flue is usually built with a slope towards the stack ; the sectional area varies with the nature of the fuel, being about one-fifth of that of the grate for bitu- minous coal, and one-seventh for anthracite. Some- times a second bed is placed behind the flue-bridge, upon which the pig iron destined for the following charge is subjected to a preliminary heating or roast- ing, by the flame passing over it on its way to the stack, in order to save time in the subsequent melting down. In like manner, when a blast is used above the grate, as in gas furnaces, it may be heated by means of a coil of horizontal V-shaped pipes of cast iron, placed on the lower part of the stack in the course of the flame, or by circulation through the hollow side frames. The stack is usually from 30 to 50 feet high, and about 20 inches square, when it serves only a single furnace ; but when the several flues are led into one, especially 268 METALLURGY OF IRON. when a part of the heat is taken away by passing the flame under steam boilers, it is necessary to increase the height to 100 feet or more, in order to overcome the additional resistance. The walls of the stack are of fire-brick, with an outer casing of common brick- work, which is tapered in thickness, being set back in steps at two or different heights; the lower part is often supported on cast-iron columns or standards. The draught is regulated by a flat plate or damper at the top of the stack, attached to one arm of a lever, which can be raised or lowered by means of a chain attached to the opposite arm, which hangs nearly down to the ground level. The working door, which is on the same side of the furnace as the fire-hole, is made of fire-clay slabs set in a cast-iron frame, and is suspended by a chain to a lever, carrying a counterbalance weight at the opposite end, in order that it may be readily lifted and lowered. It is only opened during the introduction of the charge and the removal of the puddled balls. A small rectangular or arched notch, called the stopper hole, is cut out of the edge for the introduction of the tool used in stirring or rabbling the bath of metal. The sill of the door is about 10 inches above the level of the bottom of the bed ; below it is placed the tap-hole, through which the slag or tap cinder is withdrawn from the hearth. During the operation it is plugged up with sand in the usual way. A portion of the cinder also overflows the flue- bridge, and runs down the inclined surface of the flue to the bottom of the stack, where it is allowed to accu- mulate. The side of the bed opposite to the working door is of a curved form, and is not directly accessible from the exterior in the ordinary or single furnace. In REVERBERATORY FINERY OR PUDDLING PROCESS. 2G9 large forges it is usual to place two furnaces together in one block, back to back, with their working sides facing in opposite directions. The larger or double furnaces have working doors on both sides, so that two sets of puddlers can work at the same time, the weight of the charge being of course proportionately increased. In some few instances the beds have been made of such a size as to admit of working from four points simultaneously. It is doubtful, however, whether any advantage is to be got from the increased dimensions, as the saving of fuel and time claimed can only be realised by employing men of uniform skill, and capable of working off their heats in exactly the same time, otherwise a large loss of iron from burning is likely to ensue when one man brings out his heat before the other. The working bed, or lining of the hearth, was formerly covered with sand, but is now usually made of re- fractory slags rich in oxides of iron, such as are obtained at the end of the process, the remains of old beds of a similar character, mill or hammer slag, or burnt scrap iron. In making a new bed, the cast-iron bottom-plate is covered with a layer of broken slags, 3 to 5 inches in thickness, which is then softened by long-continued heating, the surface being rendered smooth by working with a flat bar or paddle. When scrap iron is used, a quantity of about 4 cwt. is thrown into the furnace, which is then raised to a strong heat. The ball formed by the agglomeration of the particles of iron is worked down and spread as uniformly as possible over the entire bottom, care being taken to maintain a high temperature and oxidising atmosphere in the furnace during the operation. The thickness of the finished coating should not exceed 1| or 1J inches. 270 METALLURGY OF IRON. Sometimes the bottom-plate is coated with, a thin layer of fire-clay before the lining is introduced. Grey pig iron should not be puddled alone upon a new bed ; the first charges should consist of scrap iron or waste blooms, and refined metal in small quantities, until the refractory lining has become sufficiently consoli- dated, by continued oxidisation and a high temperature, to resist the solvent action of the silica produced from the oxidation of the silicon contained in the pig iron. The side-plates of the hearth are lined or fettled in a similar manner with bull-dog, a mixture of peroxide of iron and silica, produced by roasting tap cinder, hematite, or magnetic iron ore. Limestone is sometimes used for this purpose, but does not appear to be gene- rally advantageous, except as being less liable to waste, as it does not contribute to the decarburisation of the metal, and thickens the slag, and may prevent welding, producing a red short iron if mixed accidentally with the ball. The side linings are subject to considerable wear, and require to be repaired after each heat. For this purpose small heaps of fettling materials are placed by the side of each furnace. The larger holes are filled with lumps of crushed bull-dog, after which the surface is made smooth with puddler's mine, usually a soft red hematite, which is mixed to a paste with water. In Cleveland, besides the ordinary fettling materials, burnt pyrites, residues from the sulphuric acid works, called " Blue Billy/' and finely-crushed Swedish magnetic iron ore, are in use. Although the process of puddling is susceptible of considerable modification according to the nature of the pig metal employed, and that of the iron which it is desired to produce, it may be generally stated to in- clude the following operations : HEVERBERATORY FINERY OR PUDDLING PROCESS. 271 1. Melting down of the charge, with or without previous heating. 2. Incorporation of oxidising fluxes with the charge at a low heat. 3. Elimination of carbon, by stirring the contents of the furnace at a high temperature. 4. Consolidation of the reduced iron to masses or balls fit for hammering. The regulation of the temperature, and the amount of air passage through the furnace by the damper, is a point of considerable importance. The heat requires to be greatly raised towards the end, at the same time preventing an unnecessary influx of air, which would burn the iron to waste. In gas furnaces this is done by shutting off the top blast, so that the hearth is filled with an atmosphere of heated gas containing unconsumed carbonic oxide. The following is a generalised description of the steps ordinarily pursued in puddling : When the furnace is charged, the working door is shut and secured in position by iron wedges ; sometimes the joint is luted with clay; the fire is made up after cleaning and pricking the grate ; the fire-hole is stopped with lumps of coal and slack, in order that no air may enter the furnace except through the space between the grate bars during the period of melting down. In about a quarter of an hour the metal begins to soften ; the puddler then introduces a bar or rab- ble through the opening in working door, and moves the unmelted lumps from the sides into the middle of the bed, in order to bring the whole more quickly into a state of uniform fluidity, the fire being increased at the same time for about four or five minutes. As soon as the metal is completely melted, it is rendered uniform by stirring, the temperature being lowered by partially closing the 272 METALLURGY OF IRON. damper, until the surface of the bath is protected by a coating of slag against the direct action of the air. The amount of handling required in this part of the process depends upon the nature of the metal operated upon. With grey pig, which requires a higher tem- perature for fusion, but which runs very liquid, the fragments may be distributed uniformly over the bed, and melted down without being moved, if the furnace is sufficiently hot ; but otherwise, a pile of metal is formed close to the fire- bridge, and as the temperature increases, the unmelted portions are drawn back into the centre, and pressed down below the surface of the slag. When white or refined metal is used, it is said to be an advantage to bring the furnace to a high heat by firing up strongly for about a quarter or half an houi before introducing the charge ; the fusion takes place more rapidly, and with less oxidation of iron, than is the case in the ordinary way. In order to bring about the reaction of the slag upon the melted metal, it is necessary to incorporate the whole contents of the furnace well together after melt- ing. For this purpose the temperature is lowered by checking the draught, or even throwing water upon the metal, the charge being stirred at the same time. The slag is also reduced to a more basic condition by the addition of scale or mill cinder, to compensate for the silica produced from the oxidation of silicon in the pig, which, as we have already seen, always separates when the fusion takes place in an oxidising atmosphere. When the mixture is complete, and the mass is some- what stiffened, the reaction of the oxide and silicate of iron upon the combined carbon is apparent by the escape of blue flames of carbonic oxide ; and as the REVERBERATORY FINERY OR PUDDLING PROCESS. 273 temperature is increased by opening the damper, the whole of the surface of the metal commences to boil from the rapid escape of gas, and rises above the level of the working door, at the same time a portion of the molten slag flows out. The action is facilitated by con- stant stirring with the rabble or hooked bar. The puddler searches or sweeps every portion of the bed by moving the point of the tool in curved lines from the centre outwards towards the bridges on either side, commencing at the front. The sides are reached by a kind of scooping action, the rabbles being worked against the door-frame as a fulcrum. The tool must be changed every five or ten minutes, or it would soften and adhere to the iron if left too long in the furnace. When taken out it is cooled by plunging into a cistern or water bosh, which detaches the adherent cinder ; the point is afterwards dressed up into shape by forging with a light hammer. Usually four tools are required to be used in the boiling of one charge. As the carbon diminishes the ebullition becomes less violent, and the bath, from its reduced fusibility in spite of the high temperature, begins to stiffen, -and malleable iron separates, or, as it is called, comes to nature in the form of bright points, which increase to spongy masses projecting from the bath of melted slag. Owing to the high temperature and the fine state of division in which it is exposed to the oxidising atmo- sphere of the furnace, the reduced metal is raised to a brilliant white heat by partial combustion. At this point of the process it is necessary to regulate the fining by preventing the too rapid agglomeration of the reduced iron ; the whole contents of the furnace require, therefore, to be stirred and broken up again, so that every part may be brought under the influence 274 METALLURGY OF IRON. of the high temperature prevailing in the neighbour- hood of the flue-bridge, at the same time any pasty lumps of iron that may have adhered to the sides are detached. The reduced mass is subject to a final heat, in order to facilitate the separation of the cinder by rendering it perfectly fluid. The last operation consists in forming up the balls, which is done by detaching from the reduced iron masses of usually from 60 to 80 Ibs. weight each, and pressing them together with the tool until they are sufficiently coherent to be moved without falling to pieces. This may be done either by pressing against the bottom and sides of the furnace, or by a rolling motion, the iron being gathered up around a small nucleus like a snow-ball. As soon as a ball is made it is placed close against the fire-bridge, and in order to keep it out of the draught of air between the working door and the flue, the second is proceeded with until the whole of the charge has been balled up ; the working door is then closed, and the final heat is given. The removal of the balls, which are of a roughly spherical form, after they are drawn to the working door with the tool, is effected by means of a long pair of tongs with curved jaws. They are first lifted to the table in front of the working door, and afterwards either dragged along the floor or carried on a wrought- iron truck to the hammer, or such other shingling machine as may be employed. After the removal, and during the shingling of the first ball, the damper and working door are shut, in order to protect those re- maining in the furnace from unnecessary waste by oxidation while waiting their turn for hammering. The old system of puddling pig iron on a dry bed REVERBERATORY FINERY OR PUDDLING PROCESS. 275 is only applicable to white or refined metal : the chief difference between it and the method of boiling consists in the comparatively small quantity of slag formed. As soon as the metal has got into the pasty state it is broken up and constantly stirred, in order to incor- porate the oxide of iron, formed during the melting down, with the metal. The contents of the furnace are not allowed to become perfectly fluid, and the work goes on continuously from the commencement of the stirring to the balling up. Although there is less loss of iron, and a smaller consumption of fuel, owing to the rapidity with which the operation is performed, than is the case in the boiling process, the iron pro- duced is likely to be of an inferior quality, unless a very good description of pig is used. The actual use of sand bottoms is almost obsolete, as they give rise to a great waste of iron, the process being usually conducted on an iron bottom with a thin coating of cinder. According to Truran, 1 ton of puddle bars is pro- duced by 21 cwt. 1 qr. 20 Ibs. of fine metal by the dry puddling, and 21 cwt. 3 qrs. by the boiling process. The former lasts from 1 to li hours, and the latter from 1^ to 2 hours. The excellence of the iron produced depends mainly upon the prevalence of a high temperature during the period of .boiling, when the heat is continued during the balling by keeping the damper open, in order to maintain an oxidising atmosphere in the furnace ; de- carburisation is promoted, and soft or fibrous iron is obtained. On the other hand, when the draught is checked after boiling by partially closing the damper, the hearth is filled with neutral or reducing flame from the imperfect combustion of the gases produced by the fuel, and a further elimination of carbon is pre- 276 METALLURGY OF IRON. vented. The result in this case is a hard or steely iron, which breaks with a finely crystalline fracture, and may be considered as intermediate in character between soft iron and steel. By diminishing the time of boiling, and working at a low temperature, another form of granular crystalline iron may be obtained, which is hard, but deficient in tenacity, and only fit for the body or central part of common rails, where it is exposed chiefly to a compressive strain. Although the nature of the iron obtained is greatly dependent upon the manipulation, as much or more is due to the quality of pig iron operated upon. The greater the amount of impurities, especially sulphur and phosphorus, the longer will the puddling last, and consequently, the greater will be the waste of metal. With metal of low quality it is scarcely possible to produce good steely iron, as the decarburisation. must be pushed to the utmost in order to remove other foreign substances. The quantity of slag produced in puddling varies with the metal treated. With grey pig it is greatest, as the combined silicon takes up about six times its weight of iron in order to form a fusible silicate ; while refined metal, having been previously deprived in great part of its silicon in the refinery fire, makes much less. The more nearly the slag approaches in composition to a neutral (tribasic) silicate, the greater will be its fluidity, and the less its decarburising influence upon the molten pig iron, as compared with the more basic slags, containing peroxide or magnetic oxide of iron in excess, which are produced towards the end of the process. The presence of other bases in the slag, espe- cially protoxide of manganese, have a similar effect in preventing the removal of carbon, as they increase the REVERBERATORY FINERY OR PUDDLING PROCESS. 