REESE LIBRARY OF THK UNIVERSITY OF CALIFORNIA. Received '_ Accessions No._2-0*_C4 Shelf No. METALS AND THEIR CHIEF INDUSTRIAL APPLICATIONS, METALS AND THEIR CHIEF INDUSTRIAL APPLICATIONS, BEING, WITH SOME CONSIDERABLE ADDITIONS, THE SUBSTANCE OF A COURSE OF LECTURES DELIVERED AT THE ROYAL INSTITUTION OF GREAT BRITAIN IN 1877. BY CHARLES R. ALDER WRIGHT, D.Sc., &c., Lecturer on Chemistry in St. Mary's Hospital Medical School. UNIVERSITY: JSTanbon : MACMILLAN AND CO. 1878. [ The Right of Translation and Reproduction is Reserved. ] LONDON : R. CLAY, SONS, AND TAYLOR, PRINTERS, BREAD STREEI HILL, "" CONTENTS. CHAPTER I. METALS AND THEIR NATURAL SOURCES. :,HCT. PAGE 1. Distinction between elements and compounds and be- tween metals and non-metals I 2. List of elements . . 3 3. Metals of greater technical importance .... 4 4. Characteristics of metals ...... 5 5. Native metals and ores : characters of chemical actions involved in metallurgy ...... 7 6. Classification of metal-extracting processes ... 8 7. General chemical characters of metal- extracting processes 1 1 8. Native metals 12 9. Simple ores 13 10. Complex ores . . . . . . . 15 11. Relationships between heat-disturbance and chemical reactions in wet processes . . . . . .16 12. Relationships between laws connecting heat -disturbance and temperature of initial action . . . 17 13. Relationships between laws connecting heat-disturbance and temperature of initial action . . . .21 14. Reciprocal reactions ....... 23 CONTENTS. CHAPTER II. METALLURGY OF THE PRECIOUS OR NOBLE METALS. PAGE SECT. 15. GOLD : Gold- washing 24 1 6. Amalgamation process for working gold quartz . . 27 17. Refining of gold 28 1 8. Wet processes for gold extraction 29 19. SILVER : Extraction by Lead processes ; cupellation . 30 20. Liquation ; Pattmsonage ; Parkes' process . . -35 21. Wet processes for silver-extraction 37 22. Patio process of amalgamation . . . -39 23. Saxon process of amalgamation ..... 41 24. Silver refining : quartation .... . . 42 25. PLATINUM 43 26. Wollaston's process ; oxyhydrogen furnace ... 45 27. MERCURY : Aludel process 49 28. Palatinate gallery 51 CHAPTER III. METALLURGY OF THE MORE IMPORTANT BASE (READILY OXIDIZABLE) METALS. 29. IRON: Characters of chief ores 53 30. Direct and Indirect processes; steel, pig-iron, and wrought- iron 55 31. Catalan forge ; Siemens' processes .... 56 32. Blast furnace 61 33. Chemical changes taking place in the blast furnace . 62 CONTENTS. vii SECT. PAGE 34. Function of cyanides ....... 65 35. White and grey pig -67 36. Production of malleable iron from pig .... 69 37. Bessemer's process 71 38. Refinery ; puddling ....... 73 39. Rotary puddler . . . . . . . -77 40. Steel 79 41. Hardening and tempering of steel . . . . . 80 42. COPPER : Swansea process ...... 82 43. Henderson's process ....... 86 44. Mansfield process, &c. ....... 89 45. LEAD : Extraction from galena ..... 90 46. Scotch hearth ; refining ...... 90 47. TIN . .92 48. ZINC : General character and treatment of ores . . 95 49. Distillation 96 50. Separation of cadmium 98 CHAPTER IV. METALLURGY OF THE LESS IMPORTANT OXIDIZABLE METALS. 51. ALUMINIUM 100 52. Preparation from Bauxite ...... 101 53. MAGNESIUM 103 54. Use as illuminating agent ...... 104 55. NICKEL ..." 105 56. Action of carbon oxide on iron, nickel, and cobalt . 107 57. ANTIMONY 107 58. BISMUTH 109 viii CONTENTS. SECT. PAGE 59. ARSENIC no 60. MANGANESE . . . . . .. .113 61. Various other metals . . . . . . .114 CHAPTER V. PHYSICAL PROPERTIES OF METALS. 62. Lustre ; burnishing 115 63. Manufacture of mirrors : mercurial process for plates . 117 64. Manufacture of mirrors : silver process . . . .118 65. Formation of double image by glass mirror : Pepper's ghost 119 66. Colour of metals : by reflection . . . . .122 67. Colour of metals : by transmission . . . .123 68. Density 123 69. Density of alloys . . . . . ... 1 25 70. Crystallizability 126 71. Malleability and brittleness . . . . . .126 72. Goldbeating . . . . . . . .128 73. Ductility : wire-drawing 130 74. Wollaston's method for preparing extremely fine wire . 133 75. Tenacity 134 76. Influence of physical state, &c., on tenacity . . . 137 77. Influence of temperature 138 78. Influence of alloying 139 79. Other physical properties of metals .... 140 80. Pen and pin manufacture ...... 141 81. Spinning process for making tea-pots, &c. . " ' . . 143 CONTENTS. ix CHAPTER VI. THERMIC AND ELECTRIC RELATIONS OF METALS. SECT. PAGE 82. Conductibility for heat 148 83. Conductibility for electricity 149 84. Siemens' pyrometer . . . . . . .150 85. Specific heat : Dulong and Petit's law . . .152 86. Expansibility 155 87. Exertion of force during contraction . . . .156 88. Fusibility 157 89. Separation of constituents of alloys on standing . . 159 90. Foundry operations : Bell-founding . . . .161 91. Expansion during solidification 164 92. Annealing, hardening, and tempering . . . .165 93. Volatility ' . .166 94. Thermo-electricity 166 95. Peltier's experiment ; thermo-batteries . . . .168 96. Galvanism or Voltaic electricity . . . . . 1 70 97. Magnetism, electro-magnetism, and magneto -electricity . 171 98. Bell's articulating telephone 1 72 CHAPTER VII. CHEMICAL RELATIONS OF METALS. I 99, Special applications of certain metals : platinum . 175 100. Protective coatings of less oxidizable metals electro- metallurgy 176 101. Water-gilding, nickel silver, pyro-silver . . 177 102. Alloys: general features 17$ b x CONTENTS. SECT. PAGE 103. Average composition of more important alloys . .179 104. Preparation of alloys : coinage 181 105. Assaying 182 106. Poisonous action of copper, lead, tin, &c. . . . 183 107. Compounds of metals with non-metals . . .185 108. Pigments 186 109. White lead : different processes of manufacture . . 187 no. Substitutes for white lead; zinc white, tungsten white . 189 in. Lakes, mordants, &c 190 LIST OF ILLUSTRATIONS. PAGE 1 . Cradle for gold-washing 25 2. Cupel .......... 32 3. Vertical section of cupel 33 4. Plan of cupelling furnace 33 5. Vertical section of ditto . . . . .34 6. Deville's oxyhydrogen furnace . . ... 47 7. Perforation of sheet- iron by oxyhydrogen flame . . 48 8. Aludels 50 9. Palatinate gallery 51 10. Catalan forge 57 1 1 . Siemens' gas-producer -59 12. Blast furnace 60 13. Bessemer converter 71 14. Bessemer converter 72 15. Puddling furnace 74 1 6. Bank's rotary puddler 78 17. Furnace for working poor copper ores by wet process . 86 1 8. Zinc distillation ' . 97 19. Oxland's calciner in 20. Formation of two images by ordinary glass mirrors . .120 21. Pepper's ghost 121 22. Graphical representation of different densities of metals . 124 xii LIST OF ILLUSTRATIONS. FIG. PAGE 23. Section of draw-plate . . . . . . -131 24. Draw-bench . . . 132 25. Arrangement for illustrating breaking strains of different wires 136 26. Different stages in pen-manufacture .... 142 27. Tea-pot spinning, first stage . . . . . .144 28. Sections of chuck and bowled plate .... 145 29. Tea-pot spinning, final stage . . . . . .146 30. Graphical representation of different expansibilities of metals . . . . . . . . .154 31. Bell-founding ; preparation of the core . . . .162 32. Section of moulds and recently cast bell in situ . .163 33. Section of Bell's telephone . . . . . 173 METALS THEIR CHIEF INDUSTRIAL APPLICATIONS. CHAPTER I. METALS AND THEIR NATURAL SOURCES. i. BY various chemical processes the numerous animal, vegetable, and mineral products found in nature can be split up into certain definite constituents, which have hitherto resisted all attempts to decompose them further ; to these bodies the term elements is applied, substances, into the composition of which two or more elements enter, being designated as compounds. Thus by strongly heating a fragment of marble or chalk, the mineral is split up into quicklime and a heavy irrespirable gas known as carbon dioxide; by special chemical means the quicklime can be shown to be compounded of a brilliant substance termed calcium, resembling silver or tin, but rusting much more readily in the air, together with a gas, oxygen, lighter than carbon dioxide, and capable of being breathed and of supporting the combustion of inflam- mable substances with great ease; whilst the carbon dioxide can be similarly split up into charcoal or larnp- & B 2 METALS AND THEIR [CHAP. black (chemically designated carbon}, and oxygen gas identical -with that derived from the quicklime. The three substances, calcium, carbon, and oxygen having hitherto resisted all attempts to demonstrate their com- pound nature, and to break them up into simpler con- stituents, are therefore termed elements. In similar fashion other elements are obtainable from other natural products ; so that finally all the varied products of nature are found to be composed of some or other of about sixty-six elements united together in various proportions. Of these different elements fourteen differ notably from the remainder in general appearance and texture, and especially in chemical properties : thus hydrogen, oxygen, nitrogen, chlorine, and probably fluorine, are gases at the ordinary temperature, whilst bromine is vaporous at temperatures but little elevated; phosphorus, iodine, sulphur, and its rarer congeners, selenion and tellurion, with carbon, silicon, and boron, though solid at the ordinary temperature, yet differ, in many respects, widely from the other elements, which as a whole possess certain characteristics in common : these fourteen elements are therefore distinguished as .ion- metals or metalloids? the others being termed metals. Some of the non-metals, and many of the metals, occur on this globe, so far as we are acquainted with it, in much less quantity than others, and are accordingly of compara- tively little importance from an industrial point of view on account of their rarity and consequent high price; others, on account of the difficulty of extracting the metals themselves from their natural sources or of special 1 This term is apparently applied on the principle of lucus a noti lucendo, since the metalloids do not resemble the metals save in being elements. I.] CHIEF INDUSTRIAL APPLICATIONS. properties of certain of their compounds and deriva- tives, are of less importance as metals than as sources of metallic derivatives of certain kinds. 2. The following table gives the names of those ele- ments the existence of which is well authenticated ; it is probable that a few other names should also be added, metals having been described as of rare occurrence, de- signated ilmenium, neptunium, lavoesium, 6*r./ concern- ing certain of these confirmatory evidence is, however, wanting. The names printed in capitals are those of metals ; those in ordinary type non-metals ; the italics in the case of the latter, and the small-capitals in the case of metals, indicate that neither the elements them- selves nor their compounds are of great industrial import- ance ; the asterisks denote a greater degree of rarity. ALUMINIUM. ANTIMONY. ARSENIC. BARIUM. BISMUTH. Boron. Bromine. CADMIUM. CALCIUM. Carbon. *CERIUM. Chlorine. CHROMIUM COBALT. COPPER. *DlDYMIUM. *ERBIUM. Fluorine. *GALLIUM. *GLUCINUM, GOLD. Hydrogen. Iodine. *!NDIUM. *!RIDIUM. IRON. *LANTHANUM. LEAD. LITHIUM. MAGNESIUM. MANGANESE. MERCURY. * MOLYBDENUM. NICKEL. *NlOBIUM. Nitrogen. *NORIUM. *OSMIUM. Oxygen. *PALLADIUM. Phosphorus. PLATINUM. POTASSIUM. *RHODIUM. *RUBIDIUM. ^RUTHENIUM. *Selenion. Silicon. SILVER. B 2 4 METALS AND THEIR [CHAP. SODIUM. TIN. STRONTIUM. TITANIUM. Sulphur. TUNGSTEN. *TANTALUM. *URANIUM. * r rellurion. *VANADIUM. *TF.RBIUM. *YTTRIUM. *THALLIUM. ZINC. *THORINUM. ^ZIRCONIUM. 3. From the above list it appears that only twenty-one metals are of any considerable industrial importance, viz., aluminium, antimony, arsenic, bismuth, calcium, chromium, cobalt, copper, gold, iron, lead, magnesium, manganese, mercury, nickel, platinum, potassium, silver, sodium, tin, and zinc. Of the other metals a few are occasionally employed either in the free state, or as compounds of various kinds, for some specific purposes in the arts ; thus vanadium compounds have been recently introduced into the calico-printing trade ; barium sulphate is largely used as a pigment and especially as an adulterant for vvhitelead, &c., whilst barium and strontium salts are used in the manufacture of coloured fires for the theatres ; certain tungsten compounds have been employed for rendering cotton and other goods uninflammable, whilst others form pigments which will probably be hereafter more largely employed than at present. Palladium is employed to some extent by dentists ; cadmium sulphide forms a valuable yellow pigment ; uranium compounds give a peculiar colour when added to ordinary glass ; and titanium and tungsten form alloys with other metals which may probably be hereafter of considerable com- mercial importance ; but as a rule the industrial value of the other metals and their derivatives is but very small as compared with that of the twenty-one above named. Of these twenty-one, calcium, chromium, cobalt, and potassium are practically never employed industrially in I.] CHIEF INDUSTRIAL APPLICATIONS. 5 the metallic or reguline state, although their compounds are more or less largely used ; the same remark applies to a less extent to sodium ; although this metal is some- what largely manufactured for use in the production of aluminium and magnesium, its compounds are of far more practical importance than the metal itself. Antimony, bismuth, manganese, and, to a lesser extent, arsenic, are used in the metallic state in the form of alloys, whilst certain of their compounds are also of considerable in- dustrial importance ; nickel is chiefly employed to prepare certain alloys, especially " German silver," its other com- pounds being of little practical use ; magnesium, when employed in the form of metal, is mainly used as an illuminating agent, its compounds being of much more importance industrially. 4. On the whole, then, the number of metals used to any great extent in the arts in the free metallic state is but limited, being chiefly aluminium, copper, gold, iron, lead, mercury, platinum, silver, tin, and zinc ; i.e. the seven metals formerly associated with the so-called seven planets, 1 with the addition of aluminium, platinum, and zinc. To these may be further added the metals anti- mony, bismuth, manganese, and nickel, used almost wholly in the form of alloys. These metals possess to a very high extent the peculiar properties characteristic of the metallic class ; most of these properties are also possessed by the less used and the rare metals, and by alloys generally ; but in some instances certain of these characteristics are found to be wanting, although the majority of the properties peculiar to metals are pos- sessed by the particular metals or alloys in question : 1 Sun, gold ; Moon, silver ; Mercury, mercury ; Venus, copper ; Mars, iron j Jupiter, tin ; Saturn, lead. 6 METALS AND THEIR [CHAP. these characteristic qualities may be thus summarized : metals possess the power of acquiring under certain conditions a peculiar lustre; they are solid at natural temperatures (mercury freezes in the Arctic regions) and possess (with a few exceptions) at some special tem- peratures a peculiar coherence and plasticity which enables them to be fashioned into sheets, wires, or other forms, to which property most of their useful applications are due : further they possess certain chemical functions and properties summed up in the term electro-positive. One noteworthy distinction between metals and non- metals is the following, that when metals are made to mix or unite together, the resulting alloys are frequently formed without any noticeable evolution of heat and invariably still possess the metallic characteristics. Thus, if to melted lead some tin be added, the two metals simply mix together without any indications of chemical action, forming a perfectly homogeneous alloy (solder), just as metallic in its characters as either of the two constituents. If sodium be added to mercury, the evolution of light and heat attests the chemical combination of the two, but the resulting amalgam (as alloys containing mercury are termed) is just as much possessed of the character- istic properties of metals as either of its constituents. On the other hand, when a metal unites with a non- metal there is always a greater or lesser evolution of heat, and, with very few exceptions, the product of the combination is destitute of the metallic properties. Thus on burning zinc or iron in oxygen gas, or magnesium in the air ; on throwing antimony filings into chlorine gas ; x or on warming a mixture of copper or iron filings 1 It is peculiarly noteworthy that whilst combiiiations between metals and non-metals occur with great force when once started, a I.] CHIEF INDUSTRIAL APPLICATIONS. 7 and sulphur, a rapid combination between the metal and non-metal employed is brought about with the evolution of much heat and light, and products are formed in each case respectively, wholly destitute of metallic characters. In some few instances, however, small quantities of certain non-metals can be incorporated with various metals and alloys without destroying their peculiar characteristics ; in the case of steel and Bessemer metal, the presence of a small quantity of carbon in the iron or iron -manganese alloy even augments the strength and tenacity ; and the same is true as regards phosphorus in phosphor-bronze. Some few of the more important metals are occasion- ally found in nature in the free state, either alone or alloyed together, and not combined with any non- metallic element : such metals are said to be native. Ordinarily, however, metals are met with associated with non-metallic elements in the form of compounds, which are termed ores; the extraction of metals from their ores constitutes the chemical art of metallurgy, the general principle of which is the reversal of the phenomena which occur when metals and non-metals unite together, either by direct or indirect processes ; thus, when com- bination occurs the phenomenon may be typified by the symbols A+ B = AB, 1 certain temperature is essential in order to cause the action to com- mence. Thus, pure dry oxygen has no action on iron or zinc at the ordinary temperature ; nor does sulphur act on copper until the mixture is gently heated ; whilst at a temperature of - 80, liquid chlorine has no action on antimony. 1 Juxtaposition of symbols, as AB, means that the constituents A and B are chemically combined together ; whilst the separation of the symbols by the sign + indicates that these constituents are separate from one another. 8 METALS AND THEIR [CHAP. the mode of action being the kind termed synthetic ; the processes of metal extraction on the other hand are either of the kind spoken of as analytic, typified by the symbols AB = A + B (as, for example, when oxide of silver breaks up on heat- ing into oxygen and silver, or when copper chloride is electrolysed into copper and chlorine) ; or belong to the class of chemical actions known as reactions of single decomposition, represented by the symbols AB -f- C = A + BC (as, for example, where hydrogen is passed over heated silver chloride, forming silver and hydrogen chloride). This kind of reaction is by far the most common in practical metallurgy. A fourth kind of chemical action, known as double decomposition, and represented by the symbols AB + CD - AC + BD, is occasionally an intermediate step in the isolation of a metal from an ore, the object being to change one kind of metallic derivative into another more easily treated (for example, where silver sulphide is transformed into silver chloride by the agency of copper chloride as a preliminary stage in the amalgamation process, as applied to ores containing silver as sulphide). This kind of action is, however, more frequently utilized in the manu- facture of metallic derivatives, and notably of various pigments formed by precipitation ( 108). 6. Apart from the nature of the chemical changes in- volved, metal-extracting processes may be divided into the following classes, according to the physical properties I.] CHIEF INDUSTRIAL APPLICATIONS. 9 of the metals themselves and the general character of the process. Volatilization Processes: applicable when the metal is capable of being converted into vapour and recondensed at temperatures which can be readily obtained in practice : such metals are zinc, mercury, sodium, potassium, arsenic, magnesium, cadmium, and some others. Silver can be distilled in a lime crucible by the oxyhydrogen flame (Stas), and lead is sensibly volatilized during the smelting of galena, the volatilized metal being condensed again as oxide, &c., constituting the " fume " of the lead smelter. Other metals, e.g., copper and gold, are sensibly volatile at high temperatures, but this pro- perty is so faintly marked that it is not capable of being utilized in their treatment. Clearly, where it is necessary to separate two metals, one of which is volatile and one not, all that is requisite is to heat the alloy sufficiently to expel the volatile metal, which can be either recondensed or not as convenient. In this way platinum-arsenic alloys have been pro- posed for the manufacture of platinum articles, the alloy being more fusible than pure platinum ; by heating the manufactured article (e.g., a crucible) the arsenic is gradually expelled; similarly, from a ternary alloy of silver lead and zinc the zinc can be removed by distilla- tion (vide 20). Amalgamation Processes. These are really special cases of the volatilization processes ; the ore is treated with some chemical agent that will convert it into the metallic state (if not already in that condition) and then brought into contact with mercury, which dissolves the metal : from the resulting amalgam the mercury is separated by distillation. On account of the loss of mercury, and the cost of this body, this kind of io METALS AND THEIR [CHAP. process can only be economically applied to the precious or the rarer metals. % Smelting Processes. When the metal is fusible at a moderate or high temperature, it is frequently ex- tracted from its ores by the application of some chemical agents which will, at some more or less elevated tempera- ture, act on the metallic compound employed, causing the metal to become free in the liquid form. Copper, iron, lead, antimony, aluminium, and tin, in particular, are usually obtained by processes of this kind. Liquation Processes : modifications of the pre- ceding, used to separate a readily fusible metal in the free state either from an infusible rocky matrix or gangue (e.g. bismuth), or from another less fusible metal (e.g. copper and lead). The mass is simply cautiously heated, when the more fusible metal gradually melts and runs away from the other less fusible substance. In the puri- fication of crude tin as obtained by the smelter, this process is largely employed, the tin melting first and running away from the other metals present. Wet Processes I where the metal is extracted by some method which necessitates the application of chemi- cal reagents to an aqueous solution of a compound of the metal. In the treatment of complex ores this mode of operating is often combined with some process or processes belonging to other kinds. Miscellaneous Processes, ** *'"" > '"<=- C. COMPLEX ORES ; i.e., containing more than one metal. I. Alloy extracted by some or) /silver-lead alloy, spie- other process, as above . . | '*' \ geleisen. II. Special processes adopted for \ extraction of metals sepa-> ,, cupriferous pyrites. rately .......... ) 8. Native Metals. Bismuth, copper, gold, iron (associated with nickel and other metals in small quan- tities), mercury, platinum (and allied rarer metals), and silver are the metals most frequently found in the native state. Iron, when native, is usually of extra-terrestrial origin, i.e. it occurs as meteorites ; copper appears to owe its occurrence in the native state to galvanic action (ther- mo-electric currents ?) whereby soluble copper compounds formed naturally have been decomposed and metallic copper separated precisely as in ordinary electrotyping ; and the same kind of action is probably the cause of the occurrence of other native metals. The metals which most frequently occur native are for the most part, however, members of the class termed precious or noble metals, from their feeble affinity for oxygen, which renders ].] CHIEF INDUSTRIAL APPLICATIONS. 13 them incapable of rusting or tarnishing by oxidation in the air at common temperatures ; thus neither at the ordi- nary temperature, nor on heating, will platinum, gold, or silver rust or oxidize (or combine with oxygen) ; on the contrary, the oxides of these metals cease to exist on heating, the metal being set free, and oxygen being given off as a gas. It is noticeable, however, that the inability to combine directly with oxygen, and the instability of the oxide producible by indirect chemical means, exhibited by the noble metals, does not necessarily extend to their combinations with other non-metals : thus, whilst gold chloride readily breaks up on heating into gold and chlorine, silver chloride can be fused unchanged at a red heat, and mercuric chloride can be volatilized and recondensed without decomposition ; whilst gold and chlorine will readily unite at the ordinary temperature. Similarly, though sulphide of ammonium does not attack platinum, it blackens silver (by yielding sulphur thereto) just as readily as copper at the ordinary temperature ; and to this ready sulphuration of silver is due the blackening of silver goods on lying by for some time. 9- Simple Ores. The first step towards isolating a metal from any particular ore consists in obtaining this ore in a reasonably pure state, i.e. in separating from the ore itself foreign particles of the earthy or rocky matter in which it is naturally embedded, technically termed the matrix, or gangue. Frequently this is effected by hand; the lumps of material raised from the mine being dressed by a hammer, and the fragments picked over so as to separate moderately completely the gangue : in some cases the ore itself, being much heavier than the gangue, is separated therefrom by stamping to a coarse powder, and then subjecting this to a process of washing analogous to that of gold washing ( 15); special machinery is usually 14 METALS AND THEIR [CHAP. employed for this purpose. When the ore has been rendered tolerably free from earthy admixtures, &c., by washing or otherwise (and in some cases after a prelimi- nary calcination or other chemical treatment as men- tioned above), it is subjected to the action of some suitable reagent which will take away the associated non-metallic constituents by a chemical process, the end-result 1 of which is represented by the equation of single decom- position. AB + C = A + BC. 1 Although the end-result of the reaction of a substance C on a compound body AB may be such as to be represented by the above equation, yet it often happens that the result is only brought about frs the final sum of a series of chemical changes : in operating on the manufacturing scale, with tons of material in large and frequently enor- mous vessels, it often happens that these successive changes may be traced as representing clearly-defined separate stages in the process. For example, in the extraction of lead from galena, the end-result is that represented by the equation (i) PbS + O 2 = Pb + SO 2 . i.e. where lead sulphide and oxygen yield metallic lead and sulphur dioxide ; but this final change is brought about as the sum of several intermediate stages. A portion of the lead sulphide becomes con- verted into lead sulphate, thus (2} PbS + 20 2 = PbS0 4 , and this sulphate reacts on the undecomposed sulphide, forming sulphur dioxide and metallic lead (3) PbSO 4 + PbS = 2SO 2 + 2Pb. Equation (i) is thus equivalent to the sum of equations (2) and (3). Another portion of the lead sulphide becomes converted into lead oxide, thus (4) 2PbS + 3O 2 = 2SO 2 + 2PbO, and this oxide reacts on the unaltered galena, again forming sulphur dioxide and metallic lead (5) 2PbO + PbS = SO 2 + 3Pb. Here, again, equations (4) and (5^ jointly are equivalent to equation (i). In the smelting of iron oxide by the blast-furnace the inter- mediate stages are yet more numerous (vide % 33). I.] CHIEF INDUSTRIAL APPLICATIONS. 