UC-NRLF 
 
 BBB 
 
 iiitels. 
 
LIBRARY 
 
 OF THE 
 
 UNIVERSITY OF CALIFORNIA. 
 
 CtOK 
 
 
METALLURGY 
 
\ 
 
 CONVERTER FOR BESSEMERIZIKG COPPER MATTE (FRASER AND CHALMERS). 
 
METALLURGY 
 
 AN ELEMENTARY TEXT-BOOK 
 
 BY 
 
 E. L. RHEAD 
 
 LECTURER ON METALLURGY AT THE MUNICIPAL TECHNICAL SCHOOL 
 MANCHESTER 
 
 NEW IMPRESSION 
 
 LONGMANS, GREEN, AND CO. 
 
 39 PATERNOSTER ROW, LONDON 
 
 NEW YORK AND BOMBAY 
 
 1902 
 
 OF THE 
 
 UNIVERSITY 
 
' 
 
PREFACE 
 
 IN issuing this little work the author has endeavoured to 
 provide the student with a book of moderate size, giving a 
 clear and concise account of metallurgical processes, and the 
 principles upon which they are based. Details are only given 
 when necessary for the sake of clearness. 
 
 The chemical changes involved in the various processes 
 described are specially dealt with, but it must be remembered 
 that the equations given for reactions occurring at elevated 
 temperatures in most cases only partially express the truth. 
 
 The book is intended as a text-book for students com- 
 mencing the study of Metallurgy, and as a small handy book 
 of reference. It has been written in as popular a style as the 
 subject permits, to make it available for the general reader. 
 
 The author wishes to express his indebtedness to Messrs. 
 Fraser and Chalmers for several of the diagrams in the 
 chapters on Gold and Silver; and to his former students, 
 Mr. W. H. Mortimore, for Figs. 51 and 55 ; Mr. Jno. Allan 
 and Mr. W. McD. Malt for assistance in correcting the later 
 proofs. 
 
 MANCHESTER, 
 August, 1895. 
 
 112865 
 
CONTENTS 
 
 INTRODUCTION. 
 
 PAGE 
 
 Scope of Metallurgy Useful properties of metals Useful metals . i 
 CHAPTER I. 
 
 PHYSICAL PROPERTIES OF METALS. 
 
 Specific gravity Fracture Hardness Fusibility Volatility 
 Tenacity Testing Testing machines Annealing Elongation 
 Ductility Malleability Toughness Flowing power of 
 metals Welding Conductivity 2 
 
 CHAPTER II. 
 
 METALLURGICAL TERMS AND PROCESSES. 
 
 Native metals Ores Ore deposits Ore-dressing Machinery used 
 in dressing ores Gangue Smelting Reduction Air-reduc- 
 tion Concentration of ores by fusion methods Calcination 
 Reguli, mattes, and speiss Fluxes and slags Silicates 
 Refining processes Scorification Cupellation Parting, etc. . 12 
 
 CHAPTER III. 
 
 FURNACE TYPES. 
 
 Kilns and stalls Hearths Wind furnace Blast .furnace Rever- 
 beratory furnace Muffle furnace Tube and retort furnaces- 
 Regenerative furnaces Mechanical furnaces Bruckner calciner 
 White-Howell, and Oxland calciners Stetefeldt and Gersten- 
 hoffer calciners 24 
 
viii Contents. 
 
 t CHAPTER IV. 
 
 REFRACTORY MATERIALS. 
 
 PAGE 
 
 Fire-clay Fire-bricks Canister Dinas and silica bricks Sand 
 Acid and basic linings Lime Magnesia Dolomite Alumina 
 Bauxite Oxides of iron Marl Bone-ash Plumbago Cru- 
 cibles Lining of Crucibles 32 
 
 CHAPTER V. 
 
 FUELS. 
 
 Combustion Organic fuels Inorganic fuels Calorific power Cal- 
 culation and experimental determination of calorific power 
 Temperature of combustion Wood Charcoal Charcoal burn- 
 ingPeat Lignite Coal Coke Coke ovens . . . .* . 42 
 
 CHAPTER VI. 
 
 GASEOUS FUELS. 
 
 Conversion of solid fuels into gas Producer gas Coal gas Natural 
 
 gas Water gas Siemens' producer Wilson producer . . 7 2 
 
 CHAPTER VII. 
 
 IRON, ETC. 
 
 Varieties of iron Iron and carbon Iron and silicon Iron and 
 manganese Iron and sulphur Iron and phosphorus Oxides 
 of iron Barff's and Bower's processes Iron ores .... 76 
 
 CHAPTER VIII. 
 
 IRON SMELTING. 
 
 Principles of iron smelting Preparation of ores Calciners Blast 
 furnace Tuyeres Lifts Charge Blast Blowing engines 
 Hot-blast stoves Tapping 87 
 
 CHAPTER IX. 
 
 | 
 
 CHEMICAL REA'CTIONS OCCURRING IN, AND PRODUCTS OF 
 THE BLAST FURNACE. 
 
 Reduction of oxide of iron by c.arbon monoxide Carburization of 
 spongy iron Reduction of silicon, manganese, and phosphorus 
 
Contents. ix 
 
 PAGE 
 
 Introduction of sulphur Formation of cyanides in blast furnace 
 Products of blast furnace Pig iron Spiegeleisen and ferro- 
 manganese Siliconeisen Blast-furnace slag Blast-furnace 
 gases Iron founding Chilled and malleable castings . . . 106 
 
 CHAPTER X. 
 
 MALLEABLE OR WROUGHT IRON. 
 
 Direct processes Burmese Catalan forge American bloomery 
 Principles of indirect processes Refining Fining Puddling 
 Removal of sulphur from pig iron Shingling Rolling Classi- 
 fication of merchant iron 117 
 
 CHAPTER XI. 
 
 STEEL. 
 
 Hard and mild steel Properties Hardening and tempering 
 Varieties of steel Steel making Catalan forge Puddled steel 
 Cementation process Blister steel Shear steel Cast crucible 
 steel Bessemer process Basic-Bessemer process Open-hearth 
 processes Siemens process Siemens-Martin process Basic- 
 open-hearth steel Use of spiegel and ferro-manganesc . . . 136 
 
 CHAPTER XII. 
 
 COPPER. 
 
 Physical and chemical properties Alloys Ores Welsh process of 
 copper smelting Modifications " Best selected " process Re- 
 duction processes Bessemerizing copper mattes Direct process 
 Wet methods of extraction Electro refining Varieties of 
 copper 159 
 
 CHAPTER XIII. 
 
 LFAD. 
 
 Physical and chemical properties Manufacture of red lead Lead 
 ores Principles of Smelting Flintshire process Cornish pro- 
 cess Blast-furnace methods Slag hearth Ore hearth 
 Softening lead Desilverization Pattinson's, Parkes's, Cor- 
 clurie, and Rozan processes Lead fume 177 
 
Contents. 
 CHAPTER XIV. 
 
 MERCURY. 
 
 PAGE 
 
 Physical and chemical properties Amalgams Ores Principles of 
 extraction Idrian, Almaden, Alberti, Californian, and con- 
 tinuous-retort processes Purification 199 
 
 CHAPTER XV. 
 
 SILVER. 
 
 Physical and chemical properties Compounds of silver Alloys 
 Ores Patio, barrel, kettle, and pan amalgamation processes 
 Wet processes of extraction Ziervogel, Augustin, Von-Patera, 
 and Russell processes Cupellation of lead Desilverization cf 
 copper . 207 
 
 CHAPTER XVI. 
 
 GOLD. 
 
 Physical and chemical properties Occurrence AUuvial deposits 
 and placers Hydraulic mining Washing sands Gold quartz 
 Free-milling and refractory ores Treatment of tailings 
 Chlorination and cyanide processes Parting processes Refining 
 Alloys 229 
 
 CHAPTER XVII. 
 
 TIN. 
 
 Physical and chemical properties Ores Smelting Refining 
 
 Manufacture of tin plate 244 
 
 CHAPTER XVIII. 
 
 ZINC. 
 
 Physical and chemical properties Ores Extraction English, 
 
 Belgian, Silesian Blast-furnace and wet methods .... 252 
 
Contents xi 
 
 CHAPTER XIX. 
 
 OTHER METALS. 
 
 PAGE 
 
 Nickel Cobalt Manganese Chromium Magnesium Aluminium 
 
 Platinum Antimony Bismuth Cadmium 262 
 
 CHAPTER XX. 
 
 ALLOYS. 
 
 Properties of Alloys Liquation of alloys Colour and production of 
 alloys Copper-zinc, copper-tin, copper Antimony, lead-tin 
 Zinc Antimony alloys Fusible metals Quick solders Alu- 
 minium, manganese, phosphor and silicon bronze Amalgams 
 Iron alloys 265 
 
INTRODUCTION. 
 
 THE science of Metallurgy deals with the properties of metals 
 in the different conditions they may assume the changes in 
 these properties induced by the treatment to which they are 
 subjected, or brought about by the influence of other sub- 
 stances with which they may be mixed, either as impurities or 
 for some useful purpose. It also treats of the methods by 
 which they are extracted, in a more or less pure state, from the 
 substances in which they occur naturally, and the refining of 
 the crude products. 
 
 The properties on which the usefulness of a metal depends 
 are : specific gravity, hardness, toughness, tenacity, elasticity, 
 malleability, ductility, expansion by heat, fusibility, resistance 
 to atmospheric and chemical action, conductivity for electricity 
 and heat, and the manner in which it affects the properties of 
 metals with which it may be mixed. 
 
 The high specific gravity of gold reduces coins of con- 
 siderable value to a reasonable size, while the low specific 
 gravity of iron, compared with its strength, reduces the weight 
 of iron structures. A gold structure of the same strength as an 
 iron one would be nearly nine times as heavy. 1 
 
 The hardness of steel fits it for cutting-instruments. The 
 toughness, malleability, ductility, and tenacity determine the 
 
 1 Tenacity of gold 7 
 
 = = O'3O2 
 Specific gravity 19-6 
 
 Tenacity of iron _ 25 
 Specific gravity ~ 7-8 ~ 3 2 
 
Metallurgy. 
 
 workability and general usefulness of a metal for structural 
 and constructive purposes ; the fusibility and expansibility its 
 suitableness for making castings; while a greater or less 
 resistance to atmospheric corrosion is necessary for its general 
 application. 
 
 Useful Metals. Of the fifty-five elements classed as metals 
 by the chemist, only some twenty occur in such quantity, or 
 possess properties which raise them to such importance, as to 
 be of consequence to the metallurgist. These are 
 
 Iron 
 Copper 
 Zinc 
 Tin 
 
 Lead 
 
 Antimony 
 Gold 
 Silver 
 
 Platinum 
 Aluminium 
 Manganese 
 Bismuth 
 
 Chromium 
 Mercury 
 Magnesium 
 Nickel 
 
 Cobalt 
 Cadmium 
 Sodium 
 Potassium 
 
 CHAPTER I. 
 
 PHYSICAL PROPERTIES OF METAL. 
 
 Specific Gravity, or comparative density, is the weight of the 
 metal, bulk for bulk, compared with water. It is generally 
 increased by mechanical treatment, such as hammering, rolling, 
 and wire-drawing. 
 
 TABLE OF SPECIFIC GRAVITIES. 
 Water = I. 
 
 Nickel 8-8 
 
 Bismuth 9*2 
 
 Silver 10-5 
 
 Lead 11*36 
 
 Mercury I3'o 
 
 Gold 19*3 
 
 Platinum . . . . 2i'5 
 
 HARDNESS. This property is very much affected by the purity of the 
 metal and the treatment which it has undergone. Speaking generally, the 
 hardness of a metal with few exceptions is increased by the presence of 
 impurities. Gold for coinage is hardened by 8*33 per cent, of copper, and 
 the presence of a small percentage of carbon in iron converts it into steel. 
 Other examples will be found in the text. By suitable treatment, steel may 
 be made hard enough to scratch glass, or soft enough to be turned and 
 worked freely. (See Tempering Steel.) Mechanical treatment, such as 
 
 Magnesium . 
 Aluminium . 
 Antimony . 
 Zinc .... 
 
 . . 174 
 . . 2-56 
 . . 67 
 
 7'I 
 
 Tin .... 
 Iron .... 
 
 . . 7'2 
 
 7*8 
 
 Copper . 
 
 . . 8-6 
 
Physical Properties of Metal. 3 
 
 hammering, wire-drawing, rolling, and pressure in the cold state, hardens 
 metals. In this manner the bronze weapons of the ancients were hardened. 
 Heating to redness, and allowing to cool very slowly, generally has the 
 effect of softening the metal. In the case of copper this is reversed, rapid 
 cooling, such as quenching in water, softening that metal and its alloys. 
 Metals are usually softer when hot than when cold. 
 
 Fracture is the appearance presented by metals when 
 ruptured. 
 
 Metallic fractures may be classified as 
 
 Crystalline. Metals presenting this appearance are weak, as fracture 
 occurs by the separation of the adherent facets. Antimony, bismuth, and 
 zinc offer good examples of this kind of fracture. 
 
 Granular. This fracture presents the structure of a sandstone. The 
 homogeneity of the mass is greater than when crystalline, and the metal is 
 consequently stronger and more readily worked. Cast iron is a good 
 example of this structure. 
 
 Fibrous. This structure is developed to the greatest degree in wrought 
 iron by the elongation and welding together of the particles during rolling. 
 The toughness and strength of this metal are too well known to require 
 comment. 
 
 Silky. This is a finely fibrous fracture of brilliant silky lustre. It 
 is best seen in copper. Metals which possess it are strong, tough, and 
 malleable. 
 
 Conchoidal, This appearance is presented by the harder varieties of 
 steel. The metal breaks with a convex or concave surface with divergent 
 markings somewhat resembling a shell. Metals possessing this fracture 
 are hard, highly elastic, and brittle. 
 
 Columnar. The columnar structure is manifested by the tendency of 
 the metal to separate in long fingers across the thickness of the cake or 
 ingot, the pieces somewhat resembling lump starch. It is obtained by 
 heating the metal nearly to its melting-point, and then either allowing it to 
 fall on the ground, or by striking it sharply with a wooden mallet while 
 hot. Tin and lead are the best examples of this structure. 
 
 The fracture of a metal varies with the purity, temperature, and manner 
 in which the rupture has been produced : e.g. wrought iron containing 
 phosphorus breaks with a crystalline fracture ; copper at a full red heat 
 breaks with a coarsely granular fracture ; while wrought iron, if nicked all 
 round and broken short off, may present a granular fracture, but if nicked 
 on one side only, and then bent over and broken, it exhibits a fibrous 
 fracture. 
 
 Fusibility. All metals, with the exception of chromium, 
 have been reduced to a fluid condition by heat. The readi- 
 ness with which this can be done and the degree of heat 
 required to effect it vary greatly. Tin, lead, and zinc melt 
 in an ordinary fire, platinum only in the oxy-hydrogen blow- 
 pipe flame. Many metals, before fusing, pass through a soft, 
 pasty stage, e.g. iron and platinum ; others pass directly from 
 the solid to the liquid state. This applies to alloys also. The, 
 
4 Metallurgy. 
 
 alloy of two parts lead and one part tin, used by plumbers to 
 make the joints of lead pipes, is an excellent instance of this, 
 the knob of metal round the pipe being wiped on and shaped 
 with the metal in the pasty state. 
 
 Some metals contract on fusion, and are denser in the 
 fluid than the solid state at the point of melting. For this 
 reason, solid lumps of cast iron will float in fluid metal of the 
 same kind till melted. Most metals expand on liquefying, and 
 are denser in the solid state. They go through exactly the 
 reverse changes on cooling. 
 
 Metals which expand on solidifying bring out finer impres- 
 sions of moulds when used for castings. Certain qualities 
 of iron are consequently superior for this purpose, and for a 
 similar reason bismuth is added to zinc and tin alloys, for 
 casting the so-called artificial " bronzes," and for making alloys 
 for patterns. 
 
 When metals are mixed together to form alloys, the melting-point of 
 the mixture is lowered, sometimes in a remarkable degree, even below the 
 melting-point of the most fusible constituent, e.g. a mixture of I lead, 
 I tin, 2 bismuth melts in boiling water. (For melting-points of tin and 
 lead allctys, see Alloys.) This is taken advantage of in the production of 
 the so-called " fusible alloys," which are required to melt at a certain 
 temperature, and for solders. Alloys used for this purpose must melt more 
 readily than the objects to be soldered. 
 
 The fluidity of metals when melted is very variable. For casting 
 purposes, the metal must flow freely, or portions of the mould will not be 
 filled cold shorts and the sharpness will be destroyed. 
 
 TABLE OF MELTING-POINTS. 
 
 Tin 230 C. Silver .... 950 C. 
 
 Bismuth .... 268 Copper .... 1050 
 
 Lead 330 Gold 1075 
 
 Zinc 412 Cast Iron . 1200-1300 
 
 Antimony . . . 450 Iron . . . about 1600 
 
 Aluminium . . . 700 Platinum . 1770 
 
 Magnesium . . . 800 
 
 Volatility. Some metals are readily converted into vapour 
 by heat, and are described as volatile metals. Such metals can 
 be distilled, the vapour being led into condensers and cooled. 
 Mercury, zinc, cadmium, sodium, potassium, and arsenic are 
 obtained from their ores in this way, the vapour of the reduced 
 
Physical Properties of Metal. 5 
 
 metal being led away from the reduction chambers, or retorts, 
 and condensed. 
 
 NOTE. Volatility is only a relative quantity. Almost all metals are 
 volatilized to a greater or less extent at very high temperatures, such as are 
 obtainable in the electric arc and furnace, while lead, antimony, gold, 
 and silver, are sensibly volatile at furnace temperatures. 
 
 Tenacity. Resistance to fracture by a stretching force 
 is possessed by all metals in a greater or less degree. It is 
 expressed by the amount of dead weight which a bar of given 
 sectional area can support without rupture. In English 
 measures it is expressed as the number of pounds or tons 
 supported by a bar one square inch in section ; in metric 
 measure, as kilogrammes per square millimetre. 
 
 TABLE OF RELATIVE TENACITIES. 
 
 Steel 100 Gold 12 
 
 Iron . 30-40 Zinc 2 
 
 10-24 Tin 1-3 
 
 Cast Iron . 
 Wrought Copper . 
 
 18-30 Bismuth 
 
 Cast Copper . . 12-25 Lead I 
 
 Cast Silver. . . 25 Lead (wire) . . . i'$-2'$ 
 Aluminium . . 20-28 Antimony O'8 
 
 The steel taken as 100 has a tenacity of 60 tons per square inch. 
 
 This property is greatly affected by the purity of the metal. 
 The presence of certain impurities in some cases increases it, 
 while in others the tenacity is diminished by foreign matters. 
 The presence of the small amount of carbon in iron neces- 
 sary to convert it into steel is attended by a marked increase 
 in tenacity. The presence of silicon, on the other hand, 
 diminishes it. Many other cases will be found in the sequel. 
 Excess, even of a salutary kind of impurity, often lowers the 
 tensile strength, as is the case with the larger proportion of 
 carbon present in cast iron. Metal which has been mechani- 
 cally treated, as by hammering or rolling (especially in the 
 cold), or by wire-drawing, is generally stronger than cast speci- 
 mens of the same metal. Thus, steel wire, No. 14 gauge, 0*087 
 inch in diameter, drawn from steel rods having a tenacity of 
 fifty-seven tons, has a tensile strength of ninety-eight tons. 
 
 Mechanical treatment seems to produce some change in structure, 
 especially in the external parts. In a wire, a hard skin is formed on the 
 

 6 Metallurgy. 
 
 surface, the proportion of which to the whole bulk varies with the gauge 
 of the wire. If this be immersed in acid and dissolved off, the interior is 
 found to possess little or no greater tenacity than the original metal. 
 
 This increase in strength is reduced to its ordinary level by 
 heating the metal to full redness and allowing it to cool slowly, 
 i.e. annealing. 
 
 Heat, if excessive, lowers the tensile strength. The degree 
 of heat varies with different metals. The tenacity of metals 
 often changes, as the result of the situation in which it is 
 employed. Iron and steel frequently become crystalline and 
 brittle by continued vibration, or by frequent heating to redness 
 
 and cooling, and are in 
 consequence weakened. 
 Many fractures result from 
 this cause. 
 
 Tenacity is determined by- 
 straining a piece of metal of 
 known dimensions, and ob- 
 serving the amount of force 
 necessary to fracture it. 
 
 Fig. I shows forms of test- 
 pieces for various purposes be- 
 fore and after fracture. 
 
 The ends are securely 
 gripped and force applied. 
 
 The force is generally ap- 
 plied by means of hydraulic 
 pressure acting on a ram 
 to which one of the grips 
 (shackles) is attached, and the 
 
 orce expended is weighed, by either a simple or compound lever arrange- 
 ment, much on the same principle as a common steelyard. 
 
 Figs. 2 and 3 show diagrams of simple and compound lever arrange- 
 ments. 
 
 Testing-machines for determining tenacity are generally provided with 
 appliances for other purposes. 
 
 Sometimes, instead of weighing the force, the pressure employed is 
 registered by gauges, and the force calculated. 
 
 The force required to fracture a piece is generally greater 
 if applied at once than when gradually applied. 
 
 Elasticity is the amount of force which can be resisted 
 without permanent deformation or " set " being produced. It 
 will be observed from Fig. i that the pieces after testing are 
 longer than before. If during the test the strain is relieved 
 
 After Fracture 
 
 Before Fracture 
 
 After Fracture 
 FIG. i. 
 
Physical Properties of Metal. - 7 
 
 from time to time by removing the force, it will be found that 
 the piece assumes its -original length until a certain amount 
 has been exceeded. After that the test-piece becomes perma- 
 nently elongated. Up to that point the substance is perfectly 
 elastic, and the amount of force required to produce permanent 
 lengthening marks its "limit of elasticity." The proportion 
 
 Jockey 
 
 FlG. 3. 
 
 FIG. 2. 
 
 which this bears to the tenacity of the body is of importance 
 in structural work. The larger the proportion, the more 
 reliable will be the material, and the less likelihood of its 
 being affected by vibration, etc. 
 
 The " modulus of elasticity " is the force that would be 
 required to double the length of a bar if its elasticity remained 
 perfect. The " modulus " is an index of the stretching capacity 
 of the metal. 
 
 Elongation. The extent to which a metal elongates prior 
 to fracture is a matter of the greatest importance. Tough 
 metals usually show a considerable increase in length. Hard, 
 brittle metals elongate but little. 
 
 Important evidence as to the working qualities of the material is thus 
 furnished. To determine the elongation, the test-piece is measured 
 between the points at which it is gripped before and after straining till 
 fractured, and the increase stated in percentage of the original length. 
 Thus a lo-inch test-piece of boiler steel measured 12*5 inches after fracture, 
 i.e. 2 '5 inches over 10 inches = 25 per cent. Elongation is accompanied 
 by a diminution in area of section. This is measured in order to deter- 
 mine whether the elongation was local or uniformly distributed. Some- 
 times the contraction in area is confined to the region of fracture. Results 
 are thus stated 
 
8 Metallurgy. 
 
 DESCRIPTION OF SAMPLE OF MILD STEEL. 
 
 Tensile strength Elastic Elongation Contraction 
 
 in tons per square inch. limit. percent. of area. 
 
 28 15 25 40 
 
 Curves are often drawn automatically or plotted from results, showing 
 the behaviour of the piece at different loads. 
 
 Ductility is the property which permits of the body being 
 drawn out in the direction of its length that is, converted into 
 wire. The metal from which the finest wire is producible is 
 the most ductile. Wires are produced by dragging rods of 
 a convenient size through holes in a steel-faced plate, some- 
 what smaller than the rod itself, and repeating the operation 
 till it is reduced to the desired gauge. The hole is slightly 
 tapered, and the end of the rod is 
 ground down sufficient to permit 
 of its being thrust through the hole 
 * far enough to grip it tightly. The 
 metal becomes hard and brittle by 
 this treatment, and requires to be 
 frequently annealed. The ductility 
 is much less hot than cold, so that all wires are drawn cold. 
 The property is dependent principally upon the tenacity, and 
 in a less degree upon the hardness. Metals which are mode- 
 rately soft and fairly tenacious are the most ductile. The 
 tenacity must be great enough to resist the force necessary 
 to pull it through the holes, this being dependent upon the 
 hardness. 
 
 On this account gold and silver head the list of ductile metals, and iron 
 precedes copper, tin, lead, etc., whose tenacity is much inferior, although 
 they are softer than iron. 
 
 Wire-drawing in most cases increases the density, the force employed 
 being converted into pressure by the conical form of the hole through 
 which it is drawn. 
 
 ORDER OF DUCTILITY. 
 
 Gold Aluminium Zinc 
 
 Silver Iron Tin 
 
 Platinum Copper Lead 
 
 Gold wires as fine as the threads of a spider's web have 
 
 FIG. 
 
Physical Properties of Metal. 9 
 
 been drawn by enclosing the gold in silver, and dissolving off 
 the latter in nitric acid after drawing down. 
 
 Malleability. Metals which can be beaten out or other- 
 wise extended in all directions are said to be malleable, the 
 degree being measured by the thinness of the leaves it is pos- 
 sible to produce. The effect of hardness upon this property is 
 much more pronounced than on the previous one. It is owing 
 to this cause that copper stands so high, and iron so low, 
 in the scale of malleability, while in point of ductility iron 
 exceeds copper. When the pressure necessary to overcome 
 the hardness and spread the metal is greater than the tenacity, 
 rupture occurs. Malleability is seriously affected by the 
 presence of impurities, in some cases, a trace of certain sub- 
 stances being sufficient to destroy it. Traces of bismuth, 
 arsenic, or antimony in gold make the metal brittle. It is also 
 greatly affected by temperature. Iron is most malleable while 
 hot, but must not be overheated, or it becomes burnt. Com- 
 mercial zinc affords a striking instance of the effect of heat in 
 this respect. In the cold, the metal is brittle and crystalline. 
 At a temperature of 120 C. to 150 C. it is malleable, and 
 can be rolled into thin sheets ; at a somewhat higher tempera- 
 ture it becomes more brittle than when cold. Sheets of zinc 
 rolled at the proper temperature retain a considerable degree 
 of malleability, and can be bent and worked like other sheet 
 metals with a little care. 
 
 ORDER OF MALLEABILITY. 
 
 Gold Copper Lead 
 
 Silver Tin Zinc 
 
 Aluminium Platinum Iron 
 
 Plates, sheets, foil, and leaf, are terms applied to different thicknesses 
 of metal. 
 
 Plates, sheets, and foil are generally rolled. Leaf is beaten out by 
 hammering. Gold leaf 5^5 of an inch in thickness, and so thin as to 
 transmit light, is commonly produced by hammering. At the Great 
 Exhibition of 1862, sheets of Russian iron were' shown ^ of an inch 
 thick. These, it would seem, had been produced by hammering the sheets 
 in packets with charcoal powder between. Various tests are applied to 
 determine malleability, such as bending, hammering, etc. Such articles 
 as rivets and angle irons should be very malleable. 
 
io Metallurgy. 
 
 Toughness is the resistance which the metal offers to 
 fracture by bending or twisting. 
 
 Most malleable metals are tough, but not always in pro- 
 portion to their malleability. It is determined by the number 
 of times the metal can be bent to and fro before breaking, or 
 the number of twists that can be put on a wire or rod of 
 given length. 
 
 In some cases, as in testing steel rails, a heavy weight is 
 allowed to drop from a given height upon the rail resting on 
 supports. 
 
 Purity is not always associated with the extreme of tough- 
 ness. Tin, for example, renders copper tougher ; while phos- 
 phorus in iron renders it " short " in the cold, " cold short ; " 
 and sulphur makes it " short" when hot "red short." 
 
 Cold short metal works fairly well above a red heat, and 
 red short below that temperature. The term " short," as 
 here applied, means lack of toughness and malleability. 
 
 Flowing Power.- Metals which in the solid state can be 
 readily shaped into any required form by pressure are said to 
 possess the flowing property. Stampings, lead pipes and rod, 
 coins, medals, etc., are made by taking advantage of this 
 property. It does not in any way refer to the fluidity of the 
 metal when molten, the operations being conducted upon 
 the metal in the solid state. 
 
 The property seems to depend upon a combination of 
 malleability, ductility, and toughness, allied to a peculiar 
 structure giving the metal a semi-plastic character something 
 like half-dried glaziers' putty, which permits of the particles 
 rolling over each other freely. Lead possesses the power of 
 "flowing" to a great extent. In consequence of this, the 
 plumber is able to work up by gentle hammering lead vessels 
 from sheet ; the superfluous metal being gradually worked 
 away into the sides, making them thicker. 
 
 Lead pipe is squirted from a solid ingot by means of 
 hydraulic pressure, the tube being formed by a mandril or die, 
 as it passes from the press. 
 
 In striking medals and coins, a disc of metal (a blank) is 
 placed between steel dies, and the sudden application of pressure 
 
Physical Properties of Metal. 11 
 
 causes it to flow and fill all the finest lines of the die. The 
 great sharpness of medals and coins is due to this method of 
 production. If cast, the metal would solidify before com- 
 pletely filling the mould owing to its thinness. 
 
 Welding. If two pieces of certain metals are pressed 
 together under suitable conditions, they unite and form one 
 piece without the use of any solder. This is called welding. 
 It is essential that the surfaces in contact shall be perfectly 
 clean, and that they shall be in such condition as to flow 
 readily under pressure. Most metals require heating to a 
 greater or less extent before the flowing-point is reached. 
 Lead welds in the cold or when only slightly heated. Iron, on 
 the other hand, has to be heated almost to whiteness. Most 
 metals oxidize when heated, and, to ensure a good weld, it is 
 necessary to remove the oxide in order to secure perfect 
 contact between the uniting surfaces. It is, in consequence, 
 difficult to weld lead, as it oxidizes superficially in moist air, if 
 only exposed for a short period at ordinary temperatures. 
 Gold, on the other hand, if pure, unites with the greatest ease, 
 being sufficiently soft and also unoxidizable. 
 
 In welding iron, the metal is either made hot enough to 
 fuse the oxide formed, or else sand is used, which, by com- 
 bining with it, forms a fusible body (silicate of iron). In 
 either case, when the pieces are placed together, and the 
 junction hammered, the fluid matter is squeezed out (hammer- 
 slag), and chemically clean faces come into contact. Borax is 
 often used instead of sand for the same purpose. 
 
 Lead welds to tin without much difficulty. If a clean 
 sheet of lead is overlaid with a sheet of tin, and passed through 
 rolls, they unite, a compound sheet resulting. 
 
 The metals which weld readily are platinum, gold, silver, 
 lead, tin, iron, and nickel. 
 
 In electric welding, the ends to be united are placed together, and a 
 powerful electric current of low tension is passed by suitable connections 
 from. one piece across the point of contact to the other. The high resist- 
 ance at the junction, owing to the poor contact, causes the development 
 of intense local heat, vrhich is greatest at the faces to be joined. When 
 hot enough, the ends are forced together by a screw arrangement, and 
 union between the pieces takes place. (Thomson's Process.) 
 
 In welding large iron tubes made from plate, rings, etc., the electric 
 
1 2 Metallurgy. 
 
 arc is employed, the arc being sprung between the tube itself, suitably 
 supported, and carbon rods manipulated by hand, or otherwise suspended 
 above it. (Bernado's Process.) 
 
 Conductivity. Metals are, speaking generally, good 
 conductors both for heat and electricity. Their relative 
 conducting powers are as follows : 
 
 For heat. 1 For electricity. 11 
 
 Silver 1000 1000 
 
 Copper ..... 748 941 
 
 Gold 548 730 
 
 Aluminium .... 511 
 
 Zinc 266 
 
 Platinum .... 94 166 
 
 Iron 101 155 
 
 Nickel 120 
 
 Tin 154 114 
 
 Lead 79 76 
 
 Bismuth 18 n 
 
 Electrical conductivity is greatly diminished by a rise in temperature 
 and by impurities. Impure copper may have a conductivity little superior 
 to that of iron. Alloys as a rule are poor conductors, but are less affected 
 by heat. 
 
 CHAPTER II. 
 METALLURGICAL TERMS AND PROCESSES. 
 
 COMPARATIVELY few metals are found to any great extent iii 
 the metallic condition. When occurring in that form they are 
 said to be native. The whole of the platinum, and 
 practically all the gold used, is thus found. Silver, copper, 
 mercury, bismuth, and arsenic also occur native in notable 
 quantities. 
 
 Native metals occur in bodies of considerable size, as threads and 
 filiform masses penetrating the rocks, in grains more or less minute 
 distributed through the rock mass, or in alluvium, in thin flakes, and 
 associated with other substances containing the metal. 
 
 N.B. Masses of native copper 500 tons' weight have been found in 
 the Lake Superior district, and nuggets of gold weighing 183 Ibs. in 
 Victoria. Native metals are often crystalline. Alluvium is the debris 
 which results from the wearing down of rocks. 
 
 Metals generally occur in chemical combination with other 
 elements, whereby their metallic character is completely 
 
 1 Matthieson. 2 Franz and Wiedemann. 
 
Metallurgical Terms and Processes. 
 
 masked. When a mineral contains a sufficient quantity of 
 a metal combined with some element from which it can be 
 readily separated, so as to render the extraction of metal of 
 good quality profitable, it is said to be an ore of the metal. 
 The most commonly occurring compounds from which the 
 metals are principally obtained, are 
 
 Oxides 
 
 Sulphides 
 Carbonates 
 
 Metal and oxygen 
 
 Metal and Sulphur 
 
 Iron, copper, zinc, tin, manganese, 
 chromium, antimony, and alu- 
 minium 
 
 Copper, lead, zinc, antimony, silver, 
 mercury, bismuth, cadmium 
 
 Iron, copper, zinc, lead, manganese 
 
 Aluminium 
 Copper, silver 
 Lead 
 
 Cobalt and nickel 
 Copper, zinc, nickel 
 
 Metal, carbon, and oxy- 
 gen 
 
 Fluorides Metal and fluorine 
 
 Chlorides Metal and chlorine 
 
 Phosphates Metal, phosphorus, and 
 oxygen 
 
 Arsenides Metal and arsenic 
 
 Silicates Metal, silica, and oxy- 
 gen 
 
 Hydrated oxides and carbonates contain water. Oxy-chlorides 
 contain metal, oxygen, and chlorine. Bromides, iodides, and many com- 
 plex substances also occur as ores. 
 
 The quantity of metal required to make the working profitable depends 
 on the value of the metal extracted, and the form in which it occurs. A 
 few pennyweights of gold per ton of ore, if in the free state, can be satis- 
 factorily worked ; while an iron ore must contain about 20 per cent, of the 
 metal to be profitable. 
 
 Iron ores also afford a good instance of the effect of the combination in 
 which the metal exists. Iron pyrites contains 46 per cent, of iron, but it 
 is combined with sulphur, from which element it is difficult to completely 
 separate it, and the iron made from the material, after burning off the 
 sulphur, is of inferior quality owing to the tenacity with which that element 
 is retained. Antimonial gold ores furnish another example. 
 
 Ores are sometimes found in deposits following the general 
 lie of the rocks in which they occur. Such deposits are known 
 as beds. When the occurrence is irregular, the ore being 
 accumulated at certain points, the deposit is called a pocket or 
 bunch. Many ores are found in what appear to have been 
 fissures or cracks, which have been filled up with material 
 altogether differing from the rocks in which they occur. These 
 deposits are called veins or lodes. They do not follow the 
 stratification of the rocks, but cut through them at a greater or 
 less angle. Veins of quartz are often called reefs. The line 
 along which they reach the surface is the outcrop. 
 
Metallurgy. 
 
 Owing to the action of the air, moisture, etc., the upper 
 part of a vein is often entirely altered, and sometimes has 
 spread over the surface, forming a cap; or the alteration 
 
 may extend deeper, even 
 to the water-line. 
 
 Such alteration may have 
 led to a complete change of 
 the chemical character ot the 
 vein, sulphides giving rise to 
 sulphates, oxides and carbo- 
 nates to hydrated oxides, etc. 1 
 
 The rock lying on 
 either side of a vein is 
 the country rock. 
 
 Veins are filled with 
 various materials, some 
 
 FIG. 5. 
 
 of which are of a metallic and others of a non-metallic nature, 
 and often lumps of country rock are included. In Fig. 5 the 
 black portions are the ore bodies. The non -metallic portion 
 is known as veinstuff. It has generally a lower specific 
 gravity than the metallic portion. The materials commonly 
 found as veinstuffs are quartz, chlorite, felspar, mica, horn- 
 blende, and other silicates, barytes, fluor, calcite, dolomite, etc. 
 The operations necessary to separate these from the 
 metallic portion are called dressing the ores. 
 
 Much of the ore can often be separated in a sufficient 
 degree of purity by simply picking it over by hand, and break- 
 ing away adherent rock 
 with a hammer. This 
 is known as hand-pick- 
 ing. 
 
 When it is mixed 
 up with the veinstuff, 
 more elaborate treat- 
 ment is necessary. The 
 methods employed are 
 the different specific gravities of the 
 The metalliferous, portion of an 
 
 See iron. 
 
 FIG. 6. Stone-breaker. 
 
 generally based on 
 materials to be separated. 
 
Metallurgical Terms and Processes. \ 5 
 
 ore is generally heavier than the veinstuff with which it is 
 associated. 
 
 Heavy substances settle out more rapidly when agitated 
 with water, and are less easily carried forward by a running 
 stream than lighter ones, and are more quickly deposited. 
 
 The ore is first broken up, a stone-breaker, crushing-rolls, 
 
 FIG. 7. Plunger Jig. A, plunger ; c, screens ; B, driving-gear for plungers. 
 
 grinding-mill, or stamps being employed, according to the 
 degree of fineness required. The broken stuff is then separated 
 into sizes by a series of screens, the different portions being 
 separately treated. 
 
 Material which is not too fine is washed in jigs. These 
 consist of sieves or shallow boxes with bottoms of wire cloth, 
 suspended in water, and jerked up and down by mechanical 
 means ; or the water is forced upward through the material in 
 jerks by means of a plunger. The disturbance thus produced 
 causes the heavy material to gravitate to the bottom, and the 
 light matters can be scraped or washed off the top. 
 
 The fine stuff is dressed by subjecting it to the action of 
 a current of water on sloping tables. 
 
 Buddies (Fig. 8) are circular, slightly conical tables, upon 
 which the fine material, suspended in water, is fed at the apex. 
 Water is supplied, and the ore stirred by brushes attached to 
 
1 6 Metallurgy. 
 
 revolving arms. The light portions are carried away by the 
 water, and the heavy material accumulates on the cone, the 
 heaviest nearest the apex. 
 
 FIG. 8. Buddie. 
 
 Racks and Washing-tables are inclined tables on which 
 the material is placed at the higher end and washed down by 
 
 FIG. 9. Rack used in washing tin ores. 
 
 a gentle stream of water, being pushed back against the current 
 by brushes or rakes. The light stuff is washed away. 
 
 FIG. 10. Frue Vanner. 
 
 The Frue Vanner (Fig. 10), now largely employed, consists 
 of a wide endless belt of indiarubber so stretched on rollers 
 
Metallurgical Terms and Processes. 17 
 
 that the top forms an inclined table. A rapid shaking motion 
 is communicated to the table, and the belt slowly travels in an 
 upward direction. The fine stuff is fed with water from the 
 trough at the higher end, and clean water is also sprayed on 
 to the table. The current, aided by the jerking motion, 
 separates and carries off the earthy matters, and the heavy 
 metallic portions are carried on by the belt and washed off 
 in the trough under the frame. Vanners are specially suit- 
 able for treating very fine material. 
 
 The dressed ore as delivered by the miner to the smelter 
 is still impure. The earthy matters still associated with it 
 are known as gangue. 
 
 Smelting. The various operations whereby the metal is 
 separated by fusion from the ore are known as smelting. The 
 smelting campaign often involves several distinct operations. 
 
 Reduction. The separation of the metal from chemical 
 combination is known as reduction. If an oxide, this is gene- 
 rally done by heating it with carbon or carbonaceous matters, 
 such as charcoal, coal, or coke ; the carbon of these substances 
 combining with the oxygen and forming CO 2 (carbonic acid 
 gas) or CO (carbon monoxide), according to the temperature 
 at which the reduction occurs. CO itself, is a powerful 
 reducing agent, combining with oxygen, and forming CO 2 . 
 Hydrogen reduces oxides, with the formation of water (H 2 O). 
 
 Sulphides are sometimes reduced directly to the metallic 
 state by heating with iron or with iron-bearing materials. 
 Thus galena (sulphide of lead) yields sulphide of iron and 
 metallic lead 
 
 2?bS + Fe 2 = 2FeS + Pb 2 
 
 and stibnite (sulphide 'of antimony) yields sulphide of iron and 
 antimony 
 
 Sb 2 S 3 + sFe = 3 FeS + Sb 2 
 
 The substance employed to liberate the metal is the reducing 
 agent. In this case the iron unites with the sulphur, and 
 liberates the metal. 
 
 Sulphides are often reduced by air-reduction processes. 
 Thus cinnabar (sulphide of mercury) is reduced by simple 
 
 c 
 
1 8 Metallurgy. 
 
 heating in a current of air. The sulphur burns off, leaving the 
 mercury which is volatilized by the heat free. The vapour 
 is condensed. 
 
 HgS + O, = SO, + Hg 
 
 Lead and copper sulphides are also reduced by air- 
 reduction processes. 
 
 The ore, as received from the mine, is often not suitable 
 for immediate separation of the metal, either because the 
 quantity present is too small, or owing to the combination in 
 which it occurs. Copper pyrites seldom contains sufficient of 
 the metal, and zinc blende contains its zinc as sulphide, 
 whereas the metal is best obtained from the oxide. 
 
 The preliminary treatment to which the ores are subjected 
 generally takes the form of heating them in a plentiful supply 
 of air. This process is called calcination. By this means 
 the sulphur in sulphides is burnt off as sulphur dioxide, which 
 being gaseous passes away, and the metal at the same time 
 also takes up oxygen from the air, and is converted into an 
 oxide. Or the removal of the sulphur may only be partial, 
 and a sulphate may result 
 
 SO 2 
 
 The sulphides of iron, copper, lead, silver, and zinc thus form sulphates 
 during calcination. The amount formed depends on the temperature and 
 other conditions of the roasting. With the exception of lead sulphate, they 
 are decomposed by strongly heating them. Iron, copper, and zinc sul- 
 phates yield oxides. Silver sulphate is reduced to metal. 
 
 Arsenic is similarly removed as white arsenic, As 2 O 3 (see 
 Tin Smelting), and antimony to some extent as antimonious 
 oxide, Sb 2 O 3 . During calcination other changes of great 
 importance take place. Carbonates are decomposed with 
 the expulsion of carbonic acid gas (CO 2 ), leaving an oxide 
 of the metal. 
 
 ZnCO 3 = ZnO -f CO 2 
 
 Zinc carbonate Zinc Carbonic 
 
 (Calamine) oxide acid gas 
 
 Lead Oxygen Lead Sulphur 
 sulphide from air oxide dioxide 
 
 or, 2PbS H 
 
 h 70 
 
 - PbO 
 
 + PbSO 4 
 
 Lead sulphate 
 
Metallurgical Terms and Processes. 19 
 
 Moisture is expelled, and in some cases protoxides, i.e. oxides 
 containing the lowest proportion of oxygen, are converted into 
 higher oxides. This is sometimes of great importance, as in 
 iron smelting. The introduction of protoxide of iron into the 
 furnace would seriously impair its working, besides causing 
 loss of iron in the slag. All ores, therefore, containing this 
 oxide must be calcined before introduction to the furnace, 
 when the following change occurs : 
 
 + O = Fe 3 C>4 + 3CO 2 
 
 Carbonate of pro- Magnetic 
 
 toxide of iron, or oxide of 
 
 ferrous carbonate iron 
 
 Calcination also leaves the material in a more open and 
 porous state, and it is thus more readily acted upon during 
 reduction, especially by gaseous reducing agents such as carbon 
 monoxide. 
 
 The term "roasting" is often used in the same sense as "calcining." 
 In copper smelting it only applies to the operation in which the metallic 
 copper is separated, , 
 
 Most metals are converted into oxides by calcining. Gold, 
 platinum, and silver are not affected. 
 
 The calcined material may be at once reduced, or first 
 subjected to a series of operations for the purpose of con- 
 centrating the metal in smaller bulk, from which enriched 
 portion it is finally obtained. This is done by taking advan- 
 tage of some chemical property manifested by the metal being 
 worked for, to separate it from foreign matters. 
 
 NOTE. The greater part of the copper obtained, is produced from 
 copper pyrites, Cu 2 SFe 2 Sj a compound of iron and copper sulphides 
 which should contain 34 per cent, of copper. It is usually mixed, how- 
 'ever, with so large a proportion of iron pyrites, FeS 2 , that it seldom con- 
 tains more than 12 per cent, of copper, and often less. The concentration 
 of the copper is brought about by taking advantage of the superior affinity 
 of copper for sulphur and of iron for oxygen. By calcining the ore, some 
 iron and copper sulphides are changed to oxides, but on heating the 
 whole to fusion, the copper oxide is decomposed by the unaltered iron 
 sulphide remaining, copper sulphide and iron oxide resulting. The iron 
 oxide is removed by combining with silica, in the slag, the copper sulphide, 
 being heavier, sinking to the bottom of the furnace. The material is thus 
 enriched in copper, and after one or two treatments consists of practically 
 pure sulphide of copper, from which the metal is extracted. 
 
 A mixture of sulphides obtained artificially in this manner 
 by fusion is called a regulus, or matte. Cobalt and nickel are 
 
2O Metallurgy. 
 
 concentrated as arsenides. The mixture of arsenides is called 
 a speiss. 
 
 Smelting operations are conducted at a temperature above 
 the melting-point of the metal. Most metals, after reduction, 
 are obtained in a fused state, and, being heavier than the other 
 materials, run down and form a lowermost layer in the furnace 
 or crucible. Zinc, mercury, cadmium, sodium, and potassium 
 are vaporized at the temperature of reduction, and the vapours 
 are led away and condensed. 
 
 Fluxes. The infusible earthy matters often present in ores 
 may seriously impede the collection of the reduced metal, or 
 retard the reduction by enveloping it and preventing the action 
 of reducing agents, or, by combining with it chemically at the 
 high temperature, cause loss of metal in the slag. It is there- 
 fore necessary in smelting to provide means for causing them 
 to be liquefied at the furnace temperature. This is done by 
 mixing with the ore and reducing agent some substance which 
 'either melts itself and dissolves the infusible matter, or, by 
 combining with it in the furnace, forms a substance which is 
 fusible at the temperature employed. 
 
 Fluor spar, for example, dissolves barytes and phosphate of 
 lime, and lime combines with clay and forms a fusible body. 
 
 Substances added to the furnace charge for this purpose 
 are called fluxes}* 
 
 Most fluxes act to a large extent both chemically and 
 physically. The earthy matters to be removed are divisible 
 into two great classes. Those consisting of earthy metallic 
 oxides and carbonates (the CO 2 is expelled during smelting, 
 and oxides are produced), such as limestone, dolomite, etc., are 
 basic in character; silica (quartz, sand, etc.), and many other 
 substances containing it, are known as acid gangue. When 
 silica is heated with oxides of metal, combination takes place, 
 and bodies called silicates are produced. Thus, lime and silica 
 form silicate of lime, and so on. Some of these melt readily, 
 others only at the highest temperatures. The fusibility depends 
 on the nature of the metallic oxide, and on the amount present. 
 Silicates of soda and potash, lead, manganous, and ferrous 
 
 ) to flow. 
 
Metallurgical Terms and Processes. 21 
 
 silicates melt comparatively easily, but silicates of lime, mag- 
 nesia, alumina, and zinc are practically infusible at ordinary 
 furnace temperatures. When, however, more than one metallic 
 oxide (base) is present in combination with the silica, forming a 
 compound or complex silicate, the mixture of the two silicates 
 is much more readily fusible; the more fusible the silicates 
 employed are separately, the lower will be the temperature 
 at which the mixture will melt. Thus, common soft glass is 
 a mixture of silicate of soda and silicate of lime ; flint glass, of 
 silicates of lead and potash. Thus, also, by mixing silicates 
 of lime and alumina or magnesia, fusible bodies are produced. 
 
 From the foregoing it will be seen that the selection of 
 a flux will depend on the nature of the gangue to be removed. 
 If silica only, then some oxide whose silicate is fusible, as 
 oxide of iron, must be employed, or two bodies such as lime 
 and alumina or magnesia. If clay (silicate of alumina) is to 
 be removed, an addition of lime is all that is necessary. If 
 metallic oxides, or basic bodies, have to be fluxed, silica must be 
 added, and, if necessary, a second metallic oxide to produce 
 a fusible body. 
 
 The substance produced by the combination of the flux 
 with the gangue is called a slag or cinder. In most cases they 
 are mixtures of silicates, and thus partake of the chemical 
 nature of glass. Their appearance depends very much on the 
 rate of cooling, and their composition. Rapid cooling gives 
 a glassy, and slow cooling a stony, appearance. When gases 
 escape during solidification, the slag is full of holes vesicular 
 or spongy. 
 
 The principal materials employed as fluxes are 
 
 Substance, Charatter. Composition. 
 
 Lime Basic CaO 
 
 Limestone . 
 Mountain limestone 
 Alumina . 
 
 Clay Acid 
 
 Quartz, sand, etc. ... ,, 
 
 CaCO 3 
 
 CaCO,MgC0 8 
 
 A1 2 0, 
 
 A1 2 O 3 and SiO 2 , etc. 
 
 Si0 2 
 
 Fe 2 O 3 and Fe 3 O 4 
 Fluor spar 7 .... . . CaF 2 
 
 Garnet, felspar, and other natural silicates are sometimes employed. 
 Borax, and carbonate and sulphate of soda, are also used in small quantities 
 
22 Metallurgy. 
 
 in special operations. Borax is sodium biborate, and dissolves metallic 
 oxides, forming fusible borates. At high temperatures, the soda it contains 
 combines with silica, and thus acts as a flux for that substance. The use 
 of fluor as a flux for barytes and phosphate of lime (bone ash) has already 
 been referred to. Fluor is also a flux for silica. When strongly heated 
 together, a gaseous fluoride of silicon is formed and lime remains, which is 
 fluxed off in the usual manner. 
 
 2 CaF 2 + SiO 2 = SiF 4 + 2CaO 
 
 The bases generally found in slags are lime, magnesia, 
 alumina, ferrous oxide (FeO), manganous oxide, and smaller 
 quantities of potash and soda. 
 
 NOTE. The ferric and magnetic oxides of iron do not readily combine 
 with silica, but when heated with reducing agents, ferrous oxide is formed, 
 which is a powerful flux. 
 
 In many refining processes, slags are produced containing the metal 
 under treatment. These are subsequently worked up for the recovery of 
 the metal. 
 
 Most silicates are capable, when fused, of carrying in 
 suspension or solution excess either of the metallic oxide 
 present or of silica. If the metallic oxide is in excess, the 
 slag is said to be basic ; if silica, it is described as add or 
 siliceous. Silicates are generally classified according to the 
 ratio existing between the oxygen in combination with the 
 metal and silicon respectively. 
 
 Sub-silicates 
 Mono- ,, 
 Sesqui- 
 Bi- 
 Tri- 
 
 4RO.SiO 2 
 2RO.SiO 2 
 4 R0.3Si0 2 . 
 RO.SiO 2 . 
 2RO.3SiO 2 . 
 
 4 R 2 3 .3Si0 2 
 2R 2 O 3 .3SiO 2 
 
 R 2 O 3 .3SiO 2 
 2R 2 O 3 .9SiO 2 
 
 2 I 
 I I 
 I Ij 
 I 2 
 
 i 3 
 
 A slag is clean when the metal has been so completely 
 extracted as to permit of its being thrown away. An ore is 
 said to be self -fluxing or self-going when the earthy constituents 
 are fusible without the employment of a flux. When a mass 
 of materials is fused, the substances formed separate according 
 to their relative specific gravities, and the slag, being lightest, 
 floats on the top. Sometimes metal, speiss, regulus, and slag 
 are produced in the same operation. They arrange themselves 
 in the order stated. 
 
 Refining Processes. Metals when first obtained are never 
 pure, and many methods are followed for their purification. 
 The refining process adopted depends on the metal under 
 
Metallurgical Terms and Processes. 23 
 
 treatment and the impurities to be removed. In some cases, 
 as with iron and antimony, the reducing agents employed, 
 carbon and iron respectively, are taken up by the metal to a 
 certain extent. They are eliminated by heating the metal first 
 obtained with more of the ore, oxide of iron in the case of 
 iron (puddling), and sulphide of antimony with antimony. In 
 each case further reduction takes place at the expense of the 
 foreign matters present. 
 
 In most cases, however, the impurity consists of foreign 
 metals present in the ore, and simultaneously reduced, together 
 with sulphur, arsenic, etc. 
 
 These are generally removed by exposing the metal at a 
 high temperature or in a molten state, to the oxidizing influence 
 of the air in a suitable furnace. The oxides which form are 
 removed from the surface by skimming, or, if the heat is 
 sufficient, unite with silica, and form fusible silicates. The 
 method of conducting the operation, and the name it receives, 
 differ v/ith the metal under treatment. 
 
 Lead is thus improved, iron refined, copper scorified. 
 
 The term scorification (L., scorice = ashes) is also applied to a process 
 in the dry assay of gold, silver, and other ores. A quantity of the silver 
 ore is mixed with finely granulated metallic lead, placed in a clay dish 
 (scorifier), and heated in a muffle until about half the lead is oxidized. 
 The silver and gold are set free, and alloy with the residual lead. 
 
 It is sometimes possible to separate the greater part of the 
 impurity by carefully melting out the metal from the less 
 fusible impurity. This process is called liquation, and the 
 term applies generally to the separation of matters according 
 to their different melting-points, spontaneously, as during 
 solidification, or otherwise. Alloys are frequently not homo- 
 geneous from this cause. 
 
 In refining tin, the impure metal is placed on a sloping 
 bed and gently heated. The tin melts first, liquates out, and 
 drains away, leaving the bulk of the impurities at the upper 
 end of the hearth. Antimony sulphide is also separated by 
 liquation from the infusible matters with which it is associated 
 in the ore. (See also Lead Refining.) 
 
 Silver is purified by alloying it with lead and then removing 
 
24 Metallurgy. 
 
 the lead by oxidation. This is conducted on a cupel made of 
 bone ash or marl brasque (see Silver), and the process is known 
 as cupellation. The oxide of lead (litharge) formed is fusible, 
 and is either run off the surface or partially absorbed by the 
 bone-ash bed. The silver and gold being unoxidizable are 
 unaffected, and remain on the cupel. Base metals present are 
 attacked by the oxide of lead, and the oxides formed, although 
 not fusible at the temperature at which the process is carried 
 on, are dissolved by the molten litharge and carried off, 
 leaving the precious metals pure. 
 
 The separation of silver and other metals from gold is the 
 object of the operation known as parting. This process con- 
 sists of dissolving out the silver by the action of acid, leaving 
 the gold unattacked. 
 
 CHAPTER III. 
 
 FURNACE TYPES. 
 
 MOST metallurgical operations are conducted in structures 
 specially designed either for the production and employment 
 of high temperatures, or to secure perfect control of the tempe- 
 rature and gaseous atmosphere in which the process is carried 
 on. In many cases, special features are introduced with a 
 view to saving fuel. 
 
 Classification* 
 
 (1) Kilns and Stalls. Structures or enclosures in which the 
 materials are mixed with the fuel, free access of air is permitted, 
 and no fusion takes place. 
 
 (2) Hearths. Shallow and more or less open fireplaces, in 
 which the materials and fuel are mixed, a blast of air supplied, 
 and the atmosphere made more or less oxidizing by varying 
 the amount of air supplied. 
 
 (3) Wind Furnaces. Deep fireplaces, with grates at bottom 
 and flue openings at top, for heating crucibles, etc. (Fig. 50). 
 
Furnace Types. 
 
 (4) Blast Furnaces. Tall structures in which the materials 
 and fuel are mixed together, an air-blast introduced near the 
 bottom, and in which fusion of the contents is effected. 
 
 (5) Reverberatory Furnaces. Furnaces in which the fuel is 
 burnt in a separate part of the chamber, the flame and hot 
 gases only, coming into contact with the material treated. 
 
 (6) Muffle Furnaces. Chambers which are heated by the 
 flame, etc., circulating in flues Which surround them. 
 
 (7) Tube and Retort Furnaces. Furnaces in which the 
 operation is conducted in vessels fixed in a chamber and 
 heated. 
 
 (8) Regenerative Furnaces. Those in which the waste heat 
 is employed for heating the air, or air and gas, supplied to the 
 furnaces. 
 
 Kilns. Calcining operations are frequently conducted in 
 vertical chambers provided at the bottom with a grate or with 
 openings to admit air. The substance to be calcined is mixed 
 with sufficient fuel, the burning of which generates the heat 
 necessary to carry on the operation. Gjer's calciner for 
 calcining iron ore is shown on p. 91. 
 
 Kilns are sometimes heated by gas or by the waste heat 
 from furnaces. 
 
 Reguli and mattes are often calcined m stalls (Fig. n) 
 usually built in blocks, back to back. The back wall contains 
 the main flue, which communicates by the openings O, and 
 by flues in the side wall 
 with the interior of the 
 stall. The front is 
 loosely built up, and 
 the top covered with 
 small stuff and a sheet 
 of corrugated iron while 
 the operation is going 
 on. With reguli rich 
 in sulphur, a good layer of wood at the bottom, to start the 
 operation, is all the fuel required, the heat generated by the 
 burning sulphur, etc., being sufficient to carry it on. Several 
 calcinations are needed to completely remove the sulphur, a 
 
 /L 
 
 FIG. ii. 
 
26 
 
 Metallurgy. 
 
 larger proportion of fuel being required each time. Coke or 
 coal is frequently used in the later stages. 
 
 Fig. 12 represents a blast furnace. On examining the 
 figure it will be noticed that the vertical furnace chamber has 
 no grate, the bottom of the furnace being masonry or other 
 solid material. An air-blast is supplied to the furnace by 
 means of bellows, fans, blowers, or 
 blowing-engines, through nozzles, which 
 enter at D. These nozzles are called 
 tuyeres. The materials to be treated 
 are charged into the furnace along with 
 the fuel, and remain in contact with it 
 throughout. As the substances melt, 
 they run down to the bottom and accu- 
 mulate in the space below the tuyeres, 
 known as the crucible, or hearth. 
 When sufficient has collected, an open- 
 ing (kept stopped with clay) is made 
 into the furnace, and the melted matters 
 allowed to flow out, or they may flow 
 out continuously into a separate re- 
 ceiver. It is obvious that in such 
 furnaces fusions and processes of a re- 
 ducing character only can be con- 
 ducted, since the materials are heated 
 in contact with carbonaceous bodies 
 
 Foundry Cupola for employed as fuel. 
 
 Economy of Fuel in Kilns and 
 
 
 
 1 
 
 
 \; 
 
 
 1 A 
 
 
 | o DO 
 
 |D OD 
 
 I 
 
 _ r^fT*?: I^T: 
 
 5= 
 
 FIG. 
 
 door - 
 
 dean p in g Blast Furnaces._In calcining in kilns, 
 the air admitted at the bottom finds its 
 way up through the descending hot material, and cools it, thus 
 carrying the heat back into the kiln, while the descending 
 column of cold material charged in at the top deprives the 
 ascending current of hot gases (products of combustion, etc.), 
 of much of their sensible heat, carrying it thus downwards 
 into the kiln. For maximum economy of fuel, the com- 
 bustion should take place in the middle region. 
 
 In blastfurnaces, the combustion takes place near the region 
 
Furnace Types. 
 
 27 
 
 at which air is blown in, and the ascending stream of gases is 
 cooled by the material in the upper part of the furnace, the 
 degree of cooling depending on the rate of ascent and the 
 height of the column. From the blast furnaces used in smelt- 
 ing iron, they escape at a temperature of from 200 C. to 
 300 C. As the temperature of combustion is high, the carbon 
 burns to CO. Any attempt to burn this by blowing in air 
 higher up the furnace is met with the difficulty of establishing 
 a second region of combustion. 
 
 Fig. 13 represents a type known as the Reverberatory 
 Furnace. 
 
 It will be seen that the chamber in this case is horizontal, 
 and is divided into two unequal parts by a low partition (fire- 
 bridge) crossing it. The smaller part is the fireplace, closed 
 with fire-bars below, and with an opening for charging the fuel. 
 The larger portion is the laboratory of the furnace, the bottom 
 
 FIG. 13. 
 
 of which is the bed or hearth, and on this the materials are 
 treated. Flues at the end opposite to the fireplace communicate 
 with the stack or chimney. The roof gradually inclines 
 towards the flues, and reflects (reverberates) the flame and hot 
 gases from the fire downward, and, getting heated, radiates 
 heat on to the bed. In furnaces of this class, it will be 
 observed, the materials and fuel do not come into contact, and 
 hence all kinds of operations can be conducted in them. 
 Thus, by mixing reducing agents with the charge, reduction 
 can be effected (see Tin and Lead Smelting), and by 
 admitting air to the furnace-chamber, through openings in or 
 
28 
 
 Metallurgy. 
 
 near the fire-bridge, the substances under treatment are heated 
 in contact with air, and oxidation (calcination) goes on. 
 Sometimes air is blown in, as in cupellation, etc. By regulating 
 the air-supply to the fire with dampers, the atmosphere can be 
 made reducing or oxidizing as may be required. 
 
 The draught is sometimes aided by forcing air through the fire by a 
 steam-jet injector similar to that shown in Fig. 74. The steam issuing 
 at high pressure from the nozzle at the mouth of the trumpet-shaped 
 tube, entangles and carries forward the air. Not much steam is required, 
 only about 5 per cent., at a pressure of 60 Ibs. The horizontal branch 
 passes under the fire-bars, and the ash-pit is closed by doors luted round 
 with clay. 
 
 Fig. 15 shows what is known as a water-jacketed furnace. 
 In these furnaces those parts subjected to the most intense 
 heat and the action of corrosive slags, etc., are made of hollow 
 iron casings through which water circulates, the cooling action 
 of which prevents the iron from being affected 
 
 Muffle Furnaces. In some cases it is necessary, for various 
 reasons, to exclude the products of combustion as well as the 
 
 FIG. 14. Muffle Furnace. A, chamber ; B, fireplace ; c, doors ; 
 D, flues round chamber ; F, flues to stack, etc. 
 
 fuel. In such circumstances muffle furnaces are employed. 
 The muffle is a chamber surrounded by the fire, or by flues 
 through which the products of combustion and hot gases from 
 
Furnace Types. 
 
 29 
 
 the fire pass. Such a furnace as used in copper extraction is 
 shown in Fig 14. Muffle furnaces are also used in assaying 
 silver and gold. 
 
 In Regenerative Furnaces, the heat carried away to the 
 flues by the escaping gases, is employed to heat the air 
 
 FIG. 15. 
 
 supplied to the fire, and thus returned to the furnace, effecting 
 a considerable saving in fuel. In gas-fired furnaces, the gas is 
 also heated before burning. Siemens's regenerative furnace is 
 described on p. 154. 
 
 Tube and Retort Furnaces consist merely of a fire-chamber 
 .in which retorts or tubes for the reception of the materials to 
 
3O Metallurgy. 
 
 be treated are suitably supported. They are employed in the 
 extraction of bismuth, zinc, etc. (see p. 236). 
 
 Mechanical furnaces of various forms designed to effect mechanically 
 what in ordinary furnaces is done by hand are extensively employed. In 
 calcining fine materials, the continual or repeated turning over of the 
 material so as to expose it to the air, is necessary, and involves much 
 manual labour. In the Briickner furnace (Fig. 16), this is done by putting 
 the material into a brick-lined chamber, as shown, which can be caused 
 
 H- - 12' H 
 
 FIG. 16. Bruckner Calciner. 
 
 to revolve slowly. The chamber is carried on rollers, and the motion 
 communicated by the gearing shown. It makes about six revolutions per 
 minute. The fireplace is stationary, and the flue is provided with a 
 damper. In the White-Howell furnace (Fig. 17), the revolving chamber 
 is placed at a small angle ; the ore, fed continuously from a hopper at the 
 higher end, is gradually moved forward by the rotation of the chamber, being 
 
 FIG. 17. White-Howell Furnace. 
 
 picked up by projections inside, and dropped again as the furnace revolves. 
 The roasted matter is discharged at the lower end. 
 
 In Gerstenhoffer's calciner, the finely divided ore is fed onto triangular 
 shelves crossing the furnace, and arranged so that each row of shelves 
 catches what trickles from those above, and thus exposes it fully to the hot 
 air and gases from the fire. 
 
v \ C 1 ' 
 OF THE 
 
 Furnace Types. 
 
 UNIVERSITY 
 
 OT 
 
 In tower furnaces, shown in Fig. 18, the fine material is 
 fall down tall heated chambers, and meets in its descent an ascending 
 current of hot gases from the fires F, and air admitted through suitable 
 openings. The sulphur and other combustible bodies are oxidized, and 
 the gases escape by the flue B. The door at C is for the removal of 
 the roasted material, and DD to remove the dust carried over by the 
 current of gases. 
 
 In other forms of calciner, rakes and ploughs are caused to periodically 
 
 
 FIG. 18. Stetevelt Furnace. A, tower ; B, descending flue ; c, discharge 
 door ; D, dust-hoppers ; F, fireplaces ; G, feed hopper. 
 
 traverse the bed or beds, and turn over the material to expose fresh surfaces ; 
 or, as in Brunton's calciner, the bed is horizontal, and revolves. Pro- 
 jections from the roof turn the material over, and gradually move it towards 
 the edge, where it is discharged. 
 
 The structure of a furnace may be divided into two parts : 
 that portion which gives support and stability, and the portion 
 specially adapted to resist the heat and the action of fluxes 
 and slags. The latter constitutes the lining of the furnace 
 chamber. The outer supporting part generally consists of 
 common brickwork or masonry, often strengthened by iron 
 bands, and tied together by transverse rods, supported by iron 
 plates (buck plates, from "buckle," "to bend"), and strengthened 
 
32 Metallurgy. 
 
 at intervals by thick iron plates or flanges (buck staves). 
 These are fastened together by means of iron rods across the 
 furnace tie- rods to prevent accident from the expansion 
 and contraction of the masonry. The outer masonry should 
 be badly conducting material. 
 
 CHAPTER IV. 
 
 REFRACTORY MATERIALS. 
 
 THE substances employed for lining furnaces are required 
 to withstand high temperatures and the corrosive action of such 
 substances as they come into contact with in the furnace, and 
 to possess in certain cases other important characters. 
 
 Fire-clay. The most important and most generally used 
 material is fire-clay. These clays consist mainly of hydrated 
 silicate of alumina, Al 2 O32SiOo2H 2 O (alumina, silica, and water), 
 with an excess of silica, and are marked by the small amounts 
 of lime, magnesia, oxide of iron, potash, and soda which they 
 contain. From the remarks on fluxes (see p. 19), the effect 
 of these substances on clay, in producing fusibility, will be at 
 once apparent. 
 
 No silicate of alumina is quite fusible at furnace tempe- 
 ratures, and when excess of alumina or silica is present the 
 body is even more refractory. Analyses of various clays will 
 be found on p. 33. 
 
 The water of hydration present is in chemical combination, 
 and cannot be removed by drying at the boiling-point of 
 water. Its presence in the clay gives to it one of its most 
 important properties, viz. that of taking up water mechanically 
 mixed with it, and becoming soft and plastic. Clay does not 
 take up the maximum amount ajt once, but only gradually, so 
 that previous to use clay is tempered with water and mellowed 
 by exposure. The water taken up mechanically can be 
 removed by drying. 
 
 When clay is burned, the water of hydration is expelled, 
 
Refractory Materials. 
 
 33 
 
 and a hard anhydrous substance remains. This body has no 
 power of taking up water and becoming plastic, and no 
 artificial means are known of restoring the clay' to its original 
 state. The expulsion of the water during burning causes clay 
 to contract, and allowance has to be made for this. In bricks, 
 blocks, slabs, and other articles of simple form, this is done 
 by merely making the dimensions of the body just large enough 
 to allow for the contraction. 
 
 This, however, cannot be done in the case of crucibles, 
 retorts, and other fire-clay ware. Owing to the unequal con- 
 traction of parts of different thickness, they would crack or 
 become distorted in shape while being burnt, and thus rendered 
 useless. In these cases, it becomes necessary to wholly or 
 partly counteract the contraction. 
 
 This is effected by mixing with the clay substances which 
 either do not contract, or which actually expand when heated. 
 To the former class belong burnt clay (vermed grog), coke- 
 dust, graphite, etc., and to the latter class silica, sand, and 
 flint. Ground flint is principally used in pottery. A common 
 mixture for making clay crucibles and retorts consists of two 
 parts by measure of raw fire-clay or a mixture of various clays, 
 and one part of ground crucibles, etc., or other burnt fire-clay. 
 
 ANALYSES OF FIRE-CLAYS, ETC. , 
 
 
 i. 
 
 2. 
 
 3- 
 
 4- 
 
 5- 
 
 6. 
 
 Silica . . . i ' '' . ' V 
 
 46-6 
 
 46*32 
 
 63-3 
 
 60-2"; 
 
 98'ii 
 
 80 'O4 
 
 Alumina . . 
 Potash . . . \* 
 Soda . . 
 
 39'5 
 
 3974 
 
 23*3 
 
 17-9 
 
 ~ { 
 
 072 
 0-14 
 
 5 '44 
 
 Lime ... . - . 
 
 
 o"*6 
 
 O'73 ( 
 
 
 O'22 
 
 O'3I 
 
 Magnesia . . . . 
 Ferrous oxide. 
 Ferric oxide . 
 Water, etc. . . . 
 
 i3'9 
 
 ** j 
 0'44 
 { 0-27 
 '12-67 
 
 "{ 
 
 ,8 { 
 
 I0'3 
 
 i'3 
 
 2-97 
 7-58 
 
 o 18 
 o-35 
 
 0-17 
 
 2-65 
 2-3 
 
 
 lOO'O 
 
 99'8 
 
 99 '43 
 
 99*00 
 
 99-92 
 
 99-91 
 
 I. Al i O 3 2SiO 2 2H 2 O. 2. China clay. 3. Stourbridge clay (Tookey). 
 4. Newcastle fire-clay (Richardson). 5. Dinas clay (rock) (Weston). 
 6. Sheffield ganister. 
 
 D 
 
34 Metallurgy. 
 
 Fire-clays should be as free as possible from iron pyrites, FeS 2 , as this 
 body heated in air yields ferric oxide (Fe 2 O 3 ), which, in contact with 
 reducing agents such as the fuel, is reduced to the lower oxide FeO. This 
 rapidly attacks the clay, forming at the point fusible complex silicates, and 
 the surface becomes pitted, or even covered with a dark-brown slag. 
 
 The presence of organic matter is a common occurrence, as these clays 
 are generally the under clay of coal-seams. They are usually hard and 
 rock-like, with a somewhat soapy feel. The bituminous matter colours 
 them grey. 
 