277 fluidity, so that the bath of molten slag screens the surface of the metal from the direct action of the air, without introducing the compensating oxidising agency of kindred oxides upon the combined carbon, oxide of manganese being undecomposable by carbon in an oxidising atmosphere. It is on account of this pro- perty that the presence of manganese is of great value in pig iron which is intended to be converted into steel by puddling. As the fluidity of puddling-furnace slags diminishes with the increase of bases, it is advisable not to work with refined metal alone, as in that case the hearth bottom becomes covered after a time with an almost infusible layer of highly basic slag, like the butt-dog used in fettling. This inconvenience is to be avoided by adding a certain proportion of grey or white pig iron containing silicon to the charge of fine metal. Under ordinary circumstances, in puddling grey pig, the cinder is tapped off at every second heat ; but with fine metal the quantity formed is so small that it may remain. The chemi'cal changes involved in the process of puddling have been investigated by Calvert and John- son, Lan, Schilling, and Drassado, both in England, France, and Germany. The method followed by these chemists was similar in all cases. Samples of the iron and slag taken from the furnace at different times during the puddling of one charge were analysed, and the results tabulated. The order in which the foreign bodies are removed can then be seen by comparison of the analyses, assuming, of course, that the samples re- present the average composition of the contents of the furnace at each period. In the boiling process, the oxidation of carbon is effected chiefly in an indirect 278 METALLURGY OF IRON. manner by an excess of protoxide, or rather magnetic oxide, of iron contained in the slag, which oscillates in composition from a more acid to a more basic character at different stages of the process. Thus the amount of silica in the slag may be increased absolutely, at the commencement of the process, by the oxidation of silicon during the melting of the pig iron; and relatively, during the boiling part of the process, owing to the partial reduction by the carbon of the pig iron of the oxides of iron held in combination. On the other hand, the slag becomes more basic towards the end, when the carbon has been removed, and the reduced iron com- mences to burn, owing to the intense heat necessary during the operation of balling. The removal of the foreign matters in combination with the iron takes place in the following order : first, silicon ; then man- ganese, then phosphorus; and, lastly, sulphur; the latter element being most difficultly removable. In the treat- ment of grey pig iron, the graphitic carbon is trans- formed into the combined condition after the removal of the silicon during the melting of the charge ; a change that has already been noticed as occurring at the same stage in all refinery processes. The cause of the removal of phosphorus from iron in the puddling process is not well explained. Percy supposes that it may be effected by liquation as a fusible phosphide of iron, which sweats out of the pasty mass of the ball and passes into the slags, where the phosphorus is oxidised to phosphoric acid. When a sufficiently high temperature can be commanded to melt malleable iron, as is the case in Bessemer's process, the whole of the phosphorus present in the pig iron is retained in the product. This appears to be true for any kind of iron. REVERBERATORY FINERY OR PUDDLING PROCESS. 279 The addition of oxidising fluxes other than the com- pounds of iron already noticed has been advocated as a method of improving iron in the puddling furnace. The chief of these is the mixture of salt, peroxide of manganese, and clay, known as Schafhaiitrs powder, which is recommended as an addition in the boiling process, at the rate of about 14 Ibs. to an ordinary charge of 3| or 4 cwt. of pig iron. The oxygen given off by the peroxide of manganese and the chlorine of the salt are said to act directly upon arsenic, sulphur, and phosphorus, with the production of oxides or volatile chlorides ; while the bases, alumina, protoxide of man- ganese, and soda, pass into the slag, giving it increased fluidity. The latter is probably the true reason of the efficacy of this flux. Sulphate of iron has also been recommended for the same purpose. In Staffordshire two hands (puddler and underhand), in a turn of twelve hours, work off from five to seven heats, the charge being from 4 to 4J cwt. The smaller number refers to grey pig, and the larger to mixtures containing from one- third to one-fourth by weight of fine metal. The loss of weight between the pig iron charged and the puddled blooms or bars produced is from 1^ to 2 cwt. per 22 cwt. of pig metal, or from 7 to 10. per cent. The coal burnt amounts to between 20 and 22 cwt. per ton of puddled bars. The fettling materials required in the turn of twelve hours for keeping the bed in proper order are from 6 to 7 cwt. of bull- dog, and 2 to 3 cwt. of puddler's mine, in addition to the mill scale added to the charge. In Scotland, where dark grey metal rich in silicon is used without being previously refined, only from four to five heats of 4 cwt. are made in the same time. The loss of weight is from 15 to 18 per cent, from pig 280 METALLURGY OF IRON. iron to puddled bars, and the consumption of coal per ton of the latter from 25 to 26 cwt. When mixtures of fine metal and grey forge pig, partly Scotch and partly hematite, are used, the results are generally similar to those obtained in Staffordshire. In Cleveland, the consumption of small coal (nuts) is from 24 to 27 cwt. per ton of puddled bars. The whole of the above quantities are in long cwts. of 120 Ibs. each. In the "West Riding of Yorkshire, in the neighbour- hood of Leeds and Bradford, a very high quality of wrought iron is made from cold blast refined metal by puddling in small heats, the stirring being continued longer than is usually the case, in order to obtain uni- formity in the product. The furnace is of comparatively small size, with a very high stack, in order to command a strong heat. The charge, weighing 3 cwt., is heated to redness before its introduction to the puddling furnace, so that the melting down requires only from twenty to twenty- five minutes, and the whole operation about one hour and twenty minutes: some heats are made in twelve hours. The balling is performed as much as possible in a reducing atmosphere, by closing the damper, as the iron is of a bright crystalline steely character, and is not decarburised to the same extent as ordinary fibrous iron. Only three or four balls, weighing from 80 to 90 Ibs. each, are obtained in one heat, which, after shingling under a helve hammer into plates or stamps from 10 to 12 inches square, and about 2J inches thick, are broken into pieces by blows from a heavy weight falling from a considerable height. These pieces or stampings are assorted according to the fracture ; those that are most uniformly crystalline are reserved for the manufacture of hard bars, such as railway tires, while those showing fibre are better fitted REVERBERATORY FINERY OR PUDDLING PROCESS. 281 for making boiler plates and wire rods. The consump- tion of coal is very large, being 30 cwt. per ton of fine metal treated, or 37^ cwt. per ton of blooms produced. When the double furnace is used the charge is twice the ordinary weight, or from 6 to 8 cwt., the time required for working off the heat being the same. In Belgium the average weight of the charge is 230 kilogrs. (4'b' cwt., short weight). According to the quality of metal employed, the time required for each heat is from 1J to 2f hours, namely, 2 to 2f hours with grey pig, 1J to 2J hours with white pig, and 1J to 2 hours with fine metal. 'The loss of weight is from 7 to 10 per cent. The coal burned is equal in weight to that of the puddled bars produced. The general arrangements of a gas-puddling furnace, used in Carinthia are represented in the longitudinal section, Fig. 26. The fuel is air-dried wood, which is Fig. 26. Carinthian gas-puddling furnace. converted into combustible gas in the generator a, a rectangular chamber, lined with fire-brick, of a capacity of about 14 cubic feet, by a stream of air introduced at a pressure of half an inch of mercury, through the lower branch of the blast main at b. The combustion of the gases is effected by a second blast, introduced imme- diately above the fire-bridge, through the inclined twyer 282 METALLURGY OF IRON. c, which is of an oblong form, extending completely across the bridge, with an aperture of 7 inches in depth. By previously circulating through the hollow space in the cast-iron side plates of the bed, the air is heated to a temperature of 200, producing a much more active combustion than is the case when the gases are burnt with cold air. A second bed is used for heating up the metal for the following charge by the waste flame during the period of balling, an arrange- ment that, as has already been stated, is found to save both time and fuel. The remaining details do not call for any particular remarks, being of the ordinary kind adopted elsewhere. In Styria, where lignite is used for puddling, the consumption is from 22 to 24 cwt. per ton of blooms, a result that is highly favourable, not exceeding the average of furnaces where coal is burnt, allowance being made for the difference in calorific value of the two classes of fuel. This is in great part due to the high quality and small amount of carbon and silicon in the pig iron operated upon. The heat of 4 cwt. is worked off in an hour, having been brought to an orange- red heat before melting by exposure in a second hearth, during the balling of the preceding charge. The loss of weight on the metal is from 6 to 10 per cent. When peat is used, from 240 to 360 cubic feet are required in the production of a ton of blooms, or from 200 to 280 cubic feet of wood. From the published accounts of the working of furnaces using these fuels, there does not appear to be much difference whether they are burnt on a grate, or previously converted into gas, in the manner described above. The most economical work appears to be at Neuberg, in Styria, where only 100 cubic feet of air-dried wood are con- REVERBERATORY FINERY OR PTJDDLLNG PROCESS. 283 sumed in the production of a ton of blooms. The metal, of a white or strongly mottled character, smelted with charcoal from spathic ore, is puddled in a double furnace, in charges of 8 cwt. ; the heat lasts two hours, the loss of weight being from 5 to 6 per cent. At Lippitzbach, in Tyrol, one ton of blooms is pro- duced from 1-047 tons of pig iron, with a consumption of 1 -Oil tons of wood scorched or torrefied. In Staffordshire, a certain quantity of scrap iron is sometimes added in the puddling furnace, in order to improve the quality of the product as soon as the iron comes to nature. When the fragments are at a white heat, they are incorporated with the contents of the furnace, which are then balled up in the ordinary way. It is obvious that if the scrap added be of good quality, it will have a beneficial effect, by spreading the absolute amount of impurities contained in the puddled iron over a greater weight of finished iron, and thus producing a relatively purer article. The work of the puddling furnace is divided between the puddler and his underhand : the latter attends to the firing, and also does part of the stirring or rabbling ; the last and heaviest portion of the work, together with the forming the balls, being usually done by the former. The tools employed are principally of two kinds, namely, long straight chisel-edged bars or paddles, and hooked bars with similar flat ends or rabbles, weighing about 60 Ibs. each. The number of tools used in the working of one charge depends upon the quality of the iron, and may vary from three or four to eight, accord- ing to the amount of work required. When with- drawn from the furnace, the points are coated with molten cinder, which is removed by quenching the bar into a cistern of cold water or water bosh, placed by the 284 METALLURGY OF IRON. side of the stack. The cinder deposited at the bottom of the bosh is afterwards added to the charge in the boiling process. In order to lessen the great amount of labour involved in working the charge, various mechanical appliances have been proposed in substitution for manual puddling, but these have not as yet been adopted to any great extent. The different plans proposed for this purpose may be classified under two heads, namely, those imitating the motions of hand- stirring, by moving the tool through a curved path by a combination of recipro- cating rotatory mechanism, and those using rotating or oscillating hearths. Of the latter kind are the furnaces proposed by Tooth, Menelaus, Bessemer, and others. The molten iron is fined by exposing it to oxidising influences in a cylinder lined with clay, or other re- fractory material, occupying the position of the hearth in an ordinary puddling furnace, which receives a slow movement of rotation about its long axis. The charge, in addition to being turned over, is traversed from end to end of the cylinder by inclining the lining from the fireplace to the flue, and in the reverse direc- tions at opposite points of the circumference. The ball is withdrawn from the furnace by removing the puddling chamber, and tilting it up on end. These furnaces have not hitherto been successful, owing to the difficulty of getting linings to stand the scouring action of the metal. Menelaus found the best material for this purpose to be titaniferous iron ore, which was used in solid blocks. The ordinary fettling materials, such as bull-dog, were quite useless. Bessemer 's furnace has an egg-shaped puddling chamber, mounted at the top of a rocking frame. The flame of the fuel is in- REVERBERATORY FINERY OR PUDDLING PROCESS. 285 t reduced through one of the trunnions, and passes out through the opposite one. One of the simplest of the first class of contrivances or mechanical stirrers, by Eastwood, is represented in Fig. 27. The rabbling tool, a, is suspended in a stirrup at the end of the longer arm of a bent lever, which receives an alternating motion by a rod, b, connected with a crank on the main driving shaft. The centre of oscillation of the bent lever is placed at the end of Fig. 27. Eastwood's mechanical puddles an inclined jib, which can be moved laterally through a small arc by another rod, c, working on a pin attached to a screw-wheel, d, driven by a worm on the main shaft. The action is as follows : Motion is given by a chain passing over a pulley in the main shaft at e. The rabble is moved backwards and forwards across the hearth once in each revolution, at the same time that its centre is shifted by the movement of the jib 286 METALLURGY OF IRON through a small distance by the screw gearing, thus producing a compound motion in the tool, and causing it to travel over every portion of the furnace bottom. The machine is bolted to the back of the casing plate on the working side of the furnace ; the driving pulley is connected with the shaft by a fast-and-loose clutch, /, so that it may be readily put in and out of gear as required. According to Parry, the amount of phosphorus con- tained in puddled iron is from 20 to 25 per cent, of that originally present in the pig iron, and of sulphur about 20 per cent. If, therefore, the iron so obtained is reconverted into pig iron by fusion with carbon, taking care that neither sulphur nor phosphorus is re-introduced, the proportion of these substances in the iron obtained from the purified metal by a second puddling will be almost inappreciable. Thus, if in the first instance the mine pig contained 0'75 per cent, of phosphorus, this would be reduced on the first puddling to 0*15 per cent., and on the second to 0*03 per cent. Parry's process of double puddling is founded upon the above property. The material treated is the waste produced in finishing bar iron, known as crop ends ; these are melted with coke in a cupola furnace, differing from that ordinarily used by iron-founders in having a strongly-inclined twyer, in addition to the ordinary horizontal one, through which the blast is in- troduced. It is, in fact, a combination of a blast furnace with a refinery, and the product is very similar to that obtained in refining with coke, namely, a metal of low degree of carburisation, almost entirely free from silicon. This is run into moulds, and afterwards puddled in the usual way, giving a pure quality of iron, which it is suggested may be still further im- FORGE AND MILL MACHINERY. 287 proved by repeating the fusion in the cupola, and puddling a third time. The consumption of coke is at the rate of about 30 or 40 per cent, of the weight of the scrap iron converted. It is, of course, necessary to prevent the iron taking up sulphur from the ash of the coke by a proper addition of limestone or other appropriate fluxes in the cupola. For this purpose, it is suggested that the coke may be impregnated with salt or carbonate of soda by steeping it in a solution of these salts for some time before it is required for use CHAPTER XYI. FORGE AND MILL MACHINERY. THE machines used in the compression and welding of the rough balls of malleable iron into blooms are of two different kinds, namely, hammers and squeezers, the former acting by percussion, and the latter by compres- sion. In addition to these, it is usual in puddling forges to reduce the blooms obtained by hammering or squeezing to rough bars by passing them at the same heat through a rolling mill. By the term forge is usually understood those portions of iron works which are intended for the production of puddled blooms or rough bars, including the puddling furnaces, shingling machines, and puddling rolls. The remaining portion of the works, where the rough bars are reheated and reduced to finished or merchant iron, is known as the mill, and includes the reheating or balling furnaces, and the various kinds of rolling mills and finishing machinery employed in the production of plates, bars, and other merchantable products. 