UNIVERSITY OF CALIFORNIA AT LOS ANGELES TEXT-BOOKS OF SCIENCE ADAPTED FOR THE USE OF ARTISANS AND STUDENTS IN PUBLIC AND SCIENCE SCHOOLS. METALS. TEXT-BOOKS OF SCIENCE. ABNEY'S PHOTOGRAPHY. 1 1 5 Woodcuts. y. dd. ANDERSON'S The STRENGTH of MATERIALS and STRUCTURES. 66 Woodcuts. 3 s. M. ARMSTRONG'S ORGANIC CHEMISTRY. 8 Woodcuts. 3*. 6d. BALL'S ELEMENTS of ASTRONOMY. 1 36 Woodcuts. 6s. BARRY'S RAILWAY APPLIANCES. 218 Woodcuts. 4^.6^. BAUERMAN'S SYSTEMATIC MINERALOGY. 373 Woodcuts. 6s. BAUERMAN'S DESCRIPTIVE MINERALOGY. 236 Woodcuts. 6s. BLOXAM& HUNTINGTON'S METALS ; their PROPERTIES and TREATMENT. 130 Woodcuts. $s. GLAZEBROOK & SHAW'S PRACTICAL PHYSICS. 134 Woodcuts. 7 s. fxt. GLAZEBROOK'S PHYSICAL OPTICS. 183 Woodcuts. 6s. GORE'S ART of ELECTRO-METALLURGY. 56 Wood- cuts. 6s. CRIBBLE'S PRELIMINARY SURVEY. 130 Woodcuts. 6s. GRIFFIN'S ALGEBRA and TRIGONOMETRY. 3*. 6d. HOLMES'S The STEAM ENGINE. 212 Woodcuts. 6s. JENKIN'S ELECTRICITY and MAGNETISM. 177 Wood- cuts. 3^. 6W. MAXWELL'S THEORY of HEAT. 38 Woodcuts. 4.?. 6d. MERRIFIELD'S ARITHMETIC and MENSURATION. 3*. 6d. KEV, 3 s. 6d. MILLER'S INORGANIC CHEMISTRY. 72 Woodcuts. 3 s. 6d. PREECE SIVEWRIGHT'S TELEGRAPHY. 255 Wood- RUTLEV'S' The STUDY of ROCKS. 6 Plates and 88 Woodcuts. 4.5. 6rf. SHELLEY'S WORKSHOP APPLIANCES. 323 Woodcuts. THOME & BENNETT'S BOTANY. 600 Woodcuts. 6*. THORPE'S QUANTITATIVE CHEMICAL ANALYSIS. 83 Woodcuts. 4*. 6 long flame . J 75- So 4-5-5'5 15-195 3-4 50-60 fPulveru- 1 lent, or, at ] the most, t fritted Fat coals, burn- ~| ing with a \ long flame, or 1 gas coals . i 80-85 5-5-8 IO-I42 2-3 60-68 f Caked, but very fri- t able Fat coals, pro- 1 perly so- ( called, or f furnace coals ' 84-89 S-5'5 5-5-" f Caked, mo- 68-74 - derately [_ compact Fat coals, burn- 1 1 fCaked,very short flame, / or cok ing j coals . . . j 88-91 4-5-5-5 5-5-6-5 * I 74-82 ] compact, 1 but little I friable Lean (maigres) "1 ['Fritted or coals, or an- thracites . . J 90-93 4-4'S 3-5-5 1 82-90 pulveru- L lent * Including nitrogen, the proportion of which is stated rarely to exceed one per cent, of the organic constituents. The reader must carefully bear in mind that whatever classification is adopted it is only for convenience of descrip- L ign i te Coal. 29 tion. As has been shown by Dr. Percy in the following table, there are coals the analyses of which form a series unbroken in continuity from wood to anthracite. Peat appears to be inserted in the table not because it pro- perly forms a link in the chain, but rather because it is a product of more recent origin than lignite, and therefore approaches more in composition to ligneous tissue, thus filling the gap which time has made between wood and lignite. For sake of comparison carbon has been taken in all cases as 100 : Table s homing the gradual Change in Composition from Wood to Anthracite. Substance Carbon Hydrogen Oxygen Disposable hydrogen* I. Wood (the mean of seve- ral analyses) .... 100 12-18 S3-07 I -So j 2. Peat (the mean of seve- ral analyses) .... IOO 9-85 55^7 2-8 9 3. Lignite (mean of 15 varieties) IOO 837 42-42 3-07 4. Ten-yard coal of the South Staffordshire basin . IOO 6-12 21-23 3 '47 5. Steam coal from the Tyne IOO 5*OT 1 8 '32 7-62 6. Pentrefelin coal of South y* o VA Wales IOO 475 5-28 4-09 7. Anthracite from Penn- sylvania, U.S IOO 2-84 174 2-63 * The term disposable hydrogen is here used to signify the amount in excess of that required to form water with the oxygen present. Lignite. This term is synonymous with the braunkohli (brown coal) of the Germans. It is employed to designate substances which form the link between peat on the one hand and true coal on the other. In those kinds which ap- proximate most closely in their composition to peat the only essential difference is that they have been derived from woody matter, whereas peat owes its origin to mosses, for the most 30 Fuel. part, and plants of small growth. Lignites of this description still retain the structure of the original wood more or less, according to the stage of alteration which they have reached. As the original structure becomes obliterated by pressure and chemical action, the fracture tends to become con- choidal. The change which goes on during the formation of peat and lignite, and the less bituminous coals and anthra- cites from the more highly bituminous coals and lignites, is due to the gradual elimination of oxygen and hydrogen in combination with one another, but mainly with carbon, as carbonic acid and carburetted hydrogen or marsh-gas. It thus happens that certain mineral fuels might equally well be classed as coals as lignites, it being difficult to define where the one ends and the other begins. Those lignites which may be classed as fossil wood contain sometimes as much as 50 per cent of moisture, and even after being artificially dried they take up 12 to 15 per cent. The remarks which have been made with respect to the ash in peat will equally apply to lignite. Fossil wood yields on distillation about 35 to 40 per cent solid residue ; bituminous wood, which is a con- venient term by which to distinguish lignite in a somewhat more altered condition, 40 to 50 per cent. Lignites to which the term brown coal may with advantage be applied, in point of quantity of residue left after distillation do not differ sensibly from bituminous wood. Lignites of this last description do not contain, generally, more than 5 to 10 per cent of moisture. They burn with a long smoky flame. In appearance they are ' dark-brown or black, hard, tenacious, sonorous, and they break with a conchoidal fracture ; they do not alter much in structure on exposure to the air. The average composition of brown coal is as follows : Carbon . . Hydrogen Oxygen and nitrogen ..... Bituminous Coal. 31 7'he products of distillation cf dry lignite average : Carbon . ... Water.. Tarry matter Gases Lignites, with few exceptions, are non-caking ; i.e. when powdered and strongly heated, with exclusion of air, the par- ticles will not cohere together and form what is known as coke. Bituminous Coal. The kind of coal into which lignite in its most altered state merges is bituminous coal. Although these two substances in some cases may be difficult to dis- tinguish one from the other, yet that is far from being the case when average specimens of either are considered. The density of bituminous coal is, as a rule, greater than that of lignite or brown coal ; it contains less water in its natural state than lignite, and after drying at 100 C. is also less hygroscopic. It has previously been stated that bituminous coals may broadly be divided into two classes, viz. caking and non-caking. It is within the experience of all of us that some house-coal soon after it has been thrown on the fire begins to soften, finally becoming more or less pasty in con- sistency, and giving off gas which burns with a bright flame. If a lump of such coal be heated, with partial exclusion of air, then it will be found that after a short time gas ceases to come off, and the lump, which on the first application of heat became pasty, will now be a more or less hard coherent mass of coke. Coal which possesses this property is technically described as a caking coal. There is every degree of caking, some coals caking very slightly, whilst others may almost be said to fuse when heated. A non-caking coal, when treated in the way just described, leaves a residue the particles of which do not cohere in a marked degree. Before leaving this part of the subject it will be profitable to glance briefly, but systematically, at the different varieties of bituminous coal, commencing with those most nearly 32 Fuel. allied to lignites. For this purpose the French classification framed by M. Griiner can be advantageously followed, sub- stituting, however, for the terms dry, fat, and lean the more familiar expressions caking and non-caking. 1. Non-caking Coal, with a long flame. These coals when .'reated for coke crack, but preserve their original form ; and if originally in powder the particles do not become consoli- dated. Coals of this kind are hard, compact, and but little friable. A cubic metre of them weighs 700 kilogrammes. The fracture is often conchoidal, and of such a nature as to have given rise to the name splint-coal It is not common in France or Germany, but in Derbyshire, Staffordshire, and Scotland it exists in quantity ; in colour it is rarely per- fectly black ; the powder is brown. The calorific power ranges between 8,000 and 8,500, taking the two extremes of the class and assuming the absence of moisture and extra- neous matter. One part of the dried coal will convert 6 to 6*5 parts of water at o into vapour at 112 C., when only just sufficient air for combustion is supplied. In the lower part of the basins the coal passes into that comprehended in the next class, viz. : 2. Caking Coals, with long flame. As the title indicates, these coals coke ; those nearest in nature to class i, however, when powdered barely become cemented together on being heated. They go by the name of cherry-coal in the North of England. In hardness they do not equal class i, and the fracture tends less to be conchoidal ; they are also blacker and brighter. A cubic metre weighs from 700 to 750 kilogrammes. Like the last described, they burn with abundance of flame and smoke ; they take fire readily and burn rapidly. The coke is light, friable, and porous, and therefore unsuited for metallurgical purposes ; but for the manufacture of lighting-gas these coals are very valuable, the gas, though in quantity not so great as that from the non- caking coal of class i, being of greater illuminating power. Trie coke is, besides, good enough for use where it will not be Bituminous Coal. 33 subjected to much pressure or a strong blast The calorific value ranges between 8,500 and 8,800. According to trials made at Portsmouth and Woolwich, i part of this coal in its ordinary condition (say containing 5 to 8 per cent of water and ash) will. convert 7 to 775 parts of water into vapour. Coal of this description occurs notably in the neighbour- hood of Newcastle and in South Wales. To the north of Newcastle it is mostly steam-coal, and to the south gas-coal ; it is, however, all one basin. 3. Caking Coal, properly so called. Coals of this type have a less lamellated structure than the last ; they are als.o blacker, brighter, and much softer on the average, and the flame is shorter and more brilliant, giving less smoke. When heated they soften, even to fusion in some cases. Although they contain less volatile matter than those last considered, they swell up more in coking. The properties or this coal render it well suited for use in blacksmiths' forges and for making coke ; though for the latter purpose the coals of the next class are even better suited. The weight of a cubic metre is 750 to 800 kilogrammes, and the calorific power 8,800 to 9,300. In the condition in which they are obtained in com- merce, containing from 5 to 15 percent extraneous matter, including moisture, i part of these coals will vaporise 7-5 to 8-5 of water. This description of coal is found largely on the Continent : in France, particularly in the St. Etienne basin and the north ; in Belgium, in abundance in the neighbourhood of Liege and in the Mons basin ; also in Westphalia. In England they occur more especially in Durham and Yorkshire. 4. Caking Coals, with short flame. These coals have often the appearance of being made up of alternate bright and dull layers. The character of their fracture resembles class 3 ; they are less rich in volatile matter, and generally very friable, i.e. crumble under moderate pressure. They inflame with difficulty, burning with a short, blueish -white and generally smokeless flame. This coal is the best suited 34 Fuel. of all for coking, the product being compact and hard, and relatively large in quantity. A cubic metre weighs about 800 kilogrammes. This class possesses the highest calorific power of all, viz. 9,300 to 9,600. In England this coal is located more especially in the neighbourhood of Cardiff, in South Wales ; in France, near Creusot, and in the St Etienne and other basins to some extent The trials made of the Welsh coal of this type show that it is capable of vaporising 9 to 9-5 parts of water per unit of coal. As compared with the caking coal from the North of England basin, they have a greater actual calorific value, but the northern coal burns more rapidly, and in consequence produces a greater amount of heat in a given time. 5. Non-caking or Anthradtic Coals, and Anthracite. The first of these are characterised by dull streaks ; they are harder than class 4, and become more and more so as they approach anthracite in nature. The weight of a cubic metre is about 850 kilogrammes. They give but little flame, and often decrepitate in the fire, an extremely inconvenient property, for if they split up into small pieces it becomes difficult to keep up a sufficient draught through the fire to maintain the requisite temperature. Some kinds are, how- ever, successfully employed in the blast-furnaces of South Wales ; they are found in the neighbourhood of Swansea and Merthyr Tydvil. They also abound in Pennsylvania, U.S., but are not of frequent occurrence on the Continent. Their calorific power ranges between 9,200 and 9,500, and their steam-raising power is about 8-5 to 9-5 when, say, 6 per cent of ash, &c. is present It is difficult to ensure any- thing like complete combustion. With anthracite we have reached the end of the series. In the most highly altered kinds it is brilliantly black, and even when in powder has not a brown shade in it. It is hard, brittle, and generally conchoidal in fracture. It does not soil the fingers. The weight of a cubic metre is usually Coal 35 850 to 900 kilogrammes, but it may be even higher if much ash is present When heated it often decrepitates even when gradually heated. American anthracite is said not to have this property. Anthracite burns with difficulty, requiring a strong draught. The calorific value is much the same as that of the anthracitic coals, but to obtain the same effect greater care is required. South Wales, Pennsylvania, and the French Alpine districts are the localities in which anthra- cite is most abundant. General considerations. It has already been pointed out that coals having the same elementary composition may have a different calorific power, owing to the different way in which the elements are combined in the two cases. It is for a similar reason that overlapping takes place in the classifica- tion just considered. An analysis will tell us approximately in which class a certain coal should be placed ; it is, how- ever, only on submitting the fuel to distillation that the point can be conclusively settled. One coal may contain a greater percentage of carbon than another and yet produce less coke. It is important to note that these considerations apply generally only to coals from different basins. Coals from the same basin have, with few exceptions, been subjected to like conditions, and although they may be in various stages of alteration, yet the series is perfectly continuous and free from overlapping. It will be observed, on referring to the table, that at the same time that the percentage of carbon gradually increases the disposable hydrogen also increases ; i.e. the oxygen is eliminated in a greater degree than the hydrogen, until the fourth class is reached, when the hydrogen begins to decrease down to the most altered form of anthracite. This explains the fall at the same point in the calorific power, already referred to. In selecting a coal it is important to ascertain the extent to which it cakes. If it cakes very much the grate may become blocked. In order to obviate this, in some cases it 36 Fuel. is necessary to mix a certain proportion of non-caking or free-burning coal, as it is called, with the binding coal. Ash of Coal. For practical purposes it is very im- portant to note, not only the quantity of ash, but also its nature. This is done by burning off the combustible matter in a platinum crucible. In examining the ash the first thing to consider is the amount of oxide of iron present ; this is indicated by the colour. The oxide of iron in the ash is mainly derived from iron pyrites, it will therefore roughly indicate the amount of sulphur in the coal. At the temperature of most furnace operations oxide of iron forms a fusible compound, termed clinker, with the remainder of the ash. This clinker tends to block the grate and prevent proper access of air ; its consistency is determined by the proportion of oxide of iron. As a rule, the less clinker a coal makes the better. In one particular case, however, it has been made to serve a useful purpose, viz. in South Wales, where abed of clinker, supported by a few bars, is commonly allowed to form to a depth of from 12 to 20 inches at the bottom of the furnace. This clinker bed is used as a substi- tute for a grate, being broken up from time to time by means of a bar, so as to let sufficient air through. By this contrivance inferior small coal can be burnt, which would be useless in an ordinary grate. Sulphur occurs in coal, probably, in three conditions, viz. as iron pyrites, in organic combination, and as sulphate. It is, however, mainly present as iron pyrites. Coal containing much sulphur is not suited for use in those processes in the manufacture of iron in which the metal comes in direct contact with the fuel ; neither is it suited for the manufac- ture of coke. There is not the same objection to the use of sulphurous coal in reverberatory furnaces. Phosphorus, in more or less quantity, nearly always occurs in the ash of coal. This should not be lost sight of in the selection of coal for certain processes in the manufacture of iron and steel Coal Coke. 37 Arsenic sometimes exists in . coal, being doubtless present as arsenical iron pyrites. Antimony, lead, and copper have been occasionally noticed. Weathering. Coal when exposed to the action of the atmosphere undergoes certain changes, due to the action of oxygen in the presence of moisture. A certain amount of carbon and hydrogen is eliminated in combination with oxygen, and at the same time some oxygen becomes fixed ; as shown by the fact that, if a coal is dried at a temperature not exceeding 100 G, it will lose weight up to a certain point, owing to the removal of moisture and gases, and will then begin to gain in weight, the oxygen taken up more than compensating for the carbon and hydrogen lost The caking property of coal appears in some cases to be materially affected by weathering. It is said that a coal obtained at Penclawdd, near Swansea, even in so short a space of time as two days loses its power to cake. Many coals on exposure for a few months become much dete- riorated in quality. It has not yet been determined whether the change is due to the escape of volatile matter or to oxidation : it is probable that both conduce towards the result, oxidation, however, being the initial cause of the mischief. COKE bears the same relation to coal that charcoal does to wood. The first production of coke appears to have been due to an endeavour to find a substitute for wood charcoal, coal having been found not to answer the purpose. Indeed, the only method for the making of coke practised for a long time was that of burning coal in piles, much in the same way as was done with wood for the production of charcoal. The loss in this method is very considerable. As in the case of wood, coal is only treated in retorts when the principal object in view is to obtain the volatile products, as in the manufacture of illuminating gas. The coke produced in this way is never so good as that obtained by other methods, to be referred to ; it is much more tender and friable and not well suited for 8283 38 Fuel. use where considerable pressure will be put upon it, as in the blast-furnace or cupola. In coking in piles, owing to the greater density of coal, the same precautions are not required as in charcoal-burning. The process is, however, when conducted to the best advantage, essentially the same. The central chimney is made in brickwork, air spaces being left all the way up, and a cast-iron damper fitted to the top. The cover of the pile consists of powdered coke or rubbish, there not being the same occasion for a yielding cover as in charcoal-burning. When highly bituminous coal is being coked, it is often desirable to allow the heap to become thoroughly ignited throughout before applying the cover ; in such cases, also, owing to the tendency of the coal to fuse, great care has to be taken to keep the air-channels properly open. Some prefer to build the pile on moist ground, with the intention to promote the removal of sulphur ; this point will be discussed later on. The presence of moisture is also con- sidered advantageous in checking too rapid combustion. It must, however, not be lost sight of that steam is decom- posed by carbonaceous matter with the production of carburetted hydrogen, hydrogen, carbonic oxide, and car- bonic acid. The loss incurred in this way must, therefore, be set against the advantages which may accrue. In some localities rectangular kilns are in vogue, and very excellent coke is said to be produced in them, with less loss than occurs in the ordinary piles. These kilns consist of two parallel walls of brickwork, about 5 feet high, 8 feet apart, and 40 to 60 feet long ; the floor and the inner portion of the walls are of fire-brick. In each wall is a series of openings (E F), about 2 feet apart, and leading from them are vertical channels (G H). In order to charge the kiln, one end is first bricked up ; coal slack is spread over the bottom, damped, and stamped down until it reaches up to the openings (E F), i.e. about two feet from the bottom. Slightly- tapering pieces of wood, about 6 inches in diameter at the Coke. 39 thick end, and long enough to reach across the kiln, are placed with their ends in the openings (E F). The remainder of the kiln is then completely filled with slack, which is damped and stamped down as it is charged in ; the top is then covered with coal dust or loam, the end through which the charging has been effected having first been bricked up. The pieces of wood are now carefully drawn out ; thus channels are formed through which ignition can be effected, and which also serve as means by which to carry on and (: mnmiin V '," , FIG. 3. regulate the process, by the admission of a suitable quantity of air. Before lighting the kiln, by means of easily inflam- mable sticks, all the vertical flues or chimneys on one side are closed, and also the horizontal openings -on the opposite side. When the ignition has travelled through to the opposite side, the channels in the brickwork which were open are closed, and the others opened. This reversal of direction takes place, at the discretion of the workmen, every two or three hours until the process is complete ; the direction of the 4O Fuel. wind at the time will have an important influence on the working, if not carefully counteracted. This method requires about eight days for completion. Where wider kilns, e.g. 14 to 15 feet, are used, the channels are constructed by means of lumps of coal instead of the wooden poles. Unless great care be exercised very considerable loss may occur through the burning away of the coal. -There is no doubt that both this plan and that previously described are very wasteful as compared with the methods of coking in ovens, which are now almost universally adopted. The simplest form of oven is that known as the bee-hive oven. They are sometimes circular, but often square ox FIG. 4. oblong. The height and diameter vary up to about ten feet These ovens are usually built in blocks, to economise heat ; the dividing walls are about two feet thick, the inner facing being of fire-brick. At the top is an opening for the escape of the volatile products ; through it the ovens are usually charged, from coal-trucks brought immediately over the ovens by means of a branch line of rails. In front is a door through which the coke is removed ; charging is also some- times effected through this opening. The door often con- sists of a perforated plate of iron ; more generally it is formed of fire-brick enclosed in an iron frame, attached to a lever. Through the door air is admitted in suitable quantity, some of the spaces being blocked with clay when it is necessary to check too rapid action, which usually first takes place after the expiration of about two or three hours Coke. 4 r from the commencement. After the lapse of about twenty- four hours the door is entirely plastered up, and in another twelve hours, when flame will no longer issue from the top opening, that also is closed. The oven remains undisturbed for another twelve hours ; the door is then opened, and the coke raked out into iron barrows or trucks, the ovens being built at a convenient height from the ground for the purpose. The tool employed to withdraw the coke is termed a drag. It consists of a piece of flat iron, having attached to it at right angles a rod long enough to project from the front of the oven when the flat piece is in position at the back. By means of a windlass the drag is pulled out, and with it the whole of the coke. In some places the coke is pushed out from the back. It is important, in any case, that the oven should be rapidly cleared, so as to avoid its being unduly cooled down. It is preferable to quench the coke before drawing it, failing which it should be done immediately afterwards. In principle these ovens are simply reverberatory gas furnaces. The heat necessary to carry on the dry distilla- tion of the coal is obtained from the combustion of the volatile matter by means of air admitted above the fuel ; the heat thus produced is radiated from the top mainly, but also from the hot sides and bottom, and maintains the required temperature. The coking gradually extends from above downwards, and from the bottom and sides towards the middle. If the process is properly conducted only a slight consumption of the coke takes place, since the air should only come in contact with the gaseous compounds above the coke. Much economy is effected by leading the excess gases under boilers, and then burning them. More than enough steam for all the purposes of a colliery can be raised in this way. The bee-hive ovens are certainly not so economical as some which have since been invented, yet, owing to their relative small cost, the ease with which they may be put up, 42 Fuel. and the good quality of coke producible in them, they have up to the present very successfully held their own. It is observable, however, that gradually some more modern and economical inventions are superseding the old bee-hive oven. It is natural that progress in these matters should be slow : a manufacturer rightly hesitates before giving up an old tried servant for another who claims to have greater accomplish- ments, but whose trustworthiness has yet to stand the test ot time. In order to put ourselves in a position to fully appreciate the claims of modern inventions of this kind, let us consider, seriatim, what are the main objects which it is desirable to attain. I. The introduction of air in such a way as to completely burn the gaseous products of distillation, but not the coke. II. The prevention of loss of heat by radiation and con- duction, and during the drawing of the coke. III. The promotion of uniform coking, from the exterior in all directions towards the centre. IV. Rapid coking. The quality is improved and the yield increased by rapid coking. For purposes of illustration, the Appolt, Coppe*e, Carves, and Pernolet ovens have been selected. The Appolt ovens are largely used abroad, and coals differing very considerably in their character are treated successfully in them. They consist essentially of a large brick chamber, con- taining, in the most recent erections, eighteen compartments or retorts (A), tied together at a sufficient number of points to ensure solidity, but having a continuous free space round all of them. Charging is effected through an opening at the top of each retort ; the bottom is provided with a cast-iron door, over which a layer of coke dust is spread before charg- ing. The retorts are about 4 feet long and i foot 6 inches wide at the base ; they taper slightly, so that at the top they are about 3 feet 8 inches by 13 inches ; in height they are Coke Appolt Oven. 43 about 13 feet. At about 18 inches to 2 feet above the bottom of each retort are two rows of small horizontal open- ings (c), say 5 inches by 2 inches ; it is through these open- ings that the volatile products of distillation pass into the external spaces, and are there burnt, by means of a suitable quantity of air admitted through openings in the long sides of the oven. In treating highly-caking coal, other vents further up are required. The products of the combustion of the gases are taken off by means of sixteen flues, four at the bottom and four at the top of each long side of the chamber. Each set of four is led into a longitudinal flue, divided into two by a partition, and connected with a chimney similarly partitioned. Dampers are placed in the vertical flues, where they are connected with the horizontal flues. In this way the heat throughout the oven can be regulated as required. The distance between two compart- ments is about 8 inches to 10 inches. Between the walls 44 Fuel. forming the chamber and the outer mass of brickwork, which is necessary to avoid, as far as practicable, loss of heat by radiation and conduction, there is a layer of loose non-con- ducting material, such as sand or brick-earth, which allows the brickwork to expand and contract, and thus prevents the oven pulling itself to pieces, and at the same time assists in keeping the heat in. In removing the coke it is allowed FIG. 6 to fall on sloping iron plates, to avoid its being unduly broken. It is desirable that the coals should contain at least 20 per cent, of volatile matter, but, on the other hand, they should not be too strongly caking, for then the coke is very troublesome to remove from the oven. Any difficulty of this kind is easily met by mixing coals of different natures. The ovens are charged in succession ; the eighteen compart- Coke Appolt Oven. 45 ments will take about 24 tons of coal ; the coking is com- plete in about twenty-four hours. Each retort is charged again immediately after the withdrawal of the coke, so that the process once in working, there is always heat sufficient to start the coking of each fresh charge. Moist washed coal can be used in these ovens without inconvenience. The waste of coke by oxidation is in this oven reduced to a minimum, as the air, even should there be cracks in the sides of the oven, cannot reach the inside of the retorts, the gases in the surrounding space forming an absolute barrier. In this respect then, the Appolt oven has a marked advan- tage over the ordinary ovens, in which all the air is admitted into the cokin'g-chamber itself. Another advantage is the very large extent of heating surface, and the comparatively 46 Fuel. small size of the retorts, whereby rapid carbonisation is en- sured, and thereby proportionate density in the coke. The combustion of the gases is very perfect, the arrangement of the oven facilitating their thorough admixture with the proper amount of air. The arrangement for withdrawing the coke enables it to be done very rapidly, and the cooling of the ovens is proportionately less. The height of the retorts acts beneficially, as it tends to increase the density of the coke. The construction of these ovens is also favourable to the production of coke uniformly from the sides of the retort to its centre. Owing to the bad conductivity of coke for heat, the process goes on more and more slowly as the thickness of the layer inside the retort increases. The addition of water to caking coal is said to act bene- ficially in preventing it from swelling up too much and becoming fixed tightly in the retort The yield of these ovens is said to be as great as that which can be obtained in a crucible on the small scale, i.e. 10 or 12 per cent, more than that obtained in ordinary ovens. Coppee Ovens. The principle of these ovens is essentially that of the Appolt system ; the method of carrying it out is, however, somewhat different. In the Coppee system the retorts are long horizontal chambers, very much the same thing, in fact, as if the retorts of the Appolt oven were placed horizontally instead of vertically. The retorts (A), are about 9 metres long, 480 millimetres at the back, 430 at the front, and about a metre high at the crown of the arch. The tape-ring from the back to the front is to facilitate the removal of the coke, which is effected from the back by means of a ram. At each end of a retort there are two doors, the lower one being about 3 feet in height, the upper about i foot In the partition wall between each two coking-chambers there is a series of twenty-eight vertical flues, which lead the vola- tile products from the top of the retorts to a horizontal flue (c), passing under one of each pair of retorts in the direction of its length. Smaller vertical flues, through which air . is CokeCoppte Oven. 47 admitted to effect combustion, communicate with the top of each of the flues leading from the coking-chambers. The products of combustion having passed under one retort, as just described, are led into a similar channel (D) under the other retort, from the front end of which they are drawn off into the main flue (E), leading to the stack. Beneath the horizontal flues, under the retorts, are a series of channels, FIG. 8. through which cool air is circulated by means of a separate stack, the object being to keep the foundations from being damaged by excessive heat. Besides the air-channels already described for effecting combustion in the vertical flues, there are others which admit a certain amount of air into the top of the retorts. The quantity of air admitted is regulated by dampers. Having to pass for some distance 48 Fuel. through the hot masonry, the air supplied for combustion becomes heated before mixing with the volatile products from the coal. The products of combustion, before being taken up the stack, are often first led under boilers, and their 250 Coke Coppc'e Oven. 49 heat thus utilised to the utmost. The top of the ovens ; s covered with a thick layer of rubbish, to keep in the heat as much as possible. It will be observed that the way in which the air is admitted to the ovens partly resembles the method in the bee-hive oven, and partly that of the AppolL The amount of air, however, which is admitted directly into the coking- chamber of the Coppe"e oven is very small, and cannot bum the coke if properly regulated. These ovens are particularly suitable for the treatment of coals which are not very bituminous, and therefore diffi- cult to coke in ordinary ovens. The coal must be crushed to about the consistency of very coarse meal ; it is therefore easy to wash it before coking, if desired. It is found most convenient to build the ovens in batches of thirty, and to work them in pairs ; the charging is so arranged that one oven of each pair receives a fresh charge when that in the other is half coked. Coke produced in ovens is much harder and denser than that made in open heaps, and called yard-coke. The latter kind of coke, and that produced in retorts when coal is dis- tilled for the sake of its volatile products, may be used with advantage with cold blast, when the pressure of superincum- bent material is not too great. It has been pointed out that a coal which is highly caking may give trouble in an Appolt or a Coppee oven by render- ing it difficult to withdraw the coke, and that this difficulty can be overcome by mixing with the binding coal a certain amount of free-burning coal. The principle herein involved may be further extended. The slack, or small of non-caking coal, may be utilised for the production of coke by mixing it with bituminous coal. The two kinds of coal should be ground separately, the caking being reduced to a fine state of division, whilst the non-caking may be in pieces about the size of a pea. In this way even anthracite may be used, the particles becoming firmly cemented together by the ' t C 50 Fuel caking coal. In this case it is necessary to add a small umuunt of pilch as well. Other similar means have been resorted to for the utilisa- tion of small coal, in which various carbonaceous substances are employed to act as a cement. Thus, anthracite or coke breeze mixed with tar will produce a solid coke on being subjected to heat. Patent fuels consist of mixtures of this kind, moulded into the form of bricks with or without the application of heat Resin is said not to give satisfactory results as a cementing material unless mixed with tar. Mu- cilaginous substances prepared from farinaceous bodies are also used. The use of patent fuels is almost entirely con- fined to raising steam for navigation and on railways, for which purposes they answer very well, as the space occupied is small compared to that required for ordinary fuel. To render the blocks impervious to moisture, they are sometimes dipped in coal-tar oil immediately on being withdrawn from the drying oven. Removal of Sulphur from Coke. The iron pyrites (FeS >), which exists in more or less quantity in every coal, undergoes decomposition during the coking process ; one half of the sulphur is distilled off, and unites with oxygen to form sulphu- rous acid (SO 2 ), during the combustion of the volatile pro- ducts. The remainder of the sulphur will be found in the coke, in combination with the iron, as FeS. The problem we have before us is how to remove this residual sulphur from the coke, supposing it to be present in such quantity as to detract from the value of the coke for furnace purposes. It is a matter of common observation, that if water be thrown on red-hot coke or coal a strong odour of an objec- tionable kind is at once perceptible. This arises from the decomposition of tl\e protosulphide of iron, oxide of iron being formed, and the offensive gas, sulphuretted hydrogen (SH 2 ). From this it might be argued, that in order to desulphurize coke it would only be necessary to pass steam into the oven. It must, however, be borne in mind that the Coke. 51 amount of sulphur in coke, as compared with the carbon, is very small, and that it is practically impossible to ensure the steam permeating the coke throughout. The impossibility of removing anything like the whole of the sulphur in this way is still more apparent when it is remembered that red- hot carbon decomposes steam, with formation of carbonic oxide, carbonic acid, marsh gas, and some free hydrogen. It is easy to overrate the amount of sulphur removed by steam if it be judged only by the sense of smell, the odour of a little sulphuretted hydrogen being very powerful. Desulphurisation by means of air, either at the ordinary pres- sure of the atmosphere or at higher pressures, has been tried. It is obvious that the objections to the use of steam apply equally to air. The addition of such substances as carbonate of soda, lime, carbonate of lime, oxide of manganese, chloride of sodium, &C., has been tried, but only with indifferent success, not warranting the extra expense entailed. Th's method has for its object the transference of the sulphur from the iron to the substance added, which once having entered into combination with the sulphur will, for instance, prevent its passing into iron melted with the coke in a cupola. It follows, from the foregoing considerations, that at pre- sent there is no satisfactory method known by which sulphur can be removed from coke. The most satisfactory way of meeting the difficulty is to disintegrate the coal before coking it, and subject it to a washing process by means of which the shale and pyrites which it contains can be, by reason of their greater specific gravity, to a considerable extent removed. This treatment cannot be applied to non- caking coals unless they are subsequently mixed with a sufficient quantity of caking coal to make them coke. Collection of the Products of Distillation of Coal. This is done, as has already been stated, in the manufacture of ordinary lighting gas ; but