15 In this way are obtained the metals nickel, iron, tin, arsenic, silver, copper, gold, magnesium, aluminium, mer- cury, lead, antimony, zinc, sodium, potassium, &c., &c. 10. Complex Ores. In the majority of the pro- cesses to which these substances are subjected, the actions are much less simple than the foregoing cases of simple ores. Complicated series of operations have frequently to be gone through for the purpose of separating one metal or metallic compound from another ; thus in the extraction of copper from copper pyrites by the "dry process," the iron contained in the pyrites is separated by a series of operations, the end-result of which is to oxidize the iron and part of the sulphur contained in the mineral, and to form a compound of copper and sulphur, from which the copper is further series of operations. In one of the "wet pro- cesses," for treating pyrites containing copper and silver, the pyrites is first roasted to expel the majority of the sulphur and to oxidize the iron present ; the residue is then heated with common salt, whereby the copper is transformed into chloride (as are also the silver and a small portion of the iron). On treating with water or diluted hydrochloric acid the product of the action, the copper, silver, and iron chlorides formed are dissolved out, the silver chloride (if, as is usually the case, it is present in only small quantity) being retained in solution by the portion of common salt which has remained unacted upon ; from the mixture of solutions of various chlorides thus obtained, the metals are separated by further chemi- cal processes (vide 21 and 43), whilst the oxide of iron left undissolved is employed as a source of metallic iron, or for other special purposes. In some instances complex ores are treated by processes the end-result of which is to yield an alloy of two or more 16 METALS AND THEIR [CHAP. metals which are (if required) then separated by further operations : thus, spiegeleisen and ferro -manganese (alloys of iron and manganese with additional carbon), largely used in the production of Bessemer metal, are smelted from manganiferous iron ores in just the same way as iron ores themselves (minor modifications of the pro- cesses due to physical differences in the ores, &c., ex- cepted). Ores containing copper, lead, and silver are smelted together so as to obtain a ternary alloy of these metals from which a silver and lead alloy is separated by liquation, the silver being subsequently isolated by cupellation of this alloy so obtained (vide 19) : or again from a binary alloy of lead and silver, the silver is re- moved by a somewhat roundabout process, viz. mixing with fused zinc, which dissolves out, as it were, the silver from the lead and floats up to the top, much as ether when shaken up with water containing various substances in solution, will float up to the top after dissolving these bodies and separating them from the water : from the silver-zinc alloy thus produced (also containing a little lead) the zinc is thus removed by distillation, and the re- sidual silver and lead separated by cupellation (vide 20). 1 1. When the relationships are studied that exist be- tween the circumstances under which a chemical change of the kind termed single decomposition can take place, and the proportionate disturbance of the thermal equili- brium prought about during such reactions, some curious correlations are noticeable. If a body A, in uniting with a given weight of a body B, evolve a certain amount of heat Hj, and a body C in uniting with the same weight of B, evolves an amount of heat H 2 , the thermal disturb- ance during the reaction AB + C = A 4- BC I.] CHIEF INDUSTRIAL APPLICATIONS. 17 will clearly be an evolution of heat, the value of which is H 2 Hj, inasmuch as in undoing the combination AB, Hj of heat must be absorbed ; whilst in producing the combination BC, H 2 of heat is evolved. It may happen, however, that Hj is greater than H 2 , so that the value of Ho H x is negative ; that is to say, instead of an evolu- tion of heat during the reaction the chemical change is accompanied on the whole by an absorption of heat. When the body A in the above general equation is a metal, and the reaction takes place in an aqueous solu- tion (i.e. a wet process, and hence not at an elevated temperature), the value of H 2 H 1 is never negative, C being another metal, if indeed (which is doubtful) it ever be negative whatever C be. In other words, one metal can only displace another one from a solution of one of its compounds when the second metal evolves more heat in uniting with the other constituents of the compound than does the first metal. Thus, in the familiar experiments of the lead-tree and the Arbor Diana, or silver-tree (where lead is displaced from lead acetate by zinc, form- ing zinc acetate, and silver from silver nitrate by mercury, forming mercury nitrate), the chemical changes can take place because they are on the whole accompanied by evolution of heat. Similarly from the mercury nitrate solution obtained in the Arbor Diana copper will re- precipitate the mercury in solution, forming copper nitrate, from which, in turn, the copper may be thrown down by zinc or by iron, each successive change being accompanied by an evolution of heat. 12. In reactions of the above general character, when the substances employed are not in solution, the reduc- tion of a metal is sometimes accompanied by a marked heat absorption, although the reverse is more frequently the case. Whenever any considerable heat absorption c iS METALS AND THICIR occurs it is noticeable that the reduction never fakes place at low temperatures ; the reaction is only brought about when the substances are heated to some consider- able extent, the temperature of commenting action being usually higher the greater the heat absorption. Similarly the temperature at which action commences in cases where there is heat evolution is usually the lower the greater the value of the heat evolution. The character of the molecular condition of the metallic compound, how- ever (whether light and porous, or dense and heavy), considerably affects the temperature of initial action. Thus, for example, the action of carbon oxide on metallic oxides, such as copper, iron, and zinc, whereby carbon dioxide and the metals are formed, is attended with very considerable differences in heat evolution in each case : the " heats of combustion " of these metals and of carbon oxide are as follows : Kilogramme heat Metal or other com- bustible. units evolved by the union of 16 grammes of oxy- gen with the Oxide formed. Authority. c jmbustible. Copper Iron 38-30 66-45 Cupric oxide, CuO Ferrosoferric oxide, Fe 3 O 4 Andrews. Zinc 86-24 Zinc oxide, ZnO > ( Mean of results of Carbon oxide j 68-35 Carbon dioxide, CO 2 / Andrews, Favre and Silbermann, and Dulnnrj. Whence it results that if the reactions : CuO + CO Cu + CO 2 Fe 3 4 + 4 CO = 3 Fe + 4-CO, ZnO + CO Zn -f CO* I.] CHIEF INDUSTRIAL APPLICATIONS. 19 could take place at the ordinary temperature, the heat disturbances (evolution or absorption of heat) accom- panying them would be respectively (per 16 grammes of oxygen transferred from the metallic oxide to the reducing agent) : Kilogramme heat units. Reduction of copper oxide ... 68*35 - 3& 1 3 = + 3'5 ,, iron ,, ... 68*35 - 66-45 = + 1-90 ,, zinc ,, ... 68*35 - 86-24 - - I7'89 That is, the reduction of the copper oxide would be attended with a large heat evolution, that of the iron oxide with a small heat evolution, and that of the zinc oxide with a considerable heat absorption : but little difference in the relative values ensues if the heat dis- turbances be calculated on the supposition that they take place at somewhat more elevated temperatures, 200" or 300 C. for example. 1 Now it has been recently 1 These calculated values are easily obtained by means of the formula, H T = H + (hj + h s ) - (h 3 + h 4 ), where H T is the value of the heat disturbance when the reaction takes place at T (i.e. all the materials and products being at the temperature T), H being the heat disturbance at the ordinary tem- perature (15 or thereabouts). \ is the heat required to raise the metallic oxide from 15 to T h 2 ,, ,, ,, carbon oxide ,, ,, ,, carbon cliox- ) ide produced ] " h 4 ,, ,, ,, metal set free ,, ,, ,, The values of h 1? h 2 , h 3 , h 4 are calculated by the formula h = W x S x (T - 15).. where W is the weight of the substance supposed to be heated, and S its specific heat between 15 and T. Usually the correction hj balanced by the similar correction of opposite sign h 3 + h 4 . C 2 20 METALS AND THEIR [CHAP. shown by Alder-Wright and Luff 1 that the action of carbon oxide on copper oxide begins at a lower tempera- ture than that on ferric oxide, when the molecular condi- tions of the two oxides are comparable ; whilst both these kinds of oxides are affected by carbon oxide at much lower temperatures than zinc oxide. Thus Low- thian Bell found 2 that carbon oxide does not reduce zinc oxide at all at 420; whilst Alder- Wright and Luff obtained the following numbers as the temperatures of initial action of carbon oxide on copper and iron oxides : Oxides prepared by precipitation. Copper Iron oxide. oxide. Temperature at which action commences . 60 . . 90 Oxides prepared by the ignition of salts. Copper Iron oxide. oxide. Temperature at which action commences . 125 . J 2 Precisely similar results are obtained when other reducing agents are substituted for carbon oxide ; the absolute values of the heat disturbances are, of course, different for each reducing agent, but with a given reduc- ing agent the same relationship necessarily holds as with carbon oxide, viz., that the value of the heat evolution is algebraically greater with copper oxide than with iron oxide. Thus the state of aggregation of the metallic oxides being the same, or nearly so, the follow- ing values were obtained as the temperatures of initial action of hydrogen and carbon : 1 Journal of the Chemical Society, January, i8yS. 2 Chemical Phenomena of Iron Smelting, p. 91. I.] CHIEF INDUSTRIAL APPLICATIONS. Temperature of initial Reducing agent. Character of oxide used. action. Copper oxide. Iron oxide. Hydrogen Precipitated 85 195 Di'tto By ignition of salts 175 260 Carbon from sugar ... Precipitated 390 45 Carbon from another source (much lighter) By ignition of salts 390 430 Ditto ditto Precipitated 350 43 In all cases the temperature of initial action on copper oxide is sensibly lower than that on iron oxide in an analogous state of aggregation. 13. Again, on comparing the amounts of heat deve- loped during the reduction of a given metallic oxide in a given molecular state by various reagents, it is noticeable (as might indeed be expected from the pre- ceding results) that the reducing agent which causes a Jieat disturbance of higher algebraic value uniformly begins to act at the lower temperature; i.e. if there be heat evolution, the greater the evolution the lower the temperature of initial action ; and if there be heat absorption, the less the absorption the lower the temperature of initial action. Thus, the heat disturbances during the reduction of copper and iron oxides by carbon oxide, hydrogen (steam being formed), and free carbon (carbon dioxide being produced) are respectively : Copper oxide. Carbon oxide Hydrogen Carbon Iron oxide. I 90 8-63 METALS AND THEIR [CHAP. since the " heats of combustion " of hydrogen and car- bon (to steam and carbon dioxide respectively) are 57*82 and 4778 kilogramme heat units per 16 grammes of oxygen added on to the combustible ; l accordingly Alder- Wright and Luff found the following values for the temperatures of initial action of these reducing agents on several sorts of copper and iron oxides prepared so as to present considerable variation in their state of molecular aggregation. OXIDES OF COPPER. Reducing agent. Precipitated Cupnc oxide. From nitrate i by ' calcination. By continued roasting of metal. Cuprous oxide. Carbon oxide ... Hydrogen Carbon (light) ... (dense)... 60 85 35 390 125 175 39 43 146 172 430 440 HO 155 345 380 OXIDES OF IRON. Reducing agent. Precipitated feme oxide. Precipaated and gently ign.ted. From ignition of Sulphate. Carbon oxide ... 90 22O 2O2 Hydrogen 195 245 260 Carbon (light) ... 43 43 (dense)... 45 45 450 The action of carbon oxide uniformly beginning at a lower temperature than that of hydrogen, which again commences at a temperature lower than that requisite in 1 Mean results of a large number of determinations by several chemists (vide Alder-Wright, Phil. Mag. Dec., 1874). In the ca^e of hydrogen, the average heat of combustion to liquid water per 16 grammes of oxygen = 2 x 34*275 is reduced by 18 x 0*596 = 1073, the latent heat of aqueous vapour at 15 being 596 (Regnauit). i.] CHIEF INDUSTRIAL APPLICATIONS. 23 the case of carbon. From experiments not yet published it appears that precisely analogous results are given with other metallic oxides. 14. In some cases it is noticeable that if the heat dis- turbance during the reduction of a metallic oxide is not of considerable magnitude, the reaction can be inverted by modifying the conditions of the experiment ; i.e. if under certain conditions the reaction, AB + C A + BC can occur, under other conditions the opposite reaction, A + BC = AB -h C can take place ; this, however, does not very frequently occur. Two of the best illustrations of the phenomenon are afforded by iron oxide with carbon oxide and hydro- gen respectively ; the heat disturbances during the reduc- tion of the metallic oxide by these two agents are + 1*90 and 8*63 ( 13) ; accordingly, if hydrogen or carbon oxide in excess is passed over heated iron oxide reduction of the metallic oxide and oxidation of the reducing agent will take place ; but if excess of carbon dioxide or of steam be passed over heated metallic iron, oxidation of the metal occurs together with formation of carbon oxide in the one case, and of hydrogen in the other. Nickel and cobalt yield similar results (Lowthian Bell). 24 METALS AND THEIR [CHAP. CHAPTER II. METALLURGY OF THE PRECIOUS OR NOBLE METALS. 15. THE processes in actual use for the extraction of metals generally from their natural sources are so numer- ous and vary so much in details, according to circum- stances, that only a brief outline of some of the more important methods in use in the case of the chief metals can be attempted here. Gold. For the most part this element is found native ( 8), and generally in a state of considerable freedom from other metals, the natuie of the ac- companying metals, when present, varying with the locality. Silver is very frequently associated with native gold ; that from Australia and California often containing 5 to 10, or even more, per cent, of this metal, with small quantities of copper and iron in addition. Brazilian gold often contains palladium, and that from Russia platinum. In Hungary gold is found associated with tellurion, whilst the Huelva and Tharsis pyrites and many other minerals contain small quantities of this precious metal interspersed throughout masses of other metallic sulphides. As a rule, the metal occurs in quartzose and granitic rocks, but large quantities have been obtained from time immemorial from the sands of II.] CHIEF INDUSTRIAL APPLICATIONS. river-beds and from alluvial deposits of the matters washed down by streams from mountainous districts where these rocks occur. Occasionally in these deposits the gold is found in smaller or larger masses known as nuggets, some of which have been found of considerable magnitude, weighing upwards of one, and even of two cwt, and worth several thousand pounds sterling; generally, however, the gold occurs in minute grains or "dust." From alluvial soils the gold is separated by simple mechanical means, 'the earthy mass being agitated FIG . I with water in a wide shallow basin, technically termed a "pan," a peculiar motion being communicated by the hand so as to scoop out of the pan the muddy water whilst the heavier particles of metal are retained. When necessary, stones and hardened masses are pre- viously roughly pulverized, or they are mechanically picked out by the hand during washing. For systematic working a washing-machine, known as a "cradle." is employed (Fig. i), consisting of a kind of wooden box, 26 METALS AND THEIR [CHAP. some 6 or 7 feet long, and about 2 feet wide, mounted on rockers so that the bottom has a gentle slope from one end to the other ; across the bottom are nailed wooden bars (riffle-bars) so as to make a series of small shallow weirs in the cradle ; at the top end is fixed a sieve, on to which the earth is shovelled, a constant stream of water being kept running on to the mass ; the larger stones are thus left on the sieve, whilst the clayey por- tion, the small gravel, and the gold dust are washed through and deposited in the shallow pools formed by the riffle-bars. Every now and then the deposited par- ticles are removed and dried in the sun, and the lighter earthy particles blown away by the breath, and the small pebbles picked out. Where the soil is a stiff clay, the mass is stirred up with water in a tub with paddles or revolving arms before cradling ; and, occasionally, instead of carrying the washing so far as to separate all the earthy matters (which often entails loss by the washing away of the finest particles of gold), the cradling is only carried on to a certain point, the gold being extracted from the partially washed mass by amalgamation ; this operation, however, is more commonly employed in the case of the powder obtained by stamping or grinding quartzose auriferous rocks, and the washing is then more frequently effected by making the water and suspended matters pass over a series of blankets stretched tightly on frames so as to make a series of very slightly inclined planes; the woollen surfaces arrest the particles of gold with more or less earthy matters. From time to time the deposit is removed, and the gold extracted by means of mercury. Occasionally a kind of magnified cradle is used, con- sisting of a series of slightly inclined wooden troughs or sluices, 10 or 12 feet long, so that the stream from one is delivered on to the next, and so on Riffle-bars are ii] CHIEF INDUSTRIAL APPLICATIONS. 27 placed in these troughs either directly across or at an angle. When the washing has gone on for a short time mercury is allowed to flow into the upper trough ; this runs down, being retained by the riffle-bars, so that the mercury dissolves the accumulated particles of gold. In order to retain the finest particles of gold which some- times escape through being washed down too rapidly to be absorbed by the little pools of mercury in the sluices, amalgamated plates of copper are placed at the end of the lowest trough, so that the effluent "slimes" must pass over them ; the amalgam of gold and copper thus lormed is from time to time removed and worked up with the fluid mercury amalgam. 1 6. In the extraction of gold from gold quartz, the stamped rock (washed by blankets or sluices when requisite) is placed in an iron pan with a certain quantity of mercury ; a stream of water flows into the pan, the overflow passing into another pan at a lower level also containing mercury. Several pans are generally con- nected in series, each being provided with an agitator worked by steam or water power after the fashion of a mortar mill ; the gold is then dissolved out, the agitator continually bringing the auriferous particles and the mer- cury in contact. Fresh quantities of stamped quartz are continually introduced until the mercury has taken up so much gold as partially to lose its fluidity ; the amalgam is then squeezed through chamois leather, whereby a fluid amalgam, containing only a small quantity of gold, is separated, and a nearly solid rich amalgam retained. The fluid amalgam is used over again in the pans, the solid mass being carefully distilled so as to separate the mer- cury and leave the gold and other metals dissolved out. Certain auriferous minerals, when treated with mercury, do not allow the gold to be wholly dissolved out, 28 METALS AND THEIR [CKAI-. the gold becoming sulphurized or otherwise changed on the surface so as to prevent contact between the gold and the mercury. This is especially the case with ores containing sulphur, arsenic, or tellurion. To avoid this it has been proposed by Crookes, and also by Wurtz (of New York), to add small quantities of sodium to the mercury. The sodium amalgam thus obtained causes the mercury to wet the metallic particles (probably by destroying the film of gold sulphide or by preventing its formation). An additional advantage in this process is that the loss by " flouring " of the mercury (reduction to fine particles which do not again coalesce and are con- sequently washed away) is to a large extent prevented ; the mercury being always clean and bright, any small particles mechanically dislodged are readily reabsorbed into the rest of the mass of mercury. 17. When obtained from certain ores, the gold thus extracted is apt to contain small quantities of foreign metals which destroy its tenacity and other valuable properties ; in many cases these metals, if present in the mass left on distilling off the mercury, can be removed by simply melting the residue in crucibles with an oxidizing flux, such as a mixture of nitre and borax ; the foreign impurities are thus removed, being oxidized by the nitre, the oxides thus produced being taken up by the melted borax. Another method of purifying gold, especially suited for gold rendered brittle by the presence of tin and antimony, was introduced a few years ago by Mr. F. B. Miller of the Sydney Mint ; this consists of passing a stream of chlorine gas through the molten metal, when silver and baser metals are converted into chlorides, the latter being expelled if volatile, whilst the gold remains unchanged ; in this way perfectly pure gold is readily prepared, whilst the silver chloride formed can ii.] CHIEF INDUSTRIAL APPLICATIONS. 29 be readily reduced to the metallic state and the silver thus obtained separate from the gold. When the silver, in an alloy of gold and silver, largely preponderates, as is the case when silver containing small quantities of gold is extracted from such sources as Spanish pyrites, &c., a more convenient mode of separating the gold is to treat the alloy with nitric or sulphuric acid, when the silver dissolves and the gold is left undissolved ( 24). In the assaying of coinage alloys this mode of separation is largely used (vide 105). 1 8. A mode of extracting gold by purely chemical means from gold quartz and other similar sources has been proposed by Calvert : the crushed quartz is sub- jected to the action of cold chlorine gas so as to convert the gold and other metals present into chlorides which are subsequently washed out by water ; from the solution thus obtained metallic gold in a pure state is separated by adding solution of ferrous sulphate, or better, by blowing sulphur dioxide through the liquid ; l the gold thus separates as a fine powder which is allowed to subside, washed, col- lected, and fused into an ingot. If silver be also present the metal may be extracted by treating the chlorinated mass with brine, which dissolves the silver chloride, and subsequently separates the silver from the solution thus obtained ( 21). Another process, patented by Long- maid, for separating gold from substances containing it consists in fusing the ore in a reverberatory furnace with roasted pyrites, lime, and fluor spar; some gold subsides to the bottom, whilst some remains suspended and is separated by placing iron plates in the fused mass ; 1 The chemical changes thus taking place may be written : 2AuCl 3 + 6FeSO 4 = 2Au + FeCI 6 + 2Fe,(SO 4 ),, 2AuCl 3 + 3SO 2 + 6H a O = 2Au + 6HC1 + 3bO 4 H a . 30 METALS AND THEIR [CHAP. the gold adheres to these and is then dissolved off from them by immersing them in a bath of melted lead. In this way there is ultimately obtained a gold-lead alloy, from which the gold is separated by cupellation ( 19). Neither this process nor Cal vert's seems to have come into any considerable practical use, although a process much the same in principle as the latter has been worked in Silesia; this method, described by Plattner in the Jurors' Report of the 1851 Exhibition, consisted in roasting the ore (an arsenical pyrites containing gold to the extent of somewhat less than J oz. per ton) so as to drive off arsenic and sulphur, treating the residue with chlorine gas, and then dissolving out by water the chlorides of iron and gold and separating the latter by a reducing agent such as sulphuretted hydrogen. 19. Silver. Besides occurring native in Mexico, Chili, and Peru, and in smaller quantities in many other places, this metal occurs in combination with sulphur, forming several kinds of ores according to the quantity and character of the other associated substances ; also as chloride (horn silver), iodide, arsenide, bromide, and as antimony and mercury alloys. Considerate quantities are now extracted from the lead smelted from lead sul- phide containing small quantities of silver; whilst the Spanish pyrites largely used for the production of sulphuric acid yields a residue on burning off the sulphur from which silver and copper are obtained in some quantity. From these sources the silver is extracted by methods which naturally fall under one or other of the three classes known as lead processes, wet methods, and amalgamation processes, the distinctive feature of the first class being that from a suitable mixture of ores a silver-lead alloy is smelted, from which the precious metal is subsequently separated ; whilst in the second class the silver is obtained ii.] CHIEF INDUSTRIAL APPLICATIONS. 31 in aqueous solution by treatment with appropriate reagents and is thence precipitated by chemical agency ; and in the third class the silver is extracted by means of mercury somewhat after the fashion of gold ( 16), but usually by processes involving more complex chemical actions. Lead processes. When silver exists in the me- tallic state disseminated through a rocky matrix, a silver- lead alloy is readily formed by merely fusing together the ore and a sufficient quantity of metallic lead, whereby the silver is, as it were, dissolved out of the matrix by the molten lead, much as gold is out of gold quartz by mercury. When the silver is not present in the metallic state, a silver-lead alloy can be obtained by mixing with the silver ores, galena (lead sulphide), or other lead ores and then smelting the whole together so as to reduce both lead and silver to the metallic state// From the argentiferous lead thus obtained the silver is then extracted by processes the exact character of which depends upon circumstances ; if the silver-lead alloy be sufficiently rich in silver and tolerably free from copper, the lead and other foreign base metals present in greater or less quantity are re- moved by a process termed " cupellation," which consists in fusing the alloy in a shallow dish (cupel) made of porous material, such as compressed bone-ash, clay, or marl, moistened with wood-ash liquor/ whilst a stream of air plays over its surface ; the lead and foreign base metals oxidize and the oxides fuse and are partially absorbed by the cupel and partially blown away by the current of air or drawn off in the liquid state forming the lead oxides commercially known as litharge and massicot. - Finally, when all the foreign metals are oxidized a mass of fused silver is left containing in addition any gold or platinum which may happen to have been originally present ; the clearing away of the last traces of oxide produces a rather 32 METALS AND THEIR L CIIAP. singular appearance on the surface of fused metal, techni- cally termed the "brightening." The fused silver, especi- ally at high temperatures, absorbs oxygen from the air and on cooling is apt to give it out again, forming peculiar miniature volcanic cones where the escape of gas forces the yet liquid metal in the interior up through the newly- formed thin solid crust ; this phenomenon is spoken of as " vegetation," or " spitting," and with large masses of silver (one cwt. or so) is often extremely well defined, the cones being an inch or two in height. FIG. -2. Fig. 2 represents the form of cupel usually employed in this country : an egg-shaped ring of half-inch boiler plate, a, a, strengthened by cross-bars at the bottom, constitutes a sieve-like frame into which is rammed by mallets a mixture of bone-ashes and a little wood-ash moistened with weak potash solution ; the upper surface of the mass thus formed is worked into a concave form /;, b, exhibited in section in Fig. 3, the concavity being bordered by a ledge of two or three inches in width all round save at the base of the oval, where it is much wider. In this wide part of the ledge or breast are bored holes, c, c, c, for the purpose of drawing off the fused litharge by II.] CHIEF INDUSTRIAL APPLICATIONS. 