288 METALLURGY OF IRON. The oldest and simplest class of machines used in forging blooms are lever hammers. These are of two classes, namely, tilt hammers, where the axis is between the point of application of the cam and the head, and helves, or lift hammers. In the former, the head is placed near the end of the lenger arm, while the cam acts at the end or tail of the shorter one. In lifting hammers, or helves, the hammer block and the lifting cam are placed on the same side of the fulcrum. These, again, are of two kinds the tenant, nose> or frontal helve, where the cam acts upon a tongue immediately in front of the hammer-block, corresponding to a lever of the second order, and the belly helve, which has the cam shaft placed below the floor, and acting about midway between the fulcrum and the head, forms a lever of the third order, so that the anvil is free on three sides. In all of the preceding varieties the axis of rotation of the cam ring is placed at right angles to the line of the hammer. Besides these, there is another old- fashioned form known in Germany as the pitch-up hammer, which differs from the belly helve in having the line of rotation of the axis parallel to that of the hammer stem. Tilt hammers are usually made of small sizes, the head of the heaviest weighing about 5 cwt. ; they are driven at considerable speed, and are used rather in drawing out bars, making spikes, and finishing work generally, than for shingling blooms in the first state. The shaft or stem is made of one or more beams of straight- grained springy wood, according to size, hooped together with rings of "wrought iron. The pivots are either attached to a broad central hoop, or are mortised through the shaft. The head is usually shaped like that of a large sledge hammer. FORGE AND MILL MACHINERY. 289 Helve hammers, such as were formerly in general use in puddling forges, have been made of all weights up to 10 tons. The usual sizes are between 30 cwt. and 5 tons; they make between 70 and 100 strokes per minute, with lift of between 16 and 20 inches. In Staffordshire shingling helves are used from 5 to 6 tons in weight, while those for blooming piles for finished iron average from 7 to 8 tons. Seen in plan, the helve is a |" shaped mass of cast iron ; the cross arms form the bearing, the hammer face of wrought iron being keyed into a conical socket at the opposite end for con- venience of renewal. The use of the long heavy cross arm for the pivots is necessary to prevent the mass of the helve from shifting in its bearings, which are open. The height of the lift may be regulated by the amount of projection given to the tongue or wiper acted upon by the cam. In all cases it is necessary for the preservation of the machine never to allow the hammer to fall directly upon the anvil. For this purpose, when not in use, a stop or gag of iron or wood is placed between the head and the anvil, which lifts the shaft just clear of the action of the cam. Bv placing a piece of iron on the tongue of sufficient thickness to allow the cam to come in contact with it, the hammer is lifted, and the removal of the stop is again brought into working order. The foundations of forge hammers require to be very massive, in order to withstand the violent shaking to which they are subjected. Large, squared balks 01 timber upon a bed of stone masonry or concrete are usually employed, piled crossways on end for carry- ing the framings of the hammer and cam-ring shaft. The anvil is a block of cast iron several times tho weight of the hammer, standing independently, so that TJ 290 METALLURGY OF IRON. its vibration may not be transmitted to the bearings of the fixed parts. Fig. 28 is a longitudinal elevation of a frontal helve weighing 3| tons, adapted for a forge driven by Fig. 28. 70-cwt. Shingling helve. water power. The following are the weights of the principal parts : Weight of helve 70 cwt. Anvil 150 Cam ring 125 Fly wheel 120 Main shaft 90 The hammer is lifted five times in each revolution of the shaft ; the height of the lift is 16 inches. A water wheel of 25-horse power is required to drive it. In water-power forges with small hammers of from 5 to 9 cwt. a wooden spring beam is often used for augmenting the force of the blow by the violent velo- city of descent. This construction was in general use in Europe before the introduction of steam power, and numerous instances of it are still to be found in Sweden. Where water power is used, especially in small forges, FORGE AND MILL MACHINERY. 291 each hammer is generally driven by its own wheel, the axis of the latter moving the cam ring directly without intermediate gearing. In forges worked by steam power, where several machines are driven by a single engine, the hammers or helves are connected by gearing wheels to the driving main shaft, being usually placed as near to the puddling or heating furnaces as possible. The working faces of both hammers and anvils are subject to great wear, and require to be replaced at short intervals. They may be made to last for a con- siderably longer time when kept cool by a current of water circulating through them. This method was intro- duced by Condie, the inventor of the water twyer, but does not appear to have been adopted to any great extent. In erecting new forges at the present time, direct- acting steam hammers are generally preferred, instead of the helve, for shingling and balling purposes. This machine, as is well known, was introduced by Nasmyth in 1842, and still maintains its original construction in most essential particulars, although it has been largely modified in details, both by the inventor and other makers. It consists essentially of an inverted cylinder, vertical, high-pressure engine, supported by an arched or inverted Y-shaped framing, formed of two standards of cast iron. The piston rod passes through the lower cylinder cover, and is directly connected with a heavy hammer block or tup, which moves vertically between guides attached to the inner faces of the standards. In the single-acting form, the steam is employed only for lifting the hammer block, which delivers its blow with the impact due to the fall alone ; but in the double-acting or top steam hammer, the force of the blow is increased by allowing the steam to act on the upper surface and accelerate the speed of 202 METALLURGY OF IRON. descent. A great advantage possessed by the steam hammer consists in the power of regulating the force of the blow according to the necessity of the work, as the block may be stopped at any portion of its stroke by cushioning or checking the exit of the exhaust steam. In shingling blooms, for instance, at the commence- ment, it may sometimes be advisable to consolidate the ball by short, light strokes, afterwards increasing the force by working with a longer fall as the iron becomes harder and more compact. This cannot be done with a helve hammer, whose height of fall, and consequent impact, is invariable. The weight of the hammer block varies with the nature of the work. In puddling forges for shingling ordinary- sized blooms, hammers of from 30 to 60 cwt. are commonly used. One of 50 cwt. is sufficient to do the work of twelve furnaces, and may be worked by the waste heat of one or two reheating furnaces. In the blooming and forging of heavy masses, such as piles for armour plates, marine engine-crank shafts, and large, irregular forgings for ships, as well as in steel works, very much larger sizes are employed, the weight of the block ranging from 5 to 50 tons. Hammers of the largest size are usually only made single-acting; the use of steam above the piston being rarely resorted to when the weight is more than 12 or 15 tons. Fig. 29 is a side elevation of a double-acting steam hammer constructed by Thwaites and Carbutt, of Bradford; it is reduced from a drawing kindly fur- nished by the makers. The hammer block or tup, weighing 8 tons, is attached by a thin cylindrical rod, as in the original Nasmyth hammer, to the steam piston, which is 28 inches in diameter, and makes a stroke of 6 feet in length. The arrangements for admitting and FORGE AND MILL MACHINERY. 293 exhausting the steam above and below the piston are similar to those of an ordinary high-pressure steam engine. The slide valve is of a tubular form, and balanced against the steam pressure in the valve chest, Fig. 29. Thwaites and Carbutt's 8-ton double-acting steam hammer. so that it may be readily moved by hand by means of the lever, c. d is the handle which moves the steam admission or regulator valve. The length of the up stroke is determined by the tappet, a, on the hammer block, which strikes against the arm of the bent lever, i, and moves the slide valve, so as to open the exhaust passage, which allows the steam from below the piston to escape into the atmosphere at e. The principal hammerman stands on the raised platform, /, having 294 METALLURGY OF IRON the valve levers close at hand, at the same time com- manding an uninterrupted view of the work in process of forging on the anvil. In small hammers below 12 or 15 cwt., such as are used for heavy smithing, and instead of the old tilt hammer in steel works, the framing is often reduced to a single standard overhanging its base, giving a clear working space on three sides of the anvil. Wrought- iron standards have lately been introduced. Another type of steam hammer is that having a piston with two unequal surfaces exposed to the action of the steam, by employing a very thick piston rod. The lower or smaller surface is constantly in connection with the steam by an open port, while it is only allowed access to the larger face during the driving portion of the stroke. Condie's hammer is distinguished by the peculiarity of having a fixed piston and a movable cylinder, the latter being cast in one with the hammer block. The piston is suspended by a rod connected with a ball-and- socket joint to the top cross bar of the framing. In many modern hammers parallel guides below the cylinder are not used, the piston being prevented from turning by using a rod of angular or irregular section, such as a square or a cylinder, with a portion of its surface planed down to a flat face, passing through a stufling box of a similar figure. The anvils of steam hammers require to be of great weight, and so arranged as to stand completely clear of the ground carrying the framing. For moderate sizes, a convenient foundation may be made of squared timber, placed on end above a bed of broken cinder beaten hard, or concrete ; but in the monster hammers used in steel works, the anvil and its foundation are built FORGE AND MILL MACHINERY. 205 up of masses of cast iron. Thus in Krupp's 50-ton hammer, which has a maximum lift of 10 feet, the anvil, weighing 185 tons, is carried upon a substructure of cast iron, formed of eight blocks, weighing from 125 to 135 tons each. Ramsbottom's horizontal hammer consists of two blocks or rams of great weight, supported by friction wheels, travelling on a short level railway, which can be drawn together or separated by a vertical Fig. 30. Ramsbottom's duplex steam hammer. steam engine acting upon a system of link rods. There is no anvil. The mass to be hammered is supported upon a carriage on a central platform, and is struck simultaneously on either side by the meeting of the rams. The general construction of the machine is shown in Fig. 30. a a' are the two hammer blocks, which are moved by the piston, b, of an ordinary double- acting steam engine by means of the connecting rods, c c. d is the slide valve, and e the admission valve, both of which can be worked by hand levers. The ingot, in process of hammering, is fixed upright in a cast iron carrier, f, united by a link rod with a 296 METALLURGY OF IRON. lever carrying a counterbalance weight at the oppo- site end. A hand lever, g, attached to the same shaft, serves to raise or lower the ingot, so as to bring a fresh portion of its length within the range of the hammers. In the newest form of this hammer, the blocks or tups, weighing 30 tons each, are driven directly by a pair of horizontal steam engines, without the use of link rods. Each tup is driven independently by its own piston, but a provision is made for equalising the motion by a projecting arm carrying a nut, which travels on a long screw running parallel with the line of motion, whereby, in the event of one mass travelling faster than the other, the screw acts as an auxiliary driving power to the slower- going one, and brings it up to the speed of the other, so that both may strike the ingot at the same moment. Another class of hammer sometimes used for small work combines the piston and cylinder with the method of lifting by cams. The hammer resembles an ordinary stamp head, moving vertically between guides by means of a rotating shaft armed with cams. The upper part of the rod carries a piston, which compresses air in the cylinder during the up stroke, the power so expended being given out by the ex- pansion of the air during the down stroke, giving an increased force to the blow, similarly to that obtained when steam is used on the top of the piston in an ordinary steam hammer, In all cases the striking faces of hammers and anvils are made removable, and are attached by dovetailed wedges, fitting into a corresponding groove on the blocks. Besides the plain faces for ordinary forging, FORGE AND MILL MACHINERY. 297 swages and moulds are often used, as, for example, in drawing round bars, or swaging up spherical cast- steel shot. Squeezers. In these machines the welding of the ball is effected by pressure applied without impact. They are of two kinds, namely, lever and rotary squeezers. In the former class, a lever of cast iron is made to oscillate about a fixed centre by means of a crank and connecting rod attached to the end of one Fig. 31. Double squeezer. Dowlais (Truran). arm. The opposite arm carries a jaw or plate of cast iron, which may be either flat or serrated with parallel triangular teeth, working against a corresponding fixed jaw, placed in the position occupied by the anvil in an ordinary lever hammer. The ball is introduced between the jaws of the machine at the widest part, and is pushed backwards as its thickness diminishes; the ends are compressed by placing the bloom on end between the jaws at the greatest opening. Fig. 31 is a longitudinal elevation of a double squeezer, i.e., having a pair of working faces in connection with either arm of the lever, in use at Dowlais, in South Wales. The rotary squeezer consists of a cylinder, whose 298 METALLURGY OF IRON. surface is studded with, blunt triangular teeth, having its axis of rotation placed either horizontally or verti- cally within a fixed circular casing of cast iron similarly roughened, and forming from one-half to three-quarters of an entire circle. The axis of the moving cylinder is placed eccentrically with regard to that of the case, so that although their surfaces are parallel, the distance between them diminishes in the direction of the rotation. The ball is entered at the widest part, and being carried forward by the action of the cylinder, is gradually reduced in thickness by compression against the surface of the casing, and emerges at the smaller aperture ready for the rolling mill. As there is no means of regulating the distance between the two pressing surfaces, it is necessary to work with balls of a tolerably regular figure, and as much as possible of a uniform size. In Belgium one of these machines is considered able to do the shingling for fifty puddling furnaces. The speed should not exceed twelve revolu- tions per minute. Sometimes squeezers are arranged to be driven by a steam engine attached to the outer arm of the lever, but more generally they are connected to the driving shaft of a rolling mill, as, for instance, that employed in rolling blooms into puddled bars. In the manipulation of very heavy masses, such as in welding the piles for large plates, forging of steel ingots, &c., where a powerful compressing force is re^ quired, hydraulic squeezers, or forging presses, may be used with advantage. As an example of this class of machine may be mentioned HaswelFs hydraulic hammer. It consists of a large vertical cylinder hydraulic press, with its ram acting downwards against a table, representing the anvil. The ram is lifted by FORGE AND MILL MACHINERY. 