the coke produced, when the chief object is to obtain as great a quantity of volatile products K 2 52 Fuel. as possible, is lighter and more porous than that made in ovens such as have just been considered It has been attempted to produce dense hard coke, and at the same time to collect the tar, oils, ammonia, and gases. The ovens may be heated entirely by refuse coke or by the gases, or partially by gases and partially by coal or refuse coke. The Pernolet oven is one of the most important of this class. It was patented in 1862 ; an almost exactly similar patent was taken out in 1850 by Pauwels and Dubochet. Pernolet claims, firstly, to make coke suitable for metallurgical, railway, and other purposes, in greater proportion than when manufactured in the ordinary manner ; secondly, gas suitable for burning and heating ; thirdly, tar, and different oils obtainable therefrom ; and, fourthly, ammonia and ammoniacal salts. The coking is to be conducted ' very slowly ; ' air is excluded as far as possible after thorough ignition has been effected ; the products of distillation, which are either drawn off by the draught of a high chimney or by exhausting- machines, are condensed and collected by suitable machi- nery, much as in gas-works. In this country it has been tried by several large com- panies. The yield of coke is greater than that of a bee-hive oven, but not more than that of a Coppee or Appolt oven. Considerable quantities of tar, &c. have been collected, but the quality of the coke is not so good, and the expense in labour and repairs is greater. As the quality of the coke is a matter of great importance in iron smelting, it is not sur- prising that this method of making it has been practically abandoned in this country ; an additional reason is to be found in the fact that little or no real saving could, at any rate until recently, be effected, as the tar, ammonia, c. realised very low prices, owing to the large quantities produced in gas-works. The prices of these bye-products have, how- ever, within the last few years risen considerably, owing to increased demand. Coke. 53 On the Continent the Pernolet system has met with more favour, but there is no reason to believe that the coke there produced is better in quality than that obtained here. Ovens of all sorts of shapes have been tried. As the result of two years' experience by Messrs. Bell Bros, in the North of England, preference was given to the bee-hive shape ; but the process was finally abandoned, mainly, it is said, owing to the flues and floors being constantly burnt down by the excessive heat of the gases. The manufacture of good hard dense coke is incom- patible with the production in any considerable quantity of valuable condensable gaseous compounds. This follows from the established fact that the higher the temperature, and, within certain limits, the longer the coke is submitted to that temperature, the greater will be the yield, and the more dense the coke. At low temperatures volatile bodies, rich in carbon, are formed, and may be collected ; at higher temperatures these compounds are decomposed and deposit their carbon. Thus, the substances which distil off from the central cooler region of a retort will, on coming in contact with the outer layer, be decomposed, provided the tempera- ture be sufficiently high. A temperature which is not sufficiently high to effect the decomposition of the richer hydrocarbons is below that necessary to produce a good dense and hard coke. In the manufacture of good oven- coke, so called to distinguish it from gas-coke, the gas pro- duced cannot be highly luminous, for at the temperature required to produce such coke olefiant gas, the principal light-yielding constituent of gas used for illuminating purposes, would be decomposed. From what has been said it will be gathered that, pro- vided the proper conditions for obtaining a hard dense coke be attended to, there is no real objection to the collection of such tar and ammonia as may then be formed ; but these substances must always be of secondary importance, atten- tion being mainly directed to the regulation of the process 54 Fuel. so as to produce sound coke, the conduct of the process having to be varied somewhat for each kind of coal. The carrying out of these conditions is the object of the Carves system. The general arrangement is something like that of a Coppe'e oven, with the difference that the gases, although burnt on the exterior of the retorts, are first passed through a series of pipes cooled by water, forming a condenser, in which the condensable products are deposited ; the gases are next passed through scrubbers, or vessels con- taining moistened coke, which remove the ammonia, the liquor when saturated being run off into reservoirs and subsequently treated for the preparation of ammoniacal compounds. The gases, after undergoing this treatment, are admitted through a nozzle in a fire-door to a fire-grate, on which a small amount of refuse fuel is kept burning to ignite the gases and air which has been allowed to mingle with them in suitable quantity. From the fire-grate the burnt and burning gases pass through the various flues surrounding the retorts. The gases, after they have done their work in the ovens, are further utilised for raising steam. It is stated that at Besse'ges all the machinery required in the manufacture of coke and its bye-products is now being driven by steam raised in this way, and there remains a large surplus, which is used in the blowing engines for the Bessemer process, and for lifts, cranes, &c. The steam raised by this surplus heat is sufficient to furnish 400 horse-power. These ovens, we are assured, give a yield of 75 per cent, as against 55 to 65 per cent, obtained in an ordinary bee-hive oven ; the coke is also freer from ash, since, the yield being greater, the ash is diffused through a greater amount of coke in the one case than in the other. The production of every ton of coke is said to be accompanied by the formation of about four shillings' worth of bye-products. Good coke has been referred to as hard and dense. It must be understood that there is a practical limit to the Gaseous Fuel. 55 value of density ; it would not do, for instance, to compress it by artificial pressure. The most economical and generally satisfactory coke- ovens yet produced are unquestionably those based on the principles embodied in the Coppee, Appolt and Carves systems, where all spare heat is utilised for raising steam. There are yet many improvements to be made in applying these principles in practice. GASEOUS FUEL. The theoretical calorific values of carbonic oxide and of hydrogen have already been fully discussed ; it remains to show in what way these gases can best be turned to practical account. It will be recollected that the intensity of combustion of hydrogen and of carbon, when burnt in air, is practically the same, whilst the heat of combustion of carbonic oxide in burning to carbonic acid is somewhat greater than that of carbon likewise oxidised to the maximum. So far, then, as the actual intensity obtained on combustion is concerned, it would appear that it matters little whether we employ solid or gaseous fuel ; in practice this is very far from being the case. When the fuel is gaseous it is much easier, for instance, to apply heat uniformly to a given surface, or locally, as may be required in some cases, and further, the regulation of the temperature is much more within control, and complete combustion can be ensured. This is well illustrated by the system of heating coke-ovens constructed on the principle of the Coppe'e and Appolt. Another advantage, which is of great importance, is that the gases can be generated in any convenient place, and led by pipes, or other suitable means, to the spot where their combustion is required to be effected. In this way valuable space can often be economised, and working room obtained where it is most required. 56 Fuel. These are very far from being the only advantages which may be derived from the use of gaseous fuel When great intensity of heat is required it is possible to produce it by heating the gases and the air required for their combustion ; and, if desired, the gas and air can be burnt under pressure, thus still further increasing the temperature obtainable ; the only limit being that fixed by dissociation. In practice these high temperatures could not be obtained by simply heating solid fuel and the air supplied for its combustion, though there is, up to a certain point, a very decided gain in heating the air. Strictly speaking, all heating operations are conducted, to some extent at least, by means of gaseous fuel, for all fuels yield on distillation gases, with the exception, practically, of coke and anthracite ; and, apart from the products of dis- tillation, it is essential to the manner in which combustion is effected that carbonic oxide should be formed, which subsequently burns on being brought into contact with air on the exterior of the heated fuel. Thus, in reverberator}' furnaces, in which the fuel is burnt in a chamber separated from that in which the smelting or other operation is to be effected by a low wall, above which the two chambers com- municate, the heating of the bed of the furnace is. really accomplished mainly by gaseous fuel. The products due to distillation of the upper and cooler fuel, and the carbonic oxide derived from the decomposition of the carbonic acid, first formed by the admission of air i-.ndej the grate, are drawn by a chimney at the opposite end over the partition-wall or firebridge, and, becoming mixed with a suitable quantity of air, are deflected down on to the hearth. The relative amount of combustion which takes place on the hearth and above the fuel in the grate will depend on the quantity of air allowed to enter the opening through which the fuel is charged in. The principle of the modern gas-producer is essentially the same as that just described ; important modifications in construction are Fuel. 57 even yet being made. The gas-producer first assumed importance on the introduction of the Siemens' 'regenera- tive' system in 1856. The arrangement then adopted (Fig. n) is still, with little exception, the only one in use. It consists of a chamber lined with fire-brick ; one side (B) slopes at an angle of from 45 to 60 ; at the. bottom is the grate (c). The fuel is introduced into the hopper (A), the cover is replaced, and the bottom having been lowered by means of the weighted lever attached to it, the fuel falls on to the incline, down which it gradually moves to supply the place of that which has been converted into gas in the region of the 58 Fuel. grate. Air is admitted only through the grate. The opera- tion is exactly the reverse of that which takes place in a bee- hive oven. In this producer, the air being admitted at the bottom, combustion proceeds from below upwards, and the volatile portion of the fuel is distilled off without coming in contact with air, whilst that which in the coke oven would become coke is converted into carbonic oxide gas in the producer. A small quantity of water is admitted by the pipe (E) to the ash pit, where it evaporates, and, becoming decomposed by the incandescent fuel, enriches the pro- ducer-gas by the formation of carbonic oxide and free hydrogen. By means of the plug-hole (G) the interior of the producer can be inspected, and, if necessary, the fuel stoked with an iron rod. It is important that a slight outward pressure should be maintained in the flue, to prevent the gas being partially con- sumed by an indraught of air through crevices in the brick- work. If the furnace could be placed about 10 feet higher than the producer the required pressure would at once be obtained ; in practice this arrangement is rarely convenient. The following plan has been adopted. The gases, which on leaving the producer have a temperature of about 400 C, pass to the uptake (H), rising 10 to 20 feet vertically ; thence they traverse the horizontal iron cooling-tube (j), which may with advantage be several hundred feet long ; at the end of the cooling-tube the gases, having then a temperature of below 100 C, descend a tube called a down-comer into a main, whence they are drawn off as required. The effect of cooling the gases is to increase the relative weight of a given volume 50 to 60 per cent. Thus a sort of siphon action is set up, the heavier gas in the down-comer representing the longer leg of a siphon ; at the same time, by this arrange- ment an outward pressure is maintained in the flues of about T \jth to T V ns of an inch of water more than that of the external atmosphere. By cooling the gases aqueous vapour is condensed and deposited. Gaseous Fuel. 59 Although the desired results are obtained in this way, yet it will be observed that it is only arrived at by the dissi- pation of a great deal of heat Were this, however, not so, a chimney or an exhaust-engine would be required to draw the gases from the producer, so- this heat must be looked upon as doing important work. The heat withdrawn from the cooling-tube, instead of being carried off by the surround- ing air, might be imparted to water for raising steam under boilers ; such arrangements, very simple in principle, are generally extremely difficult to carry out satisfactorily in practice, each particular case requiring special treatment, in- volving numerous and expensive experiments, which, after all, may not lead to success. It has been stated that steam may with advantage be admitted with the air supplied for combustion. The advan tage which steam possesses over air is due to the large quantity of inert nitrogen in the latter. Nevertheless, it must not be forgotten that in the decomposition of steam by car- bon heat is absorbed ; if, therefore, much steam were admitted, the temperature would eventually be so much lowered that combustion would only proceed with the greatest difficulty, if at all. Up to a certain amount steam may with advantage be admitted ; beyond that it does harm. It is very important that this should be properly understood, since a great deal of misconception exists as to the use of steam. It should only be introduced when there is an excess of heat in the furnace beyond that required to carry on with sufficient rapidity the conversion of the solid fuel into gases. That heat is absorbed during the reduction of aqueous vapour by carbon is easily shown. One part by weight of hydrogen, in combining with eight parts of oxygen to form water, evolves about 34,000 units of heat, and exactly the same number of units will be absorbed again on the water being broken up into its constituents. The eight parts of oxy- gen liberated will combine with carbon, evolving 14,838 units, 60 Fuel. since carbonic oxide is the final product so far as the gas-pro- ducer is concerned ; some of the hydrogen will remain in the free state, the remainder unites with carbon to form, mainly, carburetted hydrogen gas (CH 4 ), evolving about 16,000 heat units for each unit of hydrogen. Supposing, for the sake of argument, that the whole of the hydrogen of the decomposed steam combined with carbon to form carburetted hydrogen gas, and the oxygen to form carbonic oxide, then the total heat units absorbed and evolved would stand as follows : Absorbed by decomposition of 8 pts. H 2 O = 34,462 heat units. Evolved by combination of I pt. H + 3 pts. C = 1 6,000 ,, ,, ,, 8 pts. O + 6 pts. =14,838 ,, Total evolved = 30,838 Balance in favour of absorption = 3,624 ,, ,, The following analysis of gas made in the producers at the glass-works at St. Gobain, with a closed grate and steam - injector, will give an idea of the amount of hydrogen which may remain in the free state, as compared with that car- buretted : Volume Weight Carbonic oxide . . . 24-2 . 2; S Hydrogen . . . 82 . o - 6 Carburdted hydrogen . . 2*2 . 1-4 Carbonic acid . . . 4-2 . 7-0 Nitrogen . . . . 61-2 . 65-2 loo-o . roo\> One-fourth by weight of the carburetted hydrogen con- sists of hydrogen, which in this case will therefore amount to 0-35, or about half that in the free state. The whole of the hydrogen present appears an insignificant quantity, being only about i per cent. ; but it must be recollected that ever> one part of hydrogen due to the introduction of steam means that eight parts of oxygen have been made available for combustion without nitrogen accompanying them, i.e. there, will be 8x3-33=26-64 parts less nitrogen than if air con- Gaseous Fuel. 61 taining an equivalent quantity of oxygen had been used It is not intended to imply that the whole of the hydrogen in this particular case was introduced by the steam : some of it was probably derived from the coal. In the form of producers just considered, a good deal of the hydrogen originally present as a constituent of the coal is removed in combination with carbon, as tar and hydro- carbons, which condense in the flues, and are a source of in convenience. The most recent forms of producers proposed by Dr. Siemens have for one of their principal objects to con- sume the tar, &c. in the producer. Fig. 12 illustrates the most recently patented (May 1882) producer of this latter kind. It may be worked with or without a steam-jet, as may be required. The air is admitted through openings, as shown at N, Fig. 1 2, into a chamber (L), constructed in cast iron, and having pockets (M) ; thence it is drawn off through channels (P), by the action of the steam-jet (Q), supplied through the pipe (R). s is a grating, and T a pipe through which water is supplied to an annular perforated pipe, shown in section, by means of which a spray is projected on to the clinker and ashes below. The fuel is charged in through K, and the gas passes up through the channels (11) into the main (i). The important point about this form of producer is that the volatile products of distillation, instead of passing out through the cool fuel at the top as in the ordinary arrangement, whereby tar, c. are deposited in the flues are obliged to descend through highly healed fuel, and are thus completely decomposed before reaching the flues. The spare heat is utilised to decompose steam and heat the air. The gases as they leave the producer pass round the pockets (M), strongly heating the air contained in them, which then, being specifically lighter, rises, and is drawn off through the channels (P), by the action of the steam-jet, whilst cooler air sinks into the pockets, and so on. The pockets may be replaced by coils of pipe. The Wilson gas-producer, which is being used in many 62 Fuel. Gaseous Fuel. 63 works, and the Dowson gas-producer, which has been suc- cessfully applied to the driving of machinery by means of a gas-engine, are of the last type. The idea of heating, by what is now known as the regene- rative system, the air supplied for the combustion of solid fuel occured to Robert Stirling in 1816. The method by which he proposed to carry it out, as set forth in his patent, is very crude, and would have been in that form impracticable. Still it embodies the notion which forty years afterwards was again conceived by Messrs. Frederick and C. W. Siemens, in whose hands it has brought about results of incalculable value. They, like Stirling, began with the idea of heating air for the combustion of solid fuel, the general arrangement in both cases being very similar. There was to be a single fire-place, supplied with fuel from a hopper above it, two chambers to contain the substance to be heated, and at the end of each chamber a regenerator. The regenerator in the Siemens arrangement consisted of chequer-work of brick, i.e. a chamber packed with bricks so placed as to leave spaces, through which the spent gases had to pass on their way to the chimney. Stirling proposed to use thin partitions of metal or glass. In either case the object was to cause the gases to give up their heat to the cooler fire-brick or other material. When the regenerator through which the products of combustion had been made to pass had become sufficiently heated up, the direction of the current was reversed, and the air as it entered then became heated by the hot masonry which it had to traverse, whilst the other regenerator in its turn had its temperature raised again by the products of combustion. Reversal of the direction of the currents was to be effected at such intervals as would prevent the regenerator through which the air was passing becoming cooled to too low a temperature. The conditions of this arrangement necessi- tated that the operation being carried on in each furnace should te completed in the time between the reversals a 64 state cf things at the best extremely inconvenient, and for most purposes altogether impracticable. It was at this point that the brothers Siemens conceived the idea of employing gaseous instead of solid fuel, and heating it as well as the air by means of regenerators. It would be difficult to over estimate the importance of the results which have followed the introduction of this system. By its means the highest attainable temperatures can with ease be produced, the only limit being that at which dis- sociation takes place. Furnaces on this system have been applied with very great success to the manufacture of soft steel, and for re- heating iron and steel ; also to zinc smelting, and in gas, glass, pottery, and porcelain works. It is not too much to say that there is no purpose for which a high temperature is required for which it might not with great 'advantage be employed, in respect both to general convenience and economy. Figs. 13 and 14 represent the furnace, the one being a longitudinal and the other a cross section ; the gas coming from the gas-producer passes in through the flue (H) and the reversing valve (F), by means of which it is directed into the bottom part of the regenerator chamber (c), on the left. The gas flowing up through the mass of brickwork the chamber contains, and which is placed so as to form a large aggregate surface, with intricate zigzag passages, will become heated, provided any heat has been accumulated therein. In the first place there will be no heat, and the gas will pass un- heated through this chamber and thence to the combustion- chamber of the furnace (A). At the same time, a current of air is admitted through the air-reversing valve (E), into the air regenerator chamber (D), which is larger than the gas- chamber. The air passing up through the chequer-work will reach the same point as the gas does at the entrance into the combustion-chamber of the furnace. Now, 'since both the air and gas are cold, and as they meet for the Gaseous Fuel. 56 Fuel. firnt time at the entrance into the furnace, they will, if there ignited, produce a heat not certainly superior to what would be produced if solid fuel had been burned there instead . on the contrary, gas of the description we are dealing with is a poorer fuel than solid fuel, and the heat produced in the furnace will, therefore, be very moderate indeed. But the flame, after passing over the bed of the furnace, does not go to the chimney direct, but has to pass through the two re- generative chambers (D, c), on the right, similar to those already described ; the larger proportion of the heated pro- ducts of combustion will pass through the air regenerator chamber, simply because it is the largest channel, and another portion will pass through the gas regenerator. The products of combustion pass from these chambers through the reversing valves (E, F), and are by them directed into the passage (i) leading to the chimney. The operation, therefore, is simply this : that the air and combustible gas pass up into the furnace through the one pair of chambers, and pass away, after combustion, towards the chimney through the other pair ; but in passing through the second pair the heat of the products of combustion is given up to the brickwork The upper portions of this brickwork take up the first, and, therefore, the highest degree of heat, and, as the burnt gases are passed down- ward through the regenerators, they are, by degrees, very completely deprived of their heat, and reach the bottom of the chambers and the chimney comparatively cold. After this action has been going on, say, for an hour, the reversing valves are turned over. They are simple flaps, acting like a four-way cock, and, by throwing over the levers which work them, the direction of the currents is reversed. The gas and air will enter now through the second pair of chambers, and the air passing up one regenerator and the gas passing up the other will take up heat from the bricks previously heated by the descending current. The gases so heated, say, to 1,000 F., will enter into combustion, and if the heat pro- Gaseous Fuel. 67 duced at the former operation was 1,000, it ought this time to be 2,000, because the initial point of temperature is 1,000 higher. The products of combustion will also escape at 2,000, and passing through the chequer-work of the first pair of regenerators, its uppermost ranges will be heated to very nearly 2,000. The temperature will diminish by degrees in descending till the gaseous currents have again reached the bottom nearly cold. Again reversing the process, after another hour or half-hour, as the case may be, the gas will take up heat to the extent of nearly 2,000, and since another 1,000 is again produced in combustion the temperature of the furnace will this time attain 3,000 ; and in this way it might be argued that, unless work is done in the furnace, the heat developed in combustion will, step by step, increase the temperature of the furnace, 1,000, or something less, each time a reversal of the valves takes place, till we arrive at the practical limit imposed by the melting-point of the most refractory substance we can find (pure silica, in the form of Dinas brick), of which the melting chamber is usually formed. This high temperature is obtained by a gradual process of accumulation, and without any such current as would be likely to destroy, by oxidation, the metal in the bath, or cut away the sides and roof of the melting- chamber. There is, however, a theoretical as well as a practical limit to the degree of heat obtainable in combustion, which was first pointed out by M. H. St. Claire Deville, namely, the point of dissociation at which carbonic acid would be converted back into its constituents, carbon and oxygen. If carbonic oxide, or any other combustible gas, and air enter the furnace at a temperature very nearly equal to the point of dissociation, it is evident that association or combustion cannot take place, and thus nature fortunately steps in to restrict the increase of heat by accumulation within com- paratively safe limits. In a furnace fully heated up to the melting-point of iron, this action of dissociation can be very F 2 68 Fuel. clearly observed. At first, when the gas and air are com- paratively cold, combustion takes place sluggishly, the gases will flow through the furnace and produce only a dark-red flame ; the next time the valves are reversed a whitish flame is produced ; the next time, a short white flame ; and after having reached a full white heat, exceeding the welding-point of iron, the flame will again become a long one, but this time not red and of little apparent power, but bluish-white and flowing in clouds. This indicates the near attainment of the point of dissociation ; combustion can no longer take place, except in the measure of the heat being dispersed to surrounding objects or to the metal in the furnace, and that is about the degree of heat required for the process of making steel on the open hearth. The regenerators just described are only well suited for use when very high temperatures are required. For com- paratively low temperatures the following arrangement ) which has been patented several times during this century, is better suited, though up to quite recently there have been difficulties in the way of carrying it into effect. A parallel series of long narrow passages are arranged so that the hot products of combustion may be passed through alternate passages, the intervals thus left to serve for the introduction in the opposite direction of the air to support combustion. In this way the heat of the outgoing gases would be com- municated to the air and carried back into the furnace. It was at first proposed to make the partitions of sheet iron ; this, however, did not prove satisfactory, owing to the leakage and the inability of the partitions to stand the wear and tear consequent on the high temperature. Fire-brick partitions were substituted for iron, but with no better success, as the air and gases mingled through the cracks and interstices. The objection to the use of fire-brick is said now to have been satisfactorily removed by the simple device of glazing the surface of the partitions. If this be the case, then regenerators on this system have a wide field Gaseous Fuel. 69 open to them. They cannot be employed when a very high temperature is required, as the heat is not accumulated, and the temperature of the air can never be higher than half that of the outgoing eases. Although the use of iron partitions was not successful, yet in a modified form this system has since been largely em- ployed in the manufacture of iron. The air to be heated is passed through a series of cast-uon pipes, arranged in a chamber, through which the waste gases, as they are termed, from the blast-furnace are made to circulate. There is, however, an important distinction between these gases and those obtained from reverberatory furnaces. In the latter case they have practically undergone complete combustion, whereas in the former, owing to the combustion being effected from the bottom of the furnace, and the products having to pass through incandescent fuel before escaping at the top, and for other reasons connected with dissocia- tion, the gases contain a very considerable quantity of carbonic oxide, which is capable of producing, on com- bustion in the stove for heating the pipes, a temperature very much higher than that which could be obtained were only the sensible heat being carried off by the gases available. The gases collected from the top of blast-furnaces contain on the average about 25 per cent, by volume of carbonic oxide, and hydrogen varying in quantity, according to circumstances, up to 7 or 8 per cent. From this it will be seen that, in point of heat-evolving power on com- plete combustion, blast-furnace gases are quite equal to producer gas. Until within the last few years these gases were allowed to burn uselessly at the top of the blast- furnaces ; now they are generally even yet not universally collected, and employed for heating the blast and raising steam ; in many works no other fuel being required for such purposes. The use of iron pipes has always been attended by a 70 Fuel. serious drawback, viz. that if by carelessness tne tempera- ture was allowed to get up above 1,000 E, the pipes would be ruined, so that practically about 900 F. is the maximum temperature which it is safe to work with ; more commonly 600 to 800 has been employed, until quite recently. Another objection is that leakage is liable to occur, owing to the unequal expansion and contraction of the different parts of the stove-pipes. Soon after the introduction of the regenerative system by Dr. Siemens, Mr. Cowper proposed to construct a stove on that principle, as a substitute for the iron-pipe stoves. Since their introduction these stoves have been modified in several ways, chiefly by increasing their height and arranging the passages so as to allow the gases a free passage, and at the same time to withdraw the main part of their heat Figs. 15 and 16 show the stove in its present form. The gases are drawn off from the top of the blast-furnace by a tube called a down-comer, and passing into the gas flue v, enter the stove by the valve F ; by means of the valve G a suitable quantity of air is admitted, which, mingling with the gases, effects their complete combustion in the flame-flue o, from the top of which the highly heated products pass into the regenerator p, consisting of a long column of chequer- work; from the bottom of the regenerator the gases are drawn off by the chimney, through the flue u, the draught being regulated by the valve D. The whole of the stove, with the exception of the valves, is enclosed by several courses of fire-brick, encased in iron. As the gases pass through the regenerator they give up the greater part of the heat they contain to the top layer, there being a gradual shading off, as successive courses of bricks are passed through, until the bottom is reached, when they will be found to have a temperature of only about 300 to 400 F. It should be borne in mind that some heat must be left in, to create a sufficient draft in the chimney. The temperature of the gases issuing from an iron-pipe stove Gaseous Fuel Coivper Stove. 7t OLE FOR SUN TiL L ' FIG. 15 72 Fuel, is, however, between 1,200 and 1,300 R, so that a consider- able waste of heat takes place. So soon as the top layer of the regenerator has become heated up to the temperature of the gases passing through it, it must of necessity cease to absorb heat, and the gases traverse it without undergoing any alteration until they arrive at a part of the brickwork at a lower temperature than themselves, which they then gradually raise to their own temperature. If the gases were passed through the stove for some time, the whole of it would eventually become of the same temperature as the gases, which would then issue at the same temperature as that at which they entered. In practice, to avoid loss of heat, it is desirable to stop the heating up of the stove whilst the maximum temperature is still some way from the bottom ; the gas and air are then admitted to another stove, and the chimney-valve of the heated stove having been closed the blast of cold air which it is desired to heat is passed through it, entering by the valve at the bottom of the regenerator. The air, as it traverses the regenerator, becomes heated to the temperature of the stove, and, passing down the red-hot flame-flue, is conducted to the blast-furnace Gaseous Fuel Cowper Stove. 73 through the valve E. A peep-hole through which to observe the temperature of the blast is provided at s. By means of this stove the blast can be heated to 1,500 F., the reduction in temperature after blowing cold air through it for about three hours amounting only to about 100, and 150 in four hours, as the air on entering soon becomes heated to the temperature of the stove, and then passes on without with- drawing any heat from the remainder of the regenerator above, so that the temperature continues constant as long as a certain area of the regenerator remains at its initial tem- perature. Mr. Cowper states that the saving of fuel due to the use of these stoves amounts to 20 per cent., and in some cases is as much as 7 \ cwt. of coke per ton of iron made. Dust is, as far as possible, by a special arrangement of the pipe supplying the gases, prevented from entering the regenerator ; that which finds its way in is removed every few months by turning on the cold blast, and shutting all the other valves ; a special door is then opened several times : the sudden rushing out of the compressed air dislodges and carries out the dust. In some works the same result is arrived at by firing into the stove, through openings provided for the purpose, a gun loaded with blasting powder ; the dust collects at the bottom, and is removed through doors. The friction is very much less in these stoves than when pipes are used; the power necessary to produce a blast of the required pressure is therefore also less. The height and diameter of these stoves varies, the former up to 55 feet, the latter to 25 feet. Fig. 17 shows a modification of the Cowper stove, known as the Whitwell stove. The arrangement is intended to facilitate cleaning. It is only fair to say that the Cowper stove, as now made, is said by many competent to give an opinion to present no special difficulty in this respect. Both stoves a-e capable of heating the blast to as high a temperature as is at present employed in blast-furnace practice ; they .ire both largely used, and not uncommonly are seen side by Fuct FIG. 17. Gaseous Fuel Wliitwell Stove. 