 Fire-bricks, besides being refractory, must be strong and 
 of uniform size. The refractoriness is ascertained by making 
 a test-piece from the clay, the edges of which are kept as 
 sharp as possible. This, after careful drying, is strongly 
 heated, and, after cooling, the edges examined. If they remain 
 perfectly sharp, the clay is refractory up to the temperature at 
 which it was heated. 
 
 Any softening is evidenced by the rounding off of the edges, and glazing 
 of the surface. 
 
 The resistance of fire-clay to fluxes varies wirfi its composition and 
 character. The efficiency with which it is mixed and mellowed prior to 
 use exerts considerable influence on the tenderness or otherwise of the 
 bricks made from it. 
 
 Size is an important item in the usefulness of the bricks. If not 
 uniform, much thicker joints will be required in setting them, and as these 
 joints are the weakest part of the lining, the thinner they can be made 
 the longer the lining will last. Fire-bricks are set in good fire-clay, and 
 not in ordinary lime mortar. The action of lime, if used for this purpose, is 
 obvious. It would combine with the clay at high temperatures, and flux it 
 off literally run away with the lining. 
 
 Ganister.--This substance is a highly siliceous body, as 
 will be seen from the analysis. It is a kind of sandstone 
 in which the grains are cemented by clayey matters, so that, 
 when ground down and moistened with water, it binds together 
 by pressure. Its chief peculiarity is that on burning, it neither 
 expands nor contracts to any great extent. This permits of 
 the lining being formed and burnt in the furnace itself. The 
 moistened material in the form of coarse powder is rammed 
 in between the shell and a wooden core, which is then with- 
 drawn, and the lining gradually heated up. It is used thus 
 for lining the wind furnaces, for melting crucible steel, and the 
 Bessemer converter. It is also used for patching up fire-brick 
 linings. The absence of joints, and the great refractoriness of 
 the body, make these linings very durable. Canister is also 
 made into bricks. It occurs in the coal measures. 
 
Refractory Materials. 35 
 
 Dinas and Silica Bricks. The fire-bricks thus known are 
 much more refractory than ordinary fire-bricks, so far as with- 
 standing heat is' concerned. As seen from the analysis, they 
 consist mainly of silica. The materials from which they are 
 made differ in character. Dinas bricks are made from a 
 quartzite, and silica bricks from a more granular material of 
 similar composition. The materials are crushed and mixed 
 with i to 3 per cent, of milk of lime. This mixture is 
 moulded in iron moulds having a false bottom, with the aid 
 of pressure. After careful drying, they are fired at a very high 
 temperature for several days. During the firing, the small 
 quantity of lime added unites with the silica, etc., at the 
 surface of the particles only, and frits or fuses according to 
 the temperature, thus forming a cement, in which the particles 
 of infusible silica are embedded. 
 
 NOTE. The quantity of lime added does not affect the fusibility of 
 the general mass. Its action is restricted to the surface of the particles. 
 
 Dinas bricks break with a coarse hackly fracture, in which 
 the milky particles of quartz can be distinguished from the 
 yellow matrix in which they are embedded. Silica bricks have 
 a coarse granular fracture, and feel harsh to the touch. 
 
 These bricks are tenderer than fire-bricks, and should be 
 protected from moisture. They expand strongly* when heated, 
 and hence their application is restricted to those positions where 
 this can be allowed for, or provision made to prevent mishap. 
 Their principal applications are for constructing the ports and 
 roofs, etc., of regenerative furnaces, and roofs of reverberatory 
 furnaces. Consisting as they do of silica, they are unsuited 
 for those parts of a furnace which are in contact with basic 
 and highly corrosive materials or slags. (See Basic Lining.) 
 
 Sand is extensively used for making the bottoms of furnaces. 
 The sand employed for this purpose is nearly pure silica. It 
 is used for the bottoms of regenerative open-hearth steel fur- 
 naces, and for copper-smelting furnaces. In use it becomes 
 impregnated with metallic oxides, and forms a firm durable 
 lining. Certain sandstones were formerly employed in blocks 
 for the hearths of blast furnaces. The practice is now 
 
36 Metallurgy. 
 
 abandoned, owing to the tendency of blocks of natural stone 
 to crack by heat. 
 
 Soap-stone and serpentine are used in Styria and Carinthia for lining 
 the blast furnaces. These substances are hydrated silicates of magnesia, 
 and are highly refractory. They abound in those neighbourhoods. In 
 Sweden that part of the blast furnace which is subject to the strongest 
 heat is lined with a mixture of crushed quartz and clay. 
 
 The materials hitherto considered, it will be observed, are 
 of a siliceous or acid character, and in virtue of their chemical 
 nature are unsuitable for certain purposes, as, for example, 
 where heated for a prolonged period in contact with metallic 
 oxides, which flux them away. Another and more important 
 case, is in making steel from pig iron containing//^//^'/^, in 
 the open-hearth and Bessemer processes. In the purification of 
 iron, phosphorus is removed by oxidation as phosphate of iron 
 a compound of phosphoric acid and iron oxide in the slag. 
 This compound is decomposed by silica, which combines with 
 the oxide of iron, forming silicate, and separating the phos- 
 phoric acid, which is immediately reduced, and the phosphorus 
 returned into the iron. It thus becomes impossible to remove 
 phosphorus in a furnace lined with siliceous materials. As 
 more than two-thirds of British iron contains too much phos- 
 phorus to be used for steel-making in acid-lined furnaces, its 
 removal is a matter of the greatest moment. This can be 
 effected by replacing the acid siliceous lining with a basic 
 one, i.e. a lining consisting of metallic oxides. 
 
 Few substances of this nature are available, either from 
 scarcity and consequent high cost, or from lack of refrac- 
 toriness. They are devoid of binding power. 
 
 Among metallic oxides, lime (CaO), magnesia (MgO), 
 alumina (A1 2 O 3 ), and chromic oxide (Cr 2 O 3 ), are most refractory. 
 
 Lime, when exposed to the atmosphere, absorbs moisture, 
 forms the hydrate CaH 2 O 2 , and falls to powder. Its applica- 
 tion is, therefore, very limited. It is employed in blocks for 
 the fusion of platinum by the oxy-hydrogen blowpipe. 
 
 Magnesia is free from the drawback of absorbing moisture, 
 and the heavy dense form, obtained by strongly calcining 
 magnesite, the natural carbonate of magnesia, forms an excel- 
 lent lining material, MgCO 3 = MgO + CO a . It is, however, 
 
Refractory Materials. 37 
 
 devoid of binding power, and hence something must be em- 
 ployed as a cementing body. Its principal use is for forming 
 the bottom of basic open-hearth furnaces, and for lining basic 
 Bessemer converters. For the former purpose, the strongly 
 calcined magnesite is either (i) ground down to a coarse meal, 
 and then mixed with a small quantity of slag from the furnace, 
 previously ground as fine as flour. This mixture is introduced 
 into the heated furnace in layers, when the slag softens 
 and agglutinates the mass : the quantity of slag is not 
 sufficient to affect the refractoriness of the whole (compare 
 manufacture of Dinas Bricks) ; or (2) the material may be 
 employed in the same manner as dolomite (see below). 
 
 Dolomite. The amount of magnesite available is small, but, 
 fortunately, the property of not absorbing water applies not only 
 to magnesia, but to the mixture of lime and magnesia obtained 
 by calcining dolomite (mountain limestone). This consists 
 of carbonates of lime and magnesia, and when strongly cal- 
 cined, the carbonic acid gas is expelled, and a mixture of lime 
 and magnesia remains, which is not readily affected by atmo- 
 spheric moisture. This substance is largely employed for the 
 purposes stated above, and is commonly known as the basic 
 lining. The material is produced in the densest form possible 
 by calcining at about the melting-point of cast iron, with blast 
 and hard coke, so that the maximum shrinkage takes place 
 before its employment in linings. It contracts about 50 per 
 cent, and loses nearly as much in weight. Like magnesite, it 
 has no binding property, and is used by mixing the coarsely 
 ground material with from 10 to 15 per cent, of well boiled 
 tar, into a more or less sticky mass, something like asphalte. 
 This mixture, known as " slurry," is rammed into position 
 with heated rammers, round a heated iron core, in Bessemer 
 vessels, and in the bottom and sides of the Siemens's furnace. 
 On heating the lining, the tar is decomposed, or coked, and 
 the carbon remaining cements the whole more or less firmly 
 together. In use, the lining becomes firmer and less porous 
 by impregnation. 
 
 Attempts to make the mixture into bricks and burn them 
 are only partially successful, owing to curvature during coking, 
 

 
 38 Metallurgy. 
 
 which prevents them being properly set. Clay, soluble silicate, 
 etc., have also been used as binding agents. Another difficulty 
 is the provision of a suitable material for setting. The intro- 
 duction of this lining is due to the energy of Messrs. Thomas 
 and Gilchrist, and its most recent application is in copper- 
 refining furnaces, where it promotes the removal of the arsenic 
 from the metal, and diminishes loss, lime and magnesia 
 replacing copper in the slag. The most suitable composition 
 for practical purposes, which shrinks least, is stated by the 
 above workers to be 
 
 Lime 52 per cent. 
 
 Magnesia 36 ,, 
 
 Silica . . 8 
 
 Oxide of iron and alumina / . . . . 4 ,, 
 
 Pure alumina is known as corundum and emery, substances 
 whose other properties as gems (ruby, sapphire) or as grinding 
 materials, on account of hardness, enhances their value, and 
 precludes their use as refractory materials. 
 
 Bauxite. A mixture of hydrated alumina and ferric oxide, 
 however, occurs, and is known as bauxite (from Beaux in 
 France). Its composition is very variable ; the alumina ranges 
 from 35 to 75 per cent, the oxide of iron from 2 to 38 per 
 cent., and the water from 10 to 30 per cent., while silica is 
 present in quantities of from i to 15 per cent. On heating, the 
 water is expelled. This material is made into bricks by mixing 
 it, after calcining, with a little clay and some graphite or coke- 
 dust. The clay binds the mass together, and, when burnt, 
 the coke-dust probably partly reduces the F 2 O 3 to FeO, which 
 combines with the alumina and forms a highly infusible 
 
 uminate of iron, thereby increasing the tenacity of the brick. 
 
 hese bricks have been used successfully in the bottom of 
 fjasic-steel furnaces, for the lining of Siemens's rotary furnaces, 
 and to form a parting between the basic dolomitic bottom of a 
 furnace and the silica brick sides. 
 
 If these are in contact, the lime and magnesia in the lining and the 
 slag, attack, flux off, and undermine the side walls (see Fluxes), with the 
 result that the furnaces collapse. By separating them by a course or two 
 of bauxite bricks this is avoided. Being basic, they are not themselves 
 attacked, and their dense character and composition prevents them attack- 
 ing the bricks above. Hence the term neutral course, which is applied to 
 
Refractory Materials. 39 
 
 this parting. Bauxite bricks are also used to line mechanical furnaces for 
 various purposes. 
 
 Instead of bauxite, chromite is sometimes employed for this purpose. 
 This is a mixture of oxides of iron and chromium, and is very refractory. 
 It is employed in the same manner as dolomite, being either made into 
 bricks or rammed in. 
 
 Oxides of Iron. Besides the above basic materials, various 
 substances, consisting mainly of oxides of iron (Fe 2 O 3 and 
 Fe 3 O 4 ), are employed in making the bottom and sides of 
 puddling furnaces for the conversion of cast into wrought 
 iron. They not only serve as a more or less effective pro- 
 tection to the furnace, but play a most important part in the 
 purification of the iron, and will be best studied in connection 
 with the process (see p. 126). 
 
 Besides these bodies, others are employed in special cases. 
 In cupelling lead, for instance, bone-ash (phosphate of lime) is 
 employed. This body is refractory, and is not readily attacked 
 by oxide of lead. It is also of an absorbent character. In 
 Germany and elsewhere a mixture of marl (a clay containing 
 much lime) and charcoal is employed for the same purpose, 
 under the name of braque. 
 
 Of late years the lining of the blast furnaces used in lead 
 and copper smelting, with siliceous and other materials, has 
 been largely abandoned in favour of water-jacketed furnaces. 
 The highly corrosive slags produced in these processes have 
 little or no action on the water-jacketed iron. Water-cooled 
 iron blocks are also often built into furnace structures, to 
 prevent those parts which are subject to the most intense heat 
 being unduly affected. 
 
 Plumbago (natural graphite), being a form of carbon, is 
 quite infusible. Its principal use is in making crucibles, etc. 
 The mineral, after grinding, is treated with hydrochloric acid, 
 to remove the oxide of iron, then washed and mixed with 
 enough clay to bind the material together, and give the neces- 
 sary strength. Blacklead crucibles contain from 25 to 50 per 
 cent, of graphite. 
 
 Crucibles are more or less cup-shaped vessels of refractory 
 material in which substances are melted. This is generally 
 done in wind furnaces, the pots being surrounded by the fire, 
 
4O Metallurgy. 
 
 and when the contents are melted, the crucible is grasped by 
 tongs and lifted bodily from the furnace, and its contents 
 poured out or teemed. These vessels must therefore be 
 
 (1) Refractory, to withstand the necessary degree of heat. 
 
 (2) Tough while hot, so as not to break in lifting out. 
 
 (3) Must not crack when withdrawn from the fire and 
 exposed to ordinary temperatures, i.e. must be capable of resist- 
 ing sudden and great changes of temperature. 
 
 (4) Must not be seriously attacked and corroded by the 
 materials heated in them, or by the ashes of the fuel. 
 
 (i) and (2) depend on the materials employed for making 
 the crucible, the second being generally secured by a judicious 
 mixture of various clays, etc. (3) and (4) depend largely on 
 the grain of the crucible; a coarse-grained crucible is less 
 liable to crack than a fine-grained one. This applies also to 
 the heating up of the crucible; with fine-grained pots the 
 greatest care must be taken. On the other hand, coarse- 
 grained pots are more easily attacked by fluxes and fuel ash, 
 so that these two properties do not attain a maximum in the 
 same crucible. 
 
 Three distinct varieties of crucible are employed 
 
 Clay, or white pots ; 
 
 Plumbago, or blacklead crucibles ; and 
 
 Salamander, or annealed blacklead crucibles. 
 
 Clay pots are made from various mixtures of fire-clay, 
 with the addition of grog (ground pots see Fire-clay), coke- 
 dust, etc., to counteract contraction. 
 
 Plumbago pots consist of a mixture of plumbago with suffi- 
 cient clay to bind it together. They are largely used for the 
 fusion of metals and alloys, being more refractory and less 
 acted on than clay pots. Relatively, with proper use, they 
 last three times as long as clay pots. 
 
 Salamander pots do not require the same careful and 
 gradual heating as the other varieties. They consist mainly 
 of graphite in coarse grains, and are coated with a glaze to 
 prevent them from absorbing moisture. These crucibles can 
 be introduced immediately into a hot fire without danger; 
 
Refractory Materials. 41 
 
 the coarseness of the grain, the conductivity of the material, 
 and the absence of moisture prevent cracking. Small ones 
 are specially suitable for blowpipe furnaces working with air 
 or oxygen. 
 
 Crucibles are made of various shapes, materials, and -finenesses suitable 
 for different operations. 
 
 The triangular form is specially suitable in small sizes for melting down 
 metals. The corners are convenient for pouring. 
 
 Circular shallow pots, such as the Cornish copper assay crucible, are 
 suitable when roasting as well as when fusions are to be conducted. In 
 copper assays the materials are roasted in the crucible in which they are 
 subsequently fused. 
 
 Such pots are also convenient in separating and collecting by fusion 
 substances whose specific gravities are not greatly different, or which do 
 not become perfectly fluid. Pots for tin assay, etc., are of this form. 
 
 Deeper pots are preferable where these conditions are not required. 
 
 When boiling up of the contents is likely to take place, skittle pots 
 are most suitable. The wide upper portion and contracted mouth prevent 
 the contents from frothing over. 
 
 For lifting with basket tongs from the fire, a slight contraction of the 
 top permits of the pots being grasped lower down, and lifted with greater 
 safety. 
 
 Fluxing pots are very smooth, and resist the action of such corrosive 
 bodies as oxides of lead, soda, etc., for a considerable time. 
 
 Crucible-making. Small crucibles are made in plaster moulds on a 
 revolving head, or whirling table, somewhat after the manner of pottery. 
 On drying, the clay contracts and loosens itself from the mould, is turned 
 out, thoroughly dried, and afterwards kiln burnt. 
 
 Large crucibles are made by hand and machinery. The method of 
 making these pots, for melting steel, at Sheffield is as follows : A carefully 
 tempered mixture of clays, ground crucibles, and coke-dust is made into 
 lumps of the* right size. One of these is placed in a conical iron mould 
 (the flask) previously well oiled. This is provided with a false bottom, 
 having a hole through the centre. A plug the shape of the interior of 
 the crucible with a spindle fitting into the hole of the false bottom of 
 the flask, to keep it central, is pressed down into the clay, and by 
 dint of hammering with a mallet, and twisting to and fro, the clay rises 
 and fills the space between it and the flask. When finished, an attendant 
 lifts the whole, and places it on an upright post somewhat smaller than the 
 false bottom. The flask falls by its weight, and the crucible is lifted off 
 and taken away to be dried ; or, if the top is to be narrowed, this is done 
 with a sheet-iron cone placed on it and worked to and fro as it stands on 
 the post. The crucibles, after drying, are first carefully heated mouth 
 downward in an annealing oven, some ten or twelve hours being taken 
 to raise them to dull redness. They are then placed, without cooling, on 
 their stands in the fires. These stands are blocks of similar material 
 about 2 inches thick. When fully heated, a handful of sand thrown into 
 the pot, frits, fills up the hole, and cements the pot to the stand. 
 
 Large clay crucibles cannot be heated again with safety after being 
 allowed to become cold. They are ground up, after breaking off adherent 
 slag, and used in the manufacture of others, and, in admixture with other 
 materials, for steel-casting sand. 
 
42 Metallurgy. 
 
 Brasqued Crucibles. For purposes where contact with 
 siliceous matters is objectionable, crucibles are frequently lined 
 with carbon by mixing lampblack with a mixture of equal 
 parts of treacle and water to a stiff paste. This is rammed 
 into the crucible until it is filled, and a cavity cut out, leaving 
 a lining from \ to \ an inch thick, according to size. The 
 crucibles are filled with charcoal, or closely covered and 
 heated to redness. Starch, gum, or oil may be substituted for 
 the treacle, and with large crucibles tar may be employed. 
 
 Magnesia or alumina linings may be employed where 
 carbon would be objectionable. 
 
 CHAPTER V. 
 
 FUELS. 
 
 HEAT, for practical purposes, is produced by the combustion 
 or burning of substances in air, or occasionally in pure oxygen. 
 The substance burnt combines chemically with the oxygen, 
 producing gaseous or solid compounds, which pass away to 
 the flues, or, if solid, remain behind. The chemical force 
 exerted in the act of combination appears as heat, and the 
 amount generated is in some measure an indication of the 
 stability of the compound formed. 
 
 Any substance which by oxidation is made a source of 
 heat for practical application is classed as a fuel. Most 
 substances, including all those commonly employed, such as 
 wood, charcoal, peat, coal, coke, and gas are derived, directly, 
 or indirectly, from vegetable matter, and may be described as 
 organic fuels. 
 
 Other substances less generally regarded as such are, how- 
 ever, fuels in certain operations. In calcining iron pyrites 
 (which contains 54 per cent, of sulphur) and other rich 
 sulphides, say in a Bruckner calciner (p. 29), when the 
 operation is once started, the heat developed by the burning 
 sulphur is sufficient to carry on and complete the calcination. 
 
Fuels. 43 
 
 In this case sulphur is a fuel. In the Bessemer process 
 (p. 147) for making steel, cold air is blown through molten 
 pig iron, and the impurities present oxidized out. Instead 
 of being cooled by the air, the metal becomes very much 
 hotter, chiefly by the oxidation of the silicon in the pig iron 
 to silica (Si + O 2 = SiO 2 ). In the basic Bessemer process 
 (p. 152), phosphorus takes the place of the silicon in the 
 ordinary process as a heat producer (P 2 + O 5 = P 2 O 5 ). The 
 SiO 2 and the P 2 O 5 pass into the slag in combination with 
 metallic oxides as silicates and phosphates respectively. In 
 these cases, silicon and phosphorus are the fuels consumed, and 
 sufficient heat is produced to maintain the purified (wrought) 
 iron in a fluid state. 
 
 Sulphur, silicon, and phosphorus may be classed as 
 inorganic fuels. 
 
 Organic fuels consist mainly of carbon and hydrogen, 
 with varying amounts of oxygen and nitrogen, together with 
 more or less inorganic matter, which is left behind on burning, 
 and which constitutes the ash. 
 
 Carbon and hydrogen being the only substances present 
 which burn, a consideration of them is of the greatest 
 importance. 
 
 t When oxygen occurs in a fuel, it must necessarily be in combination 
 with other constituents. Such part of the fuel as is already oxidized 
 cannot be further employed to develop heat, since the heat is produced in 
 the act of oxidation. 
 
 In considering the value of a fuel from its chemical composition, 
 it will be therefore necessary to deduct from the carbon or hydrogen 
 a sufficient quantity to combine with the oxygen present. It is usual 
 to make this deduction from the hydrogen. When hydrogen combines 
 with oxygen it forms water, thus 
 
 H 2 + O = H 2 
 
 parts by weight 2 + 16 = 18 
 
 or i part of hydrogen combines with 8 of oxygen to form 9 of water. 
 Conversely, 8 parts of oxygen require I of hydrogen, and by dividing the 
 percentage of oxygen in the fuel by 8, we obtain the amount of hydrogen 
 with which it is combined. Thus, if the fuel contains 18 per cent, of 
 oxygen and 5 per cent, of hydrogen, 3 g 8 - = 2*25 parts of hydrogen combined 
 with oxygen in the coal, so that only 5 2-25 = 275 parts of hydrogen 
 can be burnt. This is known as disposable or available hydrogen. 
 
 Calorific Power. When substances unite chemically, the 
 combination always takes place between definite proportionate 
 
44 Metallurgy. 
 
 quantities of the bodies, thus 12 parts by weight of carbon 
 
 always combine, when completely oxidized, with 32 parts of 
 
 oxygen, and produce 44 parts of carbonic acid gas, or 
 
 C + O, = CO, 
 
 12 32 44 
 
 It is equally true that a definite amount of heat is generated. 
 This can be expressed numerically. In burning 12 parts of 
 carbon in the form of purified wood charcoal, 96,960 units 
 of heat * are evolved. In burning 2 parts of hydrogen, 68,924 
 units of heat are given out. 
 
 The quantity of heat produced in completely burning 
 1 part by weight of the fuel is the calorific or heating power 
 of the fuel. 
 
 This depends to some extent on the condition of the substance. 
 Compare the calorific powers of carbon as charcoal, diamond, and graphite, 
 in the table given below. The difference is due to the different amounts 
 of heat required to bring about the molecular changes taking place in 
 burning. 
 
 . TABLE OF CALORIFIC POWERS. 2 
 
 Hydrogen . . 34,462 Carbon monoxide . 2403 
 
 Marsh gas (CH 4 ^ 13,063 Sulphur .... 2261 
 
 Charcoal. . . 8080 Oleriant gas (C 2 H 4 ) . 11,857 
 
 Graphite . . . 7797 Silicon .... 7830 
 
 Diamond . . . 777 Phosphorus . . . 5747 
 
 The calorific powers of the constituents of a fuel being 
 known, it becomes possible to calculate the calorific power of 
 a fuel from its composition. 
 
 Example. A sample of coal gave on analysis, carbon 75 per cent., 
 hydrogen 6 per cent., oxygen 15 per cent., nitrogen and ash, etc., 4 per 
 cent. The available hydrogen = oxygen * = 6 1*875 = 4*12, and 
 calorific power of fuel = 75 X 8080 + 4-12 X 34462 
 
 100 
 
 Calorific powers calculated from analyses of fuels are not 
 reliable, as we have no knowledge of the manner in which the 
 constituents of the fuel are combined. 
 
 Direct determinations of the heating power are consequently 
 made. A weighed quantity of the fuel is burnt, and the heat 
 
 1 A unit of heat is the amount required to raise unit weight (say Ib ) 
 of water through unit temperature (i). 
 
 2 The numbers given in this table are the units of water heated through 
 i Centigrade. 
 
Fuels. 
 
 45 
 
 generated is given up to a known weight of water, the tempera- 
 ture of which is previously ascertained. The temperature of 
 the water is again taken after burning the fuel, and the number 
 of degrees it has risen noted. 
 
 Then 
 
 weight of water x rise in temperature 
 - - r-i : - = 
 weight of fuel 
 
 In the weight of water allowance must be made for the heat absorbed 
 by the vessel containing it, and other parts of the apparatus ; and for 
 strict accuracy for other minor losses of heat, such as the heat carried off 
 in the gases as the temperature of the water rises, radiation, etc. For 
 practical purposes these are insignificant if ordinary care is taken. 
 
 The instruments employed in making these determinations 
 are known as calorimeters, or fuel testers. 
 
 Thomson's Calorimeter is shown in Figs. 19, 20, 21. It 
 consists of a glass vessel 12^ inches high and 4 inches wide, 
 
 FIG. 19. 
 
 B 
 FIG. 20. 
 
 FIG. 
 
 containing up to the mark 29,010 grains of water. The fuel to 
 be tested, mixed with oxidizing agents (see below), is carefully 
 introduced into the copper furnace tube, F. This is placed in 
 the socket on the base, B, which also carries three springs, S, 
 for the attachment of the cylindrical copper hood (Fig. 21). At 
 the bottom of this hood is a circle of small holes to allow the 
 gases generated to escape, and a narrow tube terminating in a 
 tap, T, rises from the top. 
 
 The fuel is ignited by a short piece of lamp-cotton soaked 
 
46 Metallurgy. 
 
 in nitre, which forms a slow-match. This is embedded half- 
 way in the mixture. As soon as it is ignited, the hood, 
 with the tap turned off, is placed over it, and the whole imme- 
 diately lifted and lowered into the water. The combustion 
 soon extends to the mixture, which burns rapidly. The gases 
 produced bubbling up from the holes, through the water, 
 are cooled. When they cease to come off, the tap is opened, 
 the water rises inside, and cools the copper furnace and body. 
 After gentle stirring, the temperature is taken, and calculation 
 made as before. 
 
 The oxidizing mixture employed consists of 3 parts of 
 potassium chlorate and i part of potassium nitrate. They 
 must be intimately mixed, quite dry, and in fine powder. 
 The quantity required to burn a sample varies from 7 to 13 
 times its weight. From 10 to 12 times serves for bituminous 
 coals. In order to obtain oxygen, these substances have 
 to be decomposed, and the escaping gases carry off some heat. 
 The loss due to these causes is estimated at one-tenth of the 
 heat observed. It is necessary, therefore, to add 10 per cent, 
 to the observed rise in temperature. The .thermometer 
 employed is exceedingly delicate, reading to y 1 ^ F. To ensure 
 steady combustion, the filling of the cylinder must be very 
 carefully done, not too much pressure being employed. 
 
 These instruments are designed to take 30 grains of the 
 fuel, and were primarily intended for testing fuels for boiler 
 purposes. 
 
 The number 29,010 was selected with a view to make the rise in 
 temperature indicate the evaporative power of the fuel. The latent heat 
 of steam is 967 F. units, and 967 X 30 = 29,010. Thus, if 30 grains 
 of fuel heat 29,010 grains of water i, I grain heats 967 grains of water 
 i, and would therefore convert I grain of water at 212 F. into steam at 
 212. Hence the rise in T 4- 10 per cent. = evaporative power. 
 
 The calorific power in heat units is obtained as before. 1 
 
 NOTE. The calorific powers given on p. 44 were made by Faure and 
 Silberman, with a most delicate calorimeter, for which see Ganot's 
 "Physics," pp. 401, 423. 
 
 In burning hydrogen, the product of combustion water 
 
 1 If a Fahrenheit thermometer is used, the results can be converted into 
 Centigrade units by multiplying the rise in the temperature by |, and 
 vice versd. 
 
Fuels. 47 
 
 is a liquid at ordinary temperatures. The calorific power 
 given above includes the total amount of heat given out. At 
 the temperature of burning, the water is in the state of steam. 
 To retain it in this condition, 1 637 units of heat per part of 
 water will be rendered latent and unavailable for heating 
 purposes. Since each part of hydrogen produces 9 of water, 
 637 x 9 = 5733 units must be deducted for this purpose. 
 The remainder, 28,729, is the heat available for raising 
 temperature. This deduction applies to all moisture present in 
 the fuel as well as that formed in burning. 
 
 In burning carbon, note should be taken that carbon forms 
 two oxides, CO and CO 2 . The calorific power of carbon 
 burning to CO is only 2473, I GSS tnan a third of its total heating 
 power. 2 This shows the importance of complete combustion 
 in order to secure economy. 
 
 The temperature produced by burning a given fuel is 
 dependent not only on the amount of heat given out, but on 
 other conditions also : the ^amount and nature of the products 
 of combustion, whether the combustion takes place in air or 
 pure oxygen, and the initial temperature. The degree of heat 
 realized is below that calculated, and is determined by the 
 stability of the products of combustion, for, when a certain 
 degree of heat has been obtained, these are dissociated as 
 rapidly as formed, and the heat thus absorbed is balanced by 
 that given out 
 
 In practice, the temperature, when burning solid fuel, 
 depends on the rapidity of combustion and the density of the 
 substance, assuming that the composition is the same. The 
 more rapid combustion which attends the employment of hot 
 air, as well as the heat carried in by the air, greatly increases 
 the temperature, while the structure of the substance influences 
 the rate at which it burns porous cellular bodies burning most 
 freely. 
 
 Dense fuels, when burning at the same rate as lighter ones, 
 
 1 This is made up of the latent heat of steam (537) and the heat required 
 to raise water to boiling-point (100 Centigrade units). 
 
 2 The remainder of the heat is given out when the CO burns to CO 2 
 CO + O = CO 2 . 
 
48 Metallurgy. 
 
 produce greater local heat, the heat-evolving and radiating 
 power being concentrated in smaller volume. 
 
 Wood is extensively employed as a fuel, where a plentiful 
 supply is obtainable and high temperatures are not required. 
 
 The organic constituents of dry wood, exclusive of ash, 
 are 
 
 Carbon 51 per cent. 
 
 Hydrogen 6 ,, 
 
 Oxygen . . . . 41*5 
 
 Nitrogen, etc. . C.V^I i'5 
 
 lOO'O 
 
 NOTE. The composition of various kinds of wood is almost identical, 
 no constituent varying much more than I per cent. The principal body 
 present in all is cellulose C 12 H 20 O 10 , with various hydrocarbon substances, 
 as turpentine, resins, etc., which influence its inflammability. Its density 
 varies from 0-4 to I "3. The large amount of oxygen will be at once noticed, 
 and from what we have previously learnt, the disposable hydrogen is only 
 
 6 - .= 0*82 per cent. All the water of composition, 41 '5 + 5*18 
 
 8 
 
 = 46-68 per cent., has to be evaporated. This, added to the fact that 
 ordinary air-dried wood retains from 15 to 20 per cent, of mechanically 
 held moisture, which has also to be expelled, will show the unsuitability 
 of wood for the production of high temperatures. If kiln-dried, it reabsorbs 
 a great part of the moisture on exposure. 
 
 The ash of wood rarely exceeds 2 per cent. It is characterized by 
 the presence of a considerable amount of potash and the absence of 
 alumina. It consists of carbonate of potash, lime, soda, iron, magnesia, 
 with a little chlorine, sulphuric and phosphoric acids, and silica. Wood 
 ashes formerly formed the chief source of potash salts. 
 
 The woods principally employed are : larch, fir, sycamore, 
 birch, elm, ash, pine, and oak. 
 
 The inflaming point of wood is about 300 C., much below 
 redness. 
 
 Charcoal. When wood is gradually heated out of contact 
 with air, it undergoes a destructive distillation. Water and 
 various other volatile compounds are expelled, some of which 
 result from decomposition of the cellulose and other bodies 
 present in wood, with the separation of free carbon. This 
 decomposition commences at about 180 C., and is completed 
 at about 400 C. The residue obtained is charcoal. It con- 
 sists of the fixed carbon of the wood, with the ash, and some 
 hydrogen and oxygen, the amount of which depends on the 
 temperature of preparation. 
 
Fuels. 49 
 
 The substances expelled consist mainly of water, wood 
 naphtha, various heavy hydrocarbons constituting tarry matters, 
 marsh gas, hydrogen, olefiant gas, carbonic oxide, carbonic 
 acid gas, pyroligneous acid (crude acetic acid), and ammoniacal 
 compounds. The valuable nature of some, and combustible 
 character of others of these substances, will be noted. 
 
 The weight of charcoal obtained varies from 15 to 25 percent., 
 rarely exceeding 20 per cent. Its volume is from 50 to 75 per 
 cent, of the wood. The yield depends on the nature of the wood, 
 the heat employed, and rapidity of charring. High temperature 
 and slow charring diminish the yield owing to the more com- 
 plete distillation which occurs. Good charcoal should be hard, 
 sonorous, give a bright fracture, not soil the hands, not friable or 
 fissured, and retain the form of the original wood. Its igniting- 
 point depends much on the temperature of preparation, as the 
 higher the temperature the denser and less easily ignited 
 it becomes. Rapid charring has the effect of making the 
 charcoal fissured. 
 
 The combustible nature of the substances expelled by 
 charring will show that, unless high local heat is required, it 
 would be more economical to simply dry the wood. The 
 quantity of heat given out by burning the wood itself is greater 
 than that given out on burning the charcoal prepared from it. 
 
 Charcoal may be prepared in two ways. The wood may 
 be charred in retorts heated externally by a fire, or it may be 
 piled in a kiln or stack, and the charring effected by a com- 
 plete or partial burning of the volatile matters which distil off 
 when the wood gets heated. The preliminary heating is 
 effected by faggots put in some convenient position in the pile. 
 
 Charring in retorts is principally followed for the sake of 
 the pyroligneous acid and tar, the charcoal being a by- 
 product. 
 
 Charcoal Burning in Piles. The piles are made either 
 circular or rectangular. In circular piles, the wood, sawn into 
 suitable lengths, is built up round a central stake or stakes, in 
 the manner shown in Figs. 22, 23, and the pile covered with 
 sods or earth, supported by branches, whose ends are stuck in 
 the ground and bent over, or, sometimes by a mixture of 
 
 E 
 
5O Metallurgy. 
 
 i 
 
 charcoal and water. This furnishes a yielding cover, but one 
 sufficiently impervious to air as to exclude excess. If three 
 central stakes are employed, the chimney thus formed is filled 
 with faggots. If only one stake is used, a passage is left at 
 one side reaching to the middle, and this is similarly filled. 
 The upper part of the heap is made up with branches and 
 irregular pieces as solidly as possible. When the pile is com- 
 pleted, the faggots are ignited and the openings left uncovered 
 until the pile has fairly caught. They are then completely 
 closed, and the pile left to itself. Volumes of dense yellow 
 
 FIG. 22. 
 
 FIG. 23. 
 
 smoke are at first given off, accompanied by much water vapour. 
 This condenses in the cover and runs down. After a time, the 
 yellow smoke changes to grey, and the cover is extended down 
 to the ground, leaving only a few small openings judiciously 
 arranged to admit .a little air, to continue the combustion of 
 the volatiles, and maintain the heat. The now thoroughly 
 dried wood is thus gradually converted into charcoal, and the 
 " coalier," or burner, completes the charring of the outer 
 portions of the heap, or any part that has not caught well, by 
 making a series of openings in the cover, commencing near 
 the top, which draw the fire and heat in that direction. The 
 smoke which first escapes gradually becomes thin, and the 
 flame of CO appears. When this occurs, the holes are stopped 
 up, or the charcoal will burn, and a new series opened lower 
 down. This is repeated till the whole pile has been charred. 
 
 The judicious arrangement of the wood so that the combustion shall 
 spread uniformly, the consolidation of the pile and making good of any 
 falling in due to contraction in the earlier stages, and the proper manage- 
 ment of the vents, are necessary to secure a satisfactory result. 
 
Fuels. 5 1 
 
 The heat is maintained by the combustion of the volatiles 
 inside the pile. If excess of air is admitted, the charcoal 
 will be partly burnt. The quality is said to be improved 
 by quenching it before it has cooled below its igniting-point. 
 This is accomplished by taking out some of the charcoal, 
 through an opening made in the cover, which is at once 
 replaced. The portion removed is cooled by water or by wet 
 sand, earth, or charcoal-powder. The quenching prevents 
 burning of the charcoal, which might occur during the cooling, 
 if the stack were not tight. 
 
 In rectangular piles (Fig. 24) the wood stack is first built, and 
 surrounded with planks supported behind by stakes driven 
 into the ground, a space being left between the pile and the 
 inner side of the planks. This is filled with charcoal-dust 
 
 FIG. 24. 
 
 moistened with water, or ashes, to protect the planks from the 
 heat. The top is covered with earth, ashes, etc., and ignition 
 is effected through the opening shown in the lower end. The 
 charring proceeds as before. These piles are 22 feet long, 
 4 broad, and from 7 to 9 feet high. Much of the acid and 
 tarry matters can be collected by iron pipes introduced 
 through the cover at the higher end of the pile, leading to 
 receivers. These piles are generally built upon sloping ground. 
 They are more common in, Norway and Sweden than else- 
 where. 
 
 Where a continuous supply of wood is obtainable (as, for 
 example, on a lake shore or river-side, by floating the wood), 
 a permanent masonry bottom is built for the piles. This slopes 
 to a cavity in the centre loosely covered with an iron plate, 
 and communicating by a passage with a tar well. The con- 
 densed tar and pyroligneous acid drain down and pass into 
 the well. 
 
52 Metallurgy. 
 
 Rectangular kilns of masonry are sometimes employed, 
 provision being made for igniting the wood, for leading away 
 the products of distillation, and for regulating the air supply. 
 
 Wood for charcoal burning should be mature, but not decayed or 
 worm-eaten. It is at its best when about thirty years old. It should be 
 felled in winter, when the sap is down, and the bark removed to facilitate 
 drying. The site selected should be near a stream or water supply, and 
 the ground not too sandy or clayey. The former is too porous, and the 
 latter cracks with the heat, and air is drawn in. If burnt, charcoal is dull, 
 soils the hands, and is light and friable. 
 
 The amount of charcoal produced varies with the method 
 of burning. It forms from 14 to 25 per cent, by weight, and 
 from 50 to 75 per cent, by volume, of the wood. It absorbs 
 about 10 per cent, of moisture on exposure to the air. 
 
 The specific gravity of charcoal varies from 0*11 to 
 0*2. If, however, air is expelled from its pores, it is found 
 to be 2. 
 
 The Composition of Charcoal varies with the temperature 
 of preparation. Ordinary charcoal, prepared between 400 
 and 1000 C., is as follows : 80 to 83 per cent, carbon ; i to 2 
 per cent, hydrogen; 14 to 15*5 per cent, oxygen and nitrogen; 
 i to 5 per cent. ash. 
 
 Peat, or Turf, is produced by the gradual accumulation of 
 dead vegetable matter, especially mosses and lower forms of 
 vegetable life, in moist situations. The moisture protects it 
 from the action of the air. Under these circumstances, a 
 gradual change in its composition goes on. The oxygen and 
 hydrogen in the original vegetable matters are slowly elimi- 
 nated, as water (H 2 O), marsh gas (CH 4 ), carbonic acid gas, etc. 
 Up to a certain point the oxygen is removed in greatest pro- 
 portion, the hydrogen in a less degree, and the carbon in the 
 least proportion. The net result of these changes is that the 
 proportion of carbon increases, the colour darkens, greater 
 density is attained, and up to a certain limit the disposable 
 hydrogen is increased. 
 
 These changes invariably occur when vegetable matter undergoes 
 alteration in absence of air, and are assisted by even very moderate degrees 
 of heat, such as the internal heat of the earth. The marsh gas, causing 
 on ignition the will-o'-the-wisp, is produced in this manner. The fire- 
 damp of the mine is also marsh gas, which has been stored in the coal 
 
Fuels. 53 
 
 under the pressure of the superincumbent material, and which, on open- 
 ing up the seam, diffuses out of the coal. CO 2 is more rarely met with 
 owing to its solubility in water, which is always filtering through the rocks 
 more or less. 
 
 The greater the degree of alteration the more widely 
 it departs in character from the original vegetable matter. It 
 is in virtue of these changes that coal, some of the varieties of 
 which consist almost entirely of carbon, have been produced 
 from the vegetable deposits of former ages. Under similar 
 conditions, the greater the age the more altered the material 
 becomes. 
 
 Peat usually occurs at the surface, filling up basin-like 
 depressions. These are known as bogs, or mosses. It follows 
 that peat, being of recent origin, is comparatively little changed, 
 and that the upper and newest layer will differ from the lower 
 and older layers. It will consequently resemble wood in 
 chemical composition. On drying, peat from the upper part 
 of a bog yields a light brownish-yellow fibrous substance, 
 forming about 70 per cent of the volume, and retaining some- 
 times over 30 per cent, of moisture after air-drying. Peat 
 from the bottom of the bog is more gummy, and on drying 
 yields a dense black compact mass, forming about 27 to 30 
 per cent, of the volume, and retaining about 20 to 30 percent, 
 of moisture after air-drying. The specific gravity of peat 
 varies from about o'i to nearly i; as taken from the bog it 
 contains from 70 to 90 per cent, of moisture. The peat after 
 removal is dried on floors, built in walls, and afterwards 
 stacked or housed. This should be done in open weather, as 
 frost seriously injures fresh peat. It never drys so firmly and 
 dense after being frozen. 
 
 The Preparation of Peat, so as to produce from it a denser 
 material more suitable for use as fuel, has received much 
 attention. 
 
 Most of the methods adopted involve compression of the 
 peat, either in a wet or air-dried state, into blocks. In others, 
 the peat is converted into pulp by grinding. This, on drying, 
 contracts to about one-fifth of its bulk, and yields a much 
 denser material containing less moisture. 
 
 The Ash of Peat, as would be expected from the situations 
 
54 Metallurgy. 
 
 in which it is found, is much higher than that of wood. It 
 ranges from 8 to nearly 30 per cent. It contains the same 
 constituents as wood ash, with the addition of alumina. It 
 contains, also, more of sulphates and phosphates, and often 
 sulphides as well. 
 
 Peat commences to distil at about 130 C, and leaves a 
 charcoal, the value of which depends on the character and 
 amount of ash of the peat. 
 
 Fossil Fuels. When deposits of vegetable matter have, 
 by alteration of the earth's surface, been submerged in the sea, 
 and other strata deposited on them, the alteration previously 
 noticed has continued, and the substance has entirely lost its 
 vegetable character and become fossilized. The extent to 
 which this has gone on depends on the age of the geological 
 formation -in which it is found, and sometimes on local 
 influences. 
 
 Those substances which are found in the newer formations 
 are called lignites (Lat, Lignum " wood"), from the distinct 
 woody character' of some of them, and those found in the 
 older formation known as the " Carboniferous " are called 
 coal. As would be expected, much difficulty is experienced in 
 drawing a sharp limit between the two, as they gradually merge 
 into each other. 
 
 Characteristic specimens, however, differ widely. Selected 
 examples of lignites and coals show a gradual passage from 
 wood to anthracite (the most altered form of coal). Such a 
 table is exhibited below. The striking feature of such an 
 arrangement is that the available hydrogen gradually increases 
 to a certain point, and the amount of fixed carbon carbon 
 not driven off when the coal is heated shows a similar 
 increase. 
 
 The effect of this upon the character of the coal is im- 
 portant. The higher members of the series, in which the 
 available hydrogen is low, burn without softening and fritting 
 together, and if the powdered fuel is heated in a vessel from 
 which air is excluded, the particles do not stick together. 
 Such substances are described as non-caking. As the available 
 hydrogen increases, the caking property becomes more and 
 
Fuels. 
 
 55 
 
 more strongly marked, until the substance becomes so rich in 
 carbon as to again become non-caking, the bituminous matters 
 produced during heating not being sufficient to bind the 
 particles together. Thus the non-caking substances are of two 
 classes : (i) those rich in oxygen, and low in available 
 hydrogen ; (2) those rich in carbon. 
 
 COMPOSITION OF FUELS. 
 
 Fuel. 
 
 c. 
 
 H. 
 
 O. 
 
 N. 
 
 Ash. 
 
 Available hydro- 
 gen. 
 
 Wood (dessicated) 
 
 Si' 1 
 
 6-2 
 
 41-4 
 
 I-I2 
 
 1-8 
 
 I-I N 
 
 
 Peat 
 
 C2"?8 7'O7 
 
 4O* CQ 2 
 
 
 2"! 
 
 ~^ 
 
 (Coppage, Ireland) ' 
 Peat, Long (France) ' . 
 
 60'9 
 
 622 
 
 32-88 2 
 
 
 2- 3 
 
 
 Lignite 
 Caroline, S. . 
 
 60-3 
 
 4-8 
 
 20'2 
 
 I'O 
 
 3-2 
 
 2'3 
 
 / Non- 
 caking. 
 
 Auckland 2 . . . 
 
 647 
 
 4-81 
 
 I8-25 
 
 I'34 
 
 10-48 
 
 2-.S3 
 
 
 Tasmania . . 
 
 69-14 
 
 S'4 
 
 18-48 
 
 1-26 
 
 5'37 
 
 3'i 
 
 
 Trinidad 
 
 75'63 
 
 5'2 
 
 I3'5I 
 
 
 2-64 
 
 3'5 / 
 
 / 
 
 Coal 
 
 
 
 
 
 
 
 Cannel, Wigan . . 
 
 80'07 
 
 S'53 
 
 8-1 2-1 
 
 27 
 
 4-5 < 
 
 
 Andrew's House, 
 
 ss-ss 
 
 5'37 
 
 4-39 1-26 
 
 2-14 
 
 4-8 
 
 
 Eanfield 
 Blaina . . . . 
 
 83-0 
 
 6-19 
 
 4-58 1-49 4-0 
 
 S'6 
 
 Caking. 
 
 Ebbw Vale . . V 
 Aberaman 
 
 89-78 
 90-94 
 
 Si 
 
 0-39 2-16 
 
 0-94 I -21 
 
 i*5 
 
 I4'5 
 
 5'i J 
 
 4'i 
 
 
 
 
 
 O. and 
 
 
 
 
 Non- 
 
 
 
 
 N. 
 
 
 
 
 caking. 
 
 Anthracite (Isere) . 
 
 94 -o 
 
 1-49 
 
 3'58 2 
 
 
 4-0 
 
 i*i 
 
 
 Lignites. Some of these are but little altered from woody 
 matter. They are of a light colour and fibrous structure. 
 These may be classified as fossil wood, or fibrous lignite. 
 Such a deposit occurs at Bovey Tracey, in Devonshire. These 
 lignites contain 30 to 50 per cent, of moisture, as won from 
 the ground, and retain 12 to 20 per cent, after air-drying. 
 O|i heating, they leave a residue of about 35 per cent. 
 
 Bituminous, or earthy, lignite is a convenient designation 
 for those more altered ,in character. The colour is dark 
 brown, the fibrous structure indistinct, and the fracture earthy. 
 They contain less moisture than fossil wood. 
 
 1 Exclusive of ash. 8 Inclusive of N. 
 
56 Metallurgy. 
 
 The residue left on heating varies from 35 to 50 per cent., 
 and 4 to 5 per cent, of tarry matters. Specific gravity ri to 1*2. 
 
 The most altered lignites resemble coal in appearance, and 
 to some extent in character. Some are black and shiny, others 
 are dull, and black-brown in colour. The fracture is flat or 
 conchoidal. All trace of woody fibre is lost. They contain 
 less moisture, and leave a fixed residue up to 60 per cent, on 
 distillation. 
 
 This class includes all the better varieties of brown coal 
 (German, Braunkohle). 
 
 The volatile matters expelled from lignite resemble more or less those 
 from coal, but are characterized by a large amount of aqueous distillate. 
 The tars average some 4 to 6 per cent. Lignites are largely used in Germany, 
 France, Italy, and Austria. 
 
 The ash of lignite consists mainly of oxide of iron, alumina, 
 silica, and sulphate of lime and iron. It varies from i to 
 50 per cent. 
 
 The average composition of the organic constituents of the 
 three varieties given below is from Regnault. 1 
 
 Fibrous lignite .... 
 
 Carbon. 
 6 3 
 72 
 
 Hydrogen. 
 
 s 
 
 c 
 
 Oxygen 
 and 
 
 Nkrogen. 
 
 32 
 23 
 
 Pitch-brown coal . . . , 
 
 77 
 
 J 
 
 7'5 
 
 o 
 
 15-5 
 
 Coal. Under this heading are included the more altered 
 forms of fossil fuel. The term " bituminous coal " is applied to 
 all those which burn with a more or less considerable amount 
 of flame of a smoky nature, somewhat resembling pitch and 
 bitumen. 
 
 Bituminous coal passes into anthracite, which burns with- 
 out flame, smoke, or smell. Coals which bum rapidly, without 
 softening and fusing together so as to arrest the draught, are 
 called free burning. f 
 
 Caking Coals include all those which soften and stick 
 together when heated. If the powder is heated in a closed 
 vessel, a more or less coherent mass of coke is obtained. 
 Free-burning coals are " non-caking," or only slightly so. 
 1 See Mills and Rowan's fuel. 
 
Fttels. 57 
 
 As almost every coal-seam differs more or less from others, 
 it is necessary to establish some method of classification. 
 
 Since the chemical composition of the coal affords little 
 clue to its behaviour in burning, the most convenient classi- 
 fication is based on the amount and nature of the residue left, 
 when the coal is heated in a closed vessel, minus the ash. 
 
 Substances used exclusively for the manufacture of gas (boghead coal, 
 etc.), or oils (paraffin coal), are not included. 
 
 Class i. Non-caking coals rich in oxygen (Percy). This 
 includes the various kinds of cannel? splint, or hard coal. 
 They bum freely, with a long flame like a candle. Cannels 
 possess a dull pitchy lustre, break with a conchoidal fracture, 
 give a brown streak, and are hard and dense. The specific 
 gravity is about 1*2. On heating, these coals retain their form, 
 but do not cake together. The lumps of residue are cracked 
 and friable. The percentage of coke varies from about 40 to 60 
 per cent. The fixed carbon present in the coke varying up to 
 53 per cent. Cannels yield on distillation a larger percentage 
 of volatile matters, and less coke than other bituminous coals. 
 The ash and sulphur are also higher. Splint or hard coal is 
 employed in blast furnaces in Scotland and Staffordshire. 
 
 The calorific power of these coals, free from water and ash, 
 varies from 8000 to 8500. They occur in Staffordshire, Derby- 
 shire, Lancashire, and Scotland. 
 
 Class 2. Caking coal, burning with long flame cherry 
 coal (fat coals Gruner). This class includes the various gas 
 and many steam coals. These coals ignite easily, and burn 
 freely with much flame and more smoke than cannel. They are 
 very black and bright, and somewhat platey in structure, much 
 more friable and not so hard as cannel, and are known as soft 
 coal. Heated in a closed vessel, they coke slightly, some to 
 a greater extent than others. The coke is light, spongy, and 
 friable ; it forms from 60 to 70 per cent, of the coal coked. 
 
 The gas is of good quality. They are largely used for 
 manufacture of gas, and for steam-raising. The calorific 
 
 1 Cannels are supposed to have been produced in a different manner 
 to coal. Some are caking in character. 
 
58 Metallurgy. 
 
 power varies from 8500 to 8800. They occur extensively in 
 South Wales and in the Newcastle, Staffordshire, and Glasgow 
 coal-fields. 
 
 Class 3. Caking or soldering coal smithy coal. Coals 
 of this class almost fuse when heated, and form a pasty 
 mass from which bubbles of gas escape, leaving a coke 
 altogether differing in form from the original. The flame is 
 bright and luminous. The coals have a velvety black colour, 
 generally soil the fingers, and have a tendency to break up 
 into small rectangular pieces. They swell considerably during 
 coking, and this reduces the density of the coke, which varies 
 in quantity from 68 to 74 per cent. The calorific power is 
 8500 to 9300, but they are unsuitable for steam-raising, and 
 many other purposes, owing to the great tendency to cake and 
 impede the draught. Many Continental coals are of this 
 character. In Britain they occur in Durham, Yorkshire, 
 Lancashire, Staffordshire, Derbyshire, South Wales, and other 
 localities. 
 
 Class 4. Coking coal (fat coal, burning with a short flame 
 Gruner). This includes those coals which, on account of 
 the large yield and dense nature of the coke, are most suitable 
 for making coke for use in blast furnaces. They are generally 
 of a soft nature, liable to fall to pieces and crush. They ignite 
 and burn less readily than preceding varieties, but do not 
 soften and swell to the same extent. The flame is short, white, 
 and almost smokeless. The coke is denser and stronger 
 than from Class 3, and the yield from 74 to 82 per cent. It 
 is the best for blast-furnace work. The calorific power is 
 from 9300 to 9500. They are less suitable for steam-raising, 
 unless forced draught is employed, than a freer-burning coal. 
 They occur in South Wales, at St. Etienne, and elsewhere. 
 
 Class 5. Non-caking coals rich in carbon (Percy), anthra- 
 citic coal. These coals gradually pass into true anthracite. 
 They are harder, burn with little or no flame, are smokeless, 
 and odourless. They ignite and burn with great difficulty, and, 
 unless forced draught is employed, perfect combustion cannot 
 be ensured. Unless slowly heated, they crackle, fly to pieces, 
 and choke the air-ways. Some kinds are less liable to do this 
 
Fuels, 59 
 
 than others, and in South Wales and Pennsylvania certain 
 varieties are used for blast-furnace work. In appearance they 
 are dull or streaky, and break with a more or less conchoidal 
 fracture. The calorific power is somewhat less than class 4, as 
 the hydrogen present is less. They leave an uncoked residue of 
 about 82 to 88 per cent. They are employed as steam coals. 
 
 Anthracite is the most altered form of coal. It has a 
 brilliant black or semi-metallic appearance, and gives a black 
 streak. It is non-caking, and most difficult to burn, requiring a 
 huge draught. It is the densest of the coals, and generates an 
 intense local heat It is more liable to fly to pieces on heating 
 than Class 5, bituminous coals. It burns without flame or 
 smell. South Wales, Pennsylvania, and the Vosges are the 
 principal localities. Anthracite leaves from 85 to 94 per cent, 
 of fixed carbon, with less than 5 per cent, of ash. 
 
 The specific gravity of coal varies from 1-25 to 1-31. It 
 is, however, influenced by "the amount of earthy matters present 
 The ash ranges from 2 to 18 per cent, and consists of lime, 
 alumina, oxide of iron, magnesia, alkalies, phosphoric, sul- 
 phuric, and hydrochloric acids, and silica. 
 
 The sulphur present in coal is of the greatest importance in 
 the use of the material for iron manufacture in blast furnaces, 
 as it is taken up by the metal. It exists in three states : (i) as 
 iron pyrites the brassy material in coal ; (2) as organic sul- 
 phur ; (4) as sulphate of lime, and sometimes of alumina. The 
 two former states are most objectionable, when used as coal in 
 iron smelting, as the sulphur, sulphuretted hydrogen, carbon 
 disulphide, and sulphide of iron, which result on heating, may 
 all transfer their sulphur to the metal. By previously convert- 
 ing the coal into coke, the organic sulphur is removed, and 
 about half the sulphur in the pyrites. 
 
 To purify the coal from pyrites and dirt, for coking, forge, 
 and other purposes, coal screenings are washed. The inorganic 
 matter, in virtue of its greater density, separating from the coal. 
 The specific gravity of pyrites is 5, nearly four times that of 
 coal. 
 
 The pyrites present in coal often contains arsenic, and 
 sometimes copper. 
 
60 Metallurgy. 
 
 Phosphorus is generally only present in very small quan- 
 tities. Chlorine is always present. It should not be over- 
 looked in coals used for steam-raising in boilers fitted with 
 copper tubes, which it rapidly corrodes. 
 
 The selection of a coal for any particular purpose depends 
 as much on its physical as its chemical character. For blast- 
 furnace work it must be hard and strong, not crumbling under 
 the pressure of the charge, and it must no be too strongly 
 caking. It must, moreover, be practically free from pyrites. 
 Certain varieties of Classes i, 2, and 5 of bituminous coal, and 
 anthracite, are used for this purpose. 
 
 In reverberatory furnaces working with draught, and for 
 steam-raising, free-burning coal is employed. 
 
 For technical purposes, the ash, fixed carbon, voktile 
 matters, sulphur, and calorific power are usually determined. 
 
 Coke. From the above consideration of coal, it will be 
 seen that certain classes are not particularly suited for use in 
 that form, either from their coking power, softness, or the 
 presence of sulphur. These defects may be overcome by con- 
 verting the coal into coke. Very soft coals often yield 
 excellent coke, and, as before pointed out, half the sulphur 
 in the pyrites present is expelled during the coking, together 
 with the organic sulphur, mainly as H 2 S and CS. 2 . So that 
 many coals unsuitable for iron manufacture yield coke which 
 is not so prejudiced. 
 
 Coke stands to coal in the same relation as does charcoal 
 to wood, and consists of the fixed carbon together with the 
 inorganic constituents of the fuel. The percentage of ash in 
 coke is consequently higher than in the coal itself. 
 
 When heated out of contact with air, coal splits up, yielding 
 hydrogen, various volatile compounds of hydrogen and carbon, 
 and of these elements with oxygen, ammonia, water, and coke. 
 The heavier of the hydrocarbons, etc., constitute tar, and the 
 water and ammonia, ammoniacal liquor. The lighter of the 
 hydrocarbons are non-condensible, and constitute coal gas. 
 From tar, bisulphide of carbon, benzol, toluol, naphtha, creo- 
 sote, phenol, anthracene, naphthalene, and pitch are obtained 
 by distillation, at a gradually increasing temperature. 
 
Fuels. 6 1 
 
 These substances are very valuable products. The com- 
 position of the tar, and the proportions of its constituents, will 
 vary greatly with the temperature of coking. Low temperature 
 favours the production of a tar low in benzol, toluol, carbolic 
 acid, etc., and containing much heavy oily paraffin. A high 
 temperature favours the production of tars rich in benzol, etc. 
 These are much the most valuable. At high temperatures 
 above 1200 C. heavy hydrocarbons are decomposed, de- 
 positing part of their carbon, and being resolved into lighter 
 bodies and hydrogen. This is often seen in gas-retorts, the 
 inner surface of the retort, with which the gas has come into 
 contact, being covered with a layer of dense carbon thus 
 deposited. This is sometimes graphitic. 
 
 If the coal while coking can be sufficiently heated to 
 decompose these in its mass, the coke obtained will be denser, 
 stronger, and mqre brilliant in appearance. The yield of coke 
 will also be greater, in proportion to the amount of carbon 
 thus retained. It follows that the quality of the coke will 
 depend not only on the nature of the coal, but also on the 
 temperature of coking, and the rapidity with which it is 
 attained, those processes producing the best coke in which the 
 highest temperature is most rapidly obtained. 
 
 As in charcoal-burning, the heat necessary may be ob- 
 tained by partially or completely burning the volatile matters, 
 in contact with the coal, or outside the coking chamber. 
 
 NOTE. In all cases where the burning goes on in contact with the 
 substance carbonized, the air supplied should pass from the unburnt to 
 the burning body. 
 
 Coking in Heaps, "Meiler," or Mounds. The coal is 
 piled up round a temporary chimney loosely built of bricks, 
 with an iron cover-plate to regulate the air supply. In some 
 cases the operation is conducted like charcoal-burning, the 
 heap being covered with earth and moistened coal- or coke- 
 dust, and vents made as required. 
 
 In another method no cover is put on till the coking is completed, 
 the pile being ignited on the top and the fire proceeding downwards and 
 throughout the mass, air finding free ingress. The combustible volatile 
 matters distilling off from below, ascend and protect the coke from burn- 
 ing. When a thin film of ash appears on the surface, showing that the 
 
62 Metallurgy. 
 
 coke is burning, a cover of earth, coal- or coke-dust is applied at that part, 
 and thus repeated till the whole is covered and the coking complete. 
 Coking in long ridges is a similar process. 
 
 Coking in Kilns. These consist of two parallel walls 
 about 5 feet high and 8 feet apart, and 40 feet long. The 
 two ends are left partly open for charging, and bricked up 
 while coking is going on. The walls are pierced at a height 
 of 2 feet from the ground with openings, from each of which 
 a vertical flue rises to the top. These openings are about 
 2 feet apart. The kiln is charged by building up one end, 
 wheeling in damp slack, and ramming it down till level 
 with the flues. Passages are then built across the kiln by 
 leaning lumps of coal together, so as to leave a channel or 
 flue, or billets of wood are placed across, and, after charging, 
 withdrawn. The kiln is then filled up, the' larger stuff being 
 placed over the air-ways, and the smallest on top. The end 
 
 FIG. 25. 
 
 is bricked up, and the top covered up with loam and coal- or 
 coke-dust. The coking is started by combustibles (chips, etc.) 
 pushed in through the horizontal flues on one side. The 
 vertical flues on that side are closed by tiles, and the horizontal 
 flues on the opposite side (see Fig. 25). On igniting the 
 sticks, the draught passes in the direction of the arrows, and 
 the combustion extends across the kiln. The amount of air 
 supplied is regulated by the opening E. After a time, the 
 vertical flues on the opposite side are closed, and the hori- 
 zontal flues opened, those open before being stopped. The 
 direction of the air current is now reversed, and by repeating 
 
Fuels. 63 
 
 this at intervals of about two hours, the whole mass is gradu- 
 ally coked. 
 
 These kilns should be sheltered from wind, which will 
 otherwise interfere with their regular working. The same 
 objection of partially burning the coke applies to these kilns as 
 well as heaps. The operation lasts about eight days. When 
 complete, the end walls are taken down, after cooling, and the 
 coke discharged. It is needless to say that the weather wet 
 or dry influences the temperature, and thus the quality, of the 
 coke. The effect of moisture will be seen later on. 
 
 Coke Ovens. Coke is now generally made in ovens, i.e. 
 closed chambers. 
 
 They may be divided into 
 
 (a) Simple chambers, to the interior of which air is 
 admitted, to burn the products of distillation. 
 
 1. Cold-air Beehive, Rectangular. 
 
 2. Hot-air (Jones and Cox's). 
 
 (p) Ovens in which the distillation products are all burnt 
 outside the chamber. Appolt and Coppe'e ovens. 
 
 (c) Ovens in which the tarry matters and ammonia are 
 removed by condensation from the gases, and the non-conden- 
 sible gases burnt outside the chamber in flues. 
 
 1. Those in which some air is admitted to the chamber 
 
 (Jamieson). 
 
 2. Those from which air is rigidly excluded (Pau- 
 
 well's, Pernolet, Simon- Carves). 
 
 3. Those in which the gases are burnt by heated air 
 
 (Simon-Carves's improved, Bauer, Otto-Hoff- 
 mann). 
 
 Beehive Ovens. These ovens are very largely in use. 
 They yield coke of good quality, and can be employed with 
 all classes of coal, whether it swells on coking or not, a con- 
 sideration not to be overlooked. On the other hand, the 
 yield is less than ovens to which air is not admitted, owing to 
 burning of the coke, and much heat is lost and time wasted. 
 The prime cost is, however, low, it costs little for repairs, and 
 requires no large amount of skill. The chamber (Fig. 26) is 
 circular, 10 to 12 feet in diameter, 2 feet to spring of dome, 
 
64 Metallurgy. 
 
 and 7 feet to the crown from the floor. The ovens are 
 lined with refractory bricks, and are built in blocks of 40 or 
 50 in a double row, back to back, on a raised platform some 2 
 feet above ground-level. The block is surrounded by a strong 
 wall, and all spaces are filled up with sand or granulated slag to 
 retain heat. A rail-track runs along the edge of the platform. 
 Each chamber is provided with a short chimney, or com- 
 municates by a short flue with a wide common flue, which runs 
 between the two rows forming the block, and terminates in a 
 stack. 1 The short flues can be closed by dampers, as shown. 
 In front is an arched opening, some 3 feet high, which serves 
 as a door for discharging the coke. 
 
 Elevation part in Section. 
 
 Section through A.B. 
 
 FIG. 26. 
 
 The coal is introduced through the top, from hopper 
 waggons running on a rail track, and raked level. 
 
 The charging opening is covered, and the cover luted. In 
 some cases the coal is shovelled in from the front. 
 
 The chambers are hot from previous charges. After 
 charging, the front is loosely bricked up. If the oven is hot 
 enough, the bricks are smeared over with loam to exclude air. 
 If not, they are left uncovered for a time, and sometimes 
 openings are made near the bottom to admit air. Distillation 
 commences at once, but the gases are incombustible at the 
 temperature of the oven. In from ij to 3 hours ignition 
 
 1 This flue gets intensely heated, and ensures combustion of the pro- 
 ducts of distillation. The hot gases are passed under boilers, to raise 
 steam, before passing to the stack. 
 
Fuels. 65 
 
 commences, and the gases burn with a long, red, lurid flame, 
 and much smoke. A small opening is then made in the top 
 of the doorway to admit air above the coal, and burn the gases 
 in the oven. 
 
 The temperature rapidly rises. The dome-shaped roof 
 reflects the heat on to the mass of coal below, and this gradually 
 gets heated through. The gases distilling off from below are 
 partly decomposed in passing through the heated upper layers, 
 and deposit carbon. The air-supply to the oven is regulated 
 so as to burn the products in the oven as completely as possible 
 without admitting any excess. When the distillation begins to 
 slacken, the holes in front are stopped one by one, until the 
 doorway is again completely closed. The chimney is also 
 stopped, and the coke is left to itself some 1 2 hours to com- 
 plete and cool. The doorway is first taken partly down, a 
 hose-pipe introduced, and the coke quenched with water, in 
 the oven, below its igniting-point. The door is then completely 
 removed, and the coke discharged with rakes and forks. It 
 breaks into columnar masses, the axes of which are vertical. 
 This is owing to the direction of the coking, which takes 
 place downwards. These ovens make from 3 to 5 tons per 
 charge, and the yield is about 60 per cent. 
 
 The rectangular oven is exactly similar in principle, but 
 the chambers are rectangular. The coking is conducted in 
 the same manner. Sometimes the whole front of these 
 ovens is open, and the bottom is made slightly sloping. 
 It is then possible to remove the coke in one mass. For 
 this purpose, before introducing the coal, a couple of strong 
 iron drag-bars, turned up at each end, are laid on the floor 
 of the oven, with the ends projecting, and the coal charged 
 in on these. When the operation is complete, a windlass is 
 attached to the projecting ends, and the whole mass dragged 
 from the oven, being quenched as it comes forward on to the 
 platform in front. The oven is thus left much hotter, and less 
 heat and time are wasted. 
 
 In others, the front is arranged like a beehive, and some- 
 times an iron frame filled with fire-brick blocks, sliding in 
 guides, and counterpoised, is used to close the mouth of the 
 
 F 
 
66 
 
 Metallurgy. 
 
 oven. Two charges a week can be worked off from each 
 chamber. The coking itself occupies about 48 to 60 hours. 
 
 Cox's coking oven has a double-arched roof. The gases 
 escape through an opening in the front of the lower arch, and 
 pass back to the flue. No air is admitted in front, but air 
 drawn from the front, through flues in the brickwork, is ad- 
 mitted by openings at the back, above the coal. The air- 
 supply is regulated by a little sliding door over the opening of 
 the flue in front. In passing through the flues it gets heated, 
 and thus a higher temperature in the oven, and more rapid 
 coking result. Some 1 2 hours are saved by this arrangement. 
 In Jones's oven, the gases, after leaving the chamber, are 
 caused to pass through flues under the chamber, before passing 
 to the chimney, thus heating the coal from below. 
 
 All these structures are built in a massive manner, and spaces 
 filled up with sand, etc. , to retain as much heat as possible. 
 
 In ovens of the second class, air is not admitted to the 
 coking chamber, but the gases, etc., are burnt outside^ in flues 
 or spaces surrounding the chamber. 
 
 In the Appolt coke oven, the chambers are tapering, vertical 
 
 brickwork retorts of rectan- 
 gular form, 13 feet high, 4 feet 
 by i foot 6 inches at base, 
 and 3 feet 8 inches by 13 
 inches at top. These retorts 
 are built in two rows, 18 or 
 24 in a block, with a sur- 
 rounding space varying from 
 7 to 1 1 inches wide, and tied 
 together and to the sur- 
 rounding wall with bricks 
 for mutual support. They 
 are a single brick thick, and 
 are supported on two parallel 
 arches. The retort bottom 
 consists of a hinged iron 
 plate, which can be lowered 
 so as to discharge the coke into the arched vault below. It is 
 
 B 
 
 FIG. 27. Appolt Coke-oven. A, coking 
 chambers ; B, combustion space ; c, open- 
 ings for escape of volatile matters into 
 combustion space ; F, flues ; G, arched spaces 
 under retorts ; H, openings to admit air. 
 
Fuels. 67 
 
 covered with coke-dust during coking. The whole block is 
 surrounded by a strong wall containing the flues, of which there 
 are 16, 8 on each side 4 communicating with the top, and 4 
 with the bottom of the combustion space. These gather into 
 two horizontal side flues, F, which lead to a main flue. Each 
 of the small flues has a damper, so as to regulate the heat 
 through the block. 
 
 Passages communicating with the outside, supply air 
 for the combustion of the volatile matters expelled from the 
 coal in the retorts. These pass into the combustion space 
 through openings 5 inches by 2 at various levels, and there 
 meeting with air, are burnt, the heat passing by conduction 
 through the brickwork of the retort. 
 
 The chambers are charged from above. Each has a 
 capacity of about 1-5- ton of coal. The working is practically 
 continuous, fresh coal being introduced immediately a charge 
 is withdrawn, and the chambers are charged in regular order 
 to keep up the supply of gas. 
 
 In these ovens, burning of the coke is avoided, and the 
 yield is greater. The time is shortened by the large amount 
 of heat stored in the mass of the masonry, and the charging of 
 the coal into very hot retorts. On account of their slight 
 build, they are unsuitable for coking coals which swell on 
 heating, owing to their liability to damage from the force 
 necessary to dislodge the coke. 
 
 To prevent damage by expansion and contraction of the 
 brickwork, a space filled with sand or loose material is built 
 in the surrounding walls. 
 
 The coke produced is of good quality, and in larger 
 quantity, since air cannot find its way into the retorts. The 
 coal is coked in about 24 hours, owing to the large heating 
 surface presented by the retorts. The pressure of the coal 
 above increases the density of the lower portions. 
 
 In the Coppee coke oven (Fig. 28), the retorts are hori- 
 zontal arched chambers, open at both ends, and tapering 
 slightly from front to back. They are about 30 feet long, 
 i foot 8 inches wide at the back and i foot 5 inches in front, 
 and 3 .feet 6 inches high. They are closed at each end by 
 
68 
 
 Metallurgy, 
 
 two doors, one 3 feet and the other about i foot high, luted 
 round to exclude air while coking is going on. A series of 
 vertical flues, V, are built in the side walls of the chamber. 
 These communicate with the coking chamber, and by the 
 passage D with the air. At C they join the horizontal arched 
 flue H running under the chamber from end to end. The 
 gases burn in these flues, the air being heated by its passage 
 through the hot masonry above the ovens, and its supply 
 
 regulated by the dampers D. 
 A very high temperature is 
 attained. 
 