299 the piston of a smaller press, with which it is connected by cross arms and side rods placed overhead. The water driven out of the large cylinder as the ram rises is returned to a vertical cylinder or accumulator, also containing a piston, to whose upper face steam can be admitted. This arrangement is used to obtain speed in moving the ram when not actually working, or while the resistance of the pile is inconsiderable. When greater pressure is wanted, a valve, connecting the press with the speed piston is shut, and the ordinary hydraulic press pumps, which are driven by a large direct-acting horizontal steam engine, are brought into action. In this way, by reserving the press pump for the heavier portion of the work, the machine may be driven nearly as quickly as a steam hammer, and owing to the substitution of an intense slow pressure, for the percussive impact of the hammer, massive foundations are not required. Rolling Mills. These are now generally used in the production of finished or merchant iron, in preference to the hammer, which is mainly confined to the old open fire forges of Sweden and Germany. In its simplest form, a rolling mill consists of two cast-iron cylinders, placed with their axes horizontally one above the other, and connected by spur gearing, so as to revolve at the same velocity when set in motion. The surface of the rolls may be either smooth, as is the case in plate mills, or grooved into various patterns in those used for the production of merchant bars. In the latter case the groove on either roll corresponds to half the section, the two together forming an aperture or rotating die corresponding to the shape required. The reduction in size of the bloom is effected by regulating the ver- tical distance between the two rolls, by the use of METALLURGY OF IRON. grooves diminishing regularly in size, or by a combina- tion of both methods. Fig. 32 is a generalised elevation of a single pair of rolls, with both angular and flat Fig. 32. Rolling mill. grooves, a combination which is not actually used in practice, but has been adopted here to avoid the employ- ment of a second figure. The journals or necks of the rolls run on brass bear- ings, which are supported in strong cast-iron frames or housings. In Fig. 32 one of these is shown in eleva- tion, and the other in front section. The motion is usually communicated by the lower roll, and transmitted to the upper one by a pair of spur-gearing wheels, which are placed either on the rolls themselves, as in the figure, or are carried by a special pair of housings. When two or more pairs of rolls are connected into FORGE AND MILL MACHINERY. 301 one system by couplings, and driven by the same motor, they are called a mill or train. The first pair of the train are generally known as the roughing rolls, and the following ones as the finishing rolls. The latter have smooth surfaces, but the former, especially in puddle-bar trains, are often roughened, in order to get a better hold on the bloom at its entry. The first pair are also called the blooming rolls, as the work done by them is chiefly confined to welding the bars com- posing the pile, while the finishing pair is mainly employed to draw out the pile so compacted. As the direction of rotation of the rolls is constant under ordinary circumstances, it is necessary, after the bar has passed through one groove, to return it by lifting it over the top roll, in order to bring it into position to pass through the next smaller one, and so on in succession. This may be easily done with blooms of small size, but is attended with considerable difficulty when it is required to handle large masses of iron, and in any case gives rise to a certain loss of time, and con- sequent waste of iron by scaling, from exposure to the atmosphere in a highly heated condition for a longer time than is absolutely required. Various contrivances have been introduced in order to roll at greater speed ; the most approved principle being the use of two or more pair compounded into one, as, for example, placing two or three pairs in advance of each other, or passing the bloom alternately through the grooves of two mills moving in opposite directions; by receiving the bar on a carriage which is rapidly driven from one to the other by steam power ; or finally, by the use of a com- bination of three rolls placed one above another in the same housing, forming the so-called three-high train, which is driven from the middle, the central roll 302 METALLURGY OF IRON. gearing forward with the lower, and back with the upper one, or the reverse, so that the bar, instead of being rolled only one way, is passed backwards and forwards by entering it between the grooves of the middle and upper and middle and lower rolls alter- nately. Yery heavy mills, such as are used for armour plates, require to be reversed at each passage of the pile ; this can be the more readily done as they are driven at a comparatively low speed. The transmis- sion of the power in rolling mills, especially those of large size, is usually effected by toothed gearing. Smaller trains are sometimes driven by straps, an arrangement which may be conveniently adopted when each mill has a separate engine. As the rolls, when at work, are subjected to sudden and great variations in torsional strain, it is customary to make the couplings uniting the different members of the train of less resisting power than the necks of the rolls, the joints being arranged at the same time so as to allow a certain amount of independent motion. The arrangement usually adopted for this purpose is shown in Fig. 32, where the bottom roll is supposed to be connected with that of another pair in the same plane on the right-hand roll. The necks are continued beyond their bearings for a short distance, but with a smaller diameter, the section being further reduced by four concave grooves or flutes, as shown in the end view at a. These are united by a loose piece of similar form, known as the breaking shaft or spindle, c b, which is secured by two loose collars, c c, overlapping the joints. The collars are pre- vented from slipping by four wooden stops placed on. the flutes of the intermediate shaft, and secured by leather straps. In the event of the rolls being brought up FORGE AND MILL MACHINERY. 303 suddenly by the resistance of the pile, the strain is taken by the breaking shaft, which, being the weakest part of the train, gives way, and saves the rolls from fracture. In some instances the breaking shaft is further reduced in area by making a deep semicircular groove round it in the middle. In rolling bars of small section, which on account of their flexibility are liable to be bent and distorted, it is necessary to keep the end straight in entering the grooves. For this purpose it is usual to attach parallel guides with plain jaws or friction rollers to the tables or aprons of such mills, which are then known as guide mills or trains. In compound mills with three rolls, the lifting of large piles from the lower to the upper level is attended with considerable labour, unless it be done by special mechanical appliances. The usual method adopted is to make the feed plates or tables movable upon vertical guides, suspending them so as to travel freely by counterbalance weights passing over guide pulleys. The lifting may be effected either by a vibrating lever receiving motion from a rotating shaft ; or more simply by a single-acting steam or water-pressure engine placed above the rolls, and connected to the tables by a cross bar and side rods. The pile, after passing a groove in the lower part, is lifted by the action of the steam or other mechanism employed, and after return- ing through the upper one, drops the table by its unbalanced weight to the lower level, and so on, rising and falling alternately, until the section is sufficiently reduced. The same kind of arrangement may also be used in heavy plate mills. The pile, after passing between the rolls, need only be deposited on the top of the upper 304 METALLURGY OF IRON. one, as the friction between the two surfaces due to the weight will be sufficient to return the pile to the former position, taking advantage of the fact that the surface above the horizontal median plane of the roll travels in the reverse direction to that below it. The set, or distance between the top and bottom rolls, is adjusted by means of screws (d d , Fig. 32) act- ing, either directly or by a cross bar, upon the bearings of the frames. Each screw is provided with a graduated head, in order that in altering the level, either end of the roll may be shifted equally. In rolling bars of irregular section, such as rails, for instance, the adjustment is only necessary in order to bring out the finished product to the proper weight, and, when once made, no alteration 7 ^ ff W J W 4. Fig. 33. Rail mill roughing rolls. Fig. 34. Rail mill finishing rolls. is necessary as long as the mill is kept on the snone work, the progressive reduction in the section of the FORGE AND MILL MACHINERY. 305 pile being effected by passing it through grooves of continually diminishing area. In order to prevent lamination between the bars composing the pile, and to render the welding as uniform as possible, it is passed through with the joints flat and edgeways alter- nately, in the manner indicated by the horizontal and vertical lines in Figs. 33, 34, which represent the sec- tion of both blooming and finishing rolls in a mill making double-headed rails. The numbers in the grooves refer to the order in which they are used. In plate mills which have no grooves the distance between the rolls must be diminished each time that the pile is passed through. The top roll must also be supported in order to prevent its falling upon the lower one when it is no longer kept up by the pile. This is usually done by carrying the lower bearing of the top roll on a A r ertical forked rod, whose lower end is in connection with a counterbalance weight sufficient to prevent the roll from falling. Great accuracy may be obtained in the adjustment of the rolls by attaching spur wheels to the heads of the setting screws, which may then be moved through equal spaces by a third wheel placed between them. In Bamsbottom's system of adjustment, adopted at Crewe, the shaft of the central pinion carries a double spiral barrel with two chains, one of which, passing over guide pulleys, is connected with the ram of a water- pressure engine, and the other coiling in the opposite direction with a counterpoise weight. The rolls are brought together by the pull of the chain from the engine, and separated by the counterpoise acting in a similar manner upon the other chain. Compound or universal rolling mills consist of a combination of a vertical with an ordinary horizontal 306 METALLURGY OF IRON. pair of plain rolls, so that tlie pile may be compressed equally in both directions, edgeways and flatways, at once. A combination of this kind, known as While's mill, has been advantageously adopted for blooming rail piles in South Wales. The horizontal rolls are driven in the usual way from below, the vertical pair being connected with them by an intermediate shaft, carrying a mitre-wheel gearing into a wheel upon one of the vertical rolls. The machine is driven at a very low speed, making only five revolutions per minute, so that the pile is subjected to a powerful and long-con- tinued pressure, as compared with the usual system of blooming in the first grooves of the roughing pair in an ordinary train, making from 80 to 100 revolutions per minute. Mills of this class may also be used in the production of bars of plain rectangular sections of a great variety of dimensions by simple adjustment of the rolls, instead of requiring a special pair of grooves for each size, as is ordinarily the case. Fig. 35 represents the arrangement of the rolls and methods of adjustment in one of the earlier forms of universal mill. In order to simplify the drawing, the whole of the driving mechanism is omitted. The vertical rolls are adjusted by the central sliding pinion on either side, which acts on the setting screws. The bearings are supported upon horizontal guide bars placed between the housings. In the newer forms of this mill only one of the vertical rolls is made movable. In rolling taper iron, such as the tongues of rail- way switches, the setting screws are provided with lifting gear, so that the distance between the rolls may be continually and uniformly varied during the final passage of the bars. In the first instance, the rolls are FORGE AND MILL MACHINERY. 307 screwed down to the proper distance for producing the thinnest section required, and the pressure is then relieved either by a train of gearing wheels, working pinions on the heads of the screws, or by allowing the Fig. 35. Universal rolling mill. upward pressure of the iron passing through the mill to lift the roll. In the latter plan, in use at the Mersey Steel and Iron Works, the pressure is exerted against a solid plunger working in a cylinder filled with water, and provided with a small discharge passage, stopped by a conical plug valve. As long as the valve is closed the water within the cylinder, from 308 METALLURGY OF IRON. its incompressibility, acts like a solid body, and keeps the rolls together ; but when the passage is opened, the pressure from below drives the plunger upwards and expels the water, thereby relieving the bearings of the top roll, which is then free to rise, the rate of its upward motion being regulated by the aperture pre- sented for the efflux of water from the cylinder. The finishing rolls of plate mills are cast with strongly- chilled surfaces, which are afterwards turned and polished, the necks and other portions being formed in sand moulds. The rolls of rolling mills are subjected to great heat when at work, from the direct contact of glowing iron, as well as from its friction in passing through the grooves. In almost all cases they are cooled with water, which is led through a gutter above the framing, and distributed in small streams over the working surfaces and necks continuously. The size and speed of rolling mills vary within very wide limits, according to the character of the work done. Thus reversing mills for heavy plates may make from 25 to 30 revolutions per minute, while small mills rolling wire are driven at from 500 to 600 revolutions in the same time. In Staffordshire the puddled bar train usually in- cludes two pairs of rolls, from 18 to 20 inches in diameter, and from 3J to 5 feet in length between the bearings. The grooves of the roughing pair are of a curved or Gothic form, as in the right half of Fig. 32, giving a rough square to the bloom. Those of the finishing pair are rectangular, like those on the left side of Fig. 32, and capable of rolling flat bars from 2J to 7 inches in breadth, and from half an inch to 2 inches in thickness. Sometimes a third pair is added FORGE AND MILL MACHINERY. 309 for rolling slabs from 7 to 15 inches wide, which are used as covering plates for piles intended for making plates. A mill of the above dimensions serves from six- teen to twenty furnaces. For ordinary- sized merchant bars, the diameter of the rolls is from 12 to 16 inches, and the length from 4 to 6 feet for the roughing, and from 3 to 3 J feet for the finishing pair. The number of revolutions is from 60 to 75 per minute, according to the size of the work. In South Wales the rolls used in blooming rail piles are from 20 to 24 inches in diameter, and from 5 to 6 feet long. When they are worked as reversing rolls the speed does not exceed from 25 to 30 revolutions per minute ; but compound (three-high) mills may be driven much faster. The finishing train makes from 80 to 100 revolutions per minute. Plate mills are usually made with three pairs of rolls. The first pair are grooved like those of a bar mill for bloom- ing the pile ; the second are the roughing pair proper ; while those of the third, or finishing pair, are cast with chilled surfaces, and are highly polished. The ordi- nary sizes are from 5 to 6 feet long, and from 20 to 24 inches in diameter.. The working speed varies from 25 to 30 revolutions per minute for heavy, and from 30 to 40 for light plates. Shears are used for cutting up puddled and other bars into lengths for piling, and also for trimming up the rough edges and ends of finished plates, bars, and sheets. For the former purpose, some form of lever shears, having one fixed and one vibrating jaw, the latter forming one arm of a straight or bent lever, moved by a crank or eccentric, is generally used. Fig. 36 is an example of a heavy shearing machine 310 METALLURGY OF IRON. used at Dowlais, in South Wales, for cutting up puddled bars into lengths for piling. When it is required to take a cut of considerable length, guillotine shears, with a diagonal-edged knife which moves vertically between parallel guides, are often used, especially in boiler and other plate work. These are generally machines requiring considerable power, and are driven by a steam engine attached to the same framing. Rails and other thick bars are finished by sawing off the rough or crop ends, and filing down the marks left by the saw while still hot Fig. 36. Cropping shear, Dowlais (Traran ). from the rolls. The circular saws used for this purpose are between 3 \ and 4J feet in diameter, and are driven either by belts, or, in some instances, by direct-acting steam turbines placed on the same shaft. The number of revolutions varies between 900 and 1,300 per minute. In the slitting mill the rolls are replaced by spindles carrying a series of steel discs, fixed a certain distance upart by stops. The discs on one spindle interlock with those on the other, forming a rotary shearing REHEATING AND WELDING. 