75 side in the same works. The figure shows the attachment to the blast main of the furnace. A is the gas valve, G the air inlets for the combustion of the gas. The air is warmed by being passed through the basement of the stove, which it thus protects from daindge by excessive heating, c is the chimney-valve. It will be observed that the chequer-work of the Cowper stove is icplaced by fire-brick partitions. At the bottom of the first and third of the smaller partitions are openings, through which a further quantity of air is admitted to complete the combustion of the gases. The cold blast enters through D, and passes out heated at B ; P P are the eye pieces through which to observe the temperature. In order to clean the stove, the gas is shut off, and the chimney- valve (c) slightly opened in order to carry the heat downwards, the first top cleaning door (F) is taken off, and the movable plug in the crown of the arch lifted. Scrapers with f-inch tubular handles are introduced, and the walls scraped down, the dust falling to the bottom; the door is then replaced, and the next compartment treated in the same way, whilst the walls are still red-hot, and so on in rotation. The dust which has been detached from the walls is removed at the bottom through the doors (E). These stoves, in America, have been made as much as 70 feet high and 21 feet in diameter, containing 30,000 square feet heat- ing surface. Refractory Materials. REFRACTORY MATERIALS. THE term REFRACTORY is necessarily relative, the degree to which a substance is refractory depending on the circum- stances under which it is employed, and notably on the nature of the substances with which it is brought in contact. For example, silica (SiO 2 ) heated alone, even to very high temperatures, is extremely refractory, i.e. it does not sensibly soften, but if it be brought into contact with some base, such as lime (CaO), oxide of lead, or oxide of copper, at an ordi- nary red heat, then union takes place with the formation of a silicate, which in every case is much more fusible than silica, though differing in degree according to the base. It is obvious from the foregoing that in the selection of materials for the construction of furnaces the chemical affinities which will be brought into action between the body of the furnace and the substances to be treated in it must be carefully con- sidered. This, however, is not the only point to be borne in mind in choosing a suitable material. Many substances are capable of resisting a very high temperature if gradually raised to it ; but have not the power of resisting sudden changes of temperature, such as occur, for instance, when large crucibles have to be removed from a furnace in order to discharge their contents, or when a crucible is heated sud- denly by placing it in a hot furnace. For these purposes such materials would be unsuitable, and it would be necessary to select some substance or combination of substances capable of resisting sudden alterations of temperature. The most important refractory material is that resulting from the so-called burning of clay. We will, therefore, first consider the composition of various kinds of clays, and the properties which give it so great a value in the arts. Clay. 77 The basis of clay is silicate of alumina, i.e. silica in chemical combination with alumina. All clays have been derived from the natural decomposition of felspars, which occur in nearly all igneous rocks and in some stratified crystalline schists. The character of each clay will be mainly determined by the nature of the rock from which it originated. The felspars consist essentially of anhydrous silicates of alumina, with variable proportions of silicates ol potash, soda, lime, and magnesia, and a little oxide of iron. The relative proportions of these alkaline bases is found to vary with the state of occurrence of the felspar ; thus, orthoclase and the other more silicious felspars containing potash are common in granite and all plutonic rocks, whilst the volcanic rocks are characterised by the presence of the less silicious felspars, containing soda and lime. By 'weathering,' i.e. exposure to the combined action of carbonic acid and water, the soda, potash, lime, and magnesia are dissolved away more or less completely, and at the same time the residual silicate of alumina becomes chemically combined with water, and is said to be hydrated. In its purest state clay would consist of silica, alumina (A1 2 O 3 ), and water, combined in proportions probably in most cases represented by the following formula : A1 2 O 3 2 SiO 2 + 2H 2 O, which corresponds to a percentage composition of 46-33 SiO 2 , 3977 A1 2 O 3 , and 13^90 H 2 O. This state of purity is closely approached in china clay, used in the pro- duction of the best porcelain. The white scaly, crystalline powder of which china clay consists, seen through the microscope, is found to be made up of flexible but inelastic hexagonal plates. These plates, with the aid of the microscope, can be discovered in greater or less quantity in every clay. The degree of purity of a clay will depend not merely on the extent to which the felspar has been decomposed, but also on the more or less completeness with which it has been separated from the containing rock by the action of running water. Thus, clay derived from orthoclase, which ?S Refractory Materials. occurs in granite, will be found more or less admixed with quartz and mica. All clays contain more or less admixed silica. It will have been remarked that during the decomposi- tion of felspar the silicate of alumina has passed from the anhydrous to the hydrated condition. It is to this, at first sight, unimportant change that clay owes its great value, for it is in consequence of the presence of this water of hydration that clay possesses its characteristic property of plasticity, or the capability of being moulded into any required form when moistened. If dry clay be moistened it can readily be made to take any required shape, and if then it be dried by the warmth of the sun, or by some similar moderate heat, it will preserve its shape, so long as it is not remoistened. If, on the other hand, the clay be subjected finally to a fairly strong heat, it will no "longer possess the property of plasticity on being remoistened : it will be rigid, and practically a totally different substance to that from which it was derived. This change, so important in its consequences, is due simply to the fact that at the higher temperature the water in chemical combination has been removed, whereas at the lower tem- perature the mechanically admixed water alone was with- drawn. The chemically combined water once driven off never again resumes its union ; to this is due the stability of the innumerable structures made from clay. Since, then, clay has been derived from the gradual decom- position of certain portions of the earth's crust, and has in most cases, by the action of running water, been accumu- lated as a bed or stratum over large areas, it is easy to under stand how it is that considerable variation in its composition and state of division may occur, even within a comparatively limited space. Clays are divisible, broadly speaking, into two classes, viz. ordinary cjays, such as are used for building houses and the cooler portions of furnaces, and fire-clays, which, as the name denotes, are capable of withstanding a strong heat Clay. 79 without rapidly deteriorating. The difference between the two kinds is due to the amount and nature of the impurities, i.e. foreign substances, which they respectively contain. The more potash or soda a clay contains the more easily fusible will it be. Oxide of iron, lime, and magnesia act in a similar manner, though to a much less extent. The fire-clays, with which we are here more especially concerned, are obtained principally from the coal measures, in which they occur in great abundance. The neighbour- hood of Stourbridge has long been celebrated for the quality of its fire-clay, which is largely used for the manufacture of bricks of various shapes, and for crucibles. During the dehydration of clay by heat contraction takes place, the amount of contraction depending on the degree of heat applied. In bricks this shrinkage is not of so much consequence ; but in crucibles, owing to the varia- tion in thickness and shape, the material would be liable to crack. In order to counteract this tendency a proportion of some substance which either expands on heating, or at any rate does not contract, is added. For this purpose burnt fire- clay is commonly mixed with the raw clay, and sometimes coke dust, graphite, or silica, which last expands on heating. When burnt clay is used, a common proportion is one-third burnt clay to two-thirds raw clay. The amount of burnt clay necessary is, however, very variable, depending on the ' fatness ' of the raw clay. It is important that the burnt clay should not be too finely powdered ; the size of the particles will depend on the use to which the material is to be put The presence of particles of iron pyrites, of any appreciable size, in fire-clay used for crucibles should be carefully guarded against, as the oxide of iron, resulting from the oxidation of the pyrites under the influence of heat, com- bines with the clay, forming a fusible substance, and causing a hole to form at that point. The power of any clay to resist a high temperature may be judged of by working up some of it with a suitable quantity o Refractory Materials. of water, shaping it into a rectangular piece with sharp edges, and then, after drying it at a gentle heat, subjecting it to the temperature which it will be required to stand, care being taken to protect the clay from the action of the ashes, if solid fuel be employed for obtaining the requisite heat. If the edges have remained quite sharp, the clay may be considered highly refractory at the temperature of the experi- ment. The manufacture of large crucibles is conducted in one of two ways. In the old method, and that still in general use, a mixture of various clays which experience has shown to be best for the purpose is ground under edge-stones, and, having been sifted, it is mixed with water and the proper proportion of burnt clay, for which the old pots are utilised. This mixture is then kneaded, by men treading barefooted, until it has acquired the requisite consistency. The crucibles are fashioned by hand, with the assistance of a block of the form of the inside. Crucibles are now also made successfully by machinery A sufficient quantity of-the substance to be made into a cru- cible is dropped into a mould, which is then made to rotate ; a fixed wooden tool, which descends nearly to the bottom of the mould, presses the lump and causes it to take the re- quired shape. The moulds are made of plaster of Paris, supported when necessary by a wooden casing on the out- side, in which case both the wood and the plaster of Paris are made in segments. The mould containing the freshly made crucible is placed in a warm place ; in a short time, owing to the plaster of Paris absorbing the moisture from the surface of the crucible, the latter readily detaches itself. Clays vary considerably in their power to resist the corroding action of metallic oxides, such as oxide of lead or oxide of copper. This is often a matter of considerable importance, and is best ascertained by direct experiment on a sample. No clay can resist the action of these oxides in their uncombined state for very long ; some sulphides, e.g. Crucibles Silicious Bricks. 8 1 galena (sulphide of lead), have the singular property of readily permeating clay crucibles without corrosion. The finer and more regular the grain of a crucible the more readily will it, as a rule, resist corrosion and permea- tion ; but unfortunately these same conditions act unfavoui- ably in another way, by increasing the liability to crack. Small crucibles are fired in kilns, and are allowed to cool down, as they can be heated up again without danger of their cracking. This cannot be done with large crucibles, such as are used for melting steel or large quantities of brass. They are first carefully air-dried, and then kept in p. warm dry place until required for use, when they are gradually heated up to redness, mouth downwards, and are, after being inverted, ready for immediate use. It has been found that if a crucible receive its first heating mouth upwards it almost invariably cracks. In cases where an extremely high temperature has to be resisted, e.g. in a Siemens steel-melting furnace or a Bessemer converter, fire-bricks made of clay cannot be employed, and some material still more refractory under the conditions has to be substituted. For this purpose silicious bricks are employed ; bricks of this kind were not known before about the year 1822, when the method of making them was discovered. The rock of which they are com- posed occurs in considerable quantity in the Vale of Neath ; it consists of about 97 per cent, of silica, the remainder being made up of alumina, oxide of iron, lime, potash, soda, and combined water. It is locally known as ' clay. ' The rock having been sufficiently disintegrated, is mixed with about i per cent, to 3 per cent of lime and some water ; it is then pressed into moulds, dried, and fired hard for about a week. On one ot these bricks being fractured, it will be seen tc consist of angular fragments of quartz, embedded in a light yellowish-brown matrix. In setting these bricks a cement of the same material must be used. Bricks of this description are now also made by grinding up fine any pure silicious G 32 Refractory Materials. rock or stone, and mixing about i per cent, of milk of lime with it The addition of extraneous material to the silicious rock is in no way analogous in purpose to the case we have recently had under consideration, viz, the mixing of burnt clay, silica, or coke dust with raw fire-clay. In the present case we are dealing with a substance devoid of plasticity, and which, being in irregular pieces of variable shape and size, can only be made into a solid mass of a required form by the assistance of some cementing material The small quantity of lime used answers this purpose very perfectly, as at a high temperature it unites with silica, forming a refractory silicate, which cements the mass together. If much lime were present the material would be insufficiently refractor}' at high temperatures. The presence of mica and oxide of iron in more than traces is also objectionable. Complex silicates, i.e. containing more than one base in combination with the same silica, are more easily fusible than single silicates, the silicates of potash and soda excepted ; it follows that the extent to which a brick is refractory will depend more on the number and relative proportion of the foreign substances present than on the actual quantity of any one of them. A clay containing a certain quantity of magnesia, and no lime, would be more refractory than if part of the magnesia were replaced by an equivalent quantity of lime. Another silicious material, known as ' ganister,' is largely used for lining Bessemer converters. The finest quality of this material is obtained near Sheffield, where it forms the under-clay of a thin coal-seam ; it also occurs in Lancashire, in the Newcastle coal-fields, in those of Yorkshire, as well as in Shropshire. This substance appears to have been deposited in shallow seas, just after the mill-stone grit, and before the soil upon which the coal-measure plants grew. Geologically, it is probably the equivalent of the silicious rock of the Vale of Neath. It differs considerably from all Bauxite. 83 other sandstones, except that from the Vale of Neath ; the particles of which it is composed are very fine, it has a waxy fracture, and is very hard and tough. Unlike other sand- stones, it has the power of binding together, when ground fine and mixed with water. A fairly good substitute for this material can be made from powdered pure silicious stone, mixed with a certain amount of aluminous clay. Natural silicious stones are occasionally used for the hearths of blast-furnaces and such purposes. They should be carefully dried before being strongly heated. The same remark applies equally to all bricks and crucibles, however produced. In some cases in which sand, or a mixture of clay and sand, would not resist sufficiently well the corrosive action of certain slags, a greater or less amount of coke dust or debris of charcoal is added. This mixture is termed 'brasque.' Crucibles for melting steel and brass are now commonly made of plumbago or graphite, mixed with a certain amount of fire-clay to give strength. Talcose slate and soap-stones are used in some localities in the construction of furnaces. Serpentine resists corrosion well, but cannot with advantage be exposed to very high temperatures. Bauxite, a mineral which occurs in considerable quantity in several localities in France, in pockets in calcareous rocks belonging to the cretaceous series, and which consists essentially of pisolitic oxide of iron in a matrix of alumina, the latter largely predominating, has a limited use for lining furnaces. It is also used as a source of the metal aluminium. Its composition is very variable, but on an average it would contain about 3 to 5 per cent silica, 23 to 25 per cent, per- oxide of iron, 50 to 60 per cent, alumina, and 10 to 15 per cent water. It also mostly contains 2 or 3 per cent, titanic acid. This material is highly refractory, owing to the aluminate of iron, which forms at a high temperature, being very infusible. In one important metallurgical operation oxide of iron is used as a furnace lining, viz. in the puddling process. 84 Refractory Materials. Here, owing to the nature of the process, either silica or clay would be rapidly corroded and cause great waste of iron, whereas oxide of iron not only protects the masonry of the furnace, but takes an essential part in the process. Iron itself in some processes is also employed, being kept sufficiently cool for the purpose by the circulation of cold water or air at the back of it We have seen how, in clay, alumina in combination with silica forms a very refractory substance. Alumina itself is even still more refractory, but owing to the difficulty of obtaining it in considerable quantity it is not available for use on a large scale. The same remark has hitherto applied to magnesia (MgO), which is also highly refractory. Lime, which is infusible at any temperature we can com- mand, is, on the other hand, extremely plentiful. In order to produce it, it is only necessary to drive off the carbonic acid from chalk or limestone by the application of heat The use of lime, however, as a refractory material for furnace purposes is rendered impossible, owing to the property it possesses of combining readily with water, with the result that it swells up, and falls to pieces ; so that, unless the lime be kept continuously at a high temperature, the structure composed of it crumbles to pieces by the mere action of the moisture in the air. For small operations, such as the fusion of platinum by the flame of an oxy- hydrogen blow-pipe, blocks of lime have found an applica- tion. The want of some substance of the nature of lime which could be employed at high temperatures has long been felt It is only recently that this want has been successfully supplied on a large scale. It has been found that magnesian limestone, which consist mainly of carbonates of lime and magnesia, unlike ordinary limestone or chalk, after it has been very strongly calcined can be reheated and cooled as often as required without crumbling. In consequence of this important discovery, iron ores, which Basic Lining. 85 previously were useless for the production of soft steel, are now being largely employed. This portion of the subject will be discussed when speaking of the manufacture of steel The most successful method of employing the magnesian limestone is, first to fire it strongly, then to grind it up fine and mix it with pitch. The bricks made from this mixture are then strongly fired. There is, however, considerable difficulty attending the construction of a lining with these bricks, because they have to be set with similar material, which it is almost impossible to fire satisfactorily, and which is very liable in any case to work out of the joints, owing to shrinkage. This difficulty is increased by the shrinkage of the bricks themselves during firing, which gives them a more or less curved form. These objections have been successfully overcome by making the material, which has been strongly calcined, into a 'slurry,' or liquid mass, and running it into a mould of the required shape and size, then by a gradually applied heat consolidating it by removing the pitch ; or the mixture of magnesian limestone and pitch may be in such proportion that on the application of heat it will fuse, the pitch finally being decomposed when the heat is increased. In this case the mixture may be shovelled into the mould in a solid condition. All sorts of magnesian limestone (dolomite) are used at different works ; but for material which is to be highly shrunk, and when it can be obtained, a limestone or mixture of the following composition is preferred : Magnesia 36 per cent. Lime ...... 52 ,, Silica 8 Alumina and oxide of iron . . 4 Too For the above analysis of what is now commonly known as ' basic ' lining I am indebted to Mr. Percy Gilchrist, one of the patentees of the process. It is being attempted to produce magnesia on a large 86 Refractory Materials. scale by precipitating it from its chloride with milk of lime. It is simply a question of cost. If it can be done econo- mically a very useful substance for the manufacture of basic bricks will be available. Magnesia exists in considerable quantity in several waste liquors. If what has been said on the subject of materials capable of resisting the action of fire has been clearly understood, it will have become evident that, unless previously fired they should only be used in such positions as will ensure their being subjected to a high temperature. It would, therefore, be objectionable to employ fire-clay mortar in a cool part of a furnace, as it would inevitably crumble out. On the other hand, ordinary mortar, which consists of sand and lime, is not suitable for use, except in the cool parts of a furnace. THE METALS. THE word METAL appears to be derived from the Greek i I Clay \ Variable, ' 1 7 to 50 Black-band Ore 1 Iron, Oxygen, "j J CarbonicAcid, 1 1 Clay, Bitumin- I Variable, 21 to 43 |_ ous matter J Iron Pyrites* . Iron, Sulphur 46 Magnetic Iron Ore, or Magnetite, derives its name from Magnesia in Asia Minor, where its power of attracting iron and steel was first observed. One variety of the ore con- stitutes the loadstone,^ which confers magnetic properties upon * Iron Pyrites is not worked as an ore of iron, on account of the great difficulty in separating all the sulphur from the metal. t Probably corrupted from lead-stone, the stone which leads or guides, ID allusion to its use for making the needle of the mariner's compass II 2 I oo Metals : their Properties and Treatment. steel. This variety occurs chiefly in Siberia and the Hartz. Some of the common varieties of the ore do not attract iron, although they are capable, like steel, of becoming magnetic when brought into contact with powerful magnets. This ore is generally met with in compact heavy masses of an iron black or grey coloui, and with considerable lustre. Its specific gravity varies from 4^9 to 5*2. It abounds chiefly in the northern parts of the globe, and is found in immense masses in Norway, Sweden, Russia, and North America, being the most important iron ore in those countries. The iron extracted from it is generally of ex- cellent quality, though it is occasionally deteriorated by sulphur and phosphorus, which are derived respectively from iron pyrites and from apatite (phosphate of lime), which are sometimes found associated with the magnetic ore. The bulk of the Swedish iron, so much valued for the manufacture of steel, is extracted from the magnetic ore at Dannemora, where it is worked in an open quarry. Magnetic iron ore often contains titanic acid, the oxide of the metal titanium, and this is especially the case with a variety of the ore which occurs as a heavy black shining sand in India, Nova Scotia, and New Zealand. Red Htzmatite has been so called from the Greek word signifying blood, on account of its dark red colour,* and is sometimes erroneously called bloodstone (the true bloodstone being a dark green variety of silica (heliotrope} with red spots). In appearance it is the most striking of the ores of iron, sometimes appearing in rounded masses having exter- nally a liver colour with considerable lustre, and internally made up of layers having the appearance of the thick shell of some huge fruit, or of bundles of fibres, which look like petrified wood. The specific gravity of this variety is magnetic. In a similar way we have load-star, the star which leads towards the pole ; loadsman, one who guides a pilot ; load or lode, the leading vein in a mine. * The termination iff, so generally found in the names of miner.ils. was originally derived from the Greek word for stone. Ores of Iron. 101 about 5 - o. Such specimens are in general remarkably hard, and are useful for burnishing metals. But it is occasionally found in much softer earthy-looking masses of a brighter colour, and not uncommonly associated with clay. Red haematite is much more generally diffused than magnetite, and is found abundantly in this country, at Whitehaven (Cumberland) and Ulverstone (Lancashire), as well as in Glamorganshire. The compact variety is exceed- ingly pure, and furnishes iron of the very best quality. For smelting purposes any ore consisting essentially of an- hydrous peroxide of iron is termed red haematite. Large quantities of uncrystallised earthy haematite, very rich in iron, are now obtained from Spain and Algeria. This ore is also abundant in Ireland (Balcarry Bay), North America, Saxony, Bohemia, and the Hartz. Specular Iron Ore is identical in composition with red haematite, though its appearance is so different, for it forms crystalline masses, and sometimes separate crystals of a steel-grey colour and brilliant lustre, whence it derives its name (speculum [Latin], a mirror). It is also called Iron- glance ( Glanz [German], lustre), and in one of its varieties, made up of shining scales, Micaceous Iron Ore (micare [Latin], to shine). When scratched with a knife, or re- duced to powder, it exhibits the red colour of haematite. The specific gravity of specular iron ore is 5-2. The island of Elba has long been noted for its specular iron ore, and it is also found in considerable quantity in Russia and Spain. The excellent iron of Nova Scotia is extracted from the specular ore of the Acadian mines. Brown Hcematite contains the same oxide of iron as red haematite, but in a state of chemical combination with water, the latter varying from ten to fourteen parts in a hundred parts of the ore. Its appearance varies widely in different specimens. Some form globular masses of considerable size, others occur in small round grains (pea iron ore); occasionally it occurs in stalactites ; the various soft earthy IO2 Metals: their Properties and Treatment. ochres* and umbers\ consist, for the most part, of brown haematite, the dark brown shade, in the latter case, being caused by the presence of an oxide of manganese. In this country brown haematite is found at Alston Moor (Cumberland) and in Durham, but it is a much more im- portant iron ore in France. Some varieties of it contain a considerable proportion of phosphorus (in the form of phos- phoric acid combined with oxide of iron), which materially affects the quality of the iron extracted from them. The Black Brush Ore of the Forest of Dean is a brown haematite containing 89 parts of peroxide of iron, and 10 parts of water, and yields most of the iron used for making tin-plate. The Lake Ores of Sweden consist of a variety of brown haematite ore which occurs at the bottom of lakes, and is collected by dredging with a kind of iron sieve attached to a long pole, and thrust down through a hole in the ice, the mud being washed away from the ore by shaking the sieve up and down under water. In this way a man will some- times collect as much as a ton of ore in a day. Spathic Iron Ore (Spath [German], spar), or sparry iron ere, is composed of carbonate of iron, or iron combined with oxygen and carbonic acid. Some specimens consist of a collection of nearly transparent shining crystals, which are almost colourless, and have the same crystalline form as cal- careous spar (carbonate of lime). It is found in extensive beds in Styria and Carinthia. Spathic ore almost invariably contains manganese, which especially adapts it for the ma- nufacture of certain kinds of steel, whence it has sometimes been termed steel ore. This ore is also found at Wearsdale in Durham, and on the Brendon Hills in Somersetshire. Clay Iron Stone, Argillaceous % Iron Ore or Clay -band * Derived from the Greek for sallow, in allusion to their yellow colour. t From umbra (Latin), shade, on account of their darker tint \ Argilla (Latin), clay. Ironstones of the Coal Measures. 1 03 contains the iron in the same form of chemical combination (carbonate of iron), in which it exists in spathic iron ore, but in a state of intimate mixture with clay. This ore is by far the most important of British iron ores, being that which is most extensively worked in this country. It occurs in great abundance around Dudley, in Staffordshire, in York- shire, Derbyshire, and in South Wales. Both this ore and the black-band ore are found in layers which occur alter- nately with beds of coal, limestone, clay, and shale, whence they are often spoken of as the Ironstones of the Coal Measures, and the circumstance that the same pit, or neigh- bouring pits, will furnish the coal employed for smelting the ore, the limestone used as a flux, and even the clay for making fire-bricks for the furnace, allows English iron to be produced at a price with which, until lately, other countries found it impossible to compete. The coal formations of Belgium and Silesia also furnish large supplies of clay iron- stone. This ore is found sometimes in continuous beds, and sometimes in irregular globular masses, imbedded in clay ; it is moderately hard and stony, and varies in colour, through different shades of grey, slaty-blue, and brown. It is lighter than the preceding ores, and a cursory observe) might regard it as a stone rather than a metallic ere. The proportions of carbonate of iron and clay contained in the ore vary considerably, the former amounting to 80 or 90 parts in the hundred in some specimens, and in others not exceeding half the weight of the ore. Blackband Ore differs from clay iron-stone only by con- taining, in addition to its other constituents, a quantity of bituminous or coaly matter, sometimes amounting to one- fifth of the weight of the ore, and imparting the colour from which it derives its name. Lanarkshire and Ayrshire, in Scotland, contain extensive deposits of blackband iron ore, first brought to light in 1801. The presence of so much combustible matter enables the ore to be calcined without IO4 Metals: their Properties and Treatment expenditure of fuel. Blackband ores are also mined in Prussia. The Northamptonshire iron ore, which is found in the oolite limestone in that county, appears to have been formed by the chemical alteration of clay ironstone, under the influence of air and water, for it contains carbonate of iron associated with clay, and with the red oxide of iron, which is formed by the action of air upon the carbonate. Since this ore contains much phosphoric acid, it is unsuited for the manufacture of malleable iron by the puddling process. Iron Pyrites* is the yellow substance, of metallic appear- ance, which is so common in lumps of coal, and may be found in rusty globular masses on the sea-beach. It is com- posed of 46^ parts of iron in chemical combination with 53^ parts of sulphur, and is extensively used as a source of sulphur in the manufacture of sulphuric acid. Attempts have been made to extract iron from this mineral after the sulphur has been burnt off, and the iron is left in combination with oxygen from the air, but they have not been attended with much success, owing to the fine state of division of the ore after calcination, and the expense of consolidating it by pressure. EXTRACTION OF IRON FROM ITS ORES, IN THE FORM OF MALLEABLE IRON, STEEL, AND PIG OR CAST IRON. Although it is commonly conceded that bronze was in general use before iron, yet there is undisputed evidence to show that malleable iron was known and employed at least 2,000 years ago. Nothing can be simpler than the extrac- tion of iron from rich ores. All that is necessary is to heat them to redness with carbonaceous matter, say charcoal, when the oxygen of the ore will combine with the carbonic * The word pyrites is derived from the Greek for fire, probably in allusion to the circumstance that when this mineral is heated it gives off sulphur, which lakes fire. The Extraction of Iron from its Ores. 10$ oxide produced from the partial oxidation of the carbon, forming carbonic acid gas, which passes off into the atmo- sphere, and metallic iron, which is set free. However pure the ore may be it will always contain some earthy matter, with which the iron, on being reduced from its ore, will be mixed. In order to separate the iron from the earthy matter the latter must be rendered fluid, so that the iron, by reason of its greater specific gravity, may sink through it and collect together. One of the principle constituents of the earthy matter is usually silica, and it so happens that protoxide of iron is the very substance which, more readily than any other available, forms a fluid compound with silica at a low temperature. The ores employed by all primitive workers were peroxides, or if a protoxide (carbonate) were used it was first calcined, which would have the effect of driving off the carbonic acid, and converting the prot- oxide into peroxide by combination with a further quantity of oxygen. During the reduction of the ore by the carbonic oxide, the peroxide is first reduced to magnetic oxide, then to protoxide, and finally to metallic iron, thus : 3Fe 2 O 3 + CO =2Fe 3 O 4 2Fe 3 O 4 +2CO= Some of the protoxide produced in contact with the earthy matter combines with it, rendering it fluid, and forming what is known as slag, a term applied to all earthy matter which has been separated in a more or less fused condition during the reduction of a metal from its ore. The result of heating an iron ore, consisting essentially of peroxide of iron, with carbon is, then, to produce a pasty mass of malleable iron, charged with more or less fluid slag, or cinder, as it is also termed. In order to remove the cinder and consolidate the iron, it only remains to subject the mass to sufficient pressure whilst still red-hot, when the slag will be squeezed out, and the metal owing to the IO6 Metals: their Properties and Treatment. property of welding, which iron possesses in a high degree, will unite to form a solid mass, which can, subsequently, by reheating and hammering, be worked into any desired form. By such simple means as these iron has been made in India from time immemorial, and it continues to be so made both there and in Africa at the present day. The most primitive method of all is that practised by the Burmese. The furnace consists simply of a hole about 10 feet deep, dug in a bank, at a distance of 2 or 3 feet from its edge. The face of the bank is strengthened by pieces of wood placed crosswise ; the lower part of the bank is dug away, and a rectangular opening, about i foot high and the whole breadth of the furnace, is made, through which the metal and slag are removed at the completion of the smelting operation. The opening at the base is closed with moist clay, through which are inserted about twenty small clay tubes, or twyers. These tubes are made by plastering moist clay over stems of wood, which are then cut into lengths of 4 inches, and burnt. The twyers thus made are placed in the opening, in a single line, about half-way up. Lighted wood is then thrown into the furnace, and on it alternate layers of charcoal and ore, until the furnace is charged to the top. After the lapse of about eight hours the slag is removed, through an opening tem- porarily made for the purpose ; this operation is repeated every half-hour, until no more slag comes away. The smelting is complete in about twenty-four hours ; the weight of the iron produced averages about 90 Ibs. In some parts of India an artificial blast is employed, pro- duced by bellows made from goat skins, or by means of some primitive form of blowing-cylinder ; the furnaces also show an advance in constructive power as compared with that just described, as they are built above ground. In Central India and the North-Western Provinces, where manufactures have received the greatest development, con- tinuous working is effected by removing the iron by means TJte Catalan Process. 107 of tongs through the top of the furnace, the slag being run out, or tapped, through a small opening at the base. In this way, the furnace not being damaged by the withdrawal of the lump of iron, it can be re-charged again whilst still hot ; ihus time, fuel, and labour are saved. In Spain a somewhat similar method of producing malleable iron direct from the ore has been in use, with but slight modification, since the earliest times of which we have any record. This process is com- monly known as the Catalan, owing to its having been princi- pally practised in the provinces of Cata- lonia, where the mag- netic ore and the haematite of the Py- renees are smelted with the charcoal made in the neigh- bouring forests. The smelting works com- prise a forge, a blow- ing-machine, and a hammer, but the first alone will be here described in order to illustrate this method of treating iron ores. The crucible or hearth is a nearly rectangular trough (M, Fig. 1 8) well built around with masonry, about 17 inches deep, 21 inches long, and 18^ inches wide. The bottom of the crucible is composed of a block of granite, which is sup- ported upon small arches to keep it dry. That side of the hearth at which the blast from the tuyere (x) enters is perpendicular, being built up of massive pieces FIG. 18. Catalan Forge. IO8 Metals: tlieir Properties and Treatment. of iron (/), the blast-pipe, or tuyere, of copper, being sup- ported upon the uppermost piece in such a manner that its inclination to the bottom of the crucible can be varied at pleasure, since this exercises much influence upon the suc- cess of the operation. The wall opposite to the blast is built up of wedge-shaped pieces of iron (s\ and presents a curved surface. The working side of the hearth is composed of three thick pieces of iron placed end to end, the side oppo- site to it being lined with fire-clay, and having a moderate inclination. Mode of Conducting the Process. The ore is crushed by the hammer, and divided by sifting into lumps (mine) and very coarse powder (greillade). The furnace being still red- hot from the last operation, it is filled with charcoal nearly to the twyer ; the hearth is then divided at a point about two-thirds distance from the twyer into two parts by a broad shovel ; on the blast side a further quantity of charcoal is added, whilst that on the other side having been rammed down firm, ore is added so as to fill that part of the furnace. On this is placed moistened charcoal dust, except at the highest point ; a good blast is then turned on, and, if the whole is in good order, jets of blue flame at once issue from the uncovered portion of the ore. After a few minutes the pressure of the blast is lowered to i -5 inch of mercury. At intervals during the process which lasts about six hours the blast is gradually raised until it reaches about 3 inches, the maximum usually employed. During the whole of the process, at short intervals, greillade and charcoal are added, and well moistened with water to prevent too rapid combustion. After about two hours from the commencement the wall of mine (i.e. ore in lumps) is pushed well forward under the twyer, and more mine is thrown into the space thus made. This part of the process is also subsequently repeated at intervals, until sufficient has been added to form a lump of iron, or masse^ of the required size. From time to time slag is removed by opening the The Catalan Process. 