 The coal is introduced 
 through openings in the top 
 of the chamber. The ovens 
 are built in blocks of thirty 
 or more, and the flues all 
 merge into one main flue. 
 The distinguishing feature of 
 the Coppee ovens is that 
 they are worked in pairs. It 
 will be observed (Fig. 28) that 
 the flues from both chambers 
 A pass into H. This flue 
 joins H' by a passage at the 
 back, so that the gases pass 
 backward through H and for- 
 ward through H' before pass 
 ing into the main smoke-flue 
 J at P. In this way, the 
 gases from each aids the coking of the other charge. One 
 retort of the pair is freshly charged when the charge in the 
 other is about half coked and is giving off volatiles rapidly. 
 The surplus heat from the latter, passing under the former, 
 increases the rapidity of coking in the earlier stages, and 
 while the amount of volatiles from the latter diminishes as 
 the coking nears completion, the newly charged one is dis- 
 tilling rapidly, and the surplus heat maintains the temperature 
 at its highest pitch to the end. A more complete combustion 
 
 F/G. 28. 
 
Fuels. 69 
 
 is also obtained of the volatiles given off at the beginning 
 of thre coking. The coke is pushed out by a ram from the 
 back, and quenched as it leaves the chamber. In coking 
 very bituminous coals in the Coppee, air can be admitted into 
 the chamber if desired. These ovens are largely used in 
 South Wales, yield excellent coke, and are less liable to damage 
 than the Appolt. They are suitable for the treatment of 
 crushed and washed coal. 
 
 In the ovens at present considered all the volatile matters 
 have been burnt. As has been shown, these contain many 
 valuable constituents, which, could they be collected without 
 impairing the character of the coke, would form an important 
 
 FIG. 29. Simon-Carves's Coking-oven. A, coking chamber : B, charging openings ; 
 c, flues ; D, pipe for removing gases, etc. ; E, door ; F, fireplace ; G, gas-main 
 supplying ovens ; H, main flue. 
 
 source of income. The whole matter rests on a question of 
 temperature, whether the necessary heat can be obtained with 
 sufficient rapidity to produce good coke, after the condensible 
 parts (tar) of the volatile matter and the ammonia have been 
 removed. This problem has been successfully solved by ovens 
 in which the regenerative or recuperative principle is applied. 
 
 The Simon-Carves oven may be taken as a type of its 
 class. It consists of a rectangular arched chamber (Fig. 29), 
 23 feet long, 6 feet 6 inches high, and 19^ inches wide, and 
 takes a charge of about 4^ tons. In the top, at B, are two 
 charging openings, through which the coal is introduced from 
 
7O Metallurgy. 
 
 hopper waggons. These are closed while coking is going on. 
 In the middle of the roof is a lo-inch opening, by which the 
 gases are drawn off through the valve D, and pass into the 
 jo-inch iron gas-main above the battery of ovens. The gases 
 are drawn off by an exhauster, and passed through a series of 
 iron pipes, which are cooled by water, to condense the tar. 
 They next pass through scrubbers and washers, in which the 
 ammonia is dissolved out, and the gases are then led back to 
 the ovens, under which they are burnt They enter by nozzles 
 into the fireplace E, on the bars of which a thin fire was 
 formerly kept. When air heated by regenerators is supplied 
 this is unnecessary, and the fireplace is abolished. 
 
 Under the chamber are two flues, C C'. The products of 
 combustion pass backward along C, and return forward by C. 
 They then rise by the vertical flue to the highest of the 
 horizontal flues in the side of the chamber, through which 
 they pass down in a zigzag manner, and away into the main 
 flue H. The recuperator for heating the air by means of the 
 waste heat consists of a series of flues,*smoke-flues, and air- 
 heating flues, alternating with each other 
 
 The whole of the ovens being at work (on gas), the working 
 is practically continuous, fresh coal being introduced immediately 
 after the removal of the coke. In starting, it is necessary to 
 heat the block of ovens to a coking heat by burning off a few 
 charges in the ordinary manner, without removal of tar, etc. 
 The combustion of the uncondensibles, after this temperature 
 has been reached, is sufficient to maintain it. The ovens are 
 built in blocks, and a high stack produces the necessary draught 
 through the flues. The yield is 15 per cent greater than the 
 beehive oven, and the coke is of good quality, although not 
 quite so dense and silvery in appearance as is produced in some 
 other ovens. The recuperator ovens work off a charge in 48 
 hours. The coking is uniform, a high temperature being main- 
 tained throughout, and the character of the coke varies little 
 on account of the thin slices in which it is coked. The familiar 
 columnar form of beehive coke is missing. 
 
 In the Otto-Hoffman, Bauer, and other ovens, regenerators 
 of chequer work are employed, which require reversal, and 
 
Fuels. 71 
 
 consequently greater attention, but, so far as economy of heat 
 is concerned, are more effective. 
 
 All ovens of this type are built of most refractory bricks. 
 One of the main difficulties is the burning out of the flues. 
 
 Qualities of Coke. Good coke should be 
 
 (1) dense and compact 
 
 (2) firm, not friable ; 
 
 (3) uniform in character ; 
 
 (4) as free from sulphur as possible ; and 
 
 (5) should have good cell structure; 
 
 in order that it may burn freely, and develop great local heat 
 under strong and hot blast, and not crumble and block the air- 
 ways under the pressure of material above. The quality pre- 
 ferred by iron smelters is that which has a silvery appearance, 
 strongly marked. 
 
 Sulphur in Coke. In coking, much of the sulphur in the 
 coal is expelled as carbon bisulphide and sulphuretted hydrogen. 
 Water thrown on red-hot coke causes sulphuretted hydrogen 
 to be generated from .sulphides it contains, and any one who 
 has stood near a mass of coke while being quenched will 
 appreciate the offensive smell of this gas which prevails in 
 the vicinity. The addition of salt, carbonate of soda, lime, 
 manganese dioxide, and other bodies, has been made to the 
 coal to be coked, with a view to retain the sulphur as sulphides 
 not decomposed by iron, that is, in a form in which it would 
 not pass into the metal smelted with it. These efforts are 
 unsuccessful from various causes. Quenching has only a 
 superficial effect, as the sulphides are only decomposed by 
 water at red heat. Proposals have also been made to pass 
 superheated steam through the mass while coking. As will 
 be seen (p. 75), at a high temperature, the coke itself decom- 
 poses the water, and a less yield is obtained. 
 
 Coking of Non-caking Coal. Coke may be produced from 
 non-caking coal by mixing it with pitch, tar, etc., before 
 coking, or by mixing it with strongly caking coal. 
 
72 Metallurgy. 
 
 CHAPTER VI. 
 
 GAS FUEL, 
 
 THREE kinds of gas are employed for heating furnaces. 
 
 (a) Air gas, or producer gas, made by passing air through 
 a deep layer of carbonaceous matter, whereby carbon monoxide 
 is produced, mixed with nitrogen (from the air), and smaller 
 amounts of other gases, dependent on the fuel used. 
 
 (b) Water gas, made by passing steam through incandescent 
 carbonaceous matter, whereby the water is decomposed and 
 carbon monoxide and hydrogen generated. 
 
 (c} Natural gas, consisting mainly, of marsh gas. 
 The advantages of gas over solid fuel are 
 
 1. More complete combustion can be ensured. 
 
 2. Better control of the temperature is obtained. 
 
 3. Greater uniformity of heating. 
 
 4. In regenerative furnaces in which it is employed a 
 great saving of fuel takes place, and high temperatures can be 
 more readily attained. 
 
 5. Better control is obtained over the atmosphere of the 
 furnace, whether oxidizing or reducing, etc. 
 
 Producer Gas. When a limited supply of air is passed 
 through a deep layer of incandescent carbonaceous matter, 
 the oxygen is converted into carbonic oxide, CO. This, 
 mixed with the nitrogen of the air and small quantities of CO 2 
 formed, and the products of distillation of the substance 
 employed hydrogen, hydrocarbons, etc. constitute producer 
 gas. Moisture entering with the air is decomposed, hydrogen 
 and CO resulting, which latter mixes with and enriches the gas. 
 
 By this means the whole of the substance fixed carbon 
 as well as volatile matters can be gasified, the only residue 
 being, as in burning, the ash. 
 
 The composition of gas thus obtained varies somewhat 
 according to the mode of production and nature of the material 
 used. If the gas be cooled to remove water vapour, even 
 wood sawdust, or any poor fuel, may be employed to produce 
 
Gas Fuel. 
 
 73 
 
 high temperature by combustion of the gas in regenerative 
 furnaces. 
 
 Three types of producers are in use. The original Siemens 
 producer, with a grate, in its present modification is shown in 
 Fig. 30. 
 
 The fuel is contained in an arched chamber, C, of the 
 form shown, the bottom of which consists of fire-bars. Under- 
 neath is an ash-pit, A, closed by the folding doors D, through 
 which the steam-jet blast-pipe P passes. The bottom of the 
 ash-pit is a water-trough, in which the ashes are cooled, and 
 the steam generated passes up into the producer. 
 
 The gases pass off by the opening O into a vertical shaft 
 
 H t . s =4, 
 
 . II, Uptake 
 
 1 1 L_ ~ \ Ground Line 
 
 S, called the " uptake." H is a hopper, from which fresh fuel is 
 charged ; 1 1 are inspection openings, closed while working ; and 
 B is a bridge hanging down from the top, so as to prevent any 
 air which may be introduced while charging from forming an 
 explosive mixture by mixing with the gas without passing through 
 the fuel. The top of the hopper is provided with a sliding 
 door, which is shut before lowering the cone, to allow the fuel 
 to descend into the chamber. The bridge also promotes the 
 decomposition of the heavy tars by causing the products of 
 distillation to descend through the heated lower portions. 
 These chambers are usually built in blocks of four, and the 
 uptake for the block is divided into four sections, each of 
 
74 
 
 Metallurgy. 
 
 which has a damper, so that any one of the producers may be 
 stopped without interfering with the others. 
 
 The Wilson gas producer is an example of the cupola 
 type of gas producers, without a grate. It is cylindrical in 
 form, and consists (Fig. 31) of an outer casing of iron plate, 
 lined with refractory brickwork. The fuel is introduced from 
 the hopper at the top, which is provided with a sliding cover. 
 The cone is counterbalanced. The bottom of the producer 
 
 FIG. 31. 
 
 is of brickwork. A raised hollow ridge of brickwork crosses 
 the bottom of the chamber. 
 
 The air forced in by the steam-jet S blowing into the 
 mouth of the trumpet tube as shown, is delivered into this 
 flue, and enters the chamber by the ports B on either side. 
 Two cleaning doors, A, are provided for the removal of the 
 clinker at intervals. While this is being done, the fuel is 
 supported on iron bars thrust across the chamber through 
 doors provided for that purpose, the steam being meanwhile 
 shut off. In the upper part of the producer is a circular flue, 
 which communicates with the fuel chamber by the openings 
 
Gas Fuel. 75 
 
 C. From this flue the gas is led away by the downtake D 
 to the gas culverts. Openings round the top of the producer 
 permit of the interior being inspected. The chamber is kept 
 full of fuel, and, as the products of distillation must descend 
 through the heated mass before getting away, the tars are 
 largely decomposed. 
 
 All steam and water vapour entering a producer is reduced 
 to CO and H (H 2 O + C = CO -f H 2 ). The oxygen obtained 
 in this way is not mixed with incombustible gases (N), as in the 
 case of air, and the gas is accordingly enriched. But as the 
 same amount of heat is absorbed in reducing the water as is 
 given out in its production, heat will be absorbed, and the 
 producer cooled accordingly. Hence the amount of steam 
 admissible is limited. 1 
 
 To decompose 9 parts of water requires 34>462 heat units 
 
 (9 parts of water yield I of hydrogen and 8 of oxygen) 
 8 parts of oxygen combining with 6 of carbon to form 
 
 CO give out 2473 x 6 = 14,838 ,, 
 
 Balance lost . . . 19,624 ,, 
 
 The quantity of hydrogen converted to CH 4 is practically 
 nil. Some H 2 S is generated. 
 
 The fuel generally used is washed coal slack, but car- 
 bonaceous matter of any kind may be employed. When coal 
 is employed, the distillation products are mixed with the gas. 
 The producers are generally at some distance from the furnaces, 
 and the gas conveyed to them in culverts. In some cases, the 
 gas producer takes the place of the fireplace in a reverberatory 
 furnace, as is the case with the Bicheroux and Boetius furnace. 
 
 In Head's new furnace, arrangements are made whereby part of the 
 CO 2 produced by burning the gas is caused to pass through the producer. 
 The CO 2 present is again reduced to CO. There is, therefore, a saving 
 in fuel, the carbon in the CO 2 being used again. Heat is, of course, 
 absorbed in its reduction. This is largely furnished by the excess of 
 heat in the gases when they enter the producer. It would be impossible 
 to return the whole of the CO 2 continuously for regeneration into CO to 
 the producers. The proportion of nitrogen in the gas is unaltered. 
 
 It will be observed that in converting solid fuel into gas, 
 part of the heat that given out by the carbon in burning to 
 
 1 Practical tests show that the best results are obtained by using 5 per 
 cent, of steam. 
 
Metallurgy. 
 
 CO in the producers is lost unless the gas passes without 
 cooling to the furnace. The great advantages derived from 
 its use, and the waste heat recovered in the regenerators, more 
 than compensate for this loss, and a great saving of fuel is 
 effected where high temperatures are required. For low 
 temperatures, gas fuel is less satisfactory. 
 
 Water Gas is a mixture of carbon monoxide and hydrogen, 
 produced by passing steam through incandescent carbonaceous 
 matter. 
 
 Natural Gas consists mainly of marsh gas, and is given 
 out in immense quantities in oil regions. It burns with 
 only a faintly luminous flame. It is applied very exten- 
 sively in Pennsylvania for furnace purposes. The supplies are 
 said to be falling off. 
 
 COMPOSITION OF GASEOUS FUELS. 
 
 
 Coal 
 
 gas. 
 
 Sie- 
 mens 
 gas. 
 
 Wilson 
 gas 
 
 Blast- 
 furnaces 
 gases. 
 
 Natural 
 gas. 
 
 Water 
 
 gas. 
 
 Carbon monoxide 
 Carbon dioxide .... 
 
 7-82 
 
 47-6 
 
 24-20 
 
 4-20 
 8-20 
 
 26-44 
 
 5-30 
 H-32 
 
 26-29 
 
 2'0 
 
 0-8 
 
 44*4 
 
 2-86 
 49*61 
 
 Marsh gas . . . 
 Other hydrocarbons . . .- 
 
 41-53 
 3-05 
 
 2-20 
 6l"2O 
 
 2'34 
 
 2- 3 
 
 9575 
 i '45 
 
 
 
 
 
 ' 
 
 j y 
 
 
 jj 
 
 Percentage of combustible 
 matters 
 
 lOO'O 
 
 34-60 
 
 40-10 
 
 30-55 
 
 99-2 
 
 94'S 1 
 
 CHAPTER VII. 
 
 IRON. 
 
 THIS metal is employed in the arts in three forms : as cast 
 iron, wrought iron, and steel of various kinds. Pure iron is a 
 soft, greyish-white metal, very malleable and ductile, and highly 
 tenacious. It is prepared by electrolyzing a solution of iron 
 
Iron. 77 
 
 and ammonium chlorides, sulphates, or oxalate, or by reducing 
 precipitated ferric oxide by heating it in a current of hydrogen. 
 Prepared thus at a low temperature, it takes fire spontaneously 
 in air, but does not if prepared at a high temperature. After 
 fusion, pure iron exhibits a crystalline, scaly fracture. It is 
 softer than wrought iron, and is not affected by heating to 
 redness and quenching in cold water. It is scarcely acted on 
 by sulphuric and hydrochloric acids in the cold, but dissolves 
 on heating. It is highly magnetic, and welds readily. Its 
 specific heat is o 1 !^, and its specific gravity 7*675. It melts 
 at a lower temperature than platinum about 1600 C. 
 In mass it is unaffected by dry or moist air, oxygen, or 
 water, if pure and free from carbonic acid gas. In the 
 presence of this body it is readily attacked. At a red heat it 
 is rapidly oxidized in air, forming a scaly coating of oxide. 
 Red-hot iron decomposes water, liberating hydrogen. 
 
 3 Fe 4- 4H 2 O = Fe 3 O 4 4- 4H 2 . 
 
 When molten, it dissolves or occludes various gases in 
 considerable quantities. Hydrogen, carbon monoxide, and 
 nitrogen are thus taken up and given out on cooling. 
 
 The above physical properties are present in a greater or 
 less degree in cast and wrought iron and steel, the extent to 
 which they are modified depending on the purity of the 
 substance. 
 
 These bodies consist of iron containing varying proportions 
 of carbon, silicon, manganese, sulphur, and phosphorus, and 
 occasionally copper, arsenic, tungsten, chromium, "and other 
 metals. 
 
 Iron and Carbon. The great differences in the properties 
 of cast and wrought iron and steel are mainly due to the 
 presence of carbon in the metal, depending on the amount and 
 the manner in which it exists in the iron. 
 
 The maximum amount of carbon taken up by pure iron is 
 stated by Riley to be 4 75 per cent. In cast iron containing 
 manganese a little over 5 per cent, may be present. Steel may 
 contain up to i '8 per cent., while the carbon in wrought iron 
 seldom exceeds 0-25, and may fall as low as 0-05. 
 
78 Metallurgy. 
 
 Carbon may be imparted to iron 
 
 (1) by heating it, embedded in charcoal, at a high tempera- 
 
 ture for a prolonged period ; 
 
 (2) by melting iron in contact with carbon, which it dissolves 
 
 (see Cast Steel) ; 
 
 (3) by the decomposition of carbon monoxide, carbon 
 
 being deposited and carbonic acid ultimately pro- 
 duced (though not by a simple reaction), as in the 
 blast furnace ; 
 
 (4) by heating it in contact with gaseous or liquid hydro- 
 
 carbons, such as paraffins, which are decomposed ; 
 
 (5) by the decomposition of cyanides, e.g. potassium ferro- 
 
 cyanide (yellow prussiate of potash), K 4 FeC 6 N 6 , as 
 in case-hardening. 
 
 When cast iron cools from fusion, the carbon may remain 
 uniformly distributed through the mass combined carbon 
 or a portion of it may separate out in scales resembling graphite. 
 The extent to which separation occurs depends on the rate of 
 cooling and the quality of the metal Slow cooling, and the 
 presence of silicon and aluminium in the metal, favour the 
 separation, while manganese retards it. When rapidly cooled, 
 nearly all the carbon remains in the combined form. The 
 properties of the iron are modified according to the amount 
 and manner in which the carbon is held. 
 
 Combined Carbon hardens the metal, lowers its melting- 
 point, destroys its malleability and welding power, and tends 
 to make it brittle. The extent to which these effects are pro- 
 duced depends on the amount. In white cast iron, containing 
 as much as 3 per cent.> the metal is brittle, breaks with a 
 silvery-white fracture, melts more readily, and passes through 
 a pasty stage in fusing. It is extremely hard, and this property 
 is permanent. In steel for cutting-instruments ^ the amount 
 varies from 0*5 to 1*5 percent. The hardness and fusibility are 
 increased, the malleability and the welding power diminished 
 in proportion to the amount of carbon present. In this case, 
 however, owing probably to its freedom from other impurities, 
 the degree of hardness can be modified by special treatment : 
 heating to redness and slow cooling rendering the metal soft, 
 
Iron. 79 
 
 while rapid cooling, such as quenching in cold water, etc., 
 renders it hard. The degree of hardness can be modified by 
 subsequently heating it to a lower temperature (see Tempering 
 Steel). When hardened, the metal is brittle. The tensile 
 strength and elasticity of steel are very high. It is magnetized 
 with greater difficulty than pure iron, but retains its magnetism. 
 
 In wrought iron and mild steels, the carbon exercises an 
 influence in the same direction in proportion to the amount 
 present Below 0-3 per cent, the metal is not sensibly hardened, 
 even on rapid cooling. 
 
 Graphitic Carbon is met with only in cast iron, and occa- 
 sionally in steel. It reduces the strength of the metal by 
 interposition between the particles, and does not affect the 
 grains of iron themselves. Hence some very grey pig irons 
 are exceedingly soft, and their melting-points very high. 1 
 
 When iron is dissolved in hydrochloric or sulphuric acid, the combined 
 carbon passes off in combination with the hydrogen as foul-smelling com- 
 pounds, soluble in alkali. Graphitic carbon remains as insoluble. Com- 
 bined carbon dissolves in nitric acid, giving a brown solution, the depth of 
 colour imparted depending on the amount present (Eggertz Colour Test). 
 
 Silicon occurs in cast iron in amounts varying from 0-5 
 to 12 per cent., being reduced in the furnace. The amount 
 present depends on the working conditions of the furnace 
 temperature, rate of driving, proportion of fuel, etc. It 
 
 1 The relations existing between carbon and iron and, in fact, be- 
 tween iron and other elements commonly associated with it is a problem 
 presenting much difficulty. The generalization given above combined 
 and free carbon only expresses part of the truth. When white cast irons, 
 free from manganese, are heated for a prolonged period, at a high tem- 
 perature, but below fusion, embedded in red hematite, the characteristic 
 brittleness is lost, and the metal becomes more or less malleable (see 
 Malleable Castings). It would appear since no appreciable diminution 
 in the amount of carbon present takes place that the carbon contained in 
 the metal separates from it and remains distributed in a finely divided state 
 throughout the mass,/h? but not crystalline. 
 
 Further, the carbon in hardened steel differs from that in the 
 annealed or unhardened metal. The two states being known as "harden- 
 ing" and "carbide" carbon respectively. Probably in both the latter 
 cases the carbon is in combination, and both exist in white iron. There 
 are, therefore, four conditions in which carbon exists in iron. 
 
 -p j (a) graphitic, in grey cast iron ; (b) amorphous (free but non- 
 " I crystalline), in annealed castings. 
 
 Combined 
 
8o Metallurgy, 
 
 renders cast iron more fusible, weak, and brittle. The extent 
 to which it occurs in other forms of iron will depend on the 
 degree of purification. In small quantity, it hardens and 
 weakens the metal. It lowers the melting-point, and its 
 presence in mild steel favours the separation of occluded gases. 
 In cast iron it tends to the separation of the carbon as graphite. 
 
 Manganese. This metal is reduced in the blast furnace. 
 Some pig irons made for special purposes ferro-manganese 
 contain up to 85 per cent, of metallic manganese. Pig 
 irons containing more than 7 and less than 20 per cent, are 
 known as " Spiegeleisen " (German = " mirror-iron "), so called 
 from the bright crystalline fracture. With larger percentages, 
 the structure becomes more granular. Ordinary pig iron 
 contains from o'o to about 2*5 per cent. Its effect is to whiten 
 the iron by retarding the separation of graphite. Manganese 
 lowers the melting-point, and cast iron containing it does not 
 pass through a pasty state before fusion. 
 
 Manganese is looked upon as the principal physician of 
 the steel maker. Iron free or nearly free from carbon, which 
 has been exposed to an oxidizing atmosphere in a fused state 
 at a high temperature, loses its nature and becomes rotten. 
 It has the properties of burnt iron. This is probably due to 
 the formation of a suboxide of iron, which is diffused through 
 the mass. Manganese has a greater affinity for oxygen than 
 has iron, and, on its addition, reduces the oxide, forms 
 manganous oxide, and passes into the slag. The iron regains 
 its malleability, etc. The addition made for this purpose 
 always slightly exceeds that required to remove the oxygen, 
 the excess necessary depending on circumstances, notably on 
 the amount of sulphur present. It varies from 0-2 to 0-5. 
 Manganese is consequently found in all mild steels made by 
 the Siemens, Bessemer, and other direct processes. It has 
 also a corrective action on the effects of sulphur. 
 
 Pig irons containing manganese are usually freer from 
 sulphur. 
 
 Irons containing much manganese lose their magnetic 
 property. 
 
 Sulphur is the greatest enemy of the iron and steel maker, 
 
Iron. 8 1 
 
 on account of its pernicious effects and the difficulty of 
 removal. It combines chemically with iron when heated with 
 it, forming several well-defined sulphides. Ferrous sulphide 
 (FeS),used for preparing sulphuretted hydrogen, and iron pyrites 
 (FeS 2 ), are the best known. Its presence in malleable iron 
 and steel induces red shortness that is, the metal cannot be 
 worked at or above red heat, but cracks under the hammer. 
 It renders iron more difficult to weld, and hence the necessity 
 of clean fuel, free from sulphur, for smithy purposes. 
 
 The removal of sulphur in purifying pig iron is difficult, 
 and requires that the slag shall be highly basic, and the fluxes 
 used free from sulphur. In pig iron its effect is to throw out 
 carbon as a scum, and whiten the iron, making it harder and 
 stronger. Up to 0*3 per cent, it is not objectionable in foundry 
 irons, for castings which do not require fitting and turning, 
 such as columns, etc. Such irons, however, cast indifferently, 
 as they flow sluggishly, and contract on solidifying. 
 
 Phosphorus. This element combines with iron with great 
 readiness, forming phosphides. It is reduced from the phos- 
 phates in the charge, in the blast furnace, and taken up by the 
 iron. It renders the metal more fusible and more fluid when 
 molten, and causes it to expand slightly on solidifying. Irons 
 containing it are employed in making fine light ornamental 
 castings. The metal is weaker and more brittle. In ordinary 
 pig iron it is present from 0*0 to i'5 per cent, depending on 
 the nature of the ore and the fluxes used. Practically all the 
 phosphorus in the charge passes into the metal, unless the 
 slags are very highly basic, and contain a large proportion of 
 oxide of iron, as in the processes for making malleable iron 
 direct from the ore. Its effect on malleable iron and steel is 
 to increase the hardness more rapidly than does carbon. This 
 hardness is not affected by heating and cooling, as is the case 
 with that element. Steel and iron containing it are cold short, 
 and brittle, although they work well when heated. Mild steel 
 should not contain more than o'o8 per cent. The presence 
 of o'2 to o'3 per cent, in malleable iron does not sensibly 
 diminish its tenacity or working properties, owing probably to 
 its structure. 
 
82 Metallurgy. 
 
 Iron and Nickel. Up to 1^5 per cent, nickel does not 
 produce any increase in the hardness of iron, but increases its 
 toughness and diminishes the tendency to corrosion. Nickel 
 steel is now being used for armour plates. 
 
 Chromium up to 1-5 per cent, increases the hardness, tena- 
 city, and ductility, without diminishing the toughness. Hence 
 its employment in shell metal. Ferro-chrome is an alloy of 
 iron and chromium used for introducing it into the steel. 
 
 Aluminium is introduced for producing sound castings in 
 mild steel. It is also added to cast iron for foundry purposes, 
 producing finer-grained and stronger castings. 
 
 Tin renders iron cold and red short, and unweldable. 
 
 Copper in small quantity renders iron red short, and lowers 
 the tenacity 
 
 Tungsten hardens iron and diminishes its malleability. 
 Mushet's steel is an alloy containing from 8 to 9 per cent, of 
 tungsten. It does not require quenching, but is self- 
 hardening that is, cannot be annealed and rendered soft by 
 prolonged heating. It is brittle, almost silvery white in colour, 
 and very fine grained. Molybdenum is being introduced for 
 the same purpose. 
 
 Oxides of Iron. Three oxides of metallurgical importance 
 are known. Ferrous oxide (FeO), ferric oxide (Fe 2 O 3 ), and 
 magnetic oxide of iron (Fe 3 O 4 ). 
 
 Ferrous Oxide (FeO) is not known in the free state. In 
 combination it forms salts as ferrous sulphate (copperas, or green 
 vitriol) and carbonate of iron. It has a great affinity for silica, 
 with which it combines to form a fusible silicate (2FeO.SiO 2 ). 
 This is the principal constituent of many slags produced in 
 refining iron, and in copper and lead smelting. When slags 
 consisting of silicate of iron are heated with carbon, as in the 
 blast furnace, a large proportion of the iron is reduced to the 
 metallic state. The resulting metal is known as "cinder" pig. 
 
 Ferric Oxide (Fe 2 O 3 ). This occurs in a hydrated form 
 (with water) as iron rust, and naturally as various ores of iron. 
 It forms in combination with acids the ferric salts. It has 
 little affinity for silica. If ferrous silicate is roasted in an 
 oxidizing atmosphere, the FeO is largely converted into Fe. 2 O 3 , 
 
Iron. 83 
 
 which separates out. When Fe. 2 O 3 is strongly heated it gives 
 up oxygen, and is converted into Fe 3 O 4 . It is reduced to the 
 metallic state by carbon, carbon monoxide, hydrogen, and 
 cyanogen, and oxidizes both silicon and manganese. 
 
 Magnetic Oxide of Iron (Fe 3 O 4 ) occurs native as magnetite. 
 It is the principal constituent of the scale which forms on 
 red-hot iron when exposed to the air, or when steam is passed 
 over red-hot iron. It is attracted by a magnet. It fuses at 
 almost white heat, and on solidifying forms a bluish-black, 
 crystalline, lustrous mass, and is present to a large extent 
 in "best tap cinder," the slag from furnaces for reheating irdn. 
 Its oxidizing power is less than ferric oxide. It is unaffected 
 by exposure, and a layer consequently protects iron from rust- 
 ing, if the coating is dense and continuous. Iron is, however, 
 electro-positive to it, and if the coating is imperfect, and the 
 iron is exposed, in the presence of moisture, an electrical action 
 is set up which results in the rapid corrosion of the metal. 
 
 BarfTs Process for protecting iron articles from rust, 
 consists of coating articles with a film of magnetic oxide by 
 bringing them, at a full red heat, into contact with superheated 
 steam. A firmly adherent, dense, but thin coating is thus 
 formed. 
 
 Bower's Process. In this process the coating is formed 
 by heating the articles in a gas furnace, the atmosphere of 
 which is made alternately oxidizing and reducing, by regu- 
 lating the air-supply. The oxidation produces a thicker 
 but more porous coating, the outer layers of which contain 
 Fe 2 O 3 . This is afterwards reduced to Fe 3 O 4 , and the coating 
 consolidated and rendered more adherent by the reduction at 
 the high temperature which prevails. 
 
 Ores of Iron. The principal ores of iron are magnetite, 
 red and brown hematites, specular iron ore, spathose, clay 
 ironstone, and black-band ore. 
 
 Magnetite (Fe 3 O 4 ), consists of iron and oxygen. When 
 pure, it contains 72*4 per cent, of metal. It is black or steel- 
 grey in colour, and often crystalline or granular. It gives a 
 black mark on unglazed porcelain (streak), is readily attracted 
 by a magnet, and often magnetized. It constitutes the " lode- 
 
84 Metallurgy. 
 
 stone." 1 Its specific gravity is 5-1, and its crystals regular 
 octahedra. It occurs abundantly in Norway, Sweden, United 
 States, Canada, Siberia, etc, in mass. 
 
 Magnetic or titaniferous iron sand consists of grains of 
 magnetite with a small quantity of oxide of titanum, derived 
 from the weathering of certain felspathic rocks in which it 
 occurs largely. The lighter matters have been washed away, 
 and the heavy magnetite, with the titanic oxide and other 
 heavy matters present has accumulated. Deposits occur on 
 the shores of Labrador, New Zealand, West Indies, Bay of 
 Naples, etc. 
 
 Red Hematite, so called on account of its red colour and 
 streak, consists of ferric oxide (Fe 2 O 3 ), and contains, when pure, 
 70 per cent, of iron. It occurs both in dense and earthy forms. 
 Kidney iron ore is a dense variety which occurs in masses 
 with a rounded exterior. The specific gravity is 5. It is 
 usually very pure, containing only silica (quartz) as impurity. 
 The more earthy forms of the ore are less pure. The soft 
 varieties are used for fettling puddling furnaces under the 
 name of " puddlers' mine." It occurs in Cumberland (round 
 Whitehaven), Lancashire (Ulverstone), Glamorganshire, and 
 Shropshire, etc., Canada. United States, Spain and Algeria, 
 Saxony, Bohemia, and the Hartz mountains. 
 
 Specular Iron Ore is crystallized ferric oxide, and has the 
 same composition as red hematite. It has a steely-grey colour, 
 often darker on the surface, and iridescent. The crystals are 
 modified rhombohedra, often, as in the black incrustations on 
 hematite, thin plates. The streak is red, and the specific 
 gravity 5 '2. " Micaceous iron ore," and "iron glance," are names 
 given to a variety with a grey metallic lustre which readily 
 separates into thin plates or scales. Some varieties are ground 
 up for paint, on account of their high density. This ore 
 occurs in Devonshire, Elba (the mine has been worked for 
 2000 years), Russia, Spain, Nova Scotia, and elsewhere. 
 
 Brown Hematite. Brown iron ore, Limonite includes a 
 series of substances consisting of hydrated ferric oxide ferric 
 
 1 Anglo-Saxon liedaii, " to lead." 
 
Iron. 8 5 
 
 oxide and water, chemically combined. It contains, when pifre, 
 60 per cent, of iron. 
 
 Brown hematite proper is a heavy dense form, sometimes 
 with radiating structure and shining exterior like kidney ore. 
 It is generally very pure. Gothite is of an iron-black colour, with 
 crystalline structure. Wood hematite resembles wood in being 
 made up of alternate light and dark concentric layers. Bog- 
 iron ore is a light, porous, dark-brown mass, often very impure. 
 Lake ore is obtained in Sweden and Finland from the bottoms 
 of shallow lakes by dredging with a net. Umber is a dark 
 brown, light, earthy body, containing often manganese, copper, 
 and cobalt. Yellow ochre is so called from its yellow colour ; 
 it is soft, earthy, and unctuous. All varieties give a yellow or 
 brownish streak. The purity of the ores varies greatly. The 
 Forest of Dean ore from the coal measures contains 89 per 
 cent. Fe. 2 O 3 and 10 per cent, of water, and yields exceptionally 
 pure iron 
 
 The brown hematites of the North of Spain, resulting 
 from the decomposition by atmospheric influences of veins 
 of spathic ore, are very pure, and often contain much manga- 
 nese. They are imported for making manganiferous pig iron, 
 and for use in steel-making. The Northamptonshire and 
 Lincolnshire ores are a light yellow and earthy, often full of 
 fossil shells from the oolite. Bog-iron ore yields iron only fit 
 for foundry purposes, owing to the large amount of sulphur 
 and phosphorus contained. The moisture present in brown 
 hematites varies from 9 to 14 per cent. In France, Germany, 
 Spain, and Canada, the principal ores smelted are of this 
 nature. Deposits occur in Devon, Glamorgan, Northampton, 
 Lincoln, Cumberland (Alston Moor), and Durham, India, etc. 
 
 Spathose (spathic or sparry iron ore), so called on account 
 of its sparry appearance, consists of crystallized ferrous car- 
 bonate, FeCO 3 (ferrous oxide combined with carbonic acid). 
 When pure it is of an ashen-grey colour, and contains 48 per 
 cent, of iron. The streak is white. It generally contains more 
 or less carbonate of lime, magnesia, and manganese, which 
 crystallize in the same form, and is often more or less 
 decomposed by weathering, with the formation of hydrated 
 
86 Metallurgy. 
 
 ferric oxide, which colours it brown. Some samples contain 
 50 per cent, of carbonate of manganese, and it was from these 
 ores that manganiferous pig iron was first produced. The 
 manganiferous brown ores of the North of Spain have been 
 produced by weathering from spathic ore. They occur in 
 Somerset, Durham, Cornwall, Isle of Man, Styria, Carinthia, 
 Westphalia, Prussia, etc. 
 
 Clay Iron Stone includes all ores of a compact, earthy, 
 stony character, varying in colour from light grey to brown. 
 
 They consist of ferrous carbonate mixed with more or less 
 clayey matter. Sometimes the deposit is nearly pure carbonate 
 of iron, but in an uncrystallized state. The brown colour is 
 due to partial decomposition with the formation of the hydrated 
 oxide (brown hematite). This ore, which is the most impor- 
 tant British ore, occurs (i) in nodules, sometimes very large, 
 made up of successive layers, in clay ; and (2) in beds, in the 
 coal measures and oolitic strata. The iron present varies 
 from 20 to 37 per cent. The ore is of low specific gravity and 
 of a stony appearance, but on calcining becomes black owing 
 to the formation of Fe 3 O 4 . Lime, magnesia, and manganese, 
 as carbonates, etc., iron pyrites, galena, zinc blende, and 
 copper pyrites, as also phosphates and sulphates, principally 
 of lime, as well as clay, frequently accompany. clay iron stone, 
 rendering the pig iron smelted from it, as a rule, less pure than. 
 from other ores. The sulphur in such iron varies, but rarely 
 exceeds 0*2 per cent, in " all mine pig." 1 The phosphorus 
 ranges from 0*2 up to 1*5. These ores are worked in South 
 Staffordshire, Derby, Notts, Leicestershire, Warwickshire, North 
 and South Wales, Cleveland district in New York, etc. 
 
 Their occurrence in conjunction with coal, limestone, and 
 fire-clay, furnishing all necessary materials for smelting on the 
 spot, has been one of the principal factors in the development 
 of the British iron trade. Similar formations occur in Belgium 
 and Silesia. 
 
 Black-band Ore is a variety of clay ironstone, admixed 
 with more or less coaly matter. This sometimes occurs in 
 
 1 A term used to designate iron made from ore without any admixture 
 of cinder from puddling and other processes. 
 
Iron Smelting. 87 
 
 layers, giving the ore a banded appearance, hence the name; 
 it is sometimes present in such large quantity as to colour the 
 ore black, the amount varying up to 30 per cent. These 
 ores occur in North Staffordshire, in Lanarkshire, and in 
 Prussia, etc. They contain from 17 to 30 per cent, of iron. 
 Owing to the bituminous matter present, it is often unnecessary 
 to add fuel in calcining the ore. 
 
 Iron Pyrites (FeS 2 ). The heavy, yellow, metallic substance 
 so frequently found as " brasses " in coal, occurs extensively. 
 It must be regarded rather as an ore of sulphur than of iron, 
 being used for the manufacture of vitriol. The residues from 
 certain varieties, after burning off the sulphur, and after treat- 
 ment for the copper they contain, are used as fettling for the 
 puddling furnace, under the name of " blue billy." It consists 
 of ferric oxide (Fe 2 O 3 ). 
 
 CHAPTER VIII. 
 
 IRON SMELTING. 
 
 Introduction. As already explained (p. 82), when oxides 
 of iron are heated with reducing agents, such as carbon (C), 
 carbon monoxide (CO), hydrogen (H), cyanogen (CN), the 
 oxygen is removed, and metallic iron' results. This reaction 
 occurs at all temperatures above redness. Apparently, therefore, 
 the production of malleable iron would be a simple matter, 
 were it not for the facts first, that the iron itself is so difficult 
 to melt, and second, the infusibility of the associated earthy 
 matters, while, if the temperature is raised, the iron takes up 
 carbon (see p. 78), and at the same time silicon and phosphorus 
 are reduced, and pass into the metal, depriving it of all its 
 malleability and other useful properties. 
 
 It follows,. therefore, that, to produce malleable iron from 
 ore direct, a low temperature must prevail, the ores must be 
 rich and fairly pure, and the earthy matters fluxed off by some 
 
88 Metallurgy. 
 
 body which will give a readily fusible slag. The only substance 
 available for this is oxide of iron itself. This removes the 
 impurities, mainly silica, as silicate of iron, and by its excess 
 prevents the iron with which it is in contact from taking up 
 carbon. It is obvious that by such methods only the better 
 classes of ore can be treated, and that the reduction is only 
 partial. This method would consequently be very wasteful, 
 while the production would be very limited as to quantity. 
 Methods of this character are still followed in India, Africa, 
 and elsewhere (see p. 118), and formerly were the only methods 
 practised. The carbon, silicon, and phosphorus which enter 
 the iron when the reduction is effected at a high temperature, 
 can be removed by heating the impure metal cast iron in 
 an oxidizing atmosphere, or with oxide of iron itself, whereby 
 it is converted into malleable iron. At the higher temperature 
 employed in making cast iron, other substances, such as lime 
 and magnesia, may take the place of the oxide of iron in fluxing 
 off the impurity, and the reduction is complete. Poorer and 
 less pure ores can thus be treated, and as the length of time 
 which the iron remains in contact with the carbon, etc., during 
 reduction is not limited, the furnaces employed may be of 
 any size compatible with efficiency, and the output thus 
 enormously increased. 
 
 This indirect production of malleable iron, by first obtain- 
 ing pig or cast iron, and purifying it, is found to be more 
 economical under ordinary conditions than the direct processes, 
 and is the one generally followed. 
 
 The ore, after the necessary preparation, is charged, together 
 with the fuel (charcoal, coal, or coke), which also serves as 
 the reducing agent, and \hzftux into a tall blast furnace, which 
 is kept full, and the materials, as they melt, sink, and make 
 way for fresh additions at the top. The iron is reduced, and 
 by taking up carbon, silicon, etc., becomes fusible at the 
 furnace temperature, and, melting down, accumulates at the 
 bottom. It is removed from time to time by making an 
 opening into the furnace, and allowing it to run out. This 
 " tap-hole " is at other times kept stopped with a mixture 
 of clay and sand. The slag, after reaching a certain height, 
 
Iron Smelting. 89 
 
 flows continuously from the furnace, and is disposed of in 
 various ways (see p. 113). 
 
 Preparation of Iron Ores. The objects aimed at are (i) to 
 remove extraneous matters completely; (2) to break down 
 the ore to pieces of such size that the reduction shall be 
 complete before it reaches that part of the furnace in which 
 the charge is melted down, otherwise oxide of iron would pass 
 into the slag. (3) In the case of spathic ores and clay iron- 
 stones, it is desirable to convert the protoxide of iron present 
 into peroxide, to prevent the passage of the iron into the slag, 
 by its combination with the silica in the charge, at a red heat 
 before reduction has been effected. 
 
 Washing. Clay, sand, and similar admixed and adherent 
 matters are removed from heavy ores by washing on iron grids 
 under a stream of water, and stirring the ore about with rakes. 
 
 Calcination. This is by far the most important process 
 to which iron ores are subject prior to introduction into the 
 furnace. It consists (see p. 18) of heating the ore with free 
 access of air. 
 
 In this country, only clay ironstones and spathic ores are 
 generally calcined ; hematites and magnetites are smelted 
 without this treatment. As they already consist of peroxides 
 of iron, and would lose nothing but some 6 to 12 per cent, of 
 water, which is expelled in the upper part of the furnace, little 
 advantage is derived, and fuel consumed for this purpose would 
 be practically wasted. 
 
 In Sweden, however, where these ores are often washed, and where, 
 owing to the lower temperature of blast employed, all the gas collected 
 from the furnace is not required to heat the air, these ores are also calcined, 
 the waste gases being employed for this purpose. 
 
 The operation is conducted in open heaps or in kilns of 
 special construction, in which less fuel is necessary and the air 
 supply and temperature can be better regulated. 
 
 Calcination in Heaps. The ore is piled up on a thin layer 
 of coal, the large blocks at the bottom and the smaller stuff 
 above, and covered with the smaller ore. In calcining clay iron- 
 stone, some 10 or 12 per cent, of small coal is mixed with the 
 ore ; but with black-band ores this is unnecessary, the burning 
 
90 Metallurgy. 
 
 off of the bituminous matter present furnishing the necessary 
 heat. The heaps are about 5 feet high, and the sides slope at 
 about 60, and are partly covered with small ore. They are 
 ignited at one end, at the base, and allowed to gradually burn 
 through, small refuse being used to check the combustion at 
 any point where it is progressing too rapidly. 
 
 Calcining in heaps is wasteful in fuel and heat, and the 
 product is not uniformly calcined. Some parts of the heap 
 will be almost fused, and in black-band ores partly reduced, 
 while others are not calcined through, and require a second 
 treatment. 
 
 To overcome these difficulties, kilns of some kind are now 
 generally adopted for all but black-band ores, fired either with 
 solid fuel or waste gas. 
 
 Calcining kilns are open-topped, circular, or rectangular 
 structures of masonry or boiler-plate, lined with fire-bricks, 
 with openings near the base for admitting air and withdrawing 
 the material They are charged from above, and generally 
 work continuously. 
 
 Rectangular kilns of masonry, with sloping sides, and lined 
 with fire-brick, are employed for calcining in South Wales. 
 
 Gjer's calciner, in use in the Cleveland district, is shown 
 in Fig. 32. It consists externally of boiler-plate, and is lined 
 with fire-brick. It is supported by a cast-iron ring resting on 
 short pillars. The descending ore is diverted outwards by the 
 cast-iron cone which projects upward into the kiln. It is 
 charged from the top, the coal and ore being brought in 
 trucks on rails. The ore, on removal, is despatched to the 
 furnace. 
 
 Fillafer's kilns, used in Styria and Carinthia, for the treat- 
 ment of spathic ores, are narrow rectangular chambers 9 feet 
 high, 4 feet 8 inches long, and 2 feet wide, with fire-bars at 
 the bottom, and a space beneath. Waste gases from the blast 
 furnace are admitted from flues in the side walls near the 
 bottom, and burn in air drawn through the grate-bars. The 
 roasted ore is discharged by withdrawing one or more bars, 
 and allowing it to fall, into the space below. 
 
 In calcining, water and carbonic acid gas are driven off, and 
 
Iron Smelting. 9 1 
 
 some of the sulphur in the pyrites present. The bituminous 
 matter in black-band ore is also burnt off. This leaves the ore 
 in an open, fissured, porous condition, in which it is readily 
 acted on in the furnace. The peroxidation of the iron has 
 already been noted. Certain pyritous ores before calcining 
 are exposed to the air, or weathered, for long periods. The 
 sulphides of iron and copper in the ore are converted into 
 sulphates. These are washed out by the rain or by drenching 
 the heap with water. By this means much sulphur is got rid 
 
 Ground Line 
 
 FIG. 32. Gjer's Calciner. 
 
 of, and a purer iron results on smelting. Weathering also 
 facilitates the detachment of pieces of adherent rock. 
 
 The size of the pieces of ore introduced into the furnace 
 depends on the nature of the ore, the fuel, and the rate of 
 reduction. The slower the descent of the material, and the 
 more open the character of the ore, the larger the pieces 
 may be. Magnetites and hematites are broken in from i to 
 2 inch cubes. The others may be in larger pieces. Stone or 
 ore breakers are used for this purpose. 
 
 The Blast Furnace used in iron smelting has undergone 
 
92 Metallurgy. 
 
 great structural changes in the last thirty years. The massive 
 masonry structures, braced with iron, formerly employed have 
 given way to the lighter type of furnace known as the cupola 
 blast furnace, and whereas formerly the top of the furnace was 
 open, and the gases were allowed to freely escape and burn 
 at the top, they are now usually closed, and the gases, which 
 resemble producer gas in composition, are collected and con- 
 ducted by iron pipes to the ground, where they are burnt for 
 heating the blast and for raising steam. 
 
 The height and capacity of furnaces has also greatly in- 
 creased, so that a "make" of 1000 tons of pig iron per week 
 per furnace is not infrequent. 
 
 A furnace of this type is shown in Fig. 33. It will 
 be observed that it consists externally of a boiler-plate 
 casing lined with refractory material, the upper part being 
 supported on columns. The furnace increases in diameter 
 from the throat downwards until a maximum diameter is 
 attained at the bosches, and then contracts more rapidly, until 
 at a point somewhat above the tuyere openings it becomes 
 nearly cylindrical, a form which it preserves to the bottom. 
 This form, which is the result of gradual development, has the 
 following advantages : The gradual increase in diameter in 
 passing downward permits of the better admixture of the 
 materials as they work outwards in descending, and by the 
 increased volume detain the ore for a proportionately longer 
 period in this part of the furnace, until certain reactions are 
 completed. In the lower part of the furnace, the rapidity with 
 which the fuel is being consumed, and the materials fused up, 
 with the consequent great contraction in bulk, necessitate the 
 rapid narrowing of the furnace chamber, in order that the 
 charge shall descend to the hearth with regularity. The exact 
 internal form, notably the height of the bosches, and the 
 diameter at this point as compared with the height of the 
 furnace, depend on the nature of the ore and fuel, and on 
 the class of iron produced in the furnace. 
 
 The casing of the furnace is made of f to \ inch boiler- 
 plate, well riveted together, and the lining is constructed of 
 5-inch fire-brick blocks, chisel dressed on both faces and 
 
Iron Smelting. 
 
 93 
 
 joints, so as to ensure perfect setting and uniformity in the 
 outline of the furnace. These may only form some 18 inches 
 of the lining, and be backed with ordinary fire-bricks, or the 
 
 FIG. 33. 
 
 whole thickness (3 feet 6 inches to 5 feet) of lining may be 
 thus made. 
 
 The upper part of the structure is carried on columns, 
 
94 
 
 Metallurgy. 
 
 which rest on a stone kerb bound with iron bands, enclosing 
 the hearth of fire-brick blocks. This stone foundation rests 
 on a bed of concrete. On the top of the columns rests a cast- 
 iron ring, some five inches thick, cast in segments, and on 
 this the superstructure is built The lower part of the furnace 
 is supported by plating also attached to the pillars. 
 
 From the tuyeres downwards the hearth is supported by 
 iron bands, and in various other ways. 
 
 The height of such furnaces varies from 60 to 100 feet, 
 
 FIG. 34. Lower part of furnace. A, blast-main (horseshoe) ; c, tuyere ; 
 E, fore hearth ; F, crucible. 
 
 and the diameter of the bosches from 17 to 30 feet. The 
 
 TT 
 
 ratio of height to diameter = varies from 2\ to 5, the 
 
 prevailing proportion being from 2\ to 3-^ ; but excellent 
 results have recently been obtained from furnaces in which 
 the ratio was increased. Such a furnace, with a height of 
 85 feet, and bosch diameter of 17 feet, has recently been put 
 to work. The height of the columns varies from 10 to 18 feet 
 
 6 inches, the diameter of the hearth from 8 to 9 feet, and 
 its depth from the tuyeres to the bottom 3 feet 6 inches. The 
 number of tuyeres ranges from 4 to 7, and they are distributed 
 at equal distances round the hearth. 
 
 Fig. 34 shows an enlarged view of the lower part of the 
 furnace. The blast is brought to the blast-main A, which 
 is an iron pipe, lined internally with fire-brick, if hot blast 
 is employed, supported on stanchions at a height of about 
 
 7 to 8 feet. It encircles the furnace except in front, and from 
 
Iron Smelting. 95 
 
 this at regular intervals the blast is conveyed to the tuyeres by 
 vertical iron pipes passing downwards, each of which is pro- 
 vided with a throttle-valve to regulate the air-supply. Sus- 
 pended from this by hangers is the " goose-neck " B, which 
 articulates with the vertical main by a ball-and-socket joint. 
 At the bend of B a mica plate is inserted, known as the 
 "furnace eye," and through it the working of the furnace 
 may be inspected. A sheet-iron blow-pipe, which slides tele- 
 scopically on B, conveys the blast through the tuyere-block, 
 C, into the furnace. These tuyeres enter the furnace through 
 small arched openings known as tuyere houses. On their lower 
 side they rest on fire-brick wedges on the top of the hearth, 
 the' remainder of the space being rilled up with fire-bricks, 
 and closely luted. They generally project a little beyond the 
 front line of the furnace, and are cooled by the circulation of 
 cold water supplied from the water main which surrounds the 
 furnace. When, as occasionally happens, the nose of a tuyere 
 is burnt off, it is removed, and a new one inserted, blast being 
 stopped for the time being. 
 
 The use of water-tuyeres became necessary with the introduction of 
 hot blast, on account of the increase in temperature in this region. With 
 cold blast, the absorption of heat by the expansion of the cold air so cooled 
 the furnace just in front of the tuyeres, that the slag solidified on the end, 
 and formed a prolongation or slag nose, from the length of which the 
 working could be judged. 
 
 Fig. 35 is the Staffordshire tuyere. It is a hollow conical 
 iron box encircling the blow-pipe, cooled by water circulating 
 between the casings. 
 
 In the Scotch tuyere, the water circulates round a coil of 
 wrought-iron pipe embedded in a cast-iron block. 
 
 The Spray tuyere is a hollow casing, and the water is 
 sprayed on the front through holes in the pipe conveying it. 
 The size of tuyere is proportioned according to the volume 
 of air and the pressure employed, so that the blast is carried 
 well into the furnace, and does not creep up the sides. The 
 blow-pipes from the goose-necks fit tightly into the tuyere, 
 and are luted round with clay, to prevent escape of air. 
 
 The hearth, or crucible, of the furnace, in which the iron 
 collects, as shown in Fig. 34, sometimes projects forward 
 
9 6 
 
 Metallurgy. 
 
 beyond the vertical, forming what is known as the " fore 
 hearth," E. This is closed by a "dam," supported by a 
 water-cooled iron plate, " dam-plate." In the top of the dam 
 is a groove, the "slag-notch," through which the slags flow 
 continuously, after reaching that level, and through which the 
 blast blows to keep it clear. The structure above the fore 
 hearth is supported by a water-cooled cast-iron girder, " tymp 
 iron," and the space between the dam and the upper part of 
 the furnace is closed by an iron plate (Fig. 34) backed with 
 fire-brick. In many furnaces the fore hearth is abolished, and 
 the slag flows out through a slagging-hole in the furnace wall. 
 The tap-hole is at the side of the dam, at the bottom. 
 
 FIG. 35. 
 
 It is a rectangular opening about 15 inches by 2, kept closed 
 until the metal has accumulated almost to the level of the slag- 
 notch, by a mixture of clay with sand, or coal-dust. This is 
 broken away by a pointed bar when the furnace is tapped, and 
 the metal allowed to flow out. While this is being done the 
 blast is shut off. 
 
 The throat of the furnace shown in Fig. 33 is closed by 
 a cup-and-cone arrangement. A truncated hollow iron cone 
 cast in pieces and bolted together, supported in the throat 
 of the furnace, and resting on the masonry by a broad flange, 
 forms the "cup" the opening into the furnace being closed 
 by the " cone " supported from one end of a lever projecting 
 over the top. At the other end is a counterpoising weight, 
 slightly heavier than the cone, and the apparatus for con- 
 trolling its motion, when it is lowered to allow of the de- 
 scent of the material (previously charged into the cup) into 
 the furnace. 
 
Iron Smelting. 97 
 
 Another method of closing the top of the furnace is some- 
 times adopted. The cone is replaced by a conical iron funnel, 
 through the stem of which the gases pass by a short vertical 
 tube into a cross-tube supported above the furnace, and thence 
 to the down-comer. The end of the vertical tube dips into 
 water in a circular trough round the stem of the funnel, thus 
 .ensuring a gas-tight joint. In this arrangement the gases are 
 removed from the central part of the furnace throat. Explosion 
 doors are arranged on the end of the cross-tube and elsewhere, 
 to prevent damage from possible explosions, arising from air 
 admitted during charging. They consist of a simple lifting 
 flap, which falls back into its place when the force has spent 
 itself. 
 
 These methods of closing the throat, when properly designed, give the 
 most regular distribution of materials attainable in mechanical charging, 
 the ore, flux, and fuel falling in an annular heap some distance from the 
 wall and from the centre. The larger stuff consequently has an equal 
 tendency to roll towards the sides and middle, and, the inequalities work- 
 ing away as the charge descends into the wider part of the furnace, uniform 
 obstruction is offered to the blast, which in consequence distributes itself 
 regularly, having no tendency to creep up the sides or middle, as would 
 be the case if the large stuff accumulated there. In the Staffordshire and 
 Barrow districts, the tops are often not completely closed. Sometimes a 
 tube some 5 feet long and 7 feet wide is hung in the throat. This is 
 kept full of material, which acts as a sort of stopper. The gases are with- 
 drawn by a flue connecting with the annular space between the tube and 
 the furnace lining. 
 
 A gallery or platform surrounds the throat of the furnace. 
 This is covered with iron plates, and slopes slightly towards 
 the edge of the cup, which stands some 3 or 4 inches above it, 
 and acts as a stop for the barrows. 
 
 The gases pass through the flue at the side into the wide 
 iron pipe "down-comer" (Fig. 33), and are 'led away to 
 boilers, stoves, etc., where they are burnt. The excess of gas 
 burns at the mouth of the standpipe seen on the right of 
 Fig. 33. Communication with the gas main is cut off when 
 the cone is lowered to introduce the charge. 
 
 Chambers in which dust is deposited, and apparatus for 
 the removal of ammonia and tar from the gases of furnaces 
 using coal as fuel, are interposed in many cases. 
 
 Lifts. The charge, consisting of ore, flux, and fuel, is raised 
 to the top by means of steam, hydraulic, or pneumatic lifts, or 
 
 H 
 
98 Metallurgy, 
 
 sometimes is drawn up inclined planes. Occasionally the 
 situation, near a hillside, permits of the trucks themselves being 
 drawn up by a locomotive. 
 
 In the water-balance lift, two cages or platforms sliding 
 between guides are connected by a steel rope passing over a 
 pulley at the top. The bottom of each cage is a water-tank. 
 Its capacity is such that, when filled, the cage, of which it is a 
 part, together with the empty barrows, is somewhat heavier 
 than the other cage with full barrows on, but the tank 
 empty. By filling the tanks at the top of the furnace, and 
 emptying them by valves in the bottom, the material can be 
 elevated by gravitation. The water required may be taken 
 from a neighbouring hillside stream, or pumped up for the 
 purpose, as at Dowlais. 
 
 In Sir Wm. Armstrong's hydraulic lifts, the movement of a 
 ram, connected with multiplying gear, through from 5 to 7 feet, 
 raises the charge to the top. 
 
 In pneumatic lifts, a counterbalanced cage is attached to a 
 piston working in a large cylinder, so that an air-pressure of 
 a few pounds applied above or below, gives the necessary 
 motion, up or down. 
 
 Steam lifts generally consist of a small winding- engine. 
 On the drum, two ropes passing over pulleys at the top, and 
 attached to cages sliding between guides, are so arranged that 
 as one cage ascends the other descends. 
 
 The Charge. The proportions of the materials in the charge 
 must be separately determined for each ore and fuel, and even 
 for each furnace, the fuel consumption being influenced by the 
 volume, temperature, and pressure of the blast, as well as by the 
 nature of the fuel. More coal, for example, must be used than 
 when coke is employed. With clay ironstones containing, after 
 calcination, 35 to 42 per cent of iron, the charge consists of 
 from 48 to 57 cwts. of ore, 19 to 25 cwts. of coke, and 10 
 to 14 cwts. of limestone per ton of iron made, the tempera- 
 ture of blast varying from 500 to 700 C., and its pressure 
 from 3^ to 5 Ibs. In furnaces using coal, 'from 2 to 2-| tons 
 replace the coke. 1 
 
 1 The coal is coked in the upper part of the furnace. 
 
Iron Smelting. 99 
 
 For red hematite the charge consists of 33 to 40 cwts. of 
 ore, containing from 50 to 60 per cent, of iron, 7 to 10 cwts. 
 of limestone, and 19 to 25 cwts. of coke, and, if very siliceous, 
 about \~ cwt. of aluminous ore (see Fluxes). 
 
 In smelting magnetites with charcoal, from 16 to 25 cwts. 
 of charcoal are consumed per ton of iron made. 
 
 Some ores contain all the ingredients necessary for fluxes, 
 and are described as self-going or self-fluxing. 
 
 The proportions existing between the ore and fuel in the 
 furnace are described as the burden. It is " light " when 
 the fuel is in large proportion, and " heavy " when the 
 quantity of fuel is diminished. 
 
 The height of the materials in the furnace is maintained at 
 a constant level the stock line fresh additions being made at 
 intervals of from 10 to 20 minutes. 
 
 The Blast. Time was when bellows worked by hand 
 supplied the air necessary for the low furnaces seldom ex- 
 ceeding 10 feet high then employed. Some of our large 
 modern furnaces require as much as 50,000 cubic feet of air 
 per minute, at a pressure of 3^ to 5 Ibs. This is supplied by 
 means of blowing-engines, some of which are capable of 
 delivering as much as 60,000 cubic feet of air per minute. 
 These engines are of various forms. A huge cylinder, some- 
 times 12 feet in diameter and i2-feet stroke, fitted with a 
 solid piston, is provided with valves in such a manner that, 
 as the piston travels to and fro, air is drawn in at one end 
 and expelled from the other, or, in other words, the cylinder is 
 double acting filling one end and discharging the other, in 
 whichever way the piston is travelling. These blowing-cylinders 
 are connected with steam-engines, by which they are worked. 
 The air is delivered at a pressure varying from a few ounces 
 up to 9 Ibs., if desired. Low pressures are employed for 
 charcoal furnaces, and the higher in coke and anthracite 
 furnaces. From 3 to 4-| or 5 Ibs. are the pressures commonly 
 employed. About 2.\ to 3 Ibs. is employed in furnaces using 
 coal. 
 
 NOTE. In the same furnace, with similar materials, the pressure of the 
 blast influences the quality of the iron produced. Low pressures and large 
 
loo Metallurgy. 
 
 volume, and consequent rapid driving, increase the make but lower the 
 grade of iron. Higher pressures, with less volume and slower driving, 
 diminish the make but improve the quality (see Reactions in Furnace). 
 
 Hot Blast. Formerly the air was supplied to the furnace 
 at the temperature of the atmosphere. In 1828, Neilson, at 
 the Clyde Iron Works, commenced the use of heated air, and 
 in a few years its use became general. 
 
 The advantages derived are 
 
 (1) The use of raw coal (of certain classes) instead of 
 coke. 
 
 (2) Much less fuel is required in the furnace, owing to the 
 heat carried in by the air. 
 
 (3) The temperature in front of the tuyeres is increased, 
 and the fusion zone of the furnace brought lower down. 
 
 (4) The furnace works with greater regularity, and is more 
 under control, not being affected by atmospheric influences. 
 
 The temperature of blast employed depends on the fuel 
 and class of iron made. With charcoal it is only heated to 
 from 200 to 350 C. ; with anthracite and coke, temperatures 
 of from 700 to 830 C. are employed The higher tempera- 
 tures tend to produce greyer irons, containing more carbon 
 and silicon. 
 
 Blast Stoves. The air is heated by passing it through cast- 
 iron pipes, or through brickwork regenerators, heated by the 
 burning of the waste gases collected from the top of the 
 furnace. 
 
 Fig. 36 shows a cast-iron pipe stove. The air circulates 
 through the pipes in the chamber, from end to end, as shown. 
 
 In pipe stoves a temperature of 550 C. 1 (1022 F.) cannot 
 be exceeded without danger of rapid oxidation and fracture of 
 the pipes. The products of combustion escape at a tempera- 
 ture equal to that to which the air is raised, and carry off at 
 least one-half of the heat generated. 
 
 In regenerative hot-blast stoves, the principle of the Sie- 
 mens regenerative furnace is embodied. The waste gases 
 collected at the throat of the furnace are burnt in the 
 
 1 This is seldom realized in practice. From 600 to 900 F. are the 
 usual temperatures. 
 
Iron Smelting. 
 
 101 
 
 Cold Bl 
 
 t Blast 
 
 stove, and the products of combustion drawn through brick- 
 work flues on their way to the stack. The heat is thus ab- 
 sorbed, and by passing 
 the blast through the 
 stove in a direction op- 
 posite to that taken by 
 products of combustion, 
 it may attain the tem- 
 perature of the stove. 
 At least two such stoves 
 working alternately 
 one being heated up 
 while the other is in use 
 for heating the blast 
 will be required. The 
 advantages derived from 
 their use are : (i) higher 
 temperature of blast ; 
 (2) less loss of heat, re- 
 sulting in greater fuel 
 economy; and (3), ab- 
 sence of difficulties 
 arising from the burn- 
 ing, cracking, and leak- 
 age of iron pipes. 
 
 Cowper's Regenerative Hot-blast Stove is shown in 
 
 Fig. 37- 
 
 The waste gases from the furnace are brought by the 
 culvert V, and enter the flame or combustion flue O, through 
 the valve F. Here they are burnt by the admission of a 
 suitable supply of air through G. The products of combus- 
 tion ascend and are drawn down through the passages in the 
 brickwork P ordinary chequers, or built of special bricks 
 in passing through which they are deprived of nearly the 
 whole of their heat. The brickwork gets first heated near the 
 top, but the heating gradually extends downwards. The 
 chequer is "carried on cast-iron grids supported by short brick 
 columns. Doors for cleaning-out purposes communicate with 
 
 Longitudinal Section, 
 
 FIG. 36. Cast-Iron Pipe Stove. 
 
102 
 
 Metallurgy. 
 
 the space beneath. In passing through the chequers, the 
 products of combustion are cooled down to about 150 to 
 
 HOLE FOR cuj) 
 
 200 C, at which temperature they pass into the chimney-flue 
 
Iron Smelting. 103 
 
 U, and thence to the stack ; the heat thus carried away doing 
 useful work by creating a draught through the stove. 
 
 When the stove has been heated to a maximum about 
 halfway down, the supply of gas is stopped, and the air- and 
 chimney-valves closed. The valve of the cold-blast main, 
 which enters the space under the chequer, and the hot-blast 
 main E, which communicates with the combustion-flue, are 
 opened. The cold air rising through the hot brickwork 
 gradually becomes heated by contact with it as it ascends, until 
 it has attained the temperature of the stove. It then passes 
 through the remaining upper portion without further absorption 
 of heat, and; being collected at the top, passes down the flame- 
 flue into the hot-blast main. 
 
 To prevent, as far as possible, dust being carried into the 
 stoves, the gases are passed through dust-boxes, in which the 
 current of gas is slowed down and the dust in large measure 
 deposited. 
 
 WhitwelPs Stove is shown in Fig. 38. The chequer-work 
 of the Cowper is replaced by vertical walls, to facilitate cleaning. 
 
 In regenerative stoves the blast is heated to temperatures 
 varying from 1200 to 1400 F., and the stoves are changed at 
 intervals of from half an hour to two hours. The large capacity 
 of these stoves renders a regulating air-vessel to equalize 
 the pressure, between the blowing engine and the furnace, 
 unnecessary. 
 
 In blowing in a furnace, as in heating up any large mass of brick- 
 work, the greatest care has to be exercised. The masonry is first dried 
 by wood fires, and then fuel gradually added until the furnace is half full ; 
 a small blast, through, say, a |-inch nozzle, is then introduced, and a 
 little limestone added to flux off fuel ash. The charging of material may 
 then commence, a much larger proportion of fuel than will ultimately be 
 used being present in the charge. The size of the nozzles is gradually 
 increased until the full volume and pressure of blast have been attained, 
 the time elapsing before this is reached sometimes being as long as 18 
 days. The ore and flux are also gradually increased until they reach .the 
 normal amount. 
 
 In "blowing out" a furnace, the burden is gradually diminished, and 
 at the last only fuel and a little limestone are fed in, so that the furnace 
 is completely cleared. 
 
 When an accumulation of material forms at any point in the furnace, 
 which from some cause or other will not work down, the irregularity is 
 described as "scaffolding," or "hanging," of the charge. 
 
 The sudden descent of the "hanging" material, owing to the melting 
 
IO4 
 
 Metallurgy. 
 
 away of the support, is called a " slip." It is sometimes attended with 
 serious consequences. 
 
 The formation of infusible masses of iron, often containing titanium, 
 
 FIG. 38. Whitwell Hot-Blast Stove. A, gas-valve; B, hot-blast main; c, chimney 
 valve; D, cold-blast main; E, doors for removing dust; F, cleaning holes through 
 which scrapers are introduced ; G, air inlets ; P, inspection openings. 
 
 in the hearth and lower part of the furnace seldom occurs since the intro- 
 duction of highly heated blast. They are known as " bears." 
 
Iron Smelting. 
 
 105 
 
 -5,5 
 
io6 Metallurgy. 
 
 The furnace being in full work, the charging of fresh 
 material at the top goes on at regular intervals. The metal 
 accumulates until the hearth is full, and is then tapped out 
 by piercing the clay stopping of the tap-hole with a pointed 
 bar. A channel leads from the front of the furnace to a sand, 
 bed which slopes very slightly from the furnace. This main 
 channel is continued, in the sand, to the front of the bed, send- 
 ing out side channels at intervals, which serve as feeders for 
 long rows of roughly made Q-shaped open moulds, lying like 
 huge combs in the sand. The feeders are picturesquely 
 named "sows," and the metal in the moulds "pigs." The row 
 of moulds furthest from the furnace is first filled, and the others 
 in succession, the metal being prevented from entering the 
 upper rows by stops. When the metal becomes solid, the pigs 
 are detached, and the sows broken up into convenient lengths 
 with sledge-hammers. 
 
 The pigs are about 4 feet long and 4 inches across the 
 surface. 
 
 Swedish pig and ferro-manganese are generally cast in wide, 
 open, iron moulds into a plate, which is broken up. 
 
 CHAPTER IX. 
 CHEMICAL REACTIONS OF BLAST FURNACES. 
 
 IN considering the chemical changes going on in the 
 furnace, the conditions under which it works must be borne 
 in mind. 
 
 The materials charged in at the top occupy a considerable 
 time in descending the furnace, varying from nine hours to two 
 or three days, according to the nature of the material, the 
 quality of thf iron being produced, and the quantity of blast; 
 the charge descends most rapidly with the heavy burdens and 
 large blast employed in making white iron. In its descent, the 
 oxide of iron is reduced to the metallic state by the carbon 
 monoxide in the ascending current of hot gases, and the 
 
CJiemical Reactions of Blast Furnaces. 107 
 
 various substances found in pig iron are introduced into the 
 metal. But little consumption of fuel takes place until it 
 arrives in the vicinity of the tuyeres. Here the oxygen of 
 the air combining with the carbon produces carbon monoxide 
 (and perhaps a little carbon dioxide, which is at once reduced 
 to monoxide by the excess of carbon present), producing heat 
 for the fusion of the metal and slags. 
 
 With hot blast this zone of fusion is immediately above the point at 
 which the blast enters. With cold blast, owing to the absorption of heat 
 by the expansion of the cold air blown in, this part of the furnace is 
 somewhat cooled, and the zone of most rapid combustion extends higher 
 up the furnace. 
 
 This gas, together with .the nitrogen of the air and any 
 hydrogen resulting from the decomposition of water-vapour in 
 the air blown in, ascends, and is the principal active reducing 
 and carburizing agent in the furnace. As the materials in the 
 lower part of the furnace are burnt away and melted up, those 
 above gradually descend, passing through hotter and hotter 
 regions till the fusion zone is reached. 
 
 The reactions by which the iron is reduced and carburized 
 are of a somewhat complicated nature, depending on the rela- 
 tive affinities of carbon and iron for oxygen, at varying 
 temperatures. 
 
 The only change taking place in the upper part is the 
 gradual heating up of the charge. When a sufficiently high 
 temperature has been attained, the reduction of the iron 
 commences. The carbon monoxide, CO, combines with the 
 oxygen in the oxide of iron, forming carbon dioxide, CO 2 , and 
 liberating the iron 
 
 Fe 3 O 4 + 4 CO = 3 Fe + 4 CO 2 
 
 This action commences at temperatures considerably below 
 a red heat, and the oxide is gradually reduced to a spongy 
 mass of metallic iron, which includes all the gangue in the ore. 
 At temperatures a little below, and above redness, spongy 
 iron decomposes carbon monoxide, carbon being deposited and 
 oxide of iron formed, which is subsequently reduced by carbon 
 
 3 Fe -f 4 CO = Fe 3 4 + 4 C 
 Fe 8 O 4 + 2C = 3 Fe -f- 2CO 2 
 
 6 ff"? s v 
 
 OF THE 
 
 UNIVERSITY ) 
 
 JJ 
 
io8 Metallurgy. 
 