311 machine, with several pairs of blunt-edged cutters. When a thin, flat bar of iron is passed through in the same manner as in an ordinary rolling mill, it is divided by the blades into thin rods of rectangular section, which are delivered in a very crooked con- dition, being bent and distorted by the pressure of the blades. These, when straightened by hand, are made up into bundles for the use of the nail forges, and are known as slit or nail rods. CHAPTER XVII REHEATING AND WELDING. THE rough bars or slabs of malleable iron, obtained in the processes of puddling and shingling, require to be subjected to further treatment in order to produce finished or merchant iron. For this purpose they are cut into short lengths, which are made into nearly cubical packets, or piles, and subjected to a further consolidation by hammering and rolling at a welding heat, until a bar with a uniformly smooth surface, free from cracks or flaws, is obtained. The operation of reheating may be performed in several different ways, as, for example, in the open hearth, in direct contact with the fuel a method that, as has already been stated, is commonly practised in making malleable iron in the hearth finery ; in the hollow fire, immediately above the fuel, but without touching it, used in the South Wales forges ; and, finally, in the reverberatory furnace, which is the plan most generally adopted at present. The reheating furnace, Fig. 37, also known as the lotting or mill furnace, is in external appearance not 312 METALLURGY OF IRON. unlike that used in puddling, being cased with cast-iron plates in a similar manner. The principal difference is in the proportion between the surface of the fire grate and that of the bed, which is less than is the case in the puddling furnace, as, although a higher tem- perature is requisite, it is less subject to fluctuations, being maintained as uniform as possible. The arch of the roof, except in special cases, is comparatively low ; and the bed, which is made of sand consolidated by pressure when in a moistened condition, slopes from the fire-bridge uniformly towards the flue, in order to Kg. 37. Reheating or balling furnace. allow the slag or cinder formed by the combination of the sand with the scale on the surface of the iron to run off freely towards the bottom of the stack, where it is let out of the furnace. This, like most of the other slags produced under similar circumstances, is in com- position essentially a tribasic silicate of protoxide of iron, and is distinguished by the name of flue cinder from that of puddling furnace, or tap cinder, the former flowing constantly, while the latter is only removed from the furnace at intervals. A small fire is usually placed in front of the stack both in reheating and pud- dling furnaces, in order to prevent the cinder from cooling and becoming solid in the tap hole. REHEATING AND WELDING. 313 Fig. 37 is a longitudinal section of a reheating fur- nace, such as is used for bars of ordinary sizes, which are finished from the pile at a single heat. The bed is made of fire-brick, covered with a thick coating of sand. In other respects it is very similar in construc- tion to the puddling furnace. In order to prevent the access of air to the bed, it is necessary to keep the fire grate thickly covered with fuel, and the door must be well stopped for the same reason. In reheating small sizes of iron, it is advantageous to use a furnace with a small hearth and large grate, so as to be able to bring up the piles rapidly to a welding heat, in order to prevent the loss by oxidation conse- quent upon unnecessary exposure. When the dimen- sions of the pile are such as to require several passages through the mill in order to reduce it to the proper section, it is often necessary to subject it to a second heating ; for this purpose, furnaces of special construc- tion are used, corresponding in dimensions to the form of the pile at the end of the first heat. "When the bed is of a large size, as, for instance, in the furnaces used for reheating unfinished plates, a second fireplace is placed at the flue end, with its axis at right angles to the principal one. This class of furnace is used in reheating long and heavy bars, and also in armour- plate mills. Piling for Merchant Iron. The amount of work put into bar iron varies with the quality. For the commoner kinds, puddled bars, or No. 1 iron, cut into lengths, are piled, and when brought to a welding heat are rolled off, either with or without first being worked into a bloom under the hammer. More usually, however, the iron of second rolling, or No. 2, is employed as the top and bottom plates of the piles, when making 314 METALLURGY OF IRON. finished, No. 3, or best iron. Beyond this, if further piled and welded, the iron is distinguished as lest best and treble best, according to the number of heatings and weldings to which it has been subjected. The harder and more granular kinds of iron, such as that used for tires in Yorkshire, are worked almost exclusively under the hammer, the rolling mill being only used in giving the proper figure to the bar at the finishing stage. The covering slabs for the tops and bottoms of rail piles are sometimes made by doubling and welding two puddled blooms together under the hammer, which are then reheated and rolled to the proper size without having first passed through the state of puddled bars. The use of single plates for the outsides of piles is necessary in order to get a clean surface, as butt joints do not weld properly unless they are covered. In all cases the ends of the bars forming the pile must be cut square, and all the surfaces in contact must be as clear as possible from scale and rust. Piles for bars should be made as thick and square as can be done consistently with the form of the blooming grooves of the mill, in order that the iron may be <"ig. 38. Sections of piles for finished iron. subjected to great longitudinal extension. The length will of course depend upon the weight of finished bar required. Fig. 38 shows the arrangement of the various qua- lities of bars and slabs in pile for different kinds of bar REHEATING AND WELDING. 315 iron. The darker- shaded parts indicate slabs of re- worked No. 2 iron, scrap bars, or similar qualities, the lighter parts being puddled bars. A is one out of many kinds of pile adopted in the manufacture of rails. B and c are Belgian piles for T and girder iron, the finished sections being given in the centre to the same scale. D is Beattie's system of piling or faggoting adopted for railway axles. It consists of a ring, built up of several segments, arranged round a central cir- cular bar. The bars composing the piles are kept together by bands of wire before they are placed in the heating furnace. The following example gives the details of manipu- lation in rolling bars of different sizes followed in a South Staffordshire forge in the year 1861 : For bars of 1 inch square the pile was made up of 6 bars, each three-quarters of an inch thick, and 4 inches wide, the top and bottom plates being of doubled blooms, while the intermediate ones were ordinary puddled bars. The length of the pile was 18 inches, and its weight 100 Ibs. Two heating furnaces were used, each containing a charge of eighteen piles, which, when at a proper welding heat, were passed eleven times through the rolls, the grooves being arranged as follows : first, two of rectangular section, then five Gothic, and, finally, four square finishers. The work done by the two furnaces in twelve hours amounted to 9 tons (long weight) of finished bars. The loss on the weight of the piles was about 15 per cent., an amount made up of 5 to 6 per cent, caused by oxidation in the furnace, and the remainder, 9 or 10 per cent., in crop ends and waste in rolling. The consumption of coal was from 50 to 55 per cent, of the weight of the finished bars. The time occupied 316 METALLURGY OF IRON. in rolling a single heat was from thirty to thirty-five minutes. In making round bars of 4 inches in diameter and 16 feet long, the pile was 10 inches wide, 11 J inches high, and 6 feet long. The top and bottom were each composed of three thicknesses of puddled scrap bars hammered and rolled, while the centre was made up of five layers of ordinary puddled bars. Three heating furnaces were used, each holding a single pile, which required from two and a half to three hours to bring it to a welding heat. In rolling, the pile was passed through eleven times, being turned a quarter round each time, so as to bring the joints into the vertical and horizontal positions alternately. The loss in the pro- cess amounted to between 30 and 32 per cent., out of which about two- thirds, or 21 per cent., was accounted for in the crop ends. The coal burnt amounted to 65 per cent, of the weight of the finished bars. In making small sizes of merchant iron, such as small round or square bars or hoops, the pile, after being partially drawn to a square bar, is cut into lengths known as billets, which are afterwards finished sepa- rately. The work is done very quickly, although, owing to the small size of the billets, the daily produce expressed in weight is not very large. When the billets are finished in one heat, the consumption of coal is from 11 to 12 cwt. per ton ; but when two heats are required, the amount is increased to 20 cwt., or equal weights with the bars produced. In South "Wales the ordinary weight of the pile for rails is about 15 cwt., long weight, four being placed in the furnace at once ; the whole of these are rolled to blooms in a triple mill in five minutes, each passing through four times alternately flat and edgeways. REHEATING AND WELDING. 317 The second heat is effected in half an hour, the furnace being similarly charged, when the blooms are passed through the rail mill nine times, the whole operation being performed in one minute. In order to keep the mill constantly at work, fourteen heating furnaces are required, ten for the first, and four for the second heat. The loss, including the crop ends, is about 20 per cent, on the weight of the pile. In some cases these are passed through a special flattening mill, in order to reduce them to a rectangular figure for greater con- venience in piling, but more generally they are converted into slabs in the same manner as ordinary puddled bars. The special application of crop ends to the manufacture of iron free from phosphorus, by Parry's process, has been previously noticed at p. 285. The total amount of coal consumed in the manu- facture of iron from the ore to the finished bars of common, or No. 2 quality, may be taken at five times the weight of the latter, with an increase of about 10 cwt. per ton for every additional heat. Plates and sheets are divided into classes accord- ing to thickness, the former term being restricted to all sizes above No. 4 of the Birmingham wire gauge, corresponding to a thickness of 0*238 inch. Sheet iron is further classified into three divisions, as follows : Singles, including from No. 4 to No. 20 gauge or 0-238 to 0-035 in. thick. Doubles 20 25 0-Q35 -020 Trebles or lattens,, 25 27 0-020 0-016 The piles for the heavier classes of plates are built up of layers of bars, placed alternately across each other, instead of having their longer sides parallel, as is the case with ordinary bar iron. The covering 318 METALLURGY OF IRON. slabs, or top and bottom plates, are flat bars, from 9 to 12 or 14 inches wide, and from 1 inch to 1 \ inches thick, which are made by doubling two puddled blooms under the shingling hammer, and rolling to the proper size at one heat. For boiler plates measuring 6 feet long, by 3 feet broad, and A of an inch thick, weighing about 2J cwt. each, the pile is made 20 inches long, 6 to 7 inches high, and 12 inches broad. The whole of the work is done at one heat ; the pile is reduced to a roughly- squared bloom by passing it lengthways through three grooves in the blooming rolls, then four times through the plate- roughing rolls in the direction of the breadth, which draws it into a thick- squared plate, and finally, three times lengthways through the finish- ing rolls. The difference in weight between the finished plate and the rough bars taken for the pile is from 20 to 22 per cent. : this amount includes the waste in reheating and scrap produced in shearing the edges to the proper size. The amount of coal consumed in the reheating furnace is from 14 to 15 cwt. per ton of plates produced. For the larger sizes of sheets, such as singles of !N"o. 12 gauge, measuring 6 feet in length by 2 feet in breadth, the piles, 20 inches in length, 7 inches in breadth, and 4 inches in height, a,re made up of the scrap and crop ends produced in making the top and bottom plates, which are three-quarters of an inch thick. The weight corresponding to the above dimensions is about 70 Ibs. Nineteen or twenty piles are placed in the heating furnace at once. In passing the blooming rolls, the pile is converted into a bar of double the original length, without any alteration in breadth, and is then cut into two parts, each of which is passed cross- REHEATING AND WELDING. 319 ways through, the roughing rolls, until it is reduced nearly to the breadth required in the finished plate. After passing four times lengthways through the finish- ing rolls, the two halves of the original bloom are placed one above another, and passed through together three or four times more ; they are then nearly cold, and are immediately taken to the annealing furnace, where they are subjected to a low heat to soften them, after which they are sheared to the proper size and finished. The rolling of thinner sheets is very similar to that last described, except that the piles are of a much simpler character, on account of their smaller weight, consisting simply of three or four plain flat bars. For doubles of 20 to 24 gauge, the rough bar is cut in two, and the halves are passed through the plate rolls, first separately, and then together, as in the preceding instance. The rough sheets are placed together in bundles of four in the annealing furnace, and after heating and passing through the finishing rolls, are subjected to a second heat in the same furnace before being sheared. Lattens or trebles of No. 27 gauge, measuring 54 inches in length, by 28 inches in breadth, and weighing 5| to 6 Ibs. per sheet, are made from roughed-down slabs 4 inches broad, and half or three-quarters of an inch thick, cut into lengths of about 18 inches. These lengths are heated to redness, and passed separately through the roughing rolls, and two or three times through the finishers, after which they are doubled, and the rolling is continued until they have cooled to a dull red heat, the original blank having by this time become extended to a sheet measuring 32 inches by 24. In rolling after the first annealing heat, four plates are taken together, and in finishing, which follows 320 METALLURGY OF IRON. final or second annealing heat, eight thicknesses are passed through at the same time. Owing to the number of reheatings, and the large amount of surface of the finished work as compared with its weight, the loss and consumption of materials are comparatively large. For the production of 1 ton of sheets sheared to the proper size, 25 cwt. of coal are required, and 25 or 26 cwt. of rough bars. Out of the waste of 5 or 6 cwt. on the latter quantity, about 4 cwt. are ac- counted for in the shearings and crop ends, produced at different stages of the process. No great amount of scaling takes place, owing to the comparatively low temperature at which the work is done. Thin sheet iron or Hack plate y intended for tinning, is made in a similar manner to that last described, the unfinished work being doubled after every heating, so that at last as many as sixteen thicknesses are passed through the mill together. When reduced to the proper dimensions, the plates are brought to a bright metallic surface by pickling in weak sulphuric acid. A final polish is given by cold rolling, after which the plates or sheets are ready for tinning. Very heavy plates, such as those used for ships' armour, are made either by hammering or rolling alone, or by a combination of both methods. In the first case, the original material is best scrap iron, made into piles weighing from 1 to 1 J cwt. each, which are bailee in threes or fours into a slab at one heat. According to the thickness of the plate required, these slabs are reheated either alone or doubled, and reduced at a second forging to an oblong slab, somewhat thicker than the finished plate, with two squared and two chamfered edges. In finishing, two pieces are joined to form a section of a plate of the required bread'th, by REHEATING AND WELDING. 