109 tap-hole. At the completion of the process a mass of metal is obtained weighing about 3 cwt, which invariably consists partly of soft iron and partly of steely iron and steel, i.e. iron containing more or less carbon, for the conditions in this furnace are very far from being uniform. Reactions in the Furnace. We have seen that in the one part of the furnace only charcoal andigreillade are introduced, and in the other only lumps of ore. That the ore should be in lumps at that part is a very important point, for in this way the hot reducing gas, carbonic oxide (CO), generated by the action of the blast on the charcoal, is able to pass freely through the mass of the ore, the effect of which is that the water of hydration and the moisture are first driven out by the heat, and then, the ore having become easily permeable, the carbonic oxide reduces it to metallic iron by successive stages, as already described. At the same time that these reactions are going on the ore has become impregnated with carbon, derived from the decomposition of the gases with which it is charged. That this would be the case, the experiments of Mr. Lowthian Bell and others can leave no manner of doubt On the twyer side, where are placed the charcoal and greillade, the latter, as the charcoal is burnt away, descends rapidly, and to a considerable extent, doubtless, escapes re- duction ; for the arrangement of the blast is such that most of the reducing gas is projected on to the lumps of ore, and does not pass up through that portion of the furnace occu- pied by the charcoal and greillade y which, besides, are con- stantly damped. The greillade is much richer in silica than the larger pieces, from which it results that the quantity of slag will vary with the greillade added, which is always very rich in oxide of iron. What happens in this process appears to be this : car- burised iron is produced by the gradual reduction and fusion of the lumps of ore, and this, coming in contact at the bottom of the furnace with slag, very rich in oxide of 1 1 o Metals : their Properties and Treatment. iron, the carbon of the one combines with the oxygen of the other, and the result is that iron containing more or less carbon is produced, according as little or much oxide was present. The obvious conclusion would be, that the less there was of greillade present, the more steely would be the iron: in practice this is found to be the case. This circumstance would naturally suggest the total suppression of the greillade when it was desired to produce steel. That would, however, be impracticable ; for it is necessary that some of the oxide of iron should remain unreduced, in order to flux off the silica, which occurs in considerable quantity in the ore. In the blast-furnace this difficulty is got over by employing lime ; but lime, at the temperature of the Catalan furnace, would not produce a sufficiently liquid slag. All that can be done, then, when it is desired to produce steel, is to employ every available means to prevent decar- burisation. In addition to using less greillade, the slag is tapped out more frequently, so that the lump of iron as it forms may remain as little time as possible in contact with it. The bank of ore is exposed for a longer time to the reducing and carburising gases, and is pushed more gently towards the twyer, so as not to become decarburised by the oxygen of the air, which has not had time to combine with the carbon of the charcoal. Lastly, manganese should be present It is found that the presence of manganese has a very important influence, which is probably due to its power to replace iron in the slag. A slag in which some of the iron is replaced by an equivalent quantity of maganese is more liquid, and, according to Fran9ois, has not the same tendency to cause decarburisation at the temperature of this process. In order, then, that steel may be produced by this process, every precaution is taken to cause as much carburisation as possible, the unavoidable presence of oxide of iron in the slag and the low temperature effectually preventing the The Catalan Process Wootz. in formation of cast iron, a more highly carburised metal than steel ; the presence of oxide of iron, indeed, making it very difficult, as we have seen, to obtain steel. It might be said: Why not increase the temperature, so as to obtain a liquid slag without using oxide of iron ? If the temperature were increased, cast iron instead of steel would be produced ; in fact, that is exactly how cast iron first came to be obtained in blast-furnaces. This process has been rather fully treated of, because the principle of it is not always well understood. Rightly looked at, it explains how steel was first obtained. In the Indian furnaces steely iron and steel are also always produced in more or less quantity. In some districts the natives so well understand the necessary conditions that they can produce steel at will in their furnaces. No matter whether it is the intention to produce malleable iron or steel, it is very difficult to obtain a homogeneous product from these furnaces. In practice the mass is broken up, and the pieces sorted according to their relative hardness and suitability for different purposes. The circumstance that when a high temperature existed in the furnace, and much charcoal was present, the iron obtained was more or less steely, we have seen, was taken advantage of in India to produce more or less steely iron, by regulating the conditions in the furnace. Once these facts had been grasped, it required no great powers of reasoning to suggest the production of steel by heating malleable iron in contact with carbonaceous matter. The steel produced in this way by the Hindoos is known as wootz ; its manu- facture dates from a very remote period, and is still carried on at the present day. They place in unbaked clay crucibles, of the capacity of a pint, a piece of malleable iron, some chopped wood, and a few leaves of certain plants ; the top of the crucible is then closed with clay, and the whole well dried near a fire. A number of these crucibles are then strongly heated for about four hours in a cavity in the 1 1 2 Metals : their Properties and Treatment. ground, by means of charcoal, and a blast of air forced in by bellows. There is some reason to believe that an excess of carbon over that required to produce the hardest steel has to be added, in order to fuse the metal at the temperature which can be commanded in these furnaces. Before being drawn out into bars the cakes of metal obtained in this way are exposed in a charcoal fire, during several hours, to a temperature a little below the melting-point, the blast of air playing upon them during the time. The object of this is, doubtless, to remove the excess of carbon by a process of cementation, which will be explained presently. In 1800 a patent was taken out by David Mushet for a process in every respect analogous to that just referred to. He appears, however, to have applied it to the manufacture of a metal low in carbon, and therefore intermediate be- tween iron and steel, partaking in a certain degree of the properties of both ; corresponding, in fact, to what we have referred to as steely iron. Since this metal must have been in a state of fusion, Mushet must have brought to bear upon it a very high temperature. The manufacture was conducted in crucibles. Malleable iron left long in contact with strongly-heated carbon, and protected from the direct action of the blast, becomes steely, and, if sufficient time be allowed, it is converted into steel without undergoing fusion or even becoming pasty. This circumstance could not long have escaped notice, and doubtless it was to the observation of this phenomenon that the method of producing steel known as the cementation process owes its origin. When or where the cementation process first came into use is not known. For many years past all the best steel for cutlery, &c. has been made in this way. The cementation furnace (Fig. 19) is dome-shaped, like the furnace of a glass-house, and is enclosed in a conical jacket of brickwork, which serves to carry off the smoke from the flues. The hearth of the furnace is divided into TJie Cementation Process. 113 two parts by the grate (G), traversing the whole length (13 or 14 feet) of the furnace, in which a coal fire is maintained, the flame of which is made to circulate above, below, and around the fire-clay chests or pots, or troughs (c), placed one on each side of the grate, before escaping through the flues in the wall (H) and through the opening (M). These troughs are 10 or 12 feet long, and about 3 feet in depth and width, so that each will contain seven or eight tons of bar-iron, together with the charcoal necessary for its conversion into steel. A small opening is left at about the middle of one end of each chest, through which the end of one of the bars undergoing cementation is allowed to project ; this p roof -bar FIG. 19. Cementation Furnace for converting Bar Iron into Steel. is withdrawn from time to time, through a small door in the wall of the furnace, for the purpose of watching the progress of the cementation. There is also a small door in the wall of the furnace, a little above the top of each trough, through which the bars of iron may be introduced and withdrawn, a larger door being made in the middle of the wall to allow the passage of the workmen. The cementing material is charcoal, in pieces from about a quarter to half an inch in diameter. Alkaline salts, and substances containing nitrogen are sometimes added, because 114 filet ak : their Properties and Treatment. they cause the formation of cyanogen, which is said to assist the acquisition of carbon by the steel. The bars of iron should he of the purest description, if the best steel is to be produced. They are about three inches broad, and one- third of an inch thick. In order to fill the troughs, the workman stands upon an iron platform between the two, and sifts the cement powdei into them, so as to form a layer of about half an inch in depth, upon which the bars are arranged, standing upon their edges, at about an inch apart More cement powder is now sifted over these, so as to fill up the intervals between them, and to cover them entirely to the depth of about an inch. Upon this a second layer of bars is placed, then more of the charcoal powder, and so on, until the trough is filled to within a few inches ; it is then covered with grinders' waste ' wheel swarf,' consisting mainly of silica and oxide of iron. The fire is gradually applied during the first two or three days, to avoid the risk of splitting the troughs. A temperature high enough to melt copper (estimated at about 2,000 of Fahrenheit's scale) is required to enable the bar iron to acquire a proper proportion of carbon, and the troughs are maintained at this temperature for a period pro- portionate to the hardness which the steel is required to possess ; four days being sufficient for producing the steel of which saws and springs are made, while six or eight days are required for shear steel, and ten days or more are required for the very hard steel of which cold chisels are made. The fire is then gradually let down, to avoid sudden change, of temperature, so that some days elapse before the troughs are cool enough to be opened. About three weeks are commonly occupied in the conversion of the bar-iron into steel : one to get up the heat, one to keep it at the required degree, and one to cool it down ; so that only about sixteen cementations can be executed in a year by a single furnace. The bars are found to have upon their surface bubbles or blisters of considerable size, whence they are called blister The Cementation Process. 115 steel. On breaking the bars the fracture exhibits a silvery lustre and a well-marked crystalline structure. The pro- portion of carbon which has entered into combination with the iron depends upon the duration of the cementing pro- cess, but it rarely exceeds fourteen parts in a thousand parts of the metal. The chemical changes which are involved in the process of cementation are not yet thoroughly understood. The passage of infusible solid carbon into the interior of the solid iron bar obviously requires explanation. It might be imagined that the external particles of iron which are in contact with the charcoal, becoming charged with carbon, impart a portion of that element to the next layer, and so on, until the particles in the very centre of the bar had acquired a share of carbon. The following explanation is that usually accepted. The small quantity of oxygen contained in the air remaining in the trough, and present in the pores of the charcoal, enters into combination with the carbon to form carbonic oxide gas; this gas, in contact with iron at a high temperature, gives up one-half of its carbon to the metal, and becomes converted into carbonic acid gas ; but this carbonic acid, in contact with the strongly-heated carbon, is reconverted into carbonic oxide, which again transfers one-half of its carbon to the metal, these changes recurring many times in the same order, until the whole of the iron is converted into steel. The observations of chemists during the last few years have shown that red-hot iron allows the passage of gas through its substance, and that this metal has the power of absorbing a considerable quantity of carbonic oxide, which renders it easy to account for the transference of carbon from the charcoal into the interior of the bar. That part of the explanation which refers to the method by which the iron acquires carbon from the carbonic oxide is most assuredly erroneous. The molecule of carbonic oxide consists of one atom- of carbon and one atom of' I 2 1 1 6 Metals : their Properties and Treatment. oxygen. Chemical theory requires that the atom should be the smallest particle of matter which can combine with other atoms. It is, therefore, manifestly absurd to talk of the iron taking half the carbon from the carbonic oxide, since the carbonic oxide contains but one atom, and atoms are indivisible. A more probable explanation is, that the carbonic oxide occluded by the iron undergoes dissociation, depositing carbon and setting free oxygen, which immediately com- bines with a further quantity of carbonic oxide, forming carbonic acid. This point will be discussed more in detail further on. Other gases containing carbon are capable of imparting that element to iron ; thus, if coal gas, which contains carbon in combination with hydrogen, be passed for an hour through an iron tube containing some soft iron wires heated to bright redness, the wires will absorb carbon from the gas, and become converted into steel. The blisters, which are distributed sparsely and irregularly over the surface of the bars, are now known to be due to the action of particles of oxide of iron, or of slag, accident- ally occurring in the iron bars, upon the carbon combined with the iron, giving rise to carbonic oxide gas, the expan- sion of which causes the blister. As might be anticipated, the blistered steel, in its present condition, is only fitted for very rough articles, such as shovels ; its largely crystalline structure renders it deficient in tenacity, and the bars are further weakened by their want of uniformity and by the presence of the blisters. Conversion of Blistered Steel into Tilted or Shear Steel. The quality of the blister steel is improved by a process similar in principle to the fagotting of bar-iron. Five bars of blister steel are bound together into a bundle, being secured by a stout steel wire ; four of the bars are about 18 inches long, and the fifth is twice that length, so that it pro- jects beyond the others, and forms a handle. This bundle Shear Steel. 117 is raised to a welding heat in a forge, sprinkled with sand to combine with the oxide of iron and to form a fusible slag, and is placed under the tilt-hammer. This hammer weighs about two hundredweight, and it is so suspended that it may be raised by cams projecting from the circumference of a wheel, the revolutions of which bring them down in succession upon the tail of the hammer, the head falling again 'upon the anvil as soon as the cam has passed. A few blows from this hammer soon weld the bars together, when the binding ring is knocked off, the bundle again heated in the forge, and hammered or tilted throughout its whole length, and on all sides, until it is reduced to a rectangular bar of the right dimensions. In order to avoid the necessity for reheating the bar during the process, the tilting must be effected with great celerity, and the hammer is made to deliver 300 or 400 blows per minute, the number being, of course, regulated by the rate at which the cam-wheel revolves. The workman, being seated upon a swinging bench which brings him upon a level with the anvil, is enabled to move to and fro with little effort, and to bring every part of the elongated bar under the strokes of the hammer. The fracture of a bar of shear steel shows it to possess a much more compact structure than the blister steel, and its tena- city and ductility have been much improved by the tilting. It is probable also that, as in forging bar-iron, the proportion of carbon has undergone a slight diminution, the steel being found to become softer after repeated tilting. If double shear steel be required, the tilted bar is broken, and the two pieces welded into a single bar. Although the want of homogeneity in steel made as just described, owing to unequal carburisation, and to the presence of slag, which always exists in more or less quantity in wrought iron, was well known, yet nothing was done to remedy it until about the year 1760, when Huntsman con- ceived and carried into effect the idea of fusing the blister steeL He had great difficulties to contend with at first, for 1 1 8 Metals : their Properties and Treatment. there were no crucibles in existence then which would stand the requisite temperature. This was the first time steel was ever obtained in the molten state, unless we regard the Indian wootz as such, which, however, when in the molten state, was probably too highly carburised to constitute steel. The fusion of blister steel was a great step forward. The molten metal is cast into ingots, and, after being carefully reheated, is drawn down under a tilt- or steam-hammer. Conversion of Blis- ter Steel into Cast Steel The blister steel is broken up into pieces of a convenient size for packing close to- gether, and about 50 Ibs. of it are introduced into a tall narrow crucible, about two feet high, made of fire-clay mixed with black- lead, and provided with a closely-fit- ting cover. Some steel-makers add a little bottle-glass, to FIG. 20. Furnace arid Pot for melting Steel. g, Grate, c, Crucible, b, Cover of Furnace. a, Chimney. fuse over the surface and prevent oxidation of the steel. The crucibles are placed in a small furnace (Fig. 20) holding six, twelve, or more, about one foot wide and two feet deep, the opening of which is usually on a level with the floor, to facilitate the lifting of the crucibles. Several of these furnaces are connected by flues with the high chimney of the works, so that a powerful draught may be produced. Hard coke broken into small pieces is employed to raise the Cast Steel. 119 crucible to a bright red heat ; the steel is then introduced, the crucible covered, and the furnace filled up with coke. When the steel is melted, the crucible is lifted out with a pair of tongs, and its contents poured into a rectangular o r octagonal mould of cast iron, which has been previously heated, and is placed vertically for the steel to be poured in. The mould is made in two halves, closely fitting together, so that it may be opened for the removal of the bar of cact steel, and is coated inside with coal-tar soot. The quality of the cast steel produced is in some measure dependent upon the temperature at which it is poured, so that an ex- perienced workman is employed for the purpose. If the steel be not kept long enough in the furnace it will teem, or pour 'fiery,' i.e. it will boil up in the moulds, owing to the escape of gas, and the ingot will be ' honey- combed ' and useless ; on the other hand, if it be left in too long it will teem ' dead,' and the bar produced from it will be of inferior quality. At the present time large quantities of cast crucible steel are made from iron which has not been converted, i.e. has not had carbon imparted to it by the cementation, or, as it is termed in the trade, converting process. Malleable iron, cut into small pieces, is charged into 'crucibles, and melted with a certain amount of carbon, the proportion of which will depend on the temper required in the steel. Towards the close of the melting operation some spiegel-eisen (iron rich in carbon and manganese) is added. In other respects the process is similar to the melting of converted iron. In the production of mild steel, i.e. steel low in carbon, if plumbago pots be used carbon need not form part of the charge ; a little spiegel-eisen is added towards the end. Much scrap, consisting of crop ends, &c. of mild steel, produced by the Bessemer and Siemens processes, is largely used in the production of crucible cast steel, the scrap being simply melted down with the necessary quantity of charcoal and spiegel-eisen. 1 2O Metals : their Properties and Treatment. These methods, now largely used in the production of crucible steel, are to all intents and purposes the same as that employed by the Hindoos in the production of wootz, with the exception that they could not produce so high a temperature as is easily attainable in this country in an ordinary furnace. The addition of manganese is another point of difference in detail of some importance. This was first suggested and patented by Josiah Heath in 1839. He had been in the Civil Service in India, where he observed the influence which manganese had on the wootz steel. By the addition of manganese during the melting operation, in the form of an alloy with iron and carbon, or as oxide of manganese with carbon, sound weldable steel was produced from iron which could not previously be employed for the purpose. Before the introduction of manganese into the crucible steel manufacture only the best Swedish brands of iron were used. The manganese acts beneficially in several ways, mainly by its having a greater affinity than iron for oxygen and sulphur. The action of manganese in improving the quality of steel is possibly analogous to that which may be supposed to be played by oxide of copper in the toughening process in copper smelting ; * i.e. it combines with the impurities (sulphur and oxygen), and although they still remain in the mass of the metal, yet they probably exist there only in the shape of mechanically admixed oxide and sulphide of man- ganese, instead of being in chemical union with the iron itself. The greatest enemy of good steel is phosphorus. If this element be present in even so small a quantity as 0-03 per cent, instruments having a good cutting edge cannot be produced from the steel containing it. Numerous attempts have been made to produce malleable iron direct from the ore (without the intervention of the blast-furnace) in a more or less spongy state, and to convert it into steel by melting it in crucibles, and imparting the Cast Steel. 121 requisite amount of carbon by the addition of pig, c. The great relative bulk of the substance to be converted into steel, the ease with which it oxidises, and the difficulty of obtaining it in a sufficiently pure state, are all against the chance of success of this method of procedure. The ex- pense becomes too great to pay commercially. The only process which shows any likelihood of overcoming these difficulties is that of Dr. C. W. Siemens, hereafter to be re- ferred to (p. 190), which is still on its trial (1882). Since the introduction of the Siemens regenerative system,* furnaces built on that principle have been largely used in the manufacture of crucible steel. The melting-chamber is a long trench with overhanging sides, arched horizontally and vertically, to prevent them sinking in, should the pillars between the ports give way. It is divided into several com- partments, each holding six pots, arranged in two rows. Each of these chambers communicates by flues with the regenerators, which are situated on each side of the melting- chamber. The gas and air meet at a point about two feet from the entrance to the melting-chamber, into which they flow together, the gas being undermost, very little mixing of the gas and air taking place up to this point, so that the full heat of the combustion of the gas is developed around the crucibles. Over each pair of pots is an opening in the arch, fitted with a fire-brick cover, which can be raised and lowered by a lever. The economy of fuel by the use of these furnaces is said to be very great as compared with the old system, about a quarter of a hundredweight of small coal doing work for which previously three tons of coke were required. The pots stand very much longer, owing to the absence of dust, which in the old melting-holes rapidly corroded them. Since in the cementation process the carburisation of the metal proceeds gradually from the exterior to the centre of * See chap, on ' Fuel,' p. 64. 122 Metals: their Properties and Treatment. the iron, it is obvious that, by stopping the process after a certain time, the piece of metal will consist of wrought iron coated to a greater or less thickness with steel, a combina- tion extremely useful for purposes in which a hard surface in conjunction with the power to resist sudden shocks is required, as, for instance, in the case of the mandrils of lathes. Cementation applied in this way is known as case- hardening. The articles to be case-hardened are placed in a fairly air-tight box, which is then filled up with some sub- stance containing animal carbon, such as leather, horns and hoofs, bone dust, &c., which has been sufficiently charred to make it powder up. The box and its contents are then very gradually raised to a red heat, at which they are main- tained until the required thickness of casing has been ob- tained. About half an hour after the temperature has reached the proper point, the case-hardening will have pro- ceeded to a depth of a sixpence, and so on. It is sufficient for most purposes to convert to the depth of T ^th of an inch. The presence of alkaline substances, such as soda or lime, assists the process. When a hard surface is wanted, which has not to stand much friction, it may be produced by simply heating the iron to redness, sprinkling over the sur face with prussiate of potash, and then plunging the metal into cold water. In this way a very hard surface, but of hardly appreciable thickness, is obtained. The principle of cementation may equally well be applied to the softening of carburised metal as to the hardening of iron. It is only necessary to reverse the conditions. The metal which it is desired to partially or wholly decarburise is heated in oxide of iron (iron scale or red haematite), when the oxide of iron or the air contained between its particles acts upon the carbon at the surface of the metal, producing carbonic acid, which diffuses into the metal, where, coming in contact with a further quantity of carbon, it is reduced to carbonic oxide, some of which gradually diffuses out again, to be again converted into carbonic acid at the expense of Theory of Cementation. 123 the oxide of iron and the air, and so on. It is not essential that a substance containing oxygen and capable of being reduced by carbonic oxide should be employed ; an inert substance, such as sand, will do perfectly well. The really essential point in the process is that the quantity of air sur- rounding the metal should be very small ; only slightly in excess of that required to reconvert the carbonic oxide into carbonic acid. Were a greater quantity of air present, the removal of the carbon would be attended by a partial oxida- tion of the iron, destroying its toughness. The same thing results if the process be carried too far. Silicon, sulphur, and phosphorus do not appear to be seriously affected during cementation. The conditions are unfavourable to their removal, even supposing that, owing to the process being carried too far, they became oxidised. At first sight it may appear difficult to reconcile the theories just put forward to account for the two opposite kinds of cementation. They are, however, perfectly in accord with the laws of chemical affinity and of dissociation. It has been supposed that in the carburising process car- bonic oxide undergoes dissociation in the pores of the iron ; it might not unnaturally be asked: Why does not the carbonic oxide produced by the reduction of the carbonic acid in the decarburising process also undergo dissociation, depositing carbon in the pores of the metal ? We will endeavour to explain this apparent anomaly. At any given temperature and pressure an atmosphere of carbonic acid, placed under conditions favourable to its reduction to carbonic oxide, will undergo a certain definite amount of change, the extent of the change being entirely dependent on the temperature and pressure. The iron in the two cases under consideration has, pro- bably, nothing to do with the matter, except in the sense that it furnishes the spaces in which the gases are placed, under the necessary conditions of temperature and pressure to initiate their dissociation. If we assume as a working 1 24 Metals : their Properties and Treatment. hypothesis that the conditions in the heated iron are such as to enable dissociation of both carbonic acid and carbonic oxide to take place, then all that happens in each case is easily explained. It will be shown that this hypothesis and the facts of the case are in perfect agreement, and it may therefore be fairly considered to constitute a true theory of the two processes under consideration. It must be borne in mind that in the dissociation of a gas a portion only of it is dissociated, the percentage being regulated entirely by the temperature and the pressure, being independent of the actual amount of any other gas also present In carburising cementation the metal is surrounded with carbonaceous matter, and the conditions are therefore favour- able to the maintenance of an atmosphere saturated in respect to carbonic oxide, but containing only a relatively small amount of carbonic acid, since any carbonic acid entering the region around the metal would be decomposed by the char- coal into carbonic oxide (CO 2 + C=2CO), so long as the atmosphere remained unsaturated with the latter. At the commencement of the operation the interstices of the iron are charged with an atmosphere the nature of which will depend on the previous treatment of the metal during its manufacture. Unless this atmosphere not only coincide exactly in composition with that on the exterior, but also be at such a tension as to ensure dissociation not setting in, diffusion will commence in both directions. It may, then, be safely inferred that diffusion would take place. The atmo- sphere which would diffuse in would consist in great part of carbonic oxide, not only for the reasons already given, but also because the diffusion equivalent of carbonic oxide is greater than that of carbonic acid in the ratio of i : o'8 ; so that supposing, for the sake of argument, the external atmo- sphere were saturated in respect both to carbonic oxide and carbonic acid, this equilibrium would be destroyed on their diffusing into the metal. The force of diffusion is inversely as the square roots of the densities of gases. Deville has Theory of Cementation. l?5 shown that at the ordinary atmospheric pressure carbonic oxide is sensibly dissociated at about a bright-red heat Now, the temperature is the same within and without the metal, and unless the pressure be too great in the interstices of the iron, the carbonic oxide will undergo dissociation therein also. Our hypothesis is, that the conditions in the iron are favourable to the dissociation of the carbonic oxide, and that the carburisation of iron in the cementation pro- cess is effected by this means. The next point to be considered, in order to prove or disprove this view, is what becomes of the oxygen liberated on the splitting up of the carbonic oxide. The oxygen cannot combine with the iron in the presence of an atmosphere supersaturated with car- bonic oxide ; but it can combine with carbonic oxide to form carbonic acid, since this latter gas will be stable, i.e. cannot undergo dissociation, the quantity present being in- sufficient to form a saturated atmosphere. There will thus be a continuous dissociation of carbonic oxide, accompanied by a proportional formation of carbonic acid, which, how- ever, can never form a saturated atmosphere, since it will gradually diffuse out from the metal, and, coming in contact with charcoal, be reduced to carbonic oxide, which, in its turn, will act as a carrier of a further quantity of carbon to the metal. The only limit to the reaction is that determined by the actual fusion of the metal at the temperature of the operation, owing to its fusing-point being lowered by its union with the carbon deposited in it Let us now turn our attention to what takes place in decarburising cementation. As already pointed out, the decarburisation is effected by the agency of carbonic acid. Dissociation in this case, in all probability, has nothing to do with the matter. For, in the first place, the quantity of carbonic acid existing in the atmosphere outside the metal must be very small, quite insufficient to constitute a saturated atmosphere ; and, secondly, the atmosphere in the interior could never become supersaturated with carbonic oxide 126 Metals: tJieir Properties and Treatment. since its formation takes place in situ, and would of necessity stop when equilibrium of tension is reached As in the case of carburising cementation, this state of equilibrium is never reached, owing to diffusion taking place continuously. There is, therefore, nothing to interfere with the complete removal of the carbon from the metal Carbonic acid dif- fuses in and is reduced by the carbon, and the carbonic oxide thus formed diffuses out, and, in contact with oxide of iron or air, becomes converted into carbonic acid, and so on, the carbonic acid acting as a carrier of oxygen. The assumption that the iron does not take a primary part in the reaction in the carburising process is supported by its evident inactivity in the decarburising process. In speaking of the production of malleable cast iron, it was pointed out that, if the air were allowed to have too free access to the surface of the iron, oxidation of the metal would take place. This fact has recently been turned to practical account, it having been found possible to so oxidise the surface of the iron as to form a protective coating against the action of damp air, in other words, to prevent rusting. Professor Barff, about ten years ago, patented a process for the protection of iron surfaces by forming on them a film of magnetic oxide. This is effected by heating the iron to redness, and passing superheated steam over it. The iron being more electro-positive than the hydrogen, decomposes the aqueous vapour, setting free the hydrogen, and taking its place in combination with the oxygen. Prompted by these results, Mr. Bower experimented to see whether the same result could not be arrived at by means of air, and he found that, by allowing air in suitable proportion to come in contact with iron heated to redness, a firmly adhering coating of magnetic oxide could be formed. If too much air is admitted a ' lobster ' results, i.e. the article becomes coated with red peroxide of iron. The process is carried out in the following manner : The articles to be coated are placed in a fire-brick chamber of Protection of Iron Surfaces. 1 27 suitable dimensions, connected with a set of gas-producers by flues, in which the gas is allowed to mix with highly heated air, slightly in excess of that required foi its complete combustion. The carbonic acid, which is at a very high temperature owing to the heat developed during its formation, and the small amount of free oxygen pass into the working- chamber, where they heat the articles up to the requisite temperature to cause them to combine with the oxygen. From the working-chamber the spent gas passes through regenerators used to heat the air required for the combustion of the producer gas. The amount of air admitted to the working is thus, it will be observed, perfectly under control. Over the exterior surface of the coating of magnetic oxide a film of sesaui-oxide forms. The foregoing part of the operation requires about half an hour. In order to remove the film of ferric oxide, carbonic oxide is next passed over the metal for about a quarter of an hour. The thickness of the coating will depend on the number of times these two operations are repeated. It is stated that for indoor work from three to four hours are sufficient, whilst for outdoor work an hour or two longer is required. So far we have traced how certain methods for the manu- facture of steel naturally grew o? t of the primitive process ol extracting iron direct from its ore. It should now be clear that the difference between iron and steel is only one of degree, depending upon the amount of carbon present. It may safely be stated that iron has never been manufactured on anything like a large scale, free from carbon ; it always contains at least a trace under such circumstances. Until recently the term steel was only applied to carburised iron which had a high tensile strength, was elastic, and would harden on being heated to a certain temperature and suddenly cooled. This definition no longer holds good, for a vast quantity of slightly carburised iron produced by modern methods now goes by the name of steel How this came about will be made clear in the sequel 128 Metals : their Properties and Treatment. It is necessary that we should now return to the study of the processes by which iron can be extracted from its ore. The more important steps in early blast-furnace development were made in Carinthia and Styria. There the dimensions of blast-furnaces were gradually increased until the limit beyond which malleable iron could no longer be made wai reached. Before this limit was arrived at, furnaces were in use in which either malleable iron or cast iron could be made by slightly altering the method of working. The same furnace was known as a Stiickofen or a JSlauofen, according to whether it was being worked for the production of malle- able iron or cast iron. The height of these furnaces was from about 10 feet to 16 feet ; in shape they commonly resembled two truncated cones placed base to base ; some- times, however, they increased in diameter regularly from top to bottom. Taking as an example a recorded case, we find that a furnace 16 feet high measured i^ feet at the top and 2 1 feet at the bottom, the diameter at the widest part, or ' boshes,' represented by the junction of the bases of the two cones, being 4 feet This furnace was worked with one twyer, made sometimes of copper and sometimes of clay, placed about 14 inches above the bottom. When malleable iron was being produced, the lump was withdrawn from the bottom of the furnace through an aperture 2 feet wide, which was kept closed during the smelting, with the excep- tion of a small hole through which the slag escaped. Much damage was often done to the furnace in withdrawing the lump of metal, owing to its adhering to the material forming the bottom, and tearing it away. From the description of the malleable iron obtained, it was evidently of a decidedly steely nature. When it was desired to produce cast iron, the direction of the twyer was altered, and also the composition of the burden, the relative proportion of charcoal being increased. When it was intended to make malleable iron, the blast was made to impinge as much as possible upon the lump of metal, to The Blast-Furnace. 129 assist which the slag was tapped out often. These latter conditions would, therefore, be reversed in order to produce cast iron, and the metal would be exposed to the action of the charcoal for a longer time and at as high a temperature as could be obtained. Even in some of the higher Indian furnaces cast iron was sometimes unintentionally produced in more or less quantity, much to the disgust of the workers, who looked upon this product as worthless. They were quite aware that the cause of cast iron forming is due to the temperature having risen too high. In making malleable iron in the blast-furnace, ores containing a considerable quantity of phosphorus might be employed, and yet the iron produced would be free from that objectionable element. If, instead of malleable iron, cast iron were made in the same furnace, all the phosphorus would pass into the metal. The reason of this is that carbon has a greater affinity than phosphorus for oxygen. When smelting for cast iron, the charge consists largely of carbonaceous matter, therefore the phosphoric acid (P2O 5 ) in the ore is soon deprived of its oxygen, and the phosphorus combines with the iron. Since carbon has a greater affinity for oxygen than phosphorus has, it also follows that, so long as the metal retains an appreciable quantity of carbon, the phosphorus cannot be removed to any great extent by oxidation. When the blast-furnace was employed for making malleable iron, the conditions were favourable to the removal of phos- phorus from the iron, the metal produced being sufficiently free from carbon to allow that portion of the phosphorus which had been reduced to reoxidise, and pass into the slag. In consequence of the comparative ease and cheapness with which cast iron could be produced from the ore as compared with malleable iron, some simple means were naturally sought by which it could be converted into malle- able iron. This was soon accomplished, in spite of the K 130 Metals : their Properties and Treatment. presence of phosphorus, and gradually cast iron became the sole product of the blast-furnace. In the furnaces we have so far considered charcoal was the only fuel employed. In course of time charcoal began to get scarce, and people were forced to consider whether coal could not in some way be used as a substitute. At first it was used only for forging iron, but in time, after many failures, it was successfully applied to smelting in the blast-furnace. The first to do this was Dud Dudley, about the middle of the seventeenth century. What means he employed are not known ; he was greatly persecuted through the jealousy of other ironmasters, and he ended his days in poverty, his secret dying with him. There is not much doubt that his secret consisted in converting the coal into coke, and employing a good blast in his furnace. Although not absolutely lost sight of, the question of substituting coal for charcoal was not further practically developed until about a hundred years after Dudley's death. About the year 1 730, one Abraham Darby took the matter in hand, and achieved success by treating the coal in the same way as in making charcoal from wood, i.e. he converted the coal into coke. With the introduction of coke commenced a new era in blast-furnace history. The bellows which had up to that time been employed were not equal to dealing with the more refractory fuel. This resulted in the introduction ot blowing-cylinders worked by water power, and in due course of time by steam power. At first single-acting cylinders were used, but in time double-acting cylinders were substituted for them. The arrangement is a very simple one. The cylinder, which may be of cast iron, is fitted with an air-tight piston, to which a reciprocating motion is imparted, causing air to be drawn in and forced out alternately, through suitably arranged valves in each end of the cylinder. The air forced through the outlet valves of the blower passes into pipes attached to both ends of the cylinder, and connected Introduction of the Hot Blast. 