 These reducing and carburizing actions go on side by side. 
 
 The spongy iron, with its deposited carbon in its further 
 descent, is subject to the oxidizing and reducing influences of 
 the carbonic oxide and carbon dioxide, and in the middle region 
 these almost balance each other, so that little change takes 
 place so far as the iron is concerned. In the lower part of the 
 furnace, any residual iron oxide is reduced, probably by cyanides 
 present, and the metal fuses, dissolving up part of the carbon 
 deposited in it, together with silicon, manganese, and phos- 
 phorus, which have been reduced in its descent. 
 
 The limestone charged in as a flux is reduced to lime, CO 2 
 being expelled, in the upper part of the furnace when the charge 
 has attained a sufficient degree of heat. When fusion occurs, 
 it combines with the gangue, and produces a slag. 
 
 The silicon in the pig is reduced from silica (SiO 2 ) in the 
 charge, in the lower and hotter regions of the furnace, by the 
 joint action of carbon and iron ; for while carbon does not 
 reduce silica alone, it does so at high temperatures in the 
 presence of iron. The amount reduced depends on the 
 temperature and the rate of descent. 
 
 Manganese is only reduced in the blast furnace by the 
 direct action of carbon at high temperatures. Carbon mon- 
 oxide only reduces oxides of manganese to the lower oxide, 
 MnO. The reduced metal alloys with the iron. 
 
 Phosphorus is introduced into the iron by the reduction of 
 phosphates in the charge, by carbon in the presence of silica at 
 high temperatures. Practically, the whole of the phosphorus in 
 the charge enters the metal 
 
 2 Ca 3 (P0 4 ) 2 + sSiO, + loC - 3 (2CaOSiO 2 ) + P 4 + loCO 
 
 Sulphur is introduced in another manner. The sulphide 
 of iron existing in the coke and other materials in the furnace 
 liquates into the iron during fusion, owing to its specific gravity 
 being greater than that of the slag. 
 
 By the use of a large proportion of lime, this may to some 
 extent be prevented, and the sulphur carried into the slag. 
 This is probably owing to the liberation of calcium by the silicon 
 in the iron, which combines with the sulphur, forming calcium 
 sulphide. 
 
Pig Iron. 109 
 
 From a consideration of the above, it will be seen that, to 
 produce a highly carburized iron, time must be given for the 
 metal to take up carbon, and a higher temperature will be 
 required in its fusion. These conditions favour also the 
 reduction of silicon, and, in order to keep that element low, 
 more lime must be employed. Hence " grey " irons are freer 
 from sulphur than " white " irons. 
 
 Alkaline cyanides are produced and accumulate in the 
 lower part of the furnace by a series of complicated reactions, 
 from traces of alkali existing in the charge, and materially 
 assist in the reduction of the last portions of iron oxide. 
 
 The first formation of the cyanide may be thus represented 
 K 2 CO 3 + 2C = sCO + K 2 
 K + C + N = KCN 
 
 NOTE. It should be noted that the lime serves a twofold purpose. 
 It combines with the silica and other gangue in the ore, and at the same 
 time prevents the silica from combining with oxide of iron, and forming 
 a scouring slag (see p. 1 14). The high temperature which prevails ensures 
 the liquefaction of the more difficultly fusible slag thus produced. 
 
 THE PRODUCTS OF THE BLAST FURNACE. 
 
 These are (i) pig iron; (2) slag; (3) furnace gases. 
 
 Pig Iron. Pig, or cast iron, is classed as grey, mottled, or 
 white, according to the appearance of the fractured surface. 
 Grey Pig Iron has a crystalline or granular appearance, a dark 
 iron-grey colour, is soft and easily turned, chipped, or filed. 
 The carbon, of which it contains a large proportion, has 
 mainly separated as graphite. 
 
 Such irons require a higher temperature to melt them than 
 white iron, but are more fluid when molten, and expand 
 slightly in solidifying. They are specially suitable for foundry 
 purposes. They are weaker than whiter iron, but less brittle. 
 The strength increases as the grain gets finer. They usually 
 contain more silicon and less sulphur than white iron. Grey 
 pig iron dissolves less gas than white, and consequently casts 
 more soundly. Greyness is not a proof of the absence of 
 phosphorus and other objectionable impurities. 
 
 They are classified as Nos. i, 2, 3, etc., according to 
 greyness. No. i being the greyest. 
 
no 
 
 Metallurgy. 
 
 Ore Limestone Fuel 
 
 Gases 
 
 Oxide 
 
 Gangue CaC0 3 As h* Carbon CO C0 2 N CH 4 &v. 
 
 Silicon Phosphor 
 Manganese 
 
 FIG. 40. Diagram showing chemical changes in blast-furnace. 
 
Pig Iron. 1 1 1 
 
 Mottled Iron presents the appearance of a matrix of white 
 iron with grey spots. Its carbon is present in both the free 
 and combined state. The quantities in the respective states 
 are about equal in most varieties. 
 
 White Cast Iron presents a white, close, and sometimes 
 crystalline appearance. Its carbon is mainly in the combined 
 form (see p. 78). It is extremely hard and brittle, and 
 usually contains more sulphur and less silicon than grey iron. 
 It melts more readily, but flows more sluggishly than grey 
 iron, giving off sparks in abundance. On this account it 
 is less suitable for making castings. It contracts slightly on 
 solidifying. Most varieties pass through a pasty state before 
 fusing, 1 in which condition, the oxides of iron and slags formed 
 in the puddling furnace can be more readily incorporated with 
 the metal, and the impurities it contains oxidized out with 
 less waste. On this account, malleable iron was formerly 
 made exclusively from irons of this class, either produced 
 directly in the blast furnace, if the ores were sufficiently 
 pure, or, if not, grey iron was made in the blast furnace, and 
 afterwards whitened (see Refining, p. 122). 
 
 When molten grey pig iron is rapidly cooled, it is rendered 
 white. On this account Swedish pig, which is cast in thin 
 plates in iron moulds, is often white top and bottom, with a 
 grey interior. The surfaces of grey pigs are often white from 
 the same cause (see Chilled Castings, p. 1 1 6). From the larger 
 proportion of sulphur usually present in white iron from the 
 furnace, they are classed as low-grade irons. 
 
 The specific gravity of white iron is greater than that of 
 grey. White has a specific gravity of 7^5 as compared with 7-1. 
 
 Grey Forge Pig is a class of iron containing less silicon 
 than other grey irons. The amounts of sulphur and phos- 
 phorus must be small. It is of fine grain. 
 
 Pig irons for trade purposes are usually classed as Foundry, Forge, 
 Bessemer, and Basic pig. Other descriptions indicating the source from 
 which they have been obtained are also used, e.g. Hematite iron, etc. 
 
 Bessemer pig iron must be practically free from phosphorus, while 
 Basic pig contains that element in considerable quantities. 
 
 Cold-blast pig, owing to the lower temperature prevailing during 
 its production, contains less silicon than the hot-blast pig of the same 
 
 1 All except those containing manganese. 
 
112 
 
 Metallurgy. 
 
 greyness. As this element greatly diminishes the strength of cast iron, 
 strong castings generally contain an admixture of cold-blast pig. Swedish 
 pig, smelted with charcoal, is also used for the same reason. 
 
 * Spiegeleisen and Ferro-manganese are the names applied to varieties 
 of pig iron containing notable quantities of manganese employed for 
 carburization in making mild steel. Spiegeleisen (German = "mirror 
 iron ") is so called from the brilliancy of its fractured surface. It is highly 
 crystalline, and breaks with broad, flat, lustrous faces, tinged somewhat with 
 yellow. Up to about 10 per cent, of manganese this becomes more pro- 
 nounced, but as the percentage increases, the size of the crystals diminishes, 
 and in those containing much manganese, the fracture, though yellowish, 
 is granular. Pig containing from about 7 to 20 per cent, is classed as 
 spiegel., and from 20 to 85 or 88 per cent as ferro. (the common contractions 
 of their names). Pig, containing less manganese than would constitute a 
 spiegel, is made for conversion into steel by the basic open-hearth process. 
 The object is to ensure the greater freedom of the iron from sulphur. 
 
 Manganiferous irons are made from spathic ores, and Spanish hematites 
 containing oxide of manganese, in the blast furnace. The conditions 
 necessary are slow reduction, high temperature, and basic slag. To secure 
 this, light burdens, small blast at high pressure and temperature, densest 
 coke, and much flux are employed. 
 
 In making ferro -manganese, the slag often contains as much as 13 per 
 cent, of manganous oxide, and is green in colour. This is necessary to 
 give fluidity to the slag. The make of a furnace working on ferro. is 
 little more than one-fifth of its output on grey forge iron. Manganiferous 
 pig contains about 5 per cent, of carbon. 
 
 Siliconeisen and silico-manganese are irons containing silicon, or silicon 
 and manganese, but practically free from sulphur, etc. From 12 to 21 
 per cent, of silicon may be present. They are employed in steel manufacture. 
 
 Glazy pig is a whitish crystallo-granular iron, in structure somewhat 
 resembling grey iron, but is brighter and whiter. It contains up to 12 per 
 cent, of silicon. 
 
 Small proportions of aluminium, chromium, copper, and 
 cdlcium frequently occur in pig iron. 
 
 ANALYSES OF PIG IRON. 
 
 
 Grey. 
 
 Mottled. 
 
 White. 
 
 
 Hematite 
 No. i 
 (Green- 
 wood). 
 
 Cold-blast 
 Bowling 
 (Abel). 
 
 Hot-blast 
 Derbyshire 
 ore. 
 
 (Bode- 
 mann.) 
 
 F rod ing- 
 ham 
 (Author). 
 
 Graphitic carbon 
 Combined carbon . 
 
 3'045 
 0704 
 
 2'99 
 
 3*35 
 
 1-99 
 278 
 
 2-98 
 
 Silicon .... 
 
 2 'OO3 
 
 0*97 
 
 1-27 
 
 0-7I 
 
 0-96 
 
 Manganese . 
 
 0-309 
 
 
 I'OI 
 
 
 
 0-505 
 
 Phosphorus . 
 
 0-037 
 
 0'5 
 
 1-09 
 
 1-23 
 
 I- 4 I 
 
 Sulphur .... 
 
 0-008 
 
 0-05 
 
 O"O2 
 
 
 
 0-28 
 
 Iron 
 
 93-800 
 
 
 93-26 
 
 93-29 
 
 93-865 
 
 
 99-906 
 
 
 100 000 
 
 lOO'OOO 
 
 lOO'OOO 
 
Blast-fzirnace Slag. 113 
 
 Blast-furnace Slag. As already noted, the slag flows 
 over the top of the dam, or through the slag notch. It is dis- 
 posed of in various ways. Sometimes it is led into circular 
 cavities in the ground, where it accumulates and solidifies, the 
 block being then lifted by a crane on to a bogie, and dragged 
 off to the tip or cinder-heap. 
 
 The more common way of removing it is to lead the molten 
 stream into slag-tubs, where it solidifies. These tubs are 
 waggons with movable iron sides, and are rectangular or 
 conical in form. They are run on rails up to the furnace front, 
 and drawn away by a locomotive when filled. After solidifying, 
 the sides are removed and the huge blocks tipped off. 
 
 In Styria, the slag is disposed of in a novel manner. It is 
 allowed to accumulate in the furnace along with the iron, on 
 the top of which it floats. When tapping takes place, the iron 
 forming the lowest layer in the furnace comes out first. As 
 soon as the slag begins to flow, it is diverted into a side 
 channel, at the end of which it meets a stream of cold water. 
 The sudden cooling reduces it to coarse sand, which the 
 velocity of the water carries forward into one of the many 
 rapid streams of the district, and thus gets rid of it. 
 
 The slag usually consists of double mono-silicate of lime 
 and alumina, with more or less magnesia, oxide of manganese, 
 and other bases. The general composition is given below : 
 
 Silica . . 
 
 40 
 
 to 47 per cent. 
 
 2 5 
 , 40 
 
 , 8 
 3 
 
 , 2 
 , 1-25 
 
 t 2 
 
 only 
 
 tO 2 
 
 Alumina . . 
 Lime 
 
 5 
 . . 30 
 j 
 
 Manganous oxide 
 
 j 
 
 
 
 Soda 
 Potash x 
 Phosphoric acid . 
 Suluhur 
 
 traces 
 jj 
 . traces 
 traces 
 
 the general formula being 3(2MOSiO 2 ) 4- 2M 2 O 3 SiO2. 
 
 The presence of manganous and ferrous oxides renders the 
 slag more readily fusible. If lime or alumina is in excess, the 
 fusibility is diminished. Magnesia is not such a good flux as 
 lime. 
 
 In the above, normal slags only have been considered. In making 
 spiegel, more manganese is present, and sometimes, owing to derangements 
 
 I 
 
1 14 Metallurgy. 
 
 in working or in the making of white low-grade iron, the oxide of iron 
 rises to as much as 8 per cent. Such a slag is known as a scouring slag ; 
 it is black in colour, and fuses readily. Its effect is to render the iron 
 whiter by the reduction of the oxide in the slag by the carbon and silicon 
 in the metal. 
 
 Blast furnace slags vary in colour from nearly white, 
 through shades of green, blue, or brown, to black. 
 
 The green tinge is due to the presence of ferrous oxide. Blue may be 
 due to alumina or alkaline sulphides. The brown colour is ascribed to 
 manganese sulphide ? If much ferrous oxide is present, its colour is bottle 
 green or black. Excess of lime makes the slag light coloured and stony. 
 
 The character of the same slag varies with the mode of 
 cooling. Rapid cooling makes it glassy ; if cooled slowly, it 
 may be stony ; while, if gas is escaping while molten, it will be 
 light and porous. 
 
 The higher temperature employed in making grey iron permits of the 
 use of larger quantities of limestone in the furnace charge. This causes 
 the slag to be lighter in colour a light greyish slag almost invariably 
 accompanying the production of grey iron. In consequence of the excess 
 of lime, the sulphur in such slags is higher than in slags produced in making 
 white iron, so that grey forge pig is superior in this respect to white forge pig 
 made from the same ore. The absorption of moisture from the air by the 
 excess of lime present often causes these slags to fall to pieces on exposure. 
 
 Slags are utilized to some extent in various ways according to their 
 nature. Certain siliceous slags can be made into blocks for paving, by 
 running the slag into iron moulds, and removing them while still hot into 
 an annealing oven and treating them like glass. 
 
 Highly basic slags free from iron are used for making inferior glass. 
 
 Excellent concrete bricks, etc., can be made by grinding down basic 
 slags and mixing with about 10 percent, of milk of lime and moulding the 
 blocks by compression. ^ In course of time they harden like stone. For 
 making bricks, the slag is granulated by water, and for concrete, broken 
 slag mixed with slag sand is employed. If very basic, no addition of lime 
 is necessary. Good cement has also been made from slag. Slag sand 
 is also used in place of ordinary sand for mortar. 
 
 Slag wool, made by blowing air through molten slag as it flows from 
 the furnace, is a good non-conducting material. Its use as a steam 
 packing, however, has not been attended with success. 
 
 The question of utilizing slag is of great importance. For each ton 
 of iron, from 10 to 30 cwts. of slag are produced. This amounts in the 
 aggregate to many thousands of tons yearly, which by its accumulation 
 encumbers the land. 
 
 Blast-furnace Gases, as taken off at the throat of the 
 furnace, consist of a mixture of 
 
 Carbon monoxide 25 to 29 per cent. 
 
 Carbonic acid gas 6 ,, II ,, 
 
 Nitrogen 54 57 >. 
 
 Hydrogen ... . . . . o 7 ,, 
 
 Marsh gas o ,, 3 ,, 
 
Iron Founding. 115 
 
 In furnaces using charcoal and coke, hydrogen and marsh gas are 
 low, being derived almost entirely from the moisture in the air blown in. 
 Ammonia and tarry matters are also present in the gases from furnaces 
 burning coal. At some iron works these are recovered before burning 
 the gases. 
 
 It will be observed that the composition of these gases is similar to 
 producer gas, with a considerable increase in the amount of CO 2 present. 
 The furnace may, in fact, be considered as a huge gas-producer. The 
 excess of CO 2 is accounted for by the reduction of the oxide of iron going 
 on in the upper part of the charge, at a temperature too low for it to be 
 converted into carbon monoxide by the carbon with which it is in 
 contact. 
 
 The volume of gas is enormous. Each ton of coal burnt yields nearly 
 4 tons of gas, measuring 130,000 cubic feet or more according to the 
 temperature. 
 
 Kish is a separation of graphite which sometimes occurs 
 while grey irons are cooling and solidifying. 
 
 IRON FOUNDING. 
 
 For the purpose of making castings, iron is melted down 
 in small blast furnaces, called "cupolas." A very satisfactory 
 type is shown in Fig. 1 2. The outer iron shell is lined with 
 fire-brick up to the level of the charging hole E, and stands 
 on a raised platform, at a convenient height for filling the 
 ladles with the metal from the tap-hole. The bottom is of 
 fire-brick, and carefully covered with ganister, or sand and clay, 
 and made to slope towards the tap-hole situated in front. At 
 the back of the furnace, at the base, is a movable plate, kept 
 in its place by an iron bar, which passes across it and through 
 two lugs on either side of the furnace. This is for the 
 removal of the residues from the furnace when melting is com- 
 pleted. In some modern cupolas, the furnace is supported on 
 pillars, and the bottom is removable. The ratio of height to 
 diameter is about as 5 : i or 6 : i. The blast is brought by the 
 pipe B to the jacket C which encircles the outer casing, and 
 from which openings, DD, at regular intervals through the 
 lining and casing, admit the air into the furnace. A fire is 
 first made in the cupola, which is then nearly half filled with 
 coke. When fairly ignited, the back plate is fixed and the 
 blast turned on. The metal is charged in pieces weighing 
 about 28 Ibs., in layers alternating with layers of coke. A 
 
Metallurgy. 
 
 little limestone is usually added to flux off the ashes of the 
 fuel. As soon as metal makes its appearance at the tapping- 
 hole, it is stopped with clay. As the iron melts, it collects at 
 
 the bottom, and is tapped 
 off into ladles as required. 
 From i to 2 cwts. of coke 
 are used per ton of iron. 
 
 The fuel used in the 
 cupola should be as free 
 from sulphur as possible. 
 Sulphur absorbed from the 
 fuel in melting has a ten- 
 dency to throw out the car- 
 bon and whiten the iron. 
 
 As cast iron flows from 
 the furnace, it throws off 
 sparks or "jumpers." This 
 happens to a less extent with 
 grey than with white irons. 
 No. .1 scarcely scintillates 
 at all. 
 
 The moulds are made in 
 " green-sand," or a mixture of green-sand with about 8 per cent. 
 of coal-dust, or in " loam." They are well vented, to permit 
 of the free escape of the gas given off. 
 
 As before noted, grey irons are best suited for foundry 
 purposes (see p. 109). If chilled on the surface, a thin skin 
 of hard white iron is produced. To prevent this, ordinary 
 sand moulds are blacked. Charred oak wood is the best 
 blacking for light work. Graphite (blacklead) is also largely 
 employed. For heavy work, the heat contained in the body 
 of metal prevents the face from being chilled. 
 
 Chilled Castings. This hardening is made use of in the 
 production of castings of which some part is subjected to wear. 
 The wearing surface, e.g. the tread of a car wheel, is rendered 
 hard by chilling the metal. This is effected by using a care- 
 fully prepared iron mould for the part which is required to be 
 hard, the rest of the article being moulded in sand in which the 
 
 FIG. 41. A, body of roll ; B, chill ; c, neck ; 
 D, wobbler end ; G, boxes ; E, running- 
 gate ; F, sand mould. 
 
Malleable or Wrought Iron. 117 
 
 "chill" is embedded. Rolls for rolling iron, zinc, etc., are 
 thus hardened on the face (see Fig. 41). This practice leaves 
 the body of the casting soft and tough, only the wearing face 
 being rendered hard. The turning, etc., of such castings can 
 only be done by specially prepared tools. 
 
 Malleable cast iron and malleable castings are made by 
 packing the articles in red hematite in pots or boxes, from 
 which air is completely excluded, and heating them for a pro- 
 longed period. 
 
 The articles are thus rendered soft and to some extent 
 malleable. A thin strip thus treated, may be bent double, but 
 generally breaks on attempting to straighten it. The strength 
 of the articles is greatly increased. Castings for annealing are 
 made in special mixtures of pure irons free from manganese, 
 having a tendency to whiteness. The reason for the change 
 during annealing is somewhat obscure. It has been sup- 
 posed that carbon is removed by the oxide of iron in which 
 they are embedded, but from analysis such does not appear 
 to be the case to any great extent. 
 
 The prolonged heating probably causes the separation of 
 the combined carbon in a finely divided state, but differing 
 from graphite, throughout the whole mass, leaving the iron 
 itself purer and more malleable. 
 
 CHAPTER X. 
 
 MALLEABLE OR WROUGHT IRON. 
 
 UNDER this heading are included all classes of iron which can 
 be hammered and forged at red heat, and are not hardened 
 by heating to redness and plunging in cold water. It is usual 
 to further restrict the term to the metal as obtained in a pasty, 
 unfused state, produced either in a direct manner from the ore, 
 or indirectly from pig iron by puddling or analagous processes. 
 Direct Processes. As previously noted (p. 87), iron oxides 
 are reduced by carbon or carbon monoxide at dull-red heat, 
 
n8 Metallurgy. 
 
 and the earthy impurities can be removed, and carburization 
 prevented, by allowing oxide of iron to pass into the slag. 
 Such a slag is readily fusible, and by hammering the pasty 
 mass obtained, the particles of malleable iron become welded 
 together, and the slag is expelled. All the iron produced by 
 the ancients was thus obtained, and many processes of a 
 similar ^character are yet in use in India, Burmah, Africa, and 
 other places, where modem civilization and its methods have 
 not yet penetrated. 
 
 Various modern " direct " processes for the treatment of 
 special materials, and with a view to the saving of fuel, have 
 also been introduced. Methods of the crudest and of the most 
 refined nature belong to this category. 
 
 In Burmah, a hole in the side of a clay bank, some 10 feet 
 deep and 2 feet jjde, does duty for a furnace. The front of 
 the bank is strel^piened by small branches interlaced and 
 supported by stakWdriven in the ground. At the bottom, an 
 opening about a fJbf high and the width of the furnace is cut 
 through the bank Ip the removal of the lump of metal and the 
 slag. This is stopped with clay. A row of clay tubes, about 
 4 inches long, made by plastering clay on bamboo, and after- 
 wards drying and burning them, is introduced about halfway 
 up the opening. These supply the air to the furnace, which 
 works entirely with natural draught. A fire is lighted, and 
 a quantity of charcoal thrown in. The rest of the furnace is 
 filled up with alternate layers of ore and charcoal, and the 
 furnace is left pretty much to itself. In a few hours, slag 
 makes its appearance at the bottom, and is tapped out and 
 examined. If free from shots of iron, it is thrown away. 
 When the furnace has burnt out, the clay breast is broken 
 down and the lump dragged out. It consists of metal, frag- 
 ments of unburnt charcoal, and slag, and weighs about 90 Ibs. 
 It is broken up and sorted, according to fracture, into soft, 
 and hard or steely iron. 
 
 In India, most native iron-makers use blast, and the 
 furnaces are generally built above ground. They range in 
 size from a chimney-pot to about 10 feet high, and the blast 
 is supplied by curious contrivances. Bellows made of goat and 
 
Malleable or Wrought Iron, 
 
 i IQ 
 
 bullock skins stripped off whole, single-acting wooden blowing- 
 cylinders, the pistons of which are stuffed with feathers, and 
 bellows not unlike ordinary smithy bellows, being employed. 
 In some furnaces, the front is broken down in order to 
 remove the iron ; but in others the metal is hauled out by 
 tongs from the top, a fresh charge being at once introduced. 1 
 
 Similar processes are 
 in use in Central Africa. 
 
 Easily reducible brown 
 hematites containing over 50 
 per cent, of iron are the ores 
 generally employed. Little 
 more than half the metal is 
 reduced, the rest passing into 
 the slag. The presence of so 
 much oxide of iron in the slag 
 prevents the reduced metal 
 from taking up carbon, and, 
 in many cases, the low tem- 
 perature which prevails is 
 unfavourable to carburization. 
 The silica and phosphorus in 
 the ore are removed in combi- 
 nation with oxide of iron in 
 the slag. 
 
 The famous Catalan, 
 Elba, and Corsican pro- 
 cesses are very similar in 
 character. They still survive to a small extent. 
 
 The forge (Fig. 42) in which the reduction is effected is 
 a rectangular hearth, one side of which curves outwards' at the 
 top. It is about 21 inches long, 19 wide, and 17 deep. The 
 bottom is a movable block of granite. The tuyere side is 
 built of malleable iron blocks, as also is the sloping side 
 facing the tuyere ; the back is of masonry, and lined with 
 fire-clay. The front consists of thick iron plates, placed edge 
 to edge, the lower end being on the ground. The tuyere 
 is of copper, and the blast-pipe lies in it loosely. It is 
 inclined so that the blast strikes downwards. A tap-hole at 
 the bottom serves to remove slag, and to introduce a bar to 
 lift up the mass of iron when the process is completed. 
 1 Modern blast furnaces are now in use in India. 
 
 FIG. 42. 
 
I2O Metallurgy. 
 
 The hearth, hot from previous working, is filled with 
 charcoal to the tuyere, and a gentle blast turned on. When 
 fairly alight, a broad shovel is placed a little in front of the 
 tuyere, so as to divide the hearth into two unequal parts. 1 The 
 tuyere side is filled with charcoal, which is moistened. On 
 the other side the charcoal is rammed down tightly, and the 
 space filled with roasted and broken ore, from which the fine 
 stuff has been riddled. This is then covered with a mixture 
 of fine ore and charcoal-dust, and finally with moistened 
 charcoal. The blast is then turned on, and in a few minutes 
 the flame of carbon monoxide makes its appearance at the top. 
 From time to time ore and charcoal are added, being pushed 
 down the sloping side of the furnace into the hearth, under 
 the tuyere, where the reduced iron accumulates. The carbon 
 is repeatedly damped to prevent its too rapid combustion. 
 The slag is removed at intervals and examined. The operation 
 is complete in five or six hours. The lump collected at the 
 bottom is raised in front of the tuyere for a few minutes to 
 raise it to a full heat and melt out slag, and is then dragged 
 from the furnace, and hammered to expel slag. It weighs 
 about 3 cwts. 
 
 The mass, which is never homogeneous, is broken up 
 and sorted. The pieces are reheated in the corner of the 
 hearth formed by the tuyere side and back, during the 
 progress of a subsequent operation, and drawn down into bars. 
 
 The reduction is effected principally by the CO, formed by 
 the air passing through the carbon before coming into contact 
 with the ore, consequent on the method of filling the hearth, 
 and the downward direction given to the blast. The siliceous 
 impurities are fluxed off by ferrous oxide formed by partial 
 reduction of the ferric oxide in the ore. A very fluid, fusible 
 slag is thus obtained, carburization at the same time being 
 prevented. This is also favoured by the low temperature 
 employed. 
 
 The blast is provided by a blowing-machine known as the 
 trompo, and the pressure varies from \ to i-| Ib. 
 
 The American bloomery is in somewhat extensive use in 
 1 After charging this is removed. 
 
Malleable or Wrought Iron. 121 
 
 Canada and the United States, and New Zealand more 
 especially, for the treatment of the titaniferous iron sands, 
 ores, etc. 1 
 
 It is a small rectangular hearth with sloping sides, and measures 
 27 to 28 inches, by 30 to 32 inches along the sides, and at the back is 
 about 33 inches deep. The sides are made of thick cast-iron plates, 
 a-nd the bottom of a water-cooled hollow casting. A single, water- 
 cooled tuyere, inclined so that the blast strikes the centre of the hearth, 
 is introduced at the back about 12 inches above the bottom ; the tuyere 
 opening is segmental in form, i| inch high and % inch wide. The front of 
 the furnace is 16 inches deep, and at this height is a flat iron plate 18 inches 
 wide. The tapping-hole is situated below this, and at the side of the hearth. 
 
 The furnace is worked by filling the hearth with charcoal, and 
 scattering the fine ore over the top of the fire at intervals, additions of 
 fuel being made from time to time. The reduction takes place as the ore 
 passes down in front of the tuyere, but the iron does not fuse. The grains 
 of reduced metal agglomerate in the bottom of the hearth, forming a mass 
 or loup, which is subsequently raised in front of the tuyere, and when 
 heated to a full welding heat, hammered to expel the slag. 
 
 The slag is similar to that obtained in the Catalan forge, and the 
 chemical reactions identical. 
 
 The blast is usually heated to about 300 C., by circulating through 
 iron pipes in a brick chamber built above the furnace, heated by the waste 
 heat. A pressure of about i| Ib. is employed. 
 
 Only rich ores containing 50 per cent, of iron or over can be economi- 
 cally treated. 
 
 One furnace produces about a ton of blooms per day of twenty-four 
 hours, the loup being removed every three hours. They work continuously 
 for a certain part of the year. 
 
 Indirect Methods. Pig iron is converted into malleable 
 iron by removing the silicon, carbon, manganese, and phos- 
 phorus by oxidation. During this treatment, part of the 
 sulphur is also removed if the slag produced is highly basic. 
 
 The above-mentioned bodies have a greater affinity for 
 oxygen than iron has, and hence, on exposing the metal during 
 fusion and while melted to a blast or current of air, they are 
 oxidized, together with a portion of the iron itself, which forms 
 such a large proportion of the whole. 
 
 The silica (SiO 2 ) phosphoric anhydride (P 2 O 5 ), manganous 
 oxide (MnO), and oxide of iron formed, unite together, 
 producing a fusible slag consisting of silicate and phosphate 
 of iron, with the excess of iron oxide. The carbon passes off 
 in the gaseous state as CO or CO** 
 
 Instead of employing an air blast, the oxidation may be 
 brought about by heating the pig iron with oxide of iron or 
 1 Sterry Hunt. 
 
122 Metallurgy. 
 
 substances containing it, such as red hematite, hammer-scale, 
 best tap-cinder, etc. The iron oxide gives up a portion of 
 its oxygen to the impurities, and they are removed into the 
 slag. 
 
 Practically the same thing occurs when an air blast is 
 employed. The oxygen first forms oxide of iron, which is 
 subsequently decomposed by the silicon, etc., present. 
 
 Upon these principles, all processes for the conversion of 
 pig iron into mild steel and wrought iron depend. The 
 essential difference lies in the fact that while mild steel is 
 obtained at the end of the process in a molten state, and is 
 run into moulds, wrought iron is obtained in an unfused, 
 spongy condition (owing to the lower temperature that 
 prevails), the particles of iron being subsequently welded 
 together. 
 
 The order of affinity for oxygen is as follows : silicon, 
 carbon, manganese, phosphorus, iron, sulphur. If it were 
 possible to make the oxidizing influences act uniformly 
 through the metal, the impurities would be removed in this 
 order. In the Bessemer process, where air is blown into the 
 molten pig iron, something closely approaching this takes 
 place (see p. 147), but in other methods overlapping occurs. 
 
 Sulphur is not removed by oxidation, but is taken up by 
 the slags, apparently by liquation, as sulphide. 
 
 Processes for producing wrought iron by subjecting pig 
 iron to a blast of air in hearths, are known as finery processes; 
 those in which it is treated with oxides of iron in a rever- 
 beratory furnace, as puddling. 
 
 Refining. All kinds of pig are not equally suitable for 
 conversion into malleable iron. Only some 80 per cent, of 
 the phosphorus present, and 40 per cent, of the sulphur, are 
 removed in finery and puddling processes. The presence of 
 too much silicon also gives trouble owing to the fluidity of the 
 metal, and consequent difficulty of working, as well as the 
 great loss in weight which occurs. 
 
 The pasty stage through which white pig iron, free from 
 manganese, passes prior to fusion, permits of easier mixture 
 with the iron oxides and oxidizing slags in the furnace, which 
 
Malleable or Wroiight Iron. 
 
 123 
 
 effect its purification ; and in consequence of its composition 
 less loss occurs. It is therefore preferred to grey iron on this 
 account, but, as its sulphur contents are usually higher, this 
 advantage is often more than counterbalanced. Unless the 
 iron is smelted from pure ores, it is now usual to produce 
 grey pig in the blast furnace, and either treat this directly or 
 subject it to a refining process previous to its actual treatment 
 for malleable iron. 
 
 Refining is a process formerly generally employed for the 
 
 FIG. 43. 
 
 conversion of grey into white iron previous to puddling or 
 blooming. 
 
 The refinery or running-out' fire, is shown in Fig. 43. It 
 consists of a rectangular hearth 4 feet square and 18 inches 
 deep, formed on three sides of water-cooled cast-iron blocks, 
 U U. The front is a cast-iron plate in which the tap-hole is 
 situated. Four columns, B B, situated at the corners of the 
 hearth, carry the brickwork stack some 16 to 18 feet high 
 on girders. The bottom is made of sandstone blocks. 
 
 The hearth is enclosed by iron plates attached to the 
 columns. Those at the back are hinged, while the front 
 plate is attached to the end of a lever and counterpoised, so 
 as to be easily raised and lowered. The hearth is provided 
 with a number of water-cooled tuyeres, usually five or six. 
 
1 24 Metallurgy. 
 
 These are inclined at an angle of about 30, and placed on 
 both sides in such manner that the tuyeres are not opposite 
 to each other. In this way the blast is uniformly distributed 
 over the hearth. In front is an iron mould for the reception 
 of the metal, and beyond this a pit for the slag, which runs 
 off the surface when the mould is full. Owing to its lower 
 melting-point, it remains fluid longer than the iron. 
 
 The blast is employed at a pressure of about 2\ Ibs. 
 per square inch. 
 
 The hearth, being hot from a previous operation, is partly 
 filled with coke, and the charge of about two tons of pig iron 
 and scrap introduced, in layers alternating with coke, through 
 the folding doors at the back. Some hammer-scale (Fe 3 O 4 ) is 
 often added. The blast is turned on, and in about a couple 
 of hours the charge is melted down. More coke is added 
 if necessary, and the blast continued for from half to three- 
 quarters of an hour, during which period bubbles of carbon 
 monoxide are seen escaping from the metal and burning on 
 top. The metal, when deemed refined, is tapped out and 
 cooled rapidly, warmer being often thrown on the surface for 
 this purpose. The plate of metal is from i to 3 inches thick. 
 
 Owing to the large amount of air supplied, the iron is 
 subjected to oxidizing influences during the whole period of 
 the operation, and, when fluid, the downward direction of the 
 tuyeres causes the blast to play continually on its surface. 
 The oxide of iron thus formed, and that added as hammer-scale, 
 attacks and oxidizes the silicon, carbon, and phosphorus in the 
 metal. 
 
 The removal of silicon from the metal in refining is most 
 marked, pig iron containing 5 per cent, being reduced to from 
 0*5 to 07. Carbon is seldom reduced more than i per cent., 
 while the removal of phosphorus is very variable. In some 
 cases it is scarcely affected. The rapid cooling ensures the 
 retention of the remaining carbon in the combined form. 
 A white, close, dense metal results known as plate metal, or 
 refined iron. 
 
 The slag consists mainly of basic silicate of iron. In this 
 process sulphur is not removed. 
 
Malleable or Wrought Iron. 125 
 
 Removal of Sulphur from Pig Iron. The purification of 
 pig iron from sulphur has received much attention. Manganese 
 and sodium carbonate are both employed for this purpose. 
 In each case, a sulphide not decomposed by iron is formed. 
 
 With sodium carbonate, silicon is also largely removed, 
 and some carbon, with separation of metallic sodium. The 
 molten pig is run into a receiver containing the carbonate. 
 
 Scheerer proposed the use of calcium chloride and salt 
 as a desulphurizer, by adding it in the puddling process. 
 Saniter's desulphurizing process consists of running the 
 molten pig into a receiver containing calcium chloride and 
 lime. Fluor spar may also be added. 
 
 NOTE. The " washing" process is a method of refining pig iron for 
 steel-making. 
 
 Finery Processes. Welsh Finery, Walloon Process, 
 Swedish-Lancashire Hearth. 
 
 In these processes, the pig iron is converted into malleable 
 iron in open hearths, in contact with the fuel. In consequence, 
 only charcoal can be employed, coke and coal not being 
 sufficiently free from sulphur. 
 
 The Swedish-Lancashire hearth is- a small rectangular 
 finery made of cast-iron plates. The top is arched over, and 
 communicates with a chamber in the flue in which the pig 
 iron is heated prior to being placed on the hearth. The 
 hearth has one tuyere, nearly horizontal, supplied with blast 
 heated to about 120 C., by circulating through iron pipes 
 placed in the flue. 
 
 The hearth is filled with charcoal, and the charge of 
 about 2 cwts. of white or mottled iron drawn from the flue, 
 the blast turned on, and the charge melted down. The 
 atmosphere is highly oxidizing, and as the drops of metal 
 sluggishly pass before the tuyere oxidation occurs. 
 
 The metal collects at the bottom, and slightly hardens. 
 The cake is broken up by the workmen, and held before the 
 tuyere, to be remelted and further oxidized. When the metal 
 gets stiff and infusible, it is raised to the top, fresh charcoal 
 added, the temperature raised, and the whole remelted. As 
 it drops down before the blast into the bath of highly basic 
 
126 
 
 Metallurgy. 
 
 slag at the bottom, its fining is completed, and the pasty mass 
 is collected into a ball, withdrawn from the furnace, and con- 
 solidated by hammering, the retained slag being thus expelled. 
 
 The Walloon process is similar. These finery processes are 
 wasteful. A loss occurs of from 15 to 20 per cent, on the 
 pig iron employed. 
 
 They are still retained in Norway and Sweden, and were 
 formerly in vogue in South Wales, for the production of tin 
 bars for tin-plate manufacture, but are now superseded, tin 
 bars of better quality being made from open-hearth steel at 
 a much reduced cost. 
 
 Puddling. This process the most important of all 
 methods of making malleable iron was introduced by Cort, in 
 1784, as a method of employing coal for fining iron. Up to 
 this period, the sulphur in coal and coke had prevented their 
 use in fineries. 
 
 The employment of reverberatory furnaces, in which the 
 fuel is burnt out of contact with the iron, completely overcame 
 the difficulty ; the sulphur, being burnt to SO 2 , has no effect on 
 the iron. 
 
 Fig. 44 shows a section of a puddling furnace. It is a 
 reverberatory furnace, the grate area of which is large in 
 proportion to the hearth space (i : 1-3- or 2). The bottom 
 
 FIG. 44. A, fire-place ; B, bed ; c, fire bridge ; D, working door ; E, flue bridge ; 
 F, flue ; G, tap-hole for slag ; H, plating of furnace. 
 
 and sides of the hearth consist of cast-iron plates suitably 
 supported, and backed with fire-brick. They are protected 
 with some material rich in oxide of iron, and kept cool by 
 the circulation of air under and round them. 
 
 Formerly brick beds and sand bottoms were employed. 
 
Malleable or Wrought Iron. 127 
 
 The working door, in front, is only opened to introduce and 
 withdraw the charge. It slides between guides, and is attached 
 to the end of a lever, and is counterpoised. The working of 
 the charge is effected through an opening in the bottom of 
 the door (the stopper-hole), through which the bars for this 
 purpose are introduced. In front of the door is a shelf or 
 fore-plate. The interior is lined with fire-brick, and the furnace 
 is supported externally by iron plates and tie-rods. A damper 
 in the flue or at the top of the stack is employed to regulate 
 the draught. 
 
 The fire- and flue-bridges are usually hollow, the circulation 
 of air keeping them cool. These, as also the sides of the 
 hearth, are sometimes kept cool by the circulation of water 
 Under the fore-plate is a tap-hole, for the removal of slag, 
 which is generally run out every second heat. 
 
 The iron plates forming the bottom and sides of the hearth 
 are protected by about 3 or 4 inches of " fettling." Bull-dog, 
 calcined pottery mine, and best tap-cinder 1 are employed for 
 this purpose. They are broken to about the size of macadam, 
 and spread on the bottom, the spaces being filled up by similar 
 material ground fine and moistened. The fire-brick lining 
 above the side plates projects slightly, so as to retain the 
 fettling. Puddler's mine (soft red hematite) and blue billy 
 (ferric oxide produced in burning pyrites for making sulphuric 
 acid) are used for making the bed even. All these substances 
 soften at the furnace temperature, and play an important part 
 in the operation. 
 
 Bull-dog is a mixture of ferric oxide (Fe ? O 3 ) and silica obtained by 
 roasting tap (puddling furnace) cinder. This consists of a very basic 
 silicate of ferrous oxide. On roasting, the FeO takes up oxygen, and is 
 converted into Fe 2 O 3 , which has very little affinity for silica, and separates 
 from it. 
 
 It is fairly refractory, except in a reducing atmosphere, when the Fe 2 O 3 
 is reduced to FeO, which at once combines with the silica. 
 
 With a new bottom, it is usual to introduce a quantity of 
 light wrought-iron scrap (bustling), gradually raise it to a 
 welding heat, and work it into a ball. The oxide produced is 
 spread over the bed. This is repeated every shift of twelve 
 
 1 It is the slag from reheating furnaces. 
 
128 Metallurgy. 
 
 hours, but the bed is repaired after every " heat " by intro- 
 ducing fresh fettling wherever necessary. 
 
 The fuel used is a free-burning coal. In furnaces using steam-jet 
 injectors, small and inferior coal may be employed, and a great saving 
 effected. The large grate space is necessary to attain the high 
 temperature required in the furnace. The depth of the fire is about 
 10 inches. When anthracite is employed, it is less, while the grate area 
 is increased, and the size of the flue diminished. 
 
 The charge generally consists of from 3 to 5 cwts. of pig 
 iron, with the addition of hammer-scale (Fe 3 O 4 ), etc., as may 
 be required. 
 
 The process may be divided into four stages : (i) Melting- 
 down stage. The pig is placed near the fire-bridge, the fire 
 made up, and the damper opened. The manner in which the 
 iron melts, and the temperature, depend on whether grey or 
 white iron is being treated. Grey iron requires a higher 
 temperature than white, and at once becomes very fluid. 
 White iron passes through a pasty state prior to perfect fusion. 
 During this stage, silicon and phosphorus are principally 
 removed by oxidation. 
 
 (2) The boiling stage. When all is melted, the damper is 
 lowered to somewhat reduce the temperature, and the metal, 
 which slightly stiffens, is thoroughly mixed with the oxides of 
 iron (hammer-scale, mill cinder, etc.) added and produced 
 during the melting-down stage. The oxides of iron in the 
 slag and lining of the furnace rapidly oxidize the remaining 
 silicon and also the carbon in the metal. The temperature of 
 the metal rises, and the whole surface is agitated by the 
 escape of the carbon monoxide generated. Each bubble as 
 it emerges bursts into flame (puddler's candles). During this 
 period, the puddler is continuously employed in rabbling 
 (stirring up) the charge, thoroughly incorporating it with the 
 oxides of iron in the cinder^ The boiling gradually subsides, 
 and the metal becomes stiffer and quieter. The carbon has 
 been reduced below i per cent., and the third stage supervenes. 
 It is usual in some districts to remove the greater part of the 
 slag at this stage by skimming it off the surface. 
 
 (3) The fining stage. During this stage, the remainder of 
 the carbon and the manganese are removed, together with 
 
Malleable or Wrought Iron. 129 
 
 some phosphorus. The movements of the metal by CO, 
 owing to its pasty state, are sluggish. The metal is raised and 
 broken up from time to time, and the damper is raised to 
 thoroughly liquefy the slag. The fluid cinder sinks, and bright 
 points gradually extending over the surface, caused by the 
 burning of the iron, show themselves, and announce that the 
 metal has "come to nature." 
 
 (4) Balling stage. The pasty, spongy mass of malleable 
 iron, now at a full welding heat, is then made into balls, 
 weighing some 70 Ibs., by pushing the spongy iron together, 
 and rolling it over the bed of the furnace. As these are made, 
 they are rolled up to the fire-bridge end, and the damper is 
 lowered. The atmosphere of the furnace thereby becoming 
 smoky and reducing, oxidation and waste of the iron is to a 
 large extent prevented. These balls are then removed sepa- 
 rately on an iron bogey to the hammer or squeezer, and 
 shingled that is, the particles of malleable iron welded 
 together and the slag squeezed out. 
 
 The whole operation takes ordinarily about i-| hour, 
 divided as follows : 30 to 35 minutes, running down ; TO to 15, 
 boiling; 10 to 20, fining; 20 to 30, balling up and shingling; 
 but may be longer or shorter according to the purity of the 
 metal treated. 
 
 The loss varies from 7 to 20 per cent., according to purity. 
 The greatest loss occurs with siliceous pig, such as is treated 
 in Scotch forges. 
 
 The process described above is that followed with grey 
 forge pig, and is technically known as pig boiling, the prin- 
 cipal decarburizing agent being the oxides of iron in the lining 
 and slag, the air only affecting the metal in the running down 
 and balling stages. Some of the chemical changes which take 
 place may be thus expressed 
 
 Fe 3 O 4 + Si = 2FeO,SiO 2 + Fe 
 2Fe 2 O 3 + 3Si = 3SiO 2 + 2Fe, 
 Fe 2 O 3 + C + SiO 2 = 2FeO,SiO 2 + CO 
 2FeO, Si0 2 + C = FeO,Si0 2 + CO + Fe 
 2FeO,SiO 2 + O = Fe 2 O 3 + SiO 2 
 
 The silica formed is fluxed off by oxide of iron, of which there is 
 always large excess, and the carbon is removed as carbon monoxide. 
 
1 30 Metallurgy. 
 
 Manganese is oxidized to MnO, which replaces FeO in the slags, rendering 
 them very fluid. The phosphorus is removed by oxidation, and passes into 
 the slag as phosphate of iron. It is probable that to some extent it 
 liquates into the slag as phosphide of iron, and is subsequently oxidized. 
 
 Dry Puddling, as it is called, as now conducted, differs 
 but little from the pig-boiling process, save that white or 
 refined iron is the metal operated on, and in consequence the 
 action is less vigorous, and the amount of slag less. The 
 temperature is lower throughout until the balling stage is 
 reached, the metal never becoming perfectly fluid, and being 
 continuously rabbled. The decarburization is mainly effected 
 by the air passing through the furnace. Formerly it was 
 conducted on a sand bottom. Owing to the nature of the 
 iron employed, there is, of course, less loss. 
 
 Tap Cinder, as the slag from puddling is called, consists of 
 basic silicate of iron, with smaller quantities of lime, alumina, 
 oxide of manganese, and phosphoric acid. Sulphur, probably 
 as iron or manganese sulphide, is also present. It is a black 
 mass, with a dull granular fracture. It may be represented by 
 the formula 2FeO,SiO 2 . In the puddling process it acts as 
 a carrier of oxygen to the impurities in the pig, the ferrous 
 oxide it contains being oxidized and subsequently reduced. It 
 contains from 40 to 60 per cent, of iron, and is tapped from 
 the furnace into rectangular iron waggons. An inferior class 
 of pig iron, known as cinder pig, is made from it by smelting in 
 the blast furnace. 
 
 The sulphur in pig iron is not removed by oxidation either in puddling 
 or finery methods. A considerable portion, however, does pass into 
 the slag, probably by liquation. Its removal is facilitated by any cause 
 which tends to prolong the operation or to render the slag fluid. For 
 this reason, manganese in iron, by prolonging the fining stage and the 
 effect of the oxide formed in giving greater fluidity to the slag, promotes 
 the elimination of this element. It appears to pass out during the whole 
 operation. Various "physics" are employed. Schaffhautl's powder is 
 a mixture of oxide of manganese, salt, and clay. Scheerer's consists of 
 calcium chloride and salt, soda-ash, etc. 
 
 Improvements in Fuddling. Besides the introduction of steam-jet 
 injectors for forcing the fire, various contrivances to diminish labour and 
 save fuel have been introduced. Mechanical rabbles, which traverse the 
 hearth, imitating more or less perfectly the motion given to the rabble by 
 the puddler, have been introduced. In all cases, however, the charge 
 must be balled up by hand. Mechanical furnaces, in which the working 
 of the ball is effected by the revolution of the chamber, have also been 
 
Malleable or Wrought Iron. 131 
 
 employed. The most successful of these is Bank's furnace, for a descrip- 
 tion of which some larger manual must be consulted. In Pernot's furnace, 
 the hearth only revolves in a plane slightly inclined to the horizontal. 
 
 Puddling furnaces heated by gas, and provided with regenerators on 
 the Siemens principle, have also been employed. 
 
 The waste heat from puddling furnaces is generally used 
 for raising steam. 
 
 Shingling and Rolling. The "balls" taken from the 
 puddling furnace consist of a sponge of malleable iron 
 saturated with slag. The consolidation and welding together 
 of the particles, and the expulsion of the slag, are technically 
 known as shingling. The freedom of the wrought iron from 
 slag will depend upon the efficiency with which the operation 
 is conducted. This process takes the form of hammering or 
 squeezing. 
 
 The crocodile squeezer is shown in Fig. 45. It consists of 
 
 FIG. 45. 
 
 two jaws, the lower of which is fixed and forms the anvil, while 
 the upper opens and closes upon it, actuated by the revolution 
 of the crank. The ball is placed between the open jaws, and 
 turned over and moved towards the back part of the jaw as 
 the mass gets reduced in bulk and consolidated by the expul- 
 sion of slag, which flows out over the sides of the anvil. Many 
 other forms of squeezer are also employed. 
 
 The . helve or shingling hammer is shown in Fig. 46. 
 The head, weighing about 8 to 10 tons, is raised (by the 
 
132 
 
 Metallurgy. 
 
 cams on the wheel revolving in front), from 15 to 20 
 inches, and allowed to fall 'on the ball placed on the anvil- 
 block. The number of blows is from 60 to 100 per minute. 
 In belly-helves, the cams act on the lever at a point midway 
 between the head and the fulcrum. 
 
 The objection to the helve is that the weight of the blow 
 is the same at the beginning of the operation, when the ball is 
 tender, as when it has become more solid. 
 
 Steam-hammers are now almost universally employed. 
 
 FIG. 46. 
 
 They consist of an inverted upright steam cylinder, to the 
 piston rod of which the head or " tup " is attached. This 
 slides between vertical guides on the standards which support 
 the cylinder. The admission of steam to the cylinder is con- 
 trolled by a handle which works the valves through a system of 
 levers. In double-acting hammers, steam is admitted below 
 the piston to raise the head, and also above the piston to force 
 it down and increase the weight of the blow. In single-acting 
 hammers, steam is only admitted below the piston to raise the 
 tup, which then falls by its own weight. The larger hammers 
 for forging purposes are of the former type. 
 
 The legs of the shingler are encased in iron guards, and the 
 face protected by an iron mask, to protect him from slag, which 
 flies about in all directions. The ball is placed on the anvil, 
 and receives at first a few light blows. This is effected by 
 admitting a little steam under the piston as the head falls, thus 
 forming a cushion and diminishing the force of the blow. The 
 
Malleable or Wrought Iron. 
 
 133 
 
 weight of the blow is gradually increased, the ball being turned 
 at each stroke, until it has been hammered into a rectangular 
 "bloom," or billet, and the slag thoroughly expelled. The 
 bloom is still hot enough to be rolled out into bars, and is 
 dragged over the iron plates of the floor to the " puddle rolls," 
 or forge train. 
 
 These consist, as shown in Fig. 47, of two pairs of 
 iron rolls, 15 to 18 inches in diameter, mounted in suitable 
 housings, the lower one being driven directly from a steam- 
 
 FIG. 47. 
 
 engine. One pair of rolls, known as the roughing or cogging 
 rolls, has a series of gothic, or V-grooves, of diminishing 
 size ; and the other, known as the finishing rolls, a series of 
 rectangular grooves. 
 
 The surface of the grooves in the roughing roll is notched 
 or chisel-cut, to enable them to grip the bloom and drag it 
 through. It is first pushed endwise into the widest of the 
 grooves in the roughing rolls. As it leaves the rolls on 
 the other side, it is seized and passed back by resting it 
 on the top of the upper roll, which, by its revolution, carries 
 it forward. It is then passed through the next groove, and 
 this is repeated until it has been reduced to the required size. 
 It afterwards makes one or more passes through the rectangular 
 grooves of the finishing roll, and is thus reduced to a flat bar, 
 which is dragged aside and allowed to cool. It then constitutes 
 "puddle bar," on the weight of which the puddler is paid. 
 The fracture is bright and crystalline, or granular. The puddle 
 rolls make about seventy revolutions per minute. The surface 
 of the rolls and the bearings are kept cool by jets of water. 
 
 Puddled bar is never homogeneous, and includes particles 
 of slag not expelled during shingling. 
 
1 34 Metallurgy. 
 
 Crown or Merchant iron, is produced by cutting the 
 puddle bar into suitable lengths and arranging them in a 
 "bundle," "pile," or " faggot," which, if large, is tied by iron 
 wire. The size of the pile depends on the size of the bars, 
 etc., to be produced. It is raised to a full welding heat in the 
 reheating or mill 'furnace ', which somewhat resembles a puddling 
 furnace, but is without a flue-bridge. 
 
 Reheating furnaces working with gas, and provided with 
 regenerators, are now commonly employed. 
 
 When fully hot, the piles are withdrawn, and the bars 
 welded together under the hammer or in a blooming-mill, the 
 pile being afterwards reduced to a size suitable for rolling. 
 
 It then passes to the mill train, which consists; as before, 
 of two sets of rolls roughing and finishing. The pile is 
 cogged down to the required extent in the roughing rolls, and 
 then passes to the finishing rolls to be converted into rounds, 
 squares, angles, or any other form (section) required. The 
 finishing train has chilled iron rolls, and the grooves are turned 
 with great accuracy. Sometimes, instead of at once finishing, 
 the billet, after rolling down, is cut up, and piled, reheated, 
 and again rolled. It then forms No. 3, or best iron, while, if 
 this is again piled and reheated, best best iron results. 
 
 The oxide of iron formed in the reheating combines with 
 the sand of which the bed is made and forms a slag, which 
 flows out of the flue towards which the bed inclines. It . is 
 known as flue cinder and mill-furnace slag. It consists of 
 ferrous silicate, with a large excess of oxide of iron, and has 
 a lustrous crystalline fracture. 
 
 Light work is guided into the rolls by various devices, and 
 is consequently known as guide iron. 
 
 In rolling plates, plain rolls are employed. The billet is 
 passed in one direction until the required width has been 
 obtained, and then turned at right angles and rolled down to 
 the desired thickness. 
 
 The distance between the rolls is regulated by setting- 
 down screws, which act on the top bearing of the upper roll ; 
 and in rolling plates, the distance between them is diminished 
 at each pass, both ends being set down by the same amount. 
 
Malleable or Wrought Iron. 
 
 135 
 
 The weight of the upper roll is counterbalanced. The rough- 
 ing rolls are of grain iron, but the finishing rolls are chilled on 
 the surface. Heavy plate mills are either provided with 
 reversing gear, or are driven 
 by reversing engines, so as 
 to obviate passing the work 
 back over the top roll. 
 
 Thin sheets are rolled 
 by doubling and passing the 
 compound sheet through 
 the rolls. Sometimes as 
 many as sixteen thicknesses 
 are being rolled at one 
 time (see Tin Plate). 
 
 For light work, to save 
 the time of passing it from 
 the back to the front, and 
 the consequent cooling 
 down which takes place, 
 three-high rolls are em- 
 ployed. The middle one 
 is driven from the engine, 
 and the others geared with 
 it. The work having passed 
 through the lower pair is 
 returned through the upper. 
 Hoops, for example, are 
 thus made. 
 
 Three-high mills for 
 heavy work are provided 
 with rising and falling 
 tables, which receive the 
 work as it leaves the rolls, 
 and raise or lower it as 
 required. 
 
 Rolls for rolling finished iron vary from 8 inches to 38 
 inches in diameter. 
 
 The rolling of malleable iron by welding together and 
 
1 36 Metallurgy. 
 
 elongating the particles of iron develops a fibrous structure, 
 which is more pronounced the greater the number of times it 
 is piled and reheated. This treatment also renders the metal 
 more uniform in character. 
 
 COMPOSITION OF MALLEABLE IRON. 
 
 Carbon o'i to 03 
 
 Silicon ... traces ,, o'l 
 
 Phosphorus 0*04 ,, o'2 
 
 Sulphur 0*02 ,, 0*15 
 
 Manganese traces ,, 0*25 
 
 Iron 99'i ,, 99-8 
 
 Burnt Iron. When iron is exposed at a very high tempera- 
 ture to an oxidizing atmosphere, it loses its malleability and is 
 known as burnt iron. Probably this is due to the formation 
 of a suboxide of iron in the metal. 
 
 Brands of Merchant Iron. (ifefr (Crown), common 
 iron, or merchant bar (puddle bar, once piled and reheated). 
 Best, twice piled and reheated. Best best, three times piled 
 and re-heated. Treble best, four times piled and reheated. 
 
 CHAPTER XI. 
 
 STEEL. 
 
 THE designation of steel was formerly confined to those 
 varieties of iron which could be hardened by heating to redness 
 and plunging in cold water. 
 
 The introduction of the Bessemer process marked a new 
 era. The metal produced by this process lacked the fibrous 
 character associated with wrought iron, and partook more or 
 less of the character of steel. Those varieties possessing more 
 than o'3 percent, of carbon sensibly harden when treated in the 
 same manner as steel, but with less carbon this is not the case. 
 Other processes producing similar soft metal sprang up, and 
 the term steel has come to include a great variety of material 
 having widely different properties. Some are softer even 
 than wrought iron, and cannot be hardened. 
 
Steel. 137 
 
 Since the hardening property is dependent on the amount 
 of carbon it contains, a classification based on the percentage 
 of that element is the most convenient, steel containing less 
 than 0*5 per cent, being classed as mild steel. Steel proper 
 contains from 0-5 to 1-5 or 17 per cent, of carbon. The 
 different nature of these metals may be shown by the use of 
 such titles as Bessemer, Siemens's or open-hearth steel. Some 
 of these contain as little as 0^3 per cent, of carbon, less than 
 is often present in wrought iron. They differ from that 
 metal in being devoid of fibre, more homogeneous, and, unlike 
 it, are obtained in a state of fusion, and cast in ingots. The 
 term ingot iron would be more applicable than steel. 
 
 Steel. The fracture of steel becomes finer the larger the 
 proportion of carbon present, but is affected by such treatment 
 as hammering cold. Steel of hard temper, 1 breaks with a 
 bright, uniform, bluish grey, finely granular fracture. After 
 hardening, the colour is somewhat whiter. 
 
 It is very malleable, but requires working more carefully and 
 at a lower temperature than wrought iron. Steel containing 
 less than 1-25 per cent, of carbon can be welded. A lower 
 temperature must be employed than for malleable iron, or the 
 steel will be burnt. To render the surfaces clean at the lower 
 heat, borax mixed with about one-tenth of its weight of 
 sal ammoniac is employed to dissolve the scale. 
 
 The specific gravity varies from 7 '624 to 7 '813, in the 
 unhardened state, to 7*55 to 775 in the hardened condition, 
 showing that expansion occurs. 
 
 The melting-point varies with the proportion of carbon. 
 The softest melts a little below 1600 C. The hardest at 
 about 1400. 
 
 The tenacity varies from 22 tons in mild steel to upwards of 
 70 tons in steel of hard temper. Its elasticity exceeds that 
 of wrought iron, while its ductility is equal to the best qualities 
 of that substance. The mild varieties suffer an elongation 
 and. diminution in area, when subjected to a stretching force, 
 greater than wrought iron. The elongation of the harder 
 varieties is much less, but the elastic limit is high. 
 1 The term " temper " applies only to the proportion of carbon present. 
 
138 Metallurgy. 
 
 Hardening and Tempering. The extent to which harden- 
 ing occurs depends on the proportion of carbon in the metal, 
 and the rate and manner of cooling. 
 
 Thus, quenching in mercury or other good conductor of 
 heat produces greater hardness and brittleness than quenching 
 in water, while quenching in oil (oil hardening) produces a 
 degree of hardness, without brittleness (owing to the slower 
 cooling action of the oil), whereby the tenacity of the steel is 
 increased. .Gun tubes are treated in this way. 
 
 Hardened steel may be rendered soft by heating for a 
 prolonged period at a high temperature, and allowing it to 
 cool down very slowly. This is called annealing. 
 
 When steel, rendered brittle by hardening, is heated at 
 temperatures below redness, the hardness is partially re- 
 moved, and it recovers to some extent its elasticity; the 
 higher the temperature attained, the softer and tougher will 
 the hardened metal become. This operation is known as 
 letiing down or tempering. If the surface of the hard steel 
 be polished, on gradually heating in air, it becomes first a 
 pale straw colour, and afterwards dark straw, golden yellow, 
 brown, brown with purple spots, purple, violet, and blue, as 
 the heating proceeds. These tints serve to mark the degree of 
 heat attained, and, in tempering tools and cutting instruments, 
 indicate to the workman the point at which they should be 
 cooled off. The colours are probably due to thin, films of 
 oxide formed on the surface. The hardness which they 
 indicate depends on the nature of the steel. Below is a table 
 giving the temperatures indicated, and some articles let down 
 to the respective tints. 
 
 220 C. light straw : lancets, razors, and surgical instruments. 
 
 230 C. dark straw : surgical instruments, razors. 
 
 245 C. full yellow : penknives, wood tools, taps, dies. 
 
 255 C. brown: cold chisels, hatchets, etc. 
 
 265 C. brown with purple spots: axes, plane-irons, pocket-knives. 
 
 275 C. purple: table-knives, large shears. 
 
 295 C. violet : swords, watch-springs, augers. 
 
 320 C. full blue : hand and pit saws, etc. 
 
 The cause of these changes in hardness is the manner in which the 
 carbon exists in the metal. In the unhardened state, the carbon is in the 
 form of carbide of iron (Fe 3 C). On heating to redness this carbide is 
 decomposed, and in the hardened metal the carbon is present in some 
 
Steel. 
 
 139 
 
 other form, known as " hardening carbon," diffused through the metal. 
 The degrees of hardness depends on the ratio between the "carbide " and 
 "hardening" carbon. In tempering, some of the hardening carbon 
 changes to carbide, the amount depending on the degree of heat 
 attained. 
 
 VARIOUS QUALITIES OF STEEL. 
 
 Description. 
 
 Percentage of 
 carbon. 
 
 Character and uses. 
 
 Mild steel . . 
 
 Die temper 
 
 Sett temper 
 
 Chisel temper 
 
 Punch temper 
 
 Turning-tool tem- 
 per 
 
 Razor temper 
 
 0*1 to 0*25 
 (0-2 ,,0-4 Mn) 
 0'3 0-4 
 
 0-4 
 
 Soft malleable metal for rivets and 
 plates. 
 
 Harder and stronger for rails, forgings, 
 etc. 
 
 For tyres and castings. 
 
 For hard wire, for guide ropes, springs, 
 etc. 
 
 Is tough, capable of resisting great 
 pressure, is very easily welded. 
 Used for stamping and pressing dies, 
 welding steel for axes, plane-irons, 
 etc. 
 
 Is hard, tough, strong, capable of re- 
 sisting sudden and great shocks, 
 blows, etc. Used for cold setts, 
 minting dies, and smiths' tools ; 
 easily welded. 
 
 Is easily forged ; hard even when let 
 down low, and sufficiently tough to 
 withstand blows ; is weldable. Used 
 for cold chisels, miners' drills, large 
 punches, etc. 
 
 Is a hard, fine-grained metal. Takes 
 and maintains a good cutting edge ; 
 is more difficult to work, but welds 
 with great care ; used for circular 
 cutters, taps, rimers, large turning 
 tools and drills, screwing dies, etc. 
 
 Is unweldable, and must be carefully 
 treated in forging, hardening, and 
 tempering ; is generally useful for 
 turning, planing, and slotting tools, 
 drills, small cutters, taps, saw-files, 
 etc. 
 
 i '5 and This and the last variety are unsuited 
 upwards. for any purpose where sudden varia- 
 tion in pressure, etc., occurs. Can 
 only be dealt with by a skilful work- 
 man, and if at all over-heated, is 
 spoilt. Used for razors, surgical 
 instruments, small tools, etc. 
 
 The harder varieties of steel occupy an intermediate 
 position, between malleable iron, on the one hand, and cast 
 
 0-6 
 
 075 
 
 0-825 
 
 I'D 
 
 I-I25 
 
 1-25 
 
140 Metallurgy. 
 
 iron on the other. The comparison ends with the carbon 
 contents of the metal, as in all steels, save special kinds to be 
 noted hereafter, the other elements present in cast iron, are 
 found only in minute quantities. They exist in appreciable 
 amounts in the metal obtained from all processes in which 
 steel is made direct from cast iron. 
 
 Steel-Making. The methods of producing steel may be 
 classed as follows : 
 
 1. Direct methods 
 
 (a) From iron ores. Catalan and analagous processes. 
 
 (b) From cast iron. Puddled steel. 
 
 2. Indirect methods 
 
 (a) By the carburization of malleable iron in an unfused 
 
 state. Cementation and case-hardening processes. 
 
 (b) By carburization of molten malleable iron. 
 
 (1) Fusion of bar iron with carbon in crucibles. 
 
 Cast crucible steel and Wootz processes. 
 
 (2) The carburization of molten malleable iron 
 
 obtained by complete or partial decarburiza- 
 tion of pig iron. Bessemer and open-hearth 
 processes. 
 
 Steel in the Catalan Forge. Excellent steel of middle 
 temper can be made in open hearths of this type, by giving 
 the tuyere less inclination, so that the blast does not play so 
 directly on the accumulating mass of metal, and removing the 
 slag more frequently than in making malleable iron. 
 
 In making steel in these hearths, less small ore is added, so that the 
 slag is less basic, and less blast employed. By these means the reduction 
 is somewhat prolonged, affording opportunity for carburization by decom- 
 position of carbon monoxide by the spongy iron, while the direction of the 
 tuyere and the removal of the slag prevent decarburization by the oxide of 
 iron it contains, and by the air. The presence of manganese in the ore is 
 also favourable to the production of steel. Its oxide gives greater fluidity 
 to the slag, and is less energetic as a decarburizing agent. 
 
 Puddled Steel. Steel can be made in the puddling furnace 
 by arresting the process before decarburization is complete, 
 sufficient carbon being left to constitute steel. White pig irons 
 containing manganese and free from sulphur are best adapted 
 for the purpose. 
 
Steel 
 
 141 
 
 Cementation Process. This is by far the most important 
 method of producing steel for cutting-instruments, i.e. steels 
 of hard temper. As previously noted, when iron is heated 
 in contact with carbon, carbon monoxide, or compounds of 
 carbon and hydrogen (hydrocarbons), to a high temperature, 
 carbon is taken up by the iron. This is the basis of the 
 process by which all the best qualities of steel for cutlery, 
 springs, etc., are produced. The superiority of the method is 
 due to the fact that practically pure iron is employed for the 
 
 FIG. 49. 
 
 purpose. Swedish bar iron, made in the Swedish Lancashire 
 hearth under charcoal, from charcoal pig, is the material 
 usually operated on, so that such steels practically consist 
 solely of iron and carbon. The bars employed are about 10 
 feet long, 3 inches wide, and f inch thick. Hammered bars 
 are preferred. Basic steel bars are also sometimes employed. 
 
 The converting furnace is shown in Fig. 49. The furnace 
 proper consists of a rectangular arched chamber, A, of fire-brick. 
 This communicates by the chimneys B B B, three on each 
 side, with the hovel C about 40 feet high, which serves as a 
 
142 Metallurgy. 
 
 chimney and diminishes the loss of heat by radiation. It gives 
 the furnace the appearance of an ordinary glass furnace. A 
 narrow fireplace, 12 to 15 inches in width, runs down the 
 middle, with a firing door at either end. On each side of the 
 fireplace is a trough or pot, D, for the reception of the bars of 
 iron. They are made of firestones, open at the top, and rest 
 on the benches E E on brick bearers, which divide the 
 space below the pots into a number of flues, F. These are 
 continued up the sides and ends of the pot ; the space above 
 the fire is similarly divided, so that the boxes may be heated as 
 uniformly as possible. 
 
 The pots are from 10 to 15 feet long, 3^ to 4 wide and 
 deep. In the end of each is a small opening, H, known as the 
 tap-hole. This is opposite a similar opening in the outer 
 wall, and through it the tap or trial bars are withdrawn, 
 from the appearance of the fracture of which, the progress of 
 the operation is judged. A manhole is provided for the pur- 
 poses of charging and discharging the pots, and is closely 
 bricked up during the conversion. 
 
 The pots are charged by first spreading a layer of charcoal 
 nubs (about as large as peas or beans) over the bottom. On 
 this a layer, of bars, about half an inch apart, is placed. 
 A second layer of charcoal, followed by bars, is then put in, 
 and so on, until the pots are full, finishing off with charcoal. 
 The charge is covered with " wheelswarf." 
 
 This is the refuse from under the grindstones, and consists of particles 
 of oxidized (rusted) iron and sand. At the high temperature of the furnace, 
 this frits and forms a rough glass, which hermetically seals the pots and 
 excludes air. 
 
 The manhole is bricked up and carefully luted, as also is 
 the space round the trial-bars. A coal fire is then made and 
 the temperature gradually raised. In about 24 hours the pots 
 are at a dull red heat, and in about 50 hours or more, the bright 
 red or yellow heat (noo to 1200 C.) required for conversion 
 is attained. This is steadily maintained for a period of from 
 4 to 8 or i o days, depending on the degree of carburization 
 required. For springs, saws, etc., 4 or 5 days suffice. For 
 shear steel, 5 or 6 days : double shear, 7 to 8 days ; and tool 
 
Steel. 143 
 
 steel, 10 days or more. The progress is judged by the appear- 
 ance of the fracture of the trial bars, a crystalline layer of 
 steel of greater or less depth is formed, enclosing a " sap " of 
 unaltered iron, but there is no sharp line of demarcation. 
 When judged complete, the fires are allowed to burn out, and 
 the furnace to cool very gradually. This occupies about a 
 week, and the pots are then discharged. The bars present 
 a blistered or warty appearance, and a laminated structure, 
 and are hence known as blister steel. 
 
 These blisters are evidently formed by the efforts of gas to escape from 
 the interior of the bar while in a pasty state. The gas is formed by the 
 action of the carbon on particles of slag, containing oxide of iron, enclosed 
 in the iron. 
 
 The bars are brittle, and are sorted out by breaking with 
 a hand hammer on a block, and examining the fracture. 
 No. i, " spring temper," shows a comparatively thin skin of 
 steel enveloping unaltered iron. In No. 4, "double shear heat," 
 the proportions. of steel and iron are about equal. In No. 6, 
 " melting heat," the "sap" has disappeared, and the conver- 
 sion has extended through the bar. The carburization is 
 probably due to the decomposition, by the iron, of carbon 
 monoxide produced from the oxygen in the small amount of 
 air retained in the pot and in the pores of the carbon (see 
 page 107). As before noted, iron at redness is easily per- 
 meated by gases, and thus carbon is carried into the interior 
 of the bar. The amount of carbon taken up varies with the 
 time and temperature up to i *5 per cent. 
 