33 means of a temporary channel, termed a "gate," d, scooped in the substance of the cupel as occasion requires. According to the amount of silver lead alloy to be worked at a time the metal ring is from two to four feet long and eighteen to thirty-six inches wide, by four to six inches deep, the thickness of bone-ash in the thinnest part being an inch or a little more. The cupel is set in brickwork under the arch of a small reverberatory furnace, represented in plan in Fig. 4, and in section FIG. 4- in Fig. 5, a, a, cupel: b, fireplace; c, bridge over which the flame from the fire passes, being reflected downwards, as it were, by the arch d, and passing to the chimney by the flue e, bars. Each cucurbit is capable of holding 60 to 80 Ibs. of a mixture of ore and from a third to a quarter of its weight of lime; from 32 to 52 cucurbits are mounted in one gallery. The heat expels mercury as vapour, which 1 The chemical change in this operation is somewhat more com- plex than in the butyrone furnace. The main action is represented by the equation 4HgS + 4CaO = 3CaS + CaSO 4 + 4-Hg, calcium sulphide and sulphate being formed. The little amount of mercurous oxide that sublimes may be regarded as formed thus ( 8HgS + 8CaO = 7CaS + CaSO 4 + 4Hg 2 O. E 2 52 METALS AND THEIR [CHAP. is condensed in stoneware receivers applied to the cucur- bits and kept half full of water ; after the operation is finished these are emptied out into a tub; the black powder (sulphide and oxide of mercury) washed out from the receiver by the water is collected and heated with lime over again. At Landsberg in Bavaria a superior distillation apparatus is used constructed after the fashion of a bench of gas retorts by the late Dr. Ure ; l whilst in other places arrangements are employed very similar to the capellina distillation apparatus used for the separation of mercury from gold and silver amalgams ( 16 and 22). Mercury as met with commercially often contains lead, tin, and other cheaper metals, fraudulently added to in- crease its weight ; these cannot always be wholly removed by redistillation, and hence must frequently be separated by chemical means, such as digesting the impure mercury with dilute nitric acid, mercurous nitrate solution, or strong sulphuric acid, when the foreign metals dissolve, their solution being probably promoted by the galvanic action set up. Of the other metals belonging to the class of noble or precious metals (palladium, iridium, rhodium, osmium, ruthenium), the first and second have been employed for certain special purposes but only to a limited extent ; thus palladium, irrespective of its use for certain scientific investigations on account of its peculiar power of con- densing hydrogen, forms a valuable alloy with silver, useful for dental purposes, mathematical instruments, &c. : whilst an alloy of platinum and iridium also possesses valuable properties, being less fusible and less attacked by corrosive agents than even platinum itself (vide 25). Dictionary of Arts, Manufactures, and Mines, Art. Mercury." in.] CHIEF INDUSTRIAL APPLICATIONS. 53 CHAPTER III. METALLURGY OF THE MORE IMPORTANT BASE (READILY OXIDIZABLE) METALS. 29. Iron. Without question iron is the metal par excellence which could least be spared by civilised nations ; invaluable as a means of currency and for other purposes as gold is, its uses are far outweighed by those of iron, a fact recognized ages ago in more senses than one when the Eastern sage predicted his downfall to Croesus, saying after having viewed his treasures, " Know, O King, that he who possesses more iron will soon become master of all this gold." Most of the practical importance of iron is due to the very different properties possessed by the pure, or nearly pure, metal (malleable iron], and by the substances formed by its union with small quantities of carbon (cast iron and steel) ; ((the former from its fibrous character and consequent great toughness, strength, and tenacity, and its power of becoming plastic and welding together, and hence being readily shaped, at a high temperature, is applicable to purposes for which no other substance could be employed ; whilst the comparative fusibility of cast iron, conjoined with its considerable strength, and the hardness and elasticity of steel when sub- jected to certain alternations of temperature, render these 54 METALS AND THEIR [CHAP. substances indispensable to the mechanical and civil engineer, as well as to almost every handicraftsman. The following table gives a general idea of the compo- sition of the more important iron ores : Haema- Brown Magnetic Spathic j Clay tite. Ore. Ore. Ore. Ironstone. 1 Ferric oxide, Fe 2 O 3 . 90 100 4070 3070 03 '03 Ferrous oxide, FeO . o-5 13-33 36-50 3555 Alumina, A1 2 O 3 . . O 2 i7 o-5 O 2. J 7 Lime, CaO . . . o-3 i7 05 0-4 114 Magnesia, MgO . . O I O 2. 02 0-4 i9 Oxide of manga- nese, MnO . . . I o-3 O I 125 O 2 Silica, SiO 2 . . . O IO i35 O IO o5 217 Carbon dioxide, CO 2 O I o5 10 37-42 2237 Phosphoric anhy- dride, P 2 O 5 . . . Sulphuric anhydride, S0 3 I I 02 trace O 2 trace trace trace 2 o3 Water, H 2 O . . . I 6 18 04 I Ferric ox- Hydrated Ferric and Ferrous Ferrous ide with ferric ox- ferrous ox- carbonate carbonate little or ide with ides with and | and gene- Essential Composition. no earthy & siliceous more or less earthy small quantities manganese | rally large carbonate;! quantities matters. and clay- of earthy crystalline. of earthy ey matters. matters. and clayey matters. Native iron, presumably of meteoric origin, is so com- paratively scarce as not to be of importance as a source of the metal ; still tools have been met with among semi- civilised nations fashioned from iron derived from this source. The leading ores of the metal are the oxides, especially the magnetic oxide (which derives its name from the fact that the natural loadstone is a variety of this sub- stance) ; the peroxide, occurring as the minerals haematite, specular iron ore, &c. ; and the hydrated peroxide, forming brown iron ore, iron ochre, &c. ; the carbonate, forming spathic iron ore when crystallized, and clay ironstone when in.] CHIEF INDUSTRIAL APPLICATIONS. 55 more or less intermixed with earthy matter ; and the sul- phides, especially pyrites. The last, however, is of more importance, industrially, as a source of sulphur than as an iron ore, although by the processes already alluded to ( 10 ; vide also 43) for extracting copper from cupriferous pyrites, a peroxide of iron can be thence pre- pared from which metallic iron can be readily obtained, and which indeed is actually made into a source of that metal in the puddling furnace ( 38). 30. From these and analogous ores metallic iron in a state of more or less purity is obtained by processes which may for practical purposes be divided into two classes. viz., those where tolerably pure iron (or steel) is obtained at one operation (direct processes] ; and those where a very impure iron is first prepared, containing several per cents, of carbon with other substances, notably sulphur, phosphorus, and silicon, which greatly add to the fusibility of the product ; from this " pig iron " or " cast iron " malleable (or nearly pure) iron is subsequently obtained by the aid of refining and purifying processes. These two methods really insensibly shade into one another, as the substances prepared by direct processes often only differ from pig iron in containing smaller quantities of impurities, having, indeed, characters intermediate be- tween those of malleable iron and of pig iron. When these impurities are limited to carbon in quantity not much exceeding about i per cent, (sulphur, phosphorus, and silicon being absent, or occurring only in traces) the substance possesses the peculiar properties of steel, i.e., it is far harder than wrought iron, especially when heated and suddenly cooled ; it further possesses a peculiar elasticity and power of retaining a sharp edge which renders it especially valuable for cutting instruments and tools generally. t\ METALS AND THEIR [CHAP. The following table illustrates the general chemical composition of malleable iron, steel, and pig iron : Malleable Iron. Steel. Pig Iron. Iron . . 99-099-5 9 8 -5 99'5 90*0 95'0 Carbon O-IG'5 0-51-5 2-54-0 Silicon. O O'2 o trace o'i 3-5 Sulphur . trace o trace trace o'5 Phosphorus 00*5 o trace trace I -5 / o trace in cemen- tation steel Manganese o trace < O'l 2'O and more trace 2 - o in Bessemer and \ analogous steels Welds readily, com- Can be welded more Will not weld, com- paratively soft, very d.fficultly fusible, or less easily, less infusible than mal- paratively readily fusible and easily Character- will not harden, leable iron, can be cast, will not harden istics. very tough and te- hardened and tem- like steel, more brit- nacious. pered. tle than tempered steel or malleable iron. 31. By processes of the direct kind, when properly worked, substances are obtained which are of the nature of malleable iron, or soft steel ; one of the oldest forms of apparatus used for this purpose is known as the " Catalan Forge " (Fig. 10) ; in principle this is much of the nature of a blacksmith's forge, a stream of air being forced through a nozzle, or " tuyere," into a charcoal fire in which lumps of iron ore to be reduced are placed, a pile of ore and charcoal being raised over the fire : to get good results a haematite or magnetic oxide of considerable purity must be employed ; according to the way in which the manipulation is effected, the substance reduced in the furnace will vary in character from nearly pure iron to soft steel : the spongy mass of metal produced is ham- mered and forged into bars whilst still red-hot. A rough III.] CHIEF INDUSTRIAL APPLICATIONS. 57 form of bellows-furnace of this description has been used in India from time immemorial, producing a metal from which steel of the finest quality (Wootz) is prepared by melting or fritting the partially carbonized iron thus pro- duced with wood in closed crucibles. Direct processes, FtG. 10. however, until of late years, have comparatively fallen into desuetude ; during the last decade several attempts have been made to revive them in a more perfect form, so as to obviate several objections to which the usual round- about methods of blast-furnace smelting, with subsequent refining and puddling processes or Bessemerizing, are 53 METALS AND THEIR [CHAP. open. Whilst it cannot be said that any of these have as yet in any considerable degree superseded the blast fur- nace, there is every reason to believe that such a result will ultimately be brought about to a greater or less extent ; the gas producers, " regenerative furnaces," and other ap- paratus constructed by Siemens affording the means of overcoming many practical difficulties that have hitherto stood in the way of direct processes being success- fully carried out, so that iron and steel can be readily produced direct from the ore on a large scale. 1 The regenerator (so called from its introducing again into the furnace the heat thence escaping in the exit gases), enabling very high temperatures to be produced with a compara- tively small expenditure of fuel, renders it possible to effect many kinds of operations which, with ordinary furnaces, are either impracticable or too costly from the amount of fuel consumed : it consists simply of vaults, or flues, in which are stacked piles of firebricks with inter- stices between, so that as the spent gases and flames from the furnace pass through, the bricks become heated up, and the waste products of combustion finally issue at the far end to the chimney almost wholly robbed of their heat. Two pairs of regenerators are usually em- ployed, the waste gases passing through one pair and heat- ing it up, whilst the gaseous fuel from a gas producer and the air to burn it are passed inwards to the furnace through the other pair previously heated ; by a suitable arrange- ment of valves and doors the gases are made to pass alternately through one and the other pair of regenerators, the fuel and blast being coincidently shunted to the pair just heated up ; in this way almost all the heat generated in the furnace is again brought back to it in the heated blast and gas, so that the practical limit to the tem- 1 Journal of the Chemical Society, 1873, p. 661. in.] CHIEF INDUSTRIAL APPLICATIONS. 59 perature attainable is simply the fusibility at intensely high temperatures of even the most refractory construc- F/G . II. tive materials obtainable. The combustible gases which serve as fuel in these furnaces are produced by the ar- rangement shown in Fig. 1 1 ; air is admitted through the 6o METALS AND THEIR [CHAP. in.] CHIEF INDUSTRIAL APPLICATIONS. 61 grate, a, and as the first products of combustion pass through the heated mass of fuel above the fire bars, all or nearly all the carbon dioxide present becomes con- verted into carbon oxide, so that the gases which issue at the gas flue, , consist of nitrogen, carbon oxide, and more or less carburetted hydrogen and hydrogen, accord- ing to the nature of the fuel burnt, &c. : thus Siemens gives the following analysis of the gas given by a mixture of 3 parts caking and i part non-caking coal : Combus- ( Carbon oxide . . .24*2 per cent, by vol. tible < Hydrogen .... 8'2 ,, ,, > 34-6 gases. ( Carburetted hydrogen 2 '2 ,, ,, Incombus- ( Carbon dioxide . . 4*2 ,, ,, ) 6$' tible gases ( Nitrogen ..... 6i'2 ,, ,, \ As the fuel sinks in the gas producer, fresh substances are introduced through the hopper, c, ashes being stoked out through the fire bars. One great advantage of this gas producer is that many kinds of refuse, of no value at all as fuel when burnt in the ordinary way, can be readily utilized and transformed into valuable gaseous fuel : whilst the gases thus produced are more convenient as fuel for many manufacturing operations than coal and such-like substances. 32. By far the greater portion of iron employed indus- trially, however, is extracted from the ores used by the aid of the " blast furnace." Fig. 12 gives a notion of the usual form of this gigantic metallurgic appliance, 70 to 80 feet and upwards being a usual height. Virtually the blast furnace is a vertical tube swelling out in the middle or rather lower down (the boshes) ; at the top end of this tube the materials employed are continually inserted, whilst at the bottom the products of the chemical actions 62 METALS AND THEIR [CHAP. taking place inside are withdrawn continuously or periodi- cally. The ore to be smelted, coke, coal, or charcoal to reduce it, and limestone or other analogous material to serve as a flux for the earthy matters present, enter at the top, whilst pig iron and a fused earthy siliceous mass known as " cinder," pass out in the fluid state at the base through arched holes, b and c, in the thick masonry of the lowest portion of the furnace, termed respectively the " tapping hole ; ' and the " cinder hole." In addition, air, usually heated (either by an arrangement analogous to Siemens' regenerator, or by a superheater, like that represented in the cut, d), is continually forced in by powerful blowing engines at the bottom through tuyeres (hot-blast] ; whilst the gaseous products of combustion and of the reduction of the ore in the furnace escape at the top. Usually the top is covered in by a cone or bell of iron, a, capable of being lowered by a counterpoise and winch when re- quired to introduce materials ; when raised, the hot exit gases pass through the side tube, /, by which they are led to fireplaces under boilers, &c., and burnt so as to generate steam, or to heat the superheaters for the hot- blast, &c. ; for the issuing gases invariably contain much carbon oxide, wherefore much more fuel is requisite to smelt iron in a blast furnace than would, theoretically, be required if the carbon of the fuel were burnt wholly to carbon dioxide. 33. Usually the ores employed are subjected to a pre- liminary calcining so as to convert ferrous carbonate into ferric oxide, to expel water, and generally to open out the texture of the ore ; calciners much resembling an ordinary limekiln are used for this purpose ; if coal be employed as fuel it is coked by the heat in the upper part of the furnace, so that what descends to the tuyeres and is there burnt by the entering hot-blast is always in.] CHIEF INDUSTRIAL APPLICATIONS. 63 carbon : this carbon is either burnt directly to carbon oxide, or else if burnt firstly to carbon dioxide, is imme- diately converted into carbon oxide by the white-hot carbon, inasmuch as little or no carbon dioxide exists in the gases inside the furnace at the tuyere level (Lowthian Bell). Virtually, therefore, the air becomes immediately converted into a mixture of about 2 volumes of nitrogen and i of carbon oxide which ascends through the furnace, producing a number of complex changes as it comes in contact with the ore, the end results of which may be thus summarized. 1 At the top of the furnace the ferric 1 Vide Lowthian Bell, Chemical Phenomena of Iron Smelting ; also Alder-Wright, On the Chemical Changes accompanying the Smelting of Iron (Lecture at the Royal Institution, Friday, March 1 3th, 1874). The actual chemical changes which take place in the blast-furnace are indicated by the following equations (so far as the carbon oxide and iron oxide are concerned) : [A] Reduction of higher oxide to lower oxide and to metal by gas- eous carbon oxide (1) Fe x O y + CO = Fe.O^j + CO 2 . (2) Fe x O y + yCO = xFe + yCO s . [B] Oxidation of metal to lower oxide and higher oxide by carbon dioxide [changes the reciprocals respectively of (i) and (2)] (3) xFe + yCO 2 = Fe x O y + yCO. (4) Fe x O y ^ x + CO 2 = Fe x O y + CO. [C] Reduction of carbon oxide to carbon (5) xFe + yCO = Fe x O y + yC. (6) Fe x O y _! + CO = Fe x O y + C. [D] Reaction of reduced carbon on iron oxide forming carbon di- oxide (7) 2Fe x O y + C = 2Fe x O y _ 1 + CO*. (8) 2Fe x O y + yC = 2xFe + yCO 2 . [E] Reaction of carbon dioxide on reduced carbon (9) CO 2 + C = 2CO. At any given point in the furnace all the chemical tendencies thus indicated are at work simultaneously to extents dependent on the temperature and other circumstances ; so that the ac ion at that point is due, as it were, to the single resultant of the various forces 64 METALS AND THEIR [CHAP. oxide is partially reduced to lower oxides, and these react again upon the carbon oxide, setting free carbon in a state of very fine division in the pores of the par- tially reduced ore : in this part of the furnace the coal (if that fuel be used) is coked, and limestone is calcined to quicklime. If carbonate of iron (raw clay ironstone, &c.) be used instead of calcined ore it becomes here con- verted into oxide, the same changes further taking place. In the middle region of the furnace, reduction goes on only to a limited extent, the iron-oxidizing tendencies nearly balancing the iron-reducing tendencies, whilst the carbon-depositing and carbon-oxidizing tendencies are also nearly balanced ; so that the chief effect produced on the ore in sinking through this part of the furnace is that its temperature is greatly raised. In the lowest portion of the furnace the reduction of the ore is completed, partly by the finely divided carbon contained in its pores, partly by the action of alkaline cyanides (formed by the mutual reaction of carbon, alka- line carbonates from the ore and fuel, &c., and the nitro- gen of the blast) : l the reduced iron melts, dissolving as it does so a quantity of the finely divided carbon with which it is surrounded ; at the high temperaiure of the vicinity of the tuyeres, the reduced iron and the carbon, &c., jointly cause the reduction of more or less silicon phosphorus and sulphur (if present), which are also dis- solved by the fluxing iron. The earthy matter of the ore, the ash of the fuel, and the lime, &c., added as flux, also melt together forming a kind of impure glass or lava involved, viz., the iron reducing tendencies [A] and [D] ; the iron oxidizing [B] and [C] ; the carbon reducing [C] ; and the carbon oxidizing tendencies fD] and [E]. 1 In the case of potassium cyanide by virtue of the reaction K 2 CO 3 + 40 + N 2 = 3CO + 2KCN. in.] CHIEF INDUSTRIAL APPLICATIONS. 65 (cinder] ; l this and the molten pig-iron sink down to the bottom of the furnace together, the latter, being heaviest, sinking to the bottom, whence it is drawn off from time to time through the " tapping hole," into moulds of sand in which it is cast into " pigs ;" the cinder flowing off constantly through the "cinder hole," excepting for a while after tapping off the pig-iron, when the cinder inside the furnace falls below the level of the cinder hole. 34. In blast furnaces that have been long in use the amount of alkaline cyanides present internally is some- thing astonishing, the small quantities of alkalies con. tinually brought into the furnace accumulating therein until relatively enormous amounts are present : this ac- cumulation is apparently brought about as follows ; the alkalies are volatilized to a considerable extent (query, in the metallic form as sodium, potassium, &c. ?) in the intensely hot lower portion of the furnace, and in this condition are largely converted into cyanides by the conjoint action of the finely divided deposited carbon and the nitrogen gas present : these cyanides are disse- minated through the gases, and on passing upwards to cooler regions are deposited (along with dust, &c., mecha- nically carried up) as a whitish sublimate, or " fume," on the surface of the ore, &c. ; the ore in descending thus becomes largely impregnated with cyanides, and when the mixture reaches the lower part of the furnace these cyanides take up oxygen, completing the reduction of the ore and forming cyanates which are immediately decom- posed by the heat ; the alkali metals of the decomposed 1 The term "slag" is often applied to this material ; but "slag" more appropriately refers to the somewhat analogous substance beaten out of the blooms during shingling after puddling ( 38), the name being derived from the German schlagen, "to beat" ; "cin- der" (query,from sintern, "to trickle"?) properly refers to the lava-like mass that runs from the blast-furnace and other analogous furnaces. F 66 METALS AND THEIR [CHAP. cyanates become again transformed into cyanides which are again filtered out of the gases in the upper parts of the furnace, and so on. To so great an extent does this accumulation of alkalies take place that as much as four cwt. of alkali-metals and two cwt. of cyanogen per ton of iron run have been found in the gases near the level of the tuyeres (Lowthian Bell). This formation and accu- mulation of alkaline cyanides serves to explain two anomalies in the working of the blast-furnace : first, on starting a newly-built blast-furnace, much more fuel is required during the first few days than after some weeks' working, even after allowance is made for the fact that a considerable amount of extra fuel is required to furnish the heat communicated to the masonry of the furnace ; direct observation shows that the cyanides present increase, by virtue of this accumulative process, part passu with the diminution in amount of extra fuel required during this period. Secondly, when analyses are made of the gases l present at different levels of the furnace, and the ratios calculated between the weights of nitrogen and carbon and nitrogen and oxygen, contained therein, it is observed that whilst at every level there is more oxygen and more carbon per 100 of nitrogen than that due to the blast alone (assuming the oxygen of the air to be wholly con- verted into carbon oxide, which gives a maximum of carbon as present in the gases) the carbon and oxygen 1 It deserves notice that in the well-known analyses of blast- furnace gases, made some years ago by Bunsen and Play fair, cyano- gen gas is represented as being present therein; the author's experience on the subject, however, leads him to the conclusion that the sub- stance viewed as cyanogen was really hydrocyanic acid vapour caused by the decomposition by carbon dioxide, moisture, &c. of the fume containing cyanide of potassium deposited in the interior of the pipe employed to collect the gases ; so that the existence of cyanogen gas in the lower levels of the blast-furnace is hardly substantiated. Vide Lowthian Bell, Chemical Phenomena of Iron Smelting, p. 138. in.] CHIEF INDUSTRIAL APPLICATIONS. 67 decrease relatively to the nitrogen for several feet upwards from the tuyere, and then increase again pretty regularly to the top. Now as any reduction of iron oxide by carbon oxide and subsequent reconversion of the carbon dioxide thus formed into carbon oxide in virtue of the CO 2 + C = 2 CO, must necessarily cause an increase in now 4Daflpcyi japp? C| T m T oxygen per 100 of nitrogen presen^ |he, app,are.nt decrease noticed from the tuyere level upw"Skrj&s fpf J5W^9 >J\S^* dozen feet or more is presumably really due to the evolution of nitrogen gas from the decomposition of the cyanates, the carbon and oxygen of these salts being mainly converted for the time being into non-gaseous compounds (probably into alkali-metal oxides and car- bonates through the further reaction of the cyanates on incompletely reduced oxides of iron), and these com- pounds being re-converted into cyanides a little higher up, thus simultaneously diminishing the nitrogen and increasing the oxygen in the gases, and therefore as a whole increasing both carbon and oxygen relatively to nitrogen in the upper levels. 35. The pig-iron thus produced in the blast furnace is virtually a solidified solution ( 102) of amorphous carbon in melted iron, more or less sulphur, silicon, phosphorus, &c., being also present, according to the nature of the ore and fuel used, and other circumstances. One peculiar circumstance connected with this substance is that under certain conditions as to the presence or otherwise of these impurities and more especially as to the time occupied in solidifying, a greater or less amount of the dissolved carbon passes spontaneously into the graphitoidal or black-lead modification which is insoluble in molten iron ; when this takes place the pig- F 2 68 METALS AND THEIR [CHAP. iron solidifies into masses exhibiting a grey colour and well-defined crystalline structure on fracture ; from the crystalline surface fragments of actual graphite can be picked out by a penknife point. When this separation and partial crystallization does not take place the fracture is whiter, and the pig more brittle. A good deal of the practical value of pig-iron for the preparation of castings depends on its being what is technically termed "grey," i.e., of such a nature that the graphitoidal separation and partial crystallization can take place readily during the time that the casting takes to solidify : and much of the art of the iron founder consists in blending pigs of various kinds so as to produce a casting of grey-iron where the granulation has taken place to just the extent requisite to give to the casting the maximum strength and power of resistance to strains. "White" pig-iron (in which little or no graphitoidal separation has taken place during the solidification of the pig after running from the furnace) is consequently of less commercial value than grey pig-iron, which again com- mands a price dependent on its grain (as well as other circumstances) : sometimes a pig will consist of white iron with patches of grey iron interspersed throughout ; in this case it is known as " mottled iron." This spontaneous allotropic alteration of the amorphous or lampblack form of carbon into the crystalline graphitoidal modification whilst dissolved in a solvent, is precisely analogous to a similar phenomenon taking place with amorphous silicon and aluminium ; by dissolving the former in the latter when molten, allowing to cool, and dissolving away the aluminium from the crystalline mass obtained, crystallized allotropic silicon can be obtained. Another phenomenon of the same character is the gradual separation of red phosphorus (insoluble in carbon disulphide) from a in.] CHIEF INDUSTRIAL APPLICATIONS. 69 solution of the yellow modification in carbon disulphide or certain organic iodides ; in these instances the action of light greatly promotes the allotropic change, if indeed it is not essential thereto ; in any case, however, the allotropic change of phosphorus is slow compared with that of carbon. 