131 with the blast main which supplies the furnaces. The arrangement of the valves and the attitude of the blowing- cylinder to the motive power have been varied in many ways ; the principle involved must always remain the same. The blowing-cylinders attached to blast-furnaces of the present day are often required to discharge 50,000 cubic feet of air per minute, and sometimes even more, at a pressure varying from about 3^ Ibs. to lolbs. per square inch, and even higher under special circumstances. In order to steady the blast a large chamber, equal in capacity to from twenty to fifty times the volume of blast passed into the furnace per second, was interposed between the blower and the furnace. The blast mains are now commonly so large that generally no other regulator is required. Valves are placed in the regulator or blast main to prevent the pressure of the blast rising beyond a certain fixed amount. Although the discovery that coke could be used for the manufacture of iron was a very important one in conse- quence of the increasing scarcity of charcoal, yet it must not be lost sight of that, owing to coke containing always more or less sulphur, it is really not so well suited as charcoal for the production of the best malleable iron. Even at the present day, where it can be obtained, charcoal is still used, notably in Sweden, and parts of America. The use of charcoal must, however, sooner or later come to an ena. The most important innovation which has ever taken place in blast-furnace practice is undoubtedly the introduc- tion of hot blast. This took place in the year in 1828. It was first carried into effect by Neilson, at the Clyde Iron Works, and notwithstanding that the idea was received with much derision at first, yet by about the year 1835 it had been universally adopted throughout Scotland. As a direct consequence of the use of a heated blast, it became possible to employ coal in the furnace, the heat being sufficient to cause the coal to coke to the necessary extent whilst still near the top. All coal cannot be used with equal advantage : 132 Metals: their Properties and Treatment. a highly caking coal would be objectionable. The splint coal of Scotland is well suited for use in blast-furnaces ; in the Staffordshire district coal is also used ; in Wales and America anthracite is similarly employed, generally, how ever, in admixture with other coal ; in Yorkshire, Durham, Cumberland, and some other localities, the blast-furnaces are fed with the best oven-coke procurable. Irrespective of the nature of the fuel used, the effect of heating the blast was to cause considerable saving in fuel, and also to increase the actual make of a furnace; the latter being to a great extent the direct consequence of the former, for to decrease the proportion of fuel in the burden is equivalent to increasing proportionally the ore. By blowing in hot air the temperature in the vicinity of the twyers is sensibly increased. With cold blast a nose of chilled slag forms at the end of the twyer, and extends itself to a greater or less distance into the furnace according to the temperature, thereby modifying the working and affect- ing the quality of the metal produced. With hot blast it is necessary to cool the twyers by passing a stream of water through a jacket surrounding them, to prevent their being fused. In the case of hot blast it is clear the conditions are more uniform and more under control ; atmospheric in- fluences can less affect the working of the furnace, and the zone of fusion is brought lower down in the furnace and concentrated within a smaller area. The importance of these considerations is apparent when we call to mind the conditions in the blast-furnace. A tall cylindrical chamber is rilled with ore, fuel, and flux, in certain proportions ; at the base air is blown in, which, coming in contact with incandescent fuel, combines with it, forming carbonic acid so long as the air is in excess, and carbonic oxide in the higher regions, where the influence of the fuel predominates. Part of the carbonic oxide as it passes through the ore reduces it, with formation of carbonic acid, in the way already explained ; another part undergoes dissociation in Chemical CJianges in the Blast- Furnace. 133 contact with metallic iron, in the interstices of the par- tially reduced ore. The carbonic acid thus formed is reduced again to carbonic oxide on coming in contact with more fuel, as it passes up ; so that a supply of carbonic oxide is maintained throughout the furnace. It has been shown that, in the primitive blast-furnaces, the earthy matter of the ore was fluxed off by means of oxide of iron. In large furnaces producing cast iron this would be impracti- cable, for oxide of iron forms an easily fusible ' scouring ' slag, which runs down into the crucible of the furnace, and meeting with the cast iron which is collecting there, de- carburises it more or less, so that an inferior white cast iron is produced, instead of a grey iron rich in carbon. Besides, oxide of iron could not remain unreduced unless an in- sufficiency of fuel were employed. In modern blast- furnaces these difficulties are avoided by using lime (CaO) as a fluxing agent. It forms a slag requiring a much higher temperature to render it fluid than is the case with oxide of iron, and, owing to the great affinity which calcium has for oxygen, it is not reduced, except in very minute quantity, either by the carbonic oxide or by the carburised metal In the higher zones of the furnace there exists, then, the following state of things : the ore has become reduced, and carbon, in a fine state of division, has been deposited throughout the mass; at the same time, the earthy matter has combined with the lime to form a slag of pasty consistency ; besides the reduced ore and slag there is also a considerable quantity of unconsumed fuel. All that remains to be done, then, is to raise the temperature of the charge, so that the iron and slag may be rendered liquid, and thus enabled to separate one from the other by reason of the difference in their specific gravities. This is effected by burning the intermixed carbon by means of a powerful blast of air. It requires but a moment's reflection to see that, as the necessary temperature for fusion is obtained by means of air introduced into the furnace, there would be a 1 34 Metals : their Properties and Treatment. great disadvantage in the fusion being effected above the point at which the air is introduced, for in that case the already fused metal would have to pass in front of the twyers, and in doing so would become to some extent decarburised. There is another point to be borne in mind, viz. that the carburisation of the metal is not effected alone b> the carbon deposited in it. It will be recollected that when iron and carbon are brought together at a high temperature, the former dissolves the latter. That the amount of carbon ultimately taken up by the metal is to some extent depen- dent on this reaction is probable. It follows that, within certain limits, the higher the temperature brought to bear upon the mixture, the more highly charged with carbon will the metal become. It is not uncommonly stated that there is no limit to the advantage to be obtained by raising the temperature. In this, as in everything, there is a well defined limit, though our ignorance may obscure it. In the first place, there is a limit to the amount of carbon which the iron is capable of taking up. Once that the slag and the metal are in a sufficiently liquid state, and the latter has taken up the maximum amount of carbon in the graphitic state, what further advantage can there be in raising the temperature ? Surely, the only result would be to extend the zone of fusion higher up in the furnace, which would be disadvantageous, and the wear of the lining of the furnace would be in- creased. Until within the last few years, the blast was heated by passing it through iron pipes heated from the exterior ; re- cently, however, fire-brick stoves, heated by the waste gases of the blast-furnace, have come largely into use for the pur- pose. (See chapter on 'Fuel,' p. 70.) At first, and for some years, the blast was only heated to a few hundred degrees, but since, the temperature has been gradually increased, until at present it is commonly employed at 900 R, and sometimes at 1,100 or 1,200. The Cowper stoves are said to be capable of raising the temperature Use of Waste Gases from Blast-Ptirnace. 135 of the blast to 1,500, but they are not generally worked at their maximum power. The utilisation of waste gases a source of great economy has only been carried into effect within the last half-century. At first it was only sought to utilise the sensible heat, a very small quantity as compared with that to be obtained by the combustion of the carbonic oxide and hydrogen contained in the gases passing out at the top of a blast-furnace, amount- ing in the case of carbonic oxide to 25 per cent by volume on an average, the hydrogen varying up to 7 or 8 per cent. FIG. up and Cone for closing the Blast-furnace, in order that the may pass into the lateral flue, as shown by the arrow. Various means have been tried with the view to collect the waste gases without interfering with the necessary arrange- ments for properly charging the furnace. That universally employed at the present day is the cup and cone (Fig. 21), or some modification of it. The ore, fuel, and flux are tipped from barrows into the annular space or cup (A), and the cone (B), which is attached by means of a chain to a lever, is lowered, allowing the charge to fall into the furnace, after which it is raised again, so as to entirely close the top 1 36 j\ let a Is : their Properties and Treatment. of the furnace. The gases are drawn off through the out- let (c). This arrangement has several great advantages. In the first place, it is very simple, and it can readily be altered without interfering with the body of the furnace ; it dis- tributes uniformly the burden in the furnace ; and, by alter- ing the dimensions of the cone, the arrangement of the charge can be regulated to suit the working of each furnace. As the charge descends more rapidly in the centre than at the sides, it is essential to the proper working of the furnace that the larger material should be in the centre, so that the current of gases may ascend freely in that direction, and not creep irregularly up the sides. This the cup and cone ac- complishes more satisfactorily than any other system which could be adopted. In one modification the exit tube for the gases is attached to the apex of the cone. With the increase in height of blast-furnaces it became necessary to have resort to mechanical contrivances for raising the charge to the top. For this purpose inclined planes were commonly in favour. They consist in a staging reaching from the ground to the top of the furnace, supported at several points, and inclined to the horizontal at an angle of about 25 to 30. On this incline travels a carriage, on which the barrows are sent up and down. In recently-con- structed works vertical lifts are usually put up. The motive power may be either steam, compressed air, or some hy- draulic arrangement. Of these, the first is that most com- monly employed. Perhaps the simplest method is that in which two drums are fixed on the same shaft, which is revolved by means of a small pair of reversing engines. Wire ropes attached to each drum pass over a pulley at the top of the furnace, and are connected with cages working between vercical guides. As one cage goes up the other is coming down, so that, to some extent, they balance one another. Amongst the pneumatic arrangements that of Gjers is the most in favour in the Cleveland district. In a cylinder, about 36 inches in diameter, works a cast-iron piston The Blast-Furnace. 127 or ram, attached to which are wire ropes, carried over pulleys, and connected with the cage at its four corners. The weight of the piston is made to exceed that of the empty lift, but FIG. 22. Blast-furnace for Smelting Iron Ores. only by such an amount that when the lift is loaded the latter shall then be somewhat heavier. Thus, when the plat- form has been unloaded, it is only necessary to apply a few 138 Metals: tJieir Properties and Treatment. pounds pressure to the piston in an upward direction tc cause it to rise, and bring down the platform or cage ; similarly, in order to raise the loaded platform, the piston is lowered by slightly exhausting the air from beneath it. The pressure and partial vacuum are readily obtained, as required, by means of pumps worked by a small engine. Blast-furnaces have been varied in shape and dimensions considerably in different localities, and in the same locality at different times. Fig. 22 will give a general idea of the way in which they were constructed up to quite recent times. Furnaces of this type of construction were to be seen in all parts of Europe. The body of the furnace is lined with some refractory sandstone, more generally with fire-clay (/'); be- tween this and another similar layer (/) is a layer of powdered coke or sand, which helps to pre- vent the furnace being pulled to pieces by the unequal ex- pansion and contraction. It will be observed that the furnace gradually widens for a certain distance, and then contracts. From the widest part (A) down to the crucible (E) is termed the 'boshes.' The tendency in more recent constructions has been to make the angle of the boshes less acute. E is the hearth or crucible, and o o points at which the twyers, varying generally in number from 3 to 5, are introduced. Three sides cf the hearth are occupied by the twyers ; the fourth is arranged for the tapping-out of the metal and slag.* This is shown in Fig. 23, a being a heavy block of stone, called the tymp-stone, supported by a cast-iron tymp-plate (b\ built into the masonry of the furnace, whilst the lower part is enclosed by the dam-stone (c\ faced * From the Scandinavian f/f, dross. FIG. 23. Boshes, Hearth, and Crucible of Blast-furnace. Tapping of the Blast- Furnace. 139 externally with a thick cast-iron dam-plate (r* spar, which is so commonly associated with copper pyrites, derives its name from its power to effect the liquefaction of earthy substances. Fluor spar is composed 55. Furnace for roasting Copper Ores. BB, Working doors. D, Vault for receiving the roasted ore. of calcium and fluorine; if it be strongly heated in contact with silica (quartz), which consists of oxygen combined with silicon, the latter takes up the fluorine to form fluoride of silicon gas, whilst the calcium and oxygen unite to produce lime, which combines with another portion of the silica to form a silicate of lime. The silicate of lime would not easily fuse into a slag by itself, but when clay and oxide of iron are present, as is always the case in the melting furnaces, a slag is readily produced. is/ Process in Copper-smelting. Calcining or Roasting to Expel Arsenic and part of the Sulphur. The roasting-furnace * From the Latin Jlue, to flow. Q 2 228 Metals: tlieir Properties and Treatment. or calciner (Figs. 55, 56, 57) is a reverberatory furnace, with a hearth (A) of large size (about sixteen feet by fourteen) to allow of the ore being spread out in a thin layer upon it. The hearth is commonly built of fire-bricks set on edge and bedded in fire-clay, and the flame is reverberated upon it by an arch of about two feet in average height. At one end of the hearth, near the fire-place, there is an opening or flue (o) through which air may be admitted to the hearth, to furnish the oxygen necessary for the chemical changes effected in the roasting process. On each side of the hearth there are FIG. 56. Furnace for roasting Copper Ores. Section through the line x Y cf the plan (fig. 57). two openings (;) closed with iron doors, through which the roasted ore is raked out into the arch (u) beneath the furnace. The ore is admitted by opening the hoppers (T) over the arch of the furnace, where it is previously warmed by the waste heat. The fuel employed in the calciners at Swansea is non-caking mixed with one-fourth of bituminous or caking coal, which is necessary to counteract the tendency of the coal to split up into small pieces and fall through the grate unburnt, the bituminous coal being softened by the heat, and binding the free-burning together. The fire of the calciners requires special management in order that the Ore upon the hearth may be brought to the proper tempera- ture. Both the free-burning and caking coal used have had the lumps screened out for household purposes. The Roasting of Copper Ores. 229 small coal would easily fall through the grate. To avoid this, a layer of clinker or fused ash from the coal is built up on the bars of the grate (F), preserving them at the same time from direct contact with the glowing coal, and air- passages are made through this layer, so that the air be- comes heated in passing through it, before actually reaching the fire, the combustion of the fuel being thus effected by a current of heated air. The oxygen of the air, passing through Fill. 57 Fi nace for roasting Copper Ores. Plan at the liae z v of the section (fig. 56). the column of heated fuel, combines with the carbon to form carbonic oxide (see p. 5), and this gas, being highly heated, takes fire in the air admitted on to the hearth of the furnace, giving a sheet of flame which is drawn through the furnace by the action of the chimney with which the flues (R) com- municate, and raises the ore to the temperature necessary for roasting it. Since the air is heavier than the burning gas, a layer of air always exists beneath the latter, separating it from the ore, thus preventing the ore from attaining its melting point, and securing a sufficient supply of oxygen. Each calciner is charged with three tons of the broken ore, which is spread evenly over the hearth, and roasted for twelve hours, being occasionally raked over through the 230 JMctals : their Properties and Treatment. \vorking-doors (/) m order to expose fresh portions to the action of the air, and to prevent any part of the ore from being melted. At this high temperature, the arsenic present in the copper ore combines with oxygen from the air to form arsenious add (white arsenic) which passes, in the form ol vapour, into the flues. About half of the sulphui in the ore also combines with oxygen to form sulphurous acid gas which passes up the chimney, a small quantity of sulphuric add being also formed and remaining in the ore as sulphate of copper. Since iron exerts the greater chemical attraction for oxy- gen, and copper for sulphur, a large proportion of iron acquires oxygen and becomes converted into an oxide oj iron, while a much smaller proportion of the copper com- bines with the oxygen from the air to form suboxide of copper. When the gases and vapours issuing from the calciners are allowed to escape directly into the air, they form a dense grey cloud of copper-smoke which contains the sulphurous acid, mixed with a little vapour of sulphuric acid, the arsenious acid, which condenses in the air to a fine powder, and some hydrofluoric acid gas, produced from the fluor spar. The injurious effect of these products upon the health and vegetation of the neighbourhood has induced the copper smelters to devise means for condensing them by passing them into flues and condensing chambers where they are met by showers of water. At some works it has been found profitable to convert the sulphurous acid into oil of vitriol instead of allowing it to escape, but in this case it is necessary to prevent the pro- ducts of combustion of the fuel from mixing with the copper- smoke. Spencers caldner employed for this purpose has the fire passing under the hearth instead of over it. This furnace is 50 feet long, and the ore is gradually raked from the cooler to the hotter end as it becomes less fusible. The waste heat of an adjoining smelting furnace is sometimes employed in these calciners, and the calcined ore is raked at once into the smelting furnace. In Gerstenhoffer s furnace the ores are Melting for Coarse Metal. 231 crushed between rollers, and allowed to fall over lows of red hot bricks in a vertical furnace, through which a blast of heated air is passed in order to burn the sulphur into sulphurous acid, which is then conducted into the leaden chambers, where it is converted into oil of vitriol. 2nd Process in Copper-smelting. Melting for Coarse Metal, to Dissolve the Oxide of Iron as a Silicate. It has been seen that the ist process has had the effect of converting a large pro- portion of the sulphuret of iron present in the pyrites into oxide of iron, which it is the object of the present process to remove by causing it to combine with silica, to form a compound capable of being melted and separated from the rest of the ore. At this stage the copper ores containing silica (quartz) can be introduced with advantage, provided that they are free from sulphur. It must not be forgotten that, during the process of calcining, a small proportion of the sulphuret of copper in the pyrites has been converted into an oxide of copper, which resembles the oxide of iron in its property of combining with silica at a high temperature, to form a melted silicate which would pass away in the slag, entailing a considerable loss of copper. This is prevented by the sulphuret of iron which is still present in the calcined ore, and, at the high temperature at which the fusion is effected, exchanges constituents with the oxide of copper, forming oxide of iron and sulphuret of copper. The slag from the 4th process, to be presently described, is also appropriately introduced in this fusion, since it contains a considerable quantity of oxide of copper, which exchanges, as above, with the sulphuret of iron in the calcined ore, fur- nishing more sulphuret of copper to pass into the coarse metal, and oxide of iron to be removed in the slag. The slag from the 4th process (called metal slag), being basic, assists in fluxing the silica in the ore. In some cases, the smelter adds some fluor spar in order to facilitate the fusion of the charge. The ore-furnace (Figs. 58, 59), as it is called, in which the melting for coarse metal is effected, is also a reverberatory 232 Metals : their Properties and Treatment. furnace, but its hearth (A) is much smaller than that of the calciner (usually about one-third of the size), because the charge has to be raised to a much higher temperature; for which reason, also, the fire-grate is larger in proportion ; the hearth is also slightly inclined on all sides towards a depres- FIG. 58. Section of Ore-furnace for smehing Copper Ores. T, Hopper for introducing the charge, p. Tap-hole for discharging the slag into the aids u. c, Flue leading o the ch ' slag- chimney. sion or cavity (B) at one side, which serves as a crucible in which the melted coarse- metal collects. The fuel is a mixture of free-burning with one-third of bituminous coal The charge of this furnace is composed of the following materials, selected for the reasons above given, viz. : Calcined or roasted ore, usually about 18 cwt. Ores containing oxide of copper and silica, 3 cwt. Metal-slag from process 4, containing oxide of iron, silica, and some oxide of copper, 6 cwt. Fluor-spar, occasionally. The slag is the first to fuse, in about ha?f-an-hour after the charge has been introduced, and by degrees the whole of the materials become liquid, and enter into violent ebullition, caused by disengagement of sulphurous acid gas, produced by a secondary decomposition of no importance from a Melting for Coarse Metal. 233 metallurgic point of view, save that the ebullition favours the intimate mixture of the melted matters on the hearth. After three or four hours, the furnace-man mixes up the melted matters with a rake, and raises the temperature very considerably, to favour the separation of the coarse metal from the slag. In about half-an-hour, the tap-hole (b, Fig. 59), which communicates with the cavity in the hearth, is opened, and the matt* or regulus of coarse metal is run ou't, KlG. 59. .flan ot Ore-furnace for smelting Copper Ores. F, The grate. R, Tank for granulating the coarse metal. through an iron gutter (a) into an iron box (G, Fig. 60), per- forated at the bottom, and standing in a cistern through which water is constantly running ; the coarse metal is thus granulated or divided into small irregular grains, in order to fit it for undergoing the next operation. Sometimes the regulus from two or three operations is allowed to accumulate in the furnace before tapping, thfe slag alone being raked out before the introduction of a fresh charge. The iron box containing the regulus is raised from out of * From the French mat, heavy. 234 Metals: their Properties and Treatment. the cistern by a winch (w), and its contents are carried to the calcining furnace. FIG. 60. Elevation of Ore-furnace for smelting Cower Ores. H, Hoppef for introducing the charge. K, Chimney, c, Fire-door, a. Pipe for supplying water to the tank. This coarse metal contains copper, iron, and sulphur in about the same proportion in which they are present in pure copper pyrites, so that the copper amounts to about 33 parts in the hundred, or nearly four times the proportion con- tained in the raw ore at the commencement of the process. The slag (ore-furnace slag) is raked out into sand-moulds (u, P^ig. 59), connected with each other by openings in their sides, where it solidifies into blocks of a black, somewhat glassy, appearance, interspersed with white fragments of quartz. It is used for rough building purposes in the neigh- bourhood of the copper works. The ore-furnace slag is composed essentially of oxide of iron (ferrous oxide) and silica combined in about equal proportions, and would be spoken of, in chemical language, as a silicate of iron or Ore-furnace Slag: 235 ferrous silicate. It contains also a little copper, usually amounting to one part in 140 parts, representing a loss to the smelter which appears unavoidable. Occasionally, a small quantity of regulus is found at the bottom of the blocks of slag, from which it is separated by hand-picking. Fig. 6 1 exhibits the general arrangements connected with the ore-furnace, and shows the furnace-man discharging the slai. FIG. 61. Copper Smelting-fu yd Process in Copper-smelting. Calcination of the Coarse Metal, to convert more of the Snlphiiret of Iron into Oxide. Now that the earthy matter has been removed in the slag, it is far easier to oxidise the sulphuret of iron than it was in the first calcining process. To effect this, three tons of the granulated coarse metal are roasted in the calcining furnace (Fig. 57) for 24 hours, the temperature being moderated at the commencement, to avoid fusion, and gradually raised in proportion as the removal of the sulphur diminishes the fusibility of the charge, which is raked over every two hours. 236 Metals : tlieir Properties and Treatment. About one-half of the sulphur is converted by the oxygen of the air into sulphurous and sulphuric acids, which escape in vapour, another portion of oxygen combining with the iron from which the sulphur has been removed, to form oxide of iron, so that the roasted coarse metal consists essentially of sulphuret of copper, oxide of iron, and some unchanged sulphuret of iron. ^th Process in Copper-smelting. Fusion of the Calcined Coarse Metal to remove all the Iron and to obtain Fine Metal. The principles involved in this process are the same as in the second process. The fusion is effected in a furnace which does not differ materially from that employed in the 2nd process, except that there is no cavity in the hearth, which is made to slope from all parts towards the tap-hole (Fig. 59). The charge consists of Calcined coarse metal (about one ton) Roaster-slag from the 5th process \ Refinery-slag from the 6th process \ Ol \ Ores containing oxide and carbonate of copper ' (The roaster and refinery slags contain silica in combination with the oxides of iron and copper.) These materials are fused together for about six hours, when they divide, as before, into a regulus or matt, and a slag, which remains above it. This regulus is called fine metal, to distinguish it from the coarse metal of the 2nd process ; it may contain from 60 to 80 per cent of copper, according to the amount of oxidised products and ores containing oxide and carbonate of copper added to the melting-charge. The different qualities are distinguished by specific terms ; thus, when the metal contains from 60 to 70 per cent, of copper and has a smooth shining fracture and blue colour, it is called blue metal ; from 75 to 78 per cent, the fracture is granular, the lustre greasy, and the colour greyish-white, it is then called white metal ; when the percentage of copper is above 78, the surface of the metal is covered with pimples, and moss copper is found in the air cavities, it is then called pimple metal. The pimples are formed by escaping sulphurous acid gas Melting for Fine Metal. 237 When it is intended to manufacture best selected copper for making brass, gun-metal, &c., the fine metal is made to undergo a partial roasting ; the various impurities which are present tend to collect in the metallic copper, which is thus separated from the melted mass of regulus. Two or more roastings may be required. The metallic copper containing the impurities is termed bottoms. The unreduced fine metal or regnle, which should now be nearly free from impurities, is treated in the ordinary way for copper. If gold, silver, tin, lead, iron, nickel, manganese, antimony, or arsenic be present in only small traces, they can. without difficulty, be entirely eliminated by the above selecting process. The composition of a sample of these bottoms is here given, in 100 parts : copper 74, tin 14, antimony 4^, lead i, iron 2^, sulphur 4. It is evident that the metallic copper which has separated has decomposed the sulphurets of tin, antimony, &c. contained in the metal, and has combined with those metals to form an alloy, which is heavier thap the metal and sinks to the bottom. In some smelting-works, where the fine metal is not obtained in so pure a condition, and contains only 60 parts of copper in the hundred, it is again submitted to the two processes of calcining and melting, exactly as in pro- cesses 3 and 4, when it yields black copper or coarse copper^ which contains from 70 to 80 parts of copper in the hundred. The metal-slag, as the slag from the 4th process is termed, presents an appearance very different from that of the ore- furnace slag ; it is very crystalline and lustrous, and consists chiefly of oxide of iron combined with silica, but it contains a considerable proportion of copper, partly in the form of an oxide in combination with silica, and partly as small particles of metallic copper, disseminated through the mass. In some specimens of the metal- slag, the copper appears in very fine brilliant filaments, forming copper-moss. This slag is usually employed as part of the charge in the 2nd process (melting for coarse metal). 238 Aletals : their Properties and Treatment. 5/// Process in Copper-smelting. Calcining or Roasting the. Fine Metal to remove Sulphur and obtain Blister- Copper. The manner in which this process is carried out is varied according to the degree of purity of the fine metal, but the chemical principles which it involves are the following : When a compound of copper with sulphur is heated in air, the sulphur combines with the oxygen of the air, and is thus gradually removed in the form of sulphurous acid gas, the copper also combining with oxygen, and being left as oxide of copper. Further, when an oxide of copper (or compound of copper with oxygen) is melted in contact with a sulphuret of copper (or compound of copper with sulphur), the oxygen of the former combines with the sulphur of the latter to form sulphurous acid gas, and the copper is sepa- rated in the metallic state. The pigs of blue metal are introduced, to the amount ot ii ton, into a reverberatory furnace, where they are roasted, at a gradually increasing temperature so as to avoid fusion, for about four hours, in order that a part of the sulphuret of copper may be converted into oxide of copper. When it is judged that this has been effected to a proper extent, the temperature is further raised so as to fuse the materials upon the hearth, the doors of the furnace being closed in order to avoid excess of air. As soon as the mass is fairly lique- fied, the temperature is somewhat reduced, being again raised towards the close. During this fusion a violent, effervescence is observed in the liquid mass, due to the escape of sulphurous acid gas, formed by the union of the sulphur from the sulphuret with die oxygen from the oxide of copper, whilst metallic copper subsides, in a fused state, and is run out into sand-moulds, where it solidifies into ingots, which preserve a blistered appearance, caused by the escape of sulphurous acid during solidification. The duration of the process depends upon the degree of purity of the blue metal under treatment, but it varies between 12 and 24 hours. A small quantity of slag (called roaster-slag) is formed during the fusion, which resembles pumice in its porous Production of Blister- Copper. 239 texture, but has a dark red- brown colour, and consists of the oxides of iron and copper combined with silica derived partly from the hearth of the furnace, and partly from the sand-moulds in which the ingots of blue metal are cast This slag contains about 16 parts of copper in a hundred, and is used as a portion of the charge in the 4th process. The roasting-furnace employed in this process is often constructed with an air-channel (Fig. 62) traversing the whole length of the fire-bridge, open to the air at both ends, and communicating with the hearth of the furnace through two openings (b b] in the brickwork. This permits the introduction of heated air into the nearth, by which the roasting is much facilitated. 6th Process of Copper-smelting. Refining and Toughening, to purify the Copper. The pigs of blister-copper are far from pure ; they contain considerable proportions of sulphur, arsenic, iron, tin, lead and other foreign substances, varying FlG - 6a - according to the descriptions of ore employed In order to remove these impurities, the oxygen of atmospheric air is brought into use. The furnace employed does not differ very materially from the melting-furnace used in the 2nd process (Fig. 58). The blister-copper to be refined is piled, in charges of 6 or 8 tons, upon the hearth, in such a manner as to allow air to circulate freely among the ingots. A moderate heat is applied at first, to allow the oxygen of the air to act upon the blister-copper, an action which is facilitated by the porous structure of the metal. The sulphur then becomes converted into sulphurous acid gas, and the arsenic into arsenious acid, which passes off in vapour, whilst the iron, tin, lead and other foreign metals are converted into oxides, as well as a portion of the copper. After being roasted for about six hours, the metal is melted, when a thin layer of slag is formed upon its sur- face ; after raking this off, a large sample of the copper is withdrawn and examined by the refiner, who can judge from the appearance of its surface if the oxidation has ?4O Metals : tJ'.e.ir Properties and Treatment. proceeded to the necessary extent In order to toughen the metal, its surface is covered with wood-charcoal or anthra- cite, which is renewed from time to time, so as to shield the copper from further oxidation, and the melted metal is stirred with a pole of young wood (usually birch), until a small sample half cut through with a chisel and then broken exhibits a fine close grain, a silky fracture, and a light-red colour, and a small ingot, cast for the purpose and ham- mered when red-hot, is found to be soft and free from cracks at the edges. The copper is then said to be at tough-pitch, and is taken out in iron ladles lined with clay, and cast into ingots of tough-cake copper. The effect of this process of poling, as it is termed, in toughening the copper, depends upon the removal of oxygen from the metal When the blister-copper has been re- fined, as above described, by being very slowly melted in contact with air, it is found to have taken up a large pro- portion of oxygen, which is contained dissolved in the metal as an oxide (suboxide) of copper. The presence of the oxy- gen, though it does not amount to more than two or three parts in a thousand of copper, has the effect of rendering the copper brittle or dry, so that a small ingot of it is easily broken when hammered, and its fracture exhibits a deep red colour, and a coarse-grained, somewhat crystalline structure. When the pole is plunged beneath the melted metal the combustible gases, generated from the wood by the heat, effect the removal of the oxygen from the metal, and bring it by degrees to tough-pitch. If, during the operation of casting the ingots, the surface of the metal on the hearth be not well covered with charcoal or anthracite, the copper will go back or become brittle again, in consequence of the absorption of oxygen from the air. If the process of poling be continued after the copper has been brought to tough-pitch, it becomes even more brittle than before it was poled, an effect which was formerly ascribed to the combination of the copper with a little car- bon from the wood ; but since analysis has failed to prove Process of Poling Copper. 241 the presence of the carbon, the following less simple expla- nation, based upon experiment, is now generally received Perfectly pure copper exhibits the malleability and ductility of the metal in the highest perfection, but these qualities are deteriorated by the presence of small proportions of the various foreign matters, such as sulphur, tin, antimony, &c., which cannot be entirely removed in the refining process. The injurious effect of these impurities, however, is counter- acted in some measure by the presence of a small proportion of oxygen (not exceeding two parts in a thousand), so that if this element be entirely removed, the copper will be over- poled, exhibiting a brittle character, due to some of the above- named impurities. On the other hand, if too much oxygen has been left in the metal, the copper is dry or underpoled. The effect of overpoling upon the metal may be remedied by allowing air to act for a short time upon the melted copper, so that a small quantity of oxygen may be absorbed by it. When the copper is intended for rolling into sheets, it is usual to add lead, in the proportion of about five parts to a thousand of copper, just before skimming the surface in order to ladle out the copper. The metal is well stirred after the addition of lead, in order that the action of the air may pro- duce an oxide of lead, which combines with the oxides of tin, antimony, and other foreign metals, to form a liquid slag, which rises to the surface of the metal and is skimmed off before casting. It is necessary that the removal of the lead from the copper by oxidation should be as complete as pos- sible, since its presence would prevent the scale of oxide of copper from being easily detached from the sheet during the process of rolling, and even -^th part of lead in 100 parts of copper suffices to injure its quality. This treatment of the metal with lead is called scarification, from the scoria or slag which forms upon the surface. The refinery slag, skimmed from the surface of the melted copper before commencing the process of poling, has a dull brown-red colour, with a purple shade, and consists almost entirely of an oxide of copper (suboxide) combined with 242 Metals : their Properties and Treatment. silica derived from the hearth and from the sand-moulds employed to cast the blistered copper. It is employed in the 4th process (fusion for fine metal). The hearths of the copper-furnaces become strongly im- pregnated with copper in course of time, and are broken out in order that the metal may be removed from them. The following modified method has been found to work successfully. By calcination or mixture a 28 per cent coarse metal is produced. With this percentage a cleaner slag is obtained than with a 35 per cent. ; a 35 per cent, has, how- ever, the advantage of calcining better in the subsequent operation. In order to obtain this latter advantage as well as a clean slag, the 28 per cent metal is melted down with the requisite amount of roaster and refinery slag, thus en- riching the metal to the required extent. This method has the additional advantage that the roaster and refinery slags being introduced at an earlier stage than in the ordinary process, the impurities have a greater chance of being eliminated. Extraction of Copper from the Bituminous Schists of Mansfeld. Although most of the copper sent into commerce is extracted by the Welsh process, other methods are some- times followed on the Continent for the treatment of poor ores, especially when coal is not abundant, for the coal required for the Welsh process amounts to eighteen times the weight of the copper. Thus, at Mansfeld, an ore is ex- tensively worked which contains not more than four parts of copper in a hundred, in the form of crystals of copper pyrites, diffused through a clay slate containing a large pro- portion of bituminous matter. The consumption of fuel in extracting the copper from this ore is only one-third of that in the Welsh process. The ore is first roasted in large heaps made up with alter- nate layers of brush-wood, the bituminous matter also serving as fuel. A heap containing 200 tons of ore will go on burning for fifteen or twenty weeks. In this process, which corre- GjJimds to the first calcination in the Welsh method, a part of Extraction of Copper at Mansfeld. 