 Blister Steel is brittle, largely crystalline, and lacks homo- 
 geneity. For most purposes it is either tilted or melted. 
 
 Shear Steel. The blister is cut into lengths, faggoted, 
 reheated, and welded, and then either drawn out under the 
 hammer or rolled, in a manner resembling the treatment of 
 iron. By this means greater uniformity of composition is 
 obtained. The metal sometimes undergoes a second piling 
 and reheating. 1 By this treatment the percentage of carbon 
 is very slightly reduced by oxidation, and only the milder 
 
 1 After once piling it is known as shear steel t and after a second 
 treatment, as double shear steel. 
 
144 
 
 Metallurgy. 
 
 tempers with less than 1*125 P er cent - f carbon can be 
 satisfactorily welded. The pile is frequently coated with clay 
 wash and borax, to protect it from oxidation and facilitate 
 welding. Tilted steel has lost the laminated appearance of 
 blister steel and is more uniform in character. 
 
 Cast Crucible Steel. Steel produced as above must 
 necessarily be far from homogeneous. In 1740, Huntsman 
 introduced the practice of melting down the blister steel 
 in crucibles, pouring it into ingot moulds, and working the 
 ingots into bars, etc. The fusion ensures uniformity of 
 character and composition, hence the term homogeneous 
 
 _L 
 
 FIG. 50. 
 
 metal or steel applied to it. Its commoner designation is 
 crucible cast steel. 
 
 The steel-melting holes or fires (see Fig. 50) are simple 
 wind furnaces of oval section, lined with ganister. They 
 are placed below the floor level for convenience of handling the 
 pots. Each fire has a separate flue, which is continued down 
 behind the furnace, and opens into the ash-pit. The draught 
 is regulated by the insertion or removal of a brick in this 
 opening. The crucibles, which are dried on shelves round the 
 melting-house, are from 16 to 19 inches high and 6 to 8 inches 
 
Steel. 145 
 
 in diameter at the mouth. Each fire takes two pots. Before 
 placing them in the furnaces they are annealed in a stove or 
 oven, mouth downwards, for some hours, gradually attaining a 
 dull red heat. The blister steel is cropped up into small 
 pieces, and the charge is introduced into the heated crucibles 
 by means of an iron funnel. The pots generally last about 
 three melts, the weight of the charge being less each time. 
 Thus a first charge of 50 Ibs. will be followed by charges of 
 45 and 40 Ibs. respectively for the second and third. 
 
 The charge having been introduced, the lid is put on, the 
 fire is made up with hard, free-burning coke, and the furnace 
 closed. This first fire burns off in about forty-five minutes, 
 and is followed by a second and third firings. The amount 
 of fuel added in the third fire is judged from the amount of 
 metal remaining unmelted, to ascertain which, the workman 
 pokes an iron bar into the pots and gives directions accord- 
 ingly, in order that all the crucibles may be ready at one time. 
 The crucibles are lifted from the fires, for teeming, by grasping 
 them round the belly with tongs having bent jaws, which 
 encircle the pots. The first melt occupies from 4 to 5 hours. 
 
 Small ingots are run from a single pot. For larger ones the pots are 
 doubled, that is, the contents of two pots are transferred to one before 
 teeming, while for still larger ones the metal from the crucibles is trans- 
 ferred to a ladle similar to that described (see p. 150), or arrangements must 
 be made to keep up a constant stream of metal into the mould. 
 
 The ingot moulds are of cast iron, and made in two 
 parts. While casting they are held together by an iron ring. 
 The moulds are warmed and reeked, that is, coated with lamp- 
 black, by smoking them with the flame of burning tar. Some- 
 times a wash of clay is applied. This treatment prevents the 
 ingots from sticking. In pouring, the hot stream of metal 
 should not touch the sides. 
 
 The pots, if in good condition, are returned, after detaching clinker, 
 tc., to the fires, ready for the next charge. If allowed to cool, they 
 cannot be reheated without cracking. In melting blister steel, it is usual 
 to add a small quantity of black oxide of manganese, which is partly 
 reduced, and manganese passes into the metal. The slag is removed 
 before teeming by moving a knob of slag (mop), attached to an iron bar, 
 over the surface of the metal, by which means the slag is cooled, collects 
 on the mop, and is removed. 
 
 L 
 
146 
 
 Metallurgy. 
 
 Direct Cast Crucible Steel. In casting large ingots of 
 crucible steel, bar iron or puddled steel is employed instead 
 of blister steel, charcoal, spiegel, and ferro-manganese being 
 added to carburize the metal to the desired degree. Ingots 
 40 tons in weight have been cast. 
 
 Fig. 5 1 shows a regenerative crucible furnace for steel melting. 
 
 FIG. 51. Regenerative Crucible Furnace. 
 
 They take from 8 to 24 pots in a double line. The roof 
 is in several sections, which can be removed as required for 
 charging or teeming purposes. Some furnaces of this type are 
 provided with a movable bottom, which can be elevated, by a 
 hydraulic ram, to the flooj level, with all the pots standing on it. 
 
 Plumbago pots, having a larger capacity than those described, are also 
 employed. They are more durable than ordinary white or black pots 
 (i.e. clay, or a mixture of clay and coke-dust), and with care will bear 
 reheating after cooling. They last from 9 to 1 1 melts. 
 
 Honeycombing. Steels, especially those of mild temper (below o'5 per 
 cent, of carbon) are liable to boil up in the mould after teeming. This 
 is due to the disengagement of dissolved gases, mainly H, N, and CO, 
 which are given off as the metal cools. The bubbles of gas cause the metal 
 to be honeycombed and vesicular. With a view to prevent boiling up, 
 a stopper, which fits loosely, is put on the top of the metal, and a little 
 
Steel. 147 
 
 sand thrown on and rotmd it to keep it down ; or sand is thrown on the 
 top of the metal and an iron cover is put on and held down by wedges 
 passing through eyes on the top of the mould. 
 
 The upper part is most affected, the gases from the lower part rising, in 
 consequence of the metal at the bottom remaining fluid for a longer time. 
 The presence of the stoppers prevents the top from cooling so rapidly. 
 
 Piping. Steel of harder temper (above 07 per cent, of carbon) settles 
 down in the mould, forming a funnel-shaped cavity or pipe. The ingot 
 is topped by breaking off the unsound part before working. Both these 
 evils may be largely mitigated by careful melting and teeming at the 
 proper temperature. 
 
 Dead-melting. If not heated a sufficient length of time, the metal is 
 not " killed," and will teem " fiery " throwing off sparks and be honey- 
 combed. If " dead-melted," this does not occur, but if left too long in 
 the fires it will teem " dead," and be weak and brittle. 
 
 Case-hardening. The surfaces of wrought iron and mild steel articles 
 subject to wear, are often superficially hardened by packing them in iron 
 boxes, with parings of horns and hoofs, leather scrap, bone-dust, and char- 
 coal, and heating to full redness. The depth of the hardening depends on 
 the length of time they are heated. Small articles are case-hardened by 
 heating them to redness and sprinkling or rubbing them in powdered 
 yellow prussiate of potash (potassium ferro-cyanide). The carburization is 
 effected by the cyanogen (CN) compounds. 
 
 Production of Steel from Pig Iron without previous con- 
 version into malleable iron. These processes involve the 
 removal from the pig of the silicon, sulphur, and phosphorus, 
 and the reduction of the amount of carbon to the quantity 
 required to convert the metal into steel. It is found more 
 satisfactory, however, to completely remove carbon as well, 
 and recarburize by the addition of carbon in some form 
 or other, generally as spiegeleisen or ferro-manganese ; but gas 
 carbon and other substances are also employed (Darby process). 
 
 Bessemer Process. In the Bessemer process the impurities 
 are burnt out of the pig by blowing air through the molten 
 metal. Referring to p. 121, it will be seen that all the im- 
 purities, except sulphur, will practically be oxidized before the 
 iron, so that by stopping the blast at the right moment, and 
 adding a quantity of spiegeleisen or other carbon-bearing 
 material, sufficient carbon may be introduced to produce steel 
 of the desired temper. 
 
 The process is generally conducted in a vessel or converter 
 of the form shown in Fig. 52. It consists of a boiler-plate 
 casing J to i inch thick, carried on a cast-iron ring, provided 
 with trunnion arms, upon which it is carried in bearings on 
 standards or other supports. Upon one of the trunnions is 
 
148 
 
 Metallurgy. 
 
 keyed a toothed wheel, which gears with a rack (Fig. 53) 
 attached to a hydraulic ram, by the movement of which the 
 converter can be rotated on its bearings through 180 to 300. 
 The other trunnion is hollow, and connects by the pipe P 
 (Fig. 52) with the blast-box B at the bottom of the converter. 
 This is a compartment into which the blast is led through the 
 hollow trunnion, and forced through the metal by means of clay 
 tuyeres T passing through the upper or guard-plate of the blast- 
 box and the lining ot the 
 vessel. The vessel is lined 
 with about 9 to 1 2 inches of 
 ganister on the sides, and 18 
 to 20 inches on the bottom, 
 introduced as described, p. 
 34. The tuyeres are slightly 
 conical in form, and are 
 about 22 inches long. They 
 are made of fire-clay, and 
 contain from 10 to 1 2-1-inch 
 
 o 
 
 holes, running in the direc- 
 tion of the length, by which 
 the air passes from the blast- 
 box to the vessel They pass 
 up through holes in the 
 guard-plate, against which 
 they are pressed by suitable 
 stops, and are embedded in 
 They only stand out slightly 
 
 FIG. 52. Bessemer Converter, as used in 
 Basic Process. 
 
 the ganister lining the bottom, 
 from the surface. 
 
 If a tuyere proves faulty in work it can be removed and replaced, by 
 taking off the bottom plate, knocking it out, and pushing up a new one in 
 its place, a little slurry of ganister being run round from the inside to make 
 the joint secure. After drying and heating the converter is again ready. 
 
 Converters with detachable duplicated bottoms are now commonly 
 employed, so that little delay is occasioned by the removal of a worn-out 
 or faulty one, and the substitution of a newly prepared bottom. The 
 vessel itself is also made in sections, as shown, and duplicate parts are kept 
 in stock. 
 
 Method of conducting the Process. The pig iron to be 
 treated is melted in cupolas, or is taken direct from the blast 
 
Steel 149 
 
 furnace, after mixing to ensure uniformity. The converter, 
 previously heated, is turned on its side, and the metal run in. 
 The full charge lies below the level of the tuyeres when in this 
 position. The blast, at a pressure of from 20 to 25 Ibs., is 
 then turned on, and afterwards the vessel is rotated into a 
 vertical position. The metal now flows over the bottom, and 
 the air passes up through it, the high pressure preventing it 
 running into the blast-box. At first only a short, yellowish- 
 red flame is seen at the mouth of the converter, accompanied 
 by sparks. During this period the temperature rapidly rises. 
 The silicon is being rapidly oxidized to silica (SiO 2 ), which, 
 combining with oxides of iron and manganese, forms silicates. 
 The flame gradually becomes larger and more luminous, and 
 is accompanied by showers of brilliant sparks, consisting 
 of slag and particles of iron. This corresponds to the 
 " boiling stage " of the puddling process, and is known as 
 the boil. The violence of the disturbance of the metal is 
 due to the rapid oxidation of the carbon with the production 
 of carbon monoxide, which escapes. During this part of the 
 process, the pressure of the blast is reduced. The luminosity 
 and volume of the flame gradually diminish, and in the 
 third or "fining" stage, during which the remainder of the 
 carbon and manganese are being removed, it fades to a pale 
 amethyst tint, and is nearly transparent. There are also fewer 
 showers of sparks. In from fifteen to twenty minutes from 
 the commencement of the blow, the flame suddenly shortens 
 or " drops." This marks the almost complete removal of the 
 carbon, and if the blast is further continued, great loss from 
 oxidation takes place, and the quality of the metal is rendered 
 much inferior. The vessel is accordingly turned down and 
 the blast shut off. A weighed quantity of spiegeleisen, 
 previously melted in a cupola, is added to the metal as it lies 
 in the converter, from a ladle. This addition is attended by 
 a violent outburst of flame and considerable agitation of the 
 metal. The spiegel imparts to the iron the requisite amount 
 of carbon to produce steel of the desired temper, and also 
 sufficient manganese to restore the malleability, which, as before 
 noted, is always lost when malleable iron in a molten -state is 
 
1 50 Metallurgy. 
 
 subject to oxidizing influences. For steel of very low temper, 
 ferro-manganese is employed, in order to introduce the necessary 
 amount of manganese without adding too much carbon. This 
 is added solid. After standing a few minutes to allow the 
 slag and metal to separate, the converter is turned down and 
 the steel run from its mouth into the ladle. Enough slag to 
 cover the metal and keep it hot is also allowed to flow into 
 the ladle. The converter is then turned completely over, and 
 the slag allowed to run out. All the movements of the vessel, 
 as also the blast, are regulated by a workman situated on an 
 elevated platform at some distance from the converter, the 
 
 FIG. 53. 
 
 progress of the operation being judged from the appearance of 
 the flame. 
 
 The ladle to which the metal is transferred is mounted as 
 shown (Fig. 53) on a hydraulic crane, in the centre of the 
 casting pit, which is circular. The converters are situated at 
 the side of the pit. The ladle can be raised and lowered, can 
 be made to travel round the pit, to and from the centre, and 
 also turned over to empty slag. It is lined with ganister, and 
 heated by a fire made in it before receiving the metal The 
 
Steel. 1 5 1 
 
 teeming is effected from the bottom, through a hole closed by 
 a fire-clay stopper, which is raised and lowered by an iron rod 
 protected with fire-clay tubes and connected with a suitable 
 lever. 
 
 The moulds are of cast iron, open top and bottom, and more or less 
 tapering. They are arranged round the side of the casting pit, standing on 
 an iron plate. The usual practice is to fill each mould separately from the 
 top, but sometimes the moulds are arranged in groups, round a central 
 one somewhat taller than the rest. The bottom of this is connected by 
 a system of fire-clay tubes opening upwards, with the bottoms of the others. 
 The metal is run into the central or feeding ingot and is conveyed to the 
 others by the clay passages. It gradually rises in the moulds until they 
 are all filled. Sounder ingots are said to be obtained in this way. In all 
 cases they are stoppered down with sand and a plate, as previously 
 described. 
 
 Chemical Changes in the Bessemer Process. The oxidation of the 
 impurities in the pig is effected by oxide of iron, formed by the air blown 
 in, so that the chemical reactions are similar to those taking place in 
 puddling. Being in a fluid state, and thoroughly agitated by the passage 
 of the air, silicon, being most oxidizable, is much more largely attacked 
 than other impurities in the first stage of the process, and is reduced to 
 about o'5 per cent. In the subsequent stages it is reduced to about 0*02 
 or 0*03 per cent. During the boil the carbon is reduced to below I per 
 cent., and in the fining stage to below O'l per cent. Manganese is attacked 
 from the beginning and throughout the process, the oxide formed com- 
 bining with the silica and forming silicate, which passes into the slag. 
 The phosphorus, as shown by its absence from the slags, is unattacked, 
 and the steel consequently contains a higher proportion than the original 
 pig iron, since a loss of some 10 per cent, occurs on the weight of pig 
 employed. This is due, as already noted on p. 36, to the siliceous nature 
 of the lining. The iron employed must therefore be free from phosphorus. 
 Sulphur also is not removed. 
 
 The blast is used cold, and yet the temperature gradually rises as the 
 process proceeds. This increase of heat is due to the oxidation going on, 
 principally of the silicon in the iron. The amount of silicon present is less 
 than the carbon, but in burning, a solid substance (SiO 2 ), which remains 
 behind in the converter, is produced, and all the heat generated is 
 communicated to the contents of the vessel (save such as is carried away 
 by the nitrogen of the air blown in). The combustion of the carbon 
 generates gaseous bodies which, escaping, carry away much of the heat. 
 Manganese, like silicon, yields a solid product of combustion, and 
 accounts, when present, for some of the heat. 
 
 During the blow the iron is oxidized and becomes "burnt," and 
 is rendered brittle and unworkable. The manganese in the spiegel added 
 combines with the oxygen, forming manganous oxide (MnO), and passes 
 into the slag. A slight excess is always employed to ensure the complete 
 removal of the oxygen. This, with the carbon contained in the spiegel, 
 enters the steel. Bessemer and open-hearth steels always contain manganese. 
 The amount should not exceed 0-5 per cent. 
 
 The metal employed is grey pig iron, and should contain about 2 to 
 2.1 per cent, of silicon, and be free from sulphur and phosphorus. Iron 
 smelted from pure ores, such as red hematite and magnetite, and known 
 
152 Metallurgy. 
 
 as Bessemer pig is employed. With the rapid, continuous working 
 practised in America a fresh quantity of pig being run in immediately 
 after teeming the previous charge, that no loss of heat occurs pig con- 
 taining not more than I per cent, of silicon is satisfactorily treated. Excess 
 of silicon increases the amount of loss. 
 
 The process described above is commonly known as the 
 acid process, from the siliceous nature of the ganister lining. 
 The slag is a basic silicate of iron and manganese. As already 
 shown, iron containing phosphorus cannot be treated under 
 these circumstances. By substituting a lining of basic 
 material, phosphorus as well as other impurities may be 
 removed. 
 
 The Basic Bessemer Process is conducted in a vessel 
 similar to that already described, but generally with a straight 
 neck, so that me metal can be poured from either side, and 
 the converter can be completely rotated by worm and wheel 
 gearing, actuated by hydraulic engines attached to the 
 standards. 
 
 The converters are made in sections, which can be readily 
 secured together by pins and cotters (see Fig. 52), so that if 
 the lining of any portion gives way another similar part can 
 be substituted without delay, an overhead travelling crane 
 which commands the converters, and hydraulic tables under 
 each converter, being provided for raising and lowering the 
 parts. 
 
 The lining employed consists of calcined dolomite or 
 magnesite (see p. 37), and is about 14 to 16 inches thick on 
 the sides, and 24 inches on the bottom. Loose tuyeres are 
 sometimes employed, but generally they are formed by ramming 
 the lining material round steel spikes, which are withdrawn 
 when the bottom is rammed up, and thus form free passages 
 for the air. The process differs somewhat from the ordinary 
 "acid" process. Before running in the iron, a quantity of 
 lime, equal to about 15 per cent, of the charge, is introduced, 
 with a little coke, into the hot converter, and blown hot. The 
 charge is then run in, in the usual manner, and the blow pro- 
 ceeds as before up to the point at which the flame drops. 
 Instead of stopping the process here, the blast is continued for 
 some two or three minutes longer to eliminate the phosphorus. 
 
Steel. 153 
 
 The vessel is then turned down, and a sample taken with a 
 spoon, hammered out, cooled, and broken. From the fracture 
 and malleability, the workman judges how long the blow must 
 be continued to complete the elimination of phosphorus. A 
 crystalline fracture indicates that the phosphorus is not com- 
 pletely removed, and the vessel is turned up, and the blowing 
 continued until the metal is dephosphorized. A second 
 sampling may be necessary. 1 
 
 The slag is then run off, to prevent precipitation of 
 phosphorus into the metal by reduction from the slag when 
 the carbon is added. Spiegel and ferro are then added in the 
 usual manner, and the charge transferred to the ladle, and 
 thence to the moulds. In some cases, where hard metal is 
 required, the carburization is effected by grey pig iron free 
 from phosphorus, added in a molten state to the metal in 
 the ladle, ferro-manganese being afterwards added. 
 
 The oxidation of impurities during the blow, up to the 
 dropping of the flame, proceeds as in the acid process, but, 
 owing to the nature of the lining and the basic character of 
 the slag, some phosphorus is also removed. In the after-blow 
 the residue of the phosphorus is oxidized, and, combining with 
 lime, forms calcium phosphate, and passes into the slag. This 
 frequently contains as much as 30 per cent, of phosphates of 
 lime and magnesia, together with 8 to 10 per cent, silica, 10 
 per cent, oxide of iron, sulphur, and some oxide of manganese. 
 It amounts to about 20 per cent, of the charge, and on account 
 of the phosphates present is ground up and used as manure. 
 
 If the pig iron treated contains much silicon, the charge becomes 'too 
 Jiot, and the corrosion of the lining is increased. Since, under ordinary 
 conditions, the presence of silicon is essential to provide heat by its oxida- 
 tion, some substitute is necessary in basic Bessemer pig. This is found in 
 the phosphorus, and as much as I '5 to 3 per cent, of that element is often 
 present. Some of the slag is returned to the blast furnace to increase* 
 the phosphorus in the pig. It lowers the melting-point of the metal 
 until decarburization is complete, and thus less heat is requisite in the 
 earlier stages. By its oxidation in the after-blow, it produces the high 
 temperature necessary to maintain the iron in the fluid state. As with 
 silicon, the product of burning is a solid, and remains in the vessel. 
 
 1 The time during which the blowing is continued after decarburization 
 is known as the " after-blow" During its continuance, red-brown smoke 
 issues from the converter. 
 
54 
 
 Metallurgy. 
 
 About i per cent, of silicon is necessary in the iron, or the blow will be 
 too cold and slow. The presence of from I to 2 per cent, of manganese is 
 also advantageous. 
 
 The removal of the phosphorus depends on the basicity of the slag, 
 and hence the addition of lime in the converter. This also diminishes 
 the wear on the lining. The loss amounts to about 15 per cent. 
 
 The charge of a converter ranges from 5 to 15 tons, and the operation 
 lasts from 15 to 25 minutes, according to weight and circumstances. 
 
 Open-hearth Processes. Under this heading are included 
 processes conducted in regenerative gas furnaces of the Siemens 
 type (see Fig. 54), the bed of which may be composed of 
 silica sand (acid), or of magnesite, dolomite, or chromite (basic). 
 
 Siemens's Regenerative Furnace is shown in Figs. 54 and 
 
 FIG. 54. Siemens's Regenerative Furnace. Longitudinal Section. 
 
 55. The furnace is a double-ended, reverberatory, gas-fired 
 furnace. The furnace chamber, A, communicates at either end 
 with the chambers B B, C C, by means of the ports and flues D D. 
 The chambers are filled with chequer brickwork, built up of 
 bricks 2 inches square. The chequers are alternately heated 
 by the passage of the hot gases from the furnace descending 
 through them on their way to the chimney-stack, and the heat 
 retained is subsequently given up to the cold air and gas passing 
 
Steel 
 
 155 
 
 upwards through them on their way to the furnace. The 
 chambers are worked in pairs, the gas and air being heated 
 in separate chambers. One pair of chambers is being heated 
 up while air and gas are passing through the other pair. The 
 smaller chambers, B, are the gas chequers, and C the air 
 chequers ; E E E are the working doors ; F is the chimney- 
 flue ; G the gas-supply culvert ; R R the valves for reversing 
 
 FIG. 55. - Cross-section ot Furnace. 
 
 the direction of the gas and air; L the launder or spout 
 for conveying the metal into the ladle ; P is the casting pit. 
 The direction of the air and gas are reversed every half-hour. 
 In this way the chequers are kept at a high temperature, 
 and the gas and air coming to the furnace, develop a much 
 higher temperature than if supplied cold. 
 
 The Siemens Process. This process is analagous to the 
 "pig boiling" puddling process, the decarburization of the 
 metal being effected by pure oxidized iron ores added to 
 the fused metal in the bath of the furnace. On this account 
 it is sometimes described as the " pig and ore " process. 
 
 The pig iron, to the extent of 5 to 40 tons, is introduced 
 on the bed of the furnace and melted. After fusion, additions 
 of red hematite, roasted pottery mine, or other pure oxidized 
 ores are made from time to time, which effect the oxidation 
 
156 Metallurgy. 
 
 and removal of the silicon, carbon, and manganese in the pig 
 in the same manner as in puddling. 
 
 At the high temperature attainable in these furnaces, how- 
 ever, the metal remains molten even after decarburization is 
 complete, and its conversion into steel is effected by the addi- 
 tion of spiegel and ferro, as in the Bessemer and Basic Bessemer 
 processes. The time occupied is, however, much longer, extend- 
 ing sometimes to 10 or 14 hours with large charges. This 
 permits of more perfect control over the composition of the 
 steel produced, as samples can be taken from time to time, 
 and the character and carbon contents of the metal rapidly 
 determined. When the carbon has been reduced below o-i 
 per cent, spiegel is added, the tap-hole is broken open and the 
 metal run into the ladle. Some ferro-manganese, broken into 
 small pieces, is generally added in the ladle as the metal flows 
 out, to replace that lost by oxidation in the furnace, and to 
 make up the amount necessary to restore the malleability and 
 carburize the iron. 
 
 In the decarburizing stage, the metal boils violently, and 
 is thus brought into contact with the oxidizing slags and the 
 atmosphere of the [furnace, but becomes quiet towards the 
 end of the operation. The addition of the spiegel causes it 
 to again become lively, and the metal is tapped on the boil. 
 
 The yield is some 2 or 3 per cent, in excess of the pig 
 iron charged, owing to the reduction of the ore added to 
 decarburize it. A cutting oxidizing flame is employed in the 
 earlier stages. 
 
 Siemens-Martin Process. In this process the percentage 
 of carbon to be removed from the metal is diminished, by 
 melting the pig iron with scrap wrought iron or steel intro- 
 duced into the furnace at the same time, or previously heated 
 and charged into the bath of molten pig iron. Scrap to the 
 extent of 8 or 10 times the weight of pig is frequently employed. 
 The charge, after fusion, contains less than i per cent, of 
 carbon. The amount of scrap added depends on the greyness 
 of the pig. No ore is added, and the decarburization is 
 effected by the oxide formed on the scrap during melting, 
 and the atmosphere of the furnace, which is oxidizing. The 
 
Steel. 157 
 
 bath is sampled from time to time, and, -when the carbon 
 has been sufficiently reduced, spiegel and ferro-manganese are 
 added as before. The loss amounts to about 7 or 8 per cent, 
 of the metal charged. 
 
 A combination of the two processes is commonly used in 
 this country, pig iron, scrap, and ore forming the furnace charge. 
 It affords a convenient method to utilize scrap. 
 
 Basic Open-hearth Processes. In furnaces with sand 
 bottoms the pig iron employed must be of Bessemer quality, 
 but with basic bottoms phosphoretted pig can be treated. As 
 in the basic Bessemer process, lime is charged in the furnace, 
 and samples are taken from time to time and tested. 
 
 As the phosphorus is not required as a heat-producer, the 
 less there is present the better. Pig containing about 1-5 to 2 
 per cent, is satisfactorily treated, but the presence of manganese 
 up to 2 or 3 per cent, is also desirable, as it prolongs the fining 
 stage and permits of the elimination of the phosphorus without 
 undue oxidation of the iron. In dephosphorizing, it is some- 
 times necessary to make small additions of ferro-manganese 
 and pig to prevent this. The metal obtained by any of these 
 processes is dealt with as in the Bessemer process. 
 
 Casting. Formerly the casting-pits were rectangular, and 
 the ladle, mounted on a carriage, travelled on rails over the 
 top of ingot moulds. 
 
 Circular or semicircular casting-pits with hydraulic central 
 cranes are being introduced. 
 
 Attempts have been made to combine the rapidity of the Bessemer 
 process with the certainty of the results obtained in the open-hearth pro- 
 cesses. 
 
 A combination of the two processes is followed by blowing the metal 
 in a converter till the carbon is sufficiently reduced, and then teeming it 
 into a heated Siemens's furnace, and completing the decarburization in the 
 ordinary manner. 
 
 Hollow rabbles introduced into the molten metal on the hearth, by 
 which air or steam can be blown through it, are in use to a limited extent. 
 Clay-covered iron tubes are employed. At Ruhort, 3 such tubes, each 
 containing 3 holes, are employed. The blast is continued for from 10 to 
 20 minutes, and the temperature rises higher than in the ordinary open- 
 hearth process. 
 
 The steel produced by the Bessemer, Siemens, and 
 analagous processes is generally of a mild character, containing 
 
158 Metallurgy. 
 
 less than 0-5 per cent, of carbon, and is employed for rails (0-3 
 to 0-4 percent, of carbon) ; boiler-, bridge-, and ship-plates, o'2 
 to 0*25 per cent, of carbon ; rivet-iron, 0*1 to 0*15 per cent, of 
 carbon ; armour-plates, guns, and other purposes where metal 
 of high ductility, elasticity, uniformity, and strength are 
 required, and also for castings. 
 
 The honeycombing previously noted in connection with crucible steel 
 is more marked. Stoppering down is resorted to, and in some cases pressure 
 is applied. 
 
 In Whitworth's fluid compressed steel, the ingot, after running in a 
 mould of special construction, is placed on the table of a hydraulic press 
 and subjected to a pressure of from 6 to 20 tons to the square inch. A 
 contraction of i^ inch per foot takes place, and a sounder ingot results. 
 
 At Krupps', the pressure of liquid CO 2 is employed for the same 
 purpose. The ingot-moulds are provided with a gas-tight cover, through 
 which a narrow pipe connected with a metallic reservoir of liquid CO 2 , 
 and provided with a stop-cock, passes. On warming the reservoir in water, 
 great pressure is exerted. 
 
 At the Edgar Thompson works, compression by high-pressure steam 
 has been tried, steam at a pressure of from 100 to 200 Ibs. per square inch 
 being employed. 
 
 In the production of sound steel castings, various physics are resorted 
 to. The introduction of from o'2 to 0*3 per cent, of silicon in mild 
 tempers, and from 0^3 to 0*4 per cent, in harder tempers, tends to increase 
 the solidity of the casting. It is introduced as ferro-silicon or ferro-silicon 
 manganese alloys of silicon with iron and manganese, but containing also 
 carbon. Aluminium is also employed for the same purpose. 
 
 Small wheels are cast on revolving tables, making some 50 or 60 
 revolutions per minute: the metal is run into the mould at the centre. 
 The rim is thereby rendered denser. 
 
 It has also been proposed by Mr. Allen to stir the metal in the ladle 
 with a revolving paddle, to disengage the gas prior to casting. 
 
 Treatment of Ingots. The ingot moulds, after the solidi- 
 fication of the metal, are lifted by cranes situated at the side of 
 the casting-pit, and the ingots allowed to cool ; or, in the newer 
 works, removed immediately to " soaking-pits," in which they 
 are kept hot till required for rolling. 
 
 These soaking-pits consist of a series of vertical chambers 
 of fire-brick below the ground-level, arranged in a double line, 
 each capable of holding an ingot, and covered with a tile and 
 commanded by cranes. The ingots are removed to them imme- 
 diately they have solidified. 
 
 The interior of the ingot when stripped is much too hot 
 to permit of it being rolled at once, and the excess of heat 
 gradually soaks out and distributes itself uniformly through the 
 
Copper. 1 59 
 
 mass. They can be kept hot for some time, and removed for 
 rolling as required. Little heat is lost, and reheating of the 
 ingots is avoided. Oxidation is prevented by the gases exuding 
 from the metal, which are of a reducing character (p. 146). 
 
 The difficulty of keeping up a supply of ingots to keep the pits hot has 
 led to the use of "soaking-furnaces," the several cells or pits of the 
 furnaces communicating with each other, a fireplace or gas-producer 
 being provided at one end of the system. 
 
 The rolling of mild steel is effected in a manner similar to 
 that followed for malleable iron. 
 
 Use of Spiegel and Ferro-manganese. In carburizing Bessemer or 
 open-hearth steel, the richness in manganese of the alloy used is mainly 
 determined by the amount of carbon desired in the resulting steel. If a 
 steel very low in carbon is required, an alloy (ferro-manganese) containing 
 much manganese is employed, to introduce the needful amount of that 
 element, without at the same time adding an excess of carbon. 1 For 
 higher carbon steel, spiegel and ferro containing less manganese are 
 employed. Steels containing a higher percentage of carbon than 0*5 
 may be made, as in the Darby process, by carburizing with gas carbon, 
 anthracite, etc. The molten metal is run into a ladle containing the 
 carburizing material, which it dissolves. An undue proportion of manganese 
 is thus avoided. 
 
 CHAPTER XII. 
 COPPER. 
 
 Physical and Chemical Properties. This metal possesses 
 a fine red colour, and is characterized, when pure, by extreme 
 toughness. Its hardness is slightly under 3. It is more malleable 
 but less ductile than iron. In the cast state, its tenacity is only 
 about 9 to 12 tons, but after rolling this is increased from 15 to 
 1 8 tons, and by wire-drawing to 30 tons. Its modulus of elas- 
 ticity as wire is 17,000,000, that of iron wire being 25,300,000. 
 Its specific gravity is 8'6, but by rolling, etc., is increased to 8*8. 
 Its melting-point is about 1050 C. Pure copper is an excellent 
 conductor of heat and electricity, but the presence of minute 
 quantities of impurity greatly impair this quality. The metal 
 
 1 The amount of carbon present in spiegel and ferro shows no great 
 variation. 
 
160 Metallurgy. 
 
 is unaltered in dry or moist air free from CO., and acid vapours. 
 A green coating of basic salts forms under these circumstances. 
 
 On heating in air, a series of coloured oxide films are 
 formed, and at a red heat a black scale of oxide, which detaches 
 itself when the metal is suddenly cooled. The outside of this 
 scale consists of black cupric oxide (CuO), but the inner layers 
 principally consist of red cuprous oxide (Cu 2 O) Cupric oxide 
 is reduced to cuprous oxide when fused with copper. Copper 
 dissolves cuprous oxide when molten, and is rendered dry and 
 brittle. " Dry " copper breaks with a dull, brick-red fracture. 
 In practice the metal is toughened by covering with anthracite, 
 and stirring it with birch poles. Hence the term "poling." 
 The reducing gases from the wood, in conjunction with the 
 anthracite, reduce the oxide, and the metal assumes its normal 
 tough condition. 
 
 If the copper is not chemically pure, it is possible to con- 
 tinue the poling too long, and the metal again becomes dry 
 and unmalleable. By leaving a little of the oxide unreduced, 
 the harmful effects of the impurities are neutralized to some 
 extent. It is described as " underpoled," " tough cake," and 
 "overpoled," according to its condition. Pure electrotype 
 copper cannot be overpoled or burnt. Underpoled copper con- 
 tracts greatly on solidifying, and a furrow is formed down the 
 middle of the ingot. Tough cake copper casts with a nearly 
 flat surface, while, if overpoled^ the metal rises in the mould, and 
 a ridge is formed. 
 
 Very small quantities of lead, arsenic, sulphur, antimony, and bismuth, 
 seriously impair the malleability, ductility, and tenacity of copper. Tin, 
 nickel, cobalt, and iron, are also often present in commercial copper. 
 They render the metal lighter in colour and somewhat harder, but do not 
 lower its tenacity. 
 
 Copper has greater affinity for sulphur and less affinity for 
 oxygen, than iron has. Two sulphides are known. Cuprous 
 sulphide, Cu 2 S, is the " white metal " of the copper smelter, 
 and is produced by heating copper and sulphur together. It 
 occurs naturally in various copper ores. 
 
 Cupric sulphide (CuS) is precipitated when a soluble sul- 
 phide is added to a solution containing copper, 
 
Copper. 16 1 
 
 The sulphides of copper are not reduced by iron or carbon. 
 When heated in air, sulphur burns off as SO 2 , and a mixture 
 of oxides and sulphate, in proportions varying with the con- 
 ditions, results. 
 
 Sulphate of copper is soluble in water, and is decomposed 
 when strongly heated. It requires a higher temperature to 
 decompose it than sulphate of iron. When sulphide of copper 
 is heated with oxide or sulphate, the sulphur and oxygen pass 
 off as SO 3 and the metal is reduced. 
 
 Cu a S + 2Cu 2 O = SO 2 + sCu 2 
 Cu 2 S + CuSO 4 - 3Cu 4- 2SO 2 
 
 Copper and phosphorus combine readily, forming phosphide 
 of copper. 
 
 Bronze includes all alloys of copper and tin. 
 
 The effect of tin in whitening copper is greater than that of 
 any other metal. The alloys have a lower melting-point, and 
 cast sounder than copper. The toughness, tenacity, and other 
 properties vary with the composition of the alloy. (See Alloys, 
 p. 268.) 
 
 Brass includes all alloys of copper and zinc. The effect of 
 zinc in whitening is much less than tin, and hence wider range 
 of colour is possible. 
 
 The malleability and tenacity of certain of these alloys is 
 little inferior to copper, e.g. Dutch metal is beaten into thin 
 leaves in imitation of gold, and brass, for wire and plate, has 
 a tenacity of 8 or 9 tons cast, which, after rolling and wire- 
 drawing, varies from 20 to 26 tons. (See Alloys, p. 267.) 
 
 ORES OF COPPER. 
 
 (i) Native copper often occurs with copper ores, some- 
 times in masses, as in the Lake Superior district, but more 
 often in arborescent and reticulated forms. In the Calumet, 
 Hecla, and other mines, about 2 per cent, of native copper, 
 mainly in small grains, is distributed through the rock. 
 
 This is extracted by dressing processes, and smelted and 
 
 M 
 
1 62 Metallurgy. 
 
 refined at one operation. The copper Barilla of Chili, was 
 a deposit of grains of copper, oxidized on the surface. 
 Native copper is usually very pure. 
 
 Cuprite, red oxide of copper, cuprous oxide (Cu 2 O) occurs, 
 crystallized and massive, in Thuringia, Chessy, near Lyons, 
 Cornwall, Siberia, United States, Cuba, Australia, etc. It 
 contains 88 '8 per cent, of copper when pure. 
 
 Tenorite, black oxide of copper (CuO) occurs extensively 
 in Chili and Australia. It is generally very impure. 
 
 Green Malachite is a hydrated carbonate of emerald green 
 colour, of the composition CuCO 3 ,CuH 2 O 2 . It is often beauti- 
 fully variegated, and is used for ornamental purposes. It 
 occurs in Siberia, Australia, and United States. It contains 
 58 per cent, of copper. 
 
 Blue Malachite, Azurite or Chessylite (2CuCO 3 ,CuH 2 O 2 ), is 
 of a deep blue colour, and generally occurs with green mala- 
 chite. An extensive deposit formerly existed at Chessy in 
 France. It contains about 55 per cent, of copper. 
 
 Chrysocolla and Dioptase are hydrated silicates of copper. 
 The former is blue and the latter green in colour. They con- 
 tain about 30 per cent, of copper. 
 
 Redruthite, copper glance (Cu 2 S), occurs native in Corn- 
 wall and elsewhere. It has a semi-metallic white appearance, 
 'and is readily scratched with a knife. It contains 80 per cent, 
 of copper. 
 
 Erubescite, Bornite, horseflesh ore (3Cu 2 S,Fe 2 S 3 ), occurs 
 extensively in South Africa, Australia, and Norway. It con- 
 sists of copper and iron sulphides, containing up to 62 per 
 cent of copper. Its colour varies from copper red to pinch- 
 beck brown, with a blue tarnish. 
 
 Copper Pyrites, yellow copper ore (Cu 2 S,Fe 2 S 3 ), is dis- 
 tinguished by its golden yellow metallic appearance. It is 
 softer than iron pyrites, and can be scratched with a knife. 
 When pure it contains 34*6 per cent, of copper, 30*5 iron, 
 34-9 sulphur. Usually, however, it is mixed with a large 
 excess of iron pyrites (FeS 2 ), and does not contain more than 
 12 per cent, of copper, and often less. It is the principal 
 English ore of copper, and occurs abundantly in Cornwall 
 
Copper. 163 
 
 and Devonshire, also in Siberia, in Sweden at Fahlun, in the 
 Hartz, and various localities in the United States. 
 
 Peacock Copper Ore is a variegated copper pyrites, but is 
 usually richer in copper. 
 
 Grey Copper Ore, tetrahedrite, Fahl ore, consists of sul- 
 phantimonides and sulpharsenides of copper and iron. It 
 often contains silver, mercury, and sometimes gold. The 
 amount of copper varies up to 38-6 per cent. It occurs 
 extensively in the Hartz Mountains, at Kremnitz in Hungary, 
 at Frieberg in Saxony, Kapnuik in Transylvania, and in Chili. 
 It is worked for copper and also for silver. 
 
 Atacamite is a natural oxychloride, occurring extensively 
 in Atacama in Chili, in Australia, and elsewhere. It is a 
 deep green in colour. 
 
 Cupreous Iron Pyrites. Besides the above, much copper 
 is extracted from the cinders from the burning of cupreous 
 iron pyrites in the manufacture of sulphuric acid. 
 
 COPPER EXTRACTION. 
 
 Bearing in mind the varied composition of the ores, it will 
 be seen that the processes of extraction will vary much accord- 
 ing as to whether one or several kinds of ore are to be treated 
 together. Thus the reduction of oxidized ores only is a 
 simple matter, but when sulphuretted and oxidized ores must 
 be treated together, the operation is more involved. This is 
 the case in this country, where the supply of oxidized ores is 
 insufficient to warrant their separate treatment. 
 
 Treatment of Sulphides with or without the Addition cf 
 " Oxidized Ores of Copper" 
 
 Reaction Process. Sulphides, with the exception of 
 copper glance, do not usually contain sufficient copper to 
 permit of its direct extraction, and undergo a series of operations, 
 the object of which is to concentrate the copper in a rich 
 regulus. These operations consist of alternate roastings ^and 
 fusions in a reducing atmosphere. In the roasting processes 
 sulphur and arsenic are oxidized and removed as sulphur 
 dioxide (SO 2 ) and arsenious oxide (As 2 O 3 ) respectively, and 
 the iron and copper are partly oxidized. 
 
1 64 Metallurgy. 
 
 Cu 2 S -f- 30 = Cu 2 O + SO 2 
 Fe 2 S 3 + 9 - Fe 2 s + 3SO, 
 FeS. 2 + 8 = FeS + SO 2 . 
 
 In the fusion which follows, the reaction of the oxide of copper 
 on the remaining sulphide of iron produces sulphide of copper 
 and oxide of iron. At the same time, many impurities are 
 removed. The iron oxide thus produced, together with that 
 formed during roasting, is removed by combining with silica, to 
 form silicate of iron, which constitutes the slag. There is always 
 sufficient silica in the charge and furnace bottom to effect this. 
 
 2Cu 2 O + 2 FeS + SiO 2 - 2Cu 2 S + 2FeO.SiO 2 
 Fe. 2 O 3 + CO -h SiO 2 = 2 FeO.SiO 2 -f CO 2 . 
 
 The sulphide of copper and unaltered iron sulphide fuse and 
 form a bottom layer in the furnace. This process is repeated 
 until the iron has been practically removed, and the regulus 
 is then treated for copper by roasting and fusion, and after- 
 wards refined. Oxidized ores and the slags produced in the 
 fusions, which contain too much copper to throw away, are 
 introduced in the fusions, and the metal they contain by 
 reaction on the sulphide of iron passes into and enriches the 
 regulus. 
 
 (i) Welsh Process. This is conducted in reverberatory 
 furnaces throughout. The ore mixture contains from 9 to 13 
 per cent, of copper as sulphide, with excess of iron pyrites 
 and silica, and the process involves at least six operations 
 
 (a) Calcining the ore ; 
 
 (b) Fusion of the calcined material with oxidized ores 
 
 and slag ; 
 
 (c) Calcining the regulus obtained in b ; 
 
 (d) Fusion of calcined regulus with slags ; 
 
 (e) Roasting and fusion of regulus with separation of 
 
 blister copper ; 
 
 (/) Refining and toughening. 
 
 (a) Calcining the Ore. This is conducted in a large 
 reverberatory furnace, the bed of which is shown in Fig. 56. 
 The bed measures about 16 feet by 14 feet and the grate 4 feet 
 
Copper. 
 
 by 3 feet. Air is admitted at the fire-bridge through open- 
 ings o. The temperature is low, and the ore is turned over 
 from time to time. About half the sulphur is removed mainly 
 as sulphur dioxide SO 2 . Some sulphur trioxide is also evolved. 
 Arsenic passes off as As 2 O 3 . This roasting on 3-ton charges 
 occupies about 24 hours. The charge is introduced from 
 hoppers on the roof of the furnace. The roasted ore is raked 
 through openings r in the bed, into the vault below, which 
 communicates with the flue, to cool. 
 
 (b) Fusion for " Coarse " Metal. The roasted ore is mixed 
 
 FIG. 56. Plan of Bed of Calcining Furnace. A, bed ; F, fireplace ; /, doors ; 
 r, openings into vault. 
 
 with oxidized ores and slags, the charge being made up as 
 follows : 
 
 Roasted ore, 60 to 66 per cent. 
 
 Oxidized ores, 10 to 14 per cent. 
 
 Metal-furnace slag from fourth process, 22 to 25 percent. 
 This is introduced in charges 'of about 25 cwts. into the 
 "ore furnace" (Fig. 57). This is also a reverberatory furnace, 
 but the grate area is much larger in proportion to the bed, a 
 higher temperature being necessary to fuse the charge. The 
 furnace is charged from the hopper A. The bed is of sand, 
 and slopes from all points towards the tapping hole B, under 
 the door C in front of the furnace. The charge gradually 
 
1 66 
 
 Metallurgy. 
 
 fuses, the oxides, sulphides, and sulphates react as described, 
 and the regulus formed separates and collects at the bottom 
 under the slag. This slag ore-furnace slag often contains 
 unfused masses of quartz and stony matters occurring in the 
 ore, and is raked off the surface of the regulus through a long 
 low opening D, at the flue end of the furnace into sand 
 moulds, E, beneath. Before tapping, three charges are gene- 
 rally fused, and the whole of the regulus is run out together 
 into sand moulds. A more uniform product is thus obtained. 
 Sometimes the regulus is granulated by tapping into a tank 
 containing water. 
 
 The metal-furnace slag sharp slag which forms part of 
 
 FIG. 57. Ore Furnace. 
 
 the furnace charge, contains about 4 per cent, of copper as 
 silicate, etc. This reacts upon the iron sulphide present, and 
 the copper passes into the regulus, thus affording a convenient 
 method of treating the cupreous slags produced in the several 
 .operations. 
 
 It is essential that the furnace charge should contain an 
 excess of sulphide of iron to ensure the complete decomposition 
 of the oxide of copper in the roasted material and in the 
 'oxides, carbonates, slags, etc., added. 
 
 The regulus obtained consists essentially of a mixture of 
 iron and copper sulphides, containing 30 to 35 Cu, 30 Fe, 28 S, 
 
Copper. 167 
 
 with small quantities of arsenic, bismuth, lead, antimony, and 
 sometimes, tin, nickel, and cobalt sulphides. It is known as 
 " coarse metal," and breaks with a coarsely granular fracture 
 of a bronze-purple colour. The slag is known as " ore-furnace 
 slag" and consists principally of silicate of iron, and contains 
 less than i per cent, of copper. 
 
 (c) Calcining Coarse Metal. The pigs of coarse metal 
 are crushed, unless it has been granulated, and the regulus is 
 roasted in the calciner for 24 hours at a low red heat, losing 
 about one-half its sulphur, mainly as SO 2 . 
 
 (d) Fusion for "Fine" Metal. The calcined coarse metal 
 is mixed with roaster and refinery slags (slags from the fifth 
 and sixth processes, containing a large proportion of cuprous 
 oxide as silicate), and also sometimes with pure oxide and 
 carbonate ores. 
 
 The mixture contains 
 
 Roasted regulus, 65 to 80 per cent. 
 
 Slag and oxidized ores, 20 to 35 per cent. 
 
 The " metal furnace " in which the fusion takes place is 
 similar to that employed in this fusion for " coarse metal." 
 The charge consists of about 30 cwts., and its fusion occupies 
 from 6 to 8 hours. The same reaction between the sul- 
 phides and oxides in the charge occur as before. 
 
 The second calcination and fusion have for their object 
 the production of a rich regulus as free as possible from iron. 
 The extent to which this has been accomplished depends on 
 the efficiency of the roasting and the amount of oxidized 
 cupreous materials added. If the oxide of copper is in- 
 sufficient to decompose the sulphide of iron present, a 
 regulus, which breaks with a smooth, shining fracture and a 
 bluish colour, containing from 55 to 66 per cent of copper, 
 known as "blue metal" results. It is a mixture of cuprous 
 and iron sulphides. 
 
 When the oxide of copper is in the required proportion, a 
 regulus which breaks with a semi-metallic, greyish-white, 
 slightly granular fracture, known as " white metal" is produced. 
 It contains from 70 to 78 per cent, of copper, and is practi- 
 cally "cuprous sulphide," Cu 2 S. "Pimple metal" contains a 
 
1 68 Metallurgy. 
 
 larger percentage of copper, and is produced when the oxide 
 of copper is in excess. 
 
 Sometimes the oxide is in excess of requirements, in which 
 case it reacts on the sulphide during fusion, and metallic 
 copper is produced with an evolution of SO 2 . The regulus 
 appears to dissolve a certain amount of the reduced copper, 
 which separates out, as the metal cools, in fine, velvety fila- 
 ments, lining cavities in the metal, and is known as " moss 
 copper" Separated copper is also found in blue metal, but is 
 absent in pure white metal. 
 
 "Metal-furnace slag" has a bluish, lustrous, semi-crystalline 
 fracture. It is essentially silicate of iron, but contains about 4 
 per cent, of copper, which is recovered in the second operation. 
 
 (e) The Roaster Stage. The pigs of fine metal are placed 
 on the bed of- the roaster furnace, which in most respects 
 resembles the metal furnace, but is, however, provided with 
 openings at the fire-bridge, for the admission of air into the 
 furnace chamber, and a basin-shaped depression in front of 
 the door. The temperature is so managed that the melting 
 down occupies from 6 to 8 hours. Extensive oxidation takes 
 place, sulphur passing off as sulphur dioxide ; thus 
 
 Cu 2 S -f 3O = CuoO + SO 2 . 
 
 When melted, the slag which has formed is skimmed off, 
 and the clear surface presents a boiling appearance, and 
 emits a frizzling sound, due to the escape of SO 2 formed by 
 the oxide reacting on the sulphide. 
 
 Cu,S + 2Cu 2 O = 3Cu 2 + SO 2 . 
 
 Metallic copper separates and sinks to the bottom of the 
 bath. When the process is judged complete, the slag is again 
 skimmed off and the copper tapped into sand moulds. The 
 length of time occupied varies from 12 to 24 hours, being 
 longest when the fine metal is least pure. 
 
 The "blister copper" is dry and unmalleable, has a dull, 
 red fracture, and contains cavities. The surface presents a 
 blistered appearance, caused by sulphur dioxide liberated during 
 solidification ; hence the name. It contains about 98 per cent, 
 of copper and less than i per cent, of iron. 
 
Copper. 169 
 
 Roaster slag has a purplish red colour, and contains from 
 17 to 40 per cent, of copper, as silicate and metal, according 
 to circumstances. 
 
 (/) Refining and Toughening. The refining furnace has 
 a sand bottom, which inclines from all parts to a basin-shaped 
 cavity near the end door. There is also no charging hopper 
 or tap-hole. Some 6 to 15 tons of pigs of blister copper are 
 piled up on the bed, and gradually melted. This occupies from 
 4 to 6 hours. The slag is skimmed off, and the surface ex- 
 posed to the oxidizing atmosphere for from 10 to 15 hours 
 longer. Copper being less oxidizable than the impurities 
 present, viz. arsenic, sulphur, iron, tin, nickel, cobalt, man- 
 ganese, bismuth, antimony, and lead, these are removed as 
 oxides ; but much copper, owing to its great excess, is also 
 oxidized, forming cuprous oxide. This, with the other metallic 
 oxides formed, combines with silica from the sand bottom, etc., 
 and constitutes the slag. Some cuprous oxide is, however, 
 dissolved by the metal, and renders it "dry" or "under- 
 poled." The attainment of this state is determined by the 
 withdrawal of samples from the bath. To remedy this, the 
 slag is again skimmed off, the surface of the copper covered 
 with coal or anthracite, and a pole of green birch or oak wood 
 is plunged into the metal and held down. The hot metal 
 causes a copious evolution of steam and reducing gases, which 
 thoroughly agitate the metal, bringing every portion of it 
 into contact with the carbonaceous matter covering it, whereby 
 the cuprous oxide in the metal is reduced. Samples are taken 
 from the bath from time to time, examined, and tested for 
 toughness and malleability. When the metal has lost its 
 dark-red, granular fracture, and breaks with a flesh-coloured 
 silky lustre, bending double when placed in a vice, the "tough 
 pitch " has been attained : the pole is withdrawn, the covering 
 pushed aside, and the metal ladled out by hand, in clay- 
 covered ladles, and cast into flat ingots weighing about 20 Ibs. 
 The ingot moulds are of cast iron or copper, and so arranged 
 that, as soon as solid, the ingots can be thrown into water. 
 During ladling the metal is apt to become oxidized and dry 
 again. When this is observed, the pole is reintroduced for a 
 
1 70 Metallurgy. 
 
 short time, and the metal brought back to toughness. The 
 time occupied is about 30 hours, from introduction of pigs 
 to end of ladling out. 
 
 Refinery slag is of a coppery-red colour. It consists 
 mainly of silicate of copper, not unfrequently with shots of 
 metal freely dispersed through it. 
 
 Modifications of the Welsh Process. In some cases, owing 
 to poorness of the ores, or the lack of oxides and slags, or 
 sometimes difference in practice, the number of operations is 
 increased, the roaster stage for the production of blister copper 
 being preceded by more calcinations and fusions, to produce a 
 satisfactory regulus. 
 
 A small quantity of lead is often added to copper intended for rolling, 
 just before ladling ; after which the scum of oxides which forms is 
 skimmed off. The amount added varies from O'l to 0*5 per cent. Its 
 object is twofold. By its oxidation it promotes the oxidation and removal 
 of foreign metals present, notably antimony, and also retards the metal 
 from "going back " by oxidation, and again becoming dry and underpoled. 
 The ingots are sounder and flatter. Copper containing not more than 0*1 
 per cent, of lead rolls well, and has a less tendency to collar the rolls. It is 
 a little more difficult to detach the scale. No addition of lead is made 
 in making best selected copper, or copper intended for making best brass, 
 gun metaJ, or German silver. 
 
 " Best selected " copper was formerly made from the purer 
 portions of the fine metal resulting from the smelting of purer 
 ores. It is found that the impurities become concentrated by 
 gravity in the lowest part of the bath, and consequently those 
 pigs which flow from the furnace first are most impure. The 
 selection of the later ones for making the best copper led to 
 the introduction of the term. Best selected copper should 
 contain only traces of arsenic, antimony, and bismuth. 
 
 Another process of selection is now followed, known as the 
 " bottoms " process. The " fine metal " obtained in the fourth 
 stage, prior to tapping, is cleared of slag and roasted. The 
 oxide of copper formed reacts on the sulphide, and copper is 
 reduced. This attacks the foreign sulphides, reduces them, 
 and alloys with the liberated metal, thus concentrating them 
 in the metallic state, and carrying them to the bottom of the 
 bath. This leaves the " fine " metal purified. The " bottoms " 
 copper contains nearly all the gold and silver, and much of 
 the tin, lead, and antimony in the charge. 
 
Copper. 
 
 171 
 
1 7 2 Metallurgy. 
 
 Instead of employing reverberatory furnaces exclusively, 
 blast furnaces of the "water-jacketed" type are commonly 
 used abroad for the fusion of ore and regulus, and the roasting 
 is done in heaps or in stalls (see p. 25). 
 
 Reduction Processes. Oxides, carbonates, and other 
 oxidized copper ores, if in sufficient quantity, may be smelted 
 in blast furnaces preferably water-jacketed with coke and 
 a suitable flux, e.g. oxide of iron, to slag off silica. By adding 
 a little iron pyrites to the charge, a small amount of copper 
 regulus is formed, as well as metallic copper, and the slags 
 are cleaned. 
 
 Sulphide of copper is not completely reduced by iron or 
 carbon. It is necessary, therefore, to convert " mattes " into 
 oxide, before reduction, by calcining. They may then be treated 
 as above. This is also done with the " fine regulus " obtained 
 at Mansfeldt in Germany, where the regulus is desilverized by 
 the Ziervogel process. The finely divided residue of oxide of 
 copper and iron is balled with a little clay and smelted for 
 " black " copper, which is afterwards refined by an air blast 
 on a small hemispherical hearth, under charcoal. 
 
 Mannhes Process for Bessemerizing Copper Mattes. Suc- 
 cessful attempts have been made to treat copper matte on the 
 Bessemer principle, by blowing air through it in the molten 
 state. The sulphur is burnt out and iron oxidized, and sufficient 
 heat developed to keep the mass molten. It is found advisable 
 to treat the matte in two stages, producing fine metal and 
 coarse copper in distinct operations. The converter is more 
 or less barrel-shaped, and the tuyeres enter at some distance 
 from the bottom, in a more or less horizontal direction. By 
 this arrangement the enriched matte or copper falls below the 
 tuyere level, and escapes further oxidation. It is run into the 
 converter at as high a temperature as possible. There is a 
 considerable saving in fuel in this method of treatment. 
 
 In a few cases the matte is Bessemerized in the rever- 
 beratory furnace, by blowing air through the bath of melted 
 sulphides, movable tuyeres being employed for that purpose. 
 By this means the sulphur is burnt out and iron oxidized and 
 removed, all the reactions of calcination and fusion taking 
 place in the fluid bath. 
 
Copper. 173 
 
 Direct Process. At Briton Ferry, working with ores of 
 special purity, the " roaster stage " is conducted in a totally 
 different fashion from that generally prevalent. A portion of the 
 fine metal is roasted " sweet " in a calciner of the revolving 
 type (Fig. 17), and mixed with a sufficient amount of the un- 
 roasted regulus determined by experiment to reduce it. The 
 mixture is then heated to fusion in a reverberatory furnace. 
 A much greater yield of copper is obtained in this way, and 
 its quality is said to be in no way inferior. The copper is 
 at once refined in the same furnace. 
 
 " Basic " linings have been introduced in the roaster and refining 
 furnaces. The loss of copper in the slag is much less, owing to the 
 absence of silica, which by combining with the oxide formed in roasting 
 retards its reaction on the sulphide. The yield of blister copper is said 
 to be 25 per cent, more than with sand bottoms. Arsenic is removed to 
 a greater extent, but bismuth and antimony in no greater degree than on 
 a siliceous bottom. In refining arsenical metal, soda ash is added as well 
 as lime. 
 
 Chili Bar, American Matte, etc. In districts where fuel 
 is dear the ores are subjected to a preliminary roasting, and 
 then fused in water-jacketed furnaces for a matte running 
 about 45 per cent, of copper. This is then roasted as com- 
 pletely as possible, and remelted with the production of blister 
 copper and cuprous sulphide (white metal). The copper 
 contains about i per cent, sulphur, in addition to the usual 
 impurities. This is marketed as Chili bar. 
 
 WET PROCESSES OF COPPER EXTRACTION. 
 
 In wet methods of extracting copper the metal must first 
 be converted into a soluble form, as sulphate or chloride, and 
 the copper deposited from solution by scrap iron. 
 
 Sulphate Roasting. The conversion of the copper in 
 pyritical ores into sulphate may be effected by careful calcin- 
 ing in a reverberatory furnace at a low heat. The sulphide of 
 copper is converted into sulphate, partly by direct oxidation, 
 thus 
 
 Cu 2 S + 50 = CuSO 4 + CuO 
 
 Cuprous Oxygen Copper Cupric oxide 
 
 sulphide sulphate 
 
 or. 2 Cu 2 S + ?O = CuSO 4 + Cu 2 O + SO, 
 
 Cuprous Oxygen Copper sulphate Cuprous Sulphur 
 
 sulphide oxide dioxide 
 
174 Metallurgy. 
 
 and partly by the SO 3 liberated from ferrous sulphate formed 
 by the calcination of the iron sulphide present, or produced by 
 the combination of oxygen with the SO 2 generated, brought 
 about by the " contact action " of the ferric oxide and silica, 
 and brickwork of the furnace 
 
 FeS 2 -f 
 
 Iron pyrites 
 
 2FeSO 4 H 
 
 Ferrous sulphate 
 
 SO, H 
 
 Sulphur 
 dioxide 
 
 CuO + 
 
 Copper 
 oxide 
 
 60 
 
 Oxygen 
 
 - 
 
 Oxygen 
 
 - 
 
 Oxygen 
 
 S0 3 
 
 Sulphur 
 trioxide 
 
 - FeS0 4 
 
 Ferrous 
 sulphate 
 
 = Fe 2 3 
 
 Ferric oxide 
 
 - S0 3 
 
 Sulphur 
 trioxide 
 
 = CuSO 4 
 
 Copper 
 sulphate 
 
 + SO 2 
 
 Sulphur 
 dioxide 
 
 + 2S0 3 
 Sulphur trioxide 
 
 Copper sulphate requires a higher temperature to decom- 
 pose it than ferrous sulphate, but is decomposed more readily 
 than silver sulphate. 
 
 There is great difficulty in getting the whole of the copper 
 sulphated. A greater amount is rendered soluble in the 
 presence of much sulphide of iron. 
 
 Bankart's and Escalle's processes, both now abandoned, 
 were based on this principle. In the former the copper 
 was precipitated by iron, and in the latter as sulphide by 
 calcium sulphide. This sulphide was subsequently reduced in 
 a special form of furnace, and refined. 
 
 Much copper is extracted by calcining "low grade" 
 pyritical ores in open heaps, washing out the sulphate formed 
 in tanks, and precipitating the copper by iron. 
 
 Certain sulphide ores oxidize spontaneously on exposure 
 to moist air. From this cause the water from copper mines, 
 and drainage from cupreous waste heaps, often contain copper 
 sulphate in solution. Extensive works were executed for 
 precipitating mine waters in the Carnon Valley in Cornwall, 
 at Pary's Mountain in Anglesea, and elsewhere. Both these 
 methods are followed at the Rio Tinto mines. 
 
 Chloridizing Processes. The conversion of copper into 
 chloride is effected by roasting sulphide ores with salt (sodium 
 chloride), or by treating with some chlorinating agent, such as 
 
Copper. 175 
 
 ferric chloride or manganese dioxide and salt, which, in the 
 presence of sulphuric acid or sulphates, generate chlorine and 
 hydrochloric acid. 
 
 Chlorinating Roasting. In roasting with salt, the sulphates 
 produced react on the salt and form sulphate of soda. 
 CuSO 4 .+ 2NaCl = CuCl 2 + Na 2 SO 4 . 
 
 Chlorine and hydrochloric acid are also generated in the 
 furnace (see p. 221). The chlorine in the salt is ultimately 
 transferred to the copper, which is converted into cupric and 
 cuprous chlorides, the former soluble in water, and the latter 
 in hydrochloric acid and chlorides. 
 
 Longmaid and Henderson's Processes. This process is 
 adopted for the treatment of the cinders from the burning of iron 
 pyrites used in the manufacture ot sulphuric acid. Portuguese, 
 Spanish, and Norwegian pyrites, so largely imported for this 
 purpose, contain from i to 2*5 per cent, of copper, which, after 
 burning off the sulphur, reaches from 2 to 5 per cent. The 
 " purple ore," as it is called, is ground down and mixed with 
 a little small green ore (unburnt pyrites) and 10 to 18 per 
 cent, rock salt in a mechanical mixer. This is roasted at a 
 very low temperature, between 400 and 500 C. (copper 
 chloride being volatile at a high temperature), for about 8 
 hours in a reverberatory or close muffle furnace (see p. 28). 
 The roasted ore after withdrawal is lixiviated in wooden tanks, 
 first with water and then with hydrochloric acid, obtained by 
 passing the furnace gases up through condensing towers where 
 the hydrochloric acid generated in roasting is dissolved out. 
 From these it is run into settling tanks placed at a lower 
 level, and then into precipitating tanks, where the copper is 
 thrown down by iron. Generally, however, the ores treated 
 contain gold and silver, and these are also extracted (see 
 Claudet's Process for Silver). The " copper precipitate " is 
 collected, fused, and refined. 
 
 In chlorination in heaps, the ore, part of which is calcined, 
 is stacked in huge heaps mixed with salt, manganese dioxide, 
 and residues from previous heaps. Open channels are left 
 for the admission of air and moisture. Decomposition sets 
 in with the production of ferric and manganese chlorides, 
 
Metallurgy. 
 
 which chlorinate the copper. The heaps are periodically 
 drenched with water; or the heaps may be drenched with 
 water containing ferrous chloride, etc., produced in the pre- 
 cipitation of the copper, to hasten the process. A series of 
 chemical reactions somewhat involved result in the con- 
 version of the copper into chloride. The copper solution is 
 precipitated by scrap iron. 
 
 Electro refining of Copper has made great strides in con- 
 sequence of the demand for pure copper for electrical work. 
 The copper to be refined is cast in thick plates, which are 
 enveloped in canvas bags. They are connected with the 
 positive pole of a dynamo, and immersed in a bath consisting 
 of a 1 5 per cent, solution of copper sulphate and 5 per cent, 
 sulphuric acid, alternating with thin plates of pure copper 
 connected with the negative pole. When the current passes 
 copper is deposited on the thin plates, and the acid liberated 
 at the + pole attacks and dissolves the copper, which in turn 
 is deposited. The impurities it contains either remain dis- 
 solved in the bath, or are left in an insoluble form as a mud, 
 which is retained in the bags. This method of refining is 
 largely followed for argentiferous " bottoms " copper, the silver 
 and gold remaining in the insoluble residues. 
 
 VARIETIES OF COMMERCIAL COPPER. 
 
 Tough Cake, or Tough Pitch Copper is ordinary copper at 
 its point of greatest malleability and toughness. 
 
 Bean Shot Copper and Feather Shot for brass making are 
 made by pouring molten copper into hot or cold water. For 
 this purpose the copper is " overpoled." 
 
 Rosette Copper is obtained in thin films of a fine red 
 colour by throwing water on the surface of the metal when 
 molten, and lifting off the solidified crusts. 
 
 Chili Bar is imported in bars weighing about 2 cwt. It 
 is somewhat less pure than blister copper, and requires 
 refining. 
 
 Copper Precipitate is the finely divided copper obtained 
 by precipitating copper from solutions by iron. Its purity 
 
Lead. 177 
 
 is very variable. The foreign matter is principally oxide of 
 iron. 
 
 Electrotype Copper. Electro deposited, or electro-refined 
 copper is produced by electro deposition, using " bottoms " 
 or other impure copper as the anode or dissolving pole. 
 
 CHAPTER XIII. 
 LEAD. 
 
 Physical Properties. The metal possesses a bluish grey 
 colour, and considerable lustre on fresh surfaces, which, how- 
 ever, are soon dimmed on exposure. It is soft enough to be 
 impressed by the nail and to mark paper. Impurities, such as 
 antimony, render it harder. It is malleable, ductile, and tough, 
 but is very deficient in tenacity. Cast lead has only a tenacity 
 of from 0-4 to 0*8 tons per square inch. After wire-drawing 
 this is increased to i to 175 tons. Its melting-point is about 
 330 C., and it volatilizes at very high temperatures. It con- 
 tracts on solidifying, and is consequently unsuitable for castings. 
 The specific gravity is 1 1*36, and is not increased by hammering. 
 When alloyed with ot er base metals, the specific gravity is 
 diminished. It welds readily if the surfaces are fresh and 
 clean, and even lead powder may be moulded by pressure 
 into solid lumps. Alloys with tin may also be thus produced, 
 and a compound sheet of the two metals may be formed by 
 placing them in contact and passing through the rolls. The 
 flowing power of the metal is great, and lead pipes and rods 
 are squirted from a press. Lead crystallizes on cooling from 
 fusion. When heated near its melting-point, it breaks with a 
 columnar fracture. 
 
 Chemical Properties. Lead oxidizes on exposure to moist 
 air, forming suboxide of lead (Pb 2 O). In a very finely divided 
 state, as obtained by heating the tartrate, it takes fire and 
 burns. When heated in air it readily combines with oxygen, 
 and forms lead monoxide, litharge (PbO). This oxide is of 
 
178 Metallurgy. 
 
 a yellow colour ; it fuses at a full red heat, and yields, on cool- 
 ing, a yellow crystalline mass. At a somewhat higher tempera- 
 ture, it combines with silica, forming a readily fusible silicate 
 of lead. 
 
 On this account it rapidly corrodes crucibles, retorts, and 
 the sides of furnaces made with siliceous materials. Hence 
 the necessity of employing bone ash or marl brasque in cupel- 
 lation (p. 225), and the advantages of using water-jacketed 
 furnaces in smelting operations. Mixtures of cuprous and lead 
 oxides are even more corrosive than litharge alone. Litharge 
 is largely used in glass making, and is made by oxidizing 
 lead on a cupel. See page 225. 
 
 It exerts an oxidizing influence on iron, copper, zinc, and 
 other metals, being reduced to lead. When heated with oxides 
 of other metals, such as copper and iron oxides, litharge fuses 
 and dissolves up the refractory oxide, forming a fusible mass. 
 The amount of litharge required varies. Thus i part of 
 cuprous oxide requires 1*5 parts of litharge, while i of tin 
 oxide requires at least 1 2. 
 
 If produced at a temperature below its fusion point, litharge 
 has a brownish-yellow colour, and is known as massicot. If 
 this is carefully heated in air. it takes up more oxygen, and 
 is converted into red lead or minium (Pb 3 O 4 ). 
 
 Manufacture of Red Lead. The metal is first "drossed," 
 or oxidized in a low, reverberatory furnace, or " oven," with 
 two narrow fireplaces, one on either side of the bed. The 
 products of combustion escape through the working door in 
 front, and are carried away by a hood surmounted by a chimney. 
 The bed of the oven slopes slightly to the middle, and from 
 back to front. In working, a dam of rough oxide, mixed with 
 lead from the grinding of previous charges, is made across the 
 front of the oven, and some 20 to 30 cwts. of lead charged in 
 and melted at a low red heat. The door is left partly open, 
 and the oxide as it forms is pushed back, and the lead splashed 
 about by a long iron paddle. The metal is continually thrown 
 over the oxide at the back. Oxidation goes on freely, and the 
 unoxidized lead drains to the front. Dressing is assisted by the 
 addition of a little antimony to the lead. When the oxidation 
 
Lead. 179 
 
 
 
 is completed, the charge is raked out into iron barrows and 
 allowed to cool. It is then ground by millstones in a stream 
 of water, which carries the fine material away in suspension. 
 The unoxidized metallic lead and heavy particles of oxide are 
 left behind in the troughs which lead to the settling tanks, 
 where the finely divided massicot is deposited. It is collected 
 and dried. It then constitutes "ground litharge." This is 
 transferred to the " colouring oven," very similar to the dressing 
 oven, except that the bed is flat It is spread in low ridges 
 over the bottom of the oven and " coloured" at a lower 
 temperature than that used in the dressing operation, being 
 turned over from time to time. The red lead while hot has a 
 deep brownish purple colour, and is examined from time to 
 time by the withdrawal of samples, and allowing to cool. 
 When the oxidation is complete, the cold sample has a bright 
 red colour. It is again ground, levigated, and after drying and 
 sieving, packed in barrels. Its composition is Pb 3 O 4 . On heat- 
 ing it gives off oxygen and forms litharge, PbO. Treated with 
 nitric acid, PbO 2 , lead peroxide is left as a purplish powder. 
 
 Action of Soft Water on Lead. Waters containing oxygen 
 in solution readily attack lead, but the action is retarded by 
 the presence of carbonates and sulphates in the water. Lead 
 pipes for conveying soft waters are coated inside with tin to 
 prevent the water from being contaminated with lead. 
 