1 36. Pig-iron which is unsuitable for use in the pro- duction of castings in the foundry, or which is not re- quired for such purposes even though suitable, is usually worked up into malleable iron by refining processes, which consist essentially in the partial oxidation of the whole by a current of hot air and the reaction of the oxide of iron thus produced on the oxidizable impurities not yet removed. 2 Certain kinds of pig-iron, however, are treated in other ways, and more especially are directly converted into varieties of steel ; thus in Bessemer's pro- cess the impurities are almost wholly burnt out by blowing a stream of hot air through the molten mass ; in this way, however, it is impossible to produce malleable iron of uniform and good quality, so that to Bessemer's original blowing process is now superadded another step intro- 1 That portion of the amorphous carbon in grey iron which, has escaped conversion into graphite is regarded by many chemists as chemically combined with the iron and not merely dissolved therein ; the fact that, on dissolving such iron in hydrochloric acid, a fraction of the carbon combines with the liberated hydrogen and escapes as a volatile body being supposed to indicate combination of the carbon with the iron. That this does not necessarily follow, however, is indicated by the circumstance that when hydrogen is liberated in pre- sence of finely divided free sulphur, traces at least of sulphuretted hydrogen, and often much larger quantities, are produced by the direct combination of the nascent hydrogen with the particles of sulphur, which in this case is clearly not combined with any metal. 2 Thus, in the case of carbon 2xFe + yO 2 = 2Fe x O y Fe x O y + yC = yCO + xFe, and similarly with phosphorus, sulphur, silicon, &c. 70 METALS AND THEIR [CHAP. duced by Mushet, consisting in the addition to the blown Bessemer product, of a certain amount of fused spiegeleisen (a highly carboniferous pig-iron also containing manganese smelted from Spathose ore and deriving its name from the mirror-like crystalline surfaces exhibited on fracture), so as to bring the percentage of carbon in the total mix- ture up to the amount requisite to form a steely-kind of product, generally designated "Bessemer steel." Only pig-iron free from phosphorus or very nearly so and con- taining but little sulphur, can be thus successfully treated, as the blowing does not remove phosphorus from the pig-iron employed and only partially removes sulphur, although other noxious impurities, especially silicon, are thus oxidized and burnt out. In Heaton's process the oxidation of the impurities is effected by running the molten pig-iron on to a mass of nitrate of soda in a suitable vessel, the salt being contained in a kind of chamber or cavity at the bottom ; in this way a rapid stream of oxygen is made to bubble through the mass, by which means the same results are produced as by blowing air through in Bessemer's process ; it is stated that sulphur and phos- phorous are removed to a greater extent in this way than by air-blowing alone. In Uchatius's process, the pig-iron, is fused with a small quantity of iron oxide in a steel melting furnace, so that the oxide is reduced by the carbon of the pig, and a steel results of quality dependent on the amount of residual carbon, &c. In Price and Nicholson's method, and in the Siemens-Martin process, the quantity of carbon in the pig is reduced to that re- quisite to form a steel by the addition of scrap or other malleable iron nearly or quite free from carbon in suitable quantities : in one of the modifications of the latter pro- cess the iron is added as a spongy mass of reduced metal obtained by the action of reducing gases on very pure iron m.l CHIEF INDUSTRIAL APPLICATIONS. 71 ores ; and in another, partially reduced ore in a fused state is added to the fused pig-iron, and spiegeleisen added if necessary to the product to give the proper carbon percentage for steel : in both these modifications Siemens' gas regenerative furnaces are all but indispens- able ( 31)- FIG. 13 37. Figs. 13 and 14 represent two sections at right angles to one another, of a " Bessemer converter," con- sisting of a pear-shaped iron vessel lined with firebrick, or better, a particular material known as " gannister," and capable of movement about a horizontal axis. One of METALS AND THEIR [CM A P. the trunnions on which it turns is hollow, and enables a blast of air to be sent into the vessel through the hollow axle, a, by a tube to the base of the converter, which is a kind of box, roofed in with a firebrick cover through which pass several tuyeres, b b b. By hydraulic power, the converter is turned into an inclined position so that the molten metal is run in at the mouth, c, the tuyeres being above the level of the fused matter collecting inside ; a gentle blast is turned on to prevent the fused metal splashing into the tuyeres and stopping them up by in.] CHIEF INDUSTRIAL APPLICATIONS. 73 solidifying in them. The blast is then turned on and the vessel brought mouth upwards : when the blowing is completed, the requisite amount of spiegel is added and the blast kept on for a short period to produce perfect intermixture ; finally the converter is inverted so that the steel runs out into a large ladle from which it is poured into suitable moulds and formed into ingots or castings. The manganese in the spiegeleisen appears largely to ameliorate the quality of the metal produced, conferring on it a higher power of welding, rolling, and working generally without cracking, and diminishing the tendency towards " red-shortness " (brittleness whilst hot) notice- able in metal containing small quantities of sulphur ; hence manganese-iron alloys rich in the former metal are often employed in lieu of spiegeleisens which only contain lesser amounts ; these- are distinguished as " ferrornanganese." This influence of manganese on the physical and useful qualities of steel has long been known in the steel trade, the addition of manganese carbide to the materials used in steel-making having been patented by Heath in 1839, and very largely adopted since in one form or other. 38. Previously to the introduction of the Bessemer process, the product of which has, to a very considerable extent, superseded malleable iron for many purposes, the production of workable soft iron from pig-iron was effected by two processes still largely employed ; in one of these, known as the " charcoal finery,' 5 the pig is melted in a small furnace and covered with a heap of charcoal (coke is frequently employed, the expense of charcoal preventing its use for any but the finest qualities, such as those employed for tin-plate making) : powerful jets of air are then directed on to it from tuyeres for some time ; in this way the silicon, sulphur, carbon, and phosphorus 74 METALS AND THEIR [CHAP. present are oxidized, and a cinder formed mainly con- sisting of silicate and phosphate of iron ; considerable loss of metal usually attends this mode of operating. The process of " puddling " is in principle the same as that of the refinery, save that the fuel is usually coal, and FIG. IS. is burnt in a separate fireplace ; the flame is made to play over the iron to be puddled by means of an arched roof, Fig. 15 (whence the term reverberatory furnace). a is the door through which fuel is introduced, b 3 the in.] CHIEF INDUSTRIAL APPLICATIONS. 75 ashpit. The hearth, or sole of the furnace, c, is separated from the fireplace by a wall of brickwork, d, termed the " bridge," over which the flame plays on to the metal on the hearth. Through a working door, e, the puddler stirs up from time to time the charge with an iron rabble, so as to expose it to the air, and thus oxidize it, and to incor- porate with it a certain amount of oxide of iron used as a covering for the hearth and termed the fettling. The hearth itself rests on iron plates, supported on iron girders, with air spaces underneath to diminish the heating action on the plates, and the whole furnace is cased externally with iron, and strongly bound together; at the end furthest from the fire is a charging door, f, through which fresh pigs are introduced, and at the extreme end, at g, a " taphole " or " cinderhole " is fixed for running off the fluid tap-cinder (silicate of iron, &c. ), formed during the process. The draught of the fire, and hence the temper- ature, is regulated by a damper, k, on the top of the chimney, opened and closed by the workman by means of a chain or rod attached to the lever ; the door- hole is provided with a door supported by a chain and counterpoise, so that when the charge is to be removed, the door is lifted and a large space then left; whilst rabbling the charge the entrance of cold air is avoided by means of a small opening or notch at the bottom of the door through which the shank of the rabble is passed : when not thus required, this opening is closed by a brick, or a shovelful of cinders, &c. As the silicon and carbon are removed from the pig-iron, the substance, at first liquid, becomes pasty, and finally spongy masses of iron separate from the fluid cinder; these are raked and worked into one mass termed a " ball " or " bloom " when the metal has wholly " come to nature " ; this is extracted from the furnace through 76 METALS AND THEIR [CHAP. the door-hole, and quickly transferred to powerful jaws or squeezers, or hammered under a steam hammer (shingled] until it forms a coherent mass ; during the shingling, silicate of iron and fused oxide of iron are squirted out on all sides by the blows, constituting "slag" (schlagen = to strike). The puddled ball is usually further worked by forming into bars under the hammer, cutting them up, welding together the fragments (after " piling " or " faggoting " them into bundles and heating to a welding heat in a " reheating furnace ") and again rolling into bars, and in some cases repeating the process ; this develops a fibrous structure in the bars or plates produced, greatly adding to their strength. Some- times the operations of refining by the finery and puddling are combined, the metal being partially purified by the first process, and then finished off by the second; indeed, by some the term "puddling" is restricted to the application of the process above described to the refined or partially purified metal, the conversion of pig iron into malleable iron in one operation being designated as "pig boiling" on account of the ebullition of the fused pig caused by the rapid escape of carbon oxide when the action is at its height : others use the term "puddling" as a generic name for both operations, and call the puddling of refined iron " dry puddling " on account of the smaller quantity of fluid cinder formed. Sometimes the " pig-boiling " operation is applied directly to the liquid metal tapped from the blast furnace without casting into pigs and cooling ; in this way fuel is saved, but many practical inconveniences are introduced. The " fettling" of the puddling furnace becomes to a considerable extent reduced to the metallic state, and thus helps to balance the loss of metal caused by oxida- tion and conversion into fluid silicate of iron, &c. (tap- in.] CHIEF INDUSTRIAL APPLICATIONS. 77 cinder]. By subjecting this silicate to a kind of liquation process, part runs away as a more fusible cinder, and part remains as a difficultly fusible mass : this latter is often used as a covering for the hearth of the puddling furnace under the name of "bulldog." 39. To avoid as much as possible the enormous amount of manual labour of a most exhausting kind entailed in these processes, machines have been con- structed to effect automatically the same kind of opera- tions : in one of these, known as " Banks' rotary puddler " (Fig. 1 6), the mechanical agitation is effected by placing the pigs inside a kind of iron drum, c, lined with rirebrick and supported on friction rollers, so that the drum itself forms the reverberatory furnace, being applied to the flue end of the fireplace, the flame from which is regulated by two air blasts, one above the fire bars, a, the other below, b; a large cog-wheel surrounds the drum so that it can be made to rotate at any required speed ; a movable hood, d, leading to the chimney is applied to the far end, supported by a crane, so that when d is thrust on one side, the end of the drum is open, serving as a charging and withdrawing door. The action of the machine in producing mechanical agitation of the charge is greatly enhanced by the peculiar form of lining employed ; some tolerably fusible iron ore is placed inside and melted by the flame ; the drum being brought to rest, a pool of liquid matter is formed at the bottom ; lumps of a very hard and infusible ore are thrown into this pool, whereby the fluid matter is chilled and solidified, thus cementing the lumps to the inside. The same process is repeated, the pool being now formed in another place, and so on, until the whole of the inside of the drum is lined with irregularly projecting infusible lumps. Several modifications of the machine have been brought out CH. in.] METALS AND THEIR APPLICATIONS. 79 subsequently by other inventors : puddling by machinery, though successful up to a certain point, can as yet, how- ever, hardly be said to have advanced far beyond the experimental stage, saving perhaps for some special kinds of material. 40. The steels formed by most of the processes above alluded to (" direct processes " and methods based on the partial decarburization of pig-iron, 31, 36), though serviceable for many purposes, are not, as a rule, well adapted to the manufacture of tools and cutting instruments generally, although steel of the highest qualities can be formed by some of theae methods by paying special care and attention, and choosing suitable substances to start with. A steelmaking process, known as cementation, and based on entirely different principles (viz., the carburization of malleable iron), is largely employed for the production of the finer kinds of steel; this process is of much greater antiquity than most of the other methods above described; it consists in packing bars of the purest malleable iron in boxes alternately with layers of charcoal (nitrogenous organic matters, such as horn-shavings, ferrocyanide of potassium &c., being often also added), and then heating the whole to a high temperature for a lengthened period (eight to twelve days). The bars of soft iron thus become carburized and converted into " blister steel " (so called from the occurrence of blisters on the bars). Probably the rationale of this conversion is the absorption of carbon oxide by the metal, and its reduction, with separation of carbon and oxidation of the metal, thus xFe + yCO = yC + Fe x O y , the iron oxide thus produced being again reduced to the So METALS AND THEIR [CHAP. metallic state by another portion of carbon oxide, thus Fe,O y + yCO = yCO 2 + xFe. That these two actions can go on simultaneously under certain conditions has been shown by Lowthian Bell (Chemical Phenomena of Iron Smelting), nickel and cobalt (but apparently no other metals) possessing the same power. The blister steel thus produced is not uniform in character, the outsides of the bars being, as might be anticipated, more highly carburized than the insides ; to obtain a homogeneous steel, the blister steel is melted and cast into ingots of " cast steel " ; " shear steel " or " tilt steel " is made by cutting up bars of blister steel, binding in bundles, heating to a welding temperature, and then hammering under a tilt hammer. ([ For cutting instruments the crystalline character possessed by cast steel is objectionable, although the uniformity of structure produced by fusion is indispensable ; hence the cast steel is heated and carefully forged and rolled so as to develop a fibrous character. 41. The great value of steel arises fro in the peculiar effects produced on it by rapid cooling after heating : it thus becomes excessively hard and considerably brittle ; by gently heating hardened steel and allowing it to cool slowly this brittleness is much diminished or altogether removed, and great elasticity communicated instead ; the degree of " temper " thus given to the steel by this annealing or tempering depends on the temperature to which the hardened steel was heated and from which it cooled down slowly; the higher the temperature, the softer the steel : in practice, this temperature is judged of by the colour exhibited by the surface of the steel in.] CHIEF INDUSTRIAL APPLICATIONS. 81 (previously polished) on heating : thus the following colours correspond to the temperatures annexed : Colour. Temperature. Pale yellow to dark straw 215 260 Brown yellow shading into purple . . . 260 275 Purple to dark blue 280300 Pale blue passing into green 305 340 Steels tempered at pale yellows are preferred for most tools for metal working ; darker straw shades for screw cutting and tools for working in wood ; brown yellow to purple shades for instruments that have to resist blows or vibration, such as chisels, hatchets, saws, &c. : dark blue and purple shades are only employed when great elasticity is required, as for clock, watch, and other springs ; whilst tempering at pale blue to green renders the steel so soft as to be quite unable to bear a cutting edge^ As soft steels can be readily welded to malleable iron, many tools are made chiefly of soft iron with a strip of steel affixed where the cutting edge or face is placed : thus in the production of dinner-knives the body of the blade is of soft iron with a comparatively thin steel face. Frequently heavy iron goods are partially steeled on the surface (case hardened} by placing them in contact with some carbonaceous matter, especially ferrocyanide of potassium, keeping at a high temperature, and finally plunging into cold water to harden : a film of steel of ^5- to f inch in thickness can thus be produced. In order to procure steels of great hardness for special purposes, various combinations of iron with minute quan- tities of other metals have been proposed, but the prac- tical value of many of these is as yet rather doubtful. Thus, according to Faraday and Stodart, rhodium, silver, G 82 METALS AND THEIR [CHAP. or chromium improves the quality when added in minute quantity to steel. Titanium steel and tungsten steel have also been prepared and manufactured ; the latter is extremely hard ; as yet, however, none of these substances have come into anything like extensive use. 42. Copper. The principal sources of this metal are the Australian ores, consisting chiefly of carbonate ; those from North America and Siberia, mainly composed of native metal ; and the various forms of copper pyrites or double sulphide of iron and copper, and copper glance largely mined (together with other cupriferous minerals), in Spain, Chili, Cuba, Saxony, Russia, Wales, and more especially Cornwall. The pyrites of the Huelva and Tharsis Mines in Spain and Portugal contains only small quantities of copper, and is ordinarily treated by a wet process ( 43) after the sulphur present has been utilized for the manufacture of oil of vitriol : certain ores, consisting of copper carbonate disseminated through sandstone and other rocks, are occasionally worked by another more simple wet process consisting of the solu- tion of the copper by treatment with hydrochloric or sulphuric acid, and its precipitation from the solution by scrap-iron. 1 In a similar fashion copper is extracted from the pump-waters of the copper-mines by simply passing them into reservoirs or tanks containing scrap-iron ; the copper gets into solution in the water from the sponta- neous oxidation of the copper pyrites forming soluble copper and iron sulphates. The chief method of extract- ing copper from its ores however is that known as the " Swansea process," from its being carried out on a vast 1 CuC0 3 + 2HC1 = C0 2 + H 2 + CuCl 2 CuCl 2 + Fe = Cu + FeCl 2 . in.] CHIEF INDUSTRIAL APPLICATIONS. 83 scale at that locality, something like 20,000 tons of copper being annually smelted there. The principle of the pro- cess is simple enough, it being based on the circumstances that if copper pyrites be exposed to the action of hot air, the iron sulphide is oxidized first, so that copper sulphide free from iron is first obtained ; and that when this is further oxidized, the copper oxide formed reacts on the yet unoxidized sulphide, forming sulphur dioxide, which escapes, and metallic copper : the practical carrying out of these operations, however, is sufficiently complex, at least six stages being recognisable : these consist of (a) preliminary calcination of ore, whereby much of the iron sulphide is converted into oxide whilst arsenic and sulphur are expelled as oxides : (&) first fusion of calcined ore ; in this process lime, sand, fluorspar or other fluxes are added when requisite, so that the earthy matters of the ore and the majority of the iron oxide fuse together to a cinder, whilst impure cuprous sulphide sinks to the bottom, whence it is drawn off through a tap-hole in^the furnace and run into water. By judiciously mixing together suitable ores, such as carbonate and roasted copper pyrites, &c., with suitable admixtures of ores containing siliceous gangue, or of siliceous cinder from later operations, a tolerably uniform product is obtained, designated "first matt" or "coarse metal" The object of running the fused matt into water is to disintegrate it and render it ready for the third operation (<:), which consists of roasting the granulated coarse metal for several hours, so as to remove much sulphur and oxidize most of the remaining iron, (d) melting calcined coarse metal ; the roasted coarse metal is mixed with suitable quantities of a rich copper ore containing silica with but little iron, or certain qualities of cinder from the subsequent operations, and the whole fused so as to form another siliceous iron G 2 84 METALS AND THEIR [CHAP. cinder, and a nearly pure cuprous sulphide or " fine metal" (second matt) : the cinder thus produced generally con- tains copper which is extracted by using it for admixture with other substances in the production of coarse metal or by other special treatment. The fine metal thus produced is cast into pigs, and consists of nearly pure cuprous sulphide, with a small admixture of iron sulphide, so that the term " metal," as applied to it and to the first matt, is, strictly speaking, incorrect In the fifth opera- tion (e) actual metallic copper is produced, the pigs of " fine metal " being roasted in a reverberatory furnace ( 38), so as to burn off much of the sulphur and form copper oxide ; on raising the temperature so as to fuse the whole, the molten mass appears to "boil," from the rapid evolution of sulphur dioxide, metallic copper being set free ; ultimately this is drawn off by a tapping hole ; the scoriae from this operation are generally highly cupriferous and are worked in with the mixture employed in the fourth stage (d). The copper thus produced is run into moulds and is then designated " blister copper," as it is full of cavities from the gases with which it is charged ; it generally retains small quantities of foreign substances, such as iron, sulphur, arsenic, &c. To remote these the sixth operation (/) of refining is resorted to ; this consists in roasting the ingots of blister copper so as to oxidize them superficially, the porous character of the metal allowing also of a considerable amount of internal oxida- tion ; finally, the heat is raised so as to fuse the whole, when the oxide of copper previously formed oxidizes most of the impurities, producing a much purer metal : the scoriae are raked off and the oxide of copper dissemi- nated through the molten metal removed by placing powdered charcoal or anthracite on its surface, and stirring up the whole with a pole of green wood, usually in.] CHIEF INDUSTRIAL APPLICATIONS. 85 birch : if the metal be " over-poled " it becomes some- what brittle, probably from its taking up a little carbon : this is removed by skimming off the anthracite and exposing the fused copper to the air a while. When the poling operation has been carried on to the right extent (known by continually sampling the metal by means of a ladle and examining the physical characters of the small ingot produced by quickly cooling the ladle and contents in water), the copper is cast into ingots, or is granulated by pouring into water, forming, according as the water is cold or hot, feather-shot copper or bean shot, the latter being in rounded granules, the former in less regular shapes. Sometimes operations c and d are again repeated in order to obtain a yet better " fine metal ; " not unfre- quently a little lead is added in the refining operation. This metal oxidizes in the hot air-current, ana the oxide so produced facilitates the removal of arsenic, iron, anti- mony, &c., by yielding oxygen to these impurities : finally the lead is itself removed by continually stirring the fused metal and raking off the scoriae before poling. In some cases, the cinders of the various operations are not directly intermixed with fresh materials for one or other of the above-mentioned stages, but are subjected to special fusion operations with a view to obtaining from them the copper present intermixed with lesser quantities of the valueless silicates of iron, &c., constituting the majority of the cinder : these special treatments of scoriae, when adopted, are usually applied to the cinder from operations b and d; that from the former often contains metallic grains of copper diffused through the mass, which are united together by simple careful fusion ; that from the latter process is fused with coal or other reducing agents, when the copper present is reduced along with portions METALS AND THEIR [CHAP. of other metals, forming a white brittle alloy which is worked up with a fresh charge of coarse metal in the fourth operation (d). 43. The wet process by which poor cupriferous pyrites is worked for copper is commonly known as " Hender- son's process," from the name of the patentee. This consists in roasting the " burnt ore " of the vitriol-maker (pyrites that has been burnt in specially-constructed roasters or " kilns," so as to utilize the sulphur dioxide produced) with common salt in a peculiarly constructed kind of furnace where the flame does not play directly on the materials to be heated, but passes from the fire over a thin brick-arched roof surmounting the bed or " sole " of the furnace, so that the substances to be roasted are heated by radiation from the nearly red-hot brick arch ; in fact resembling in construction the " salt-cake in.] CHIEF INDUSTRIAL APPLICATIONS. 87 furnace " of the alkali-maker, saving that, as a somewhat less heat is required, the flame is not made to pass through flues under the sole of the furnace after heating the radiating brick arch. Fig. 17 gives a general idea of the character of furnace employed ; the flame from the fire, a, passes between the external roof of the furnace cc, and the thin inner arched roof d d, and thence to the chimney through the underground flue e (practically, the waste heat is utilized before the gases pass to the chimney by making them heat evaporating pans, &c.) ; b is the ashpit, and ////working doors for stirring the charge from time to time as the operation progresses. The bed of the furnace is supported over a series of arches (something like a railway viaduct) ; in the centre of each arched vault thus formed is a cavity, h h h /i, left in the brick- work of the sole, closed by a tile, so that when the charge is sufficiently roasted the substance is withdrawn from the furnace through these perforations into " bogies," or trucks, placed underneath to receive it, fresh materials being added through the hopper, k. The burnt ore usually contains about 3 to 3*5 per cent, of sulphur and 3 to 4 of copper ; if too little sulphur be present rela- tively to the copper it is mixed with a suitable quantity of the dust of unburnt cupriferous pyrites, so as to make the sulphur and copper stand to one another in about the ratio of three to two : about four parts of salt for one of copper are then added, and the whole roasted in the furnace for about six hours, the heat being not allowed to become too great, otherwise the copper chloride formed is further decomposed and rendered less readily soluble in water. Fumes of hydrochloric acid are evolved and con- densed by a tower filled with coke kept moist by water trickling down exactly as in the salt-cake process; a certain amount of the chlorides of copper, iron, and arsenic is 88 METALS AND THEIR [CHAP. also thus condensed. The acid liquor thus produced is used to wash out the last portions of copper from the residue left on treating with water (lixiviating} the mix- ture of chlorides of sodium, copper, and iron, sulphate of soda, and ferric oxide, &c., formed by the roasting in the furnace. Usually the pyrites contains minute quantities of silver which become transformed into chloride, and this, though almost insoluble in water, is sufficiently soluble in brine to be dissolved out by the aqueous solu- tion obtained, a considerable amount of the salt originally added remaining unchanged and thus furnishing the solvent. From the first aqueous liquors the silver is separated as described in 21 ; from the residual liquors left after precipitation of the silver the copper is thrown down by means of scrap-iron. Usually the liquors obtained by washing the insoluble residue left after the first lixiviation with water with the acid watery solution from the tower furnish a less pure copper on treatment with iron, and therefore are worked up apart. When the roasting has been properly conducted, the substance finally left undissolved is all but free from copper, and consists mainly of ferric oxide with more or less quartzose matter. This " purple ore " is sometimes of sufficiently good colour to be used as a pigment ; it furnishes a good material for "fettling" puddling furnaces ( 38), and is sometimes used up in the copper extraction works as a sou r ce of metallic iron to precipitate the copper, the oxide being dried and reduced either by heating with small coal, or by the gases produced in an arrangement somewhat analogous to a Siemens' gas-producer ( 31) : the copper precipitated by the reduced purple ore is somewhat contaminated with unreduced iron oxide, coke dust, quartz, &c., but these impurities are readily removed during the melting and refining processes through which in.] CHIEF INDUSTRIAL APPLICATIONS. 