243 the sulphur passes off as sulphurous acid, and much of the iron is converted into an oxide. The next process is similar to the Welsh fusion for coarse metal, and con- sists in melting the roasted ore with some fluor spar, to serve as a flux, some copper-ore containing carbonate of lime, for the same purpose, and some slags containing oxide of copper to decompose the sulphuret of iron and remove the iron as a silicate (page 235). The fusion is not conducted in a reverberatory fur- nace, as in the Welsh process, but in a small blast-furnace (Figs 63, 64), about 14 feet high, and 3 feet in its greatest width. The blast is supplied by two tuyeres (/) placed side by side, about 2 feet above the bottom of the furnace, from which the melted matters are conducted through two channels (o o') into two basins (c c') about 3 feet in diameter and 20 inches deep, lined with a mixture of clay and charcoal dust ; when one of these basins is filled, the channel communicating with it is closed, and the melted matters from the furnace are run into the other basin. The furnace is provided with a chimney (G) 30 or 40 feet high. The fuel employed is either char- coal or a mixture of char- coal and gas-coke, which is charged alternately with the ore, as in an iron blast-fur- nace. The chemical changes which take place in the fui- nace resemble those in the Welsh process of melting for coarse metal, and the liquid matter which flows into the FIG. 63. Blast-furnace employed for smelt- ing the Bituminous Schists at Mansfeld. FIG. 64. Hearth of Blast-furnace employed at Mansfeld. 244 Metals : their Properties and Treatment. receiving basins divides into two portions, the lower layer consisting of the sulphurets of copper and iron, and the upper layer of slag composed chiefly of silicate of iron containing but little copper. The slag is ladled out into moulds and employed for building. The matt, as the lower layer is called, is removed in crusts, as it solidifies. If the matt contains less than thirty parts of copper in the hundred, it is again roasted and treated as before, so as to remove more of the sulphuret of iron ; but if it contains more than this pro- portion, it is at once roasted in a special open furnace (Fig. 65), which consists of six separate com- partments or stalls FIG. 6 5 .-Roasting-staIls employed at Mansfeld. w i tn fl ues running up the back walls in order to create a draught. The matt is placed upon a wood fire in the first compartment, which is then closed by build ing up a temporary wall ; when it has been calcined here for a certain time, it is transferred to the second compartment, and then to the third. It is now introduced into a wooden vessel and washed with water in order to dissolve the sul- phate of copper which has been formed by the combination of the oxygen of the air with the sulphuret of copper. The washed matt is roasted again in the fourth, fifth, and sixth compartments, in succession, being treated with water after every roasting. The solution of sulphate of copper thus obtained is evaporated and crystallised, yielding blue vitriol, which is sent into commerce. This operation of roasting, which lasts seven or eight Aveeks, corresponds to the calcination of the coarse metal in the Welsh process. The roasted matt, containing oxide of iron and sulphuret of copper, is treated as in the melting for fine metal, being fused with siliceous slags which dissolve the oxide of iron. Refining of Black Copper at Mansfeld. 245 The fusion is effected in a blast furnace similar to that de- f cribed above, but of smaller dimensions. The liquid matter in the receiving basins divides into rhree layers, the upper- most consisting of slag, the middle layer of a matt containing 60 or 70 parts of copper in the hundred, combined with sulphur (representing the fine metal of the Welsh copper smelting), which is again roasted and smelted, and the lowest layer of black copper, which consists of impure metallic copper, containing about 95 parts of copper in the hundred, with 3 or 4 parts of iron, i part of sulphur, and sometimes as much as 120 ounces of silver to the ton. When a sufficient quantity of silver is present to pay for extraction, the black copper is subjected to a process for that purpose, which will be described under silver, and is afterwards refined. The refining of the black copper, after separating the silver, is conducted in a reverberatory furnace (Figs. 66, 67), the hearth (A) of which is lined with clay and powdered charcoal, upon which the black copper is melted with the flame of a wood fire in the grate (F) and air is thrown upon its surface through two tuyeres (/), when the oxygen of the air removes the sulphur as sulphurous acid, and converts the foreign metals into oxides which collect as a slag upon the surface. When the refining is nearly completed, a red slag containing much red oxide of copper forms, and a small sample is withdrawn and carefully examined by forging. If it be deemed sufficiently pure, the copper is run out, through the openings (p\ into receiving basins (B) and removed in rosettes by throwing water upon it, and taking off the films of metal thus solidified. The rosettes thus obtained consist of dry copper, containing too large a proportion of red oxide. It is refined in the German hearth (Figs. 68, 69) which con- sists of a basin (c) about 16 inches wide, lined with a mix- ture of clay and powdered charcoal, and furnished with a blast-pipe (T) like that of a blacksmith's forge. The copper being melted in this basin, is covered with charcoal and kept fused until the copper is at tough-pitch in consequence of the reduction of a sufficient proportion of the red oxide of 246 Metals : their Properties and Treatment. copper, the same attention and judgment being necessary as in the Welsh process of poling (page 241). The retinea metal is then ladled into ingot-moulds. FtG. 66. Section of Furnace for made at the line : sfining Black Copper, at Mansfeld, af the plan, Fig. 67. When the black copper is not rich enough to be treated for silver, it is at once refined in the German hearth just FIG. 67. Plan of Furnace for refining Black Copper, at Mansfeld, >n. Fig. 66. made at the line v u of the section, described, but the process is conducted on the principle of the refining of blistered copper in the Welsh process, the impurities being oxidised by the air from the blast-pipe. Refining Copper in the German Hearth. 247 The hearth being filled with glowing charcoal, the black copper is placed upon it and gradually fused in the blast, so that the sulphur may burn off as sulphurous acid, and the foreign metals may be converted into oxides which are run off by a channel (//') provided for them. Alternate charges of black copper and charcoal are added from time to time, and the process continued until the workman perceives, by the inspection of a small sample, that the operation of refining is completed, when the surface is skimmed, and the copper removed in rosettes which are afterwards toughened as de- scribed above. The rosettes first removed are sometimes ~~ FIG. 63. FIG. 69. in Hearth used for refining Rosette Copper, at Mansfeld. rich in nickel, and are subjected to a special treatment for the extraction of that metal, which is valuable in itself and injurious to the quality of the copper. Precipitate Copper from Pyrites. A very considerable quantity of copper is extracted from the residues after roasting pyrites (chiefly Spanish) at the alkali works for the sake of the sulphur, which is converted into oil of vitriol. These residues contain 2 or 3 parts of copper in 100, with very small quantities of silver. They are mixed with com- mon salt (chloride of sodium), and moderately heated in a reverberatory furnace, when the copper and silver are con- verted into chlorides of those metals. On washing the roasted mass with water, these chlorides are dissolved, for the chloride of silver, though insoluble in water, dissolves in a solution of common salt. The silver is separated from the solution by adding some iodide of zinc, which precipitates 248 Metals : their Properties and Treatment. the silver as iodide of silver, and the copper is afterwards obtained by putting in some scrap iron, which combines with the chlorine and causes the separation of metallic copper, to be afterwards melted. The iodide of silver is placed in con- tact with metallic zinc, which separates the silver, combining with the iodine to form iodide of zinc, which is employed to precipitate the silver from a fresh batch of the material. VARIOUS DESCRIPTIONS OF COMMERCIAL COPPER. Cement Copper is extracted from the water which is pumped out of copper mines, or is collected from waste heaps, called blue water, its colour being due to the presence of sulphate of copper, produced by the action of the air upon the combination of copper and suipnur present in the ore. This water is pumped into tanks containing scrap iron, which gradually enters into solution as sulphate of iron, the copper being deposited in the metallic state. The fine red colour of the copper, and the pale green of the sulphate of iron, give the contents of the tanks a very beautiful appearance, especially in the sunshine. The copper of cementation thus produced, being almost chemically pure, is of very excellent quality. At Schmollnitz in Hungary, and in the Island of Anglesea, cement copper is largely prepared in this manner. Rosette Copper or Rose Copper is made chiefly at Chessy in France, by throwing water upon the surface of the melted copper, and removing the solidified metal in films, which have a beautiful red coating of an oxide (suboxide) of copper, formed by the action of the oxygen of the water upon the metal. These rosettes are plunged into water as soon as they are removed, for if they were allowed to cool in the air the further oxidation would produce a thick scale on the surface, spoiling the colour of the copper. Japan Copper resembles the preceding in colour, and is cast into ingots weighing only six ounces each, for exporta- tion to the East Indies. It is coloured by being cast under warm water on canvas. Copper is sometimes cast into thin plates by pouring into Effect of Impurities on Copper, 249 the mould enough metal to form a single plate, which is allowed to cool before pouring in a fresh quantity, when a film of suboxide of copper is formed upon the surface of the first plate, which prevents it from adhering to the next, so that the plates are easily separated when the moulding-case is removed. Bean-shot Copper \s made by pouring melted copper through a perforated ladle into a vessel of hot water, when it forms round fragments like shot, which are very convenient for the manufacture of brass. When cold water is used, the metal is obtained, in flakes, which are termed feathered shot. In order to remove the scale of oxide from rolled copper plates before sending them into the market, the somewhat inexplicable course is adopted of washing them with urine, then heating them in a reverberatory furnace and plunging them while hot into water, when the scale detaches itself. The sheets are then smoothed between rollers. Effect of the presence of Foreign Matters upon the quality of Copper. From the circumstance that the refiner tests the quality of copper by forging a hot sample, it will be inferred that the effect of impurities upon its malleability and tenacity is more perceptible at a high than at a low temperature. The foreign matters which commercial copper is liable to contain are arsenic, sulphur, antimony, tin, bismuth, lead, silver, iron, and nickel. Of these, sulphur and antimony are generally considered the most injurious in diminishing the malleability and tenacity of the metal. Arsenic is very com- monly found in copper, amounting, in some of the Spanish coppers, to as much as one part in a thousand, and was formerly supposed to be as injurious to the quality of the copper as antimony is, but modern experience has shown that copper may be easily rolled and drawn into wire even when it contains a considerable proportion of arsenic. A small proportion of tin is believed to increase the toughness of copper, but bismuth and nickel have the opposite effect. 250 Metals: their Properties and Treatment. The conducting power of copper for electricity is reduced in a most striking manner by the presence of foreign matters, so that, in the construction of telegraphic apparatus, it is important that the purest attainable copper wire should be employed. Pure copper is scarcely inferior to silver (see p. 95) in its conducting power, and the conducting power of the native copper from Lake Superior, which is almost pure, stands to that of pure copper in the proportion of 93 to 100, whilst the Australian (Burra Burra) copper, also very pure, has a conducting power of 89, and the Spanish copper, which contains much arsenic, has a conducting power only one-seventh of that of pure copp er, or in the proportion of 14 to 100. The addition of a small proportion of phosphorus (about five parts in a thousand) to copper is found to harden it and somewhat to increase its tenacity ; it is also said to render it less liable to corrosion when exposed to the action of sea- water. By adding arsenic to copper, in about the proportion of one to ten, a white somewhat malleable metal is obtained, which is not easily tarnished by air, and is much harder than copper. This compound, which is employed for clock dials and for thermometer and barometer scales, is made by heating five parts of copper clippings with two parts of white arsenic (arsenious acid) arranged in alternate layers and covered with common salt, in a covered earthen crucible. TIN. This metal is scarcely, if ever, found in the metallic state, but is extracted from the ore known as tinstone, which is an oxide of tin, or combination of the metal with oxygea Cornwall has been noted for its tin mines from a very remote period; tinstone is also found in Australia, Bohemia, Saxony, Treatment of Tin Ores. 251 Malacca, and Banca, the straits tin obtained from the last- named localities being much valued on account of its purity. Siberia, Sweden, and North and South America also furnish tin ore, though in smaller quantity. Tinstone is found either as stream tin ore or mine tin ore. The former is also called alluvial * tin ore from its occurrence in the niine- ral matter deposited by torrents in the valleys adjacent to the veins of mine tin ore, and is much purer than the latter, because it has been mechanically separated, by the action of the stream, from the foreign minerals which were associated with it in the vein. Occasionally, it is found in well-formed prismatic crystals which are perfectly pure oxide of tin. The mine tin ore occurs in veins traversing rocks of quartz, granite, or clay-slate, where it is associated with arsenical pyrites (see p. 2 24), copper pyrites, specular iron ore, and a remarkably heavy crystalline mineral called wolfram (tungs- tate of iron and manganese) which consists of tungstic acid (an oxide of the metal tungsten} combined with the oxides of iron and manganese. In order to obtain the tinstone in a sufficiently pure state for smelting, the ore is stamped to powder, washed, and calcined. The processes which are put in operation in order to obtain marketable tin from the raw ore may be summed up under the following heads : 1. Mechanical preparation of the ore. 2. Calcining or roasting. 3. Washing the roasted ore. 4. Smelting. 5. Refining. i. Mechanical Preparation of Tin Ores. The mine tin ore, as it is raised from the mine, is roughly cleansed from earthy matters by washing it upon a grating under a stream of water. It is then picked over and broken with a mallet, the pieces of copper pyrites being placed aside to be smelted for * Alluvia (Latin), an inundation. 2$2 Metals : their Properties and Treatment. that metal, and the iron and arsenical pyrites rejected. The tin ore is then crushed in the stamp-chest (c, Fig. 70) which is a wooden trough lined at the bottom with stamped ore, and provided with a number of massive wooden stampers (B) shod with blocks of cast iron weighing about 2\ cwts. These are raised by cams fixed to an axle (A) which is made to revolve by water or steam power, so that each stamper may give about twenty blows in a minute, fall- ing through a space of 8 or 10 inches. These heavy blows G. 70. Section of Stamping speedily reduce the ore to powder, and a stream of water, which constantly flows into the trough carries this powder through openings in three sides of it, which are closed with iron plates perforated with about 160 holes in the square inch, so that the larger fragments may not pass through. The holes in the iron plates are conical, having their narrower openings inside the trough, to prevent them from becoming choked. The water carries the powdered ore into a series of reservoirs, in which the ore settles down, whilst the water Treatment of Tin Ores, 253 flows away. Since the tinstone is much heavier than the other substances present in the ore (its specific gravity being FIG. 71. Rack for washing Ores. 6-5) the greater part of it is deposited in the first reservoir, the successive deposits becoming poorer as the stream flows on, and the sand, which has a specific gravity of about 27, FIG. 72. Section of Rack for washing Ores. being in great measure carried away. Various mechanical contrivances are adopted for effecting a further purification of the slimes deposited in the reservoirs, in all of which 254 Metals: their Properties and Treatment. advantage is taken of the high specific gravity of the tinstone. The rack (Figs. 71, 72) which may serve as an illustration of these, is an inclined plane of wood with a shallow ledge (g), about 9 feet long, having one end 5 or 6 inches higher than the other. It is swung upon a pivot (p) at each end, so that it may be tipped and its contents emptied over the side. About 25 Ibs. of the slimes are spread upon an inclined shelf (H), whence they are washed by a stream of water on to the inclined plane (F), when the sand and other earthy portions are carried away by the water, whilst the heavier tinstone, with some pyrites, &c., are left upon the plane; the deposit formed upon the higher portion of the incline is fit for the second process (calcining or roasting), but that formed on the lower part requires another washing. When a sufficient quantity of deposit has been collected on the table, the latter is tipped up sideways, and the upper and lower deposits allowed to fall into separate receptacles. The buddle is a fixed inclined plane worked in a similar manner. The tossing-tub, dolly or kieve, is a tub in which powdered ore is stirred up with water and allowed to settle, the subsidence being hastened by striking the sides of the tub ; the lower part of the sediment is of course the richest in the heavier tin ore. 2. Calcining or Roasting the Tin Ore. The arsenical pyrites and copper pyrites are too heavy to be entirely removed by stamping and washing, so that the ore is next treated in the burning-house, where it is roasted in order to expel the arsenic and sulphur. This is effected in reverberatory fur- naces, furnished with horizontal flues several hundred yards long, in which the white arsenic, formed by the arsenic in the pyrites and the oxygen of the air, is deposited in the solid state. From 6 to 8 cwts. of prepared ore is roasted at once, the temperature being very moderate at first, to avoid the fusion of the pyrites, and the ore being frequently raked over to expose fresh surfaces to the oxidising action of the air. The roasting occupies from 12 to 18 hours, and when Roasting of Tin Ore. 255 FIG. 73. Brunton's Calducr. 256 Metals : their Properties and Treatment. it is completed, nearly the whole of the arsenic has been expelled in the form of vapour of arsenious acid (white arsenic), and much of the sulphur in the pyrites has com- bined with oxygen, and passed off as sulphurous acid gas ; a great portion of the sulphuret of copper in the copper py- rites has also combined with oxygen to form sulphate of copper, a change which is completed by allowing the roasted ore to remain exposed to the air, in a moist state,for some days. Brunton's Calcwer (Fig. 73), which is adopted in some FIG. 74. Saxon Furnaces for calcining Tin Ore. a, Hearth. *, Grate. d. Fire-bridge, g. Chimney. A, Flue. ', Channel for conveyttg the fumes into the condensing chambers. works for roasting tin ores, consists of a circular table (T) of cast iron 8 or 10 feet in diameter, covered with fire-brick, made to revolve at three or four turns in an hour on the hearth of a reverberatory furnace with two grates. The tin ore is allowed to fall from a hopper (H) upon the centre of the table, where it is distributed and turned over by the spider (s), an iron frame with projecting arms, which is suspended from the arch of the furnace. By one of these arms the ore which has been gradually carried, by the rotatory motion, to the circumference, is delivered, in a roasted condition, through Smelting of Tin Ore. 257 an aperture (o) under the chimney. In this furnace the roasting operation is carried on without interruption. In Saxony, the roasting is conducted by a wood fire in reverberatory furnaces (Fig. 74) connected with a flue above 100 feet long, in which the arsenious acid (white arsenic) produced by the oxidation of the arsenical pyrites is de- posited. 12 cwts. are roasted in each furnace in 24 hours, yielding 5 or 6 cwts. of white arsenic. Common salt is sometimes added to the tin ore pre- viously to the roasting, when the chloride of sodium con- verts part of the arsenic and sulphur into chlorides which pass off in the form of vapour. 3. Washing the Roasted Tin Ore. The next process con- sists in stirring the roasted ore with water, in a wooden tank, when the sulphate of copper is dissolved by the water, and is drawn off after the ore has settled down, the copper being recovered from the solution by leaving it in contact with iron, as in the case of the blue water of the Anglesea copper-mines (p. 248). By another washing upon the rack, or some similar arrangement, the lighter oxide of iron pro- duced by the roasting of the pyrites is now removed, and the prepared tin ore or black tin, containing above 60 parts of tin in the hundred, is ready for smelting. 4. Smelting the prepared Tin Ore. The furnaces (Fig. 75) generally employed in the smelt ing-houses of Cornwall are reverberatory furnaces, having a low arch, with air channels under the fire-bridge and hearth, to prevent injury from the high temperature, the draught being produced by a chimney 40 or 50 feet high. Coal is burnt upon the grate, the flame of which heats the material upon the hearth. About a ton of the prepared ore (oxide of tin) is mixed with one-fifth to one-eighth of its weight of ground anthracite coal, and with a little lime which is intended to flux or liquefy the small quantity of silica still mingled with the ore. Occasionally fluor spar is added with the same object The mixture is damped with water, to prevent it from dusting, and thrown 258 Metals : their Properties and Treatment. upon the hearth of the reverberatory furnace. The doors are closed, but the temperature is kept low at first, for other- wise the oxide of tin would combine with the silica and the lime to form a glass or slag, causing a great loss of tin. The temperature is gradually raised for about five hours, by which time it should have reached its maximum. The charge is then well rabbled, and some culm having been thrown on the surface, the door is closed again, and heat applied for a further period of about three-quarters of an FIG. 75. Furnace for smelting Tin Ores. A, Fire-door. B, Charging-door. C, Working-door. E, Door for moderating the daught whilst charging the furnace, lest the ore-dust be blown into the flue F, Air-channel under hearth. hour, at the expiration of which the charge is again rabbled, and then left at rest for about fifteen minutes to regain the proper temperature for tapping. There are three principal products resulting from this smelting operation, viz. metal, glass, and slag. The ' glass,' which is the true slag, being perfectly fluid, is tapped out of the furnace with the metal. It is essentially a silicate of iron, but contains also any earthy matter from the ore, or added as flux, and a variable amount of tin as silicate. The glass, after it has been run from the furnace into the basin, separates into two layers. Liquation and Boiling. 259 The one called bottle-slag, resembling bottle-glass, is thrown away ; the other, a heavy black slag, is subsequently, when sufficient has accumulated, remelted. The slag, so called, is a scoriaceous pasty substance, consisting of anthracite, shots of tin, and 'glass.' The greater part of it remains behind in the hearth after the metal has been tapped ; it is removed through the end door, and subsequently stamped and washed to separate the tin. 5. Refining the Metallic Tin. The ingots of tin, as obtained from the smelting-furnace, contain various impurities. Not only are particles of slag, and of the oxide of tin, entangled in the metal, but small quantities of iron, arsenic, copper,' sulphur and tungsten are present in it, and must be re- moved in order to obtain marketable tin. This is effected by successive operations, which are known as liquation and boiling. The process of liquation consists in melting out the tin and leaving the impurities behind. The ingots of tin are moderately heated upon the hearth of a reverberatory furnace similar to that employed for smelting the ore, when the bulk of the metal liquefies and is allowed to flow out of the furnace into a refining-basin, leaving a residue of impurities upon the hearth. Fresh ingots are introduced from time to time, until about five tons of tin have collected in the refining-basin, which is the case in about an hour after the commencement of the process. The boiling consists in plunging into the tin contained in the refining basin, which is heated by a separate fire, stakes or logs of wet wood, which are held down under the metal by a lever-arm fixed above the refining- basin. The heat of the melted metal causes a brisk evolution of steam, which throws the metal up, exposing a large surface to the action of the air, whereby the impurities become oxidised, and are removed from the surface in the form of dross. After about three hours the wood is taken out, and the s 2 260 Metals .\ their Properties and Treatment. melted tin allowed to remain quiet for two hours, when the foreign matters which still remain dissolved in the tin gradually accumulate towards the bottom of the basin, leaving the upper part of the metal nearly pure. (Some- times tossing is substituted for boiling, that is, the tin is well agitated by raising a ladleful of the metal to a considerable height, and pouring it into the bath.) The tin is then ladled out into moulds, either of granite or cast iron, and cast into ingots weighing about 3 cwt. each,* those cast from the upper or purer part of the metal being distinguished as refined tin, those from the middle layer as common tin, and those from the bottom being so impure that they must be again subjected to the refining process. The refined tin is very brittle at a temperature somewhat below its melting- point, so that when the ingots are heated and allowed to fall from a height, they break up into irregular prismatic fragments, which are called grain tin.\ The refiner tests the purity of the tin by casting a small quantity in a stone ingot mould, when the refined tin remains bright and smooth after cooling, the common tin becomes partly frosted on the surface, and the impure tin is frosted all over. The metallic residue left upon the hearth in the process of liquation allows tin of inferior purity to melt out when a stronger heat is applied ; this is run out into a small iron basin, allowed to rest, and the upper part of the melted metal ladled into moulds to be afterwards refined : a white brittle alloy, known as ' hardhead,' containing tin, iron, and other foreign metals, is found deposited at the bottom of the basin. The refined tin will contain 99^ parts of tin in the hundred, the common tin 98^ parts, and the last portion, * Banca tin is sold in blocks of 40 and 120 Ibs. each ; Malacca tin in pyramids weighing about I Ib. each. t Only the best tin from specially pure ores is sold in the market as grain tin. Smelting of Tin Ore in the Blast-furnace. 261 which requires a second refining, contains only 95 parts. The temperature at which tin is melted before casting is said to be of importance, its malleability being injured if it be cast at too low a temperature. Reduction of Stream Tin Ore in the Blast-furnace or Blow- ing-house. This operation is attended with greater consump- tion of fuel and loss of tin than that practised in England, but it is largely employed in the tin-works of Saxony. The blast-furnace (A, Fig. 76) is only ten feet high, cylindrical in shape, and surmounted by a conical hood divided into com- partments for collecting the dust carried up by the blast, which is forced in by a blast-pipe at o, near the bottom of the furnace. The sides and bottom of the furnace are built of granite, the bottom (D) being a single block hollowed out for the reception of the tin which flows out, together with the slag, into a basin of granite (B) lined with a coating of clay and char- coaL If the tin ore con- tains much oxide of iron, some quartz is employed as a flux ; but if much silica is already contained in the ore, lime or finery cinder (p. 163) is employed to form a fusible slag. The prepared tin ore and wood charcoal are constantly charged in at the top of the furnace, so as to keep it full, when the carbonic oxide, produced by the combination of the carbon with the oxygen of the air, abstracts the oxygen from the oxide of tin (see p. 132), and the metallic tin runs down to the bottom of the furnace, accompanied by a small quantity of slag formed by the fusion of the silica in the ore FIG. 76. Blast-furnace or Blowing-house for smelting Tin Ores. 262 Metals : their Properties and Treatment. with the dshes of the charcoal, and runs out into the fore- hearth (B), from which the slag is removed into a tank of water, the tin remaining liquid in the basin. When the latter is full of tin, it is discharged, through a tap-hole, into an iron basin (c), where it is further treated like the tin ob- tained by liquation (p. 259). The loss of tin in the blowing houses is twice or three times as great as in the smelting- houses, and is due to volatilisation of the metal. At Altenberg, in Saxony, where the ores contain bismuth, they are treated, after roasting, with muriatic acid, for the extraction of that metal. The Saxony tin generally contains a little bismuth. Treatment of Tin Ores containing Wolfram. Since wolfram is even heavier than tinstone, its specific gravity being 7-5, and that of tin- stone 6-5, the tin ore can- not be freed from wolfram by washing. Moreover, the compounds of tungstic acid obtained from wolfram have received, of late years, some important applica- tions in the useful arts) thus tungstate of soda is a most effective application for rendering muslin uninflammable ; tungstate of baryta is employed as a substitute for white lead. Accord- ingly, when the prepared tin ore contains any considerable proportion of wolfram, the quantity of this latter is ascertained by chemical analysis, and enough sulphate of soda (salt-cake from the alkali-works) is added to furnish a little more soda than is necessary to form tungstate of soda with the tungstic acid which is present. Some coal dust is added to the mixture, which is then FIG. 77. Blowing-house at Altent F, Crucible. G, Inclined plane slag, i, Fore-hearth. Treatment of Tin Ore containing Tungsten. 263 heated on the cast-iron hearth of a reverberatory furnace, when the carbon removes the oxygen from the sulphate of soda, leaving a combination of sulphur with sodium (sul- phuret of sodium). A little air is then allowed access to the FlG. 78. Reverberatory Furnace for manufacture of Tungstate of Soda from Tin Ores. B, Opening for introducing the charge. D, Working-door. K, Opening for discharging the contents of the hearth, t, Vault for re- ceiving the finished charge. heated mass, when its oxygen converts tho sulphur into sul- phurous acid gas, and the sodium into soda, which combines with the tungstic acid to form tungstate of soda. The furnace (Fig. 78) is so constructed that the flame from the 264 Metals : their Properties and Treatment. grate (c), after passing over the hearth (A) of the furnace, may return underneath it, so as to heat the charge uniformly. The mass is transferred from the furnace into tanks of water which dissolves the tungstate of soda, to be afterwards ob- tained in crystals by evaporating the solution. The oxides of iron and manganese derived from the wolfram are still contained in the tin ore, but they are so much lighter that they can easily be separated from it by washing, when the tin ore is ready to be smelted in the usual way. Tin is remarkable for its property of creaking when bent ; a bar of the metal, when bent to and fro, emitting a sound as if grains of sand were intermixed with the particles of metal. It has been noticed, in the general consideration of the properties of metals (p. 96), that tin is more easily melted than any other simple metal in common use, and that it is possessed of a high degree of malleability, which is turned to advantage in the manufacture of tin-foil, by rolling and hammering the metal into extremely thin leaves. Tin is so little acted upon or corroded by air or by weak acids, that it is employed as a coating to protect the surfaces of other metals, such as iron, copper, and brass. Tin-plate is iron covered with a thin coating of tin, and since its manufacture is an important branch of English industry, an outline of it may be here given. Manufacture of Tin-plate. The sheet iron employed for the manufacture of the best tin-plate is refined with charcoal (p. 1 66), though iron refined with coke is sometimes em- ployed, the tin-plate being distinguished accordingly as char- coal-plate and coke-plate. The last term, however, now usually refers to plate which has been made from puddled iron. A somewhat red-short (p. 1 88), iron from the Forest of Dean is extensively employed for the purpose, being possessed of great toughness when cold. In order to obtain iron plates of the required thickness, the bars, |ths of an* inch thick, are cut into pieces 15 inches long and 6 inches wide. Each of these, having been heated Manufacture of Tin Plate. 26$ to redness, is rolled until its width is increased to 15 inches. It is then again heated, and rolled in the opposite direction until it is 5^ feet long. The plate is next sprinkled with a little coal-dust to prevent it from sticking together, doubled, again heated, and passed between very smooth rollers until the original length of the doubled plate (2| feet) has been increased to five feet. After being again doubled and heated, the four-fold plate is rolled out from 30 inches to 43 inches. It is then cut to the proper dimensions (not exceed- ing 1 8 inches by 13), the plates separated, and prepared for tinning. At this stage they are termed black plates. The plates must be rendered perfectly clean and bright, for the slightest impurity would prevent the proper adhesion of the tin. (1) The plates are bent so that they will stand on end, and arranged in a reverberatory furnace in order that they may be heated to redness. (2) They are immersed in a mixture of four pounds of muriatic acid with three gallons of water for a few minutes, after which they are (3) Again heated to redness, when the oxide of iron comes off the surface in scales. (4) They are hammered straight and passed between rollers of cast iron hardened by chilling (p. 154). (5) The plates are placed separately, on their edges, in sour bran-water, and occasionally turned, for ten or twelve hours. (6) They are pickled, that is, immersed and stirred about for an hour, in a leaden trough containing diluted sulphuric acid, at a temperature of 90 or 100 F., until they are per- fectly bright, the acid having dissolved off all the oxide. The sulphuric acid employed must be free from arsenic, which is apt to produce black spots upon the metal. This operation requires much care and attention on the part of the workmen. (7) The plates are scoured with sand, under water, and are left under clean water (or sometimes under lime-water), which hinders rusting, until they are required. 266 Metals : their Properties and Treatment. (8) The brightened plates are rubbed with bran in order to dry them, and the drying is completed by leaving them for an hour in a cast-iron pot filled with melted tallow. The process employed in some modern tin-plate works for preparing the plates to be tinned is much simpler than that just described. (1) They are pickled in warm diluted sulphuric acid tor about twenty minutes, which dissolves the black oxide of iron from the surface, the cleansing being completed by scouring them with sand and water. (2) The plates are annealed by being heated to redness, for twelve hours, in an air-tight cast-iron box capable of con- taining i, 800 of them, placed in a reverberatory furnace ; they are allowed to remain in the box till quite cold, when they are found to have acquired a deep purple colour, from a thin coating of oxide. (3) They are <: > fndin d e d pian'e depth, 9 \ inches wide at the mouth, bSS&SS cinders ^d 6i inches at the bottom, the sides being i inch thick, and the bot- tom i^ inch. Eight of these crucibles are heated by a single coal- fire (Fig. 86), the flame of which passes up and circulates around them, and afterwards heats two empty crucibles placed above them, and intended for the subsequent casting of the brass. Suitable proportions of the metals are : 41 Ibs. of old brass. 55 Ibs. of best selected bean-shot copper. 24 Ibs. of zinc. The crucibles are filled with the pieces of old brass, which are melted down, and leave room for the other metals. Half of the zinc is then introduced, in small lumps, and covered with coal dust ; then half of the copper and another Brass-founding. 