 Lead and Sulphur. Lead combines readily with sulphur 
 when heated, forming a brittle, grey, crystalline mass of lead 
 sulphide (PbS). It has a high metallic lustre, and melts at a 
 higher temperature than the metal. At a full red heat it is 
 decomposed by iron, sulphide of iron and metallic lead result- 
 ing ; thus 
 
 2 PbS + Fe 2 - 2FeS + Pb 2 
 
 When calcined it is partly converted into oxide and partly 
 into sulphate, SO 2 passing off. 
 
 The sulphate, which is also produced by the addition of 
 sulphuric acid to a soluble salt of lead, is a white substance 
 not readily decomposed by heat. It is insoluble in water. 
 Heated with carbon, it is reduced to sulphide. 
 
 When sulphide of lead is heated with oxide or sulphate, 
 
i8o Metallurgy. 
 
 the sulphur and oxygen combine and pass off as SO 2 , metallic 
 lead separating thus 
 
 2PbO + PbS = 3 Pb + SO, 
 PbS + ]PbSO 4 = Pb 2 + 2SO,. 
 
 Lead Ores. The principal ores of lead are the sulphide, 
 carbonate, and chlorophosphate. 
 
 Galena, blue lead ore, lead sulphide (PbS), is the most 
 important and abundant. It is found both crystalline and 
 massive. It has a grey metallic lustre, and is heavy, having 
 a specific gravity of about 7-5. It is brittle, and contains 86'6 
 per cent, of lead. Galena occurs widely distributed in the 
 older rocks. It is usually associated with quartz, fluor, calcite, 
 barytes, and spathic iron ore in the veins, and frequently with 
 copper pyrites and zinc ores. It often contains silver, some- 
 times in considerable quantity. Such ores are described as 
 argentiferous. Iron, antimony, copper, and zinc are commonly 
 present, and gold and bismuth also frequently occur in it. The 
 localities are very numerous. 
 
 Cerusite, lead carbonate, or white lead ore (PbCO 3 ), 
 also occurs. Its colour is white or yellowish, and its lustre 
 adamantine to earthy. It has a specific gravity of 6-5, and 
 contains 75 per cent, of lead. It is frequently argentiferous, 
 like galena. The deposits at Leadville, in Colorado, and at 
 Broken Hill, in Australia, are of this character. 
 
 Anglesite, lead sulphate (PbSO 4 ), also occurs, associated 
 with galena and other lead ores. 
 
 Pyromorphite, green lead ore, linnets, chlorophosphate of 
 lead (3Pb 3 (POj) 2 , PbCl 2 ) occurs in hexagonal crystals and as 
 green and brown masses. Its specific gravity varies from 
 5 '5 to 7 -2. Ores in which the phosphorus is replaced by 
 arsenic are known as mimetesite. In addition to the above, 
 many compounds of lead occur naturally, among which may 
 be mentioned Boulangerite (3?bS, Sb 2 S 3 ) and Jamesonite, 
 another antimonial sulphide of lead. 
 
 LEAD SMELTING. 
 
 So many lead ores contain silver that the metallurgical 
 treatment of the two metals is hardly separable. In this 
 
Lead. 181 
 
 chapter we purpose dealing with the extraction and refining of 
 lead, and such processes for the concentration of the silver as 
 are conducted upon the lead, and to leave the actual recovery 
 of the silver to be dealt with when treating of that metal. 
 Extraction processes may be grouped, in much the same 
 manner as in copper smelting, into reaction and reduction 
 processes. 
 
 The reaction process for gelena is based on similar chemical 
 changes to those which occur in copper smelting, viz. the mutual 
 reaction of the unaltered sulphide upon oxide and sulphate 
 formed by roasting the sulphide. In the case of lead, how- 
 ever, the operation is simplified. The ore as received from 
 the miner contains a sufficient percentage of metal to permit 
 of its direct treatment. 
 
 The reduction processes may be divided into carbon 
 reduction, where that element forms the reducing agent, and 
 iron reduction processes, where iron, or iron bearing materials, 
 such as oxides of iron, or iron slags, form part of the charge, 
 and liberate the lead from combination. 
 
 Reaction Processes. To this category belong the Flint- 
 shire, Derbyshire, Spanish, French, and Bleiberg methods of 
 smelting galena. 
 
 The form of furnace employed and the details of the 
 process vary greatly, having regard to the puriiy of the galena 
 or its admixture with carbonate, sulphate, etc. 
 
 The Flintshire furnace is shown in Fig. 59. It is a 
 reverberatory furnace, having three doors opening on either 
 side of the hearth. The side on which the firing door is 
 situated is known as the " labourers' side," and that opposite 
 as the " working side." The bed which consists of slag from 
 previous operations, spread over the hearth while in a pasty 
 state is level with the doors on the labourers' side, but, on 
 the working side, slopes so as to form a well some 18 inches 
 deep, immediately in front of the middle door. A tap-hole, 
 B, communicating with the bottom of this, is provided for 
 tapping out the lead. A second tap-hole above this, for the 
 removal of fused slag, is provided in some furnaces. Outside 
 the furnace is an iron pot, into which the metal is tapped. At 
 
i82 Metallurgy. 
 
 the top of the furnace is a hopper, from which the ore is 
 introduced into the furnace. 
 
 The process is conducted as follows. The charge of about 
 a ton is let down from the hopper into the furnace, still red 
 hot from a previous charge, and spread from the labourers' 
 side over the furnace bed, clear of the well. It is then calcined 
 at dull redness for from one and a half to two hours, being 
 stirred and turned over from time to time to expose it to the 
 air, to admit which the doors are left partly open. The 
 temperature is not sufficient to melt the galena, which, it may 
 
 FIG. 59. Lead Smelting Furnace. 
 
 be noted, has a higher melting-point than lead itself. During 
 this stage oxidation occurs freely, oxide and sulphate of lead 
 being formed. 
 
 The doors are now closed, the fire made up, and the 
 temperature raised to full redness, when the reaction between 
 the oxide, sulphide, and sulphate produce a copious separation 
 of lead, which collects in the well of the furnace. The tempera- 
 ture at this point is also somewhat below the melting-point of 
 galena. 
 
 The unreduced mass becomes soft and pasty. It is 
 pushed out of the basin and spread over the hearth. To 
 prevent its fusion, the doors are opened to cool it somewhat, 
 and it is stiffened " set up " by the addition of a little lime. 
 
 The charge is then melted " flowed " down by increasing 
 
Lead. 183 
 
 the temperature, for which purpose the doors are closed, the 
 damper opened, and a fresh fire made. The lime decomposes 
 any silicate of lead formed, producing silicate of lime, and 
 liberating oxide of lead. This, reacting on the unreduced 
 sulphide present, a further separation of lead occurs. Lime 
 is again thrown in and mixed with the slags to render them 
 pasty, and they are again spread over the hearth and roasted 
 for from half to one hour. At the end of this period the 
 temperature is raised to its highest point, and the whole is 
 melted a second time. The oxide produced during the roast- 
 ing and that liberated from silicate by the lime added is in 
 this stage often more than sufficient to decompose the remain- 
 ing sulphide, and a little coal slack is often added to assist in 
 its reduction. This also reduces any sulphate to sulphide, 
 which reacts on the oxide, producing lead. The metal is then 
 tapped into the lead-pot in front. 
 
 The slags are dried by further additions of lime, and are 
 withdrawn in a pasty state from the furnace. They are known 
 as grey slags, and usually amount to about 20 per cent, of the 
 charge. They contain about 40 per cent, of lead as silicate, 
 which is recovered in slag hearths. 
 
 Setting up by lime has a twofold object. Its principal use is to stiffen 
 the slags and render them infusible during the roasting periods, so that 
 the gabna contained in the charge shall not become bound up, and 
 protected from the action of the air. In the fusions it probably liberates 
 oxide of lead from the silicate. 
 
 The metal in the lead-pot is covered with slags, matte, and 
 dross, which retains much metallic lead in globules. Coal 
 slack is thrown on top and stirred into the hot metal. The 
 gas produced burns on top, heats the slag, and releases the 
 shots of metal. The skimmings are either thrown back into 
 the furnace at once, to further separate lead, or are added to 
 the succeeding charge near the end of the preliminary calcining. 
 
 The stages of the process are known as " fires." 
 
 When barytes occurs as gangue in the ore, it is necessary 
 to add fluor spar as a flux, or to mix it with ore containing 
 fluor. The amount of blende in the ore also influences the 
 fusibility of the slags. 
 
 The processes in use at Cueron, Blieberg, and elsewhere 
 
1 84 Metallurgy. 
 
 are of a similar character. This process is only applicable to 
 pure ores. Foreign sulphides such as antimonite and even 
 copper pyrites combine with galena, and form readily fusible 
 double sulphides, which melt or clot, and arrest the roasting. 
 
 In smelting lead ores containing antimony in reverberatory 
 furnaces by the reaction process, the lead obtained in the 
 earlier stages is freer from that element than that subsequently 
 produced. 
 
 Reduction Processes. These are conducted in both rever- 
 beratory and blast furnaces. They are employed for the 
 treatment of impure ores and slags, and for reducing the oxides, 
 dross, or abstriches produced in the purification of lead. 
 
 In the treatment of raw ores, iron is the reducing agent 
 generally employed. With poor ores containing much iron 
 sulphide, a preliminary roasting and fusion are resorted to, for 
 the purpose of fluxing of! the iron and concentrating the lead. 
 
 The Cornish Process. This process is followed to some 
 extent for the treatment of impure ores containing copper and 
 antimony, reguli containing lead, and also for the treatment of 
 slags. 
 
 The ore or regulus is first roasted in a separate calciner, 
 much as in copper smelting, for from 15 to 18 hours. 
 
 It is then smelted in a furnace resembling a Flintshire fur- 
 nace. The charge of 2 tons is melted down in from 2 to 3 hours. 
 
 With pure ores, or with substances rich in silver, the lead 
 which separates by "reaction" is removed and dealt with 
 separately. In the former case it is purer, and in the latter 
 richer in silver than that subsequently produced. 
 
 Lime and anthracite culm are then added and well mixed. 
 The materials, thus rendered stiff, are spread over the hearth, 
 and some 2 cwts. of scrap iron added. The doors are closed 
 and luted, and the charge remelted at a high temperature. 
 The products separate in layers, which follow each other when 
 the furnace is tapped. Lead, which is received in the lead-pot 
 in front ; regulus, or slurry, which is a mixture of iron sulphide, 
 with the copper and some lead sulphide which flows over the 
 top of the lead-pot into the pot below; and slag, which is 
 generally so free from lead and copper as to be thrown away. 
 
Lead. 
 
 The process occupies about 8 hours. 
 
 In this process the lead first obtained is the result of reaction between 
 oxide, sulphide, and sulphate ; in the second stage the sulphide and silicate 
 present are reduced by the iron. The anthracite reduces the oxidized 
 matters present. 
 
 2PbO,SiO 2 
 2FeO,SiO 2 
 
 2Fe 
 Pb 2 . 
 
 Lead Smelting in Blast 
 Furnaces. Blast furnaces 
 are now largely employed 
 in lead smelting, water- 
 jacketed furnaces (Fig. 60) 
 being principally employed. 
 The ore, unless an oxi- 
 dized one (carbonate, phos- 
 phate, etc.), is first roasted 
 in a reverberatory furnace, 
 being finally heated till it 
 clots together. It is then 
 mixed with iron-bearing 
 materials, such as pyrites 
 cinders from the manu- 
 facture of sulphuric acid, 
 iron ores, or puddling and 
 mill furnace slags, which 
 yield metallic iron during 
 the smelting, and suitable /\_ 
 fluxing agents, e.g. lime. 
 The ore mixture is then 
 smelted with coke as fuel. 
 The oxide of lead is re- 
 duced partly by the CO 
 generated, and also by FlG 
 iron reduced by CO in 
 the furnace. 2?bO + Fe 2 
 + SiO 2 =2FeO,SiO 2 +Pb 2 . 
 
 The oxide of iron combines with silica in the charge and 
 passes into the slag. 
 
 SECTION AT C.D. 
 
 a, hearth bottom ; b, channels in brick- 
 work ; dd, tap holes ; e, slag lip ; f, blast 
 pipes ; g, water-jacket ; z", blast main ; k, sup- 
 porting ring ; m, charging pipe ; n, waste gas 
 pipe ; o, charging floor ; /, slag pot. 
 
1 86 Metallurgy. 
 
 In these furnaces that portion of the furnace in the vicinity of the 
 tuyeres, which is most seriously corroded by the metallic oxides and slags, 
 when consisting of siliceous materials, is formed of hollow iron casings 
 only, through which water circulates to keep them cool. 
 
 
 
 Any sulphide of lead is reduced by the iron, iron sulphide 
 being formed. 
 
 Three products are obtained : Work lead (containing the 
 greater part of the silver and gold, as well as antimony, tin, 
 bismuth, copper, and traces of cobalt, nickel, and arsenic). 
 
 Matte, consisting of sulphide of iron and nearly the whole 
 of the copper in the charge. 
 
 It sometimes contains 10 to 12 per cent, of lead and some silver, gold, 
 etc. It is roasted and resmelted in a separate furnace when it yields 
 lead (often rich in silver), a second matte richer in copper, and slag. 
 The second^ matte is again roasted and smelted, yielding a regulus contain- 
 ing over 20 per cent, of copper and slag. This matte is treated for copper. 
 Sufficient sulphur is left in the mattes after calcining to serve as a vehicle 
 for concentrating the copper. The oxide of iron formed during roasting 
 is fluxed off by the addition of silica in the fusion (see Copper). Sings 
 from the smelting of first matt^generally contain lead and are resmelted. 
 Lead obtained from matte is very impure. 
 
 Slag. This is essentially silicate of iron, but often con- 
 tains also notable quantities of lime, alumina, and oxide of zinc 
 (2FeO,SiO 2 -f- 2CaOSiO 2 ). If lead is present beyond i per cent., a 
 
 it is resmelted with the calcined regulus. - 
 * t 
 
 It must be remembered that .the precious metals have a tendency *o 
 "associate themselves with the metallic products of an operation. In the 
 above case there are two .such products, viz. the lead which carries the 
 greater part and the matte which also contains a portion of the precious 
 metals. In the subsequent treatment much of the silver or gold in the 
 matte passes into the lead obtained. What remains ultimately passes into 
 the copper extracted from tlTe concentrated matte, from which it is 
 ultimately recovered. 
 
 The Slag Hearth is a small blast furnace used for the treat- 
 ment of the rich slags obtained in smelting in reverberatory 
 furnaces. 
 
 The lead is present in the form of silicate, sulphide, and 
 sulphate, and^is much as 40 per cent, is often present. This 
 silicate requires a very high temperature for its reduction by 
 coke. It is more easily reduced by iron. 
 
 The slags contain, it" must be remembered, a considerable 
 quantity of lime from the " setting up." By mixing them with 
 
Lead. 
 
 1 8 7 
 
 coal ashes, iron slag, etc. (containing oxide of iron, silica, and 
 alumina), clayey matters (old clay furnace beds or broken 
 brickbats), the alumina and other oxides thus introduced 
 combine with the silica and lime at the high temperature 
 employed, liberating the oxide of lead in the slag, which 
 is reduced by the coke employed as fuel. The. lead produced 
 is very impure, and is known as slag lead. The slag known 
 as black slag is free, or nearly free from lead, and consists 
 of silicates of lime, alumina, iron (hence the colour), and 
 other oxides. 
 
 The furnace is shown in Fig. 6r. It is rectangular in 
 form, about 26 inches by 22, internal measurement. The 
 hearth itself is 3 feet deep, 
 but it is surmounted with 
 a brickwork hood, or cover, 
 which communicates with 
 flues leading to the stack 
 for the condensation of 
 fume. 
 
 The back and side walls 
 of the furnace are built of 
 fire-brick, but below the 
 tuyere at the back is a 
 cast-iron plate (a). The 
 front also consists of an 
 iron plate (b), the lower 
 edge of which is supported some 7 inches above the , cast- 
 iron bed-plate (c), leaving an opening across the front of the- 
 furnace, stopped with clay while working. The bed-plate (c) 
 slopes slightly towards the front to permit the separated 
 lead and slags to flow into the cast-iron receptacle (d) in front. 
 This is divided into two unequal parts by a partition which 
 passes nearly to the bottom. The larger compartment is the 
 width of the bed-plate, and is filled with cinders. The lead, 
 and sfegs flow into it from the furnace. TheTTnetal niters to 
 the bottom and passes into the smaller division, from which 
 it is ladled while the slags flow over the top of the ashes 
 into the pit (s) beyond. 
 
 FIG..I. Slag Hearth. 
 
1 88 Metallurgy. 
 
 Water flowing through the pit granulates and breaks up 
 the slag, any entangled lead being readily recovered. The 
 tuyere, which is horizontal, enters at the back, and the charging 
 opening is at the side. The lower part of the hearth nearly to 
 the level of the tuyere, and the first compartment of the lead- 
 pot, are filled with cinders, which serve as a strainer for the 
 lead, which flows out from the bottom through openings in 
 the clay stopping. They also protect it from oxidation. 
 
 The fire being lighted, coke is introduced, the fire blown 
 up, and the furnace thoroughly heated. Alternate layers of 
 slag and coke are then introduced, and the supply continued as 
 the charge melts down. The slag is removed from time to time 
 by making an opening in the clay breast through the cinder 
 bottom. After working some seven hours, the supply of 
 material is stopped and the fire allowed to burn out The 
 furnace is cleared out, cooled, and prepared for the next shift. 
 
 In the ordinary slag hearth the working cannot be made continuous, as 
 the furnace would get too hot. This would cause serious loss by volati- 
 lization, and the furnace walls would be much corroded. 
 
 In many works, circular cupolas, with three or more tuyeres and a fore 
 hearth (syphon tap), are employed for the reduction of slags, e.g. the 
 Spanish slag hearth and Economic furnace. Water- jacketed, Pilz, and 
 Rachette furnaces 1 are also employed. 
 
 Combined Reaction and Reduction Processes. The ore 
 hearth, still in use in Scotland and the north of England, justly 
 holds its own for the production of very pure lead. 
 
 The hearth or furnace (Fig. 62) is built of cast-iron plates 
 and blocks, surmounted by a brickwork hood, which com- 
 municates with flues. 
 
 The bottom consists of a rectangular cast-iron trough, N, 
 the sump 3 inches thick, measuring about 2 2 inches square, 
 and some 4-^ to 6-J- inches deep. This is bedded in sand on a 
 raised platform some 12 or 13 inches high. The sides and 
 back of the hearth consist of square prisms of iron, 6 to 8 
 inches thick, lying on each other and resting on the edge of 
 the sump, forming a hearth some 16 to 18 inches deep, open 
 in front. A sliding door of plate iron is sometimes provided. 
 
 1 Rectangular blast furnaces. 
 
Lead. 
 
 1 80 
 
 A single horizontal tuyere enters at the back, a little 
 above the sump. In front of the hearth is a sloping iron plate 
 the workstone W. The upper edge of this is level with 
 the sump, and the lower rests on the masonry platform. It 
 measures about 3 feet by \\ feet, and has a raised rim running 
 round the sides and lower 
 edge, a groove being cut 
 diagonally across it, from 
 top to bottom, down which 
 the metal runs after filling 
 the sump. The lead-pot 
 .P is placed in front of 
 the workstone. 
 
 NOTE. In some hearths the 
 size above the workstone can be 
 regulated by a movable cast- 
 iron prism, which can be packed 
 up to the desired height by fire- 
 bricks and moved towards or FIG. 62. 
 from the back. 
 
 The charging hole is at the side. 
 
 Formerly raw ore was treated in these hearths, but it is now more 
 general to partially roast and agglutinate the ore to prevent loss by being 
 blown away and carried into the flues. 
 
 Coal and peat are used as fuel. 
 
 In Scotland the hearth is worked continuously, in shifts of 
 6 hours. In the north of England it works intermittently. 
 The process is conducted as follows : Assuming that the 
 hearth is in operation, the sump being full of lead and the 
 hearth a glowing red, a quantity of half-smelted material 
 browse is thrown in next the tuyere, to assist in the distribu- 
 tion of the blast, and ore and fuel added. The hearth is kept 
 full of materials. At intervals of a few minutes the workman 
 draws the charge from the hearth on to the workstone, by 
 means of a hooked bar, breaks up the glowing mass, and picks 
 out the slags. The unsmelted portion is returned to the 
 hearth, after an addition of lime, and fresh materials are added 
 on top. Much lead drains out of the charge while on the 
 workstone, and is conducted by the groove into the lead-pot, 
 into which the reduced lead overflows from the sump. 
 
Metallurgy. 
 
 The reduction of lead in this process is due, partly to "reaction," as 
 in the Flintshire and analagous processes, and partly to direct reduction 
 by the carbon of the fuel. The oxides and sulphate produced in the 
 preliminary roasting, or by the excess of air bloivn in, if raw galena is being 
 smelted, react on the unaltered portions of the sulphide, \\hile the oxide 
 is reduced to some extent by the fuel. No desulphurizing. agent is added, 
 as in the water-jacket furnace and Cornish process. 
 
 The addition of lime stiffens the charge. If the slag 
 melts too easily, excess of silicate of lead is present, which, by 
 its ready fusion, may enclose portions of the charge and 
 prevent its reduction, in addition to the loss of lead in the 
 slag. The slag consists of silicates of lead and lime, with 
 sulphate and sulphide of lead, and other bodies. It is smelted 
 in the usual way. 
 
 A hearth yields about 70 cwts. of lead in 24 hours, and 
 consumes about 1 2 cwts. of coal. 
 
 The metal from the ore hearth is of good quality, owing to 
 the operation being conducted at too low a temperature to 
 effect the reduction of the impurities. The loss of lead in the 
 slags is small, being less than 4 per cent, of the lead in the 
 ore. The loss as fume is much greater with raw than with 
 roasted ore. It varies from 7 to 20 per cent, of the lead. 
 
 A blind chamber behind the hearth is provided for the 
 deposit of portions of the charge carried off by the violence of 
 the blast. These are known as " hearth ends." 
 
 Softening or Improvement of Hard Lead. The pig lead, 
 as obtained from many operations, contains various impurities, 
 antimony, tin, copper, zinc, sulphur, iron, silver, and bismuth 
 being often present. Their effect is to harden the lead and 
 unfit it for the purposes to which it is generally applied. The 
 foreign metals are removed by oxidation, the lead being exposed 
 at a red heat to the action of the air in a reverberatory furnace, 
 the bed of which sometimes consists of a cast-iron pan some 
 10 feet long, 5-5- feet wide, and 10 inches deep or one of 
 wrought iron, with a fire-brick lining, or is made of slags. In 
 the latter cases higher temperatures can be employed, and the 
 process occupies less time. The lead is ladled or run in from 
 a melting-pot, or the pig lead may be melted in the furnace. 
 
 The oxides which form, consisting of oxide of lead mixed 
 with those of the impurities, are skimmed off from time to 
 
Lead, 191 
 
 time, to expose fresh surfaces, lime being added, if fused, to 
 stiffen them. Samples of the metal are withdrawn and cast. 
 When the lead shows a peculiar flaky appearance, the opera- 
 tion is judged complete, and the lead is ladled out or run into 
 iron pig moulds. 
 
 The oxides which form in the earlier stage of the refining 
 are richer in tin ; those which form later on, in antimony. 
 
 When much copper is present, the lead is liquated before 
 softening, as that element is not removed to any great extent. 
 This is accomplished at Clausthal on the bed of a rever- 
 beratory furnace, which slopes slightly upwards from the fire- 
 place. The temperature of the flue-end of the hearth is below 
 the melting-point of lead. The metal is introduced there, 
 and gradually moved forward. The lead melts and drains 
 away, and the residues are moved gradually nearer the fire to 
 sweat out all the lead, and are then raked out of the furnace. 
 This residue contains the copper and nickel and cobalt, and 
 often some arsenic and sulphur. 
 
 Reduction of Litharge and Drosses. The "drosses," or 
 " abstriches " impure litharge formed during softening or 
 other operations, are reduced by intimately mixing them with 
 small coal, grinding them together under edge-runners, and 
 smelting in a reverberatory furnace, the bed of which is pro- 
 tected from corrosion by a layer of coke ; this is formed by 
 introducing a few inches of moistened caking-coal slack into 
 the furnace, and beating it down. The bed slopes slightly, 
 and the reduced lead drains into a basin in front. 
 
 Small water-jacketed furnaces are now largely employed for this purpose. 
 The hard lead obtained, marked H, is richer in antimony, etc., and is 
 again softened. The dross yields on reduction hard hard HH lead, 
 and so on. This is repeated, until lead rich in antimony sometimes more 
 than 50 per cent. is obtained. This is sold to the type-founders (see 
 Alloys). 
 
 Desilverization of Lead. Silver, as before noted, is com- 
 monly found in lead ores, and during smelting passes into 
 the metal. Lead containing more than 3 ounces to the ton is 
 treated for its extraction. Two methods are followed for this 
 purpose. 
 
 Pattinsonising In Pattinson's process, advantage is taken 
 
192 Metallurgy. 
 
 of the fact that alloys of lead with silver containing less 
 than 1-8 per cent. 1 of silver, have a lower melting-point 
 than pure lead, and that lead in the solid state is denser than 
 when molten. In consequence of this, if a large body of lead 
 be melted and cooled slowly with constant stirring, the lead 
 which first crystallizes is poorer in silver than that which remains 
 fluid. By removing the crystals with perforated ladles, a fluid 
 alloy richer in silver and a lead poorer than the original are 
 
 FIG. 63. 
 
 obtained. The crystals removed are, of course, covered with 
 the fluid alloy, and thus, in the process of removal, some silver 
 is also carried off. By repeating the process on the enriched 
 alloy, the silver contents of the fluid portion are again increased, 
 until an alloy containing sufficient silver to be cupelled is 
 obtained. Or the rich alloy may be treated by the Parke's 
 process, which see. 
 
 1 640 ozs. per ton. 
 
Lead. 193 
 
 The process is conducted in a series of iron pans set side 
 by side, as shown in Fig. 63, each capable of holding from TO 
 to 15 tons of lead. A 1 5-ton boiler is 5 feet 2 inches in 
 diameter, and has a capacity of 43 cubic feet. A full set of 
 pots numbers 13. Each pot is heated by its own fire, which is 
 controlled by a damper. The products of combustion pass 
 from the fireplace into a flue encircling the pot, and thence 
 to the main flue. 
 
 The crystals are removed by a perforated ladle made of 
 half-inch iron plate, 16 to 20 inches in diameter, 4 to 6 inches 
 deep, with a handle about 9 feet long, about half the length 
 being iron and the other wood. A chisel-ended iron bar is 
 used to break up the lead crusts and for stirring, and a flat, 
 perforated shovel for skimming. 
 
 Small pots filled with melted lead, between each pair of boilers, are some- 
 times provided for keeping the ladles hot, and the range of boilers is 
 commanded by a crane for the transference of the ladlesful of crystals 
 removed, or pivoted rests some 18 inches high with a roller top are 
 placed between the pots. These are used as fulcrums for resting the 
 handle of the ladle while fishing out the crystals and "turning over " from 
 one pot to the next. 
 
 The lead to be desilverized is first melted in one of 
 the pots, and got sufficiently hot to oxidize. A scum of dross 
 forms, and is removed. (If very impure, it is necessary to 
 liquate and soften before Pattinsonizing.) The fires are 
 then withdrawn, and the cooling down facilitated by sprinkling 
 water on the surface. The crusts of lead which form are 
 pushed down into the metal, until there is difficulty in melting 
 them, when the water is stopped and the bath thoroughly 
 paddled. As the mass further cools, the lead begins to solidify 
 in crystals. These are larger as the alloy is poorer in silver. 
 Being heavier than the molten alloy, they sink, and the lead 
 requires to be continually stirred and broken up, to prevent 
 the formation of masses of crystals, which would entangle rich 
 lead. The temperature must be carefully managed, or the 
 crystallization will either be too slow, or masses of crystals will 
 form. When the formation of crystals has progressed suffi- 
 ciently, they are removed by the ladles, and transferred to the 
 next pot to the left, which is already hot enough to melt them. 
 
 o 
 
1 94 Metallurgy. 
 
 Each ladleful as it is raised to the surface is allowed to drain, 
 and shaken to remove the liquid as much as possible. In this 
 manner two-thirds or seven-eighths of the lead is removed. 
 The former method is known as the " high " and the latter as 
 the " low " system. 
 
 Working on the high system all the lead removed is thrown 
 into the next pot In the "low" system of working the last 
 eighth contains too much silver, and is thrown on the ground, 
 to be used with lead of the same richness in silver. The fluid 
 alloy remaining in the pot is transferred to the next pot to the 
 right. Working on the high system, it contains about twice 
 the proportion of silver in the original lead, while the poor lead 
 passing to the left averages about one-half. 
 
 By repeating the process on the enriched lead the propor- 
 tion is again doubled, while the poor lead, similarly treated, 
 will be again halved. Starting with a lo-oz. lead, one-third 
 rich lead assaying 20 ozs., and two-thirds poor lead assaying 
 5 ozs. to the ton will be first obtained. On again treating the 
 enriched alloy, 40 ozs. rich and 10 ozs. poor will be obtained. 
 A third treatment yields 80 ozs. rich and 20 ozs. poor ; a 
 fourth, 1 60 rich and 40 ozs. poor; a fifth, 320 ozs. rich and 
 80 ozs. poor, and so on. 
 
 The poor lead, from the first crystallization, on a second 
 treatment, yields 10 ozs. rich and 2\ poor ; a third treatment 
 gives 5 ozs. rich and i^- poor; and k fourth treatment gives 
 2-*- ozs. rich and f poor. These figures are only approximate ; 
 in practice they are not always realized. 
 
 In actual work, alternate pots are generally being crystal- 
 lized at the same time, so that the rich third from the one, 
 and the poor two-thirds from the other, make up a charge for 
 the intervening pot. 
 
 When less than i oz. of silver per ton is present, the poor 
 crystals are transferred to the market pot on the extreme left, 
 which has a capacity of only about two-thirds of the others, 
 and from which the lead is cast into pigs. 
 
 The rich lead containing from 600 to 700 ozs. per ton 
 is cupelled (see page 225). 
 
 The Pattinson process is n.ow mainly followed for the 
 
Lead. 195 
 
 enrichment of leads too pcor to be treated by zinc, as described 
 (see Parkes's Process). 
 
 The oxidation of the lead which accompanies the repeated 
 meltings so purifies it that, by the time it reaches the market pot, 
 there is no need for further softening, and it is cast into pigs. 
 
 NOTE. The copper, antimony, bismuth, and iron remain mostly in 
 the fluid portion, and would give trouble especially antimony in the 
 cupellation of the enriched lead. Before Pattinsonizing, it is " improved " 
 if more than 0*5 per cent, impurity is present. 
 
 Bozan Process Pattinsonizing by steam. This method was introduced 
 by Messrs. Luce and Rozan, at Marseilles, and has been adopted to some 
 extent. The novelty consists in the method of stirring up the molten lead 
 by means of steam at high pressure forced through the lead, the surface 
 being cooled by water as before. The crystals are not removed, but the 
 liquid enriched alloy is run off and the crystals remain in the pot. Lead of 
 the same richness is run in from a melting-pot above, and the operation 
 repeated. A great saving in labour, fuel, and drosses results. 
 
 Parkes's Process Desilverizing by zinc. This process has 
 displaced, to a very large extent, the Pattinson method of 
 desilvering. Or the " work lead " is Pattinsonized until it has 
 attained a richness of about 40 to 60 ozs., and is then treated 
 with zinc 
 
 The process depends on two facts. First, that zinc and 
 lead melted together do not alloy, but separate according to 
 their specific gravities, the zinc rising to the surface, carrying 
 only some 2 per cent, of lead. 
 
 Second. Silver (as well as copper, etc.) alloys with zinc 
 more readily than with lead, and hence, when that metal is 
 mixed with argentiferous lead, the silver is collected in the 
 zinc scum which rises to the top and is removed. 
 
 The method of carrying out the process varies somewhat 
 in different works, and the quantity of zinc required depends 
 on the amount of silver present. 
 
 The arrangement of zincing portion of a Parkes plant is 
 shown in Fig. 64. The two large pots, A, are capable of 
 holding about 25 tons of lead, and are employed in the addition 
 of the zinc. The smaller ones, B, have a capacity of about 6 
 tons, and are for the treatment of the zinc crusts on removal. 
 D is a reverberatory furnace for re moving the zinc taken 
 up by the lead, by oxidation. 
 
196 
 
 Metallurgy. 
 
 The lead is melted in one of the pots A, heated to the 
 melting-point of zinc, and skimmed. A portion of the zinc is 
 then added, and when this has melted, a farther addition of 
 zinc is made, and the whole is well paddled for some 15 
 minutes. The pot is then covered over and allowed to rest 
 for a period, varying from i to 3 hours. 
 
 While at rest, the zinc gradually rises to the top, carrying 
 with it the silver. As it cools, it forms a crust on top, in 
 which a good deal of lead is entangled. The zinc crust is 
 removed by a ladle into the middle of the smaller pots, and 
 the pot thoroughly skimmed till the lead begins to set. The 
 
 
 
 00 
 
 FIG. 64. 
 
 pot is again heated up, and a second addition of zinc made to 
 the lead, well paddled in, and again allowed to cool. The 
 amount added depends on the amount of silver remaining in 
 the lead. The crusts formed are removed as before. After 
 this second treatment, the lead is desilverized and is then run 
 or syphoned off into the improving furnace D, to remove the 
 zinc present in the lead. This amounts to about -| per cent 
 The lead is skimmed from time to time. Samples taken out 
 are cast in moulds and examined. When the surface indicates 
 a sufficient degree of purity, the lead is run from the furnace 
 into a lead-pot, E, allowed to cool down, and cast. 
 
 NOTE. With lead containing more than 80 ozs. of silver, the addition 
 of the zinc in three portions is advisable. 
 
 The first crusts removed to the smaller pots are gently 
 heated to liquate out the adherent lead. This is either cupelled, 
 or generally returned to the zincing-pot with the next charge. 
 After liquation, the crusts are transferred into the right-hand 
 pot, and sent off to be distilled (see p. 197). The last 
 
Lead. 
 
 197 
 
 crusts are used as the first addition of zinc made to the 
 next charge. 
 
 The total amount of zinc required varies. A 20-oz. lead 
 requires 30 Ibs. of zinc per ton, equal to i '33 per cent. ; a 40-oz. 
 lead requires 35 Ibs., equal to 1*56 percent.; and a 6o-oz. 
 lead about 38 Ibs., equal to 1-69 per cent. ; while a 5oo-oz. 
 lead requires about 2\ per cent. 
 
 In Cordurie's process, the zinc to be added is enclosed in a perforated 
 cast-iron box, fixed on the end of a revolving vertical shaft. Immediately 
 above the box is a propeller-shaped paddle, which as the zinc melts 
 distributes it uniformly through the lead and thoroughly mixes it. Three 
 zincifications are made. 
 
 The softening is effected by running the lead into a pot situated at 
 a lower level, heating it to redness, and blowing superheated steam 
 through it, succeeded by a mixture of steam and air. The zinc and iron 
 present decompose the steam and are oxidized, hydrogen being liberated. 
 Later, the copper and antimony remaining are oxidized by the air. 
 
 zinc crusts carry in 
 
 Treatment of Zinc Crusts. The 
 addition to the silver 
 a large proportion of 
 lead, together with the 
 copper, and some anti- 
 mony, arsenic, and { 
 nickel. 
 
 The zinc is distilled 
 off in large plumbago 
 crucibles, provided with 
 condensers, as shown 
 in Fig. 65, about 18 
 inches in diameter and 
 27 to 30 inches high, 
 provided with a cover, 
 as shown. A clay pipe 
 leads from a hole in 
 the side to the con- 
 denser, C, standing in front, in which the recovered zinc 
 condenses. A little lime and coal-dust are often added. The 
 residual lead is cast in moulds, and afterwards cupelled. Any 
 bismuth, antimony, copper, etc., in the crusts remain with 
 the lead. 
 
 FIG. 65. 
 
198 
 
 Metallurgy. 
 
 Lead Fume. The gases passing away from the various 
 furnaces carry with them considerable quantities of dust and 
 volatile compounds of lead. These are deposited in the flues 
 
 Lead Ores 
 
 Liquation and 
 Softening Furnaces 
 
 Silver 
 jjT~ (Market) 
 
 FIG. 66. Synopsis of Lead Smelting and Desilverizing Processes. 
 
 through which the gases are conveyed to the chimney-stack, and 
 constitute "lead fume." It consists of lead oxide, sulphide, 
 and sulphate, with some lime, oxide of iron, alumina, etc., carried 
 
OF THE 
 
 * 
 
 Mercury. 
 
 . 
 over as fine dust, and some silver. Zinc oxide is o 
 
 especially in blast-furnace flues. A crust of this substance is 
 often found in the upper part of the furnace when smelting 
 zinciferous ores in blast furnaces. 
 
 For the condensation of the fume, and to minimize the 
 nuisance arising from noxious vapours, the flues are sometimes 
 from 3 to 5 miles long, and measure as much as 8 feet by 9, 
 with which all the furnaces are connected. 
 
 Staggs, Stokoe, and French and Wilson have introduced 
 condensers in which the gases are washed, or caused to pass 
 through a wet filter of faggots or gauze, and thus deposit the 
 solid matter. 
 
 The fume is smelted in blast furnaces, being previously 
 agglomerated by heat to facilitate charging. 
 
 CHAPTER XIV. 
 
 MERCURY. 
 
 THIS is the only metal which is fluid at ordinary temperatures. 
 About 39 C. it freezes to a leaden grey, hard, malleable 
 mass, contracting considerably on solidifying. 
 
 Its silvery white colour, and the readiness with which it 
 moves about, owing to not wetting the surfaces (except 
 metallic) with which it comes in contact, has earned for it the 
 name of quicksilver (German, " quick silber "). Its specific 
 gravity is about 13*6, which when solid becomes about 14*2. 
 At a temperature of 357*25 C. it boils, giving a colourless 
 vapour, but gives off vapour at much lower temperature, even 
 below 40 C. 1 (see Condensation). Its low specific heat, high 
 conductivity, and high boiling-point render it suitable for the 
 construction of thermometers; its fluidity and high specific 
 gravity for barometers. When in a very fine state of division, 
 
 1 A gold leaf suspended over mercury at the ordinary temperature is 
 whitened in course of time, being attacked by the vapour evolved. 
 
200 Metallurgy. 
 
 and a film of foreign matter interposes, the globules will not 
 unite together, the mercury is said to be floured. 
 
 It is permanent in air, oxygen, etc., at ordinary temperatures, 
 but when heated near its boiling-point in air it oxidizes, forming 
 red oxide of mercury. This is reduced to metal, with the 
 separation of oxygen at a somewhat higher temperature. It is 
 attacked by chlorine and ferric and cupric chlorides. 
 
 It is unattacked by hydrochloric acid, and but slowly, 
 by sulphuric acid, unless hot and concentrated, when sulphurous 
 acid gas is evolved and sulphate of mercury formed. Strong 
 nitric acid rapidly dissolves the metal, but when dilute and 
 cold has little action. Mercury compounds are readily de- 
 composed by iron, copper, and other metals. 
 
 Mercury combines directly with sulphur, producing mercuric sulphide, 
 or vermilion. It is prepared by heating mercury and sulphur together in 
 an iron pan, with constant stirring, when a black brittle mass is produced. 
 This is introduced at intervals into long, upright, iron retorts, or tall 
 earthen jars, the lower parts of which are heated to redness. The 
 sulphide volatilizes and condenses in a crystalline form in the cool upper 
 parts. This deposit is red, and is ground, levigated, and dried. It is the 
 vermilion of commerce. 
 
 Amalgams. Mercury attacks and dissolves most metals, 
 forming liquid alloys when the mercury is in excess. If the 
 excess is removed by squeezing through chamois leather, a 
 semi-solid amalgam is generally obtained. The remainder of 
 the mercury is expelled on heating, and the other metal remains. 
 
 Gold, silver, zinc, tin, lead, antimony, bismuth, copper, 
 and the alkali metals may be amalgamated by addition to 
 mercury. Copper is best amalgamated by decomposing a 
 salt of mercury by metallic copper, as the surface is not 
 readily attacked by the metal. Mercurous nitrate is generally 
 employed. Iron is not attacked directly, but iron amalgam 
 may be obtained by the electrolysis of ferrous chloride with 
 a negative pole of mercury. 
 
 The presence of these amalgams renders mercury less mobile, 
 and when base metals are present, the oxidation which takes 
 place, owing to the fine state of division of the metal in solution, 
 causes the mercury to leave a "tail" behind it, if run down a 
 slightly inclined porcelain tile. When pure it leaves no tail. 
 
Mercury. 201 
 
 The amalgam with tin is used for silvering looking-glasses ; 
 amalgams with copper, tin and cadmium, silver and gold are 
 used as tooth stoppings. The density of the copper amalgam 
 is the same solid as plastic, to which state it may be reduced 
 by slightly warming and working in a mortar. It is used for 
 sealing bottles. 
 
 Metals are not readily attacked by mercury unless the surface is clean. 
 Hence the presence of free acid aids amalgamation by removing films of 
 oxide, etc. Sodium amalgam is often added to mercury in the amalgama- 
 tion of gold and silver ores to prevent the mercury becoming " dead " and 
 inactive by the oxidation of other metals, such as copper, etc., which may 
 be taken up by it. Such mercury is apt to get into a finely divided state, 
 the oxide films preventing the globules from coalescing, and it " sickens " 
 or becomes "floured," in which case both the mercury and the precious 
 metal it contains will probably pass into the residues or "tailings " and be 
 lost. The sodium, by liberating hydrogen from the water present at the 
 surface of the globules, prevents oxidation. 
 
 The silvering of mirrors is accomplished by squeezing mercury from 
 a chamois leather bag over a sheet of tinfoil lying on a polished slab, 
 forming a thin film of the amalgam. The carefully cleaned glass is then 
 pushed gradually on, taking care to prevent air bubbles getting between, 
 covered with felt and weighted. By inclining the slab and increasing the 
 inclination from time to time, the excess of mercury is drained away and 
 the amalgam adheres to the glass. The resulting film contains about 20 
 per cent, of mercury and 80 per cent, of tin. 
 
 ORES OF MERCURY. 
 
 "Native" Mercury occurs in globules in cinnabar, and 
 amalgams of gold and silver are also found. 
 
 Cinnabar. Mercuric sulphide (HgS) is the principal ore. 
 It is a heavy mineral, of a vivid red colour ; but some varieties 
 are purplish. Its specific gravity is about 8. Large deposits 
 occur at Almaden in Spain, Idria in Carniola, Bavaria, Cali- 
 fornia, Chili, Peru, China, and elsewhere. Like hematite, it 
 gives a red streak, but is volatilized by heat. The Idrian 
 deposits have been worked about 400 years. Cinnabar when 
 pure contains 85 per cent, of mercury, but the ores frequently 
 contain less than 2 per cent, and are often bituminous in 
 character. Mercury is often a constituent of fahl ore (p. 210). 
 
 Smelting, or Extraction. The principles involved in the 
 separation of mercury from cinnabar are very simple. When 
 heated in a current of air, the sulphur is burnt off as SO 2 , and 
 the metal volatilized. 
 
202 
 
 Metallurgy. 
 
 It therefore only remains to efficiently condense the vapour. 
 This, owing to the readiness with which the metal gives off 
 vapour, is a matter of much difficulty. 
 
 Cinnabar is decomposed when heated with lime, sulphide 
 and sulphate of lime being produced thus : 
 
 4HgS + 4CaO = 
 
 CaS0 4 
 
 Iron reduces it to mercury ; sulphide of iron resulting. 
 
 Idrian Furnace. Fig. 67 shows the furnace employed at 
 Idria. The cinnabar is placed on arches ,/, r t in the central- 
 chamber, over the fireplace. The larger lumps are placed in 
 the lowest arch. The upper arch is occupied by small ore or 
 
 FIG. 67. 
 
 dust, on trays, as shown, or moulded into blocks with a little 
 clay. The products of the combustion and the SO 2 and mercury 
 vapour are led to the condensing chambers C, of which there 
 are six on each side, by the passages s'. Each chamber com- 
 municates with the next alternately at top and bottom. The 
 greater part of the metal is condensed in the first 2 or 3 
 chambers. The remainder is deposited as soot or dust in 
 the succeeding chambers. The floors of these chambers 
 incline towards an outlet at the stde, by which the condensed 
 mercury drains away, and is carried by a channel to the locked 
 tank in which it collects. In the last chamber the con- 
 densation is assisted by water spray or by canvas screens 
 stretched across it, covered with wet sawdust. The furnace 
 and condensers are about 180 feet long and 30 feet high. The 
 
Mercury. 
 
 203 
 
 charge for the double furnace is nearly 100 tons. The 
 operation takes about a week to complete, of which five 
 days are occupied in cooling, and only about 12 hours 
 in distillation. About 4 tons of mercury are obtained from 
 each charge. 
 
 In Hahner's modification of the Idrian furnace, the ore, 
 mixed with charcoal, is fed into the central shaft from a. hopper 
 above, and the furnace works continuously. The condensing 
 chambers are prevented from becoming overheated by cover- 
 ing them with iron plates and cooling by a spray of cold water. 
 The spent ore is removed at intervals through the grate 
 at the bottom of the shaft. 
 
 Aludel Furnace. Fig. 68 shows the Aludel furnace in use 
 at Alnladen in Spain. The ore is placed in the chamber F, 
 
 FIG. 68. B, fireplace ; c, perforated arch ; F, ore chamber; D F, charging openings; 
 G, chimney for fire ; L, openings to aludels ; H, aludels ; K, mercury gutter ; 
 i, condensing chamber. 
 
 resting on perforated arch C, over the fireplace B. A quantity 
 of spent ore or quartz is placed in the bottom, then poor ores 
 followed by richer ones. The powdered ores are made into 
 balls and placed on the top. A wood fire is first made in B, and 
 the whole thoroughly heated. The fires are then withdrawn 
 and air admitted. In passing through the grate, spent ore, etc., 
 at the bottom, it becomes heated, and calcines and reduces the 
 cinnabar. The vapour and gases pass out by the passages L, 
 and through rows of "aludels" resting on sloping masonry 
 roofs or benches. The aludels are earthenware, pear-shaped 
 
204 
 
 Metallurgy. 
 
 FIG. 69. 
 
 condensers (Fig. 69) 16 inches long; the neck is 4^ inches, the 
 wider end about 7 inches, and the middle 1 1 inches in diameter. 
 These are fitted together and luted with clay. The middle 
 ones have a hole on the under side which permits the con- 
 densed mercury to drain into 
 the trough K, by which it is 
 conveyed away. From the 
 aludels the vapours pass into the chamber I, from which they 
 escape by the small chimney. The operation lasts about 
 24 hours, and the cooling down 3 or 4 days. The con- 
 densation in both these 
 furnaces is imperfect. 
 
 Muffle, or Retort, 
 Furnaces are used for re- 
 ducing the pure "fines" 
 (small ore), and the fume 
 which collects in the con- 
 densers nearest the ore 
 chamber, which consists 
 mainly of sulphide and 
 sulphate. From 10 to 20 
 per cent, of quicklime is 
 added and the mixture 
 made into bricks. These 
 are heated and the vapour 
 condensed in iron tubes 
 dipping under water. 
 
 The Albert! Furnace 
 is a long-bedded, rever- 
 beratory furnace, the flues 
 of which consist of large 
 water-cooled iron pipes. 
 Poor ores are treated in 
 ' these furnaces, but the acid 
 
 FIG. 7 o.-Californ;an Furnace. yapOUrS attack the iron. 
 
 Channel Furnaces. The beds of these furnaces are steeply 
 inclined planes divided into channels down which the ores 
 rickle, being roasted by an ascending current of air and 
 
Mercury. 
 
 205 
 
 hot gases from a fire situated at the bottom of the incline. 
 The vapours are led into condensers. 
 
 Shaft Furnaces are employed in California. These fur- 
 naces work continuously. The ore chamber D (Fig. 70) is 
 cylindrical in form, standing on a hexagonal base. Three 
 fireplaces C, with ash-pits, etc., communicate with the chamber 
 on alternate sides of the hexagon. Below the fireplaces the 
 chamber contracts and the calcined ore is withdrawn through 
 openings at the side. The top of the chamber is closed by 
 a cup-and-cone arrangement, the cup being covered by a 
 gas-tight cover, which is always in position before the cone is 
 lowered to admit the charge, thus preventing escape of vapours. 
 The gases are led away by inclined iron pipes to condensers. 
 Peep-holes, for the inspection of the furnace, are also provided. 
 The chamber is 19 feet from base of cone to bell, and 6 feet 
 wide. It roasts about 10 tons per day. In starting, the shaft 
 is filled to the level of the fireplaces with spent ore, and then 
 to within 3 feet of the top with ore mixed with i to 2 per cent, 
 of coke or charcoal The fires in C are lighted, wood being 
 used as fuel, and the whole furnace heated 
 to full redness. Some spent ore is then 
 removed through E and fresh ore ad- 
 mitted from the top. Fresh additions are 
 made about every two hours. 
 
 Hiittner and Scott's furnace for the 
 continuous treatment of fines is shown in 
 Fig. 71. The fine ore is fed in from the 
 hopper at the top of the chamber, on to 
 a series of sloping shelves, and passes in 
 a zigzag fashion down the furnace, being 
 turned over and over in its descent. The 
 chamber is 27 feet high, 25-5- inches wide, 
 and 1 1 feet 6 inches long. At one end is 
 a fireplace supplied with hot-air heated 
 by iron pipes placed in the condensing 
 chambers. The hot gases, mixed with hot 
 air, are admitted to the .ore chamber by a series of openings 
 at one end, under each shelf, and pass av,ay to the. condensers 
 
206 
 
 Metallurgy. 
 
 by corresponding openings at the opposite end of the furnace. 
 The furnace treats about i-| tons per hour, and the spent ore 
 is removed at intervals. 
 
 A continuous retort furnace erected by the " El Pouvenir " 
 Company in Spain, is shown in Fig. 72. 1 The retorts A are 
 of cast iron, and are supported above a fireplace B. The 
 mouth inclines upwards and communicates with the condensing 
 apparatus C, by a flue as shown. A hydraulic exhaust injector 
 
 FIG. 72. 
 
 D draws the vapours through the condenser and permits of 
 the lower end of the retort being opened to remove a portion 
 of the charge without escape of vapour. The ore is fed in at 
 the top, about ~ cwt. every hour and a half, giving an average 
 of f ton per retort per day. Rich ores are mixed with lime. 
 Two large condensing chambers are provided. From the 
 second they pass into a smaller chamber containing water, 
 and then to the exhaust. 
 
 In shaft furnaces at the same works the hydraulic exhaust 
 is also employed. The fireplace is placed below a per- 
 forated arch, as at Almaden, but the top is provided with 
 charging apparatus, and the ore is discharged after calcination 
 through openings at the side. 
 
 The condensation of mercury offers a difficult problem. In calcining 
 furnaces of all types, the large volume of gases to be cooled (products of 
 
 "Journal Soc. Chem., Ind," : 1890, p. 93. 
 
Silver. 207 
 
 combustion of fuel, nitrogen of the air, sulphur dioxide, and mercury 
 vapour), and the % ease with which mercury gives off vapour, render its 
 perfect recovery difficult. The gases often contain less than I per cent, 
 by volume of mercury vapour. Except in the condensers nearest the ore 
 chambers, iron cannot be used on account of the acid liquors (H 2 SO S and 
 H 2 SO 4 ), which condense when sufficiently cool. Other metals cannot be 
 used as they are attacked by mercury. 
 
 It is therefore necessary to employ large condensers, as at Idria, to slow 
 down the current to completely cool them, and to admit the vapour as 
 near the boiling-point as possible. With furnaces working continuously, 
 auxiliary cooling appliances, such as earthenware or iron pipes, with or 
 without water cooling, are necessary. Glass chambers in wooden frames 
 have been largely adopted for gases comparatively cool, communicating 
 alternately at the top and bottom. Mercurial vapours are highly poisonous, 
 producing salivation. 
 
 Purification of Mercury. Commercial mercury often con- 
 tains lead, zinc, bismuth, and other impurities. The presence 
 of these may be detected by allowing it to run down a white 
 tile. If impurities are present, the metal leaves a tail. 
 Mercury is purified by squeezing through chamois leather and 
 subsequent re-distillation. It may also be purified by exposing 
 it in a thin layer to the action of dilute nitric acid, mercurous 
 nitrate, or ferric chloride solution. The impurities are dis- 
 solved together with some mercury. It comes into the market 
 in screw-necked iron bottles, containing ^ to f cwt. each. 
 
 CHAPTER XV. 
 SILVER. 
 
 Physical Properties. This metal is characterized by its white- 
 ness and brilliant lustre. It is somewhat softer than copper, 
 but harder than gold. It is exceedingly malleable, being 
 in this respect only inferior to gold, with which it may be 
 alloyed without seriously impairing the malleability of that 
 metal. It is highly ductile, and has a tensile strength of 14 
 tons per square inch. Its specific gravity is 10-5. It is the 
 best conductor of heat and electricity. At about 950 C. it 
 melts, and at high temperatures is sensibly volatile. In the 
 electric furnace it boils and distils. 
 
 Chemical Properties. The metal is unoxidized when 
 
208 Metallurgy. 
 
 heated in air or oxygen, but molten silver dissolves about 22 
 times its volume of oxygen, which is given out on solidifying, 
 the metal often being projected from the surface in curious 
 growths. This phenomenon is known as " spitting," and does 
 not occur if the metal is impure. The metal contracts on 
 cooling. Silver oxide otherwise produced is decomposed by 
 heat into silver and oxygen. 
 
 Silver combines readily with sulphur, forming silver sul- 
 phide (Ag 2 S), a soft, dark-grey, fusible body. The blackening 
 of silver when exposed, is due to the formation of this body by 
 sulphur compounds in the atmosphere. This compound is 
 also precipitated by adding sodium sulphide to a soluble salt 
 of silver. 
 
 Sulphide of silver roasted in air is partly decomposed, 
 sulphur dioxide and silver resulting, and is partially converted 
 into sulphate. This conversion into sulphate takes place to a 
 greater extent in the presence of sulphides and sulphates of 
 other metals. Silver sulphate is soluble in wafer containing 
 free sulphuric acid, and is decomposed by heat, metallic silver 
 resulting. Silver sulphide is converted into chloride by the 
 action of ferric, cuprous, and cupric chlorides. 
 
 Silver combines directly with chlorine, forming silver 
 chloride, which is not decomposed by heat. This compound 
 is also produced when hydrochloric acid, or a soluble chloride 
 is added to a silver solution, and by roasting the sulphide with 
 salt in the presence of moist air. It is insoluble in acids, 1 but 
 dissolves in strong brine (sodium chloride) and other chlorides 
 (especially ferric and cupric chlorides), in sodium thiosulphate 
 (forming AgjSaOa.Na&O*, if the sodium salt is in excess), in 
 potassium cyanide (forming AgCN.KCN), and in ammonia. 
 It fuses at a red heat, and is volatile at high temperatures. 
 
 Chloride of silver is reduced by " nascent " hydrogen, 
 mercury, and by fusion with carbonate of soda. 
 
 AgCl -f H = Ag + HC1 
 2AgCl 4- Na. 2 CO 3 = 2NaCl + COX + O -f Ag 2 
 
 1 AgCl is somewhat soluble in hydrochloric acid. The strong acid 
 dissolves I in 200 parts, and when diluted with an equal bulk of water, 
 i part in 600. 
 
Silver. 
 
 209 
 
 Silver is deposited from solution in the metallic state by 
 zinc, copper, iron, and other metals, and cuprous oxide. 
 
 Sulphuric acid dissolves it when heated, forming sulphate. 
 
 Ag a + 2H 2 SO 4 - Ag 2 S0 4 + 2H 2 + S0 2 
 Nitric dissolves it readily, silver nitrate being formed. 
 6Ag + 8HNO 3 - 6AgNO a + 2ND + 4H 2 O 
 
 Hydrochloric acid has no action upon it. 
 
 Silver nitrate (AgNO 3 ) is a white solid, soluble in water. 
 It crystallizes in flat tabular crystals. It is fusible without 
 decomposition, but at a higher temperature, much below red- 
 ness, it gives off oxygen and forms AgNO 2 . At a red heat it 
 is decomposed, yielding metallic silver. 
 
 This is made use of in the separation of silver and copper nitrates. 
 The latter decomposes at a much lower temperature than the silver 
 nitrate, and by careful heating may be resolved into oxide, leaving the 
 silver nitrate unaltered. When a sample, treated with water, gives no 
 blue colour on the addition of ammonia, the mass is boiled with water, 
 to dissolve the silver nitrate, and filtered from the insoluble copper oxide. 
 Boiling the mixed nitrates with silver oxide also throws down the copper 
 as oxide. 
 
 Large quantities of nitrate of silver are produced in parting 
 silver and gold. 
 
 Alloys. Silver is too soft for use in the pure state, and is 
 hardened by alloying it with copper. English sterling silver 
 "standard silver" consists of an alloy of 925 parts of silver 
 per 1000 alloyed with 75 of copper. This is equivalent to 
 ii ozs. 2 dwts. of silver per Ib. troy. Alloys which contain 
 more silver per Ib. are described as " better," and those con- 
 taining less as " worse" than standard. The Indian rupee, 
 ii ozs. 8 dwts. per Ib., is 6 dwts. better, and the French 
 standard alloy contains 10 ozs. 16 dwts. only, and is described 
 as 6 dwts. worse. 
 
 The degree of purity is now often expressed in parts of 
 silver per 1000 ; thus " 900 fine " implies that the alloy contains 
 900 parts of fine silver and 100 of alloy per 1000. 
 
 Frosted Silver. Silver is frosted by heating silver alloyed with copper 
 in air. The copper oxidizes, and the oxide is dissolved off with sulphuric 
 
210 Metallurgy. 
 
 acid or ammonia, or by boiling with cream of tartar and salt. This leaves 
 a " dead " surface consisting of finely divided silver. 
 
 Oxidized Silver. This effect is produced by treating the silver with 
 a soluble sulphide, such as sulphide of potash, and is due to the films of 
 silver sulphide formed. 
 
 ORES OF SILVER. 
 
 " Native " silver occurs associated with ores of the metal 
 with gold, in electrum ; with mercury, in amalgam. 
 
 Silver Sulphide (Ag 2 S) Argentite occurs as a soft, malle- 
 able, grayish-black substance, which is readily fusible. It con- 
 tains 87 per cent, of silver. Deposits containing it in a state oi 
 purity occur in Norway, Hungary, Saxony, Bohemia, Mexico, 
 and the United States. It is the principal ore of silver. 
 
 Horn Silver Silver Chloride (AgCl) is found in South 
 America. The bromide and iodide also occur. 
 
 Pyrargyrite. Dark-red silver ore is a sulphantimonide of 
 silver (3Ag 2 S.Sb 2 S 3 ) found in Mexico, South America, Transyl- 
 vania, and elsewhere. Proustite light-red silver ore is a 
 sulpharsenide (3Ag 2 S.As 2 S 3 ). Stephanite is another mineral 
 of the same class. 
 
 Polybasite and Argentiferous Fahl Ore are compounds of 
 copper, silver, arsenic, and antimony sulphides. The latter 
 often contains other metals also. 
 
 Silver occurs in the ores of many other metals, probably as 
 sulphide. Lead, zinc, and copper ores often contain it, and 
 small quantities occur in iron pyrites and mispickel (arsenical 
 iron pyrites). The production of silver from these sources is 
 nearly one-half of the total extracted. 
 
 Extraction Processes. The high price of silver permits 
 of poor ores being treated and the adoption of more costly 
 methods. Hence chemical methods, preceded by careful 
 mechanical preparation, are often followed. 
 
 The treatment of silver ores proper may be divided into 
 Amalgamation processes. 
 Wet processes. 
 
 Smelting with lead, or lead ores. 
 Smelting with copper ores. 
 
 Amalgamation Processes include those in which the silver 
 
Silver. 211 
 
 is obtained as an amalgam with mercury, from which it is 
 recovered by distillation and volatilizing the mercury. They 
 may be divided into "floor," " barrel," and " pan" amalgama- 
 tion processes. If not present as free silver or as chloride, 
 the first step of the process is to convert the metal into chloride. 
 Floor Amalgamation. In the "patio" process, still 
 followed in Mexico and South America, the ores are hand- 
 picked, and then contain some 80 ozs. of silver per ton, as 
 native silver, chloride, and sulphide. Base ores containing 
 large amounts of foreign sulphides are unsuitable for treatment 
 by this process. The ore is first reduced to a fine state of 
 division by stamping or grinding. 
 
 The quimbalete consists of a large boulder lashed to the middle of a 
 long pole, rocking on a flat stone, worked by men sitting astride the ends 
 of the pole, and working see-saw fashion, the ores being thrown under the 
 boulder. 
 
 The trapiche is a large stone wheel, 6 feet in diameter and 5 feet across ; 
 the axle on which it revolves is attached to a perpendicular shaft driven by 
 a horizontal water-wheel on the top. The wheel travels round a stone 
 track, and the ores are gradually crushed. 
 
 The arastra, for fine grinding, is a circular trough paved with hard 
 stone. In the centre is an upright post to which projecting arms are 
 attached. Heavy stones are lashed to these, by thongs of raw hide, and 
 they are dragged round by mules attached to the ends of the arms, which 
 project over the edge of the trough. Water is added, and, if much free 
 silver or gold is present, a little mercury, to amalgamate them. The ore 
 is thus reduced to mud. 
 
 The Chilian mill for grinding ores is in principle like an ordinary 
 mortar-mill. 
 
 The operations are conducted as follows : (i) The mud 
 is taken to the amalgamating floor, or patio a paved court 
 and spread out in a layer 6 inches to a foot thick. Some 
 3 to 5 per cent, of salt is added and well trodden in by mules 
 for several hours, after which the heap is allowed to rest. 
 
 (2) Next morning a quantity of roasted copper pyrites 
 magistral 1 is scattered over the heap, and some mercury. 
 This, after mixing with shovels, is well trampled in ; the 
 turning over and trampling are repeated every other day for 
 some days. 
 
 (3) Mercury to the extent of some 5 or 6 times the weight 
 of silver present is sprinkled over the heap from canvas bags, 
 
 1 This contains both copper and iron sulphates, and plays a material 
 pail in the reactions which occur. 
 
212 Metallurgy. 
 
 and trampled in. If much antimony and arsenic, or other 
 foreign sulphides are present, a hot solution of copper sulphate 
 is added, together with copper precipitate (finely divided 
 copper) (see p. 176), and thoroughly incorporated. 
 
 (4) After a further rest with repeated tramplings, a final 
 addition of mercury is made to collect the amalgam, and after 
 mixing, the stuff is conveyed to tanks, where it is stirred up 
 with water, and the heavy amalgam settles out. The earthy 
 matters are carried away by the water current. 
 
 The amalgam is treated in the ordinary manner (see p. 219). 
 
 In this process a complicated series of reactions occur. 
 Copper chloride is formed by the reaction of the salt and 
 copper sulphate. 
 
 CuSO 4 + 2NaCl = CuCl 2 + Na,SO 4 
 This attacks the metallic silver, thus : 
 
 2 CuCl 2 + Ag 2 = 2AgCl -f- Cu 2 CI 2 
 
 This cuprous chloride, which is soluble in the excess of salt 
 employed, reacts on the sulphide of silver and converts it 
 into chloride. 
 
 Ag 2 S + Cu 2 Cl 2 = 2AgCl + Cu 2 S 
 Some free sulphur is also separated, probably thus : 
 Ag 2 S + 2CuCl 2 = Cu 2 Cl 2 4- 2AgCl +S 
 
 The above reactions in some degree represent the chlori- 
 nation, but the changes are very obscure. The silver chloride 
 is decomposed by mercury, thus : 
 
 2AgCl 4- Hg 2 - Hg 2 CL + A g2 
 
 the metal being dissolved by the excess of mercury. The 
 operation occupies from 2 to 7 weeks. 
 
 NOTE. The addition of copper precipitate is to ensure the reduction of 
 the cupric salt to the cuprous state, or it will attack the mercury, forming 
 calomel, and will thus increase the consumpt of mercury. 
 
 2CuCl 2 + Hg = Hg 2 Cl 2 + Cu 2 Cl 2 
 
 2CuCl 2 + Cu = 2Cu 2 Cl 2 
 
 Formerly lime was added, to precipitate the copper, if in excess ; but 
 this hinders the chlorination by forming an inactive chloride. 
 
 Barrel Amalgamation was formerly practised at Freiberg^ 
 
Silver. 2 1 3 
 
 The chlorination of the metal is effected by roasting the ore 
 with salt as described (pp. 175 and 221). The roasted ore is 
 next put into barrels, supported horizontally, capable of hold- 
 mg about a ton, and water added to make it into a stiff paste 
 (pulp), some i-j to if cwt. of sheet-iron scrap added, and 
 the barrels revolved on trunnions for several hours. The 
 chloride is reduced by the iron, thus : 
 
 2 AgCl -f Fe = FeCl 2 + Ag 2 
 
 Mercury is then added to amalgamate the reduced silver, and 
 the barrels again revolved some 16 hours. The contents 
 of the barrels are then thinned by the addition of water, the 
 amalgam collected together by slow revolution, and run off 
 by a plug in the side. A little fresh mercury is added to 
 collect any residual metal, a"nd the barrels again revolved. 
 This is run off as before. The residues are run into settlers 
 and agitators tanks with a current of water flowing through 
 by which the light matters are carried off and the amalgam 
 (if any) sinks. 
 
 In the Krolinke, or Aaron process, in use at Benton, the 
 roasting with salt is dispensed with. The chlorination of the 
 silver is effected by an addition of cuprous chloride and salt. 
 The cuprous chloride is prepared by boiling copper sulphate 
 with salt and copper, or in other ways. The barrels may be 
 arranged vertically or horizontally, and steam is blown in to 
 heat the contents. Metallic copper is employed to reduce 
 the silver, and the amalgamation with mercury takes place as 
 before. The loss of mercury is greatly reduced, calomel not 
 being formed. Aaron states that it can be brought as low as 
 2 Ibs. per ton. 1 Iron borings are sometimes used for the 
 reduction. Base ores can be treated by this process, a yield 
 of 80 to 95 per cent, being obtained. 
 
 In both these processes there is considerable loss of 
 mercury by "flouring" that is, the mercury is broken up into 
 fine particles, which will not coalesce to form a globule, 
 and are carried off and lost. The addition of a little sodium 
 amalgam is made to prevent this. 
 
 1 Iron, Nos. 93 and 94. 
 
214 
 
 Metallurgy. 
 
 Kettle Amalgamation (Cazo Process). The ores treated 
 by this process are mainly chlorides, bromides, and iodides. The 
 ore is ground to a pulp in the mill, or arastra, and transferred 
 to kettles with bottoms made of copper. From 5 to 10 per 
 cent, of salt is added, and the mass heated with continual 
 stirring. Mercury is added, and the heat is continued for 
 some hours, till amalgamation is complete. The mass is then 
 thinned with water, and the amalgam collected as before. 
 The chloride, etc., is decomposed by the copper, 
 2AgCl + Cu 3 = Ag 2 + Cu 2 Cl 2 
 
 yielding silver and cuprous chloride. This, in the presence 
 of salt, reacts to some extent on the sulphides, after the 
 
 FIG. 73. Amalgamatory Pan. 
 
 manner of the "patio" process, but sulphide ores generally 
 retain enough silver to be subsequently treated on the " floor." 
 Pan Amalgamation. The foregoing methods have gene- 
 rally given way to treatment in pans, a great saving in time 
 being effected. 
 
Silver 
 
 215 
 
 The pans employed in these processes vary somewhat in 
 construction. One form is shown in Fig. 73. It consists of 
 
216 
 
 Metallurgy. 
 
 a cast-iron pan some 5 feet in diameter, with a steam-jacketed 
 bottom. Up the centre a hollow pillar rises, through which 
 a shaft passes. To this the cast-iron muller is attached in a 
 manner which permits of its being raised or lowered to any 
 desired height by means of the hand-wheels on top. The 
 crushed ore is ground between the flat faces of the muller and 
 the bottom of the pan, motion being communicated by the 
 bevel-wheel gearing under the bench on which the pan rests. 
 Steam is admitted to keep the contents hot. A plug is pro- 
 vided for running off the pulp after amalgamation. 
 
 Instead of iron sides, wooden staves hooped with iron are employed, 
 and copper bottoms and linings are sometimes employed. 
 
 Two methods of treating the ores are followed. In one, 
 they are treated direct, and in the other they undergo a 
 previous roasting with salt to chlorinate the silver. 
 
 In the direct process the ore is broken in a "stone- 
 breaker," or "ore crusher" of the Blake type, A (Fig. 74), 
 passes to a stamp battery, B, and is crushed " wet " that is, 
 with a supply of water (see Gold, p. 234), a 30-mesh screen being 
 employed. From the battery the crushed ore passes over the 
 
 amalgamated copper plates C 
 to catch any free gold present, 
 and then to the tanks D in 
 which the mud settles. 
 
 The mud (pulp) is charged 
 into the pans E, water added 
 to a pasty consistency, and the 
 muller lowered and revolved 
 at the rate of 80 to 100 revo- 
 lutions per minute. Salt and 
 copper sulphate are also 
 added, and the temperature is 
 maintained at about 90 C. 
 This grinding is continued 
 . 75. Settler. some 3 or 4 hours. The pulp 
 
 will then pass through an 80- 
 
 mesh sieve. About 10 or 15 per cent, of mercury is then added, 
 and the muller, somewhat raised, is again revolved for 2 or 3 
 
Silver. 217 
 
 hours, to thoroughly incorporate the mercury. The pulp is 
 then thinned by the addition of water, and run off by t? e plug 
 into the settler F, which resembles the amalgamator, save 
 that the muller is replaced by a stirrer (Fig. 75), which makes 
 some 10 revolutions per minute. Here the amalgam settles 
 out. The mud is drawn off by opening the holes in suc- 
 cession, into another settler the agitator and then passed on 
 to " frue vanners," or is treated on buddies, for the separation 
 of the pyrites, etc. (concentrates), which often carry gold, 
 while the light stuff is washed away. 
 
 /;/ amalgamation processes preceded by roasting, the ores are 
 crushed "dry." 
 
 In "dry" crushing, the ore, after being broken, is dried, a 
 rotary furnace being employed. The dried ore is stamped, 
 and the crushed ore falling through the screens is conveyed 
 away by means of Archimedian screws, travelling belts, or 
 elevators. Fig. 76 shows a "dry "-crushing mill. The powdered 
 ore is next mixed with about 20 per cent, of salt, and roasted. 
 Generally revolving furnaces of the Bruckner type (Fig. 16) 
 are employed. Stevelet calciners (Fig. 18), and long-bedded 
 reverberatory furnaces are also employed. This roasting 
 occupies about 8 hours. The ore is then transferred to the 
 amalgamators and treated as before. The yield by this 
 treatment is much greater than in wet crushing, but the items 
 of labour and fuel consumption are increased, while the output 
 of a plant is seriously diminished. 
 