321 joining the tapered edges together on the shorter sides, and finally, the length is made up by adding as many pairs as may be necessary. For convenience of manipu- lation, a staff, or porter bar, with a capstan-headed ring fixed to it, is welded to one of the unfinished plates, in order that it may readily be turned on the anvil, as is usual in all large for gin gs. The final forging, to reduce the plate to the proper thickness, is effected at a moderate red heat, water being constantly thrown on the surface to clean it from scale. When finished, it is annealed by heating to redness and slow cooling. By the use of tapered edges the surfaces of contact cross the finished plate obliquely. Rolled armour plates are put together as follows : The balls from the puddling furnace are shingled and rolled to slabs about 12 inches broad, 30 inches long, and 1 inch thick. Five or six of these slabs are in a second heat rolled to a slab about 4 feet square. At the third piling, five or six slabs of the second heat are welded and rolled into a plate 8 feet long, 4^ feet broad, and 2J inches thick, weighing rather more than 30 cwt., and made up of between twenty- five and thirty-six original inch slabs of No. 1 iron. The edges of the plates require to be kept as true as possible, so that a certain amount of shearing may be necessary at the intermediate step of the process. For the finished plates of 4J or 5J inches in thickness, four of the large 30-cwt. plates are piled together, and re- heated in a furnace having a fireplace at either end. In order that the whole pile may be uniformly heated, the lower surface, instead of touching the bed of the furnace, is supported on six small pillars of brickwork, so as to allow the flame to pass below it. The door of the furnace is placed parallel to the axis of the rolling 322 METALLURGY OF IRON. mill, and the pile, when sufficiently heated, is drawn forward with tongs, and received on a truck, which runs upon a railway directly to the rolls. A similar truck is placed on the opposite side of the mill, and the pile is passed forwards and backwards by reversing the rolls until it is reduced to the proper thickness. The plate, after leaving the rolls, while still hot, is placed upon a cast-iron table, and rendered perfectly smooth and flat by passing a roller weighing 7 tons over it. When cold, the rough edges are dressed up square on a planing machine. The surfaces of these trucks incline towards the rolls, or are provided with friction rollers, so that the pile may be easily pushed between them by hand, the force of the rolls being suffi- cient to drive it up the incline of the receiving surface. It will be seen that the finished plate consists of between 100 and 144 slabs, compressed to about -aV or ^ of their original thickness. The composite character of rolled bar iron made from large piles may be rendered evident by etching a polished transverse section with weak sulphuric acid, when a series of irregular curved lines will be developed, corresponding to the original surfaces of contact of the component slabs. Uniformity in the character of the lines is a sign of good welding ; but black irregular patches indicate that the cinder has not been entirely expelled. Application of the Waste Heat of Puddling and Re- heating Furnaces. Under ordinary circumstances, the heat developed by the coal burnt in the fireplaces of these furnaces is but imperfectly utilised, as the flame leaving the hearth at the welding temperature of iron escapes into the atmosphere at the top of the stack, carrying away an amount of heat greatly in excess of REHEATING AND WELDING. 323 that necessary to keep up the draught of air through the fire. In order to economise some portion of this heat, various methods have been adopted of interposing cooling substances by passing the flame through the flues of steam boilers or blast-heating stoves. The former method is used for furnaces fired with solid fuel, while the latter is more especially adopted for e-as furnaces. A more complete method than either o Jr is the so-called regenerative gas furnace of Siemens, where the waste heat is applied in raising both the gases used as fuel and the air for burning them to a high temperature previously to their arrival at the point of combustion, by which means a very high and uniform heat is attainable. The commonest form of boiler used for raising steam by the waste heat of forge and mill furnaces is a vertical cylinder with a hemispherical dome. The flame either passes round the outside, or through a central flue connected with the external shell by a series of horizontal tubes. Generally two furnaces are in connection with the same boiler. A more perfect method, but one that can only be adopted in large works, is to lead the flame from a considerable number of furnaces into a single horizontal flue of propor- tionately larige section, which carries it through the heating tubes of the boiler. The resistance opposed by the interposed obstacles is overcome by the draught of a tall chimney. In this way there is no chance of the working either of the furnaces or boilers being checked by alternations of temperature, as may some- times be the case when only one or two furnaces are used with a separate boiler. In Hungary and Austria different combinations of reheating and puddling furnaces fired with gaseous 324 METALLURGY OF IRON. fuel have been recently adopted. At Bhonitz a furnace of this kind has an ordinary gas generating chamber for burning wood, combined with three hearths placed in one longitudinal series. The first of these is intended for reheating blooms and billets of iron. It receives the full stream of the heated gases which contain no uncombined oxygen from the generator before they reach the point of final com- bustion at the top blast jets, which are placed in the usual position above the fire-bridge of the puddling hearth. The third bed is used for warming up the pig iron before melting it in the puddling process. Lastly, the flame, before entering the stack, is carried round a blast-heating arrangement consisting of two vertical cast-iron pipes, divided by central partitions, which raises the air employed in the top blast to a temperature of 200. A furnace of this class is found to be productive of a certain economy in iron, 129J Ibs. of pig iron being suflicient to produce 100 Ibs. of billets instead of 134 Ibs., as was the case when the puddling and reheating were effected in separate furnaces. The saving of fuel is, however, very considerable, 7*9 cubic feet of wood being now found sufficient when 18 cubic feet were formerly required. A somewhat similar combination to the preceding is applied to the waste heat of an open reheating fire at Reichenau. The hearth is of the usual rectangular form, but is blown with two twyers instead of one. The fuel employed is charcoal. The hood covering the hearth resembles the roof over the fireplace of a reverberatory furnace. The flame, together with a considerable quantity of inflammable gas derived from the incomplete combustion of charcoal dust or braise REHEATING AND WELDING. 325 on the first hearth, is led into the second, or puddling bed, where it meets the second blast, which is heated to about 200, and is introduced through a line of narrow twyers, extending along the fire-bridge, and inclined at a considerable angle to the direction of the gaseous current. Behind the puddling bed are placed two others, for warming the iron at various stages in the process, which may be distinguished as Nos. III. and IV., and the lower part of the stack contains the blast-heating pipes, which are of the horizontal serpen- tine form. The different parts of this furnace used are as follows : The puddled balls from the second bed, after being shingled into blooms, are subjected to a preliminary heat in the fourth, or last, which also serves for heating the pig iron previously to puddling, and are then transferred to the charcoal fire, No. I., where they are brought up to the proper temperature for conversion into puddled slabs or rough bars. The finished iron, which in this case is intended for waggon tires, is produced by reheating the rough bars of the preceding operation in hearth No. III., and drawing them to the proper shape under the hammer. This is said to be a very economical furnace, in spite of its apparent complication. The consumption of materials in the different stages is as follows : 160 Ibs. pig iron give 100 Ibs. blooms; 114 Ibs. blooms ,, 100 Ibs. puddled bars ; 104 Ibs. puddled bars 100 Ibs. finished tire iron ; corresponding to a total consumption of 126 Ibs. of pig iron and 12 cubic feet of charcoal per 100 Ibs. of finished iron. Siemens' regenerative gas furnace, as applied to puddling, is similar in general character to the cast- 326 METALLURGY OF IRON. steel melting furnace described at p. 358, supposing a puddling chamber to be substituted for that contain- ing the melting pot a in Fig. 43. The puddling bed is made of cast-iron plates, surrounded by hollow boxes cooled with water in the usual way ; the bridges and flues at either end are exactly similar, so that the current of heated gases may be made to travel in either direction without affecting the working of the furnace. Below the ground level are placed four large vaulted chambers, separated from each other by thick walls, and filled with fire-bricks arranged in cellular piles, similar to those in Cowper's stove, as shown in Fig. 15, p. 170. These, the so-called regenerators, are employed to keep back a portion of the heat carried away by the gases after they have done their work in the puddling chamber, and which, in furnaces of the ordinary construction, is lost by allowing the flame to pass directly into the chimney. The heat taken up by the bricks is transferred to the inflammable gases used as fuel, and the air intended for burning them before their admission to the point of actual com- bustion, by which means a much higher temperature can be obtained than is possible with furnaces of the ordinary form, burning solid fuel on a grate. In Figs. 39 and 40 (taken from Tomlinson's " Cyclo- paedia") the principal details of the regenerative fur- nace are shown as applied to plate-glass melting, and although intended for a different purpose from that at present under consideration, will be sufficient to illus- trate the principle of the invention, the whole of the construction being generally similar, with the exception of course of the chamber containing the melting pots r>, which we must imagine to be replaced by a puddling furnace of the form indicated in the preceding paragraph. REHEATING AND WELDING. 327 The gas producer, Fig. 39, is a large chamber, of triangular section, capable of holding several tons of 328 METALLURGY OF IRON. fuel, small coal or slack being usually employed. The charging is effected through the stoppered hole a. The coal travels slowly down the inclined wall b, becoming gradually heated and parting with its volatile matters until it reaches the step grate c. This is formed of a number of broad thin- edged bars, overlapping each other like the laths of a Venetian blind, so as to leave only a series of narrow spaces between them for the admission of air. The combustion goes on very slowly, the small amount of carbonic acid produced at the bars being immediately decomposed by the thick column of incandescent fuel above, so that the contents of the chamber are gradually converted into inflammable gas, chiefly carbonic oxide, which, diluted with the nitrogen of the air remaining after combustion, is subsequently employed as fuel in the puddling furnaces. At one time a certain amount of steam was introduced from a perforated pipe at d, which was filled with water and heated by the spare heat of the fire. The steam, in its passage over the ignited carbon, was decomposed with the formation of carbonic oxide and hydrogen, whereby the calorific value of the gas was considerably increased. This part of the process has since been given up, owing to the difficulty of regulating the amount of steam injected, and the great absorption of heat caused by the decomposition was found to give rise to an injurious local cooling unless the operation was very carefully watched. The gas evolved from the generator passes through the valve g into the stack H, whence it issues at a tem- perature of about 200. In traversing the horizontal iron pipe p, it loses about one-half of its heat, so that its density is sufficiently increased in the descending pipe p' to establish a continuous draught from the gas pro- REHEATING AND WELDING. 329 duced towards the furnace without the use of a special chimney. The position of the two generators f'"f"" is shown in the half plan at L M in Fig. 40. The other two, Plan atL.M. Fig. 40. Siemens' furnace. Plan of flues. /'/", are similarly placed, as indicated by the dotted lines. The arrangement of the bricks will be under- stood from the section in Fig. 39, as well as that already given in Fig. 15. They are worked in pairs, two being heated by the waste flame, while others are giving up their heat to the cold gases and air. Owing to the large amount f surface presented by the bricks, the absorption of the surplus is effected with compa- rative rapidity, and the temperature of the current escaping to the chimney is reduced nearly to the boiling point of water. As soon as the brickwork has attained the proper temperature in two of the chambers, the current is turned into the adjoining pair by reversing the valves r r, Fig. 39, and r r", Fig. 40, and the heat accumulated in the brickwork is abstracted 030 METALLURGY OF IRON. by cold air, to pass th rough, one, and gas through the other, until the second pair is heated, and so on, the process being kept up continuously, notwithstanding tlie intermittent action of the regenerators taken sepa- rately. When applied to puddling iron, a current of heated gas is brought into the furnace by a narrow rectangular chamber, opening into a slit in the body of the fire- bridge. The air comes through a parallel flue behind, and at a higher level, in order that it may, from its spe- cifically greater weight, fall towards the upward stream of gas, and become perfectly mixed. As in all other gas furnaces, the nature of the atmosphere may be perfectly regulated by varying the amount of air introduced. This is a point of great importance in reheating furnaces, where it is necessary to keep out free air as much as pos- sible, in order to prevent the iron from burning to waste. The regenerative principle has been adopted by Lundin, at Munkforss, in "Wermland, for a gas- welding furnace, fired with a very unpromising material, namely, sawdust, containing from 50 to 60 per cent, of water. A condenser containing a series of pipes, terminated with finely-perforated injection roses, adjoins the gas producer, so that the issuing current of gas is imme- diately brought in contact with a shower of finely- divided water, the jets being arranged to cross each other, and reach every part of the condensing chamber. The temperature is thus reduced from 350 or 400 to 35 or 40, and nearly the whole of the steam mixed with the gas is condensed, together with the tar, pyro- ligneous acid, and such other volatile substances pro- duced from the destructive distillation of the sawdust as may be susceptible of condensation by the action of water. In addition, to the water jets, a second con- METHODS OF PRODUCING STEEL. 331 densing chamber is used ; this is filled with wrought- iron bars, piled like the bricks in the regenerators, which are cooled by a constant flow of water. The gas issuing from the condenser, after cooling and drying, is said to retain only 4 per cent, of water vapour. Of course a considerable amount of heat is lost by the enforced cooling, and has to be taken up again in the regenerators ; but this disadvantage is small as compared with the increased heating power gained by the removal of the water. The regenerators for heating the gas are one-fourth larger in area than those through which the air passes. The consumption of sawdust by this furnace is at the rate of from 11 to 14 cubic feet for each 100 Ibs. of finished iron. CHAPTER XVIII. METHODS OF PRODUCING STEEL. Methods of Producing Steel. It has already been stated that steel forms an intermediate link between ordinary cast and malleable iron, and unites in a greater or less degree the properties of both. Its distinguishing characteristic, however, is the power of being hardened or softened at pleasure by sudden or slow cooling from a high temperature. The following are the principal methods of making steel : 1. By the Catalan forge, directly from the ore. 2. Prom pig iron, by fusion and partial oxidation in the hearth finery. 3. From the same metal, by a similar process in the puddling furnace. 332 METALLURGY OF 1ROX. 4. By exposing bar iron to the action of solid or gaseous carbonaceous matter at a temperature below its melting point. This method is known as conversion by cementation, and the amount of change produced is mainly dependent upon the time employed. When merely a surface coating of steel is required, the process adopted is known as case-hardening; while, on the other hand, if sufficiently long continued, the iron may be completely converted into cast iron. A process which may be regarded as the reverse of cementation is practised to a certain extent upon cast iron, by exposing it to heat in closed vessels filled with finely-powdered hematite. The surface of the casting is decarburised at the expense of the oxygen of the peroxide of iron, with the production of a malleable coating. This is known as the method of making malleable cast iron. In the above processes steel is produced without melting, and is converted into bars by hammering and rolling, in a similar manner to that adopted in the manufacture of malleable iron. A more homogeneous product may be obtained by fusion, according to the following methods : 5. The cemented or blister steel produced in No. 4 is broken up into small pieces and melted in crucibles, with or without fluxes, in quantities of from 60 to 80 Ibs. This is the original method of making cast steel introduced by Huntsman, in the neighbourhood of Sheffield, and is still largely used in the same district for the production of the higher class of cutlery and tool steel. 6. By blowing air through molten pig iron until it is wholly or partially decarburised. In the former case the necessary amount of carbon is restored by the METHODS OF PRODUCING STEEL. 