291 layer of coal-dust ; the rest of the metals is then introduced in the same way, the whole covered with a layer of coal-dust, and the crucibles exposed to the fire for about four hours, when the brass is ready for casting. One of the hot empty crucibles is taken out of the furnace, and placed in another fire so as to keep it red-hot whilst four of the crucibles cf brass are emptied into it ; the surface is then skimmed, and the brass is poured into moulds made of slabs of granite mounted in an iron frame, the joints being cemented with clay. The presence of iron in brass is very objectionable, as it gives rise to deficient tenacity and malleability. The colour of the alloy of zinc and copper is of course dependent upon the proportions in which the metals are employed. Those alloys which contain more than 80 parts of copper in the hundred exhibit a reddish-yellow colour, in which the red predominates as the quantity of copper increases, the colour becoming yellow when less than 80 per cent of copper is present. If the amount of copper be less than 30 parts in the hundred the alloy is no longer yellow, but approaches more nearly to the colour of zinc. The various alloys used to imitate gold, before the art of electro-gilding was introduced,were all modifications of brass. Dutch metal or Dutch leaf gold, which is one of the most malleable of alloys, is composed of 1 1 parts of copper and 2 parts of zinc. It is cast into thin plates between slabs of granite, and rolled into sheets, being occasionally annealed (p. 91). When these are very thin, several are passed through the rolling-press together, and they are eventually cut up, and beaten out to extreme tenuity in piles of 40 and 80, under a hammer worked by water-power, making three or four hundred strokes per minute. Bronze-powder (or at least one kind of it), used for decorative purposes, is made by reducing the thin leaves of Dutch metal to a fine powder. Such powders are made of different shades, from dark copper colour to pale gold, by varying the proportion of copper. The grinding is effected with a very little oil, to prevent the metal from being tarnished by oxidation, u 2 292 Metals : tJtcir Properties and Treatment, Pinchbeck is composed of 3 parts of copper to i part of zinc, Prince's metal of equal weights of the two metals. Mosaic gold contains about equal parts of copper and zinc. The same name is sometimes applied to a compound of sulphur with tin. A little tin is added to the brass intended for engraving, since it causes it to break up more easily under the action of the graver. The addition of a little lead (about 3 oz. to 10 Ibs.) much facilitates the working of brass at the lathe and with the file, since it prevents the shavings and filings from greasing, or adhering to the tools. Brass is liable to be rendered very brittle when placed in situations where it is exposed to continual vibration. This seems to be due to the development of a crystalline struc- ture in the metal, and has occasionally caused the snapping of the suspending chains of chandeliers. The lacquering of brass, in order to protect it from being tarnished by the air, consists simply in varnishing it with shellac dissolved in spirit and coloured with saffron, annatto, dragon's blood, &c., so as to give it a golden hue. Brass is bronzed by coating it with a thin film of arsenic, mercury, or platinum, the last being used only for small articles, such as instruments, on account of its high price. A solution of white arsenic (arsenious acid) in muriatic (hydrochloric) acid, or of corrosive sublimate (chloride of mercury) in vinegar, is brushed over the brass, previously warmed, when the zinc in the brass chemically displaces the arsenic or the mercury from the liquid, and one of these metals is deposited as a coating upon the brass. In bronz- ing with platinum, a solution of muriate of platina (chloride of platinum) is applied in a similar way. There is much art in obtaining a durable bronze coating of any desired shade of colour. A mixture of chloride of platinum, corrosive sub- limate, and vinegar, is used for bronzing the sights of guns. Pins which are made of brass wire are tinned by boiling them with granulated tin water, and cream of tartar (bitar- trate of potash), when the latter, being strongly acid, slowly Varieties of Brass. 293 dissolves the tin, which is afterwards displaced from the solution and deposited upon the brass, because the tin and brass, in contact, form a galvanic couple, which decomposes the salt of tin, precipitating that metal upon the surface of the brass, which is the negative plate of the galvanic pair. In tinning or whitening pins, about 6 Ibs. of pins are spread over the bottom of a copper vessel, and covered with 7 or 8 Ibs of grain tin ; another layer of pins is then intro- duced, afterwards more tin, and so on, until the vessel is filled. Water is then poured in, the vessel heated, and ^ Ib. of cream of tartar sprinkled over the surface. After boiling for an hour the tinning is completed. Malleable Brass or Muntz's Metal, or Yellow Sheathing. This is an alloy of 3 parts of copper and 2 parts of zinc, which differs from common brass in being malleable when hot. It is of course cheaper than ordinary brass, on account of the predominance of the cheaper zinc, and can be more easily rolled into thin sheets. When used for sheathing ships, it keeps cleaner than copper. The nails employed for securing the sheathing contain, in 100 parts, 87 copper, 4 zinc, and 9 tin, the latter giving them hardness. Aich Metal, or Gedge's Metal, is an alloy of zinc and copper in nearly the same proportions as are contained in Muntz's metal, but it contains also a little iron. In consists, in a hundred parts, of Copper ..... 60-0 Zinc ...... 38-2 Iron 1-8 This remarkable alloy is very malleable at a red heat, and may be hammered, rolled, or drawn into wire, with the additional advantage of being readily cast. It has been employed in Austria for casting cannon, and some Chinese cannon have been found to consist of a similar alloy. Sterro-metal* is another very strong and elastic alloy used by Austrian engineers for the pumps of hydraulic presses. It * Named from the Greek adjective, strong, firm. 294 Metals : their Properties and Treatment. contains copper, zinc, iron and tin, in the following propor- tions in a hundred parts, the proportions varying between the assigned limits, according to the purpose for which it is required : Copper . . 55 to 60 Iron . . . 2 to 4 Zinc . . 34 to 44 Tin . . . I to 2 Good specimens of sterro-metal have been found to offer far more resistance than gun-metal to transverse fracture, and it is only two-thirds of the price. It is said that this alloy was accidentally discovered in an attempt to employ, for the manufacture of brass, the alloy of iron and zinc found at the bottom of the zinc-pots in making galvanised iron (p. 287). A very hard white alloy of 77 parts of zinc, 1 7 of tin, and 6 of copper, is sometimes employed for bearings of the driving wheels of locomotives ; and another alloy, containing 90 of copper, 5 of zinc, and 5 of antimony, is used for sockets in which the steel or iron pivots of machinery are to work. Aluminium -bronze is an alloy of 9 parts of copper and i part of aluminium. In colour it much resembles gold, but is much harder and lighter. It is extensively used as a cheap imitation of gold, but it becomes tarnished in course of time. It has also been employed instead of steel for perforating postage-stamps, &c., and is said not to be so soon blunted. [For alloys of zinc and copper with nickel see NICKEL.] NICKEL AND COBALT. These two metals almost invariably occur in the same ore. They are so closely allied in nature that their separation from one another is attended with a considerable amount of difficulty. Their properties very nearly resemble those of iron. Both are slightly more fusible than the latter sub- stance ; they are magnetic, but much less so than iron. In respect to tenacity, malleability, and ductility they rival it to the extent that, with our present knowledge, it cannot be Nickel and Cobalt. . 295 Stated which possesses these properties in the greater degree. Nickel and cobalt are both whiter than iron ; nickel has a slight yellowish tinge, whilst cobalt has a bluish shade in it. The atomic weight of nickel is given as 58*8, and that of cobalt as 587. The following specific gravities have recently been deter- mined in the author's laboratory : I. II. 111. Mean Grain nickel (a) . . 7-942 8-044 ' 7-993 Malleable cast nickel (l>) . 8-364 8-375 8-333 8-357 Malleable nickel rolled 1 g g . 688 _ g and stamped (c) . J HTwo specimens of same samp.e. Three I. a spoon ; II. a fork. , The specific gravity of cobalt after fusion is stated to be 8-7. Rammelsberg gives its mean specific gravity as 8-957. Nickel and cobalt behave towards carbon in the same way that iron does. The principal ores of nickel are Kupfer- nickel and silicate of nickel. Kupfer-nickel is an arsenide of nickel (NiAs), found in the Erzgebirge, near Schneeberg and Freiberg, in Westphalia, Hessia, Bohemia, Thuringia, Hungary, Norway, and Bolivia. It is of a pale copper colour, which becomes black on exposure. Kupfer-nickel is usually associated with some or all of the following sub- stances : cobalt, silver, antimony, iron, copper, and sulphur, in variable quantities; nickel also occurs in small quantities combined with sulphur or antimony. Silicate of nickel has within recent years been found in large quantity in New Caledonia. It occurs in the form of an hydrated silicate of nickel and magnesia, free from arsenic and sulphur, containing about 7 to 10 per cent, of nickel ; there is usually some oxide of iron present, mechani- cally mixed. The cobalt ores are essentially the same as those of nickel, with the exception of the New Caledonian ore, which is practically free from cobalt. Nickel and cobalt are extracted from the ores in which they are contained, as sulphides, arsenides, and antimonides 296 Metals : their Properties and Treatment. by concentrating them in the dry way in the form of an arsenide called speise, the copper at the same time being obtained in a separate layer in combination with sulphur, forming a regulus. These ores being very complex, a con- siderable amount of experience is required to treat them successfully, for although the tendency is for the nickel and cobalt to unite themselves to arsenic in preference to sul- phur, and the copper to combine with sulphur, yet some of the nickel and cobalt will be found in the regulus and some of the copper in the speise. The presence of iron, antimony, silver, lead, zinc, bismuth, &c. still further complicates the process. Sulphate of baryta (heavy spar) may, when it is required to add sulphur, be conveniently employed for the purpose, as it forms an easily fusible slag, and does not introduce iron into the speise. The following is a general description of the treatment of speise at the works of the well-known nickel and cobalt refiners, Messrs. Henry Wiggin & Co., Birmingham. The arsenide is roasted in reverberatory furnaces, in order to drive off in the form of arsenious acid as much as possible of the arsenic, which is condensed in coke-towers, and subsequently used up in the works. The calcined ore is treated with hydrochloric acid in large earthen receptacles, and the solution, containing nickel, cobalt, copper, iron, arsenic, and, perhaps, lead and bismuth, &c, is ladled out into wooden vats. The residue is again calcined and lixiviated and finally resmelted, as it still contains i or 2 per cent, of nickel The solution is diluted and sesqui-oxidised by the addition of chloride of lime (bleaching powder), the quantity added having been adjusted to the iron by analysis. Milk of lime is also added in suitable proportion, to throw down the whole of the sesqui-oxide of iron, which at the same time carries the arsenic with it in combination, as basic arseniate of iron. The precipitate is transferred to a filter, consisting of flannel strained over a wooden frame, and there well washed. It contains sufficient arsenic to make it worth while to use it in smelting operations on Treatment of Nickel Ores. 207 the works. The solution is next treated with sulphuretted hydrogen, which precipitates the copper, bismuth, and lead, as sulphides. Only nickel and cobalt remain to be dealt with. The cobalt is thrown down at a higher temperature as sesqui-oxide by the addition of bleaching power, and the nickel subsequently as hydrated oxide by means of milk of lime. Oxide of cobalt imparts a fine azure-blue colour to glass, pottery, and enamels, even one-thousandth part producing an appreciable amount of colour. The oxide of nickel can readily be reduced to the metallic state by making it into a paste with fioui or oil, breaking it up into small pieces, and heating it to a bright red in cruci- bles with charcoal. The product is known as grain nickel. The New Caledonian ore, a pale green silicate, is stated now for the most part to be smelted in blast-furnaces on the spot, much in the same way that iron is treated, and the metal exported to this and other countries in the form of pigs, containing about 5 per cent, of carbon and silicon, and occasionally a little antimony. The difference in cost for carriage between the ore and the pig amounts to about 20 per cent The New Caledonian pig is refined without expense for arsenic by mixing it with a suitable proportion of arsenical ore. The New Caledonian ore is sometimes treated in the neighbourhood of Birmingham in the following manner, as are also other ores and products containing nickel, and free from arsenic : The ore is first fused with iron pyrites, by which means the nickel is separated in the form of a sulphide. The regulus of mixed sulphides is next treated for the sepa- ration of iron and sulphur, much in the same way as in the Swansea method of copper smelting, i.e. by a series of calci- nations and smeltings, the ' metal ' in some cases being finally roasted in a fused state, or treated with nitre to remove the last traces of iron. All the iron having been removed, the remaining sulphur is easily got rid of, and the more or less pure oxide of nickel thus obtained is reduced 298 Metals : tJieir Properties and Treatment. to the metallic state in the same way as already described in treating of the wet process. It might obviously be rendered purer, if required, by treatment by wet processes such as have already been described. In any case this would be unnecessary when the New Caledonian ore alone was used Grain nickel is largely used for making German silver a white alloy of copper, zinc, and nickel, used as a cheap sub- stitute for silver, or for silver-plating on. The relative pro- portions of the constituents of German silver, or nickel silver, as it is also called, vary according to the purpose to which it is to be put. The commonest made contains about 8 copper, 2 nickel, 3-5 zinc. With a lower amount of zinc the alloy would tarnish very rapidly. With the same quantities of copper and zinc as in the foregoing, and 3 parts of nickel instead of 2 parts, a high-class German silver is obtained, corresponding in colour to silver a little below standard. When the proportion of nickel is increased to 4, the alloy is known as electrum ; it has a bluish shade in it, and is said to tarnish less readily than silver. The proportion of nickel in this alloy cannot, it is stated, be increased beyond 6 parts without injuring its mechanical properties. For the purposes named the following proportions are said to be used : (a) Forks and spoons 2 copper, i nickel, i zinc ; () knife and fork handles 5 copper, 2 nickel, 2 zinc ; (c) for rolling into sheets 3 copper, i nickel, i zinc. For castings, eg. candlesticks, spurs, bells, &c., 3 parts of lead should be added to the alloy (a), or 2 parts to the alloy (b). The addition of about i per cent of iron to these alloys renders them much whiter, but it makes them harder and more brittle. The iron must first be alloyed with the copper by fusion under charcoal, the product being subsequently alloyed with the remainder of the ingredients. Nickel itself cannot be satisfactorily alloyed with the other constituents of German silver by fusing them altogether. It is best done by melting the copper and nickel together first, and then adding the zinc, either unalloyed or alloyed with copper also. Nickel silver, after cooling from a state of fusion, has The Production of Malleable Nickel. 299 a coarse crystalline fracture ; by heating it to redness and cooling it again the structure is modified, and the alloy can be rolled, and hammered like brass. Coin containing nickel is in use in several countries. German silver was originally made from an ore containing copper, nickel, and zinc, found at Suhl, in Germany. A white alloy called arguzoid has recently been brought out. It is stated to be very tough and to possess mechanical properties superior to brass. Its composition is approxi- mately : Copper Zinc . Nickel Tin . Lead . 56-0 per cent 23-0 13'S 4'0 3'5 100 -o Hitherto nickel has only been used in alloy with other metals as a whitening agent. The reason of this was that it could not be obtained in a workable form. The metal resulting from the fusion of grain nickel is always wanting in malleability and ductility, behaving in a similar way to wrought iron which has undergone fusion, and probably for a similar reason. Dr. Fleitmann in the year 1879 succeeded in rendering nickel malleable by adding to it, whilst in a state effusion, one-eighth per cent of magnesium, introduced through a hole in the top of the crucible, a few lumps of charcoal having been previously added. In this way it is possible to produce malleable nickel, which can be welded to iron or steel at a white heat and rolled into thin sheets with- out separation. Fleitmann failed to get the same results by the use of manganese, aluminium, or calcium. Mr. Alfred Smeaton Johnstone, of the firm of Messrs. Wiggin : Co., who had previously been experimenting with manganese, has, however, succeeded perfectly in rendering both nickel and cobalt malleable by means of manganese. Commercial manganese (about 95 per cent) or any ferro-manganese may be used for the purpose, the presence of iron not destroying the malleability of the nickel or cobalt Thus, the analogy 300 Metals : their Properties and Treatment. between the treatment of nickel and cobalt and iron which have undergone fusion is perfect The manganese is added a little at a time to the fused nickel or cobalt, which is kept well stirred during the time, and finally poured out into moulds when tranquil. The metal is considerably agitated by the escape of gas during the addition of the manganese. For most purposes the addition of 2 per cent of metallic manganese is sufficient ; but when the maximum degree of malleability and ductility is required, the quantity added may be increased to as much as 5 per cent, beyond which there is no gain under ordinary circumstances. Zinc can be successfully alloyed with nickel by reducing their oxides in a state of admixture. By rapidly fusing the alloy thus obtained, a tough, malleable, and ductile metal can be made. The melting-point of nickel is too high to admit of zinc being introduced into it after the nickel is molten. The addition of one-tenth per cent, of magnesium is said to improve the working properties of this alloy. It is not likely that important applications will be long wanting for a metal possessing such valuable properties as malleable nickel, the price (about 4^. a Ib.) being com- paratively low. Malleable nickel anodes are already being substituted for the old cast anodes. The former certainly have a great advantage in their uniformity of strbcture, which not only prevents their being eaten away irregularly, but also avoids loss of energy through secondary currents. Whether the presence of manganese will prove an objection remains to be seen. In any case, with proper care in the manufacture, it could in all probability be reduced to so small an amount as to be innocuous. We are guided to this conclusion as to the possibility of controlling the manganese by our knowledge of the parallel case of Siemens steel. The greater rarity and consequent higher price of cobalt precludes its general use in the solid metallic state. It is, however, being used for electro-plating, the articles coated with it being sold as superior nickel-plate. Occurrence of Lead in Nature. 301 The use of oxide of cobalt as a colouring agent has already been referred to. It is largely employed in the form of s/na/t, a silicate of cobalt and potash. Great care has to be exercised in the manufacture, any impurities deteriorating the quality of the colour. When iron and copper are pre- sent, in order to separate them advantage is taken of their greater affinity for oxygen ; whilst nickel can be separated by reason of its having a greater affinity than cobalt for arsenic, so that the cobalt can be obtained as silicate and the nickel as speise in two distinct layers. LEAD. Whether lead in the metallic state has ever been found as a true natural product appears to be doubtful, since the small quantities which have been found associated with the ores of lead may have been accidentally reduced. Although minerals containing lead are pretty abundant, there are only two which are found in sufficient quantity to serve as sources from which to extract the metal on the large scale. Ores of Lead. Composition S^ofLead} . Lead, Sulphur White Lead Ore or\ Lead, Oxygen, , Carbonate of Lead / ' Carbonic Acid 77 5 Galena is by far the most abundant of the compounds of lead. It forms extensive veins, traversing clay slate in Corn- wall, and limestone in Derbyshire and Cumberland. It is also found in Flintshire (Holy well), Scotland (Leadhills), and the Isle of Man. Spain yields abundance of galena in Catalonia, Grenada, and at Linares in the Sierra Morena, where it occurs in granite. This ore is also abundant in the Upper Hartz, at Freiberg in Saxony, and in the United 302 Metals : their Properties and Treatment. States of America. Few ores are so easily recognised at once as galena ; it is distinguished by its lustre, which is almost metallic, its dark grey colour, and its great weight (specific gravity, 7-5). It can generally be easily split up into rect- angular fragments, and often occurs in distinct cubical crystals of large size. Galena almost invariably contains silver, which takes the place of a part of the lead in its combination with sulphur, without producing any alteration in the crystalline form and general appearance of the ore. A galena containing two parts of silver in a thousand would be spoken of as an argen- tiferous galena* because even that small proportion of metal can be profitably extracted from the lead after smelting it from the ore. Antimony is also found in many specimens of galena, as a sulphuret of antimony, and its presence has a serious influence upon the quality of the lead extracted from the ore. The minerals commonly associated with galena in the vein are blende (sulphuret of zinc) and copper pyrites, whilst caii'k or heavy spar (sulphate of barytesj, calc-spar (carbonate of lime), and fluor-spar (fluoride of calcium) are often found adjacent. White-lead ore or carbonate of lead is a much less important ore, often occurring in veins of galena, and apparently pro- duced by a chemical alteration of this ore. When pure, it is a white crystalline mineral, but it has often an earthy appear- ance, and it is so unlike galena that miners have been known to reject it as worthless. Sometimes it has a dark colour, from the presence of a little galena intermixed with it Car- bonate of lead is found in considerable quantity nearAix-la- Chapelle, as well as in Spain, and in the valley of the Mississippi. This ore is so seldom smelted apart from galena, that it is not necessary to describe its treatment separately. * Argentum, Latin for silver ; ftro, I bear. Extraction of Lead from Galena. 303 Sulphate of lead (composed of lead, sulphur, and oxygen), or Anglesite, is very rarely found in any quantity. Australia furnishes some of it, containing a considerable proportion of silver. In order to prepare the lead-ore for smelting, it is sorted oy hand, the worthless pieces being rejected, and broken up, either with a hammer or between crushing-cylinders ; it is then washed, in much the same way as the ore of tin (p. 251), in order to separate, as far as possible, the foreign matters mingled with it. The differences in the ore have led to the adoption of different methods of conducting the operation of smelting; thus in Derbyshire and Flintshire, where the lead ores are rich and contain very little quartz (silica), the galena is smelted in reverberatory furnaces, whilst at Alston Moor, and generally in the lead-works of the North, small blast furnaces are employed. - Smelting of Galena in the Reverberatory furnace. The chemical principles upon which metallic lead is separated from galena are similar to those involved in the last stage of the extraction of copper (roasting the fine metal for blistered copper, p. 238), the sulphur being finally expelled in the form of sulphurous acid, produced by its combination with oxygen previously taken up from the air. The galena is first roasted until a part of it has become converted into oxide of lead, its sulphur having combined with oxygen and been removed as sulphurous acid. _ Ga!ena Oxygen Lead Sulphur from the air &* Oxide of Lead Sulphterous Acid Gas and l^ad Oxygen Sulphur Oxygen During this roasting process, another portion of the galena is converted by the oxygen of the air into sulphate of lead. When the roasting has proceeded far enough, the oxide of lead and sulphate of lead are melted with that portion of the 304 Metals: tJieir Properties and Treatment. galena which has escaped alteration, when the whole of the sulphur is converted into sulphurous acid, and the lead is left in the metallic state. Galena Lead Sulphur Sulphurous Acid Gas Sulphur Oxygen Again Galena Lead Sulphur Sulphurous Acid Gas and and and Oxide of Lead Lead Oxygen Lead Sulphate of Lead Sulphu, Oxygen Lead Sulphur Oxygen and Lead give give FIG. 8/. Keverbe g Galena. The reverberator}' furnace in which the smelting of galena is effected is represented in Figs. 87, 88. The hearth (B) is about eight feet by six, and is separated from the grate (F) by a fire-bridge which rises to within about eighteen inches from the arch (AA'), the latter gradually descending, as it ap- proaches the chimney, until it is within about six inches of the hearth. The flame and products of combustion, after passing over the hearth, are conducted by two openings into Rwerberatory Furnace for Lead Ores. 305 a flue about eighteen inches wide ; this flue makes a bend downwards towards the top, and is carried into a chimney between fifty and sixty feet high. The flue is so constructed that it may be readily opened to clear out the deposit from the lead fumes. The fire- door (p), for throwing the coal upon the grate, and the ash-pit (F) are on opposite sides of the furnace ; that upon which the fire-door is situate is called the labourer's side, whilst that opposite is the working side. On the labourer's side, there are three openings (0), about six inches square, at equal distances, which can be closed when necessary with iron plates. There are three corre- FIG. S3. Plan of Reverberatory Furnace for smelting Galena. spending openings on the working side of the furnace, as well as two tapping-holes for the lead and slag respectively. The hearth of the furnace is lined with the slags from previous operations, which are spread over it while in a pasty state, before solidifying, and fashioned to the proper shape as shown in Fig. 89. On the labourer's side, it is nearly up to the level of the working doors, but on the oppo- site side it is hollowed out so as to be eighteen inches below the middle door ; this being the lowest part of the hearth, where the melted lead collects, a tap-hole is provided for running off the metal, and at some distance above it is the aperture for the escape of the slag. Adjacent to the tap- x ^o6 Metals : their Properties and Treatment. hole there is a basin outside the furnace for the reception of the lead. The Derbyshire ores commonly contain heavy spar (sulphate of baryta), which, owing to its high specific gravity, cannot be separated by washing from the galena. If the ore does not already contain it, fluor-spar is added to flux the heavy spar. The operation of smelting galena in the reverberatory furnace consists of four consecutive stages, distinguished as first, second, third, and fourth fires. First fire. As soon as the lead smelted in the preceding FJG. 89. Hearth of Reverberatory Furnace for smelting Galena. operation has been tapped into the outer basin, and while the furnace is still glowing, the fresh charge of about a ton of ore is introduced through a hopper (T, Fig. 87) in the arch of the furnace. No regular fire is made up, but only a little coal is thrown into the grate to keep up a mcderate temperature, for if this were raised too high at first, the galena would fuse, and the roasting would be rendered im- |x>ssible. A workman stationed at the labourer's side spreads the ore uniformly over the surface with a rake, after Smelting of Galena. 307 which the doors are closed and the draught moderated by lowering the damper. Since there is little fuel upon the grate, a considerable quantity of unconsumed oxygen of the air passes over the hearth of the furnace, so that some oxide of lead and sulphate of lead are soon formed. After the roasting has been continued for some time, the skimmings from the lead, run into the outer basin at the end of the last smelting, are thrown into the hearth. These skimmings consist chiefly of a mixture of sulphur with a large proportion of lead, which is thus rendered less fusible. This dross is speedily acted on by the oxide and sulphate of lead, as above explained, with separation of metallic lead which runs down into the hollow, and is drawn out through the tap-hole into the basin. This first portion of lead con- tains a larger proportion of silver than that tapped at a later period of the process. The workman occasionally turns over the ore to expose fresh surfaces, and, if necessary, throws a little small coal upon the charge to prevent the oxidation from being carried too far. About an hour after 1 he commencement, a large quantity of lead is run off, being chiefly derived from the action of the skimmings upon the roasted galena. After an hour and a half from the commencement, all the doors are thrown open, and the ore is well turned over by two workmen placed on opposite sides of the furnace, after which the doors are closed. At the end of two hours, the first fire is completed, a sufficient proportion of the galena having been converted by the roasting into oxide and sul- phate of lead. Second fire. The damper of the furnace is now partly raised, and more coal is thrown into the grate, so as to bring the temperature up to a bright red heat. The sulphuret of lead in the ore now acts upon the oxide and sulphate formed during the previous roasting, and the melted lead begins to run out in abundance. The workman stationed on the working side thrusts the pasty slags out of 308 Metals : their Properties and Treatment. the basin, whilst the man on the labourer's side spreads them over the rest of the hearth ; a little quicklime is now thrown in to assist stiffening the unreduced portion. Were the stiffening effected at this stage entirely by means of lime, the unreduced portion would be rendered too infusible for subsequent operations, so it is made sufficiently pasty partly by opening the fire-door and lowering the temperature. The charge is well worked and calcined for about an hour. The thickening of the charge not only allows any reduced lead to drain out, but also and this is the main object prevents the galena from sinking below the slag, and being thus removed from the action of the air. Third fire. The doors are all shut, and the damper entirely opened, more fuel being thrown upon the grate so as to raise the hearth to a still higher temperature for about three quarters of an hour, when the doors are again opened, the slags spread over the hearth, and a fresh quantity of lime thrown upon them. The lime enters into combination with any silica which may have united with the oxide of lead, and sets the latter free to act upon any portions of un- altered sulphuret of lead. The lime also acts advantage- ously by diminishing the fusibility of the mass and thus facilitating the contact between the sulphuret of lead and the oxide. This third fire also occupies about an hour. Fourth fire. The grate is again charged with fuel and the doors closed for about three quarters of an hour, the furnace being thus raised to its highest temperature. The tap-hole is then opened to allow the lead to run into the outer basin (G, Fig. 88), and some lime is mixed with the slags in order to dry up or partly solidify them, when they are raked out through the openings on the labourer's side, and the furnace is ready to receive a fresh charge of ore. A little small coal - is sometimes thrown upon the hearth at the conclusion of the fourth fire, to remove the oxygen from any oxide of lead vhich may still remain. The iron of the tools employed in stirring the contents of the hearth is seriously corroded by the sulphur in the ore. Smelting of Galena. 309 The whole operation of smelting in the reverberatory furnace lasts about five hours, and the coal consumed is about 1 2 cwts. for every ton of ore. The rich scum which forms on the metal in the pot con- tains a considerable quantity of lead mechanically intermixed, to effect the separation of which the workman agitates the lead vigorously with a paddle, at the same time throwing some coal slack into the pot and igniting, by means of a shovelful of hot cinders, the gases thus generated. In this way the dross is prevented from solidifying and the greater part of the entrapped lead separated. The slag amounts to about one-fourth of the weight of the ore, and sometimes contains as much as 40 parts of lead in the hundred, so that it is smelted in the slag-hearth, to be described hereafter. At Bleiberg in Cariuthia, the lead is extracted from galena by a process much resembling that just described ; but wood is employed as fuel, the grate being at the side instead of at the end of the hearth, and the hearth of the furnace is a single inclined plane, allowing the reduced lead to flow at once out of the furnace. The first portion of lead which runs out is known as virgin lead, and is purer than the pressed lead obtained later in the process when the tempera- ture is much higher. The Carinthian lead (Villacher lead, from the town of Villach) is in high repute for its purity. In Nassau, a furnace more nearly resembling the English reverberatory is employed, and towards the end of the pro- cess, some green wood is added to the charge upon the hearth, in order that the steam and gases evolved from it may agitate and mix the pasty mass. The lead collected in the basin outside the furnace is stirred with wood (like tin, see p. 259) before being run into pigs. In some of the Continental furnaces, metallic iron is added to the charge in order to combine with the sulphur in the galena, and separate the lead in the metallic state. When galena containing much antimony is smelted in the reverberatory furnace, a portion of the oxide of lead com- 310 Metals : their Properties and Treatment. bines with the oxide of antimony to form a compound which can only be decomposed by the coal at a very high temperature, so that the first portions of lead obtained are much purer from antimony than those at the end of the process. Smelting of I^ad Ore in the Scotch Furnace or Ore-hearth. Since this is a blast furnace, it is found advantageous to roast the ore before smelting it, in order that it may be rendered more porous and may offer less obstruction to the blast. The ore is spread over the hearth of a reverberatory fur- nace, not unlike that employed for roasting copper ores (p. 229), in charges of about half a ton, and roasted at a moderate heat for about eight hours, being frequently turned over as is usual in roasting operations. Some antimony is thus expelled from the ore, which would otherwise harden the lead ; a considerable quantity of sulphur also burns off. The roasted ore is raked out of the furnace into a pit filled with water, which causes it to fly into fragments suitable for charging into the ore-hearth. The ore-hearth (Fig. 90) is a small square forge or blast furnace about two feet high, and 18 inches by 12 internal area. It is arched over at the top, so that the kadfnmemzy be conducted into a long flue, sometimes five feet high and three feet wide, in which a large quantity of oxide of lead and sulphate of lead is deposited. At the Allenheads works, this flue is carried up the side of a hill for three miles before it terminates in the chimney, in order to secure per- fect deposition of the lead fume, which would otherwise involve very considerable waste ; for although lead is not, like zinc, a metal capable of being distilled, both the metal and its sulphuret, when heated in a strong current of air, are liable to be carried off in the form of vapours, which after- wards combine with oxygen from the air, and are deposited as oxide and sulphate in the flues ; these deposits are afterwards heated in the calcining furnace till they can be Tlie Ore Heartk. 3 1 1 made to stick together, and are then smelted in another fur- nace called the slag-hearth. A rain chamber is often pro- vided, in which the condensation of the fume is assisted by water ; and the great length of flue renders it necessary to assist the draught by large exhausting pumps. Since a very moderate temperature is required in this fur- nace, the sides and bottom are lined with cast-iron plates, and in front of the furnace, where there is an opening about Fro. 90. Scotch Fi a foot high, a sloping iron plate a b (work-stone] is fixed, upon which the materials can be raked out when necessary, for examination and manipulation by the smelter. The bottom of the furnace, upon which the melted lead collects, is about 4^ inches below the upper surface of this iron plate, in the edge of which there is a groove cut, near to the side of the furnace, through which the melted lead may run when it rises to a sufficient height, into a gutter (/) which conveys it 3 1 2 Metah ; their Properties and Treatment. into a cast-irou pot (F) heated by a separate fire, and called the melting-pot. The blast-pipe enters at the back of the furnace, about 1 1 inches from the bottom. Peat is the principal fuel employed in the furnace, in the form of square blocks, with which the furnace is filled at the commencement, some judgment being required in their arrangement, and the fire is lighted by placing one of the blocks, already kindled, in front of the blast-pipe, when the combustion soon spreads throughout the furnace. The first charge introduced into the ore-hearth does not consist of the roasted ore, but of the residue from a previous smelting operation, which is called browse, and consists of partly reduced ore mixed up with cinders; before this is thrown in, a little coal is put on the fire to raise the temperature, and in a short time the charge is raked out upon the work-stone in front of the furnace, and examined, in order that I\IQ grey slag* a shining glassy mass, may be picked out and thrown on one side. This grey slag contains a quantity of silicate of lead, with silicate of lime, &c., and requires a higher temperature for the extraction of its lead than is attainable in this furnace ; it is therefore smelted in the s/ag- hearth* to be presently noticed. The browse cleaned from slag is thrown back into the fur- nace, and its behaviour observed ; should it appear to melt too readily, it is rendered less fusible by adding a little lime, lest it should run down to the bottom of the furnace with the metallic lead ; on the other hand, if it does not become soft enough to permit the lead to separate, lime must also be added to soften it. These apparently opposite effects of the addition of lime are due to the bases not readily fusible per se at that temperature being present in excess, thus thickening the slag ; whilst, in the second case, they are only in sufficient quantity to form fusible compounds with the silica, &c. A peat is now placed before the opening of the blast- pipe, in order to prevent any dust from entering it, and a quantity ot roasted ore with a little coal is thrown in. After The Slag-Hearth. 