 The loss of mercury is about 2 pounds per ton of ore treated. It is 
 customary to add a little sodium or zinc amalgam, to keep the mercury 
 f rom flouring, the hydrogen evolved keeping the mercury bright and lively, 
 and preventing the formation of a film on the small globules, which pre- 
 vents them from coalescing. Potassium cyanide, in small quantities, is 
 often used for the same purpose. In wet 'ci-ushing, mercury is also 
 introduced into the mortar-box to retain gold. 
 
 In the roasting of dry-crushed ores with salt, there is a liability to form 
 gold chloride, which is soluble, and will be lost if not completely decom- 
 posed in the pans. 
 
 In " wet " crushing, the sulphide of silverin the ore seems to be partially 
 decomposed by the iron of the pan during amalgamation, with the forma- 
 tion of sulphide of iron, assisted by the cuprous chloride, produced when 
 salt and copper sulphate are added. 
 
 The best grinding is secured with a thin pulp, and the best amalgama- 
 tion with thick pulp, which prevents the mercury from settling out. It is 
 
218 
 
 Metallurgy. 
 
 usual to add residues to thicken the pulp prior to adding mercury. It is 
 soft enough if the muller will turn in it. 
 
 Treatment of Amalgam. The amalgam from the settlers 
 
Silver. 
 
 219 
 
 and agitator is often transferred to a smaller " clean-up" pan, 
 and stirred with water to free it from heavy particles. 
 
 It is then strained through canvas bags, or squeezed 
 through washleather, or by hydraulic pressure, in cylinders, the 
 ends of which are made of wood cut 
 across the grain. The excess of mercury 
 which is thus removed is used again. 
 It contains silver, but this is recovered in 
 the subsequent working. The pasty 
 amalgam which remains is then " retorted " 
 to expel the mercury. One form of retort 
 is shown in Fig. 78. The amalgam is 
 put into the crucible, which is of iron, 
 the head adapted, and the mercury as it 
 
 ' ' J FIG. 77. Amalgam Safe, 
 
 distils off is condensed by the water- with strainer. 
 cooled tube. The crucible is coated with Ijmewash. 
 
 The porous mass obtained is subsequently melted down in 
 crucibles, and cast into bars weighing about 1000 ozs. The 
 
 FIG. 78. Retort. 
 
 crude bullion contains bismuth, antimony, copper, zinc, 
 arsenic, etc. It is subsequently refined. This is partially 
 effected by exposing the surface to the air while molten, and 
 
220 Metallurgy. 
 
 permitting the impurities to. oxidize, the scum of oxides being 
 scraped off. It is afterwards refined by cupellation. 
 
 Wet Processes. Wet methods of silver extractioh depend 
 on the solubility of sulphate and chloride of silver in water or 
 other solvent (see p. 208). They are largely employed in the 
 treatment of copper mattes and bottoms, and certain classes 
 of ore containing large quantities of foreign sulphides. 
 
 Ziervogel Process. In this process the silver is converted 
 into sulphate, by roasting. This is dissolved out by water, 
 and the silver precipitated from solution by copper. 
 
 Sulphating roasting. This depends on the fact already 
 mentioned that if a mixture of iron, copper, silver, zinc, and 
 lead sulphides be roasted, they are partly converted into oxides 
 and. partly into sulphates (see p. 173). 
 
 NOTE. The production of sulphates is largely clue to the formation of 
 SO 3 by the SO 2 from the roasting mass, combining with oxygen under the 
 influence of the "contact action" of the brickwork and siliceous matters 
 in the ore a sort of catalysis. This combines with the oxides. A slow 
 current of air favours its production. 
 
 If carefully heated, the sulphates decompose in the order 
 named. The SO 3 , liberated in the decomposition of the iron 
 and copper sulphates, attacks the silver, and tends to its complete 
 conversion into sulphate. 
 
 Roasting Copper Mattes. They are first roasted to remove 
 the greater part of the sulphur, and then ground very fine and 
 carefully roasted at a low and gradually increasing temperature 
 in a double- or triple-bedded reverberatory calcining furnace. 
 The matte is first introduced on the bed farthest from the 
 fire, and is moved forward towards the fireplace. When the 
 iron and copper sulphates formed during the roasting are 
 nearly decomposed determined by boiling a sample with 
 water and observing the colour the material is raked out. 
 
 Argentiferous copper ores are generally run down for matte, 
 which is thus treated. 
 
 The roasted material is then treated with water containing 
 a little free sulphuric acid leached in wooden tanks capable 
 of holding about 1000 gallons. From these the liquor is run 
 into settling tanks, at a lower level, and thence into tanks 
 
Silver. 221 
 
 containing copper, where the silver is precipitated. Two sets 
 of precipitating tanks are usually employed, the first contain- 
 ing heavy copper scrap or bars, and the latter precipitate and 
 bean shot- copper. 
 
 Ag 2 SO 4 4- Cu = CuSO 4 4- Ag s 
 
 The copper is recovered by throwing it down with iron in 
 similar tanks. 
 
 The residues contain the gold, a portion of the silver (owing to imper- 
 fect sulphating), copper, and iron as oxides, lead as sulphate. If bismuth 
 and antimony are present in the matte, more silver is retained, owing to 
 the formation of insoluble compounds. 
 
 The residues are smelted for copper by the "best select" 
 process. The bottoms obtained are treated by electrolysis, or 
 in a manner subsequently described. 
 
 Augustin's Process. This consists of roasting the material 
 mixed with salt for the purpose of converting the silver into 
 chloride, which is then dissolved out by brine and precipitated 
 by copper. 
 
 Chlorinating roasting. The silver is converted 
 
 (1) Into chloride either by the action of free chlorine, 
 generated thus 
 
 (a) 2NaCl 4-O + SiO 2 = Na 2 SiO 3 + CI a 
 
 (b) 2HC1 + O = H 2 4- C1 2 
 
 (2) Or by the action of hydrochloric acid gas, produced 
 thus 
 
 2 NaCl 4- H 2 O 4- SiO 2 = Na 2 O.Si(X 4- 2HCI 
 2FeS0 4 4- 4NaCl 4- 2H 2 O + O = Fe 2 O 3 4- 2Na 2 SO 4 4- 4HC1 
 
 the moisture being present in the atmosphere of the furnace ; 
 
 (3) By the action of chlorides of copper and iron produced 
 by the reaction of sulphates on the salt added. 
 
 The leaching and precipitation are carried out as before. 
 
 In the treatment of copper bottoms, the two processes are often com- 
 bined (at Freiberg, and some works in this country). The bottoms are 
 granulated in water, and roasted to oxide, CuO, mixed with sulphur or 
 sulphate of iron, and Ziervogelized. 
 
 The residues contain the gold and much silver, and are Augustinized. 
 The gold passes into solution as chloride, and is, of course, precipitated by 
 the copper. Great care is required in roasting, or the gold chloride will 
 be decomposed by overheating, the metal remaining in the residue. 
 
222 Metallurgy. 
 
 Claudet's Process is in extensive use for the recovery of 
 silver from the cinders of iron pyrites used in vitriol manu- 
 facture, and is employed as an adjunct to the extraction of 
 copper by Longmaid's process (p. 175). In the chlorinating 
 roasting for copper, the silver is also chlorinated, and in the 
 lixiviation with water is dissolved out by the excess of salt 
 added in roasting. The first leachings, after cooling and 
 settling in tanks during which much lead sulphate and 
 chloride separates out are assayed for the amount of silver 
 they contain. A soluble iodide is then added in sufficient 
 quantity to precipitate it as insoluble silver iodide 
 
 2AgCl + ZnI 2 - 2AgI -f ZnC! 2 
 
 Care must be taken that the iodide is not in excess, or the fol- 
 lowing reaction will occur, cuprous iodide being precipitated 
 
 2 ZnI 2 + 2CuCL = 2 ZnCl 2 + Cu 2 I 2 + L 
 
 and iodine liberated. The iodide is well stirred in. and the 
 precipitate allowed to settle. 
 
 After the withdrawal of the liquor, the mud is moistened 
 with hydrochloric acid and treated with zinc, when the nascent 
 hydrogen reduces the silver iodide, and zinc iodide and metallic 
 silver result. 
 
 Zn -f 2HC1 = ZnCl 2 + H 2 
 
 H, -f 2AgI = Ag 2 + 2HI 
 
 ZnCl 2 + 2HI = 2 HC1 + ZnL 
 
 During the reduction the mass is kept warm by jets of steam. 
 
 The mud, or precipitate, after reduction, contains 6 to 
 12 per cent, of silver, a little gold, and a large percentage of 
 lead and oxide of zinc, with sulphuric acid, lime, etc. The 
 lead is reduced by the action of the zinc. 
 
 Von Patera's Process. The solution of the chloride pro- 
 duced in chlorinating roasting by thiosulphate of soda, "hypo- 
 sulphite," and precipitation of the silver as sulphide by sodium 
 or calcium sulphides, was first proposed by Von Patera. Of 
 late years, it has come prominently to the fore in a more or 
 less modified form, and is the most important " wet " process 
 for the treatment of silver ores. 
 
Silver. 223 
 
 In the American silver mills, where this process is pursued, 
 the dried and crushed ore is chlorinated by roasting with salt 
 
 After roasting especially in White-Howell calciners the 
 ore is left for some hours in heaps, the chlorination proceeding 
 after withdrawal from the furnace. It is then transferred to 
 lixiviating vats, and leached with hot water to remove all 
 soluble matters zinc, manganese, copper, lead, and other 
 chlorides till the effluent liquor gives no precipitate with 
 sodium sulphide. Some silver chloride is also dissolved. The 
 stronger liquors from the first leachings are run into tanks, 
 and the silver they contain is precipitated by the careful addition 
 of sodium sulphide. It is thrown down before the other metals 
 present are completely precipitated. This precipitate contains 
 about 4 to 6 per cent, of silver. 
 
 The ore is then leached with sodium thiosulphate solution, 
 of strength varying from \ to i per cent., according to the 
 richness in silver. The solution is run by gutters under or 
 alongside the tanks, into deep precipitation tanks holding about 
 1000 gallons (5 feet diameter and 8 feet deep), sodium 
 sulphide solution is added, and silver sulphide precipitated 
 thus 
 
 (Ag 2 S 2 3 ,Na 2 S 2 3 ) + Na 2 S = Ag 2 S + 2 Na 2 S 2 O 3 
 The regenerated thiosulphate solution is available for use again. 
 
 Treatment of Sulphide Precipitates. The sulphide pre- 
 cipitates are roasted in a furnace, and, if poor in silver, smelted 
 with lead, which decomposes the sulphide and takes up the 
 metal. 
 
 The lead is cupelled to extract the silver. If the sulphide 
 is pure, after roasting, it is melted in crucibles with carbon. 
 
 In roasting, and in treatment by lead, there is great liability to loss by 
 volatilization and dusting. The flue dust from these furnaces assays up 
 to 1 200 ounces of silver per ton. 
 
 Formerly the silver precipitate was run down in crucibles with scrap 
 iron, silver being liberated and iron sulphide formed. The regulus retained 
 silver, and was re-treated. Calcium thiosulphate and calcium sulphide 
 replace the soda salts in the "Kiss" process. 
 
 Treatment of Base Ores. Ores containing much lead and zinc sulphides, 
 antimony, arsenic, and bismuth, are unsuitable for treatment by the ordi- 
 nary " hypo " process, the chlorinating and leaching being rendered difficult 
 and incomplete in the presence of those bodies. Hence some of the 
 silver remains in the mass as sulphide, and is not removed by hypo. 
 
224 Metallurgy. 
 
 This difficulty is overcome in the Bussell process, by following the 
 ordinary thiosulphate leaching with a supplementary one by the double 
 thiosulphate of soda and copper, formed by running the thiosulphate 
 solution through a perforated box containing copper sulphate immersed 
 in the leaching vat just above the ore. This method is rendered necessary 
 by the decomposition of the double salt on exposure, and to prevent this 
 the tanks are closed in. The double salt has the composition 
 
 2Na 2 S 2 3 ,3Cu 2 S 2 3 
 and the reaction is 
 
 2Na 2 S 2 3 ,3Cu 2 S 2 3 + sAg 2 S = 2Na 2 S 2 O 3 ,3Ag 2 S 2 O 3 + 3 Cu 2 S 
 
 The action of the extra solution is not rapid, and circulating pumps are 
 employed to keep it in motion throughout the mass. Undecomposed 
 sulphide of silver is thus dissolved out, and the silver in the residues is 
 greatly reduced. The silver is precipitated by sodium sulphide as before. 
 
 The sulphide precipitates are, however, very impure, containing only 
 25 to 40 per cent, of silver. The excess of copper used in the extra 
 solution is precipitated with the silver. Greater expense is entailed in 
 refining in consequence. To obviate this, it has been proposed to treat 
 the precipitate obtained from the extra solution with sodium nitrate and 
 sulphuric acid, whereby the mixed sulphides are converted into soluble 
 sulphates. The nitric acid fumes evolved are condensed, and the sulphur 
 which separates used for making sodium sulphide. 
 
 The silver from the sulphate in the solution is then precipitated by 
 copper, and the copper subsequently by iron. 
 
 In dealing with ores containing much galena, the lead sulphate and 
 chloride formed in roasting dissolve in the hyposulphite. The lead is 
 removed by the addition of sodium carbonate before precipitating the silver. 
 
 In zinc ores treated by this process, the zinc sulphate formed is dis- 
 solved out in the preliminary leaching with water. 
 
 In these processes, any gold contained in the ore is 
 extracted to a large extent, and is precipitated with the silver 
 as sulphide. During the roasting it, too, is chlorinated, and 
 thus dissolved out. 
 
 Th.e wooden tanks employed in these lixiviation processes are either 
 round or square, well coated on the inside with tar. The capacity varies 
 from 5 to 60 tons of material. They are provided with a perforated false 
 bottom covered with canvas, on which a layer of filtering material, 
 about a foot thick, is laid. This material consists of gravel and silver 
 sand, in layers, or of sawdust, according to circumstances. Over the top 
 of the filter is another canvas covering. 
 
 The leaching liquor is frequently poured on the top of the ore, but 
 sometimes is introduced by a pipe below the false bottom, and allowed to 
 percolate upwards until the mass is soaked, after which it is poured on 
 top as usual. Below the false bottom is an opening in the side of the 
 tank, by which the liquors are run off and carried by gutters into the 
 settling and precipitation tanks. These, for convenience, should, if pos- 
 sible, be placed at a lower level. Steam-jet injectors are employed to- 
 elevate the liquors, if necessary. 
 
Silver. 
 
 225 
 
 Silver from Lead. Pattinson's process for the concentra- 
 tion of the small amount of silver occurring in lead has been 
 noted on p. 191, and the melting with lead of the roasted 
 sulphide precipitates obtained in the Von Patera, on p. 223. 
 Silver ores, if pure sulphides, are sometimes added to a bath of 
 Detail of F. 
 
 FIG. 79. Self- sluicing Lixiviation-tank. p, false bottom ; a, air pipe ; s, pipe for 
 removal of liquor ; /", trough leading to precipitating tanks ; m t plug for 
 removal of residues ; n, sluicing pipe for ejecting residues. 
 
 lead in a reverberatory furnace, much in the same manner as 
 the poor Von Patera precipitates. The silver compounds are 
 decomposed by the lead, and the silver passes into and alloys 
 with the excess. A highly argentiferous lead is also obtained 
 by the treatment of the zinc crusts removed in Parke's process 
 for desilverizing lead (p. 197). 
 
 Cupellation of Rich Lead. The lead is separated from the 
 silver and gold by exposing the surface of the molten metal at 
 a red heat to the action of a blast of air. The lead combines 
 with oxygen, forming litharge (PbO), which melts, and is 
 blown off the top, thus exposing fresh surfaces to the action ot 
 the air. Copper and other base metals present are also 
 oxidized, and the oxides dissolved in the melted lead oxide 
 and carried away by it. The silver and gold, which are 
 unoxidizable, are left behind. Some little is, however, carried 
 away in the oxide, particularly when the alloy becomes 
 very rich. Bismuth remains until the last. In the English 
 
 Q 
 
226 
 
 Metallurgy. 
 
 cupellation furnace, this oxidation is conducted on a bone-ash 
 cupel, and some of the litharge is absorbed by the porous 
 material. The bed of the German cupellation furnace is made 
 of marl brasque a mixture of marl, or clay and lime with 
 wood ashes. 
 
 The English cupel or test is made by ramming bone-ash, 
 moistened with a solution of pearl-ash, into an iron frame, with 
 mallets. The frame, A, is elliptical in shape, 4 to 5 feet long 
 and 2 feet 6 inches to 3 feet wide, made of 5-inch flat iron, 
 from \ to f inch thick. Five iron ribs, 3 to 4 inches wide 
 and \ an inch thick, cross the bottom (Fig. 80). The bone- 
 ash is rammed in in layers, and a cavity, E, scooped out with 
 
 a trowel, leaving the sides about 2 inches thick round the top 
 and 3 at the bottom, and the bottom itself about i^ inch 
 thick. At one end, some 5 inches of bone-ash are left, and 
 an opening, F, is made clean through the bottom, leaving a 
 2-inch dam, B. The litharge is thus prevented from coming 
 into contact with the ironwork and corroding it. The cupel 
 holds about 5 cwts. of lead. 
 
 This cupel forms the hearth of the cupellation furnace 
 (Fig. 81). G is the fireplace, C the hearth, and B the stack. 
 A tuyere, N, having a downward direction, enters at the back, 
 
Silver. 
 
 227 
 
 and over the door is a hood, H, to carry away the fumes of PbO. 
 P is a pot in which the lead is melted. Coal is used as fuel. 
 
 The cupel, carefully dried for some days, is placed on a 
 truck, run under the furnace, and lifted into its place, in which 
 it fits loosely. It is secured by wedges, crossbars, or by 
 projecting eyes, and the edge of the iron ring covered with 
 bone-ash. After carefully heating to redness, lead is intro- 
 duced from the lead- 
 pot, or in pigs, through 
 a channel at the back. 
 The blast is supplied 
 by a fan, or occasionally 
 by a steam jet. The 
 litharge which forms is 
 removed by making a 
 little gutter in the bridge 
 in front, through which 
 it flows into conical 
 iron moulds on wheels, 
 placed beneath to re- 
 ceive it. The tempera- 
 ture of the furnace is 
 cherry redness. As the 
 lead is removed by oxi- 
 dation, fresh additions 
 are made to keep up the 
 level in the cupel. 
 
 In working on Pat- 
 tinson lead containing from 500 to 700 ozs. to the ton, the 
 operation is conducted in two stages. In the initial stage 
 a lead containing 8 per cent. 4000 to 5000 ozs. per ton 
 is produced. The litharge produced in this stage is poor 
 enough in silver to be sent into the market. It is sold for 
 glass-making, etc. The enriched lead is then generally re- 
 moved, being run into pigs by boring a hole through the bottom 
 of the cupel. More poor lead is then treated in the same 
 cupel after stopping the hole. 
 
 The rich lead is then similarly treated on a new test, the 
 
 FIG. 81. 
 
228 Metallurgy. 
 
 litharge being saved separately. It is reduced as described, 
 (page 191), and yields lead containing some 40 ozs. of silver 
 per ton. As the cupellation approaches completion the surface 
 of the metal becomes iridescent (rainbow tinted) and strikingly 
 beautiful. As the last film of oxide clears off, the metal flashes 
 out brightly, presenting a clear, brilliant, bluish-white appear- 
 ance, the surface reflecting the roof of the furnace. This is 
 known as the " brightening " or " coruscation." The cooling 
 of the silver must be effected slowly to prevent loss by " spit- 
 ting." This, as already indicated, is prevented by a small 
 amount of impurity, and its occurrence is an index of the 
 purity of the metal. Many curious and fantastic forms result 
 by the throwing up of the surface, partly caused by the escape 
 of oxygen and partly by contraction of the mass expelling 
 the fluid interior. 
 
 In an ordinary furnace from 4 to 5 cwts. of lead are 
 oxidized per hour, some i-J- cwt. of coal being required. 
 
 The silver is generally about 995 to 998 fine. The cupels 
 are broken up and the parts saturated with litharge smelted 
 with fluor spar in a blast furnace to recover the lead. 
 
 Electrical Befining. In Keith's process, the rich lead is made the 
 anode (dissolving pole), and a sheet of pure lead the cathode. A solution 
 of lead sulphate in acetate of soda is employed as the electrolyte. The 
 depositing tanks are arranged in series, and a strong current is employed. 
 The anodes are enclosed in muslin bags, and, as they dissolve, the precious 
 metals and other insoluble matters are retained. The lead is deposited in 
 a crystalline or pulverulent form, and falls to the bottom of the tanks, from 
 which it is removed, compressed and melted. It carries about half a 
 pennyweight of silver to the ton. The residues in the bags are cupelled 
 with lead. 
 
 Refining. The refining of impure silver is effected either 
 by cupellation, or, if very impure, such as is sometimes obtained 
 by amalgamation methods, by melting it and exposing it to 
 the air in crucibles. Copper, iron, etc., may thus be largely 
 removed as dross. The purified metal is then refined on bone- 
 ash cupels. 
 
 Separation of Silver from Copper. Formerly a method of 
 separating silver from argentiferous copper by means of lead 
 was largely practised. The copper, melted with about four 
 times its weight of lead, was cast into flat cakes 18 inches in 
 
Gold. 229 
 
 diameter and 3 inches thick. These were then carefully 
 heated and the lead allowed to liquate out," carrying the silver 
 with it. The residues were subjected to a second liquation 
 at a higher temperature. The Argentiferous lead was after- 
 wards cupelled. 
 
 CHAPTER XVI. 
 GOLD, 
 
 THE fine yellow colour and brilliant appearance of this metal 
 are well known. It is comparatively soft, being only slightly 
 harder than lead when pure and unalloyed with base metals. 
 It is the most malleable and ductile among metals, leaf 
 2 s'oVoo f an mc h thick being obtained by hammering, and a 
 grain can be drawn into wire 500 feet long. Its tenacity is 
 about 7 tons per square inch. These properties are influenced 
 greatly by minute quantities of impurity, notably lead, bismuth, 
 antimony, and arsenic. Its alloys with silver and pure copper 
 are harder, but extremely malleable and ductile. It has a 
 melting-point of about 1075 C., an d volatilizes at very high 
 temperatures, as in an electric furnace. When molten it 
 appears greenish, and if undisturbed as it cools, suddenly flashes 
 out bright when at a temperature of about 600, after which it 
 cools and solidifies. It contracts considerably on solidifying. 
 Pure gold welds with the greatest ease. Its flowing power is 
 high, and it is an excellent conductor of heat and electricity. 
 Its specific gravity is 19*3. 
 
 The metal is unaffected by dry or moist air, and resists the 
 action of acids (save selenic), alkalies, and sulphuretted hydro- 
 gen. It is readily attacked by chlorine, and also by iodine 
 and bromine. A mixture of nitric and hydrochloric acids 
 (aqua regia) dissolves gold, because free chlorine is generated. 
 The gas attacks gold most rapidly at the moment of liberation 
 (nascent state), and is less active when diluted with air or any 
 inert gas. The chloride (AuCl 3 ) is very soluble in water. It is 
 decomposed at high temperatures, gold and chlorine resulting. 
 
230 Metallurgy. 
 
 Gold is slowly dissolved by cyanide of potassium in presence 
 of air or oxygen. 
 
 2 Au + 4KCN + H 2 O -f O - 2AuCN.KCN -f 2KHO 
 
 The addition of a little bromine or cyanogen bromide 
 hastens the solution. It is precipitated from its solution as 
 chloride by most metals, and also by sulphate of iron, chloride 
 of antimony, oxalic acid, carbon, and carbonaceous bodies. 
 The solution of gold in potassium cyanide is not precipitated 
 by ferrous sulphate or ordinary reducing agents. Metals, as, 
 for example, zinc, throw it down readily. Mercury readily 
 amalgamates gold. 
 
 Occurrence. Gold occurs naturally in the free state, but to 
 some extent also as telluride, and possibly as sulphide. It 
 is intimately associated with iron pyrites and other sulphides, 
 the greater part of the gold in some ores being contained in 
 the pyritical contents. Native gold occurs in matrix, generally 
 in veins of quartzose and other hard rocks, forming reefs or 
 dykes, and in deposits formed of the ddbris produced by 
 the weathering of such rocks, such as " alluvium" river sand, 
 etc. In the latter formations, owing to the action of running 
 water, the lightest portions have been transported furthest, 
 and an accumulation of the coarser gold has taken place 
 nearest to the broken-down rock, owing to the high specific 
 gravity of the metal Alluvial deposits are, in consequence, 
 often richer than the mother rock from which they are derived. 
 The gold occurs in all degrees of coarseness, from microscopic 
 particles to masses of considerable size. These are known as 
 " nuggets." The "Maitland Bar" nugget from New South 
 Wales, exhibited at the Mining Exhibition of 1890, contained 
 313-093 ozs. of fine gold. Gold is very widely distributed in 
 small quantities. 
 
 In Great Britain, it has been found in Cornwall, Wales, 
 Perthshire, and Sutherlandshire ; in Ireland, in Wicklow, and 
 in the Isle of Man. 
 
 In Europe, Hungary, Transylvania, Sweden, Spain, and 
 Italy also furnish gold. 
 
 Rich deposits occur in India, Ceylon, China, Japan, 
 Siberia, the Ural Mountains, and in South Africa. 
 
Gold. 231 
 
 In the New World, the gold-bearing rocks occupy the west 
 coast, following the line of the mountains. Alaska, British 
 Columbia, California, Mexico, Bolivia, Peru, Chili, Columbia, 
 and Brazil are all rich in gold. Australia is at present one of 
 the principal gold-producing countries. 
 
 The high value of the metal enables deposits which contain 
 very little gold in some cases only a few grains per ton 
 to be profitably worked. Much depends on the nature of the 
 deposit and the method adopted. 
 
 Alluvial Deposits, Placers, etc. The mining and extrac- 
 tion of gold are almost inseparable. Alluvial deposits differ 
 very much in character, from loose sand, pebbles, etc., 
 through stiff earth, to hard conglomerate, the pebbles of which 
 are firmly cemented together. The " banket ore " of South 
 Africa is of this class, although the pieces are angular. It 
 appears to be more of a " breccia." 
 
 The gold in alluvium occurs in nuggets of varying size, 
 and in grains. In surface deposits (placers), generally shallow, 
 the ground is first picked over for nuggets. The sand and 
 gravel are then washed, the lighter materials being thus 
 removed, and gold remains. 
 
 Panning out consists of washing the "pay-dirt" in a shallow 
 iron pan with a depression in the middle for retaining the gold. 
 The earth is placed in the pan and washed under water, a 
 circular motion being given to it. Light matters are carried 
 over the edge, and the gold gradually finds its way to the bottom, 
 together with other heavy matters. This residue is dried, and 
 the lighter materials blown away, leaving the gold. In Africa 
 the natives wash the river sand in gourds, mixing it up with 
 water and pouring off the matter held in suspension, and store 
 the gold dust obtained in quills. 
 
 Hydraulic Mining. In this method of working, the 
 auriferous gravel is dislodged by means of a powerful jet 
 of water directed against the bank by means of an iron 
 nozzle (monitor). The quantity of water required for this 
 purpose is enormous. It is sometimes carried for miles 
 down hillsides and across valleys, in pipes on trestles (flumes), 
 and is delivered at high pressures, sometimes under a head 
 
232 Metallurgy. 
 
 of 200 feet. The dislodged material is carried by the 
 stream of water down a series of long wooden troughs, the 
 "sluice," made in i2-feet lengths, fitted together, which have 
 a slope of about an inch to the foot, more or less. The 
 bottoms of these are crossed at intervals by movable wooden 
 or iron bars, riffles, behind which the heavy particles of gold, 
 which move more slowly and have a greater tendency to settle, 
 lodge. The lighter gravel, etc., is carried on by the current. 
 Perforated iron plates, grizzlys, are introduced at intervals in 
 the bottom of the sluices. The coarse gravel is carried on 
 over these, but the finer portions fall through the plate on to 
 a second sluice at a lower level, with a separate water supply. 
 The inclination of this is less than the first, and the lower 
 velocity of the stream favours the collection of the fine 
 particles. 
 
 Mercury is fed in small quantities from time to time at the 
 top of the sluice. It lodges behind the riffles and catches the 
 particles of gold which come in contact with it. Amalga- 
 mated copper plates are often suspended in the sluice to 
 catch the " float gold " (very small flattened particles which 
 float on the surface). 
 
 The amalgam is removed at intervals. For this purpose 
 the water is stopped, the gravel cleaned out and the riffle bars 
 lifted in order, commencing at the top, and the amalgam 
 collected. The upper part of the sluice is cleaned up at fre- 
 quent intervals, the greater part of the gold being caught there. 
 After squeezing out the excess of mercury through chamois 
 leather, the amalgam is retorted. 
 
 Washing Sands, etc. Baize, blankets, and hides, with the 
 hairy side up, are sometimes employed in the washing of fine 
 sands and stamped material. They are attached to sloping 
 boards which form the bottom of shallow sluices. The sand 
 is thrown on at the top, washed down by a stream of water, 
 and brushed by a workman against the stream. From time 
 to time the blankets, etc., are removed, and the gold, etc., 
 shaken out into a trough of water and amalgamated with 
 mercury. The amalgam is afterwards retorted. 
 
 A very effective method of treating fine sands is to boil 
 
Gold. 233 
 
 them with water and mercury. Chinamen find it profitable to 
 work over the " panned-out placers " in California in this way. 
 
 Hard " cements " (consolidated alluvium) are often ground 
 in mills resembling mortar-mills, the "pulp" or ground material 
 being carried away over amalgamated copper plates. 
 
 Treatment of Gold Quartz. Much depends on the mode 
 of occurrence of the gold and the nature of the quartz. In 
 some ores it occurs entirely in the free state, a'nd free from 
 pyrites. These are often ferruginous, the oxide of iron result- 
 ing from the decomposition of iron pyrites. The gold often 
 exists in largest quantity in the oxide of iron, showing it to 
 have been derived from the pyrites. Such ores generally 
 become pyritous below the water line. " Gossans " consist 
 mainly of this decomposed pyritous material. 
 
 In quartz containing pyrites, much of the gold is often 
 contained in the pyrites. Most of this escapes extraction by 
 the ordinary amalgamation processes, either owing to its extreme 
 state of division, or to combination as sulphide in the pyrites. 
 It passes into the "tailings," as the residues from amalgamation 
 are called. Such ores are described as ''refractory," and 
 require special treatment. Ores in which all the gold is 
 recovered by simple crushing and amalgamation are described 
 as " free milling." 
 
 Amalgamation of Free-milling Ores. The quartz is first 
 broken into about inch cubes in a stone breaker or ore crusher 
 (Fig. 82), the jaws being so adjusted as to deliver it of the 
 required size. 
 
 The ore is next crushed to fine powder under stamps, or by 
 rolls, or grinding mills. 
 
 Fig. 83 shows a stamp battery. The stamps consist of 
 heavy cast-iron "heads," or "bosses," A, shod with steel, 
 attached to long wrought-iron or steel stems sliding in hard- 
 wood "guides," BB. These are lifted by the "cams," C, 
 attached to the revolving " cam shaft," D, driven by the 
 pulley, E, acting on the "tappets," F, keyed on the stems. 
 The cams are right- and left-handed, so that each head is 
 raised twice at each revolution. Under each stamp is a steel- 
 faced " die," G, between which and the falling head the ore is 
 
234 
 
 Metallurgy. 
 
 crushed. The dies are contained in the cast-iron " mortar-box," 
 H, which is supported on a wooden foundation on pads of 
 indiarubber a quarter of an inch thick. One or both sides of 
 the mortar is fitted with "screens," I, of perforated sheet iron 
 or thick wire cloth, and a stream of water is fed in from a pipe. 
 Some 72 gallons per hour per head is required, but it may be 
 recovered in settlers with a loss of about 25 per cent. The 
 
 FIG. 82. Wet-crushing Gold-mill. 
 
 ore is fed in on the side opposite the screens (if single dis- 
 charge), often by an automatic contrivance. The action of the 
 cams on the tappets not only raises the head, but turns it 
 partially round each stroke, and thus causes it and the die to 
 wear uniformly. For gold crushing, the mortar-box is lined 
 with amalgamated copper plates, and much of the coarse gold 
 is caught in the mortar. A little mercury half a thimbleful 
 is fed in at intervals for this purpose. Levers on "jack" 
 shafts, K, are provided for holding up the stamps. 
 
 The heads, with attachments, weigh from 4 to 9 cwts., but 
 for quartz, generally about 7 cwts. 
 
 They have a drop of about 10 to 12 inches, and give from 
 70 to 80 blows per minute, the cam shaft making from 35 
 to 40 revolutions per minute. The fall of the head splashes 
 the pulp against the screen and assists in forcing it through. 
 
Gold. 235 
 
 The screens have a mesh of from 30 to 60 per linear inch. 
 
 FIG. 83. 
 
 Each head will crush 2 to 2\ tons per. day (wet crushing). 
 
 F/G. 84. Stamp Battery. 
 
 The fine material, " pulp," is carried by the water through 
 
Metallurgy. 
 
 the screens, on to amalgamated copper plates (Fig. 84), slightly 
 inclined, over which it is carried by the current, the free gold 
 dragging along the bottom and being arrested by the mercury. 
 
 The plate next the mortar is sometimes silver-plated, to 
 prevent the deadening of the mercury by oxidation of the 
 copper dissolved in it, making it much less active. 
 
 From the plates the " tailings " may pass to amalgamators 
 or to vanners, as subsequently described. 
 
 Stamp batteries, "dry" or "wet," are open to several objections. 
 The principal one is its tendency to cut up and flatten out coarse particles 
 of gold. By the repeated hammering a hard surface is developed, and 
 fine particles of foreign matters driven into the soft metal. This renders 
 it very difficult to amalgamate, the mercury only attacking it with extreme 
 
 slowness. There is also 
 liability to loss from 
 the production of ' 'float 
 gold." 
 
 Rolls are open to 
 fewer objections, crack- 
 ing open .the ore and 
 exposing the metal. 
 Fig. 85 shows the 
 Huntingdon Mill. The 
 pan is of cast iron, with 
 a steel belt round the 
 lower part inside. Four 
 mullers are supported 
 vertically on rods, on 
 which they revolve by 
 friction against the side 
 of the pan. The head 
 from which they are 
 FlG 8 carried is revolved at 70 
 
 revolutions per minute. 
 
 The mullers are pressed by centrifugal force against the ring, and the ore 
 coming between is crushed. Above the steel roller path is a screen occupy- 
 ing half the circumference of the pan. A stream of water is fed in above, 
 and stirrers are provided to ensure complete crushing. For soft ores a 
 mill having a 5-foot pan is about equal to a lo-head stamp battery, and 
 requires only about half the power to drive it. 
 
 Cleaning up. The mill is stopped periodically for the 
 purpose of collecting the amalgam which is carefully removed 
 from the amalgamated plates. It is worked up with fresh 
 mercury either by hand or in pans (clean-up pans), and well 
 washed with water to remove earthy and other matters. It is 
 then squeezed in bags of canvas or chamois leather to expel 
 
Gold. 
 
 237 
 
 the excess of mercury. This is not free from gold, but is 
 re-used. The pasty amalgam remaining in the bag is retorted 
 to remove the mercury. The gold which remains is melted in 
 crucibles and refined. 
 
 Loss of Mercury. This arises from two causes, " sicken- 
 ing" and "flouring." In the former case, the mercury is con- 
 verted into a black powder and carried away. It is caused by the 
 presence in the ore of certain minerals, e.g. antimony sulphide. 
 
 " Flouring " is breaking up of the mercury into minute 
 globules, which are lost. 
 
 Treatment of Tailings in Amalgamators. The slimes, or 
 tailings, may be passed into amalgamators, in which they are 
 ground up with mercury (Fig. 86). 
 
 The pulp is fed into the hopper, A, and passes down the 
 hollow shaft, B, to which is attached the iron muller. C. 
 This is slowly rotated; the 
 outer pan, D, contains mer- 
 cury, below which the mul- 
 ler dips. 
 
 The pulp is delivered, 
 by the openings E, under 
 the muller ; which, by its 
 revolution, thoroughly in- 
 corporates the tailings with 
 the mercury. They escape 
 over the edge of the pan, 
 and may be delivered to a 
 second set of amalgamators 
 at a lower level, or pass 
 direct to settlers. 
 
 The Hungarian mill for 
 the amalgamation of iron 
 pyrites is in principle exactly 
 similar, but is driven from 
 
 belOW. Amalgamators Of FIG. * -Continuous Amalgamating Pan, 
 
 other types are also employed, e.g. Berdan pan. 
 
 The tailings are more commonly treated on Frue vanners or 
 other contrivances for the recovery of the heavy sulphides 
 
238 Metallurgy, 
 
 iron pyrites, galena, copper pyrites, etc. which they contain, 
 and which often cany a considerable portion of the gold 
 present in the ore. This is not recovered by simple crushing. 
 The " concentrates," as they are termed, are either ground in 
 iron pans with mercury, as in the treatment of silver ores 
 (p. 214), or are roasted and treated by chlorination (see below). 
 In some cases the whole of the pulp is treated without con- 
 centration with potassium cyanide (see p. 241). 
 
 Chlorination Processes. As noted (p. 229) gold is readily 
 attacked by chlorine gas, and the chloride formed is soluble 
 in water. In 1853 Plattner proposed to extract gold in this 
 way. Only ores in which the gold is free can be thus treated. 
 It is employed for the treatment of the pyritical concentrates 
 obtained from the tailings. 
 
 They are first roasted to remove sulphur and open up the 
 ore. This converts the iron into ferric oxide a form in which 
 it is not acted on by the chlorine and leaves the gold free. 
 
 This is effected in a Bruckner, or other calciner. The 
 roasted ore is moistened and put into well-tarred vats provided 
 with false bottoms and tightly fitting covers, with a bung-hole 
 in the top. When full, the vats are covered and luted, the 
 bung-hole being left open. Chlorine from a generator (see 
 Fig. 86) is admitted under the ore, and, when it has displaced 
 the air, and is escaping freely, the opening in the top is closed, 
 and the gas allowed to operate for some 24 to 72 hours. The 
 excess of chlorine is blown out, and the chloride formed 
 dissolved out with water. The solution, after settling, is run 
 into the precipitating tanks, which are lead lined, and pro- 
 vided with stirrers, and sufficient ferrous sulphate is added to 
 precipitate the gold. 
 
 6FeSO 4 + 2AuCl 3 = 2Fe 2 (S0 4 ) 3 -f Fe 2 Cl 6 + Au 2 
 
 The precipitate is allowed to settle and the clear liquor 
 siphoned off through a sawdust filter. The solutions obtained 
 from several batches of ore are usually treated before 
 gathering the precipitated gold. After treatment with acid, to 
 dissolve out any basic salts of iron which may have been 
 formed, it is fused up. Its purity varies from 920 to 990 parts 
 of gold per 1000. 
 
Gold. 
 
 239 
 
 The chlorine is generated in a lead still from salt, man- 
 ganese, dioxide, and sulphuric acid. 
 
 Modern chlorinating vats are generally mounted on 
 trunnions to facilitate the removal of the residues. 
 
 Many modifications of the process are in use. The 
 improvements principally relate to 
 
 i. Chlorination of the material under pressure : 
 
 (a) Of the gas itself. 
 
 (b) Of air pressure (Newberry Vautin). 
 
 (c) Hydraulic pressure (Pollok). 
 
 Vertical Section. 
 
 FIG. 87. Gold Chlorinating Plant. 
 
 2. Agitation of the ore during chlorination : 
 
 (a) By agitators (Cobley and Wright, De Lucy and 
 
 others). 
 
 (b) By revolving barrels (Duflos, Primard, Mears, 
 
 Newberry, Vautin, Pollok, etc.). 
 
 3. Filtration by suction and centrifugal force (Aarons, 
 Newberry and Vautin), etc. 
 
 4. Generation of chlorine in the vats by the action of 
 sulphuric acid on bleaching powder mixed with the ore, and 
 absorption of the excess of chlorine by passing it through milk 
 of lime. 
 
240 Metallurgy. 
 
 5. Heating up liquors to expel excess of chlorine prior to 
 precipitation. 
 
 6. Precipitation by charcoal, bitumens, and other reagents 
 (the charcoal filters are burnt and the ashes fused with borax 
 to recover the gold). 
 
 By these means the time occupied is shortened. 
 
 Extraction of Silver. When the ore or concentrates 
 contain silver, a little salt, about i per cent, is added towards 
 the end of the roasting, and the chloride of silver formed is 
 dissolved out by hyposulphite of soda after the removal of the 
 gold chloride (see p. 222). 
 
 The Cyanide Process, introduced by Messrs. MacArthur 
 and Forrest, has already been extensively adopted, and 
 promises to displace chlorination processes, if a cheaper 
 method of making cyanide can be found. 
 
 It depends on the well-known fact that potassium cyanide 
 attacks gold in the presence of oxygen, and if in a fine state 
 of division, rapidly dissolves it. Weak solutions are found to 
 be more active than strong ones, on account of the greater 
 solubility of oxygen in them (Journal of Chemical Society, 1893). f_ 
 
 One great advantage possessed by this process is that raw"~"| 
 pulp may be treated directly, no previous calcining or con- / 
 centration by washing on vanners or buddies, etc., being 
 necessary. 
 
 The strength of solution varies from 0-4 to i per cent., but 
 0*5 is said to be efficacious. The tailings, or concentrates, 
 are left in contact with the solution for from 60 to 72 hours, 
 circulating pumps being employed. The clear liquid is then 
 run through boxes containing zinc shavings. The gold is 
 precipitated by the zinc as a black powder. It is collected 
 periodically, washed to free it from zinc, as far as possible, and 
 melted in crucibles. A very coarse bullion is obtained, and 
 slag. This is melted with lead and cupelled, to recover the 
 gold it contains. About 90 per cent, of the gold is obtained, 
 and the liquors may be re-used. The foreign matters in the 
 ores are not attacked. 
 
 Refractory ores which cannot be successfully treated in any 
 other direct way may be thus dealt with. The process is largely 
 
Gold. 24 1 
 
 used in South Africa. It is not applicable to coarse gold, and 
 is used for tailings and concentrates only. The danger arising 
 from the use of such a powerful poison as cyanide, is very small, 
 if cleanliness and perfect ventilation are attended to. 
 
 In the Siemens-Halske process the gold is precipitated by 
 electro-deposition. 
 
 Sulman adds cyanogen bromide to the ordinary solution, 
 which greatly reduces the time, and is more effective. The 
 precipitation is effected by zinc fume instead of shavings (see 
 p. 261). 
 
 Tailings containing much pyrites (especially copper) are difficult to 
 treat. On exposure to the atmosphere in the moist state, they oxidize. 
 Free acid and soluble salts are formed, which greatly increase the con- 
 sumption of cyanide. Lime is used to neutralize the ore and decompose 
 soluble sulphates. 
 
 Parting. Native gold and bullion almost invariably con- 
 tain silver and other metals from which it must be separated. 
 The base metals may be removed by cupellation, or, if fairly 
 pure, by fusion with nitre and borax ; but silver, platinum, etc., 
 will remain, and must be removed by chemical means. This 
 process is known as "parting," and consists of dissolving out 
 the silver by acids. 
 
 Alloys of even base metals with gold, are not attacked 
 unless the base metal is in large excess ; and hence, if a 
 sufficient proportion of silver is not present, enough must be 
 added to ensure it being acted on. 
 
 Sulphuric Acid Parting. Silver is soluble in hot, strong 
 sulphuric acid, forming sulphate of silver. The alloy to be 
 parted must contain not less than 80 per cent of silver; 
 generally the alloys treated contain very much more. The 
 metal is granulated by pouring it into cold water, so as to 
 offer a large surface to the action of the acid. 
 
 The parting pans are usually of white cast iron, about 2 
 feet wide, provided with a lid and a pipe by which the SO 2 , 
 generated, is conveyed into a lead chamber for reconversion 
 into sulphuric acid, to be re-used. 
 
 Ag 2 + 2 H 2 SO 4 = Ag 2 S0 4 + 2H,0 + SO 2 
 The pots are heated by fires from below. The granulated 
 
242 Metallurgy. 
 
 metal is treated with about 2\ times its weight of strong acid, 
 at a temperature about the boiling-point of sulphuric acid. 
 The sulphate of silver which forms separates in a pasty mass of 
 small crystals. This is thrown into water in a lead-lined tank 
 and heated by steam. The sulphate dissolves, and the gold 
 settles out and is washed and collected. It still retains silver, 
 and is next treated with sulphuric acid and sulphate of soda 
 in the proportions of 3 to 5, and strongly heated. 
 
 The sulphate raises the boiling-point of the acid, and 
 enables it to attack the remaining silver. A second treatment 
 is sometimes necessary. What remains in the pans is then 
 boiled with acid, and the residue washed, dried, and fused. 
 
 The solution of sulphate of silver is decomposed by 
 copper (Ag 2 SO 4 + Cu = CuSO 4 = Ag 2 ), and the precipitated 
 silver compressed by hydraulic pressure, dried, melted in 
 crucibles, and cast into ingots. The copper is afterwards 
 deposited by iron ; or the solution is concentrated, and the 
 copper sulphate allowed to crystallize out, and sent into 
 the market, the mother liquor being further concentrated in 
 glass or platinum vessels, to recover the excess acid for re-use. 
 
 Silver containing more than three grains of gold per pound can be 
 economically treated by this method. Much old silver plate was sacrificed 
 for the gold contained in it when this process was introduced, the older 
 method of parting by nitric acid being too expensive. 
 
 Parting with Nitric Acid. In this process, nitric acid is 
 substituted for sulphuric acid. The operation is conducted in 
 platinum, glass, or porcelain stills, with covers connected with 
 condensers, to recover the acid which is boiled off. Nitric 
 acid does not readily attack the alloy unless it contains about 
 three times as much silver as gold. If less is present, it is 
 melted with more silver, to make up that amount. This is 
 known as inquartation. The alloy is granulated and boiled 
 with about twice its weight of nitric acid, diluted with one- 
 third its bulk of water. Red fumes are evolved as long as 
 silver is dissolving. 
 
 6Ag +8HNO 3 = 6AgNO 3 + 4H 2 O + 2NO 
 The solution of nitrate of silver is drawn off, and the 
 
Gold. 243 
 
 residual gold treated with a little strong nitric acid, and after 
 washing, melted under borax and cast into ingots. 
 
 The silver is recovered by adding hydrochloric acid to the 
 solution of silver nitrate, which precipitates the silver as 
 chloride. 
 
 The acid is added cautiously so as to leave a little silver unprecipitated 
 in order that the nitric acid formed may be re-used. 
 
 AgN0 3 + HC1 = AgCl + HN0 3 
 
 If free HC1 were present in the acid used for parting, the gold also 
 would be attacked by the chlorine generated. It is detected by the 
 addition of silver nitrate to the acid. 
 
 The silver chloride is reduced by zinc. 
 
 Separation from Platinum. In parting with nitric acid, platinum, if 
 present to a less extent than 9 per cent., is dissolved out with the 
 silver. If much platinum is alloyed with the gold, it is best separated by 
 solution in aqua regia and precipitation of the platinum by sal-ammoniac. 
 
 Alluvial gold often contains grains of a heavy, hard alloy of osm.- 
 iridium, which is not taken up by the gold. In the American Mint, this 
 is separated by melting the metal in tall crucibles, when it sinks owing to 
 its greater specific gravity. Silver is also alloyed with the metal to lower 
 its specific gravity and permit the osm.-iridium to sink more rapidly. 
 The upper layers are ladled out and parted, and a fresh batch treated. 
 The residue at the bottom is remelted with silver several times to diminish 
 the gold present, and then parted with nitric acid. The silver dissolves, 
 and the grains of osm.-iridium remain mixed with a little pulverulent gold, 
 which is separated by washing. 
 
 Toughening Brittle Gold. Mere traces of arsenic, anti- 
 mony, bismuth, and lead suffice to render gold brittle. It is 
 toughened by treating the molten metal with mercuric chloride, 
 or by passing chlorine through it by means of a clay tube, as 
 practised at the Royal Mint (Miller's Process). The bismuth, 
 arsenic, and antimony chlorides volatilize. If silver is pre- 
 sent the silver chloride formed fuses and rises to the top. The 
 gold is not attacked, gold chloride being decomposed at high 
 temperatures. 
 
 Smelting with Lead. Old crucibles that have been used 
 for gold and silver melting are first picked over, ground, and 
 amalgamated. The residues are then smelted with lead- 
 yielding materials, and the resulting metal cupelled to extract 
 the gold. " Sweep " (sweepings) is similarly treated. Ores 
 are also sometimes smelted with lead. 
 
244 Metallurgy. 
 
 Alloys. THe common method of expressing the quality of 
 a gold alloy is in " carats " and carat grains (4 e.g. = i 
 carat). 
 
 Pure gold is 24 carats fine; i8-carat gold contains f gold 
 and \ alloy, or 750 parts per thousand; Q-carat gold, 375 
 parts per thousand. English-coinage gold is 22 carat, or 916*6 
 parts per thousand. Its specific gravity is 17-157. The alloy 
 is copper, which is added to harden it. A new sovereign 
 weighs 123-! grains, but is legal tender so long as it does not 
 fall below 122^ grains, f grain being allowed for wear. It 
 is estimated to circulate for 18 years without becoming 
 light The weight of metal in the coin is worth its face value. 
 The French and United States standard alloy is 900 fine, or 
 21 carats 2f carat-grains. The terms "worse" and "better" 
 are applied as in silver. Thus the above alloy is o carats i-f 
 carat-grains worse than English gold. 
 
 Articles of gold jewellery down to 9 carats are stamped by 
 the Goldsmith's Company with a Hall-mark, indicating the 
 quality, the year of production, and the Assay Office at which 
 the tests were made. 
 
 Copper and silver are usually alloyed for the purpose of 
 hardening gold, when malleability is required for purposes of 
 working. Zinc is sometimes added when rigidity and hardness 
 are most important. Pencil-cases and watch-guards often con- 
 tain the latter metal. 
 
 CHAPTER XVII. 
 
 TIN. 
 
 Physical Properties. Tin is a white metal with a faintly 
 yellowish tinge. It has a high lustre, and is very malleable. 
 Foil, y-^oo- of an inch tnick > can be obtained by beating. It 
 is ductile, but its tenacity -is low only about 2-1 tons per 
 square inch. Its melting-point is 230 C., and it is not sensibly 
 
Tin. 245 
 
 volatile at furnace temperatures if closely covered to exclude 
 air. Near the melting-point it is brittle, and a cake of tin 
 heated till the edges begin to melt and then dropped on the 
 ground, breaks up into peculiar long-shaped, columnar pieces 
 known as "grain tin." Tin which is impure does not readily 
 do this. When bent, a strip of tin emits a peculiar crackling 
 sound known as the cry. This is supposed to be due to the 
 internal friction between the crystalline particles. 
 
 Tin is readily obtained in crystals, like antimony or 
 bismuth. If the surface of an ingot is treated with a 
 mixture of sulphuric and nitric acids, beautiful crystalline 
 markings make their appearance. This is known as the 
 moiree metallique, and is used as a metallic ornamentation, 
 being coated with coloured varnishes. The metal is a poor 
 conductor of heat and electricity. 
 
 Pure tin, when cast in a mould, at a low temperature, 
 solidifies with a bright metallic appearance ; but if impure, it 
 presents a more or less frosted appearance, according to the 
 amount of impurity present. 
 
 Commercial tin often contains small quantities of lead, 
 copper, arsenic, antimony, and tungsten. 
 
 The metal is not affected by dry or moist air at ordinary 
 temperatures. Heated in air, it oxidizes, forming stannic oxide 
 (SnO 2 ). It combines readily with sulphur, forming SnS. 
 This when roasted does not form sulphate, but yields SnO 2 
 and SO 2 . It is decomposed when heated with metallic iron. 
 Tin dissolves in hydrochloric and sulphuric acids. Nitric 
 acid acts violently on it, and converts it into an oxide. It 
 is also soluble in caustic soda and potash, forming stannates. 
 
 It is not readily attacked by vegetable acids or animal 
 juices, and tin plate is hence largely employed in the 
 canning industry. For the same reason it is used for coating 
 the interior of vessels for cooking purposes. 
 
 ORES OF TIN. 
 
 Cassiterite Tinstone (SnO a ). This is the only important 
 ore of tin. It is yellowish-brown or black in colour, and occurs 
 
246 Metallurgy. 
 
 crystallized, in well-defined veins, and in grains, sometimes 
 distributed through a mass of rock, such as granite. It has a 
 specific gravity of 6-5 to 7. It has a high lustre, and is too 
 hard to scratch with a knife. In the vein it is associated with 
 galena, blende, copper, and iron pyrites, arsenical iron pyrites, 
 and other minerals. Wolfram (tungstate of iron), another 
 remarkably heavy mineral, is also associated with it. A vast 
 number of non-metallic minerals occur* as associates. Fluor, 
 garnet, mica, chlorite, granite, gneiss, and porphyry may be 
 mentioned. Stream tin ore is tinstone which has accumulated 
 by the weathering of the rocks containing it. The lighter 
 portions have been removed by the action of running water, 
 and the tinstone and associated heavy minerals left. Wood 
 tin is tinstone showing concentric markings more or less 
 resembling wood. Tin ores are often very impure, sometimes 
 not containing more than i per cent, of tinstone. Its high 
 specific gravity facilitates dressing operations, and such ores, 
 by careful picking, stamping, and washing, can be profitably 
 worked. - Tin ore is found in Cornwall and Devon, Germany, 
 Spain, Russia, Malacca (Banca), Australia, United States, and 
 Mexico. 
 
 The ore is carefully dressed by hand picking, stamping, 
 and washing, to remove gangue. The copper and arsenical 
 pyrites are not completely removed, and the wolfram also 
 remains with the tinstone. 
 
 Bell-metal ore, or tin pyrites, is a mixture of copper, iron, 
 and tin sulphides. 
 
 Smelting. The ore is first carefully calcined in a large, 
 low, reverberatory furnace, being turned over every 20 minutes 
 or so. In Brunton's calciner the bed is circular, and revolves 
 on a vertical axis, the turning over being done mechanically. 
 In roasting tin ores a moderate heat is necessary at first, to 
 avoid clotting of the sulphides present. 
 
 During roasting the arsenic combines with oxygen, and is 
 converted into white arsenic (A 2 O 3 ), which is volatilized and 
 deposited in long flues provided for that purpose, from which 
 it is collected. Sulphur burns off as SO 2 , and the copper is 
 largely converted into sulphate. 
 
Tin. 
 
 247 
 
 The ore after this roasting is moistened, and left in a heap 
 for a few days, to allow more soluble sulphates to form. It is 
 then thrown into a tank and agitated with water. Copper 
 sulphate and other soluble matters are dissolved, and the 
 sediment consists mainly of stannic and ferric oxides. The 
 lower layers contain the larger proportion of oxide of tin owing 
 to the greater rapidity with which it settles, on account of its 
 high specific gravity. The ferric oxide is separated by wash- 
 ing, and the concentrated oxide is known as black tin. It 
 is sorted into various grades according to purity. 1 
 
 Reduction. In this country this is effected by heating the 
 tin oxide mixed with carbon in the form of anthracite, in 
 reverberatory furnaces, of the form shown in Fig. 88. The 
 bed measures about 15 feet by 9 feet, and slopes towards the 
 tap-hole 0, outside which is the 
 " float," or tin-pot ; which is 
 lined with clay to prevent the 
 metal taking up iron. The stack 
 is 40 or 50 feet high. The bed 
 is of fire-clay resting on slate 
 slabs supported by iron bars, and 
 the fire-bridge is about 14 inches 
 high. 
 
 The charge consists of about 
 a ton of black tin mixed with 
 about 3 to 4 cwts. (20 per cent.) 
 of anthracite powder, according 
 to purity. If silica is present a 
 little lime or fluor spar is added 
 as a flux. The mixture is damped 
 
 , , _ FIG. 88. Furnace for smelting 1 in Ores. 
 
 to prevent dusting, and after in- 
 troduction into the furnace, the doors are closed and luted 
 round. A low temperature is maintained for some time to 
 
 1 Removal of Tungsten. In the preliminary calcination wolfram is not 
 affected. It is removed when necessary or desirable, by mixing the 
 black tin with sufficient carbonate or sulphate of soda and heating in 
 a special furnace to decompose the wolfram, yielding tungstate of soda 
 and oxide of iron. The tungstate of soda is dissolved out by water and 
 crystallized, and the oxide of iron removed by washing as before (Oxlands' 
 Process). 
 
248 Metallurgy. 
 
 ensure reduction of the tin oxide and prevent the formation 
 of silicate. In 4 to 5 hours the charge is well stirred up, 
 anthracite culm thrown in, and the charge again heated for 
 another hour. After again rabbling, the metal is allowed to 
 subside, and is then tapped into the float. 
 The reduction takes place as follows 
 
 2SnO 2 4- 2C 2 = Sn 2 + 4 CO 
 
 A fluid slag, known by the smelter as "glass," runs from 
 the furnace with the metal. It consists of silicates of iron, 
 lime, and alumina. Oxide of tungsten is often present. It 
 sometimes contains as much as 20 per cent, of tin. It is 
 allowed to accumulate, and resmelted to extract the metal. 
 
 A pasty mass, consisting of shots of tin, anthracite, and 
 slag is left on the furnace bottom, and is raked out by the 
 smelter. The tin contained in it is separated by stamping 
 and washing. 
 
 The metal is ladled from the tin-pot into pig moulds, or, 
 if pure, is run into the " boiling " pot. 
 
 Reduction in Blast Furnaces. Tin ore is also reduced in 
 small blast furnaces, with charcoal as fuel. The materials are 
 charged in at the top, and the furnace works continuously. 
 
 The loss of tin in the slags is much greater, but the tin 
 obtained is very pure. 
 
 Smelting in blast furnaces is abandoned in this country, but 
 in Saxony, the East Indies, and other places is still continued. 
 About 32 cwts. of charcoal per ton of tin are consumed in 
 smelting. 
 
 Refining. This involves two operations liquation and 
 boiling. 
 
 Liquation. The pigs of tin, which weigh from 3 to 4 cwts. 
 each, are piled on the hearth of a reverberatory furnace, with 
 a bed somewhat more sloping than the reduction furnace, and 
 heated carefully to the melting-point of tin. Some 18 tons of 
 pigs are treated at once. The temperature is very carefully 
 regulated. The purer tin melts, drains away, and flows out 
 into the refining kettle. The impurities remain in an unfused 
 state on the hearth, as a metallic, yellowish white, hard, brittle 
 mass, often porous, known as hard head. It contains iron. 
 
Tin. 249 
 
 tin, arsenic, sulphur, and a little copper. Sweating at a 
 higher temperature yields a further quantity of less pure tin, 
 which must be further treated. 
 
 Boiling. The metal from the liquation furnace runs into 
 the "refining kettle" in front. This is an iron pot about 
 4 feet 6 inches in diameter, heated by its own fire. Above 
 the kettle is a lever attachment, by which logs of green wood 
 can be held down in the molten metal. 
 
 The steam and gases disengaged by the action of heat 
 agitate the metal and expose it to the air, and although tin 
 is more readily oxidized than copper, bismuth, antimony, or 
 lead, a scum of dross, consisting of iron, sulphur, arsenic, etc. 
 forms on the top and is removed from time to time. 
 
 This is continued for from i to 8 hours, according to 
 purity and the quality of tin required. For grain tin it is pro- 
 longed. This process is less an oxidation process than the 
 effect of cooling at the surface, of metals less fusible than tin, 
 which collect and form the scum. Tossing consists of lifting 
 the metal from the pot in ladles and pouring it back again 
 from a height of several feet. This is sometimes done instead 
 of boiling. 
 
 For "common" tin the metal is ladled into the moulds, 
 usually of granite, while boiling. For grain tin the metal after 
 boiling is allowed to stand. The impurities yet remaining 
 subside, and the upper purer layers are devoted to this purpose. 
 The lowest layers require liquating again. Grain and refined 
 tin are made from purer ores than common tin. 
 
 The purity of tin is tested by casting a small ingot in a 
 stone mould. When pure, the edges are well rounded, and 
 the surface remains brilliant when cold. Frosting of the 
 surface on solidifying is an indication of impurity. 
 
 MANUFACTURE OF TIN PLATE. 
 
 The principal uses of tin are the manufacture of alloys 
 (see p. 265) for making tin plate, tinning cooking utensils, 
 and for tinfoil. 
 
 Tin plates are sheets of iron coated with tin. The metal 
 readily alloys with iron, and when heated somewhat above its 
 
250 Metallurgy. 
 
 melting-point, will adhere to a clean iron surface, forming at the 
 surface of contact an alloy with the iron, to which a thin film 
 .of tin adheres. The adhesion of the film of tin depends on 
 the homogeneity and purity of the iron employed, soft pure 
 metal being most readily tinned. Such plates are also best 
 suited for the use of the tinman, being more readily bent and 
 worked. 
 
 The plates are rolled from "tin bars." These are about 
 6 inches wide and f of an inch thick. They are cropped into 
 i5-inch lengths, reheated, and rolled square. They are again 
 reheated and rolled to about four times the length by chilled 
 rolls. The plate is doubled on itself, reheated, and again 
 rolled, again doubled, reheated, and rolled, and so on. The 
 compound sheet passes through the mill as one sheet, some- 
 times as many as 32 thicknesses being rolled together. The 
 sheets are cut to the required size and separated. A little 
 coal-dust is sometimes sprinkled over the plates to prevent 
 them sticking together, and the reheating is carefully managed 
 to avoid overheating and consequent sticking together. 
 
 Formerly iron of special quality, smelted and refined with 
 charcoal, was employed, but open-hearth steel is now generally 
 used. 
 
 Preparation of Plates. (i) The sheets of iron (black 
 plates) are carefully annealed at a red heat. This is often 
 dispensed with. 
 
 (2) They are then pickled in weak sulphuric acid at about 
 1 00 F., for about 20 minutes, well scoured with sand, and 
 washed to remove scale (bright plates). 
 
 (3) The plates are annealed at a cherry-red heat in 
 wrought-iron boxes from 10 to 12 hours, the air being excluded. 
 
 (4) The plates are cold rolled under chilled rolls to give 
 an uniform, smooth surface. 
 
 (5) A second annealing of shorter duration and at a lower 
 temperature than the first to remove the hardness produced by 
 rolling is sometimes given. 
 
 (6) Another pickling in weaker acid than before, followed 
 by scouring and washing to remove the thin film of oxide 
 formed in the annealing processes. 
 
Tin. 251 
 
 The plates are then placed in water or lime water until 
 required. 
 
 Tinning. The sheets are first placed in a grease-pot con-, 
 taining melted tallow or palm-oil, somewhat strongly heated, 
 and left till all the water has been driven off and the plates are 
 uniformly heated and coated with grease. 
 
 From the " grease-pot " they pass into a hot bath of molten 
 tin (tinman's pot), covered with grease or with zinc chloride, 
 and strongly heated. Here the alloy on the surface is pro- 
 duced. It next passes to the "wash-pot," which is divided 
 into two compartments, and contains tin, but at a lower tem- 
 perature. In the first compartment the coating of tin is 
 rendered uniform. The plates are lifted separately, and the 
 surface brushed over with a hemp mop, and examined by the 
 workman. If satisfactory, the plate is dipped rapidly into the 
 second compartment, which contains pure tin, to remove the 
 marks of the brush. It is then transferred to a grease-pot, 
 where it passes through a pair of rolls, which squeeze off the 
 excess of tin and improve the surface. The plates are then 
 cleaned from grease in bran, rubbed with chamois leather or 
 woolly sheepskin, and examined, faulty plates being rejected. 
 
 Formerly the plates, after tinning, were allowed to drain in 
 a hot grease-pot, and the wire of tin which formed removed by 
 immersion in a " list " pot, having about a quarter of an inch 
 of molten tin at the bottom, in which the wire melted off. 
 
 Machinery has to some extent replaced hand labour for 
 immersing the plates, particularly for large sizes and inferior 
 qualities. The plates are carried through the several baths 
 in succession by an arrangement of rolls and endless chain 
 belts. Terne plate is an inferior quality coated with a lead-tin 
 alloy. 
 
 Tinning Copper Articles. The surface is first carefully 
 cleaned, and the metal heated somewhat above the melting- 
 point of tin, a little powdered resin or ammonium chloride is 
 dusted over, and molten tin is then wiped over the surface 
 with tow. A quarter of an ounce of tin will cover 2 square 
 feet of surface, giving a durable coating. 
 
 Brass pins are tinned by boiling them with cream of tartar, 
 
252 Metallurgy. 
 
 alum, salt, and granulated tin, in water. The tin is slowly dis- 
 solved by the liquor, and the zinc in the brass precipitates 
 it on the surface. 
 
 Alloys of Tin (see p. 265). 
 
 CHAPTER XVIII. 
 ZINC. 
 
 THIS metal is commonly known as " spelter." 1 It has a bluish- 
 white colour and high lustre. The brightness of the fracture is 
 dimmed by impurity, notably by iron. Commercial zinc is 
 highly crystalline, hard, and brittle. When pure, however, the 
 metal is malleable, and ordinary zinc becomes sufficiently 
 malleable to be rolled into sheets when heated to 120 to 150 
 C. If heated over 200, the metal is more brittle than when 
 cold, and can be powdered. It is harder than tin and softer 
 than copper. It has a specific gravity of 7*1 when cast, but this 
 may be increased to 7*2 or 7*3 by rolling. It fuses at 412 C., 
 and is very fluid. It contracts very little in solidifying, and 
 hence is suitable for castings. The nature of the casting is 
 influenced by the temperature of pouring. If poured very hot, 
 the castings are crystalline ; but if near the melting-point, they 
 are more granular. Zinc boils at the melting-point of silver, 
 950 C., and the vapour burns in air with a bluish-white and very 
 brilliant flame, forming oxide of zinc (ZnO). The tenacity 
 of cast zinc is 1*25 tons. After rolling and annealing zinc 
 has a tenacity of 7 to 8 tons, and wire, 10 tons per square inch. 
 The elasticity is high. Rolled zinc retains in some measure 
 its malleability, and the hardness induced is removed by 
 annealing at a low temperature. Zinc was formerly solely 
 used for brass-making, the fact of its being malleable when 
 slightly heated having been discovered early in the present 
 century. The first rolling-mills were erected in Birmingham. 
 
 A little lead (under i per cent.) added to zinc intended for 
 rolling is of advantage, but this renders it unsuitable for making 
 strong brass. 
 
 1 Brazing spelter is an alloy of equal parts of copper and zinc. 
 
Zinc. 253 
 
 Chemical Properties. Above its boiling-point zinc burns 
 to ZnO " philosopher's wool." Thus produced, it is in a 
 light, feathery condition, hence the name. This oxide is 
 white, non- volatile, and 'infusible at furnace temperatures, but 
 becomes yellow when heated, and at very high temperatures 
 agglutinates. It combines with silica and forms a very refrac- 
 tory silicate. It is reduced by carbon monoxide, carbon, 
 hydrogen, and iron at temperatures above its boiling-point. 
 Like iron, zinc is oxidized by carbon dioxide and steam. 
 
 Zinc is little affected by ordinary atmospheric influences. 
 On exposure to moist air it becomes coated with a film of 
 oxide of zinc, which, being insoluble, protects the metal from 
 further action. This property is applied in coating iron 
 articles with the metal by dipping them in a bath of molten 
 zinc, the process being known as galvanizing. Before dipping, 
 they are pickled in dilute hydrochloric acid, to remove the 
 scale, and afterwards scoured, if necessary, and washed. 
 They. are then introduced into the molten zinc, covered with 
 sal-ammoniac, which acts as a flux. Tin and lead are some- 
 times added to the bath, to improve the appearance. 
 
 Electro cold galvanizing is being successfully introduced. 
 
 Zinc is superior to tin as a coating for iron for atmospheric 
 work, as it is electro positive to iron, and if the iron is laid 
 bare at any point, the electric conditions set up, result in the 
 zinc being dissolved and the iron preserved. Tin, on the 
 other hand, assists in the more rapid attack on the iron at the 
 bare place, owing to its being electro negative. Zinc being, 
 however, readily attacked by vegetable acids, and also by 
 alkalies, it cannot be used in contact with those bodies, nor in 
 canning meats, fruits, etc. In towns where sulphurous acid 
 and other acid vapours exist in the atmosphere, both zinc and 
 galvanized articles are readily attacked. Salts in solution 
 cause the action of water on it to be more rapid. The purer 
 the zinc the less rapidly this occurs. 
 
 Pure zinc is not acted on by water, and but slowly by 
 H 2 SO 4 and HC1, but readily dissolves in nitric acid. 
 
 Zinc precipitates gold, silver, copper, platinum, bismuth, 
 antimony, lead, tin, mercury, and arsenic from solution. 
 
254 Metallurgy. 
 
 It does not readily combine with sulphur, but the sulphide 
 is obtained by heating the oxide with sulphur, and by projecting 
 a mixture of zinc-powder and sulphur into a red-hot crucible, 
 ZnS being formed. This sulphide is practically infusible, and 
 on roasting behaves like copper and lead sulphides, sulphur 
 dioxide is evolved, and sulphate and oxide of zinc formed. A 
 higher temperature is required to decompose zinc sulphate than 
 is required for silver sulphate. Zinc sulphide is sometimes re- 
 moved from ores by roasting at a low heat, and drenching the 
 roasted mass with water to dissolve out the soluble sulphate of 
 zinc formed. Sulphide of zinc is reduced completely by carbon 
 and iron at high temperature, the zinc being volatilized. 
 
 ZINC ORES. 
 
 Red Zinc Ore Spartalite zincite (ZnO) is generally 
 red, owing to the presence of manganese. It is found associ- 
 ated with franklinite at Franklin, New Jersey. 
 
 Calamine carbonate of zinc (ZnCO 3 ) varies in colour, 
 from white to brown. The brown colour is due to oxide of 
 iron. It is generally of an earthy character. Some specimens 
 are like entwined reeds, hence the name. It occurs in Flint, 
 Somerset, Mendip Hills, Alston Moor in Cumberland, Lead 
 hills in Scotland, Tarnowitz, in Silesia, Rhine Provinces, 
 and Belgium (Aix-la-Chapelle), and in Spain. It usually 
 occurs in limestone rocks, and is associated with the silicate. 
 The Silesian calamines contain as much as 8 per cent, of 
 silicate, and carry from 6 to 45 per cent, of zinc. Blende, 
 galena, and sulphate of lead often accompany calamine. Lead 
 and iron are both objectionable in zinc ores, on account of the 
 corrosion of the retorts at the high temperature employed, by 
 the oxides of those metals. Calamines are carefully dressed 
 to remove lead as completely as possible before smelting. 
 
 Electric Calamine hydrated silicate of zinc is found 
 associated with the carbonate. 
 
 Blende black jack zinc sulphide (ZnS) is the commonest 
 zinc ore. It varies in colour from pale yellow to black, and 
 has a resinous lustre. Pure ZnS is white, and the dark colour 
 of blende is due to iron and other impurities. It is generally 
 
Zinc. 255 
 
 dark-coloured and crystalline. It commonly occurs associated 
 with galena and pyrites, in limestone and other rocks. It is 
 separated by careful dressing. It occurs in North Wales, 
 Derbyshire, Isle of Man, Cumberland, Cornwall, Freiberg, 
 United States, Russia, and many other localities. 
 