89 the copper is put before it is suitable for manufacturing purposes. The theory of this wet process for copper extraction is that under the oxidizing influence of the hot air in the roaster the copper sulphide and common salt become transformed into copper chloride and sodium sulphate, thus : Cu 2 S + S + 4NaCl + 4O 2 = 2CuCl 2 + 2Na 2 SO. t , the extra sulphur (assuming the copper to be present as cuprous sulphide) being derived from iron sulphide also present, the iron of which becomes converted partially into ferric oxide and partially into ferric chloride by a somewhat analogous action. 44. Many other processes for the extraction of copper are in use in various localities ; for the most part these are modifications of the Swansea method. At Mansfeld, in Saxony, an alloy, containing about 95 per cent, of copper and 3 of iron, with small quantities of silver, sulphur, and other impurities, is smelted in a small blast-furnace, by means of charcoal and coke, from the well-calcined ore of the locality. This is an argillaceous schist, throughout which copper pyrites is disseminated to the extent of a few per cent. only. From the alloy thus obtained the silver is separated by liquation with lead ( 20) ; or the silver is removed from the calcined ore before its treatment in the blast-furnace by heating the ore with salt, and then putting it through the Freiberg amalgamation process ( 23). Finally the impure copper left after liquation, and that directly smelted after removal of silver, are refined by roasting in air and fusion, &c., as in the Swansea process. Similar modes of procedure are employed at some works in Sweden and Norway. 90 METALS AND THEIR [CHAP. 45- Lead. By far the most common ore of this metal is galena, or lead sulphide ; the sulphate also occurs in moderate quantity in Australia and the United States, whilst the oxide, chloride, carbonate, phosphate, and chromate, though not exactly rare minerals, are still so far scarce as not to constitute any very considerable sources of the metal. Galena almost invariably contains silver in quantity varying with the locality, from less than an ounce to several hundred ounces per ton of metal ; usually gold is also present to a much less extent. As a first step the galena is separated as far as possible from siliceous gangue by crushing and washing with water so as to wash away the lighter earthy particles ; the ore is then roasted on the bed of a reverberatory furnace, usually with the addition of a little lime to serve as a flux for the residual gangue, &c., the whole mass being stirred up with a rabble from time to time so as to facilitate oxidation. In this way a mixture of lead oxide and sulphate is formed. When this change has progressed sufficiently far the temperature is raised by regulating the dampers ; the mass fuses and boils some- what as in the analogous operation of smelting copper by the Swansea process ( 42), and from the same cause, viz., the evolution of sulphur dioxide and formation of metal (vide 9, foot-note). The cinder formed in this operation often retains lead, which is separated by a further operation, somewhat as the analogous copper scoriae from the first melting in the Swansea method. 46. In some places the calcination of the ore and the subsequent fusion and reduction are made into two distinct operations carried out in separate furnaces. Sometimes the complete separation of lead in the second stage is facilitated by the addition of pieces of metallic iron, which, combining with the sulphur, liberates metallic in.] CHIEF INDUSTRIAL APPLICATIONS. 91 lead. In what is termed the " Scotch hearth " the re- duction is effected in a forge supplied with a blast of air from a tuyere, peat being the fuel preferred. The calcined and semi-fused ore, technically termed " browse " or " brouze," is placed on the glowing peats, and a little lime added ; ultimately most of the metal is separated and collects in a cavity at the side of the furnace, flowing out from the hearth when the fused metal rises up to a certain level ; the remainder forms with the earthy matter a " grey slag," which is usually smelted by a separate process to recover the residual lead. At Frei- berg a blast-furnace some 20 to 25 feet in height is employed for the smelting of an ore which contains silver and copper. When much siliceous matter is present in the lead ore, the slags are apt to contain much silicate of lead. To avoid the loss of lead thus rendered imminent cast-iron is mixed with the ore and the whole smelted in a blast furnace. Whatever mode of smelting is adopted, arrange- ments are employed for intercepting and condensing the fumes of lead carried away from the furnace by the escaping gases : either a series of condensing chambers is provided through which the gases pass before entering the chimney, or, where circumstances permit, a long gallery or tunnel is employed as the chimney, running up the side of a hill for a long distance, in some cases several miles. The ** fume " which collects in these flues and chambers is periodically collected and smelted to obtain the contained metal. Frequently the lead smelted from galena is somewhat impure, containing tin, antimony, copper, &c. Lead prepared from a given ore in the Scotch hearth is generally more pure than that otherwise smelted, because a perceptibly lower temperature is employed in the 92 METALS AND THEIR [CHAP. reducing operation, and hence foreign metals are reduced to a lesser extent. In order to remove silver, the processes of Pattinson or of Parkes ( 20) are employed. To' soften and refine lead containing foreign metals the lead is melted in a pot and then run on to the hearth of a reverberatory furnace, or it is fused in the reverberatory itself. The contained metals and some lead then oxidize and form scoriae, which are removed by skimming. When the scoriae consist of little but lead oxide (which is known by their appearance, or judged by taking a sample of the melted lead, cooling it, and examining its pnysical character and appearance when solid), the purified lead is run into moulds, forming pig-lead. With tolerably pure lead this refining operation is complete in a few hours, whilst with impure leads, such as those from Spanish ores, it is not complete till after two or three weeks heating and oxidation. 47- Tin. There is good evidence that this metal was known about 3,000 years ago, it being apparently re- ferred to in the Mosiac books. Since the term " Kas- siteros " is, according to Humboldt, derived from the Sanscrit " Kastera," and the word tin (tenn, Swedish ; den, Icelandic ; zmn, German ; tiatn, French ; stannum, Latin) from the Malay and Japanese timah, it is probable that the earliest sources of this metal were rather the Indian islands than the south-west coast of England, although it is tolerably certain that the Phoenicians traded with Cornwall at a period antecedent to the foundation of Rome. At present the chief sources of the ores of this metal are Cornwall, Banca, and Malacca ; some more or less considerable amounts being also derived from Bohemia, Saxony, Austria, Australia, the United States, Mexico, South America, and a few other places. The chief ores are the oxide (cassiterite> or tin-stone) and an in.] CHIEF INDUSTRIAL APPLICATIONS. 93 impure sulphide (tin pyrites, or stannine\ of which the former is much the more important. Frequently it is met with in the beds of streams (whence the term stream- tin), as rounded masses of tin-stone washed out from the veins higher up. This form of ore yields a very pure metal, and is consequently sought after with eagerness, not only in streams but in alluvial and estuarian deposits. Mine-ti?i, or ores brought up from the mines, is of varying character. Sometimes it is mixed with large amounts of wolfram, arsenical pyrites or copper pyrites, when special modes of treatment are necessary. Gene- rally a certain amount of foreign metallic ores and of gangue is contained. These are separated, firstly, by stamping and washing the ores so as to separate by gravity the heavy tin-stone particles from those of lighter minerals and stones ; and, secondly, by calcining or roasting in a reverberatory furnace with continual stir- ring, or in an automatic calciner, such as that used for the production of arsenic ( 59). By this means sulphur and arsenic are expelled, iron is oxidized, and copper is partially converted into sulphate. After this roasting the ore is weathered, or exposed to the open air, for some time, so as to complete the oxidation of the copper pyrites. The sulphate of copper thus formed is dissolved out by water, and the copper thence obtained by pre- cipitation with metallic iron ( 42). The oxide of iron is mostly removed by washing, being comparatively light. The roasted and washed ore is then heated with " culm " (a kind of anthracite), and a little of some flux, such as fluor- spar or lime, in a reverberatory furnace, care being taken that the temperature is not too high, otherwise much tin would be lost in the slag. The metal readily subsides in a fused state, and is then drawn off through a tapping hole into an iron vessel in which it is allowed to stand 94 METALS AND THEIR [CHAT. (whilst still kept fused) for some time, so that all scoriae may rise to the surface. 1 Finally the metal is cast into ingots, whilst the slags and scoriae are generally worked over again so as to recover any globules of metal retained, &c. If the tin is fairly pure, the ingots will be capable of breaking up into peculiarly-shaped elongated splinters (known as " grain tin "), when they are thrown down on a hard floor from some little height whilst heated nearly to the melting-point. Accordingly tin is often sent into the market in this form, as a sort of guarantee of its purity. Impure metal requires refining : this is effected by a liquation process, the ingots being gently heated in a reverberatory furnace ; tolerably pure tin flows away first, copper, iron, &c., remaining as an unfused mass, known as " hardhead " ; the last portions thus running away are so far impure as to require refining over again. The purer tin thus sweated out is then stirred up in a melting-pot with wet wooden poles, whereby some of the impurities (as well as some of the tin itself) are oxidized and brought to the surface as a scum, which is carefully removed and utilized as an impure tin ore. After standing some time in a fused state, nearly perfectly pure tin rises to the top, whilst the heavier portion at the bottom contains most of the residual impurities. The top portion is carefully ladled off and sold as "refined tin," and the bottom portion either liquated or refined over again, or sent into the market as " block tin " in ingots. This is usually too much contaminated with other metals to be capable of forming good "grains " by falling on a hard surface whilst hot. 1 The reduction is brought about by the conjoint action of the carbon of the intermixed culm and the carbon oxide of the gases in the furnace SnOo + C = CO, SnOg + 2CO = 2COj, in.] CHIEF INDUSTRIAL APPLICATIONS. 95 Formerly tin was often smelted by means of a small blast-furnace with charcoal, and this process is still used on the Continent; but it is considered by English smelters that this method furnishes a smaller yield and is more costly than that above described ; hence it has been given up in this country. A machine for perform- ing automatically the calcining and stirring operations in the preliminary treatment of the mine-tin is sometimes adopted, and a little salt added to facilitate the expul- sion of arsenic and sulphur and the conversion of copper pyrites into soluble copper compounds (as in Henderson's process for the extraction of copper from low percentaged cupriferous pyrites, 43). 48. Zinc. The peculiar properties of the alloy of this metal with copper, termed brass, have been known from a very early period, many of the so-called antique bronzes containing so much more zinc than tin as to approach much more nearly to brasses than to bronzes in character and composition : these alloys were probably obtained by smelting together a natural or artificial mixture of minerals containing copper and zinc, the processes for the isolation of the latter metal being of comparatively modern origin, depending on the volatility of the metal at a red-heat, i.e. being pro- cesses of distillation. The chief ores of zinc worked for metallurgical purposes come from New Jersey and the United States, Belgium, Silesia, and Spain, considerable deposits being also found in various parts of Great Britain. They consist mainly of oxide, sulphide, carbonate and silicate, the former being found in New Jersey : zinc blende (the sulphide) usually accompanies galena and sometimes pyrites, whilst calcimine (the carbonate) is found in Derbyshire without intermixture with lead ores, though often it occurs in the vicinity of galena : the 96 METALS AND THEIR [CHAP. silicate (electric calcimine) is chiefly imported into this country. When blende (known as " black jack" from its colour when tolerably pure save a little iron sulphide) is em- ployed as a source of zinc it is subjected to a pro- longed roasting for the purpose of burning off the sulphur and forming an oxide of zinc; 1 if lead be con- tained this roasting must be carried on for a longer period than if the blende be free from this metal : from the oxide thus produced the metallic zinc is reduced by mixing with small coal (anthracite) and heating in a distilling arrangement, in principle not unlike the " capellina " apparatus used for silver amalgam ( 22), or in fireclay retorts like those used in the gasworks. Calamine is usually roasted before being submitted to the distillation process, for the purpose of expelling moisture and carbon dioxide and of opening the pores of the mass and rendering it easy to pulverize and mix with the powdered anthracite ; frequently a mixture of calcined blende and calamine, or of red zinc ore (oxide of zinc) and calamine is employed instead of one kind of ore only. 49. The character of the distilling arrangement em- ployed varies considerably in different localities ; one of the oldest forms (Fig. 18) consist of a number of large crucibles filled with the mixture of zinc ore and small coal and heated by a reverberatory furnace ; each crucible is closed with a cover luted on air-tight : the vapour of zinc and the carbon oxide formed by the heating are con- ducted out of the crucible through a hole in the bottom, into which is cemented a fireclay pipe passing down through the floor of the reverberatory furnace into a vault below \ iron tubes are affixed to the lower ends of 1 2ZnS + 3O 2 = 2ZnO + 2SO a . III.] CHIEF INDUSTRIAL APPLICATIONS. 97 these fireclay pipes, dipping downwards into vessels containing water, so that the zinc condenses in the tubes and runs down into the vessels underneath. To prevent the mass in the crucibles falling down the tubes blocks of wood are inserted into the fireclay pipes ; these become carbonized by the heat, and are then sufficiently porous to allow of the vapours passing downwards through them, whilst retaining sufficient strength to prevent the superincumbent solid matter from breaking through them. The iron tubes are cleared out by a rod from time to time lest the condensed zinc and the " fume," or oxide, carried over should block them up. In Silesia retorts are used shaped like small gas retorts or large muffles ; the vapours are led away into a rectangular downward condensing tube, luted on to H 98 METALS AND THEIR [CJJAP. the mouth of the retort ; several of these retorts, some- times twenty, are mounted in a " bench" and heated by the same furnace. In what is termed the Belgian pro- cess, a large number of retorts are employed mounted in a kind of kiln, each retort being placed at an angle of about 30 with the horizon, the mouths being lowest : short clay condensing pipes are luted into the mouths of the retorts : to these are affixed conical wrought-iron pipes with a narrow terminal orifice some J inch in diameter : the metallic zinc collects in the clay pipes, whilst the iron conical terminals retain a considerable amount of zinc oxide which is collected and used over again with a fresh charge. As many as eighty retorts are sometimes mounted in the same bench, to equalize the rate of working off; those at the top are usually made smaller and are charged with more easily reducible ores, so that the lesser heat communicated to them may not interfere with the process, as a whole, by causing delay through great differences in the time required to work off the charge in each retort. The waste heat from the bench of retorts is employed to roast and calcine ores for a new operation, and to dry and season the fireclay retorts and tubes kept in stock for renewals in case of breakages, &c. 50. When the zinc ores used contain cadmium, this metal is chiefly contained in the first portions of zinc that distil over ; the fume which is condensed at the same time is brownish and contains much cadmium oxide j from this fume, or from the cadmiferous zinc, metallic cadmium can be separated, best by a wet process, consisting of solution in acid, precipitation of cadmium sulphide by a current of sulphuretted hydrogen, whereby this metal is completely separated from zinc, conversion of the sulphide into carbonate by solution in acid and in.] CHIEF INDUSTRIAL APPLICATIONS. 99 precipitation by an alkaline carbonate, and finally dis- tillation of the carbonate (or of the oxide prepared therefrom by gentle ignition) with lamp-black, whereby metallic cadmium is obtained as a distillate. Metallic cadmium, however, is but little used, the main industrial application of this element being the use of its sulphide as a brilliant yellow pigment : certain of its salts (iodide and bromide) are also employed in medicine and for photography. H 2 ioo METALS AND THEIR [CHAP. CHAPTER IV. METALLURGY OF THE LESS IMPORTANT OXIDIZABLE METALS. 51. OF the remaining metals, few are of great indus- trial importance in the reguline state ; aluminium and, in a less degree, magnesium are used to some extent, whilst the former of these, as well as nickel, antimony, bismuth, arsenic, and manganese, are of value for the preparation of sundry important alloys. Aluminium. The metallurgy of aluminium differs from that of any other of the above described metals, inasmuch as it is impossible to obtain the free metal from any of its natural sources, abundant though these are, by the ordinary methods of smelting, &c.; and pro- cesses for converting these natural sources into com- pounds that can be economically dealt with are a necessary first step towards the extraction of the metal. Till about twenty years ago aluminium was simply known as a chemical curiosity obtained in an impure state by Davy, and subsequently in a purer condition by Wohler, CErsted, and Bunsen, the last of whom prepared it by electrolysing the double chloride of aluminium and sodium or potassium whilst in a fused condition. Deville, about 1856, obtained the metal on a larger scale by iv.] CHIEF INDUSTRIAL APPLICATIONS. 101 acting on sodium with the vapour of aluminium chloride, prepared by heating strongly in a current of chlorine gas a mixture of pure alumina (oxide of aluminium) and carbon : although carbon alone will not remove oxygen from alumina, yet, when to the affinity of carbon for oxygen that of aluminium for chlorine is superadded, the oxide of aluminium is broken up, carbon oxide and aluminium chloride being formed. The process of Deville is now modified by employing the double chloride of aluminium and sodium, and fusing this compound with sodium and a flux of cryolite (a double fluoride of alumi- nium and sodium found in Greenland) : the sodium then takes away the chlorine from the aluminium, setting free the metal and forming sodium chloride. Cryolite alone and sodium may also be employed, the sodium in this case taking fluorine from the aluminium and forming sodium fluoride. The two essentials in the process are the preparation of sodium on a manufacturing scale, and the formation of a pure alumina free from silica, for the preparation of the aluminium and sodium chloride ; this latter point is of the utmost importance, as, if not attended to, the aluminium finally produced is apt to contain silicon, which destroys the malleability of the metal and renders it crystalline and unsuitable for most of its ap- plications. Clay, common enough everywhere, is there- fore usually wholly unsuitable as a first raw material in the aluminium manufacture on account of its containing silica, generally in such a condition as to render it very difficult to separate from ordinary clay a pure alumina, excepting by the somewhat expensive process of manufac- turing crystallized alum from the clay and precipitating alumina therefrom. 52. A variety of indurated clay, known as bauxite, is, however, found at Baux in the South of France and 102 METALS AND THEIR [CHAP. elsewhere, from which it is not difficult to separate a pure oxide of aluminium by an inexpensive process, which was for some time worked by Messrs. Bell, .Bros., at Washington near Newcastle : l this consists in heating in a furnace a mixture of ground bauxite 2 and soda ash (carbonate of sodium), whereby aluminate of soda soluble in water is formed, whilst the silica is either unacted on or is transformed into a silico-aluminate of soda not dissolved by water ; on lixiviating the product with water the peroxide of iron present and the silico-aluminate of soda, &c., are left undissolved, and the aluminate of soda 1 The production of aluminium at these works has been given up for several years, the manufacture not proving as remunerative as was at first anticipated. The chemical reactions taking place during the process are as follows : Production of sodium aluminate A1 2 O 3 + Na 2 C0 3 = CO 2 + 2AlNaO 2 . Decomposition of sodium aluminate by carbon dioxide (in solution) 2AlNaO 2 + CO 2 + 3H 2 O = Na 2 CO 3 + 2A1 (OH) 3 . Formation of alumina from the hydrate 2A1(OH) 3 - 3H 2 O + A1 2 O 3 . Production of aluminium sodium chloride A1 2 O 3 + 2NaCl + 3C + 3C1 2 = 3CO + 2AlNaCI 4 . Manufacture of sodium from sodium carbonate Na 2 CO 3 + 2C = 2Na + 3CO. Extraction of aluminium from double sodium chloride AlNaCl 4 + 3Na = Al + 4NaCl. Extraction of aluminium from cryolite AlNaF 3 + 3Na = Al 2 Average composition of bauxite : URR. SlRMKNS. French. Austrian. Irish. Silica 2-8 3 '5 6-3 3'5 Alumina .... 57 '4 59 '2 64-2 35' Ferric oxide . 25'5 24'5 2-4 38-0 Calcium carbonate . 0-4 ) Titanic oxide . . . 3'i I 12-8 27-1 1 2'O Water 10-8 1 21'5 IQO'O 100-0 iv. ] CHIEF INDUSTRIAL APPLICATIONS. 103 is dissolved out ; by adding to the clarified solution the appropriate quantity of hydrochloric acid (or, better still, by impregnating it with carbonic acid gas) pure alumina is precipitated as a hydrate. This alumina is then dried, mixed with common salt (chloride of sodium) and charcoal, and formed into balls about the size of an orange ; vertical earthen retorts are then filled up with these balls, and heated to redness, whilst a stream of chlorine is passed through them ; the chloride of alumi- nium thus formed unites with the sodium chloride and distils over or sublimes as the double chloride, from which the metal is obtained by fusion with sodium. The sodium required in this manufacture is simply prepared by heating to a very bright red heat a mixture of soda ash, charcoal or coke powder, and a little ground chalk; the action that ensues is of much the same character as that taking place in the distillation of zinc ( 48) ; the sodium is reduced to the metallic state and distils over into peculiarly shaped condensers in which it collects, being preserved from oxidation by a layer of coal naphtha. 53- Magnesium. The process employed for the production of this metal is in principle much the same as that used for aluminium, viz., decomposing the chloride (or double sodium or potassium chloride) with metallic sodium. To prepare the double sodium chloride, mag- ncsite (native magnesium carbonate) or the artificial carbonate prepared from Epsom salts (sulphate of magnesia) by precipitation with an alkaline carbonate, or that extracted from dolomite (native double carbonate of lime and magnesia) by Pattinson's process, 1 is dissolved 1 The dolomite is partially calcined, pulverized, and placed in a closed vessel with water ; carbon dioxide gas is then forced in by 104 METALS AND THEIR [CHAP. in hydrochloric acid, and an equivalent quantity of salt added; the whole is then evaporated to dryness and fused : or Epsom salts are decomposed by barium chlo- ride and the solution of magnesium chloride separated from the precipitated barium sulphate and evaporated down after addition of salt. The double potassium chloride occurs naturally as the mineral carnallite; from either double chloride magnesium is readily reduced by simply fusing with sodium and a little fluor spar as a flux. 1 The metal thus obtained is purified by distilla- tion in a current of hydrogen gas, the volatility of magne- sium at a high temperature under these circumstances being sufficient for the purpose. 54. The chief use of the metal being to produce a brilliant light by its combustion, it is sent into the market mainly in the form of filings for mixture with pyrotechnic materials to add to their brilliancy when burnt, and as wire or ribbon, prepared by squirting ( 74) the metal, heated till just fluid, through a conical orifice so that it solidifies as it is ejected, forming a continuous thin rod or wire ; by passing this between powerful rollers it is flattened into a ribbon. In order to burn these wires or ribbons a spirit or other lamp is provided, to which is attached a small machine contain- ing bobbins of the wire or ribbon connected with a clockwork arrangement so constructed that, on releasing a detent, the wires are slowly passed into the spirit flame in such a manner as to keep up a continuous magnesium a pump ; under a powerful pressure, magnesia is dissolved out as bicarbonate to the almost total exclusion of lime. The clear solu- tion of bicarbonate of magnesia ( " Dinneford's Fluid Magnesia") on heating gives magnesium carbonate as a precipitate and free carbon dioxide gas which is used over again for another operation. 1 MgNaCl 3 + 2Na = Mg + sNaCl. iv.] CHIEF INDUSTRIAL APPLICATIONS. 