333 addition of highly- carburised pig, such as spiegel- eisen, in small quantity. This is what is known as Bessemer' s process. In addition to the above processes, several new methods of making cast steel have been proposed and adopted to a certain extent, but not generally. The essence of these methods consist in fusing cast iron with oxidising, or wrought iron with carburising additions, or by fusing cast and wrought iron in proper proportions alone, as in the last step of the Bessemer process. The following are some of the more promi- nent : Uchatius' Process. This consists in melting in cru- cibles granulated pig iron with peroxide of iron, pro- duced from roasted spathic iron ore, and a small quantity of oxide of manganese. By varying the proportions of metal and ore, and especially by the addition of a certain quantity of malleable scrap iron, a softer or milder steel may be obtained. Obuchow's method of producing cast steel is generally similar to that of Uchatius. White pig iron is fused with malleable iron or steel scrap, with variable addi- tions of magnetic iron ore, titaniferous black sand, such as is obtained in gold-washing, arsenious acid, nitre, and clay, or with arsenious acid and magnetite alone. The operation is conducted as follows : The scrap iron, magnetic oxide, and clay are placed in a large clay crucible which has been previously brought up nearly to a white heat ; the cast iron is then run in melted from a cupola, and the crucible is heated until the contents are perfectly fluid ; the remaining ingredients, namely, arsenious acid and nitre, are then added, the whole being well stirred. The steel is cast in closed cast-iron moulds, and the ingots, as soon as they have 334 METALLURGY OF IRON. cooled down to a red heat, are removed, and taken at once to the hammer and tilted. Price and Nicholson's process consists in melting mal- leable iron with refined metal, that is, pig iron free from silicon, the relative proportions of the two metals being adjusted according to the character of the steel that it is desired to produce. Indian cast steel, or Wootz, is made from malleable iron cut into small pieces, which are charged in quantities of about 1 Ib. weight in clay crucibles, together with about 10 per cent, of dried wood of Cassia auriculata, and two or three leaves of Asclepias gigantea. The covers of the crucibles are luted on with clay, and when dry, some twenty are heated together in a charcoal hearth for about two hours. On breaking the crucible after fusion, a round cake of steel is obtained, about 1 inch in thickness and 5 inches in diameter, which is perfectly smelted, and usually pre- sents a series of finely- radiating striations on its upper surface. Wootz is extremely hard, containing a large amount of carbon, and requires great care in tempering and forging. The addition of charcoal or other carbonaceous matter in the fusion of blister steel furnishes a ready method of controlling the hardness of cast steel, and is commonly practised, especially where a proportion of malleable iron is added to the charge. The same effect may be produced by the use of crucibles made of blacklead instead of clay, the carbon required for the conversion of the malleable iron into steel being fur- nished by the substance of the crucible : the latter modification is said to be largely used by Brupp at Essen, in Westphalia. In making the so-called natural steel in open fires, METHODS OF PRODUCING STEEL. 335 a method that was formerly practised to a considerable extent in Styria, Westphalia, and other parts of Europe, but which is now being rapidly superseded by more improved processes, the hearth differs from that used in making malleable iron by having less depth, while the twyer is at a lower level and more strongly inclined, as the molten mass is not brought directly before the twyer, but is decarburised under the joint influence of the blast and slag, with an increased expenditure of time and fuel. As a rule, about double the quantity of coal and one-half more time is required to convert a charge of pig iron into steel than would be the case if the same weight was operated upon for malleable iron. The best varieties of pig iron for the purpose are those containing a considerable quantity of carbon, such as spiegeleisen, or the strongly-mottled variety called blumige floss, containing flowers or spots of grey upon a white ground. Dark grey pig can be used, but should first be subjected to refining. In Styria the process is conducted on hearths, with a bottom of charcoal dust about 12 inches thick. The first portion of the charge, weighing 120 Ibs., is melted down with a small quantity of cinder, the latter being strewed over the coals, the reheating of the blooms (masseln), about ten or twelve in all, from the former operation, going on at the same time. When only two blooms are left, a further addition of pig iron is made to the extent of from 30 to 60 Ibs., and the blowing is continued until the hearth is filled to within 1 or 2 inches of the twyer. The fire is then allowed to go down quickly, the slag is tapped through a hole in the front plate into a trough filled with water, and the lump of crude steel remaining ia the hearth is allowed to cool, out of contact of the air, by covering it with 836 METALLURGY OF IRON. a shovelful of moistened cinders. In about a quarter or half an hour after stopping the blast, the lump is lifted out of the furnace, and is then divided under the hammer into ten or twelve pieces, which, as has already been stated, are reheated during the fining of the next charge. The bars drawn under the hammer are hardened by quenching in cold water, and broken, in order to test their quality. They are sorted according to hardness into several classes, distinguished by special names. The best are known as chisel or tool steel, noble steel, and crude steel, below which come a variety of steely irons, used for scythe-making, waggon-wheel tires, and similar purposes. Usually the forges are small, each containing two fires and a hammer, having three water wheels, two for the bellows, and one driving the hammer, which weighs from 5 to 6 cwt., making from 70 to 120 strokes per minute, with a maximum lift of about 2 feet. When small- sized bars or scythes are made in the same forge, a lighter tilt-hammer of 3 or 4 cwt. is generally used. With both fires at work, four men produce about 12 or 15 cwt. of crude steel blooms in sixteen hours. The consumption of charcoal is about 30 cubic feet per cwt. under ordinary condi- tions, but may be reduced to between 22 and 25 cubic feet by using covered hearths and hot blast. The proportional yield of the different kinds of steel is as follows for every 100 parts of pig iron treated : 60 parts of steel of all kinds (crude, noble, and chisel stee]). 20 ,, mock, or over-refined steel, containing soft iron. 10 steely iron of different kinds. 10 loss. 100 METHODS OF PRODUCING STEEL. 337 The Carinthian process is carried out with much larger quantities of pig iron at one time than the Styrian. The charge, weighing ahout 5 cwt., is melted down in a hearth some 2 feet square, with an effective depth of from 7 to 9 inches below the twyer. The bottom of the hearth is lined with charcoal dust or brasque in the usual way. The twyer is about 1J inches wide, and plunges from 10 to 16. The charge is kept melted before the blast for three hours, as in the ordinary process of refining, and after re- moval of the slag, is converted into thin plates by throwing water on the surface, and chopping off the chilled metal in crusts or discs of about 1 or 1J inch thick. After the fire is made up, the first portion of the bloom obtained in the preceding operation is reheated and hammered an operation requiring about an hour and a half. A quantity of from 40 to 70 Ibs. of pig iron, with a little cinder, is then melted down gradu-, ally, and upon this the refined metal of the first opera- tion is added by small quantities at a time, until the whole charge forms a more or less pasty or imperfectly fluid mass (sauer) on the hearth bottom, which is broken up with a bar and pile into a heap in the centre. The amount of working depends upon the feel of the iron. If it dries too rapidly, fresh pig iron must be added, while in the opposite case of being too fluid, oxidation is promoted by the addition of hammer scale. The upper portion of the mass, being under the influence of the blast, loses its carbon ; while the lower part, being in contact with the glowing charcoal forming the hearth, remains in the condition of cast iron. After making up the pile, the second portion of the previous bloom is reheated, and when this is finished, the con- tents of the hearth, having subsided to a uniform, level 338 METALLURGY OF IHOTs. surface, are found to be sufficiently fined to allow the formation of a fresh bloom, which is broken out and divided into two parts for further treatment. The half blooms are again divided, and finally finished into bars, which are hardened, broken, and selected in the same way as in Styria. It will be seen that the same hearth is, in addition to its proper work, made to do duty alternately as a refinery and reheating fire, an arrangement that must be attended with considerable waste both of time and fuel. The loss upon the pig iron is from 20 to 30 per cent., including the reheating ; the consumption of charcoal is from 40 to 50 cubic feet per cwt. About 75 per cent, of the produce is good steel, which is reheated in special small fires, and drawn under light hammers into bars, which are packed in cases and sold as Brescian steel. The so-called true Brescian process practised at Paal, in Styria, differs in certain details of manipula- tion from the preceding, the most important point being, that in reheating the blooms, they are plunged into the bath of molten pig iron, whereby they undergo a kind of surface hardening by cementation. In Siegen, where spiegeleisen is, or was, formerly treated in the open fire, the charge is melted down in small quantities of 60 or 80 Ibs. weight upon a bottom of mottled iron. As soon as fusion commences the slag is tapped to within 2 J inches of the bottom, and further additions of spiegeleisen are made in diminishing quan- tities, from 40 Ibs. at the fifth to 20 Ibs. at the seventh and last charge. It is sought as much as possible to keep the mass at the consistency of soft butter during the entire operation. The bloom (schret) ultimately obtained weighs 4 cwt., the time required being about METHODS OF PRODUCING STEEL. 339 eight hours. It is divided into seven or eight pieces, which are tilted into bars, with a loss of about 20 per cent. Beckoned upon the pig iron, the loss is 30 per cent., 100 Ibs. giving 70 Ibs. of steel, of which about three-fourths are of good quality, and capable of being properly hardened, and the remainder mild steel or steely iron. It is doubtful whether this process is still practised, having latterly been superseded by the method of steel puddling. Puddled Steel. There is no essential difference between the methods of making wrought iron and steel in the puddling furnace, other than the degree of decarburisation to which the pig iron is subjected. The most highly-carburised varieties of pig iron, especially those containing manganese, such as spiegeleisen, are best adapted for the process. The furnace is usually of a somewhat smaller size than that employed for making malleable iron ; or rather, the size of the bed is diminished in proportion to that of the fireplace and stack, in order to be able to command a very high temperature. The charge does not usually exceed 3 or 3J cwt., which is introduced in fragments as nearly as possible of the same size and thickness, and spread out so as to expose a large surface to the flame, in order that fusion may be effected uniformly and without much oxidation. The use of only one kind or class of pig iron is also necessary, otherwise, supposing white and grey iron to be mixed, a portion of the charge would probably fine and come to nature while the more fusible part was still unchanged. This is exactly the reverse condition to that required in puddling for malleable iron, where a mixture of two different kinds of pigs has an advantageous effect in accelerating the process. In steel puddling, on the other hand, the 340 METALLURGY OF IRON. charge is rendered perfectly fluid, and covered with molten slag, in order that the fining may go on slowly and uniformly. The presence of protoxide of manganese in the slag is important, as contributing fluidity without increasing the decarburising influence. By keeping the contents of the furnace well stirred together during the second part of the process, the iron separated in the malleable condition may, in the event of its becoming too much decarburised, be brought back to the proper condition by dissolving it in the unaltered pig iron below, in a somewhat similar manner to that practised in the Siegen open- fire process, where the iron is prevented from drying to too stiff a consistency by the addition of fresh quantities of pig iron at intervals. In order to induce fining in the molten mass, the damper must be closed until the charge thickens and commences to rise, when the heat must be carefully raised during the time of stirring, which usually takes from thirty-five to forty- five minutes, or somewhat longer than is the case in puddling for malleable iron. The high temperature prevailing in the furnace keeps the contents of the hearth well melted, and by continued stirring, fresh particles of metal are constantly brought to the surface of the fluid covering of slag. The appearance of fine, white, brilliant grains is a sign of the process going on well, and indicates the formation of steel of good quality and uniform texture. If, on the other hand, the separated grains are large, and resemble snow- flakes, the product is likely to be of a coarse fracture, and imperfectly refined. The slag must be less basic than that formed in puddling for malleable iron, as the presence of a large excess of oxides of iron not only METHODS OF PRODUCING STEEL. 341 reduces the fluidity, but acts too energetically on the removal of the combined carbon from the pig iron. The balling of the granular clots of steel as they come to nature is an operation requiring considerable skill; it must be done in a neutral or rion- oxidising atmosphere, such as is obtained by shutting the damper, and keeping the hearth filled with flame and smoke with an ordinary furnace, or 'shutting off the top blast when a gas furnace is used. The balls are shingled at a lower temperature than those of malleable iron, and when they cannot be immediately taken to the hammer, are protected against oxidation by rolling them in the melted slag, so as to obtain a superficial crust or varnish, which excludes the air from contact with the heated metal. The slowness of the fining process, and the extra amount of stirring required, are sufficient to explain the apparent anomaly that a partial should require longer time than a complete decarburisation. Under ordinary circumstances the time required for working off a heat is in either case as follows : Fibrous Iron. Steel. Melting down . . 30 to 40 minutes 40 to 50 minutes. Stirring .... 30 35 45 50 Boiling and fining . 25 30 20 25 Balling .... 10 10 85 115 105 135 As originally described in the specification of Biepe, by whom the process was introduced into England, the charge recommended to be used is 280 Ibs., which is to be exposed to a red heat until the metal begins to fuse, 342 METALLURGY OF IRON. when the temperature is reduced by lowering the damper. Forge or mill cinder, to the extent of twelve or sixteen shovelsful, is then added, and when the whole was melted, a small quantity of peroxide of manganese salt and clay ground together. After this mixture has acted for a few minutes the damper is fully opened, and about 40 Ibs. of pig iron is placed upon an elevated bed of cinder near the fire-bridge. When this begins to trickle down, and the boiling of the contents of the furnace commences, it is raked into the hearth, and the whole mass is well mixed together. When the grains of steel begin to break through the cinder, as already described, the damper is to be partially closed, and the operation of stirring below the cinder com- menced, taking care that the heat be not raised above cherry redness, or the welding temperature of shear steel. The remainder of the process of balling is done with a closed damper, as already described. It appears to be doubtful, according to the state- ments of most of the recent writers on the subject, whether the process can be properly conducted at the low temperature specified. The use of the highest heat attainable in the puddling furnace was afterwards claimed by another patentee, and on subsequent litiga- tion, the term "cherry redness" was explained as mean- ing a bright red heat when the furnace was illuminated by direct sunlight. Parry states that if the heat be too high during the boiling, the mixed cinder and metal separate from each other, and the decarburisation proceeds slowly ; while, on the other hand, if the tem- perature be too low, the cinder and metal cannot be properly mixed, being of too stiff a consistency, and the steel will not be homogeneous. The temperature must be raised to a full yellow heat on the appearance METHODS OF PRODUCING STEEL. 