 EXTRACTION OF ZINC. 
 
 Zinc is extracted, in the treatment of simple ores, by the 
 reduction of the oxide with carbon or carbonaceous matters, 
 at a temperature above the boiling-point, so that the reduced 
 metal is vapourized. The reduction is conducted in closed 
 retorts, and the zinc vapour is led into condensers outside 
 the furnace, and condensed. The discovery was made by 
 Henckel, in 1721. 
 
 ZnO 4- C = Zn -f CO 
 
 All ores are roasted to convert them into oxides, for 
 although carbonate of zinc would readily reduce without cal- 
 cining, the conversion of the CO 2 expelled from it into CO, 
 would entail a large consumption of carbon, and a large increase 
 in the volume of gas escaping from the condensers, with con- 
 sequent greater loss of zinc. 
 
 ZnCO 3 = ZnO -f CO 2 
 C0 2 + C = 2CO 
 
 Calamines are readily calcined on the bed of a reverberatory 
 furnace, or often by the waste heat from the smelting furnaces. 
 In Silesia, the small ore is treated in reverberatory furnaces, and 
 the lump ore in kilns into which it is charged at the top with a 
 little coal, and withdrawn at the bottom. Care is taken to keep 
 the temperature too low to reduce and volatilize the zinc. 
 
 Blendes are usually calcined in long-bedded furnaces, with 
 depositing flues, and the SO 2 is sometimes used for vitriol 
 manufacture. At Oberhausen, it is used in manufacture of 
 anhydrous sulphurous acid. 
 
 NOTE. It is exceedingly difficult to calcine blendes "sweet," but the 
 little sulphur remaining does not interfere with the reduction of the zinc ; 
 it is present as sulphate, which is decomposed by the higher temperature 
 of reduction, and yields ZnO, which is reduced. 
 
 ZnSO 4 = ZnO + SO 2 + O 
 
256 
 
 Metallurgy. 
 
 The reduction of the calcined ore is effected in closed 
 vessels, crucibles or retorts, connected with suitable condensers. 
 It is important (i) that the condensers should be of ample 
 size, (2) that the exit for the gases should be contracted so 
 as to prevent the oxidation of the zinc distilled off by the 
 entrance of air into the condenser; (3) that the gases in 
 the retorts and condenser should contain as little CO 2 as 
 possible, or oxidation of the reduced metal will occur. To this 
 end a high temperature and excess of carbon are necessary. 
 
 English Process. In this process, introduced by Cham- 
 pion, at Bristol, early in the last century, the zinc ore 
 (calamine) was mixed with carbon, and heated in large fire- 
 clay crucibles, 4 feet high and 2\ wide at the top, having a 
 
 hole in the bottom, to 
 which a sheet-iron pipe, 
 6 inches in diameter, 
 passing through the bot- 
 tom of the furnace into 
 a vault below, was ap- 
 plied. The lids of the 
 pots were cemented on. 
 The zinc vapour de- 
 scended and was con- 
 densed in the tube 
 " Distillation per descen- 
 sum." The method is 
 wasteful, and has been 
 entirely abandoned. 
 
 The Carinthian Pro- 
 cess was somewhat simi- 
 lar, but fire-clay tubes 
 were employed instead 
 of crucibles. The zinc 
 condensed in the lower 
 
 FIG. 89. Belgian Furnace. 
 
 part of the tube which projected through the furnace bottom. 
 The process is not now employed. 
 
 The Belgian Process was introduced in 1810. It is con- 
 ducted in cylindrical or elliptical retorts closed at one end and 
 
Zinc. 
 
 257 
 
 open at the other. They are about 39 inches long, 8 inches 
 in diameter, and are supported at the ends, resting on the back 
 and front walls of the furnace. They are somewhat inclined to 
 the front, the open end being the lower, and are arranged in 
 tiers one above the other. 
 
 Figs. 89, 90 show the arrangement. A (Fig. 89) is the 
 furnace chamber the back wall 
 being vertical, with projecting 
 ledges on which the ends of 
 the cylinders rest. B is the fire- 
 place ; c the flues. The front 
 of the chamber is closed by a 
 cast-iron frame, D, protected on 
 the inner side with fire-brick. 
 Each of the compartments of the 
 frame holds two retorts, which 
 lie with their mouths resting on 
 the framework. Each furnace 
 holds from 40 to 80 of such 
 crucibles, and they are built in 
 blocks of four, back to back, 
 with a common stack. The metal 
 is condensed in fire-clay re- 
 ceivers of the form shown in 
 Fig. 91 ; one of which is adapted 
 to the mouth of each retort. A 
 sheet-iron cone with a small 
 aperture fits on this to condense 
 fume. Before their introduc- 
 tion into the furnace, the retorts 
 are carefully heated to redness. The spaces in the front 
 frame are stopped with clay (cement of ground pots and 
 raw clay), and the temperature 
 gradually raised during 12 hours, 
 the mouths of the crucibles being 
 
 FIG. 91. Condenser with fume 
 lOOSely Stopped With Clay plUgS. condenser attached. 
 
 The charge is a mixture of calcined calamine or blende with 
 carbonaceous matters anthracite or other non-caking coal, 
 
 FIG. 90. Belgian furnace. 
 
258 Metallurgy. 
 
 coke-dust, etc., as finely divided as possible, and slightly 
 moistened. It is introduced by means of a scoop with a long 
 candle. Each crucible receives a charge of from 13 to 27 Ibs., 
 the lower ones, being most strongly heated, receive the heavier 
 charges. 
 
 After charging, the condensers are adapted (resting on 
 a brick) and luted round. As soon as distillation com- 
 mences, the fume-condensers are put on, a wet rag being 
 often applied at the joint to prevent escape. The operation 
 is judged by the flame of carbon monoxide which is ignited, 
 and burns at the small opening at the mouth of the fume- 
 condenser. At first the fumes are brown, and result from the 
 cadmium contained in the ore which distils off first. This is 
 succeeded by the greenish-white characteristic zinc flame, with 
 white fumes, which continues as long as the operation lasts. 
 The metal is scraped out of the condensers, which are hot 
 enough to keep it molten, at intervals; the fume condenser 
 is removed for this purpose. The distillation occupies about 
 12 hours. When completed, the residues are raked out of the 
 retorts into the pit below, and recharging commences. 
 
 The yield of zinc by this process from ore containing 50 
 per cent, varies from 30 to 40 per cent. About one-half the 
 remainder is recovered from the residue (fume, etc., caught 
 in the fume-condenser), and the rest is lost, mainly as vapour, 
 partly due to imperfect condensation and partly to cracked 
 retorts, etc. 
 
 The fume is of course returned to the retorts for reduction. 
 
 The zinc is received from the condensers by a large iron 
 ladle, and, after skimming, is cast into ingots. Gas firing has 
 now become common. 
 
 Silesian Process. The retorts employed in this process 
 are Q-shaped, and are supported throughout their length, 
 thus permitting of the employment of a more intense heat 
 without collapsing. They are about 39 inches long, 8 wide, 
 and 12 to 1 8 inches high. One end of the muffle is closed. 
 At the other end an opening at the top is provided for adapting 
 the condenser, and another below for introducing the charge. 
 This is, when working, closed by a flat fire-clay stopping. 
 
Zinc. 259 
 
 The furnace is shown in Figs. 92, 93. It is divided into 
 a series of bays on either side of the fireplace, each capable of 
 containing two muffles, which rest on the bed, and are thus 
 heated only on the crown and sides. The roof is dome-shaped. 
 The ends of the retorts project through the side-walls of the 
 furnace into a small outer chamber. From 12 to 32 muffles 
 are contained in a furnace. The condenser is shown in Fig. 93, 
 the metal flowing into a receptacle at b. An opening, q, at the 
 bend, which is covered by a plate luted on during the distil- 
 lation, is provided for removing obstructions. 
 
 This form of condenser has been largely superseded by that 
 shown in Fig. 91, capped by fume-condensers, as in the Belgian 
 process. 
 
 The operation lasts 24 hours, and the charge varies from 
 200 to 500 Ibs. per muffle. The muffles last about 4 or 5 
 
 FIG. 92. 
 
 weeks. Cracks are stopped with a wash of clay applied by a 
 mop. 
 
 The loss of zinc in this process is somewhat greater than in 
 the Belgian (though the residues contain less zinc), owing to 
 greater leakage by cracking of the retorts. 
 
 Furnaces with a double row of muffles, one above the 
 other, are employed at Freiberg and elsewhere, 64 muffles being 
 sometimes used in a furnace of this kind. 
 
 Gas firing is now superseding the use of solid fuel. The 
 type of furnace used is one in which the producer is attached 
 to the furnace, the gas passing directly into the furnace 
 
2(X> 
 
 Metallurgy. 
 
 chamber, or into a small combustion chamber, prior to 
 entering the furnace. The air supplied for its combustion is 
 heated by circulating through flues under the bed, heated by 
 the waste heat from the furnace. Chambers for the calcination 
 of calamine and the preliminary heating of muffles are also some- 
 
 Fio. 93. /, muffles ; y, charging door ; p, condenser ', b, receptacle for zinc ; ft, 
 place ; x, vaults. 
 
 fire- 
 
 times arranged to be heated by waste gases from the furnace. 
 
 Furnaces in which both Belgian and Silesian retorts are 
 employed are also in use. The Silesian muffles occupy the 
 lower part of the furnace, and the Belgian retorts are placed 
 above. The more refractory ores Ire treated in the Silesian 
 muffles. 
 
 Crude zinc contains iron, sulphur, arsenic, cadmium, and 
 lead. The lead is volatilized and carried over in the distillation, 
 as much as 4 per cent, being sometimes present. This is 
 removed by fusion in a reverberatory furnace having a well 
 at the lowest point of its inclined bed. The lead separates 
 out and falls to the bottom of the well, and the zinc is ladled 
 
Zinc. 2 f I 
 
 out. It still retains a little lead. Redistilled zinc contains 
 about 0*2 per cent. Zinc for rolling is thus treated, as more 
 than i per cent, seriously impairs its malleability. 
 
 Treatment of Zinc Fume. The zinc fume which collects 
 in the fume-condenser consists of oxide of zinc and finely 
 divided metal. It is returned to the retorts and redistilled 
 with carbon, or treated by the Montefiore process. 
 
 In this process the zinc-dust and oxide are placed in upright 
 clay tubes, the ends of which pass through the bottom of the 
 furnace. They are heated to 500 or more, and the finely 
 divided zinc caused to run together by compression with a clay 
 piston attached to an iron bar introduced into the *tube. In 
 from 2 to 3 hours the clay stopping at the bottom of the tube 
 is pierced, and the collected metal flows out. The contents 
 of the tube are again stirred up and compressed, and a second 
 flow of metal obtained. As much as 80 per cent, of the zinc 
 in the fume is thus obtained. 
 
 Blast-furnace Methods. Proposals have been made for 
 the reduction and volatilization of zinc in blast furnaces, the 
 metal being obtained by arranging a series of condensing flues. 
 The large volume of escaping gases which would render its 
 complete deposition almost impossible, the oxidation by air 
 and carbonic acid gas in the escaping gases which are, of 
 course, mixed with the zinc vapour and many other reasons 
 render this matter one of the greatest difficulty. In the most 
 feasible methods the gases from the furnace are led through 
 heated chambers or towers containing coke at high tempera- 
 ture, whereby CO 2 is reduced to CO, and any zinc oxidized 
 again reduced. The metal is then obtained in condensing 
 pipes kept hot enough to melt the zinc. 
 
 WET METHODS OF EXTRACTION. 
 
 Many wet methods have been proposed for the treatment 
 of complex ores containing large amounts of iron, copper, and 
 lead, which cannot be roasted and treated in the ordinary 
 manner, owing to rapid corrosion of the retorts. The zinc, 
 having been obtained in a soluble form, is precipitated as 
 oxide by lime, and reduced, or the solution electrolised. 
 
262 Metallurgy. 
 
 CHAPTER XIX. 
 NICKEL. 
 
 THIS white, hard metal is used to a considerable extent, on account of 
 its resistance to atmospheric action and its whitening effect on copper in 
 the manufacture of German silver. It is also alloyed with steel. It is 
 malleable, ductile, tenacious, and weldable ; fuses at about the same 
 temperature as iron, and is affected in the same way by the same impurities 
 as that metal. Its specific gravity is 8'8, and, like iron, it is magnetic. It 
 oxidizes when strongly heated, and combines readily with sulphur and 
 arsenic, and is soluble in acids. It is found with iron in meteorites. In 
 nature it occurs principally in combination with arsenic and sulphur, or 
 as a hydrated silicate. 
 
 ArsenicaJ ores are concentrated much as in copper smelting for the 
 production of a spdss. 
 
 The process of extraction from speiss is essentially a chemical process, 
 the nickel being obtained as oxide. This is mixed with lampblack and 
 oil, the mixture compressed and strongly heated. The oxide is reduced 
 by the carbon. 
 
 The silicate is run down in small cupolas with gypsum (sulphate of 
 lime) or alkali waste (calcium sulphide) ; a matte of nickel and iron sulphide 
 is obtained. The iron is removed as in copper smelting, and the pure 
 sulphide obtained is roasted to oxide and reduced as before. ^ 
 
 The formation of a compound of nickel with carbon monoxide (Ni(CO) 4 ), 
 when CO is passed over freshly reduced oxide of nickel, is the basis of a 
 new process for obtaining the metal. The nickel carbonyl is decomposed 
 by passing its vapour through strongly heated tubes, when the metal is 
 deposited on the sides. 
 
 Nickel is rendered malleable by the addition of small quantities of 
 magnesium or manganese. 
 
 COBALT. 
 
 The principal uses of this metal are for colouring glass and glazes for 
 earthenware. Its oxide gives a fine blue colour to glass. Its use in the 
 metallic state is very limited. It is harder and more tenacious than iron, 
 and is used to some extent for electroplating as superior "nickel" plate, 
 and in alloy, for increasing the elasticity of bronzes. Its properties are 
 similar to those of nickel and iron. 
 
 MANGANESE. 
 
 This metal has no application in the arts, except in alloy with other 
 metals. It is a hard metal, and takes a fine polish. Its colour is white. 
 It oxidizes quickly in moist air, and is dissolved by acids. Its affinity for 
 oxygen is so great that the oxide is not reduced to metal when heated in 
 hydrogen or carbon monoxide, only manganese protoxide being produced. 
 The oxide is reduced when heated with carbon. The metal is also pro- 
 duced by the reduction of the chloride, in admixture with potassium 
 chloride, by metallic magnesium or sodium in crucibles. It readily takes 
 up carbon and silicon. 
 
Nickel. 263 
 
 Rich alloys with iron, for use in steel making, are produced in the 
 blast-furnace by smelting ores containing oxide of manganese, such as the 
 Spanish manganiferous hematites. 
 
 It is also used in the manufacture of bronzes. 
 
 CHROMIUM. 
 
 This metal is only used in alloy, generally in steel, on which it confers 
 increased elasticity and hardness. Pure chromium is more infusible than 
 platinum, and is as hard as emery. It is permanent in air, and may be 
 heated to redness without oxidation. 
 
 The metal is obtained by reduction of the oxide at high temperature 
 with carbon in lime crucibles, by electrolysis of the double chloride of 
 chromium and ammonium, or by fusion of the sesqui- chloride with zinc or 
 magnesium, the excess of zinc being afterwards removed by acid. Chro- 
 mium is unattacked by nitric acid, but dissolves in sulphuric and hydro- 
 chloric acids. 
 
 MAGNESIUM. 
 
 This is a brilliant silver-white metal, which, however, rapidly tarnishes 
 in moist air. Its specific gravity is only 1*74. It is highly tenacious, 
 about 14-5 tons per square inch. It fuses at about 800 C., and at a high 
 temperature can be vapourized and distilled, like zinc. It burns in air 
 with a brilliant white light, and is used for photographic purposes. 
 Heated to 450 C. it can be worked, rolled, and pressed readily, giving 
 forms of great exactness and sharpness. 
 
 It is malleable, but not ductile, except at elevated temperatures. 
 Magnesium wire is made by squirting the metal, in a heated state, through 
 holes in a steel plate. The ribbon is made by flattening the wire in 
 heated rolls. 
 
 Minerals containing magnesium are abundant : magnesite, the car- 
 bonate (MgCO 3 ) ; dolomite (CaCO 3 MgCO 3 ) ; carnallite (MgCl 2 .KC1.6H 2 O), 
 kainit (MgSO 4 .KC1.6H 2 O) and Kieserite (MgSO 4 H 2 O) occur at Stassfurth. 
 
 The metal is prepared by decomposing a mixture of magnesium chlo- 
 ride mixed with sodium or potassium chloride, by metallic sodium, equal to 
 \ or \ of its weight, in iron crucibles heated to redness. The resulting chloride 
 of sodium is dissolved in water, and the magnesium purified by distillation 
 in a wrought-iron still, provided with a lid secured by a screw. The still 
 is connected by a tube which passes nearly to the cover, with an iron 
 condenser beneath. The air is removed by a current of coal gas, befoje 
 heating up the still. The metal is remelted and cast into ingots. 
 
 The metal may also be produced by electrolysis of the fused chlorides. 
 (See Aluminium.) 
 
 ALUMINIUM. 
 
 This metal, although fairly hard, is characterized by its extreme light- 
 ness. Its specific gravity when cast is only 2*56, which on rolling is 
 increased to 2 '68. It is highly malleable and ductile. Its tenacity is 
 about 17 tons per square inch, and its elasticity is about equal to that of 
 silver. At about 700 C. it melts, and contracts on solidifying. 
 
 In mass, it is unalterable in dry or moist air, at any temperature, but 
 when finely divided, takes fire and burns on heating, forming the oxide 
 A1 2 O 3 , which is not reducible by carbon at furnace temperatures. 
 
264 
 
 Metallurgy. 
 
 It was formerly obtained by decomposing the double chloride of sodium 
 and aluminium with metallic sodium. In the methods now followed for its 
 extraction, the melted fluoride, or oxide, is decomposed by an electric current, 
 the metal being liberated, as in the Covvles, Hall, and Heroult processes. 
 
 PLATINUM 
 
 Is a silvery or tin-white metal, almost as hard as copper. It is exceed- 
 ingly malleable and ductile, being only inferior to gold and silver in these 
 respects. Its specific gravity is 21-5. It is only fusible at the highest 
 temperatures, e.g. in the oxy-hydrogen blow-pipe flame. It occludes 
 
 oxygen like silver when molten. At 
 a red heat it occludes nearly 4 times 
 its volume of hydrogen. Its ex- 
 pansion by heat is 0^0000264 per 
 degree, and is nearly equal to that 
 of glass, 00000258. Wires can, 
 therefore, be fused into glass with- 
 out risk of breaking away a point 
 of great importance in the manu- 
 facture of electric lamps, etc. It 
 welds when strongly heated. 
 
 Owin? to its not being readily 
 attacked by acids or chemical re- 
 agents, it is largely used for making 
 chemical vessels, such as crucibles 
 and dishes, stills for concentrating 
 vitriol, parting, etc. 
 
 It occurs native, in grains in 
 alluvial deposits, and associated with 
 the rare metals, rhodium, osmium, 
 iridium, ruthenium, rubidium. After 
 chemical treatment, it is finally ob- 
 tained as the double chloride of 
 ammonium and platinum. This is 
 FIG. 94 .-Lime furnace for fusion of platinum, decomposed by heat, leaving finely 
 
 divided, spongy platinum, which is 
 
 fused by an oxy-hydrogen jet in a small furnace made of blocks of lime 
 ( Fig. 94) ; or the ore is smelted with galena, and the lead obtained cupelled. 
 
 ANTIMONY. 
 
 This metal has a bluish-white colour, and is highly crystalline and 
 brittle. The surface exhibits fern-like markings. It has a specific gravity 
 of 67 to 6'8, melts at about 450 C., and slowly volatilizes at a white 
 heat. It expands slightly on solidifying, a property which it imparts 
 to its alloys. 
 
 Its principal use is for hardening alloys of lead and tin, and it forms 
 a constituent of type, stereotype, and Britannia metals. 
 
 Antimony occurs in nature principally as the sulphide stibnite 
 (Sb 2 S 3 ) from which it is obtained by heating with iron, in crucibles. 
 
 Sb 2 S 3 + 3Fe = sFeS + Sb 2 
 
 The crude metal is subsequently refined. The excess of iron is removed 
 by heating the crude metal with more stibnite and fluxes, and "starred." 
 
Nickel. 265 
 
 BISMUTH. 
 
 This is a highly crystalline, brittle metal, of a white colour with a tinge 
 of pink. Its specific gravity is 9'82. It melts at 268 C., and volatilizes 
 at high temperatures. The vapour burns with a bluish flame. It expands 
 on solidifying. 
 
 Its principal use is for adding to alloys of lead and tin whose melting- 
 point it lowers for making "quick" solders for pewter, and fusible 
 alloys (see p. 269). 
 
 It occurs native and as sulphide. The metal is simply liquated out of 
 the ores in which it is native, and the sulphide is decomposed by iron, 
 sodium carbonate being used as a flux. A considerable quantity of bismuth 
 is extracted from the cupels used for cupelling rich silver lead alloys. 
 
 CADMIUM. 
 
 Cadmium is closely allied to zinc, with which metal it is generally 
 found associated. It is more volatile than zinc, and in the distillation of 
 rhat metal comes over first. The vapour burns in air, giving brown fumes 
 of cadmium oxide, CdO. 
 
 CHAPTER XX. 
 ALLOYS. 
 
 METALS are frequently mixed with each other for the purpose 
 of modifying their properties in order to fit them for special 
 applications. The principal objects are: (i) to harden; (2) 
 to increase the strength, toughness, elasticity, or power of 
 elongation ; (3) to facilitate the production of sound and 
 workable castings; (4) to lower the melting-point; (5) to 
 modify the colour or structure ; (6) to resist corrosion. 
 
 Thus gold is hardened for coinage and other purposes by the addition 
 of copper and silver and occasionally zinc and other metals. Silver by 
 copper, and so on. Copper is hardened by zinc, and its colour altered to 
 yellow shades, in the various forms of brass. In gun-metal its strength ' is 
 increased by the addition of tin ; its elasticity, strength, and power of 
 elongation by nickel ; while addition of zinc, etc., increases the soundness 
 of the castings obtained. 
 
 Speaking generally, the alloying of one metal with another lowers the 
 melting-point of the less fusible, and sometimes reduces it below that of 
 the more fusible constituent. 
 
 The introduction of zinc and aluminium into copper to produce imita- 
 tion gold alloys, and of nickel into brass to produce " nickel " silver alloys, 
 are instances of modified colour. 
 
 The following list gives the metals in the order in which they affect 
 
 1 In the cast state. 
 
266 Metallurgy 
 
 the colour of the alloy into which they enter, each metal producing a 
 greater effect than that following it : 
 
 1. Tin 4. Manganese 7. Zinc 10. Silver 
 
 2. Nickel 5. Iron 8. Lead n. Gold 
 
 3. Aluminium 6. Copper 9. Platinum 
 
 Thus an alloy of I part tin and 2 parts copper is white, but nearly 
 2 parts of zinc must be added to I of copper to whiten it. Most metals 
 alloy together when melted, but many have a tendency to separate while 
 cooling, owing to the difference in specific gravities. In the production 
 of castings where this tendency is manifested, the alloy should be poured 
 at as low a temperature as possible while ensuring the rilling of the 
 mould. The specific gravity of alloys often differs somewhat from that 
 of the mean of the constituents, being sometimes above and sometimes 
 below. 
 
 Heat is frequently evolved by the combination of metals. The tendency 
 of metals to alloy with each other varies greatly ; thus, copper and zinc alloy 
 well in all proportions ; of the copper-tin alloys, those represented by the 
 formulae Cu s Sn, Cu 4 Sn, Cu 7 Sn, are the only ones that show no tendency 
 to liquate, while the copper-lead alloys can be almost completely separated 
 by liquation (see Silver, p. 228) ; similarly lead and zinc do not alloy 
 (p. 198). The liquation of an alloy causes it to solidify piecemeal. 
 Definite alloys separate at different temperatures throughout the mass, 
 before complete solidification of the whole takes place. This can often be 
 made apparent by etching the surface with acid. 
 
 The purity of the metals employed is of great importance, since minute 
 quantities of impurity frequently exert a marked influence on the properties, 
 0*2 per cent, of bismuth in copper, used for alloying with gold for coinage, 
 destroys the malleability to such an extent as to unfit it for that purpose. 1 
 
 Production of Alloys. (i) by fusing the metals together, or mixing 
 them in the molten state ; (2) by compression of the finely divided metals 
 (p. 177) ; (3) by electro deposition. 
 
 In making alloys, the metals, if not volatile and their fusing-points 
 not too widely apart, may be melted together ; but if, as in the case of the 
 copper-tin alloys, one metal is much more readily fusible, it is best added 
 after fusion of the other has been effected. 
 
 When one of the metals is volatile, as in the copper-zinc alloys, the 
 volatile metal should be added at as low a temperature as possible after 
 fusion of the copper, in successive portions, each being kept below the 
 surface till melted. In this way it is taken up by the copper as it melts, 
 and is less readily volatilized. The first portions added lower the 
 melting-point, and also cool the mass by absorption of heat in melting. 
 Less loss of zinc occurs in this way. The mixture should be stirred. 
 Oxidation should be prevented during melting by a covering of coke or 
 other carbonaceous body. 
 
 Copper-Zinc Alloys. These are commonly known as 
 brass, but alloys containing tin also, are often thus designated. 
 The zinc hardens the copper, causes it to cast sounder, and 
 diminishes the toughness so as to permit of more easy working. 
 
 1 Roberts-Austen, S. and A. Join , 1888. 
 
A Hoys. 
 
 267 
 
 The alloys are strong, and many of them are malleable. Lead 
 diminishes the strength. Brass seldom consists merely of 
 copper and zinc; iron, lead, etc., are often added for special 
 purposes. 
 
 TABLE OF COPPER-ZINC ALLOYS. 
 
 Copper. 
 
 Zinc. 
 
 Tin. 
 
 Iron. 
 
 Properties. 
 
 Description. 
 
 55-60 
 
 38-44 
 
 *'5-4 
 
 Strong as mild steel, 
 
 Aich, Delta, and 
 
 
 
 
 highly elastic, less mal- 
 
 Sterro metal. 
 
 
 
 
 leable than other alloys. 
 
 
 83 
 
 17 
 
 
 
 Softer than most alloys. 
 
 Red brass, tenacity 
 
 
 
 
 
 
 14*5 tons. 
 
 72 
 
 28 
 
 
 Malleable, ductile ; rolls 
 
 Best brass, Bristol 
 
 
 
 
 well ; bright yellow 
 
 sheet. 
 
 
 
 
 colour. 
 
 
 66-6 
 
 33'3 
 
 
 
 Casts and works well. 
 
 Ordinary English 
 
 
 
 
 
 
 brass. 
 
 60 
 
 40 
 
 
 
 Rolls well hot ; resists 
 
 Muntz or yellow 
 
 
 
 
 
 corrosion. 
 
 metal for sheath- 
 
 
 
 
 
 ings. 
 
 50 
 
 50 
 
 
 
 Yellow, unsuitable for 
 
 Common brass and 
 
 
 
 
 
 rolling and drawing. 
 
 brazing spelter. 
 
 66-73 
 
 27-34 
 
 
 
 Yellow, suitable for roll- 
 
 Pinwire brass. 
 
 
 
 
 
 ing and wire-drawing ; 
 
 
 
 
 
 
 very malleable and 
 
 
 
 
 
 
 ductile. 
 
 
 80-84' 
 
 15-20 
 
 
 
 Highly malleable yellow 
 
 Dutch, Bath, or 
 
 
 
 
 
 alloys. 
 
 gilding metal. 
 
 
 
 
 
 
 Oreide gold. 
 
 75 
 
 20-25 
 
 o-5 
 
 
 Yellow, malleable j suit- 
 
 Mannheim, or Mo- 
 
 
 
 
 
 able for stamped work. 
 
 saic gold, Similor, 
 
 
 
 
 
 
 Princes metal. 
 
 20-47 
 
 53-80 
 
 
 
 Brittle, but will bear ' White brass ; imi- 
 
 
 
 
 
 slight pressure. 
 
 tation platinum. 
 
 "Tombac" is a name given to alloys ranging from nearly 
 pure copper to 30 per cent of zinc. 
 
 ENGINEER'S BRASS. 
 
 This generally contains tin in addition to copper and zinc. 
 Its composition varies from 75 to 90 per cent, copper, 2 to 
 1 6 per cent, of tin, and from 2 to 20 per cent, of zinc. It is 
 tougher and stronger than ordinary brass. 
 1 Tin sometimes added. 
 
263 
 
 Metallurgy 
 
 TABLE OF COPPER-TIN ALLOYS. 
 
 Copper. 
 
 Tin. 
 
 Zinc. 
 
 Lead. 
 
 Properties. 
 
 Description. 
 
 90 
 
 IO 
 
 
 
 Very tough, finely granu- 
 
 Gun metal. 
 
 
 
 
 
 lar, yellowish grey frac- 
 
 
 
 
 
 
 ture, tenacious ( 1 8 tons). 
 
 
 75-80 
 
 20-25 
 
 
 
 Hard, sonorous, brittle, 
 
 Bell metal. 
 
 
 
 
 
 homogeneous, granular. 
 
 
 95 
 
 4 
 
 I 
 
 
 
 Coinage bronze. 
 
 82-92 
 
 2-6 
 
 3-8 
 
 0-3 
 
 
 Statuary bronze. 
 
 66-6 
 
 33'3 
 
 
 
 Hard, brittle, silver white, 
 
 Speculum metal ; 
 
 
 
 
 
 conchoidal fracture, 
 
 zinc, nickel, silver, 
 
 
 
 
 
 takes a high polish, and 
 
 and arsenic are 
 
 
 
 
 
 is used for reflectors, 
 
 sometimes added. 
 
 
 
 
 
 etc. 
 
 
 
 
 
 
 
 
 Copper- Antimony Alloys. These metals alloy well. The 
 alloy of equal parts of the two metals has a fine violet colour. 
 It is hard, crystalline, and very brittle, and has no application 
 in the arts. It is known as " Regulus of Venus." Antimony 
 is sometimes mixed with brass to resist action of acids. 
 
 Tin, Lead, Antimony, and Zinc Alloys. These comprise 
 the soft solders, type metals, stereotype metals, pewters, etc. 
 
 Tin. 
 
 Lead. 
 
 Zinc. 
 
 Anti- 
 mony. 
 
 Properties. 
 
 Description. 
 
 II 
 
 
 i 
 
 
 Very malleable and white. 
 
 Spurious silver leaf. 
 
 5 
 
 
 So 
 
 
 Casts well, fairly hard. 
 
 Pattern alloy. 
 
 45 
 
 IO 
 
 45 
 
 
 Casts well and works 
 
 For small orna- 
 
 
 
 
 
 easily under graver. 
 
 ments. 
 
 3 
 
 I 
 
 
 
 Hard and tenacious. 
 
 Fine solder. 
 
 2 
 
 I 
 
 
 
 Lowest melting-point of 
 
 Fine solder. 
 
 
 
 
 
 series. 
 
 
 I 
 
 I 
 
 
 
 
 Tinman's solder. 
 
 I 
 
 2 
 
 
 
 Like most others of the 
 
 Plumber's metal. 
 
 
 
 
 
 series becomes plastic 
 
 
 
 
 Cu 
 
 
 before solidifying. 
 
 
 75-94 
 
 0-8 
 
 1-9 
 
 5-25 
 
 White, rolls and works 
 
 Britannia metal, for 
 
 
 80 
 
 
 2O 
 
 well. 
 Expands on cooling. 
 
 spoons and plate. 
 Type metal. 
 
 20 
 
 60 
 
 
 20 
 
 Lower melting point. 
 
 For small type and 
 
 
 
 
 
 Bismuth often added 
 
 stereotype. 
 
 
 
 
 
 to lower melting-point. 
 
 
A Hoys. 
 
 269 
 
 FUSIBLE METALS AND ALLOYS. 
 
 Tin, Lead, Bismuth Alloys, used for fusible plugs and 
 4C quick " solders for pewter, etc. 
 
 Tin. 
 
 Lead 
 
 Bismuth. 
 
 Cadmium. 
 
 Melting-point. 
 
 Uses and Remarks. 
 
 2O 
 
 30 
 
 50 
 
 
 197 F. 
 
 For fusible plugs, taking 
 
 I2-.S 
 
 25 
 
 5 I2'5 
 
 150 F. 
 
 impressions of dies, etc. 
 
 
 
 
 
 
 Expands on cooling. 
 
 58-8 
 
 29-4 
 
 n-8 
 
 
 
 Pewterer's solder has a 
 
 
 
 
 
 
 lower melting-point than 
 work to be soldered. 
 
 
 
 
 
 
 GOLD, SILVER, AND PLATINUM ALLOYS. 
 
 Gold. 
 
 Silver. 
 
 Platinum. 
 
 Copper. 
 
 Zinc. 
 
 Description. 
 
 
 92-5 
 
 
 7'5 
 
 
 English standard silver. 
 
 
 90 
 
 
 10 
 
 
 French and German coinage. 
 
 
 75 
 
 
 25 
 
 
 German silver plate. 
 
 
 91-66 
 
 
 8-34 
 
 
 Indian rupee, Brazilian coin. 
 
 
 94*5 
 
 
 5 '5 
 
 
 Netherlands coin. 
 
 
 66-6 
 
 
 22'2 
 
 Ill 
 
 Silver solder. 
 
 91-66 
 
 
 
 8-33 
 
 
 British, Turkish, Brazilian gold 
 
 ; 
 
 
 
 
 
 coin. 
 
 9S'9 
 
 
 
 ri 
 
 
 Hungarian ducat. 
 
 90 
 
 
 
 10 
 
 
 German, French, Italian, Belgian, 
 
 
 
 
 
 
 Spanish, United States, Swiss, 
 
 
 
 
 
 
 and Russian gold coins. 
 
 10 
 
 6 
 
 
 4 
 
 
 Gold solder. 
 
 
 65-83 
 
 17-35 
 
 
 
 Dental alloys. 
 
 See also p. 209 and 244. 
 
 ALUMINIUM AND MANGANESE BRONZES. 
 
 Aluminium Bronze. The proportion of aluminium alloyed with the 
 copper varies from I to 10 per cent. The alloys are as strong as mild 
 steel, highly malleable, elastic and ductile. The presence of other metals 
 impairs its quality. An alloy containing 10 per cent, has a tensile 
 strength of 40 to 45 tons per square inch. 
 
 Manganese Bronzes contain copper, manganese, zinc, and tin. Some- 
 times they are characterized by hardness, elasticity and strength combined 
 with toughness and resistance to corrosion. They can be rolled and forged 
 hot. An important application is for the propellers of steam-ships. It 
 is also used for general engineering brass work. The manganese is 
 .generally introduced in the form of ferro-manganese. 
 
2/0 
 
 Metallurgy. 
 
 Phosphor Bronze is a bronze containing a small proportion of phosphorus, 
 introduced either as phosphor tin (obtained by dissolving phosphorus in 
 molten tin ; it contains up to 20 per cent, of phosphorus) or phosphor 
 copper, after fusion of the ordinary ingredients. The tin varies from 4 to 
 lo per cent., and the phosphorus from O'l to I. Where toughness and 
 ductility are required, the phosphorus should not exceed o'l. Metals 
 containing more, increase in hardness and are used for valves, bushes, cog- 
 wheels, etc. It should be cast at as low a temperature as possible. 
 
 Silicon bronze contains silicon. It is harder and stronger than ordi- 
 nary bronze. 
 
 The beneficial effects of phosphorus and silicon are generally attributed 
 to the powerful deoxidizing influence they exert on account of their affinity 
 for oxygen. 
 
 NICKEL ALLOYS. 
 
 Nickel. 
 
 Copper. 
 
 Zinc. 
 
 Iron. 
 
 Tin. 
 
 Description. 
 
 I4-3I-5 
 
 40-56 
 
 23-26 
 
 2'3\ 
 
 3'5J 
 
 0-4 
 
 Arguizoid, Chinese white copper. 
 
 IS 
 
 60 
 
 25 
 
 
 
 Common German silver. 
 
 21 
 
 S6 
 
 23 
 
 
 
 Medium ,, ,, 
 
 25 
 28-3 
 
 
 
 25 
 
 33'3 
 
 
 
 Good 
 Best 
 
 20 
 
 80 
 
 
 
 
 Cupro-nickel. 
 
 These alloys are white in colour, tough, and malleable. 
 For rolling, a little lead is often added. The last is used as a 
 sheath for the bullets of rifles, being hard and very suitable for 
 drawing. 
 
 AMALGAMS. (See MERCURY.) 
 
 Amalgams of tin and mercury, and mercury with cadmium, 
 are employed for filling teeth. These amalgams become 
 plastic by pounding or kneading when slightly warmed as in 
 the hand, but set hard without contraction. A copper 
 amalgam was formerly much employed, but it requires stronger 
 heat to make it plastic. The alloy on the backs of looking- 
 glasses contains 80 per cent, of tin and 20 of mercury 
 (see Mercury). Sodium amalgam is produced by adding 
 sodium to mercury ; the combination causes great evolution of 
 heat It is prepared in considerable quantities for export. 
 For this purpose it is packed in lime, to prevent access of 
 moisture or carbon dioxide, in metal-lined cases. The 
 
Alloys. 271 
 
 amalgam contains about 3 per cent, of sodium, and is 
 tolerably hard and semi-crystalline. 
 
 IRON ALLOYS. 
 
 Nickel Steel. Nickel steel is being largely used for armour- 
 plates. Generally from 1*5 to 2 per cent, of nickel is present. 
 It increases the toughness of the metal, and diminishes 
 atmospheric action and the action of sea water. 
 
 " Harveyized," armour plates are nickel-steel plates, case 
 hardened on the surface by heating in contact with animal 
 charcoal after the manner of making blister steel. 
 
 Chrome Steel. This usually contains about i -5 per cent, 
 of chromium. Its presence increases the tenacity and hard- 
 ness without diminishing the toughness, while the metal welds 
 readily. It is used in the manufacture of shell-cases. 
 
 Tungsten Steel. Mushet's special steel is a self-hardening 
 tool steel, containing up to 9 per cent, of tungsten. It is 
 extremely hard and strong, breaks with a conchoidal fracture, 
 which has a faintly yellowish or brownish tinge. 
 
 Molybdenum is being introduced for the same purpose, a 
 smaller quantity producing similar results. 
 
 Aluminium is added to steel to produce sound castings. 
 The "Mitis" castings owe their superiority to the presence 
 of this metal. 
 
 Manganese Steel. Manganese in excess produces great 
 hardness. The alloy is tough, but almost unforgeable. It 
 contains from 9 to 13 per cent. It is very fluid when molten, 
 and casts soundly. 
 
 Iron and Zinc. Iron dissolves in zinc, heated to nearly 
 its boiling-point to a considerable extent. The iron in delta 
 metal is introduced by saturating molten zinc with iron, and 
 adding this alloy to the copper in sufficient amount. A hard 
 alloy of zinc and iron forms in galvanizing pots, and zinc 
 melted in iron vessels takes up iron. 
 
INDEX 
 
 Aaron process (silver), 213 
 " Acid " linings, 36 
 Advantages of hot blast, 100 
 " After-blow, "the, 153 
 Air reduction processes, 17 
 Alberti furnace, 204 
 Alloys, 4, 265 
 , liquation of, 266 
 
 , production of, 266 
 
 " All mine" pig, 87 
 Alluvial deposits, 231 
 Almaden furnace, 203 
 Aludel furnace, 203 
 Alumina, 38 
 Aluminium, 263 
 
 , in bronze, 269 
 
 , in steel, 271 
 
 Amalgams, 200 
 
 , native, 201 
 
 , treatment of, 218 
 
 Amalgamating pan, 214 
 Amalgamation processes (silver), 
 
 210 
 
 barrel, 212 
 
 floor, 211 
 
 kettle, 214 
 
 pan, 214 
 
 for gold, 233 
 Amalgamator ior tailings, 137 
 American bloom ery, 1 20 
 
 matte, 173 
 
 Ammonia, recovery of, 115 
 Ammoniacal liquor from coke ovens, 
 
 60 
 Analyses of fire clays, 33 
 
 of gaseous fuels, 76 
 
 of pig iron, 112 
 
 of lurnace gases, 114 
 
 Anglesite, 180 
 Annealing, 6, 8 
 
 Anthiacite, 59 
 Antimony, 264 
 
 , alloys, 268 
 
 ores, 264 
 Antimonite, 264 
 Appolt coke oven, 66 
 Arastra, 211 
 Argentite, 210 
 Arsenides, 13 
 Ash of coal, 59 
 -- of coke, 71 
 
 of lignite, 56 
 
 of peat 53 
 
 of wood, 48 
 
 Atacamite, 163 
 Augustin's process, 221 
 Available hydrogen in fuels, 43 
 Azurite, 162 
 
 B 
 
 Barff's process, 83 
 Barrel amalgamation, 212 
 Base silver ores, treatment of, 223 
 "Basic" linings, 36 
 Basic-Bessemer process, 152 
 
 pi g) I53 
 
 Basic open hearth processes (steel), 
 
 157 
 
 Bauxite, 38 
 " Bears," 103 
 Beds. Ore, 13 
 Beehive coke oven, 63 
 Bell metal, 26 
 
 ore, 246 
 
 Belgram process (zinc), 256 
 
 Berdan pan, 237 
 
 Best selected copper, 170 
 
 tap cinder, 127 
 
 Bernardo's welding process, 12 
 Bessemer process, 147 
 pig iron, 151 
 
 T 
 
2 74 
 
 Index. 
 
 Bessemerizing copper mattes, 172 
 
 Bessemer and Siemens process. 
 Combined, 157 
 
 Bismuth, 265 
 
 , alloys of, 269 
 
 Bituminous coal, 56 
 
 Blackband iron ore, 86 
 
 Black tin, 247 
 
 plates, 249 
 
 slag, 187 
 
 Blast, the hot, 99 
 
 furnaces, 25 
 
 furnace used in iron smelting, 9 1 
 
 , the charging of, 97 
 
 charge, the, 99 
 
 , derangements in work- 
 ing, 103 
 
 , tapping of the, 106 
 
 , chemical', reactions in, 
 
 106 
 slag, 113 
 
 , utilization of, 114 
 
 gases, 114 
 
 Blast stoves, hot, 101 
 
 Blende, Zinc, 254 
 
 Blister copper, 168 
 
 , desilverization of, 220, 
 
 228 
 
 Blister steel, 143 
 " Blowing in " of 
 103 
 
 blast furnace, 
 
 out of blast furnace, 103 
 Blue Billy, 87 
 
 metal, 167 
 
 malachite, 162 
 
 Bog-iron ore, 85 
 Bone-ash, 39, 226 
 Borax, 21 
 Bornite, 164 
 Bottom's copper, I/O 
 
 , desilverization of, 222 
 
 Bower's process, 83 
 Brass, 161 
 Brasque, marl, 39 
 Brasqued crucibles, 42 
 Bronze, 161 
 Brown coal, 56 
 
 hematite, 84 
 
 Erunton's calciner, 30 
 Buck plates, staves, etc., 31 
 Buddies, 15 
 Bull dog, 127 
 Bunch. Ore, 13 
 
 Burmese method of smelting iron, 
 119 
 
 Burnt Iron, So 
 Bustling, 127 
 
 Cadmium, 265 
 Caking coal, 58 
 Calamine, 254 
 
 , electric, 254 
 
 Calcination, 18 
 
 Calcining ores and mattes in kilns, 
 
 2 4 
 kilns, 90 
 
 in open heaps, 89 
 
 Calorific power, 43 
 
 , Calculation of, 44 
 
 , Determination of, by 
 
 Thomson's calorimeter, 45 
 
 , Table of, 44 
 
 Cap, Ore, 13 
 
 Carat, 244 
 
 Carbon, Carbide, 79, 138 
 
 , Combined, 78 
 
 , Graphitic, 79 
 
 , Hardening, 79, 138 
 
 in iron, 78 
 
 in organic fuels, 43 
 
 in steel, 139 
 
 , modes of imparting, to iron, 
 
 78 
 
 Carbonates, 13 
 
 , Decomposition by heat, 18 
 
 Case hardening, 147 
 
 Cassiterite, 245 
 
 Cast iron, 109 
 
 , carbon in, 78 
 
 , pipe stoves, 100 
 
 Catalan process, 1 19 
 
 for making steel, 141 
 
 Cazo process (silver), 214 
 
 Cementation process, for making 
 steel, 141 
 
 Cerusite, 180 
 
 Channel furnace (mercury), 204 
 
 Charcoal, 48 
 
 burning, 49 
 
 Charge, Blast lurnace, 98 
 
 Chemical reactions in basic Bes- 
 semer process, 153 
 
 Bessemer process, 151 
 
 blast furnace, 1 06 
 
 (diagram), IIO 
 
 copper smelting, 163, 168 
 
 puddling, 129 
 
 Mexican process (silver), 212 
 
Index. 
 
 275 
 
 Chemical reactions in "Russell" 
 
 process, 224 
 Chequer work, 154 
 Chessylite, 162 
 Chili bar, 173 
 Chilian mill, 211 
 Chilled castings, 116 
 Chlorine in coal, 60 
 Chloride of gold, 230 
 
 - of silver, 208 
 Chlorides, 13 
 
 Chlorinating roasting, 175, 221 
 Chlorination processes (gold), 238 
 Chromium, 263 
 
 Chrome steel, 271 
 Chrysocolla, 162 
 Cinder, 21 
 Cinnabar, 201 
 Classification of coal, 57 
 
 - of pig iron, 109 
 Claudet's process, 222 
 Clay crucibles, 39 
 
 - , Dinas, 33 
 
 - , Fire, 32 
 
 - iron stone, 80 
 Clean slag, 22 
 Coal, 56 
 
 - , Bituminous, 56 
 
 - , Caking, 58 
 
 - , Chlorine in, 60 
 
 - , Free-burning, 58 
 
 - , Gas, 57 
 
 - , Non-caking, 54 
 
 - , Sulphur in, 59 
 
 , Technical examination of, 60 
 
 - , Varieties of, 57 
 
 _ 
 washing, 59 
 
 Coarse metal, 167 
 Cobalt, 262 
 Coining, 10 
 Coke, 60 
 
 - , qualities of, 7 1 
 
 - , sulphur in, 71 
 Coke ovens, 63 * 
 -- , Appolt, 66 
 -- , Beehive, 63 
 -- , Coppee, 67 
 
 - -- , Cox's, 66 
 
 - -- , Jones's, 66 
 -- , Otto- Hoffmann, 70 
 -- , rectangular, 65 
 -- , Simon-Carves, 69 , 
 Coking kilns, 62 
 
 - in heaps, 61 
 
 Coking of non-caking coal, 81 
 Cold-blast iron, in 
 "Cold short" iron, 10 
 Combination by weight, 43 
 Combined carbon, 78 
 Combustion, 42 
 Composition of pig iron, 112 
 
 of slags, 22 
 
 of wrought iron, 136 
 
 Compressed steel, 158 
 Condensation of lead fume, 198 
 
 of mercury, 206 
 
 Conductivity, 12 
 
 of alloys, 12 
 
 Contraction in area of test-piece, 7 
 Converting furnace, 141 
 Coppee coke oven, 67 
 j Copper, 159 
 
 alloys, 267, 268 
 , best selected, 170 
 
 "bottoms," 170 
 
 blister, 168 
 
 "burnt," 1 60 
 
 chemical properties, 160 
 
 "dry," 1 60 
 
 electro refining of, 176 
 
 extraction, 163 
 
 , wet methods of, 173 
 
 glance, 162 
 
 , impurities in, 160 
 
 , naiive, 161 
 
 ores, 161 
 
 , "overpoled," 160 
 
 oxides, 1 60 
 
 , physical properties, 159 
 
 poling, 169 
 
 pyrites, 162 
 
 , reduction process, 1 72 
 
 , direct, 173 
 
 refining, 169 
 
 , separation of silver from, 2 
 
 228 
 
 smelting, 164 
 
 , diagram, 171 
 
 , use of basic bottoms in, 
 
 173 
 
 sulphate, 161 
 
 sulphides, 160 
 
 tough cake, 160 
 
 , varieties of, 176 
 
 Copper, wet methods of, extraction, 
 
 173 
 
 Copper-zinc alloys, 267 
 Copper-zinc, 268 
 Cordurie's process, 197 
 
2 7 6 
 
 Index. 
 
 Cornish process (lead), 184 
 Country rock, 14 
 Cowper's hot-blast stove, 101 
 Cox's coke oven, 66 
 Crocodile squeezer, 131 
 Crown iron, 133 
 Crucibles, brasqued, 42 
 
 , clay, 39 
 
 plumbago or black lead, 40 
 
 salamander, 40 
 
 Crucible cast steel, 144 
 
 making, 41 
 
 Cup-and-cone arrangement, 96 
 
 and funnel arrangement, 97 
 
 Cupels, 226 
 Cupellation, 24, 225 
 
 furnace, 227 
 
 Cupola, foundry, 25 
 
 Cuprite, 162 
 
 Cuprous chloride process (silver), 
 
 213 
 
 Cyanides in blast furnace, 109 
 Cyanide process (gold), 240 
 
 Dank's furnace, 131 
 Dead melting of steel, 147 
 Desilverization of lead, 191 
 
 by zinc, 195 
 
 by copper mattes, 220 
 
 Desulphurization of coke, 72 
 Dinas bricks, 35 
 
 Direct processes for making mal- 
 leable iron, 117 
 
 process (copper), 173 
 
 Disposable hydrogen in fuel, 43 
 Distillation of amalgam, 219 
 
 of Parke's crusts, 197 
 
 Dolomite, 36 
 Dressing ores, 14 
 Dry crushing, 217 
 
 puddling, 130 
 
 Ductility, 8 
 
 E 
 
 Economy of fuel in kilns and blast 
 
 furnaces, 12 
 Effects of heat on conductivity, 12 
 
 on ductility, 8 
 
 on hardness, 3 
 
 on malleability, 9 
 
 on tenacity, 6 
 
 of impurities on conductivity, 
 
 12 
 
 Effects of impurities on hardness, 
 
 2 
 
 on malleability, 9 
 
 on tenacity, 5 
 
 of mechanical treatment on 
 
 hardness, 2 
 
 on specific gravity, 2 
 
 on tenacity, 5 
 
 of weathering on ores, 14 
 
 Elasticity, 6 
 Elastic limit, 7 
 Electro-refining of copper, 176 
 
 of lead, 228 
 
 deposition of zinc, 261 
 
 Electric Calamine, 254 
 
 welding, 1 1 
 
 Elongation, 7 
 Engineer's brass, 267 
 English process (zinc), 256 
 Erubescite, 162 
 " Extra " solution, 224 
 
 Fahl ore, 163, 210 
 Ferric oxide, 82 
 Ferrous oxide, 82 
 
 silicate, 82 
 
 carbonate, 85 
 
 Ferro-manganese, 112 
 
 , use of, 159 
 
 Fillafer's calciner, 90 
 Finery processes (iron), 125 
 Firebricks, 34 
 Fireclay, 32 
 
 , testing of, 34 
 
 Flintshire process of lead-smelting, 
 
 181 
 
 Flowing power, 10 
 Flue cinder, 134 
 Fluorides, 13 
 Fluor spar, 22 
 Fluxes, 20 
 Forge pig iron, in 
 Fossil fuels, 54 
 Foundry cupola, 25, 115 
 Foundry irons, 109 
 Fracture, 3 
 Free-burning coal, 58 
 Free-milling ores, 233 
 Freiberg process (silver), 212 
 : for desilverizing copper. 
 
 22: 
 
 Frue Vanner, 16 
 Fuel, 42 
 
Index. 
 
 277 
 
 Furnaces, classification of, 24 
 Furnace cinder, 21 
 Fusibility, 3 
 
 , table of, 3 
 
 of silicates, 20 
 
 Fusible metals, 269 
 
 G 
 
 Galena, 180 
 
 Galvanized iron, 253 
 
 Gangue, 17 
 
 Canister, 34 
 
 Gas coal, 57 
 
 Gas, blast furnace, 114 
 
 , coal, 60, 76 
 
 , natural, 76 
 
 , producer, 72 
 
 , Siemens', 76 
 
 water, 76 
 
 , Wilson, 76 
 
 Gaseous fuels, table of, 76 
 
 German silver, 270 
 
 Gjers calciner, 90 
 
 Glazy pig iron, 112 
 
 Gold, 229 
 
 alloys, 244, 269 
 
 alluvial deposits and placers, 
 
 231 
 
 chemical properties, 229 
 
 extraction by chlorination pro- 
 cesses, 238 
 
 , float, 232 
 
 , hydraulic mining, 231 
 
 , native, 230 
 
 mills, 234 
 
 panning, 231 
 
 physical properties, 229 
 
 , precipitation of, 230, 238 
 
 , quartz, 233 
 
 , refractory, 233 
 
 , separation of osm iridium, 243 
 
 , of platinum, 243 
 
 r , of silver, 243 
 
 Gold sands, washing of, 232 
 
 smelting with lead, 243 
 
 , toughening brittle, 243 
 
 Gothite, 85 f 
 
 Graphite, 39 
 
 from pig iron, 115 
 
 Graphitic carbon, 79 
 Green lead ore, 180 
 Green malachite, 162 
 Grey copper ore, 163 
 Grey pig iron, 109 
 
 Grey slag (lead), 183 
 "Grog," 33 
 Guide iron, 134 
 
 H 
 
 Hahner's furnace, 203 
 Hall marks, 244 
 Hammer scale, 83 
 
 steam, 132 
 
 Hand picking, 14 
 
 Hardness, 2 
 
 Hardening and tempering steel, 138 
 
 Hard lead, 191 
 
 , softening, 190 
 
 Harveyized armour plates, 271 
 Head's furnace, 75 
 Heaps, coking in, 61 
 
 , calcining in, 89 
 
 Hearths, 24 
 Hearth, Slag, 186 
 Heat of combustion, 43 
 
 , regeneration of, 29, 154 
 
 , unit of, 44 
 
 Helve Hammer, 131 
 
 Hematite, 84 
 
 Henderson's process, 175 
 
 Honey-combining in steel, 146 
 
 Horn silver, 210 
 
 Hot blast, loo 
 
 Hungarian mill, 237 
 
 Huntingdon mill, 236 
 
 Hiittner and Scott's furnace, 205 
 
 Hydrated ores, 13 
 
 Hydraulic mining, 231 
 
 lifts, 98 
 
 Hydrogen in organic fuels, 43 
 
 " Hypo " process (Von Patera), 222 
 
 Idrian furnace, 202 
 Improvements in puddling, 130 
 Impurities in pig iron, 77 
 Inorganic fuels, 42, 43 
 Incomplete combustion of carbon, 
 
 47 
 
 Inquartation, 242 t 
 
 Iron, 76 
 
 alloys, 271 
 
 , burnt, 80 
 
 , carbonate of, 45 
 
 , cold blast, 1 1 1 
 
 , forms of, 77 
 founding, 115 
 
 T 3 
 
278 
 
 Index. 
 
 Iron, malleable, 117 
 
 merchant, 134 
 
 ores, 83 
 
 , calcination of, 89 
 
 , preparation of, 89 
 
 , oxides, 82 
 
 , pig, 109 
 
 pipe stoves, 100 
 
 , properties of, 76 
 
 pyrites, 87 
 
 , reduction process for lead, 
 
 185 
 
 , silicate of, 82 
 
 smelting, 87 
 
 diagram, 105 
 
 and carbon, 77 
 
 and manganese, 80 
 
 and phosphorus, 81 
 
 and silicon, 79 
 
 and sulphur, 80 
 
 and nickel, etc., 82 
 
 Jigging machines, 15 
 
 K 
 
 Kilns, 25 
 
 , coking, 62 
 
 , calcining, 90 
 
 Kish, 115 
 
 Krolinke process (silver), 213 
 
 Lake ores, 85 
 Leaching, 220 
 Lead, 177 
 
 , action of water on, 179 
 
 alloys, 268 
 
 carbonate, 180 
 
 , chemical properties of, 177 
 
 , electro-refining of, 228 
 
 fume, 198 
 
 ores, 1 80 
 
 pipe, 10 
 
 physical properties, 1 77 
 
 smelting, 1 80 
 
 diagram, 198 
 
 in blast furnaces, 185 
 
 softening, 190 
 
 slag, 1 88 
 
 sulphide, 1 79 
 
 -= sulphate, 179 
 
 Lead working, 10 
 Lifts, 97 
 Lignite, 55 
 Lime, 36 
 
 Limit of elasticity, 7 
 Limonite, 84 
 Lining crucibles, 42 
 Liquation, 23 
 
 of alloys, 266 
 
 of lead, 191 
 
 of tin, 248 
 
 Litharge, 177 
 Lixiviation, 220 
 Lixiviating tanks, 224 
 Lodes, mineral, 13 
 Longmaid's process, 1/5 
 Luce and Rozan process, 195 
 
 M 
 
 McArthur- Forest process (gold), 240 
 
 Magnesia, 36 
 
 Magnesite, 36 
 
 Magnesian limestone, 37 
 
 Magnesium, 263 
 
 Magnetite, 83 
 
 Magnetic oxide of iron, 83 
 
 Malleability, 9 
 
 Malleable castings, 117 
 
 iron, 117 
 
 , composition of, 136 
 
 Malachite, 162 
 Manganese, 262 
 
 bronze, 269 
 
 in iron, 80 
 
 in steel, 271 
 
 Mannhes process, 172 
 
 Mansfeldt process, 172 
 
 Marl, 39 
 
 Martin-Siemens process, 156 
 
 Massicot, 178 
 
 Matte, 19 
 
 Mear's process (gold), 239 
 
 " Meiler," coking in, 61 
 
 Merchant iron, 134 
 
 Metallurgical terms and processes, 
 
 12 
 
 Metal furnace, 167 
 
 slag, 1 68 
 
 Method of stating test results, 8 
 Mercury, 199 
 
 , extraction of, 201 
 
 , native, 201 
 
 , ores of, 20 1 
 
Index. 
 
 279 
 
 Mercury, muffle and retort furnaces 
 for, 204 
 
 , purification of, 207 
 
 sulphide, 201 
 
 Mexican amalgamation process, 211 
 Micaceous iron ore, 84 
 Mild steel, 137 
 Mill furnace, 134 
 
 cinder, 134 
 
 Miller's process, 243 
 Minium, 178 
 Mirrors, silvering of, 2OI 
 Modulus of elasticity, 7 
 Moiree metallique, 245 
 Molybdenum in steel, 271 
 Montefiore process, 261 
 Moss copper, 168 
 Mottled iron, in 
 Muffle furnace, 28 
 Mushet steel, 271 
 
 Native metals, 12 
 
 Natural gas, 76 
 
 Newberry-Vautin process (gold), 
 
 239 
 Nickel, 262 
 
 alloys, 270 
 
 carbonyl, 262 
 
 speiss, 262 
 
 steel, 271 
 
 Nitric acid parting, 242 
 Non-caking coal, 54 
 Nuggets, gold, 230 
 
 O 
 
 Oil-hardening steel, 138 
 Open-hearth steel processes, 154 
 Ores, 13 
 Ore dressing, 14 
 
 furnace, 166 
 
 slag, 167 
 
 hearth, the, 188 
 
 Organic fuels, 42 
 Otto-Hoffmann coke oven, 70 
 Outcrop, 13 
 Oxidized ores, 13 
 
 Pan amalgamation, 214 
 Panning out, 231 
 
 Parkes's process, 195 
 
 Parting, 24, 241 
 
 " Patio " amalgamation process. 
 
 211 
 
 Pattinson's process, 191 
 Pattinsonizing by steam, 195 
 Peacock copper ore, 163 
 Peat, 52 
 
 , preparation of, 53 
 
 Pewter, 268 
 Phosphates, 13 
 Phosphor bronze, 270 
 Phosphorus in iron and steel, 81 
 Pig iron, 109 
 
 , basic, 153 
 
 , Bessemer, 151 
 
 , forge, ill 
 
 , foundry, 109 
 
 , boiling, 128 
 
 Piling, 134 
 
 Pilz furnace, iSS 
 
 Pimple metal, 167 
 
 Piping, 147 
 
 Pipe-charging apparatus, 97 
 
 Placers (gold), 231 
 
 Plates, 9 
 
 Plate rolling, 134 
 
 Platinum, 264 
 
 alloys, 269 
 
 , separation from gold, 243 
 
 Plumbago, 39 
 Pneumatic lifts, 98 
 Pockets of ore, 13 
 Pollok process (gold), 239 
 Polybasite, 210 
 Preparation of iron ores, 89 
 Preservation of iron from rust, 83 
 Principles of iron smelting, 87 
 
 of converting pig into malleable 
 
 iron, 121 
 Producer gas, 72 
 Proustite, 210 
 Puddling, 126 
 
 furnace, 126 
 
 Puddle rolls, 133 
 Puddled bar, 133 
 
 steel, 140 
 
 Puddler's mine, 127 
 Pyrargyrite, 210 
 Pyromorphite, 180 
 
 Quicksilver, 199 
 Quick solders, 269 
 
280 
 
 Index. 
 
 R 
 
 Rachette furnace, 188 
 Rack for washing ores, 16 
 Rectangular coking oven, 65 
 Red copper ore, 162 
 
 hematite, 84 
 
 lead, 178 
 
 short, 9 
 
 silver ores, 210 
 
 zinc ore, 254 
 Redruthite, 162 
 Reducing agents, 17 
 Reduction, 17 
 Reefs, 13 
 
 Refinery for pig iron, 123 
 Refining, 22 
 
 copper, 169 
 
 gold, 241 
 pig iron, 123 
 
 silver, 228 
 
 tin, 248 
 
 Refractory materials, 32 
 Regeneration of heat, 29, 154 
 Regenerative furnaces, 29, 146, 154 
 Regulus, 19 
 
 of Venus, 268 
 
 Reheating furnace, 134 
 Remedies for flouring, 217 
 Removal of sulphur and ai-senic by 
 calcination, 18, 164, 264 
 
 of sulphur from pig iron and 
 
 steel, 125 
 
 of gangue by fluxes, 20 
 
 Retort furnaces, 29, 256 
 Reverberatory furnaces, 27 
 
 gas, 154 
 
 Riffles, 252 
 
 Roasting, 19 
 
 Roaster stage for blister copper, 168 
 
 slag, 169 
 
 Rolls, crushing, 15 
 
 , finishing, 133 
 
 , mill, 134 
 
 , plate, 134 
 
 , puddle, 133 
 
 , roughing, 133 
 
 , three-high, 135 
 
 Rozan process, 195 
 Russell process (silver), 224 
 
 Salt, addition of, in roasting, 175, 
 221 
 
 Sand, 35 
 
 Saniter desulphurizing process, 125 
 
 Scale, hammer, 83 
 
 " Scaffolding,' 103 
 
 Scorification, 23 
 
 Scotch ore hearth, 188 
 
 -tuyere, 95 
 
 Self-fluxing ores, 22 
 
 Setting up, 182 
 
 Settlers, 216 
 
 Shaft furnace (mercury), 205 
 
 Sharp slag, 166 
 
 Shear steel, 144 
 
 Sheet rolling, 135 
 
 Shingling, 131 
 
 hammer, 131 
 
 Shortness, red and cold, 10 
 Siemens-Martin process, 156 
 Siemens' furnace, 154 
 
 gas, 76 
 
 gas producer, 73 
 
 process, 155 
 
 Silesian process (zinc), 258 
 Silica bricks, 35 
 Silicate of iron, 22 
 Silicates, 13, 32 
 Silicon in iron, 79 
 Silico-manganese, 112 
 Siliconeisen, 112 
 Silicon spaegel, 112 
 Silver, 207 
 
 , alloys of, 209 
 
 , chemical properties, 208 
 
 chloride, 208 
 
 electro-refining, 228 
 
 extraction as sulphate, 220 
 
 , frosted, 209 
 
 glance, 210 
 
 nitrate, 209 
 
 ores, 210 
 
 , oxidized, 210 
 
 processes, 210 
 
 , properties of, 207 
 
 , precipitation of, 222 
 
 precipitates, treatment of, 223 
 
 , separation of, from copper 
 
 and mattes, 220 
 , of, from gold, 241 
 
 , spitting of, 208 
 
 , sulphide, 208 
 
 sulphate, 208 
 
 , wet process for extraction of, 
 
 220 
 
 Simon-Carves coke oven, 69 
 Slag, 21, 113 
 
Index. 
 
 281 
 
 Slag, black, 187 
 
 , grey, 183 
 
 hearth, 186 
 
 wool, 114 
 
 Sluice, 232 
 Smelting, 17 
 Soaking furnace, 159 
 
 pit, 158 
 
 Sodium, reduction by, 263 
 
 Sodium carbonate, 21 
 
 Softening hard lead, 190 
 
 Solders, 268 
 
 Spanish ore, 85 
 
 Spathose, 85 
 
 Specific gravity of metals, 2 
 
 -, table of, 2 
 
 Specular iron ore, 84 
 Speculum metal, 268 
 Speiss, 20, 262 
 Spelter, 252 
 Spiegeleisen, 112 
 
 , use of, 159 
 
 Stamp battery, 233 
 Stampings, 10 
 Standard gold, 244 
 
 silver, 209 
 
 Starring, 264 
 
 Statement of results of test, 7 
 Steam hammer, 132 
 Steel, 136 
 
 basic, 152 
 
 Bessemer, 137 
 
 blister, 143 
 castings, 158 
 
 cementation, 141 
 
 crucible cast, 144 
 
 fluid compressed, 158 
 
 hardening and tempering} 
 138 
 
 ingots, treatment of, 158 
 
 making, 140 
 
 mild, 137, 139 
 
 puddled, 140 
 
 shear, 144 
 
 Siemens, 137 
 
 varieties of, 139 
 
 tempering of, 138 
 
 working of, 138 
 Stephanite, 210 
 Stetveldt calciner, 31 
 Stibnite, 264 
 Stone-breaker, 14 
 Stream tin ore, 246 
 Suitability of metals for castings, 4 
 Sulman's process (gold), 241 
 
 Sulphates, production of, by roast- 
 ing sulphides, 18, 161, 181 
 
 Sulphating roasting, 173, 220 
 
 Sulphide ores, 13 
 
 Sulphur in coal, 59 
 
 in coke, 71 
 
 , removal of, from pig iron, 125 
 
 Sulphuretted hydrogen in producer 
 gas, 75 
 
 Sulphuric acid parting, 241 
 
 "Sweep," 243 
 
 Swedish- Lancashire hearth, 125 
 
 Table of calorific powers, 44 
 of conductivity, 12 
 
 of copper-tin alloys, 268 
 
 of copper-zinc alloys, 267 
 
 of ductility, 8 
 
 of fluxes, 21 
 
 of melting-points, 4 
 
 of relative tenacities, 5 
 
 of specific gravity, 2 
 
 Tailings, 233 
 
 , treatment of, 237, 240 
 
 , amalgamator for, 237 
 
 Tap-cinder, 130 
 Tar, 60 
 
 , recoveiy from coke ovens, 69 
 
 Technical examination of coal, 60 
 
 Teeming, 145 
 
 Tempering steel, 138 
 
 Temperature, 47 
 
 Tenacity, 5 
 
 Tenorite, 162 
 
 Test pieces, 6 
 
 Test (cupel), 227 
 
 Testing machines, 6 
 
 of fire clay, 34 
 
 Thomas-Gilchrist process (Basic- 
 Bessemer), 152 
 Thomson's calorimeter, 45 
 
 electric welding process, 1 1 
 
 Three-high rolls, 135 
 Tie rods, 32 
 Tin, 244 
 
 alloys, 268 
 
 bars, 250 
 
 , black, 247 
 
 boiling, 249 
 
 , cry of, 245 
 
 grain, 245 
 
 , impurities in, 
 
 ores, 245 
 
 245 
 
282 
 
 Index. 
 
 Tin oxide, 245 
 
 plate, 249 
 
 pyrites, 246 
 
 , reduction in blast furnaces, 
 
 248 
 refining, 248 
 
 , removal of tungsten from, 
 
 247 
 
 smelting, 246 
 
 stone, 245 
 
 , stream, 246 
 
 Tinning, 250 
 Tough copper, 1 60 
 Toughness, 10 
 Tower calciner, 31 
 Treatment of steel ingots, 158 
 
 of zinc crusts, 197 
 
 Trompe, 120 
 
 Tungsten, removal from tin, 247 
 
 Tungsten steel, 82 
 
 Turf, 52 
 
 Tuyeres, 95 
 
 Type metal, 268 
 
 Types of furnace, 24 
 
 U 
 
 Unit of heat, 44 
 Useful metals, 2 
 
 properties of metals, I 
 
 Utilization of slag, 114 
 
 Varieties of copper, 176 
 
 of steel, 139 
 
 Veins (mineral), 13 
 Veinstuff, 14 
 Volatility of metals, 4 
 Von-Patera process, 222 
 
 W 
 
 Walloon process, 125 
 Washing tables, 16 
 Washoe process (pan amalgama- 
 tion), 214 
 
 Waste heat, regeneration of, 154 
 Water-balance left, 98 
 Water blocks, 28 
 jacketed furnace, 28, 39, 185 
 
 Water gas, 76 
 
 tuyeres, 95 
 
 Weathering of ores, 91 
 Welding, n 
 
 , electric, n 
 
 Welsh finery (iron), 125 
 Welsh process of copper smelting, 
 164 
 
 , modification of, 170 
 
 Wet processes of extracting copper, 
 
 173 
 
 gold, 238 
 
 silver, 220 
 
 zinc, 261 
 
 White lead ore, 180 
 
 metal, 167 
 
 pig iron, 1 1 1 
 
 White- Howell calciner, 30 
 Whit well stove, 103 
 Wilson gas producer, 74 
 Wire-drawing, 8 
 Wolfram, 246 
 Wood, 48 
 
 hematite, 85 
 
 tin, 246 
 
 Wrought iron, 117 
 
 Y 
 
 Yellow copper ore, 162 
 
 ochre, 85 
 
 Young's modulus, 7 
 
 Ziervogel's process, 220 
 Zinc, 252 
 
 alloys, 267, 268 
 
 blende, 254 
 
 carbonate, 254 
 
 , chemical properties, 252 
 
 crusts, treatment of, 197 
 
 fume, 26 
 
 furnaces, gas fired, 259 
 
 ores, 254 
 
 , desilverization of, 224 
 
 , properties of, 252 
 
 silicate, 254 
 
 smelting, 255 
 
 in blast furnaces, 261 
 
 sulphide, 254 
 
 , wet methods of extracting, 261 
 
 PRINTED BY WILLIAM CLOWES AND SpjjjS. IIMITHD LONDON AND BECCLES. 
 
 A 
 
 OF THE 
 
 UNIVERSITY 
 
 OF 
 

UNIVERSITY OF CALIFORNIA LIBRARY 
 
 This feook is DUE on the last date stamped below. 
 
 l""^ ^^Sjf^ 
 ts oa,fii 
 
 
 Fine 
 
 NOV 12 1947 
 
 OEC 18 194? 
 
 LD 21-100m-12,'46(A2012sl6)4120 
 
1 1