105 flame. Another mode of attaining the same result is to allow the filings of the metal (mixed when necessary with sand, &c., to dilute them) to fall through a narrow tube into the spirit flame from a small hopper above ; by means of a slide valve, the supply can be controlled or shut off altogether. An ingenious adaptation of this form of magnesium lamp has been proposed for the transmission of signals from ships, &c., by night. By opening the slide valve of a large arrangement on this principle for an instant only, a brilliant instantaneous flash of light is developed, visible in fine weather at long distances. By keeping the valve open for a some- what longer period, a more continued blaze is produced ; so that by properly regulating the intervals between the opening and shutting of the valve, any required signals may be telegraphed according to the Morse Code, the instantaneous flash representing the dot, and the some- what more lengthened one the line or dash. The light given out by burning magnesium is very rich in actinic rays and is, consequently, of value for photographing in the absence of sunlight. 55. Nickel. The principal minerals containing this metal are generally of so far complex a character that a succession of processes is requisite in order firstly to obtain a nickel compound free from other metals, and secondly, to reduce this compound to the metallic state. A considerable amount of nickel is extracted from "Speiss," a residuum left in the preparation of "smalt," which is an impure silicate of cobalt, prepared by fusing with siliceous matters and pearl-ash the roasted and washed cobalt and nickel arsenides and sulphides consti- tuting the chief ores of these metals. During this process an arsenide of nickel (containing also sulphur, iron, copper, &c.) separates in the fused state and sinks to the 106 METALS AND THEIR [CHAP. bottom of the smalt melting pot. From this sp^iss nickel is separated in the form of oxide by continued roasting, to drive off some of the arsenic and sulphur, solution of the residue in hydrochloric acid or aqua regia, careful precipitation of iron by means of a regulated addition of lime, with a little bleaching powder, separation from the filtered liquid of copper, bismuth, lead, &c., by passing through it a current of sulphuretted hydrogen gas, and finally precipitation from the clarified fluid of cobalt in the form of peroxide by addition of bleaching powder after neutralization by lime, and subsequently of nickel oxide by further addition of lime or soda to the filtrate from the cobalt precipitate. Other nickeliferous minerals admit of the nickel being separated by pro- cesses somewhat more simple than these, but generally consisting of the same kinds of operations, viz., solution in some appropriate acid, removal of foreign metals by sulphuretted hydrogen or other appropriate reagent, and. finally, conversion either into oxide or carbonate after separation from cobalt by means of bleaching powder or other chemical means. 1 In order to obtain the metal from these compounds they are mixed with flour or oil, &c., and strongly heated, when more or less compact lumps of reduced nickel are formed. If higher tempera- tures still be employed, the metal can be obtained in the fused state and cast into ingots ; as thus prepared, the nickel contains a small quantity of carbon which communicates to it a higher degree of fusibility (as with iron, 30). Occasionally the oxide is converted into oxalate ; on heating this salt in a well-covered crucible metallic nickel is left. It has been proposed to smelt an alloy of copper and nickel by mixing together the 1 Vide A. H. Allen, Journal of the Society of Arts, February 1878. iv.] CHIEF INDUSTRIAL APPLICATIONS. 107 purified nickel oxide and copper oxide or carbonate and reducing the mixture by means of hydrogen, or carbon oxide, or by heating with charcoal powder or coal dust, the reduced alloy being ultimately fused and cast into ingots. Similar processes have been found to answer well in the case of other comparatively costly alloys ; it is stated, however, that the nickel-copper alloy thus obtained does not answer so well for the manufacture of German silver ( 103) as metallic nickel and copper prepared separately. One chief application of nickel in the metallic state is as a coating for other more oxidizable metals, especially iron and steel, the nickel being deposited thereon by electroplating processes ( 100). 56. It is noteworthy that nickel, cobalt, and iron, the three metals most magnetic in characters, and otherwise associated and allied in various respects, also possess the peculiar power of decomposing carbon oxide and setting free carbon therefrom at temperatures close to a low red heat. 1 This action is capable of going on to an indefinite extent, as the metallic oxide formed by the action becomes again reduced by a second portion of carbon oxide, thus (1) xM + yCO = M x O y + yC. (2) M x O y + zCO = M x O y _ z + zCO 2 . (3) MxO y _ z + zCO M x O y -f zC. So that a continuous deposition of carbon and forma- tion of carbon dioxide goes on in virtue of reactions (2) and (3). No other metals appear to possess this peculiar property. 57- Antimony. Besides occurring as sulphide, occasionally intermixed or combined with the sulphides 1 Lowthian Bell, Chemical Phenomena of Iron Smelting. io8 METALS AND THEIR [CHAP. of other metals such as copper, iron, lead, silver, and nickel, antimony is found as a native alloy with silver and arsenic, and sometimes iron in addition, and also as oxide and oxysulphide; the chief ore, how- ever, is the sesquisulphide Sb 2 S 3 , stibnite, which usually occurs in veins in calcareous or siliceous rocks, and sometimes imbedded in barytes (heavy spar or barium sulphate). From the gangue it is often separated by a process of liquation, the sulphide being readily fusible ; the crude sulphide thus obtained is roasted to drive off arsenic and some of the sulphur; the mixture of oxide and sulphide thus obtained is then heated with charcoal and soda ash or potashes, whereby metallic antimony is formed which sinks to the bottom of the crucible, a fusible impure sulphide of antimony and sodium (or potassium) floating on the top : this is separated and utilized in the manufacture of antimonial compounds such as tartar emetic, Kermes mineral, &c. Occasionally the sulphide (separated from gangue by liquation or not according to the richness of the ore) is simply fused in a crucible with scrap-iron, whereby iron sulphide is formed and metallic antimony; or a com- bination of this method and the preceding is employed, the crude sulphide being roasted, and the impure oxy- sulphide thus formed being heated with potashes or soda ash, or, better still, salt-cake (sulphate of soda) and scrap-iron. If iron, copper, &c., be present in the metal thus obtained to an injurious extent, they may be removed either by powdering, mixing with antimony oxide and fusing so as to oxidize the impurities ; or by treating the fused metal with small quantities of nitre, whereby the same result is brought about ; another mode of purifying consists in fusing the metal in coarse powder with soda ash and a little antimony sulphide ; in this iv.] CHIEF INDUSTRIAL APPLICATIONS. 109 way sodium sulphide is formed which sulphurizes and removes most of the impurities. A method that has been found by Berthier to give good results as to yield and purity of metal is to heat in a suitable reverberatory furnace a mixture of antimony sulphide, iron oxide from the rolling-mills (smithy scales), soda-ash or salt-cake, and charcoal powder ; or a mixture of antimony sulphide, scrap-iron, and salt-cake. 58. Bismuth. For the most part this metal occurs in the native state disseminated throughout quartzose rocks ; from these it is readily separated by simple liquation, the crude metal thus obtained being purified by fusion with a small quantity of nitre, whereby arsenic, iron, lead, sulphur, &c., are oxidized and removed. When other natural bismuth compounds are worked up, the most satisfactory process consists in obtaining the metal in solution, as nitrate, by treating the ores with nitric acid, addition of a large bulk of water so as to precipitate basic bismuth nitrate (subnitrate), 1 and reduction of this salt, after washing and drying, with charcoal in a crucible : a metal free from most of the ordinary impurities is thus obtained ; it is, however, liable to contain small quantities of arsenic, the amount of which may be lessened or altogether removed by digesting the precipitated sub- nitrate with caustic soda solution, whereby the arsenic compounds carried down with the precipitate are mostly dissolved out : this method of treatment is also applicable for the refining of crude bismuth containing lead, iron, &c. Often silver is present in crude bismuth; to separate the two metals the mixture is dissolved in nitric acid and the silver precipitated as chloride from the solution before adding water to throw down the bismuth; or the whole is cupelled (bismuth answering 1 Probably Bi(NO 3 ) 3 + 2H 2 O = 2HNO 3 + Bi(NO 3 )(OH) 2 . i io METALS AND THEIR APPLICATIONS. [CH. iv. in the operation as well as lead), and the bismuth re- covered from .the oxide formed, the saturated cupels, c., either by the wet process or by heating with coal, &c., to reduce the oxide. At Joachimsthal an ore con- taining bismuth, nickel, cobalt, and other metals is heated with scrap-iron and soda ash, with lime and fluor spar as fluxes : bismuth is thus reduced and sinks to the bottom along with a nickeliferous speiss cobalt( 55). 59- Arsenic. The industrial applications of this metal in areguline state are extremely few, the chief use of it being to form an alloy with lead for the purpose of shot manufacture, and a brilliant alloy known as speculum metal when combined with copper and tin in certain proportions : it is also employed for some few other purposes, such as the manufacture of opal glass. In the roasting of arsenical ores of various kinds, notably copper pyrites and nickel and cobalt ores, the fumes evolved in the furnace contain considerable amounts of arsenious oxide, As 2 O 3 ; to collect this, and especially to prevent poisoning the air of the neighbour- hood, these fumes are made to pass through a series of chambers opening one into the other, some arranged horizontally, and the last of the series vertically, constitut- ing a kind of tower ; in these the arsenious oxide is deposited along with other matters mechanically carried over, whilst the sulphur dioxide and other permanent gases escape by a flue from the highest chamber of the series. Fig. 19 represents the rotary calciner of Oxland and Hocking used for the roasting of arsenical pyrites for the purpose of preparing arsenious oxide therefrom : a cylinder of wrought iron a, a, a, a, such as an old boiler with the ends cut off, is lined with firebrick, ledges or shelves protruding from the lining radially towards the axis : the cylinder is supported on bearing wheels, b, b, 112 METALS AND THEIR [CHAP. arranged on a gentle slope, and kept in motion (about fifteen revolutions to the hour) by means of a large cog- wheel applied externally, ^, and turned by water or steam power. The flame from a fire, d, plays into the cylinder at one end, and the gaseous products of combustion and of the roasting escape at the other into the first of the series of condensing chambers, e. As the cylinder revolves, the substance to be roasted is continually taken up by the shelves, and poured through the hot air inside in a shower when the shelves arrive near the top of the revolution, so as to keep up a con- tinuous and very effective agitation of the whole mass. Fresh unroasted ore is continually added by a small shoot, /, at the upper end, the completely roasted ore escaping at the lower end at g. In this way the labour required in stirring, &c., in the ordinary calcining furnaces is saved, the operation proceeding automatically : when the ores operated on do not contain sufficient arsenic to render it worth while to apply condensing chambers, the cylinder can be adjusted simply to the flue leading to the chimney ; in this way the calcination of tin ores ( 47), and copper pyrites ( 42), and zinc blende ( 48), &c., can be effectually and economically carried out. The arsenious oxide deposited in the condensing chambers is purified by a process of sublimation before sending into the market ; the majority of arsenical com- pounds in use are made from the purified oxide direct without passing through the reguline condition at all. From the oxide, the metal is readily obtained by mixing with charcoal powder, or with black flux (an intimate mixture of potassium carbonate and charcoal prepared by calcining tartar in a closed vessel) and heating, vrhen the metal sublimes. It can also be obtained in a less pure condition by heating arsenical pyrites iv.] CHIEF INDUSTRIAL APPLICATIONS. 113 sulphide of arsenic and iron) mixed with scrap-iron in a retort ; sulphide of iron is thus formed, whilst the arsenic is volatilized and condenses in a receiver placed so that the vapours may sublime into it. 60. Manganese. Practically, manganese is only prepared in the form of alloys, of which the most important, spicgeleiscn and ferromanganese^ are obtained by smelting a manganiferous iron ore, or a mixture of manganese oxide and an iron ore, in blast furnaces, &c., precisely as pig-iron is prepared ( 32). In this way a highly carboniferous pig-iron is obtained, containing more or less manganese according to the ore employed. When only a few per cents, of manganese are present, the sub- stance is usually termed spiegeleisen, on account of the fractured surfaces of the pigs exhibiting brilliant mirror- like planes. When the percentage of manganese is up- wards of 7 or 8 per cent, (occasionally running up to 40 or 50 or more per cent), the term " ferromanganese " is usually assigned to the alloy. No distinct line of demarca- tion between spiegeleisen and ferromanganese can, how- ever, be laid down, the one insensibly grading into the other. Other manganese alloys have been proposed for special purposes, but have not as yet come into anything like general use ; recently a manganese substitute for German silver has been prepared, consisting of about 8 parts manganese, 4 zinc, 34 copper, and i iron ; whilst a man- ganese-bronze has also been brought out as a cannon metal, and is stated to possess great toughness, and to be equal to the best wrought iron in firmness and extensi- bility, whilst it can be easily forged, rolled, and drawn at red heat. If these statements are substantiated on further trial, no doubt the new alloy will come into extensive use. 114 METALS AND THEIR [CHAP. 6 1. Of the other oxidizable metals none have any spe- cial importance as regards their industrial applications in the reguline state, and very few of them are ever pre- pared in that condition save by the manufacturers of the rarer chemicals. Cadmium, occasionally employed for the production of very fusible alloys ( 88), is usually obtained along with zinc, and is extracted as indicated in ( 50). Tungsten has been recently proposed by Dr. Versmann, as a substitute for nickel in German silver, a highly sonorous alloy being obtained by reducing simultaneously tungstic and copper oxides, and fusing the resulting alloy with zinc or brass ; the same metal has been suggested as a hardening and ameliorating ingre- dient in steel, as have also chromium $n.& titanium (41). Few indeed of the remaining metals of this class are of any large industrial importance even in the state of com- pounds, potassium, sodium, and calcium being the main exceptions. Certain of the compounds of barium, stron- tium, chromium, and cobalt are also of considerable im- portance for a few special purposes and manufactures ; vanadium compounds have been recently introduced for developing certain colours in calico-printing, &c., and cerium salts have been used medicinally, whilst molybdlc oxide is a valuable analytical reagent; but for the most part the remainder of the oxidizable metals and their compounds have as yet received no industrial applications. v.] CHIEF INDUSTRIAL APPLICATIONS. 115 UNIVERSITY; CHAPTER V. PHYSICAL PROPERTIES OF METALS. 62. Lustre. One of the most characteristic pro- perties of metals is the power possessed by them when in more or less compact masses of acquiring (by polish- ing, pressure, or other mechanical treatment) such a condition of surface that light incident thereon is for the most part again reflected, whereby a peculiar glistening appearance is presented, known as the metallic lustrf. When fused, lumps are cut with a sharp instrument, or when the metals form crystalline masses which are broken across, the severed surfaces exhibit this peculiar feature ; and in many cases when the metal is obtained by chemical action from certain of its compounds, so as to form a deposit on a glass surface (e.g. silver), or if the vapour of the metal be condensed on such a surface (e.g. arsenic), the glass presents the well-known appearance of a mirror of more or less brilliancy according to the nature of the metal, and the way in which it is precipitated on the surface. When prepared by certain chemical processes, the metals often present the appearance of lustre- less minute particles, generally black when very small. Metals in this " spongy" condition, however, can oft en be made to exhibit a considerable amount of brilliancy by I 2 ii6 ; METALS AND THEIR [CHAP. strongly compressing a portion of the dry powder against a polished steel or agate surface, when the powder more or less agglutinates into cakes exhibiting lustre on the sides that were next to the polished surfaces ; or by sim- ply rubbing in a smooth mortar with a pestle a little of the powder, brilliant streaks are produced by the pressure. Gold, platinum, and silver in particular exhibit this pro- perty, the ordinary metals having a strong tendency, when in a fine state of division, to oxidize or rust on the sur- face ; and this greatly interferes with the coherence of the compressed masses, and with their brilliancy when rubbed or polished. If a little spongy silver (prepared by boil- ing pure silver chloride with sugar and caustic soda, thoroughly washing, and drying) be placed between a pair of dies and compressed by a coining press, a slightly brittle but still coherent coin will be obtained, exhibiting considerable brilliancy on the surfaces that were in con- tact with the polished portions of the die-surfaces ; and an analogous result is obtained if precipitated gold of a dull brown shade (thrown down by ferrous sulphate from gold chloride solution) be employed instead of silver. The peculiar lustre characteristic of metals is, however, not wholly confined to these substances ; certain minerals, e.g. galena, and some of the non-metals, e.g. graphite, occur in nature in masses exhibiting a metal-Hke lustre when fractured, whilst selenion, silicon, and other non- metals can be artificially prepared in states where they exhibit a closely similar lustre, as can also various com- pound substances, e.g. mosaic gold (tin disulphide). The effect of pressure in heightening the brilliancy of a metallic surface is well seen in the industrial process of burnishing; when a layer of metal, such as gold or silver, is deposited by electrical or chemical means on the sur- face of an object to be silvered or gilt, it usually happens v.] CHIEF INDUSTRIAL APPLICATIONS. 117 that the freshly covered surface is more or less deficient in lustre, or, as it is technically termed, "dead" ; by the skilled application of pressure with a burnisher of polished steel or stone the dead surface is compressed and made to shine with brilliancy. For the final touches on electro- silvered or gilt articles, and for the gilding on china, &c., a burnisher is preferred made of "bloodstone," a com- pact variety of haematite. The ordinary household pro- cesses of cleaning and polishing steel and other metallic articles partly depend on the pressure exerted on the surface, although the main action consists in abrading, by means of a fine crystalline powder (usually prepared chalk, or peroxide of iron prepared by calcination of green vitriol or by levigation of burnt pyrites, &c.), the particles of rusted or tarnished metal, so as to display the underlying pure metallic surface. 63. Owing to the influence of the air, moisture, vapours arising from putrefaction, &c., metallic surfaces, even when highly polished and brilliant, become more or less rapidly tarnished, so that the power of reflecting light is to a considerable extent lost. Before the invention of glass, polished metallic surfaces were employed as mirrors; and for reflecting telescopes such surfaces are still in use. Now, however, it is usual to employ as mirrors glass sur- faces, behind which a thin coating of some lustrous metallic mass is placed, so that the smooth surface of the glass at once determines the peculiar reflective power of the metal applied to it, and preserves the metal from mechanical injury and from the corrosion of the air. For this reason these household appliances are ordinarily termed "looking-glasses," although strictly speaking it is not the glass that is the essential part. Three principal methods of applying these metallic substances to glass are in use; the best plate-glass ii8 METALS AND THEIR [CHAP. mirrors (perfectly plane surfaces) are prepared by spread- ing out on a table surrounded with a deep groove or gutter, and capable of being raised on hinges so as to be placed at any angle with the horizon, a sheet of tinfoil, and smoothing it with a soft brush ; mercury is then poured on and gently rubbed over the tinfoil with a hare's-foot or a roll of flannel so as to penetrate and brighten the tin ; more mercury is then poured on, and the surface cleansed from dross, &c. ; finally, the per- fectly clean sheet of glass is dexterously slid over the brilliant mercurial surface in such a way as to avoid en- closing any particles of dust or air-bubbles between the metal and glass. The table is then slightly raised at one end, so that the surplus mercury may gradually run off and be caught in the gutter ; and the slope is increased daily, a piece of flannel being placed on the glass with weights on it to facilitate the draining off of the mercury. After two to four weeks, according to the size of the plate, the mirror is complete, the tin amalgam having then completely set, and being tolerably firmly adherent to the glass, although easily rubbed off and scratched on account of its slight tenacity. To preserve the back of the mirror from injury a suitable wooden frame is provided, in which the whole is fixed, when a finished mirror is the result. 64. For curved surfaces, such as the insides of globes, flasks, &c., for ornamental purposes, a somewhat different plan is employed : a fluid or semi-fluid amalgam capable of adhering to glass is poured into the vessel to be "sil- vered," and shaken about therein until the inner surface is covered with a film of the composition ; the surplus amalgam is then poured out and used for other similar objects. A mixture of one part each of lead, tin, and bismuth, with two parts of mercury, answers well, the v.] CHIEF INDUSTRIAL APPLICATIONS. 119 mixture being made perfectly fluid by slightly warming it before pouring into the vessel to be silvered. It is noticeable that an alloy of three parts of potassium and one of sodium is fluid at the ordinary temperature, being the only metal or mixture of metals known possessing this character, mercury, solutions of metals in mercury, and the newly discovered metal gallium (under certain conditions) excepted. This mixture possesses the power of adhering to the inside of a glass bottle forming a well- defined mirror; fused stereotype metal, plumber's solder, and analogous alloys ( 103) can also, with careful management, be poured into hot glass bottles and shaken over the surface so as to form mirrors of considerable brilliancy, although this method is never practically used. A method which has of late years come largely into use for silvering mirrors of various kinds, and notably the reflectors of telescopes and lighthouses, is based on the power of certain chemical reagents to throw down silver in the metallic state from certain of its solutions, &c., the reduced silver in many cases adhering firmly to the surface of the vessel in which the action takes place, or to objects immersed in the liquid. Thus, if calcium tartrate in a moist state be placed in a glass vessel with a crystal of silver nitrate and a drop of ammonia solution, and the mixture cautiously heated, and made to flow successively over the whole inner surface of the glass, a fine mirror may be developed. Aldehyde, oil of cloves and other essential oils, grape-sugar, and some other organic substances, may also be employed as reducing agents, especially the first substance. 65. If a " mirror " (i.e. a glass surface with a brilliant metallic film behind) be carefully examined, it will be found that in most positions it will give a double image 120 METALS AND THEIR [CHAP. of any object reflected, one image being usually more brilliant than the other. Fig. 20 illustrates how this is brought about ; a ray of light from an object at a, strikes the glass surface at b, and is reflected to the eye of the observer at P, so that an image is seen situated at m. Another ray of light incident on the glass at a point c, is partly reflected along cf } this portion of the ray consequently never reaching the eye at P at all ; the rest FIG. 20 of the ray enters the glass, being refracted along c d; at the junction of the glass and metallic surfaces reflection takes place along de, and at e the ray is refracted along eP, thus also reaching the eye of the observer, but necessarily causing the image formed to be seen ap- parently situated at n, a point different from m. The relative quantities of light passing along e P and b P (that is, the relative brightnesses of the two images) depend on the degree of obliquity of the incident light c; the greater v.] CHIEF INDUSTRIAL APPLICATIONS. 121 the angle ab P (i.e. the more obliquely the light falls on the mirror), the brighter is the image at n. The power of glass thus to reflect light to a considerable extent without any metallic film behind is utilized in the illusion known popularly as " Pepper's ghost," which consists simply of a large pane of glass sloping forwards from the stage at an angle of about 45 (Fig. 21.) Objects such as A , placed between the footlights J5 t and the pane of glass F in a horizontal position, and strongly illu- minated, will produce to a spectator in front at P, a FIG. 21. virtual image or " ghost," apparently situated at CD, the illusion being heightened by hiding, by means of screens, all the apparatus in front of the pane from the audience, and darkening that part of the stage behind the pane, the real objects furnishing the ghosts being placed on a dead-black ground. When the lights E are extinguished, and other lights illuminating the stage behind the pane turned on, the ghosts disappear, whilst the real actors at D C on the stage behind the pane become visible through the transparent glass. 122 METALS AND THEIR [CHAP. 66. Colour by Reflection and Transmis- sion. As a rule, metals reflect visible light of all degrees of refrangibility nearly alike, i.e. most metals appear of a white colour. Copper, however, possesses the power of reflecting red rays more powerfully than others, and consequently appears red : similarly, gold possesses a bright yellow or orange colour, and the alkaline-earthy metals calcium, barium, and strontium, appear slightly yellow. Brass, aluminium bronze, and other alloys of copper possess a rich yellow colour, the shade depending on the composition ; as a rule, the alloys of a coloured and a colourless metal exhibit a regular gradation of tint, the colour becoming less intense as the percentage of colourless metal increases. Although the light reflected from polished surfaces of most metals is nearly white, yet frequently there is a slight tinge of some colour ; thus whilst tin, silver, platinum, and others have a nearly pure white colour, and hence appear alike when equally burnished, lead and zinc have a bluish shade, and iron and arsenic a greyish hue ; these faint tints are best seen by repeatedly reflecting light from the metallic surface, as when a tube polished internally^ and open at both ends, is looked into obliquely. The deepening of the yellow tint exhibited when light is once reflected from a gold surface to a red-orange by repeated reflections is readily seen by looking obliquely into an empty metal tankard gilded internally. The pigments and colouring materials largely used in the arts under the name of bronze powders, are mainly divers coloured alloys stamped and ground to fine powders, and in some cases subjected subsequently to heating and sulphurising pro- cesses so as to develop peculiar shades ; tinsel is usually paper overlaid with a thin film of silver or other white alloy, and coated over with a transparent coloured v.] CHIEF INDUSTRIAL APPLICATIONS. 