343 of the floating granules in the slag. The fire should be made up at the end of the boiling process, in order to prevent the passage of air by opening the fire-hole during the balling. It is necessary to shingle the balls as soon as possible, in order to prevent the decarburising action of the rich slag retained by capillary attraction upon the spongy particles of steel. When the slag is poor in protoxide of iron it sets very quickly, and when more basic, acts powerfully in removing carbon. The presence of oxide of manganese is advantageous, as communicating fluidity without increasing the oxidising effect a point of considerable importance, as the shingling takes place at a lower temperature than is the case with , malleable iron. In some cases an addition of peroxide of manganese is made immediately before balling, or the mixture of peroxide of manganese, clay, and salt, already mentioned as recommended by Schaf- haiitl for improving ordinary iron, is added at inter- vals after the melting down of the pig iron during the stirring. At Lohe, in Siegen, twelve heats of 3J cwt. of white fibrous " steel " pig iron are puddled in the turn of twelve hours. Each charge yields from seven to eight balls, weighing 40 Ibs. each. The lo*ss upon the pig iron is 9 per cent, in puddling, with a further amount of 1 1 per cent, upon the reheating, which is done in covered hearths with a single twyer, somewhat like the South Wales hollow fire. The blooms are drawn into bars under a tilt hammer. The produce is assorted accord- ing to the fracture : 78 per cent, is good hard steel, capable of being broken when cooled in water ; the remaining 22 per cent, is more or less mixed with soft iron. The total expenditure of coal is double the 344 METALLURGY OF IRON. weight of the steel produced : out of this 84 per cent, goes for puddling, and the remaining 1 6 per cent, for reheating. These quantities refer to Ruhe coal, which is not of a very high quality. The total production for twelve hours is about 34 cwt. When grey pig iron is used, either alone or mixed with mottled, it is necessary to add from 10 to 15 per cent, of scale and cinder. In such cases the consump- tion of coal may be somewhat increased, as the process lasts a little longer than when working with iron smelted from spathic ores. In Styrian works using lignite, with the advantage of good pig iron, the consumption is from 32 to 42 cwt. per ton of steel bloom made, without counting charcoal and wood for reheating. The use of gas furnaces is said to be of great advantage in the steel-puddling process, both as regards saving of fuel and diminishing the waste of iron. At Kirch- hunden, in Siegen, the saving is stated at from 35 to 40 per cent, in the coal, and from 9 to 10 per cent, on the amount of iron burnt. According to observations made in several localities, the consumption of fuel is dimi- nished when the sides of the hearth are cooled by a circulation of air instead of water. The chemical changes going on in the process of steel puddling have been investigated by Schilling and other- chemists in a similar manner to that followed originally by Calvert and Johnson. The following are Schilling's results of the composition of the metal and slag at dif- ferent points of the process, as carried out at Zorge, in Hanover. The charge consisted of white pig iron from Grittelde, and grey from Zorge, mixed in equal weights. The fuel employed in the blast furnace was charcoal, the consumption being at the rate of 100 Ibs. for every 87 Ibs. of pig iron produced : METHODS OF PRODUCING STEEL. 345 u, i i h* M 1 b V b 00 . 10 1 1 fr4 1 3 (N 1 ,H 1 M 1 S? g CO p 1 o t^ CO T-l M ^H CO * ,-4 o O CO r-> W 1 ^ c. r-H lf "^ 1 ^, CO 1 " r- 1 CO ^ o n 1 3 b 6 cp b b 1 1-4 r-t 00 5. s 1 1 1 1 1 o I 1 rH CO CO i-l O 0> '0 CO i 1 1-85 267 , 46-2 WikmanhyttaUchatius steel 1-22 33-8 , 66-9 Carlsdal Bessemer steel . . . 1-19 31-4 , 64-8 , ,, Uchatius . . . 1-16 33-2 , 647 Hogbo Bessemer . . . I'M 0-018 39-6 59-0 hammered 0-68 31-8 46-8 Krup's cast steel 0-62 0-020 23-7 39-5 Hogbo Bessemer iron 0-33 24-1 33-0 Low Moor rolled tire bar . . 0-21 0-068 16-7 27-3 Lesjofors rolled bar made in \ the Lancashire hearth . J 0-06 0-022 14-0 22-5 The tensile strength, alone is not a sufficient measure of the quality of malleable iron, as a metal of great strength may be deficient in softness, and incapable of being forged. This is tested by hammering the sample both hot and cold, when it should bend without fracture to a certain amount, the angle varying with the tem- perature and thickness of the metal. The resistance of rails to percussive strain is tested in the following manner : The rail under trial is placed horizontally, and keyed fast in the jaws of a pair of chairs about 3 feet apart, attached to a heavy anvil. A heavy weight is then allowed to fall from a considerable height, so as to strike the top flange midway between the points of support. At Sheffield, steel rails are sub- jected to the action of a pile ram or monkey weighing 20 cwt., which is allowed to fall from a height of from 20 to 30 feet. The quality of the welding may be best rendered apparent by etching a polished surface with acid. The following are the tests prescribed by the Admiralty for plate iron intended for use in the navy, and may be taken as indicating the average strength of iron of fair quality : ANALYSIS OF CAST AND WROUGHT IRON AND STEEL. 393 PLATE IRON, FIltST CLASS, OR B.B. SECOND CLASS,OR H. Lengthways. Cross ways. Lngthwys. Crosswnys. Tensile strength, per square inch, 22 tons 18 tons 20 tons 17 tons Forge test, hot. All plates of T inch in thickness and be- low must be capable of - 125 90 90 60 bending hot without frac- ture through an angle of J Forge test, cold. Plates should admit of bending cold with . out fracture as follows : 1 in. in thickness to an angle of 16 5 10 i5> ?' 25 10 20 5 35 15 30 10 55 )9 70 30 55 20 inch and under 90 40 75 30 Plates should be tested, both hot and cold, on a cast- iron slab having a fair surface, with an edge at right angles, the corner being rounded off with a radius of half an inch. The portion of plate tested to be 4 feet in length across the grain, and the full width of the plate with the grain. The bend should be made at from 3 to 6 inches from the edge. All plates to be free from lamination and injurious surface defects. The tests to be applied to one plate of each lot of fifty of the same thickness. Strength of Cast Iron. The resistance of cast iron to strains applied in different directions is subject to very considerable variation, according to its composition and quality. The softest, or No. 1 pig, is usually deficient in strength as compared with the lower qualities made from the same ores. It is customary in founding, there- fore, to work with two or more different kinds of metal, in order to obtain mixtures combining the qualities of the different components, or sometimes a proportion of 394 METALLURGY OF IRON. malleable scrap or refined iron is added to grey iron for the same purpose. Silicon is generally reputed to be a source of weak- ness in cast iron, such as the dark grey No. 1 Scotch pig smelted from blackband ; and it is for this reason, probably, that hot blast metal is of smaller tenacity than that made with cold blast from the same materials. White or mottled pig iron is remarkable for its extreme hardness, especially when cast in chill moulds. The following are the maximum and minimum limits of strength in British pig iron, as deduced from obser- vations made at Woolwich in 1856-59 : Per square inch. Minimum. Maximum. Specific gravity . . 6*886 . . 7*289 Tensile strength . . 4'85 tons . 14-05 tons Transverse ,, . . 1'37 ,, . 4*47 ,, Torsional . . 1-74 ,, . 3*44 ,, Crushing ,, . . 22-54 . 58*42 The transverse resistance was measured by the force necessary to break a bar of an inch square when loaded at the same distance from the point of support. The torsional strength was measured by applying a twisting strain to a bar reduced to the same ratio at a distance of 8 inches from its bearings. The lowest values were obtained with pig iron smelted from sandy brown hematite, and the highest from hema- tite or argillaceous carbonates, either alone or mixed and smelted with cold blast. INDEX. Aluminous fluxes, analyses of, 123. Ammonia, production of, in blast fur- naces, 229. Analyses of blackband ores, 77. Analyses of carboniferous brown hema- tites, 65. Analyses of cast iron, 234, 235. Analyses of clay iron ores, 75. Analyses of Cleveland ores, 78. Analyses of iron ores, method of, 79. Analyses of magnetic ores, 56, 57- Analyses of spathic ores, 73. Anthracite furnaces of South Wales, 212. Anthracite furnaces of the United States, 215. Antimony and iron, alloys of, 46. Armour plates, methods of manufac- ture of, 320. Arsenic and iron, compounds of, 30. Bar iron, details of manufacture, 315. Barrow-in-Funiess, Bessemer con- verters at, 377. Barrow-in-Furness, charges of fur- naces at, 214. Bears of blast furnaces, 195. Belgium, details of puddling furnaces in, 281. Belgium, dressing of iron ores in, 100. Belgium, yield of blast furnaces in, 215. Bergaraask finery process, 259. Berthier's method of assaying iron ore, 80. Bessemer's process, 363. Bessemtr steel, composition and classi- fication of, 376. Blackband ironstones, analyses of, 77. Blackband, method of roasting, 108. Blake's rock breaker, 105. Blast furnaces, temperature of, 228. Blast, methods of determining volume, 172. Blast regulators, 159. Blowing eugine, construction and de- tails of, 151. Blowing in blast furnace?, methods of, 193. Blowing out blast furnaces, 195. Bog and lake ores, analyses of, 70. Boiling process of puddling, 265. Brendon Hills, spathic ores of, 73. Brescian steel process, 338. Brown hematites, analyses of, 65, 67. Bull-dog, 35. Calder hot blast stove, 1 61. Capacity and production of blast fur- naces, 196. Carbon and iron, compounds of, 36. Carbonate of protoxide of iron, 19. Carbon, determination of, in iron, 380. Carinthian forge steel process, 337. Carinthian gas puddling furnace, 281. Caron on carbon in iron, 38. Case-hardening, methods of, 353. Cast iron, anafyses of, 234, 235. Cast iron, commercial classilication of, 231. 396 INDEX. Cast iron, composition of, 43. Cast iron, difference between grey and white, 37. Cast steel, production of, 355. Catalan forge process, 237. Cementation, production of steel by, 41. Charging barrows, use of, 183. Chemical changes in puddling, 277, 344. Chlorine and iron, compounds of, 33. Chromium, alloy of, with iron, 46. Clay ironstone, analyses of, 75. Clay ironstone, roasting in clamps, 107. Cleveland, details of blast furnaces in, 212. Cleveland, iron ores of, 77. Cleveland ironstone, analyses of, 78. Coal measures, clay iron ores of, 73. Cobalt, alloy of, with iron, 46. Copper, action of, on iron, 44. Cowper's method of cleansing gases from dust, 231. Cowper's stove, 167. Cup and cone, 180. Descent of charges in blast furnaces, time of, 197. Desulphurising ores by steam, 119. Dry assay of iron ore, 80. Dust of gas flues, composition of, 230. Eastwood's mechanical puddler, 285. Eggertz's method of analysing iron, 386. Eisenerz, crusher at, 104. Eisenerz, spathic ores of, 73. Elba, 'specular iron of, 65, 210. Ferric acid, 25. Fettling, materials used for, 270. Forest of Dean, brown iron ores of, 64. Forge, small cinder, use of, 123. Form of blast furnaces, 183. Foundation of forge hammers, 289. Franche Comte finery process, 259, 262. Franklinite, 25, 49. Freray on nitrogen in steel, 42. Gas-collecting apparatus for blast fur- naces, 179. Gases of blast furnace, composition of, 230. Gas-heated stoves, 167. Gas producer, Siemens', 231. Gas puddling furnace, 267. Gellivara, magnetic iron ores of, 56. Gjers' calcining kiln, 112. Gjers' pneumatic lift, 151. Gold aud iron, alloy of, 46. Graphitic and combined carbon in iron. 37. Graphitic carbon, determination of, Q QO 606. Gurlt's method of making wrought iron, 242. Hardening and tempering steel, 378. Harz, weathering of ores in, 103. Haswell's hydraulic hammer, 298. Hearth of blast furnace, construction of, 143. Heat, consumption of, in blast fur- nace operations, 217- Helves, varieties of, 288. Hematite, brown, 51. Hematite, red, 49. Hematite, red, in Lancashire and Cum- berland, 62, 214. Hollow fire, South Wales, 262. Horseshoe pipe stove, 161. Hot blast, determination- of tempera- ture of, 228. Hot blast stoves or ovens, 176. Hot blast twyers, details of, 177. Hydrates of oxides of iron, 18. Hydrates of peroxide of iron, 22. llmenite, or titanic iron ore, 50. Indian methods of making wrought iron, 243. Iron, physical and chemical properties of, 13, 389. Iron pyrites, 32. Karsten's table of compounds of iron and carbon, 37. Kilns, roasting, for iron ores, 110. Kirkless Hall, blast furnace at, 214. INDEX. 397 Lake Superior blast furnaces, charges and yields of, 206. Lancashire, furnaces smelting hema- tite, 214. Lancashire hearth, used in Sweden, 259, 262. Langen's gas apparatus, 182. Lang's treatment of cinders, 126. Lever hammers, varieties ot, 288. Lifts for blast furnaces, construction of, 349. Lignite, puddling with, in Styria, 282. Limestones, analyses of, 122. Low Moor, puddling process at, 280. Lundin's gas furnace, 330. Magnetic iron ores, analyses of, 56, 57. Magnetic oxide of iron, 23, 48. Magnetic pyrites, 32. Magnetism ot iron, 14. Magnoferrite, 21, 25. Malleable cast iron, 354. Marguerite's method of wet assay, 8?. Martial regulus, 46. Martite, 21. Mechanical properties of iron and steel, 389. Mechanical puddling, methods of, 284. Melting points of rnetals, 174. Meteoric iron, nickel in, 46. Minary and Soudry's treatment of cinders, 126. Mixture and descent of charges in blast furnaces, lb'9. Miisen, spathic ores of, 73. Mushet's cast steel process, 361. Nassau, red iron ores of, 66. Natural or forge steel processes, 334. Nitrogen and iron, 26. Obuchow's cast steel process, 333. Open-topped furnaces, methods uf col- lecting gas from, 179. Oxides of iron, 17. Parry's method of puddling, 286. Parry's method of retiimig, 250. Passivity of iron, 15. Peat, puddling with, in Styria, 282. Penny's method of wet assay, 87. Phosphate of irou vivianite, 28. Phosphides of iron, Percy on, 28. Phosphorus, action of, on iron, 29. Phosphorus in iron, determination of, 384. Phosphorus in iron ores, 29. Phosphorus, removal of, iii puddling, 278. Piles for merchant iron, details of, 313. Pisolitic ores dressed by jigging, 100. Pistol pipe stove, 163. Plate and sheet iron, manufacture of, 317. Platinum and steel alloy, 47. Planner's fluxes for irou assaying, 83. Pneumatic lift, 151. Position of hot blast stoves, 176. Pouillet's pyrometric method, 175. Pressure gauges, 171. Price and Nicholson's cast steel pro- cess, 334. Protosulphide of iron, 31. Protoxide of iron, 17. Puddled iron, qualities of, 276. Puddling furnace, construction of, 265. Puddling, methods of, 271. Pyrometers for hot blast, 174. Pyrometric alloys, melting points of, 174. Rachette's blast furnace, 188. Kail rolling mill, 304. Rails, details of manufacture, 316. Ramsbottom's duplex hammer, 295. Red iron ores, analyses of, 63. Refinery, details ot, 244. Reheating furnace, details of, 311. Rolling mill, details of, 299. Rouge, methods of production of, 20. Round and oval ovens, 163. Scale oxide, 18. Schafhautl's powder used in puddling, 279. Scotland, blackband iron ores of, 76. Scotland, working details of blast fur- nace in, 213. 398 INDEX. Secondary formations, brown iron ores of, 66. Sections of blast furnaces, 198. Shears, cropping, varieties of, 309. Siderite, 52. Siegen blast furnaces, charges and yields of, 202. Siegen forge steel process, 338. Siegen, kilns used in, 114. Siemens' cast steel furnace, 360. Siemens' gas producer and furnaces, 325. Silesian gas refinery, 249. Silicate of protoxide of iron, 35. Silicates, fusibility of, 128. Silicon and iron, compounds of, 34. Silver and iron, 46. Slatrs, blast furnace, composition of, 129. Slags, blast furnace, physical character of, 13 2. Slags of blast furnace, method of re- moving, 145. Slags of puddling furnaces, composi- tion of, 276, 278, 346. Slide blowing engines, 153. South Staffordshire blast furnaces, charges and yields of, 209. South Staffordshire, consumption of iron ort-s in, 208. South "Wales, calcining kilns used in, 111. South Wales, charges and yields of blast furnaces in, 211. South "Wales, finery process, 260. Spathic iron ore, analyses of, 73. Specific gravities of iron and steel, 377 379. Specular iron ore, volcanic, 20. Specular schist of Lake Superior, 206. Speiss, or arsenides of iron, 30. Spiegeleisen, views on its composition, 38. Spiral stove, 165. Squeezers, varieties of, 297. Stacks, blast furnace, construction of, 139. Steam hammers, varieties of, 291. Steel, methods of producing, 331. Steel puddling, method of, 339. Stolberg, dressing of iron ores at, 99. Stoppage of blast furnaces, 195. Strength of cast iron and steel, 393. Styriau blast furnaces, charges and yields of, 200. Styrian forge steel process, 335. Styriau kiln for pyritic ores, 117. Styria, spathic iron ores of, 73. Sulphate of protoxide of iron, 33. Sulphur, action of, on cast iron, 41. Sulphur and iron, compounds of, 31. Sulphur, determination of, in iron ores, 384. Surface of heating stoves, 171. Swedish blast furnaces, charges and yields of, 204. Swedish finery process, 262. Swedish gas kiln, 115. Swedish method of assay, 84. Swedish method of charging blast fur- naces, 192. Swedish method of collecting gasts, 179. Tapping operation of blast furnaces, 193. Tests for wrought iron, 392. Thomas and Laurent's stove, 166. Tilt hammer, Swedish, for crushing, 104. Tin and iron, alloys of, 45. Titanium, action of, on iron, 48. Traversella, magnetic ores of, 58. Tunesten, action of, on iron and steel, 47. Twyers, arrangement of, 176. Uchatius' cast steel process, 333. Universal rolling mill, 305. Uulined crucible?, assay in, 83. Valves for blast engines, forms of, 152. Vanadium and iron, 47- Walloon finery process, 262. Wasseralfingen stove, 165. Waste gases of blast furnaces, composi- tion of, 226. Waste heat of mill furnaces, utilisa- tion of, 322. INDEX. 399 Water balance lift, 150. Water twyer, 178. Water tymp, 144. Weisbach's formula for calculating hot blast, 172. Westphalia, roasting pyritic ores in, 108. Whitwell's stove, 169. Wootz, method of making, 334. 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