123 varnish, or is paper coated with a white or bronze pow- dered metal, and rolled till the surface is brightly lustrous. 67. Few metals can be reduced to so fine a degree of tenuity as to allow light to pass through them readily ; when this can be done it is usually found that one kind of light is absorbed more readily than others, so that the transmitted light is coloured, being deficient in the more absorbed rays. The transmitted light is sometimes com- plementary to the reflected colour, or nearly so, but not invariably : thus gold can be reduced by beating to leaves of thickness not exceeding -^ ouVorr mcn ( 7 2 )> an< ^ * n this condition permits a green light to pass through, the colour being dependent on the amount of silver added to the gold, the light being more inclined to violet with much silver : by passing electric sparks in vacuo through glass tubes into which metal wires are fused, the glass becomes coated with a continuous film of metallic par- ticles detached from the wires by the sparks ; a film of gold thus prepared transmits a fine green light, whilst silver gives a beautiful blue shade. Copper transmits a dull green, and platinum a bluish-grey : zinc and cadmium furnish a deep bluish-grey, whilst iron films transmit a tint nearly neutral, but slightly brownish. 68. Density. Most of the metals used in the arts in the free state are of considerable density, aluminium being by far the lightest, a circumstance which, together with its considerable strength and power of resisting the tarnishing effects of the air, renders it peculiarly suitable for numerous purposes : the draw-tubes of telescopes, opera glasses, &c.-, and the graduated circles of surveying instruments, &c., are often made of this metal for these reasons. According to the way in which a piece of metal has been obtained, its density will vary somewhat, being increased by hammering or any mechanical action 124 METALS AND THEIR [CHAP. which forces the particles together, e.g. wire drawing or sheet-rolling. The following table gives the numerical values of the average densities of most of the more im- FIG. 22 . Platinum Gold Mercury Palladium Lead Silver Bismuth Copper Nickel Cadmium Iron Tin Zinc Antimony Arsenic Aluminium Magnesium Sodium Potassium Lithium portant metals, whilst Fig. 22 exhibits the same numbers graphically, the lengths of the lines applied to each metal being in the ratios of these numbers. Specific Gravity of Metals ( Water = i), Platinum Gold . Mercury Palladium Lead . Silver . Bismuth Copper Nickel . Cadmium 21-5 19 "3 13-6 ii-S 11-3 10-6 9'8 8-9 8-8 87 Iron . 7-8 Tin .... / Zinc . 7*1 Antimony . Arsenic . . . 5-6 Aluminium 2 '6 Magnesium Sodium . . . Potassium . . * 1-8 0-97 0-86 Lithium . . o'59 v.] CHIEF INDUSTRIAL APPLICATIONS. 125 These numbers necessarily represent the numbers of grammes weighed by one cubic centimetre of each metal ; when multiplied by 1,000 they represent approximately the number of ounces per cubic foot. Independently of the changes in density produced by differences in the state of physical aggregation of metals, alterations of temperature of course affect this property, since expansion is caused by increase of temperature, and consequently a given bulk of metal will weigh less at a high temperature than at a lower one. 69. It is noticeable that the specific gravity of an alloy always approximates more or less closely to that calcu- tated on the assumption that the constituent metals hang together side by side without interference : i.e. the bulk of an alloy approximates to the united bulks of the con- stituents. Thus an alloy of equal volumes of platinum and aluminium would, on this assumption, have a specific gravity of 12*05, the calculation running thus : Grammes. 100 cubic centimetres of platinum .... weigh 2, 1 50 100 ,, ,, ,, aluminium ... ,, 260 200 ,, ,, ,, the alloy .... ,, 2,410 or, i cubic centimetre of the alloy weighs ^'grammes = 12 '05 On the other hand an alloy of equal weights of these two metals would have a specific gravity of 4-64. 100 grammes of platinum occupy -~ = 4*65 cubic cents. 100 ,, aluminium ,, ^ = 38 '46 ,, ,, 200 the alloy 43-11 whence I cubic cent, weighs - j- = 4*64 grammes. 126 METALS AND TKEIR [CHAP. In the case of most alloys this proposition is not exactly true, there being generally more or less expansion or contraction during the mixture of the constituents, so that the specific gravity of the alloy becomes either raised above or lowered below that thus calculated sometimes this difference is somewhat marked, but usually it is not great enough materially to vitiate the generality of the above rule. 70. Crystallisability. Some few metals readily assume the crystalline condition on slow cooling after fusion ; notably this is the case with bismuth ; others do not readily become crystalline, and on this property depends much of their usefulness, as a crystalline texture denotes comparative brittleness. Wrought iron occasion- ally passes from its normal fibrous texture to a crystalline state ; this effect appears to be brought about by long continued vibration and subjection to blows, and has been accordingly the cause of various accidents, e.g. when a railway axle having become crystalline through long use, breaks owing to the diminished strength thereby caused. Many metals can be obtained crystalline when deposited from a solution by galvanic action ; thus lead and silver when slowly precipitated by other metals occur in finely developed crystalline arborescences, the formation of which constitutes the familiar experiments of the " lead- tree " and " silver-tree "or Arbor Diana. Many * ' native " metals (e.g. copper) occur crystallised, being presumably produced by actions of this kind. Frequently the presence of a minute quantity of a foreign metal greatly promotes the crystallisation of a metal which becomes crystalline only with difficulty when perfectly pure. 71- Malleability and Brittleness. Many metals are sufficiently devoid of the character known as brittleness, or tendency to fly to pieces when struck or v.] CHIEF INDUSTRIAL APPLICATIONS. 127 pressed, to be hammered out into thin leaves, or rolled out into thin sheets; some metals are readily " malleable " at one temperature but brittle at another : in all cases the presence of minute amounts of other metals or non- metallic impurities exerts a marked influence on the degree in which this quality is possessed. Zinc is crystalline and brittle at ordinary temperatures, but can readily be rolled into thin sheets at 100 150, whilst at about 200 and upwards it again becomes brittle, and can be powdered in a mortar ; sheet zinc for gutters, &c., is therefore rolled hot. Gold is rendered brittle by the presence of traces of antimony ; and similar effects on the malleability of many metals are produced by small admixtures with certain otr^er metals, &c. The ten chief metals (4) all possess the power of being extended into thin sheets under the rolling press, and into leaves of greater or less tenuity under the hammer, but to very different extents ; lead and zinc falling short of the others, the former on account of its extreme softness and consequent want of tenacity when reduced to thin leaves, the latter on account of the difficulty of working very thin sheets of the metal at the temperature at which its malleability is most marked. They may be thus arranged in order of malleability, the first two being nearly equal : GOLD, SILVER, COPPER, PLATINUM, IRON, ALUMINIUM, TIN, ZINC, LEAD, MERCURY (solid). It is very probable that mercury (in a frozen state) should be ranged higher up in the series ; palladium, like platinum, is highly malleable, though less so than gold or silver, which possess the property to an extraor- dinary extent ; in the ordinary process of gold-beating 128 METALS AND THEIR [CHAP. leaves are obtained so thin that one grain of finished leaves covers at least thirty-five square inches, whilst the extension of this metal can be pushed much further, so that coherent leaves of -gruinnr mcn m thickness have been obtained, one grain of gold covering about seventy- five square inches : the usual thickness of English gold leaf is about double this, or aW.irsu mcn - Silver can similarly be beaten until a given weight of metal is even more extended, one grain covering ninety-eight square inches. The leaves however are not quite so thin as gold leaves, on account of the lower specific gravity of silver. Iron has been beaten into leaves of -grVo" mc ^ m thickness. 72. The manufacture of thin leaf gold (gold-beating) is carried out in the following way. Gold is alloyed with small quantities of other metals according to the colour required in the finished leaf; thus there were exhibited in the 1851 Exhibition by Messrs. Marshall leaves of twelve colours grading from red to nearly white, and designated as red : pale red : extra deep : deep : orange : lemon : deep pale : pale : pale-pale : deep party : party : and fine gold. The deeper colours are obtained with gold alloyed with from twelve to sixteen grains of copper per ounce and no silver; the middle ones with six to eight grains of copper and twelve to twenty of silver ; and the paler ones with from two to twenty grains of silver, copper being omitted. As a curious fact, if silver be added to alloy containing more than eight or ten grains of copper the malleability is sensibly diminished, although no marked ill result is brought about by the addition of silver to fine gold or to gold containing only small quantities of copper. Ordi- nary gold leaf, such as is used for decorative purposes, contains about twelve grains of silver and nine of copper per ounce. The alloy is heated in crucibles to some- v.] CHIEF INDUSTRIAL APPLICATIONS. 129 what above its melting-point, cast into ingots, and rolled into ribbons about one-and-a-half inch wide and of such thinness that an ounce extends to a length of about ten feet : no marked difference in malleability is noticeable whether the cast ingot be cooled quickly or slowly. The ribbon is then cut into pieces weighing about six grains each, which are piled between sheets of vellum or parch- ment paper to the number of about 160 or 170: the cutch thus produced is beaten with a seventeen-pound hammer for about twenty minutes, at the end of which time the metal has become extended nearly to the size of the parchments (some three inches square). The rough squares thus formed are quartered and piled again between sheets of prepared gut (goldbeater 's skin) forming a shoder (or sholder) consisting of some 700 pieces of metal, the contents of a cutch after quartering being all placed in the same shoder. The beating is then carried on for about two hours with a nine-pound hammer : when the leaves have become extended to the dimensions of the shoder (some four-and-a-half inches square) they are again quartered by a tool made of bamboo sharpened to a cutting edge. These quarters are again piled be- tween fine skins five inches square forming a mould, the contents of one shoder filling three moulds (about 900 leaves to the mould). Finally, the mould is beaten for about two hours more till the metal extends to the edges of the skins and here and there flows over : from the finished leaf thus produced squares of three inches and three- eighths are cut from the central portions by a bamboo tool, and piled in a " book " made of soft paper rubbed over with red ochre or red chalk. During the earlier part of the beating the blows are directed mainly towards the centre, which causes cracks and rents towards the edges of the leaves ; these cracks, however, become per- K J30 METALS AND THEIR [CHAP. fectly closed up again subsequently as the blows fall on the other portions, the edges of the cracks welding to- gether perfectly, so that the finished leaf -exhibits no trace of them. The leaves first begin to show light through when the thickness is about 1 5 ^ inch, the colour being green with gold containing little or no silver, but verging towards pale violet when much of the latter metal is present. The beating is rarely continued until the leaves are less than 2 ^ inch in thickness, as the saving of precious metal hardly compensates for the extra labour and the greater waste (through spoiled leaves, and the "pouring over," at the edges of the mould) : moreover the thinnest possible leaf does not "cover" so well, being more translucent. Fine gold beats as well as, but not better than that containing small quantities of alloy, whilst it is superior in welding power, so that the leaves are more apt to stick together when one part touches another, and so on. The "mould" skins when old are generally employed for the " shoder," in which the excellence of the skin surface is not of so much moment. 73- Ductility. Although the property of being drawn into wire is closely allied to that of being rolled or hammered into foil and leaves, yet the two are not neces- sarily possessed to equal extents by the same metal ; gold, silver, and platinum are pre-eminently "ductile," whilst copper and iron are but little inferior to them in this respect. Aluminium and zinc can be obtained in tolerably thin wire, whilst lead and tin have so little cohesion that they cannot be drawn beyond a very limited degree of fineness. On the small scale, wires are readily obtained by casting the metals into thin pencils, 1 slightly pointing 1 For metals of moderately-low melting-points the fused substance may be drawn up into a hot thin glass tube or pipe-stem by suction, and allowed to solidify therein. By fusing the metal in the bowl of a tobacco-pipe and tilting this so that the stem is inclined down- v.] CHIEF INDUSTRIAL APPLICATIONS. 131 the ends of these and passing them into a funnel-shaped hole in a steel plate (draw-plate) of suitable size, gripping with pliers the protruding pointed part, and forcibly pulling the whole bar through the hole, the process being then repeated with a slightly smaller hole. Fig. 23 F 1C 23 represents the section of the draw-plate through the holes ; a series of holes are generally worked in the same plate gradually diminishing in diameter from one end of the plate to the other, the complete perforated plate being often termed a " jigger." To obtain greater steadiness in the pull, the pliers should be attached to a band or cord which is gradually wound up on an axle by a handle, the pliers being so constructed that the greater the force required to draw the wire through, the more firmly they grip the end of it : this is easily effected by turning up the handle ends (the plane in which the jaws open being horizontal) and passing over them a triangle of iron to the base of which the band is attached (Fig. 24) : the greater the strain on the band, the more firmly is the wire held : the draw-plate is kept in position by being pressed against two vertical projections or "chucks." It is generally necessary to "anneal" the wire from time to time, otherwise it becomes hard and more or less liable to crack or break after having passed through a certain number of holes : " hard-drawn " (or unannealed) wires, however, are usually considerably wards, the molten metal can often be made to form a rough wire or thin rod in the stem, readily obtainable by breaking away the pipe- clay after cooling. K 2 CH. v.] METALS AND THEIR APPLICATIONS. 133 more capable of resisting tensile strains than the same wires after annealing ( 76). In drawing wire on a manufacturing scale, the process is just the same in principle, only, instead of drawing the wire through the draw-plate by hand by means of a wheel and axle, &c., the wire is pulled through by hand with pliers for a foot or two, and this portion then fastened to a revolving drum which then pulls the rest of the wire through, coiling up the drawn-out portion on the drum ; the wire is then passed through the next smaller hole, being uncoiled from the first drum, and coiled again on a second in so doing, and so on until drawn to the re- quired degree of fineness. In this way great lengths of wire are drawn at one operation. 74. Wollaston succeeded in obtaining wires of platinum, gold, and iron of excessive tenuity by first drawing the metals into fine wire, and then casting round this wire a cylinder of another metal, and drawing the compound cylinder again to the utmost possible extent; both the outside metal and the internal wire were thus elongated together ; finally, the outside metal was dissolved off by some appropriate solvent, and thus the internal wire was left. To prepare the platinum and gold wires silver was used for the external cylinder, the silver being finally dissolved off by nitric acid. To make the iron wire, silver was also used .for the cylinder, but was ultimately dissolved off by means of mercury. In this way a pla- tinum wire was obtained less than -^^^ inch in diameter. Some metals require to be heated in order to acquire sufficient softness to enable them to be readily drawn into wire ; thus with aluminium. Others are in practice often used in a heated state to facilitate the operation, although the heating is not essential to the ductility of the body. Thus with steel and iron wires or rods of 134 METALS AND THEIR [CHAP. considerable thickness, tha " drawing" operation being modified into a kind of rolling, the hot metal being passed between grooved rollers of successively smaller and smaller grooves. Those alloys which are brittle are necessarily non- ductile, but alloys which are malleable are usually more or less ductile. Brass, a particularly malleable alloy, is also excessively ductile, wires of this alloy having been drawn so fine by means of an ordinary drawbench that seven feet of wire only weighed one grain. It is notice- able that "virgin" brass (made by mixing fresh copper and zinc together, not by remelting old alloy, &c.) is much more ductile than other kinds of brass, even though apparently of the same chemical composition. Many metals which are only drawn into wire with difficulty, can be obtained in a wire-like form by an in- genious process called " squirting." The metal is melted and allowed to cool, and when close upon the solidifying point is forced by mechanical means (hydraulic pressure, &c.) through an orifice of the requisite diameter ; the metal, coming in contact with the air, is quickly chilled, and solidifies to a wire or rod, which is wound on a drum as fast as it is prepared. By an appropriately formed jet or orifice a long continuous tube may be squirted instead of a rod. In this way the ordinary tin, lead, and " compo " tubing used for gas, water, spirits, &c., is manufactured, as is also magnesium wire. Rifle bullets are made by squirting lead into rods half an inch thick or so, from which portions are cut off and squeezed into shape by machinery. 75- Tenacity. The more crystalline a metal or alloy is the less is its power of resisting strains and stresses of various kinds ; the more fibrous in structure the better will it resist strain, especially in the direction of the fibres. v.] CHIEF INDUSTRIAL APPLICATIONS. 135 By forming metals into wires of equal dimensions, and then determining the weight requisite to break these wires, the differences in tenacity exhibited by metals and alloys may be readily demonstrated. A convenient apparatus for this purpose is made of an iron tripod six or seven feet high (Fig. 25), the legs of which are stayed together at the bottom and in the middle ; from the top of the tripod is suspended by a stout hook a dynamometer or spring balance furnished with a hook at the bottom, whilst about half way up the tripod is affixed a horizontal axle, supported by the stays in such a position that the centre of the axle is perpendicularly beneath the hook of the dynamometer. This axle is provided with a winch, and round it is coiled a stout rope or leather band with a hook at the end. The wire to be tested is formed into a ring about three or four inches in diameter, the ends being intertwisted and soldered together ; the hooks attached to the bottom of the dyna- mometer and to the rope are then inserted in this ring, and the handle turned so as to wind up the rope and stretch the ring until its form becomes a narrow oblong. The tension is then increased by winding the rope until the wire breaks ; the reading of the dynamometer is noted by an assistant at the moment of rupture. In this kind of way the order of tenacity of the metals is found to be as follows : 25 Iron. 1 6 Copper. 14 Platinum. 12 Aluminium. 10 Silver. 8 Gold. 7 Zinc. I -5 Tin. I Lead. 136 A1ETALS AND THEIR [CHAP. . 25. CHIEF INDUSTRIAL APPLICATIONS. 137 76. These numbers represent the relative average breaking strains of wires of the same dimensions. The actual value obtained with any particular wire, how- ever, is largely influenced by the purity of the metal, by the character of the strain (whether applied sud- denly, or slowly and gradually), and by the physical condition of the wire (whether hard drawn or annealed). Thus, VVertheim 1 obtained the following values repre- senting the weights in kilogrammes required to break wires one square millimetre in section : Gradual strain. Strain suddenly appiitd. Cast steel, hard drawn .... 65*7 83-8 7O O QQ'I ,, annealed 40 'o C VQ Iron wire, hard drawn .... ,, annealed 61-1 4.6 Q 6 5 -I CQ 7 Copper wire, hard drawn ,, annealed . . . Platinum wire, hard drawn . . annealed . Palladium wire, hard drawn . . ,, annealed . . Silver wire, hard drawn . ,, annealed 40-3 305 34'i 23'5 27-4 29 'o i6'o 41 'o 317 35 'o 277 27-2 29-6 i6'5 Commercial zinc, drawn . . . ,, annealed . Pure zinc, cast 128 4,-ir 15-8 14-4 Gold wire, hard drawn .... ,, annealed .... 27-0 lO'I 28-4 1 1 'i Cadmium, drawn . . . 2'2A ,, annealed I '2C 4-8 ,, drawn 1 *5 2 'O7 2-^6 ,, annealed .... i -So 2'OJ. Tin wire, hard drawn . 2'4.C VOO ,, annealed .... I '7O 6 ^ ^'62 1 AnnaLs de Chimis, [iii.] xxii. 440. 138 METALS AND THEIR [CHAP. Somewhat different values have been obtained by other experimenters, the differences being probably mainly due to the presence of minute traces of impurity in the metals examined, &c. Thus Matthiessen gives the fol- lowing values, somewhat different from the above. The numbers represent the number of pounds weight re- quired to break hard-drawn double wires, No. 23 gauge. Steel above 200 Iron 8090 Platinum 4550 Silver 45 50 Copper 2530 Gold 2025 Tin under 7 Lead 7 77. Wires sometimes vary much in tenacity at different temperatures ; as might be anticipated d priori, those metals which melt most easily become most weakened on heating. Thus Wertheim (foe. at.} found the following values for various annealed wires (as before in kilo- grammes per wire of one square millimetre section). At 15. At 100. At 200. Iron . ... 4.6 'Q CI'I 4.6 'Q Copper ao*e 22'I Platinum . . . . . 2V5 22-6 IQ'7 Silver . ... i6'o I4'O 14 'O Zinc . . . 14. '4- 12*2 7'3 Gold IO'l J2 '6 I2'I Cadmium .... 4/8 2'6 Lead J3 '5 _ Tin 17 0-85 Thus lead, tin, cadmium and zinc, which melt the lowest of the above, are only from one-half to one-third as strong v-3 CHIEF INDUSTRIAL APPLICATIONS. 139 at 200 as at 15 ; copper, silver, and platinum are much less weakened on heating ; whilst iron and gold are actually stronger at 1 00 than at 15, and are but little weaker at 200 than at 100. 78. Certain alloys possess much greater strength than their constituents, and on this property depends much of their practical use; thus gun-metal, standard gold (gold copper alloy), a silver platinum alloy used for electrical purposes, steel, and phosphor bronze (which last two may be regarded as analogous to alloys) are much more tenacious than either of their constituents severally : thus Matthiessen found the following values (as before in Ibs. per double wire, hard drawn, No. 23 gauge). Alloys. Gun- metal containing 12 per cent, tin . 8090 Standard gold : gold copper alloy (22 carat gold) . . . 7075 \ Silver platinum alloy \ (| silver, ^platinum) 75 80 Steel above 200 As a general rule, however, the effect of alloying metals together is to impair their tenacity ; thus gold is rendered brittle by the presence of a trace of antimony, and an alloy of two parts tin and one of platinum is quite brittle. As already stated, the union of non-metals with metals usually wholly destroys the metallic characters, and in particular this chemical union usually gives rise to a product possessing but little toughness and tenacity such as is requisite for manufacturing purposes (such products as glass, earthenware, bricks, and various minerals, &c., excepted). Steel and phosphor bronze, however, as above Metals separately. Copper . 25-30 ) Tin . . under 7 \ Copper. 2 $ 3 I Gold . 20- -25 \ Silver 455 1 Platinum 4550 i Iron. 8090 140 METALS AND THEIR [CHAP. stated, form notable exceptions to this rule, the presence of one per cent, or less of carbon in the first, and of a like quantity of phosphorus in the second, communicating to the substances iron and bronze a considerably greater power of resisting wear and tear and other special qualities. The accurate determination of the tensile strength of wire ropes, bars, &c., of their power of resisting crushing and transverse strains, bending and twisting agencies, c., is of very great importance to the architect and engineer. Ingenious and powerful machinery for this purpose has been constructed by Mr. David Kirkaldy, 1 whose machines will measure any kind of strain or stress from 10 to 1,000,000 Ibs. applied not only to metals, but to wood and building materials generally. Modifications of this testing machinery are employed in some iron- works, &c. for the purpose of continually examining the strength and value of certain of the products (e.g. Besse- mer rails and the like). 79- Other physical properties. Closely con- nected with the physical structure which enables metals to exhibit the phenomena of crystallization, malleability, and ductility is the power which some possess of return- ing to their original shape when deflected therefrom by some external force not too great (elasticity) ; a property possessed to an extreme degree by good steel. The operations of wire-drawing, rolling, hammering, and the like generally increase the elasticity of metals, whilst annealing and fusing usually diminish it. Some metals are almost wholly devoid of elasticity ; thus lead scarcely exhibits a trace of this property, being so soft that it is 1 Testing and Experimental Works, 99, Southwark Street, S.E. The specimens in Mr. Kirkaldy's museum, illustrating the results arrived at with many years employment of his testing machinery on all sorts of material, are of a most interesting and instructive character. v.] CHIEF INDUSTRIAL APPLICATIONS. 141 readily abraded by the nail. Some metals and alloys, when worked into appropriate shapes and struck, continue vibrating for some time, and hence are powerfully sonorous (e.g. aluminium, bell metal, steel, standard gold, &c.). The chief value of many metals and alloys for indus- trial purposes lies in their possession to a greater or less extent of a combination of properties of somewhat opposite kinds ; whilst they possess sufficient rigidity to keep their shape even with moderately hard usage and to bear "wear and tear," when once fashioned into articles of domestic and everyday use, they have the power of yielding to pressure, &c. to a sufficient extent to enable them to be readily worked into these forms. In some cases the requisite softness for this latter purpose is hardly attained until the temperature is considerably raised ; thus most articles of wrought iron are made when the metal is softened by heat so as to yield readily to percussion (forging} and other shaping processes. Closely connected with this softening or incipient conversion into a pliable mass by heat, is the phenomenon of welding, or the adherence together of two separate metallic masses when united by pressure in such a way as to form a join as strong as the other parts. Iron and platinum possess this power at a high temperature ; sodium and some of the rarer metals at the ordinary temperature ; gold also can be welded cold, under certain conditions, as in gold- beating ( 72). On the possession of these properties depend most of the metal-fashioning crafts, those where the metals are fused and cast ( 90) being the main exceptions. 80. Thus in the manufacture of steel pens, as carried out by Messrs. Gillott & Sons, there are no less than eighteen stages between the conditions of bar steel and finished pen ; and most of the stages are different appli- 142 METALS AND THEIR [CHAP. cations of these properties of metals in reference to the shaping of the material into the required form. The bar steel is first converted into thin sheets, which are again rolled to the requisite degree of thinness ; from the rolled steel " blanks " are punched out by a machine, leaving a kind of skeleton or network of "scrap steel" (Fig. 26), which is melted up or welded together and used over again. Two " side slits " are then made in the blank (No. 2), and F/C. 26. a somewhat wider centre slit (No. 3) pierced, a portion of metal being punched out in making this orifice ; the metal is then annealed and marked with the maker's name ; a device or trade mark is raised by embossing (No. 4), and then the hitherto flat pen is converted into a portion of a cylinder, or curved (technically, " raised ") by a suitable machine (No. 5); after which it is hardened, tempered, and cleaned by scouring with emery, &c. ; the tip is then " straight-ground," i.e. the metal is thinned v.] CHIEF INDUSTRIAL APPLICATIONS. 143 at the writing end by grinding in the direction of the length of the pen, after which it is " cross-ground," in the transverse direction. Finally the slit from the nib to the punched-out central part is cut, and the pen is coloured and varnished for sale. Similarly the production of an ordinary pin necessitates a number of stages in the shaping process, which is thus carried out by Messrs. Taylor of Birmingham. Virgin brass ( 74) having been cast into thin elongated bars, is drawn into wire of the required diameter, which is sup- plied to the pin-making machine from a drum on which it is coiled. The end of the wire is adjusted to the machine, which gradually draws it through a series of pegs so arranged as to straighten the wire and take the curve from the drum out of it ; the wire next passes into a kind of die, when a rapidly acting hammer strikes the slightly projecting end in such a fashion as to flatten it out and fit it into an expansion in the end of the die groove forming the " solid head " (formerly the head was made of a coil of thinner wire slipped over the pin wire, and hammered into shape ; such heads were liable to come off). The head being completed, a knife cuts off the proper length from the wire, and the partially made pin is detached from the die and falls into a groove in which it is suspended by the head whilst the other end is abraded to a point by a kind of revolving cylindrical file. All these operations are performed automatically by the machine, and so rapidly that 200 complete pins are turned out of the machine per minute. Finally the pins are cleansed by agitation in barrels with fuller's earth and water, washed, and coated with tin by boiling with granulated tin and cream of tartar, &c. Si. Again, the manufacture of table-spoons and forks, many kinds of brass-work, cutlery, percussion-caps, copper '44 METALS AND THEIR [CHAP v.] CHIEF INDUSTRIAL APPLICATIONS. 145 pans and kettles, medals and coins, and a thousand-and- one articles of e very-day use, all depend upon the possi- bility of forcing the metal into various shapes without fracturing it, by mechanical processes, such as forging, punching, pressing, embossing, and the like. One of the prettiest illustrations of the application of pressing and shaping force is afforded by the processes in use for "teapot spinning," i.e. the production of a Britannia- metal teapot by a process technically termed spinning. The alloy ( 103) being rolled into sheets of convenient thickness, a circular disc is cut out and placed in a kind of lathe as represented in Fig. 27, the metal disc being pressed against a nearly hemispherical wooden chuck a. The lathe being set in motion, the workman presses against the off-side of the disc with a peculiarly shaped tool, b, held steadily by means of the rest, c, so as gra- dually to bend the disc over the mould, a, and so to convert the disc into a bowl. The bowl thus formed is taken off the lathe and set with the convex part fixed into the concavity of a hollowed-out chuck (shown in section a, Fig. 28) by the aid of two differently shaped tools held one in each hand and applied, the one within and the other without the rim of the bowl, the metal is gradually bent inwards as it revolves, so as finally to take an almost globular shape : Fig. 29 indicates the closing stage of this operation, the nearly globular bowl thus en. v.] METALS AND THEIR APPLICATIONS. 147 formed being shown in section in Fig. 28, b. Finally the lid, spout, handle, c., are attached, and the whole brightened and polished for the market. During the spinning the edge of the disc, some forty or fifty inches in circumference, becomes diminished to almost half that in the bowl, and to about one quarter in the globular pot, the metal being thus as it were pressed in upon itself, as well as somewhat extended, the superficial area of the outside of the globular pot being somewhat greater than that of one side of the circular disc used in the first instance. In a similar fashion jugs and analogous vessels are " spun up," out of plates, the lips for pouring being subsequently shaped by carefully hammering or pressing out the metal on a wooden or metal mould. Silver articles, e.g. bowls, teapots, &c., are frequently curved by an analogous operation ; the second stage, however, cannot so well be applied to silver, so that if a closed-in vessel is required like a teapot, it is usually made in two halves, neatly soldered together. L 2 143 METALS AND THEIR [CHAP. CHAPTER VI. THERMIC AND ELECTRIC RELATIONS OF METALS. 82. WHEN heat is applied to a metal or alloy, the substance increases in temperature, the heat passing from the parts directly heated to the rest of the mass by the process of conduction: simultaneously the whole increases in size (expansion} and ultimately softens and liquefies : if the heat be kept high enough, volatilisation to a greater or less extent usually takes place, this phenome- non sometimes occurring without previous fusion, as in the case of arsenic. Metals possess the power of conduction to very dif- ferent extents ; thus Wiedemann and Franz give the following values : Conductivity of Metals for Heat. Silver loo'O Copper 73-5 Gold 53-2 Tin I4'5 Iron 1 1 '9 Lead . . . 8-5 Platinum 8 '4 Bismuth I '8 Amongst the practical applications made of the high power of conducting heat possessed by some of the vi.] CHIEF INDUSTRIAL APPLICATIONS. 149 metals may be instanced the Davy lamp, in which ignition of an explosive mixture of fire-damp and air outside the lamp by the flame inside is prevented (with due care), inasmuch as the temperature produced by the burning of the inflammable air inside the lamp is so far reduced by the wire-gauze cover conducting away the heat, that inflammation of the gaseous mixture through the gauze does not take place, the temperature just outside not reaching that required to ignite the explosive mixture. The conductivities of alloys are in some few cases almost exactly those that may be calculated from the conductivities of the constituents on the assumption (as in the case of specific gravity) that each metal exists in the alloy side by side without mutual interference ; so that an alloy of this kind composed of equal volumes of any two metals will possess a conductivity equal to the arithmetical means of the conducting powers of the two constituents. In other cases, however, a wide difference exists between the conductivity thus calculated and that observed. According to Matthiessen all the metals except lead, tin, zinc, and cadmium, when alloyed to- gether, or with one of these four, so as to form a binary alloy, yield a product of which the conductivity is uni- formly more or less below that calculated on the above assumption ; whilst any pair out of these four yield a binary alloy the conductivity of which agrees very closely with that calculated. 83. Conductivity for Electricity. it is worth noticing in passing that the conductivities of metals for electricity are in many cases closely allied to those for heat ; there is a high probability that these two powers are really identical, and that in those cases where a discrepancy exists, the cause of this is a different or 150 METALS AND THEIR [CHAP. imperfect state of purity in one or other of the substances examined. Thus the following table gives the results of most carefully made experiments by Matthiessen on the electric conductivities of various metals in a high state of purity : and on contrasting these with the values given by Wiedemann and Franz for heat conductivities ( 82), it is at once visible that, save in the cases of copper, gold, and platinum, the two series are practically identical. These three exceptional metals happen to be greatly in- fluenced in conductivity by the presence of traces of impurity : moreover the relative values obtained at one temperature are not quite the same as those at another, the electric conductivities of metals being diminished by rise of temperature, but not always at the same rate in each case. Silver. . ico'oo Iron .... i6'8i Copper . 62-95 Tin I2 '36 Gold . . 77-96 Lead .... 8-32 Aluminium 56-06 Antimony. . . 462 Zinc . . 29-02 Bismuth ... 1*24 Platinum 18*03 A pretty illustration of the different conducting powers for electricity exhibited by different metals is afforded by passing a tolerably powerful current through a chain made of alternate links of silver and platinum wire ; the latter being the worse conductor (i.e. offering more Resis- tance) becomes much more heated, so that the links are heated alternately to dull redness or somewhat below, and to bright incandescence. 84. The conducting power of a given wire varies considerably according as the wire is hard-drawn, or has been annealed ; as a rule annealing improves conduc- tivity. The influence of small quantities of impurities in diminishing conductivity is probably due largely to the vi.] CHIEF INDUSTRIAL APPLICATIONS. 151 hardening effect thus produced; thus o'2 per cent, of iron in a copper wire diminishes the conductivity to only three-quarters of the original amount, and a trace of arsenic to one-third : on the other hand, the effect of heating a metal is to diminish its conductivity, although it might be supposed that the effect of a rise of tempera- ture would be a ^^^"-softening. Most metals lose about 30 per cent, of their conductivity at o on heating to 100, the loss being slightly different in each case : iron loses 38 per cent. This alteration in conductivity on heating has been utilized by Siemens in the construc- tion of a valuable pyrometer, which may be briefly described as a coil of platinum wire suitably protected and attached to a hollow iron pole, so that the end where the coil is can be thrust into the furnace, &c., the tempera- ture of which is to be measured. A current of electricity is led, by insulated wires passing through the hollow pole, to the coil, the current forking before reaching the coil, so that there are two return currents, one passing through the coil, the other not. By making this latter pass through a known resistance, and then measuring the relative cur- rents passing through the coil and through the known resistance, the resistance of the coil when heated is ascer- tained ; and as its original resistance is known, and the rate at which platinum alters in resistance with the tem- perature is known, the temperature to which the platinum coil is heated can be readily calculated. In the later forms of the instrument the relative strengths of the two currents are determined by enclosing in the two branches of the circuit two ingeniously- contrived voltameters, so that the columns of gas produced after a few minutes' action can be read off; from these numbers, the temperature of the coil is known by reference to a specially constructed table. 152 METALS AND THEIR [CHAP. The conductivities for electricity of alloys appear to follow the same laws as those for heat, the four metals lead, tin, zinc, and cadmium constituting a class separate from the others ( 82.) The effect of temperature on the conductivity of an alloy is in some cases much the same as upon a simple metal, a rise of temperature from o to 100 diminishing the conducting power from 25 to 30 per cent Other alloys suffer much less diminution thus, German silver loses only about 4 per cent, and a silver-platinum alloy of two parts silver and one platinum only 3 i per cent ; hence these alloys are valuable for the preparation of standards of electrical resistance. Non-metallic substances as a rule are increased in conducting power by heat 85. Specific Heat. In order to raise the tem- perature of equal masses of various metals through the same range, very different amounts of heat are requisite : Dulong and Petit have shown that the amounts of heat required to raise the temperature of i gramme of any metal from o to i (the " specific heats " of the metals respectively) are very nearly inversely proportional to the " combining numbers " of these metals as deduced from their chemical behaviour ; the actual values of the specific heats are such that the following equation always holds approximately, SxC-6- 3 , when S is the specific heat and C the combining num- ber of any given metal. This rule, moreover, is not con- fined to metals, all non-metals that are solid at the ordinary temperatures being found also to conform to it with three exceptions, viz., carbon, silicon, and boron ; whilst from the recent researches of Weber and others, it seems that although these bodies are exceptional vi.] CHIEF INDUSTRIAL APPLICATIONS. when the specific heats at the ordinary temperatures are taken, they conform to the rule at high temperatures. Thus the following table exhibits the relationship between the combining numbers and specific heats of the more important metals : Metals. Combining Number. Specific Heat (Regnault). Product. Aluminium . . 27 0-2143 5'8 Antimony . 122 0-0508 6*1 Arsenic .... 75 0*0814 6-1 Bismuth . . . 2IO 0'03o8 6*5 Cadmium . 112 0*0567 6*3 Copper .... 63-5 0-095I 6-0 Gold .... 196 0^0324 6-4 Lead .... 207 0*0314 6-4 Iron . . . c;6 0*1138 6*r Magnesium . . j^ 24 0-2499 6-0 Manganese. . . 55 O'I2I7 67 Mercury (solid) 200 0-325 6 '5 Nickel .... 59 0-1089 6-4 Palladium . . . 106 0-0593 6'3 Platinum 197-6 0-0329 6*5 Potassium . . . 39'i 0-1695 6-5 Silver .... 10$ 0*0570 6-2 Sodium .... 23 0-2934 67 Tin 118 0*0562 6-6 Zinc 65 0*0956 6'2 This relationship may be illustrated in the- following way : two blocks of lead and zinc are prepared weigh- ing respectively 207 and 65 grammes ; these are im- mersed in water kept boiling for some minutes so as to acquire the temperature of 100, and are then lifted out and quickly transferred to two similar vessels each containing 500 ccs. of water: two beakers answer well, the blocks of metal being gently lifted and lowered in by 154 METALS AND THEIR [CHAP means of pieces of string or thin wire attached to them. After two or three minutes the water in each beaker is stirred up well to make it acquire a uniform temperature, when it is found that each possesses sensibly the same temperature, so that a Matthiessen's differential thermo- meter (a differential air-thermometer with two pendent F 1C. 30. 'tf> 70 bulbs) exhibits no motion of the index column of liquid when one bulb is placed in one and the other in the other beaker ; i.e. the same amount of heat is communi- cated to the water by 65 grammes of zinc as by 20; grammes of lead. vi.] CHIEF INDUSTRIAL APPLICATIONS. 155 When metals are alloyed together, the specific heat of the alloy is very close to that calculated from the com- position of the alloy and the specific heats of the compo- nents, the relations of alloys generally to specific heat and specific gravity being alike in these respects ( 69). 86. Expansibility- The rate at which metals in- crease in bulk as the temperature rises is usually nearly proportionate to the increase in temperature, though not absolutely so. Slight differences in purity appear greatly to affect the co-efficient of expansion, somewhat con- siderable differences in the numbers obtained by different experimenters being occasionally noticeable. The follow- ing table illustrates the average numerical values of the increments in length of bars of different metals found by various observers on heating from o to 100; the expansions in area being almost exactly double, and those in volume treble, these numbers. Fig. 30 indicates the same values drawn graphically to scale, the original length of the bars being 500 inches (or 303 times that of the longest line). Increase in length of 10,000 units on heating from o to 100. Cadmium Zinc. Lead Tin . Silver Copper 33 29 28-5 24 20 18 Gold . Bismuth Iron . Antimony Palladium Platinum The different expansibility of metals is well illustrated by taking a compound bar of two metals riveted to- gether; if the bar be flat to start with, on heating it becomes sensibly curved, the most expansible metal being outside. This property is made use of in the 156 METALS AND THEIR [CHAP. construction of Martin's compensating pendulum, where the lengthening of the rod of the pendulum on increase in temperature is just compensated by the rise in the position of the centre of oscillation of the whole pendulum, by the raising of weights fixed at the ends of a compound bar traversing horizontally the pendulum rod, and fixed thereto at its centre, the most expansible metal being placed downwards. Similarly Breguefs thermometer acts by the twisting or untwisting of a spiral composed of two or more metals of different expansibility, an index being moved over a dial by the motion of one end of the spiral, the other being held fast by a clamp : Harrison's gridiron pendulum, where the expansions of different metals are ingeniously con- trived so as to counteract one another, and Grahams mercurial pendulum (a reservoir of mercury at the end of a steel rod), similarly, are practical applications of the different expansibilities of different metals, whilst the mercurial thermometer and several forms of pyrometers for the measurement of high temperature all depend on the expansion of mercury or other metals. 87. In the act of expansion an enormous amount of force is exerted ; conversely, if the ends of a heated bar of metal be fixed to two obstacles, and the bar be allowed to cool, either the obstacles are forced nearer together or the bar becomes permanently extended. To elongate a bar of iron one square inch in section by Y^-.VTTTT f ^ ts length requires a tensile force of one ton (Barlow) : now if a bar of these dimensions be heated to 100 and then allowed to cool to o, it diminishes in length T^-^nr ^ ^ ts length; and hence, to prevent it contracting, a force of not less than twelve tons must be applied. Thus a rod of cast-iron is readily broken if passed through a perforation in a hot iron vi.] CHIEF INDUSTRIAL APPLICATIONS. 157 bar fixed in a frame so that when the bar shrinks on cooling the centre of the rod is forcibly pulled inwards, the ends of the rod being prevented from moving by being fixed against two projecting parts of the frame. Great care has accordingly to be used when metal girders are employed for constructive purposes, &c., as, if due space be not left for expansion and con- traction, the bars forcibly thrust or pull out of their proper positions the walls, &c., into which they are built : on the other hand, if a rod of iron be passed through a building, and plates fixed to its projecting ends so as to press against the wall when the rod is expanded by heating, the walls will be forcibly drawn inwards during contraction on cooling, and thus bulg- ing walls may be gradually restored to the perpendicular. In this way the Conservatoire des Arts et Metiers in Paris was preserved from falling, as have several other build- ings subsequently. The tires of wheels are put on hot, and the rivets of boiler-plates, &c., are applied hot, so as to bind together more firmly the parts to be united through the shrinkage on cooling. Alloys usually expand at about the same rate as would a compound bar of the same length composed of the constituent metals placed end to end so as to be present in the same proportions as in the alloy. 88. Fusibility. Most metals when heated suffi- ciently pass into the liquid state ; but the temperature required to produce this phenomenon varies much : the following table illustrates the different fusion-points of various metals. Different experimenters have given considerably different figures in various cases, the dis- crepancies being doubtless due to imperfect purity of the bodies examined, and to the circumstance that it is not easy to measure elevated temperatures very exactly. 158 METALS AND THEIR [CHAP. Deg. Deg. Mercury . - 39 Zinc . . . near 420 Potassium . . + 62 Antimony . . 450 Sodium 97 Silver . . . 1 020 Tin . Bismuth near 230 270 Copper . . Gold . . . 1090 IIOO Cadmium 320 Iron . . . 1500 Lead . 330 Platinum . . 2OOO Mercury is the only metal fluid at ordinary tempera- ture; next to it in fusibility comes the newly discovered element gallium, which melts at a little above 30 (Lecoq de Boisbaudran). Alloys almost invariably melt at temperatures con- siderably below those calculated from the quantities of metals present and their respective fusing-points ; this property leads to the practical employment of many such alloys for casting, soldering, &c. In illustration of 'this property it may be noticed that a mixture of potassium and sodium is fluid at the ordinary temperature. An alloy of three parts lead and one tin (melting respectively at near 330 and near 230) fuses at 283, the calculated melting-point being * ^3 5- 4 or 305; whilst one of rather more than seven parts lead to twelve of tin (corresponding to the formula Sn s Pb) melts at 181 (Pillichody), the calculated melt- ing-point being near 265. On addition of bismuth to a lead-tin alloy, the fusing-point is still further lowered ; thus the ternary alloy known as " fusible metal" (lead five parts; tin three ; bismuth eight) melts at 100, whilst the similar alloy (lead two parts ; tin three ; bismuth five) melts at 93. On further adding cadmium to a bismuth- lead-tin alloy a still further reduction in melting-point ensues ; thus " Wood's alloy " (bismuth fifteen parts ; lead eight; tin four; cadmium three) melts completely at 63 C, vi.] CHIEF INDUSTRIAL APPLICATIONS. 159 becoming soft at 57. Such alloys therefore readily melt in the steam of boiling water, and the last in the vapour of boiling absolute alcohol. The use of solders of various kinds for uniting metal-work depends on the low melt- ing points of the various alloys used ; on applying a certain degree of heat, insufficient to fuse the metal- work itself, the soldering applied melts and adheres to the surfaces like quicksilver; on cooling, the solder solidifies and thus permanently fastens together the metals, much as papers are pasted together. It is noteworthy that in cases where a large amount of heat is liberated during the intermixture or combination of the constituent metals in an alloy, the melting-point of the alloy is not always lower than that calculated from the quantities of the constituents and their melting-points. Thus the addition of a few per cents of sodium (melting at -f 97) to mercury (melting at 39) gives an alloy or amalgam solid at the ordinary temperature, and therefore melting far above the calculated point. 89. Although by incorporating metals together in a state of fusion a tolerably intimate mixture is produced, yet it sometimes happens that oh standing in a fluid state for some time, more or less separation of the two bodies occurs ; or rather, two alloys separate from one another, differing in composition, one metal usually predominat- ing in one and the other in the other. Thus if equal weights of bismuth and zinc be mixed in the melted state and cast in a red-hot ingot mould which is main- tained at a high temperature for some little time so as to allow of separation taking place during cooling, the lower part of the ingot will consist of a bismuth-zinc alloy containing 8-14 per cent, of zinc, whilst the upper one will be a zinc-bismuth alloy containing 2-4 per cent, of bismuth (Matthiessen). The same kind of thing 160 METALS AND THEIR [CHAP. happens with lead and zinc, the heavier alloy contain- ing 1-6 per cent, of zinc, and the lighter 1-2 per cent, of lead. This result is precisely analogous to what takes place on shaking anhydrous ether and water together; on standing, water falls to the bottom, containing a small amount of ether dissolved, whilst ether floats to the top, retaining a minute quantity of water in solution. A similar result is obtained if fusel oil (coloured red by a little magenta) be shaken up with chloride of copper solution (green) : this mixture is neutral in colour, but speedily separates again in a red and green layer. This tendency towards separation is peculiarly incon- venient in various kinds of castings, and has to be over- come by special devices. The grain of grey cast-iron is partly due to a partial separation of the dissolved carbon during cooling ( 35) ; bell-metal is very liable to separate more or less, so that different portions of a large bell may have perceptibly different compositions ; the art of the bell-founder partly consists in adding together the constituents in such proportions, and so manipulating, as to prevent as far as possible this tendency to separate. The standard silver of Great Britain (silver-copper alloy containing silver 92-5, copper 7-5 per cent.) has a ten- dency to separate in this way, the outsides of cast bars of this alloy being slightly poorer in silver than the centres ; silver-copper alloy containing 7 1 '9 per cent, of silver has, however, no tendency to separate ; whilst alloys con- taining still less silver separate somewhat, but in these cases the outsides of the bars become the richest in silver. This tendency is occasionally utilized to effect the partial separation of metals from one another, especially if there be a decided difference in fusibility ; thus Pattin- son's lead desilverizing process depends on this principle vi.] CHIEF INDUSTRIAL APPLICATIONS. 161 the alloy richest in lead being the most fusible ; again the process termed " eliquation," or " liquation," is another case in point: to extract small quantities of silver from copper, the whole is melted with lead and the mass heated ; a lead-silver alloy then separates from a copper-lead alloy, the former running out in a fused state, the latter remaining as a spongy skeleton of the mass ( 2). 90. In order to prepare a " casting," it is necessary that hollow moulds should be constructed, into which the molten metal is poured from a crucible or melting-pot, or allowed to run from the melting furnace by a gutter according to the size of the object to be cast. Accord- ing to the shape of the object the construction of these moulds varies ; if small solid castings are to be made, and the metal fuses readily, the moulds are made of metal, plaster of Paris, or other similar material, being composed of two halves which when put together will enclose a cavity (e.g. a pistol-bullet mould) : if the casting is of any size, two holes are constructed in the mould, one to pour the metal in, and the other to allow the enclosed air, &c. to issue freely. For objects of cast-iron, gun-metal, and the like, moulds of clay and loam, sandy earth, &c., are employed, and, if the ob- ject be tubular or hollow, are so constructed that a central core is erected on the floor of the founding-pit, and round this a larger hollow mould is set so as to leave a space between the core and the outer mould ; the metal being then run into this space, the required object is obtained. Thus, in founding a large bell, a hollow core is built up of brickwork, a a a, Fig. 31, and plastered over with clay, b b b ; the soft clay surface is then turned to the exact shape of the inner surface of the bell by cutting away the superfluous clay by M 162 METALS AND THEIR [CHAP. means of a "crook," c, consisting of a wooden board or metal sheet held by an arm attached to a vertical axle, e, which is passed through the hollow part of the core to a bearing on the floor to give steadiness; as the shaft revolves, the clay is cut away to the required extent by the revolving crook. To the same arm is fixed Pic. 31. n a similar cutter, d, shaped exactly to the outside section of the intended bell ; when the core is shaped it is dried by kindling a fire in the hollow part, and is then covered with a greasy composition (to prevent adher- ence) ; haybands are then twisted round it, and clay spread over the covering; the cutter