3 1 3 about twenty minutes, the charge is again raked out on to the work-stone, the grey slag picked out, the remainder thrown back into the furnace, and a fresh charge of roasted ore and coal added. These operations are repeated during 14 or 15 hours, in which period one or two tons of lead will have collected in the outer basin, according to the richness of the ore, and the proportion (varying from -jVth to -^th of the whole) which has been removed in the grey slag. The separation of the metallic lead is partly due to the action of the sulphuret upon the sulphate and oxide of lead, as explained at p. 304, and partly to the removal of oxygen from the oxide by the carbon of the fuel. The lead extracted in the ore-hearth is purer and softer than that obtained by the reverberatory furnace, the tempe- rature being so low that the other metals contained in the ore are not reduced. Smelting of Sfags, &<:., in the Slag-hearth. In this opera- tion the object is to extract as much of the lead as possible from the slags and other residues, without reference to its purity, by the employment of a very high temperature, so as to completely liquefy the slag. The general construction of the fur.iace (Figs. 91, 92) is not very different from that of the ore-hearth, but it is larger, being 3 feet high, and 26 inches by 22, internal area. The sides are built of sand- stone, in order to resist the much higher temperature of this furnace. The bottom (A) of the furnace consists of a cast- iron plate, and is covered with a layer, about 16 inches thick, of porous cinders tightly rammed down, which serves as a strainer to separate the lead from the slag, since the melted metal easily percolates into the porous cinders, which protect it from being oxydised again by the air, and runs thence into a receptacle (B) outside the furnace, which is also filled up with similar cinders, and has an opening through which the lead flows into an iron pot (E) kept hot over a separate fire. The slag runs off the surface of the 314 Metals: their Properties and Treatment. layer of cinders, both in the furnace and in the receiving basin, and falls into a cistern of water (c), where it breaks up, so that the lead entangled in it is easily separated by wash- ing. The fire is lighted with peats as in the ore-hearth, the learth for extracting Lead. blast being forced through a nozzle at the back of the furnace, about four inches above the layer of cinders. Some coke is then thrown in, and about six hours after, when the temperature is sufficiently high, a charge of the slags, &c., which are to be smelted. Coke and slags are thus added in FIG. 1,2. Plan of Slag-hearth. alternate charges, as in the iron blast-furnace, until the fur- nace requires repair. The charge for the slag-hearth commonly consists of: 100 parts of slag from the reverberatory furnace; 20 coal-ashes ; 'i .< clay-hearths of old furnaces, impregnated with lead; f . , rich slag from a previous operation. Econoinico Furnace, 3^5 The silica and alumina present in the clay and in the coal-ashes combine with the lime and oxide of iron in the slag from the reverberatory furnaces, and form an easily- fusible slag. The lead is reduced to the metallic state mainly by the action of the heated carbon, which removes the oxygen from the oxide of lead. The coke is piled up towards the front, and the charge towards the back of the furnace, and a nose or prolongation of the tuyere is allowed to be formed by the solidified slag, so as to carry the blast up the centre of the furnace. When a cold-blast is em- ployed, this nose is apt to become too long, so that air heated to about 300 F. is found to answer better, beside effecting a considerable saving of fuel. If the blast is too hot, the slag will not be chilled so as to form a nose. A very inferior description of lead (slag-lead] is obtained from the slag-hearth. In some parts of Spain, lead is extracted from the slags of the Roman lead-furnaces. Richardson's Furnace, or the Economico Furnace, which is employed in Newcastle and the neighbourhood instead of the slag-hearth, as well as for the extraction of lead from the ore, is a modification of the Castilian furnace (Fig. 93), being also a blast-furnace, in which the blast is either supplied by a blowing-engine through three tuyeres or blast-pipes, or is drawn into the furnace through five or six openings, by the action of a small chimney. The body (A) of the furnace is circular and is built of fire-brick, about 8^ feet high and 2^ feet in diameter, the bottom (B) being lined with a mixture of clay and powdered coke, well beaten down, and holloAved out to receive the lead. The ore, or mixture of ore and slag, smelted in this furnace, must not contain more than 30 parts of lead in the hundred. The ore is roasted previously to its introduction into the furnace, which is charged with ore and fuel through an opening (i) in the square brick structure sup- ported on four pillars, which surmounts the furnace, and, if necessary, the charge is sprinkled with water from a rose, to -Castilian Furnace for Lead A, Body of the furnace. B, Cru- , Ma; -jr the lead. G, H, Spout for overflow of slag. i. < Margins-door, k.. V\tu cible for receiving the lead, c, Blast-pipe. D, Masonry enclosing the top of the furnace. E, Cast-iron pillars, f. Receptacle for the lend. G, Slot fa t.h". tapping-hole. p vj. Ground line. Calcination of Hard Lead. 3 1 7 prevent the dust from being carried into the flue. The slag flows over the side of the hearth, as in an iron blast-furnace, into cast-iron waggons, whilst the lead accumulates in the cavity at the bottom, and is tapped out from time to time into an iron basin (F). Limestone is sometimes mixed with the charge, to flux the siliceous matters. At Clausthal in the Hartz, the galena is reduced by fusing it in a small blast-furnace or cupola-furnace with granu- lated cast-iron, which combines with the sulphur to form a sulphuret of iron, and sets the lead at liberty. The sulphuret of copper which is present in the ore is not decomposed in the process, but forms a matt upon the surface of the lead, and after converting the sulphuret of iron into oxide by roasting, and removing the oxide by fusion with siliceous matters, the sulphuret of copper is sent to the copper smelting-works. At some works, slags from the refining of iron (p. 163) are employed to assist in the decomposition of the sulphuret of lead. When ores in a finely divided state form part of the charge of the slag-hearths and cupola fur- naces on the Continent, they are often mixed with clay or lime and moulded into bricks before being thrown into the furnace. Softening of Lead in the Calcining or Improving Furnace. The lead obtained by either of the above processes some- times contains considerable quantities of silver, antimony, copper, and iron, which harden the metal and render it unsuitable for some of its applications. English lead is the purest which is to be found in commerce, and Spanish lead is the most impure ; the composition of two samples in 100 parts is here contrasted : English Spanish Lead .... 99^27 95'8i Antimony . . . 0-57 3-66 Copper . . . . 0-12 0-32 Iron .... O'O4 O'2i Even the English specimen is sufficiently impure to be designated a hard lead. 3 1 8 Metals : their Properties and Treatment. When the lead contains any notable proportion of silver, it is treated by a special process to be described hereafter, but when the hardness is due to the presence of antimony, &c., the lead is softened or improved by exposing the melted metal in a very shallow pan to the action of the oxygen of the air, which converts the antimony, copper, iron, and a considerable portion of the lead, into oxides, which collect as a dross upon the surface, and are skimmed off at intervals, until the lead is found to be sufficiently softened. The improving furnace (Figs. 94, 95) is a reverberatory furnace with a low arch, 18 inches above the hearth near the fire-bridge, and 6 inches near the chimney, towards which the flame is drawn by two flues (F). Since a large FIG. 94. Calcining Furnace for improving Hard Lead spreading flame is required, the fireplace (D) is 5 feet long and 1 8 inches wide, being divided from the hearth by a fire- bridge 27 inches wide and 16 inches above the hearth (B). In the hearth of the furnace there is set, with a space round it to allow for expansion, a cast-iron pan measuring 10 feet by 5, which is 8 inches deep at the end nearest the grate, and 9 inches at the other end ; at this deepest end there is an iron gutter (/) stopped up during the process, by an iron plug with a weighted lever through which the lead may be run out when it is sufficiently refined. Eight or ten tons of the hard lead are melted in an iron pot (G) and ladled into a gutter (H) through which they run into the improving pan, which has been already heated to Improvement of Hard L cad. 319 dull redness ; the gutter is then closed by a damper, and the improving process commences. Its duration depends upon the amount of the foreign metals (especially of anti- mony) which the lead contains, a single day's calcination being sufficient to soften some leads, whilst others require two or three weeks' exposure to the action of the air which passes through the furnace. The dross is raked off occa- sionally, so as to expose the surface of the metal, and the progress of the refining is observed by ladling a small sample into an ingot-mould, when its surface assumes a peculiar crystalline appearance if the refining is completed. The FIG. 95. Plan of Improving Furnace. refiner also judges that the lead is sufficiently softened, if a rainbow or iridescent film is formed upon the surface when a rake is pushed over it from the working door. The softened lead should not form round globules when poured upon a heated iron plate. The dross, which consists chiefly of the oxides of antimony and lead, is mixed with coal and ground under edge-runners, previously to being smelted in a small reverberatory furnace, the hearth of which gradually slopes down towards the chimney, where there is a cavity for the reception of the metal, which constantly flows out through the tap-hole into an iron pot, to be afterwards transferred to the pig-moulds. 320 Metals : tJicir Properties and Treatment. The hard lead thus obtained is either again calcined \vith a fresh portion of metal, or if it contains a very large propor- tion of antimony (of which some specimens contain a third of their weight), it is sold to the type-founders. The process of improving the moderately hard lead pro- duced at Altenau in the Upper Hartz resembles the boiling of tin, and consists in melting about 1 1 tons of the metal in an iron pot 5^ feet deep and 3 feet wide, and stirring it for two hours with a birchen pole moved by machinery, when the violent bubbling of the gases through the metal continually renews the surface in contact with the air, causing the formation of dross containing the impurities. In France, the improving furnaces often have two fires, one at each end of the pan. Another method of improving very hard lead consists in melting it, as above, in a cast-iron pan, and throwing upon the skimmed surface a small quantity of a mixture of Peru- vian saltpetre (nitrate of soda), soda and lime, the addition being repeated until the metal is sufficiently softened ; the oxygen of the saltpetre converts the antimony into antimonic acid which combines with the soda and lime, and is removed as dross, together with a considerable quantity of oxide of lead Refining of Lead containing Silver by Pattinson's Process. This very simple and beautiful process, which was introduced in 1829, has not only greatly improved the quality of lead, but has very much increased the production of silver in England; previously to that date no process existed by which the silver could be removed so as to leave the lead in the metallic state, and it was necessary to convert the whole of the lead into an oxide in order to separate the silver, this oxide being afterwards smelted to recover the lead. Since this could not be made to pay unless the lead contained at least eleven ounces of silver in the ton, any smaller quantity of silver was left in the lead sent into the market, the lead being thereby hardened, and the silver entirely lost for all Pattinson's Process. 321 useful purposes. After the introduction of Pattinson's pro- cess, much of the old lead was eagerly bought up for the sake of the silver which it contained. The process depends upon the property of lead to crystal- lise at a lower temperature than an alloy of lead and silver, so that if melted lead containing a small proportion of silver be allowed to cool slowly and constantly stirred, the small crystals of lead which are formed at first will contain little or no silver, that metal remaining in the liquid portion. To carry out this principle, a series of melting-pots is em- ployed. The number of pots as well as their form and general arrangement will differ somewhat in different esta- FIG. 96. Foes for desilverising Lead. blishments, but for the sake of illustration, a desiherising plant containing five pots may be taken (Fig. 96). These pots are made of cast iron and set in masonry ; the working- pots, i, 2, 3, and 4, are oval in shape, their mouths being 40 inches by 26, and they are shaped at the bottom like the small end of an egg. 5 is the market-pot for melting the desilverised lead before casting it into pigs ; it is smaller than the others. The smallest pots (about two feet in diameter), between i and 2, and between 3 and 4, are the temper-pots, for containing the melted lead in which the perforated ladle (Fig. 97) is warmed, which is used for fishing out the crystals of lead. This is an iron ladle about 18 inches wide and 5 inches deep, with an iron handle of 4^ Y 322 Metals: their Properties and Treatment. feet and a wooden handle of about 5 feet in length ; the holes in the ladle are \ inch wide and inch apart. Each pot is heated by a separate fire. The lead to be refined is usually in pigs (or salmons) weighing from 120 to 140 Ibs. each. About 64 of these (or 4 tons) are melted in pot i. (See Fig. 98.) When they are perfectly melted, the fire is raked out, and the oxide is skimmed from the surface of the lead. In order to hasten the cooling of the metal, one or two pigs of cold lead are thrown in, or a little water is thrown upon the surface so as to form a solid crust, which is then pushed down into the liquid metal. This is continued until crystals of lead begin to J. ti form. The workman then detaches any lead which has solidified on the sides of the pot, and stirs- the melted metal with an iron bar in order to preserve an equal temperature throughout. I Another workman takes the perforated ladle out of the temper-pot in which it has been heated, and fishes up the crystals which have formed. The handle of the ladle is then rested upon a pig of lead faced with iron placed at the edge of the pot to serve as a fulcrum, and the workman seizes the end of the long handle, and jumps down from the platform around the pots on to the floor, thus tilting the ladle up out of the melted lead, over which he shakes it violently so as to drain all the liquid metal back into the pot. The ladle is then swung by a crane over pot 2, into which the crystals are thrown ; after this has been repeated for an hour, only about one ton of lead richer in silver is left in pot i, the quantity being ascer- tained by trying the depth of the metal in the pot. The removal of the crystals is still proceeded with, but P Pattinsous Process. 323 since these will now contain too much silver to be introduced into pot 2, they are thrown upon the ground in order to be afterwards melted up with more lead in pot i. When only ton of the rich liquid alloy is left in pot i, it contains about three times as much silver as the original lead, and is ladled out and cast into eight pigs, which often contain as much as 150 ozs. of silver in the ton, together with any copper and FIG. 98. Desilverizing Lead by Pattinson's Process. antimony which were contained in the original lead ; whilst any arsenic which was present will have passed into the crystals. The half-ton of crystals which have been thrown upon the ground are now melted in pot i with a fresh quan- tity of the original lead, and treated as before. The three tons of crystals of lead poor in silver which were transferred to pot 2, are made up to four tons by adding 324 Metals: tJicir Properties and Treatment. lead of the same richness in silver, and submitted to a repe- tition of the same treatment, about three-fourths of it being transferred, in crystals, to pot 3, one-eighth of it, in the form of richer crystals, being thrown upon the ground to be re- melted in pot 2, and the remainder, which is left in the liquid state at the bottom, is ladled out into pot i. The crystals in pot 3 are treated in the same way, the portion remaining liquid being transferred to pot 2, and the poorer crystals melted in pot 4. Finally the crystals of poor lead formed in pot 4 are ladled into pot 5, to be cast into pigs, which are treated again, if necessary, until the silver is at last reduced to half an ounce in the ton. By a single operation in the four pots, as just described, the silver in the market- able lead is reduced to one-tenth of its original amount. The process of cupellation for extracting the silver from the rich lead is described under Silver. The quality of the lead is greatly improved by Pattinson's process, not only because the bulk of the antimony and copper remain with the silver in the liquid portion, but because these and other impurities which tend to harden the lead are converted into dross by the oxygen of the air, pre- cisely as in the improving or calcining process. The description just given refers to an operation with Pat- tinson's process, upon the low system, as it is termed, in which |ths of the contents of each pan are removed in crystals, whilst according to the high system only f rds are removed. The high system is preferred for the treatment of the leads richer in silver and of otherwise impure quality, as many as fifteen pans being sometimes employed, so that there is a greater chance of oxidising the impurities. Both systems are combined in some establishments, in order to suit the different descriptions of lead. In working the high system, it is generally found that the crystals taken out of a given pot contain about half as much silver as the alloy originally contained; thus nine tons of a silver-lead containing ten ounces of silver to the ton would yield six tons of crystals Pattinsons Process. 3 2 5 containing only five ounces co the ton, and three tons of liquid alloy containing twenty ounces to the ton. Where many pans are employed, they are commonly hemispherical, being about 5 feet wide and 2\ feet deep. If the lead contains as much as 60 ozs. of silver in the ton, the third pan is selected for melting it, but if it contains only seven ounces in the ton, it is melted in the yth pan, an intermediate pan being selected in other cases. As much as twelve tons of lead are sometimes melted, to begin with, upon the high system, and two-thirds of it are ladled out in crystals into the next left-hand pan an opera- tion requiring about two hours. The liquid alloy is then chilled into a pasty condition by throwing water upon it. and ladled out into the next right-hand pan, the melting- pot being again charged with twelve tons of the original lead; after a sufficient quantity of metal has accumulated in the adjacent pots, the crystal! ising operation is repeated with their contents, the two-thirds of crystals being always trans- ferred to the next left-hand pan, and the one-third of liquid alloy to the next right-hand pan. Supposing, therefore, the rule to hold good, that the crystals contain half as much, and the liquid twice as much silver as the silver-lead from which they were obtained, the lead would be found, after passing through four pots to the right of the melting-pot, to contain sixteen times as much silver as the original lead, whilst, after it had passed through four pots to the left of the melting-pot, it would contain only one-sixteenth of the original proportion of silver, as indicated below, where a lead containing seven ounces of silver in the ton is supposed to have been melted originally in pot No. 7. 44802. 224 OZ. II20Z. 5602. 28 OZ. 14 OZ. per ton. per Ion. per ton. per ton. per ton. per ton. No. 7. No. No. 9. No. 10. No. n 7 oz. 3| oz. i\ oz. \ oz. T 7 5 oz. per ton. per ton. per ton. per ton. per ton. 326 Metals : their Properties and Treatment. Instead of waiting until the proper quantity of metal for crystallising has accumulated in a given pot, the right com- plement of a sample of lead of the richness suitable to that pot is commonly added from the stock kept in the establish- ment A modification of the Pattinson process, in which hand- labour is largely superseded by the use of machinery, is in use at some works. In this process the agitation of the metal during crystallisation is affected by means of steam. Two pots only are required, one placed above the other ; the lower one, which has a capacity of about 36 tons at least double the upper one is raised above the floor about 1 2 inches. The lower pot is covered in at the top with doors and communicates with condensers. A crane is so placed that it can command the two pots and the ingot moulds. The lead to be desilverised is charged into the top pot by means of the crane ; when it has melted the door is re- moved, and the lead run into the lower pot among the crystals resulting from a previous operation : the crystals melt ; the pot is then drossed and a jet of steam introduced. The steam is uniformly distributed by means of a baffle- plate placed above the nozzle. To hasten the formation of crystals, small jets of water are made to play on the surface ; the cooled portion sinks into the molten mass, and gradually lowers its temperature to the crystallising point, the action taking place uniformly, owing to the mixing effect of the steam-jet. This part of the operation is carried on until two-thirds of the pot have crystallised ; the third remaining liquid is then drained off through two pipes, controlled by valves, the crystals being retained in the pot by means of perforated plates. A 36-ton pot can be worked off in about an hour. After the lead has been tapped out from the working-pot, a fresh charge of lead is run in, having the same richness as the residual crystals from the last opera- tion, and so on. By the use of this process subsequent softening of the lead is rendered unnecessary, such impurities as antimony, Parked Process. 327 arsenic, copper, zinc, and iron, being removed by the poling action of the steam ; zinc and iron being directly oxidised with liberation of hydrogen. There is admittedly a saving in fuel and labour in this process, and also the cost of softening is avoided. These advantages are, however, about counter-balanced by the original outlay for plant and the expenses for repairs. The only method which in any way rivals the Pattinson process, and then only for special classes of lead, is that introduced by Parkes. This process depends on the two following facts : 1. That lead and zinc, however intimately mixed, do not alloy, and on being slowly cooled almost completely separate from one another into two layers. 2. That silver has a greater tendency to alloy itself with zinc than with lead. Consequently, if zinc be melted and well stirred in with lead containing silver, on slowly cooling the mixture the zinc will rise to the surface, carrying with it the silver. The charge of silver-lead is usually about 15 tons ; its temperature has to be raised to a point considerably above that required for Pattinsonising. The quantity of zinc added is regulated by the amount of silver contained in the lead ; for lead containing about 50 ozs. of silver to the ton the zinc required would be about i^ per cent, of the charge. The zinc is added in several portions, the pot being cooled after each addition, causing a crust of argentiferous zinc to form on the surface, which is lifted out of the pot, and, having been drained as much as possible of the more fusible lead, is placed in a smaller pot for subsequent treatment The lead is finally obtained free from silver, and containing only \ to | of i per cent, of zinc, which is sometimes left in, but generally removed by melting the lead in a rever beratory furnace, and exposing its surface to the action of the air until the zinc is all oxidised out, which is readily affected, especially if it be poled with green wood. " In some works the zinc is removed by oxidising it with steam : 328 Metals: their Properties and Treatment. the advantage of this plan is doubtful. As much lead as possible is allowed to sweat out from the zinc crusts in the pots, after which they are mixed with lime and carbonaceous matter, and placed in retorts or crucibles, where the zinc is distilled off and condensed as far as possible. The residue, containing the silver and some lead, is melted, and the argentiferous lead cupelled for the extraction of the silver. In this process the cost of plant and the expenses for labour are small, the lead can be rapidly treated, and only a small working stock is required. Against this has to be set the cost of the zinc lost, which is considerable. Uses of Lead. Many of the uses of lead result from its softness and plasticity, properties which it possesses in a higher degree than any other metal commonly used in the metallic state. The ease with which it may be rolled into sheets recommends it for roofing and for lining sinks, cisterns, &c., particularly since it can be easily adapted to any shape with the aid of a mallet. Again, its softness enables it to be made into pipes, either by casting a very thick cylinder round an iron core and drawing it through progressively diminishing steel dies, or by forcing the melted metal, by hydraulic pressure, through a steel cylinder with a core, from which the solidified metal issues with the required form and dimensions. The great weight of the metal (specific gravity 1 1 '4) is unfavourable to its employment for roofing, and its ready fusibility (at 620 F.) is another disadvantage, the terrors of a conflagration being sometimes aggravated by the pouring down of the melted lead from the roof. The poisonous nature of the compounds of lead renders it dangerous to use it for cisterns and pipes with which water, and especially soft water, is to remain in contact for any considerable period, for although lead itself is not acted upon by water, the oxygen of the air, which is always held in solution by water, readily converts a portion of the lead into an oxide of lead, which is dissolved in small quantity by the water ; even if a very minute proportion of oxide of Alloys of Lead and Antimony. 329 lead be dissolved in the water, repeated doses of it will give rise, in tlie course of time, to the most painful symptoms, Leaden pipes coated internally with tin, to resist the action of water and air, are made by drawing out two concentric cylinders of lead and tin. The use of lead in connection with cider-vats and presses is highly blameable, for the lead is dissolved in large quantity in contact with the acid liquid, and a moderate draught of such cider may easily contain a poisonous dose of the metal. The want of tenacity exhibited by lead prevents it from being drawn into thin wire. Its softness enables lead to mark paper, which rubs off minute particles of the metal ; the pencils in use for metallic memorandum books are composed of lead hardened by the addition of tin and bismuth. The easy fusibility of lead adapts it to the use of the type-founder, but it is far too soft to be employed alone for this purpose, and is therefore hardened by the addition of antimony. Type-metal is an alloy of lead with one-third or one-fourth of its weight of antimony. An improved description of type-metal, lately introduced, is composed of two parts of lead, one part of tin, and one of antimony. Another alloy employed for the same purpose contains fifteen parts of lead, one part of tin, and four parts of antimony. The high specific gravity as well as the fusibility of lead recommend it for making bullets and small shot, where great momentum is required in a small compass. Rifle bullets must be made of very pure soft lead in order that they may easily take the grooves of the rifle, and the iron projectiles of rifled ordnance are coated with lead for a similar reason, but a somewhat harder lead is employed here ; the surface of the shot or shell to be coated is thoroughly cleansed, then clipped into solution of sal-ammoniac, and afterwards into melted zinc, the coating with this metal being found to cause a firmer adhesion of the lead into which the missile is next plunged. 330 Metals : their Properties and Treatment. Bullets intended to be discharged from smooth-bore small arms, especially those for breech-loaders, which are of small size, are commonly hardened by the addition of one-fifth of their weight of antimony, in order to give them greater penetration. The bullets employed in shrapnel shells are also composed of four parts of lead and one part of antimony, partly for the sake of penetration, and partly that they may scatter better, bullets of soft lead being liable either to be jammed together by the force of the explosion, or so dis- torted as to make a very short flight when the shell bursts. Small shot for fowling-pieces are composed of lead con- taining from three to six parts of arsenic in a thousand, which has the effect, not only of hardening the lead slightly, but also of enabling it to take a nearly spherical form when the melted metal is dropped through a colander into water. Another condition for securing spherical shot is the proper cooling of the drops before they fall into the water, for if they are suddenly chilled and solidified externally long before the inner portion solidifies, the shrinking of the latter, as it cools, causes the outer layer to collapse, and the shot becomes deformed. Probably the effect of arsenic in securing the spherical shape is due to its diminishing the contraction of the still liquid lead as it cools after the outer portion has solidified. In order to cool the drops before they enter the water, they are commonly allowed to fall through the air from a considerable height, either in a shot-tower, or in the disused shaft of a mine ; or the same object is sometimes attained by employing a rapid blast of air, when a high fall may be dispensed with. The larger the size of the shot, the more preliminary cooling will they require, so that large shot are allowed to fall through 150 feet, and small shot through 100 feet. In order to prepare the metal, it is usual to alloy a quantity of lead with a large amount of arsenic, and to add this to melted lead in the proper proportion. A ton of soft lead is melted in an iron pot, and 40 Ibs. of arsenic added to it; the pot is covered with an iron lid, and the Uses of Lead. 331 joints cemented with clay to prevent the arsenical vapour from escaping ; the metal is kept melted for three or foui hours, then carefully skimmed, and cast into pigs. The arsenic is added sometimes in the metallic state, sometimes as white arsenic (arsenious acid, composed of arsenic and oxygen) or as orpimcnt (sulphuret of arsenic), the two last being decomposed by the lead, and converting a portion of that metal into oxide or sulphuret. Two or three tons of inferior lead having been melted, five or six pigs of the arsenical lead are added, and well stirred up with it ; a small sample is allowed to fall from a height, through a per- forated ladle, into water; if the drops become flattened, too much arsenic has been added, if they are pear-shaped, there is too little. The colanders are wrought-iron bowls about 10 inches wide, perforated with smooth holes varying in size with ihe description of shot required. In order some- what to delay the passage of the melted lead through the holes, the colanders are lined with the cream or scum of oxide which forms upon the surface of the metal. The temperature of the lead when poured into the colanders is scarcely adequate to scorch straw. The drops then fall from the top of the shot-tower into a vessel of water at the bottom. They are afterwards dried on a hot plate, sifted into different sizes, the deformed shot rejected by gently shaking on a slightly inclined table, when only the spherical shot roll down, and these are polished in a revolving cask containing a little plumbago. Lead is extensively employed in the construction of vessels for various chemical manufactures, since it resists the action of sulphuric, muriatic, and fluoric acids in a far higher degree than iron, copper, zinc, or tin. Even nitric acid, if strong, scarcely attacks lead, though the diluted acid readily dissolves it. The large chambers in which sulphu- ric acid is manufactured are built of leaden plates weighing 5 or 6 Ibs. per square foot. Here the fusibility of the metal becomes an advantage, for they have to be united by being 332 Metals: their Properties and Treatment. burned together, that is, by directing a hydrogen flame along the edges of the plates so as to unite them without the inter- vention of solder, which would soon be corroded under the action of the acid. This is sometimes called autogenous soldering. Notwithstanding that lead is unacted upon in the cold by strong acids, it is very soon extensively corroded when ex- posed to the action of air in the presence of carbonic acid, and becomes eventually converted into a mass of white lead or (basic) carbonate of lead. Since carbonic acid is produced abundantly by the decay and putrefaction of animal and vegetable matters, metallic lead is much affected when kept in contact with such substances in the presence of air, the oxygen of which unites with the lead to produce an oxide of lead which then combines with the carbonic acid and forms a carbonate. The lead of old coffins is sometimes found to have become almost entirely converted into an earthy-look- ing mass of white lead in this way, a very thin plate of lead remaining in the centre. The oldest process for the manu- facture of white lead depends upon the corrosion of the lead in this manner. In breech-loading cartridges, where grease is employed as a lubricator, the bullets have sometimes become partly con- verted into white lead, and have thus increased so much in bulk as to burst open the copper case of the cartridge and render it useless. Alloys of Lead and Tin. Pezvter* is an alloy of four parts of tin with one part of lead; it is harder, possesses more tenacity, and melts more easily than either of the metals separately, and provided that the lead does not exceed this proportion, the alloy may be used for drinking-vessels without any danger of lead-poisoning. Since, however, lead is far cheaper than tin, a larger proportion than one-fifth of lead is often employed, when the lead is apt to be dissolved if left in contact with the acetic acid always present in beer. * Probably corrupted from the French, fotie, pot. Potte detain is the French for pewter. Soldering. 333 Pewter made with the above proportions has the specific gravity 7*8, so that specimens having a higher specific gra- vity than this will be known to contain more lead. The solder employed by the pewterer is a very fusible alloy of tin, lead, and bismuth. The solder used for tin- plate is an alloy of lead and tin. Common solder contains equal weights of the two metals ; fine solder contains two parts of tin and one of lead ; coarse solder, two parts of lead and one of tin. In making solder, the proportions of the metals can be judged of from the appearance of the alloy. When it contains a little more than one-third of its weight of tin, its surface, on cooling, exhibits circular spots due to a partial separation of the metals ; but these disappear when the alloy contains two-thirds of its weight of tin. These alloys melt at a much lower temperature than either of their constituent metals. Common solder melts at 385 F. ; fine solder at 372 F., whilst the melting-point of tin is 442 F., and that of lead is 620 F. Soldering is scarcely to be regarded as a merely mechani- cal adhesion, but depends probably, in part, upon the forma- tion of an alloy between the solder and the surface of the metal to be soldered. Hence it is absolutely necessary that the surfaces to be united by the intervention of solder should be perfectly bright and free from oxide. Several substances are employed to ensure this at the moment of applying the solder; one of the commonest is muriatic (hydrochloric) acid killed vr'\\h zinc, that is, in which a lump of zinc has been dissolved, partly with the object of saturating a portion of the acid, partly to form a chloride of zinc which melts over the surface of the work, dissolving any oxide, and protecting the metal from the oxidising action of the air. Sal-ammoniac (muriate of ammonia), which contains hydro- chloric acid combined with ammonia, is also employed, the hydrochloric acid removing any oxide from the metallic surface; sometimes a combination of sal-ammoniac and chloride of zinc is used. Rosin in powder is often sprinkled over the metal to be soldered, when the heat melts it and 334 Metals: their Properties and Treatment. forms a varnish to protect its surface from the oxygen of the . air. Hard soldering or brazing, for uniting the edges of iron, copper, or brass, is effected with an alloy of brass and zinc made by adding zinc to brass melted in a covered crucible ; the alloy is granulated by pouring it through a bundle of twigs held over a tub of water, and before being used for brazing it is mixed with a little moistened borax, which melts when the heat is applied, dissolving off any oxide from the metals, and protecting them from the action of the air. For fine work, a little silver is added to the alloy, which is thus rendered much more liquid when fused. Tcnie-plate resembles ordinary tin-plate, but is coated with an alloy of tin and lead ; it is _ largely exported to Canada, where it is employed for roofing. SILVER. This metal being, in general, a far less chemically active metal than the preceding, that is, being less likely to enter into and remain in a state of chemical combination with other substances, is much more frequently met with in the metallic or native state. Native silver has generally the appearance of metallic twigs and branches, which are sometimes composed of crystals of silver strung together. The silver-mines of Potosi exhibit such specimens. Native silver is also found at Kongsberg in Norway, at Andreasberg in the Hartz, Freiberg in Saxony, and Schemnitz in Hungary. The native metal generally contains small quantities of gold and copper. At Kongsberg a yellow alloy is found which contains silver with more than one-fifth of its weight of gold. An amalgam of silver with mercury is found in large quantity in the silver-mines of Coquimbo, Chili. Ores of Silver. 335 Sulphuret of silver, or silver-glance, containing, in its pure state, 87 parts of silver combined with 13 of sulphur, is one of the commonest forms of combination in which silver occurs in nature. It has been found, in a pure state, in Cornwall, Norway, Hungary, Saxony, Bohemia, Mexico, Peru and the United States. It has a slight lustre, and a dark grey colour, possessing also, which is remarkable in an ore of this description, a good deal of malleability and flexibility, and it is so soft that it may be cut with a knife. It is also distinguished by its fusibility, being easily melted even in an ordinary flame. The sulphuret of silver is more abundant in association with the sulphurets of other metals; thus, in argentiferous galena, with sulphuret of lead ; in grey copper ore, with the sulphurets of copper, antimony, arsenic, iron, and zinc ; in brittle silver ore, with the sulphurets of antimony, iron, and copper ; in red silver ore, with sulphuret of antimony or sulphuret of arsenic. Blende, iron pyrites, mispickel, and some other minerals sometimes contain a minute proportion of silver, which may be extracted with profit, incidentally to other processes. Horn-silver or chloride of silver contains, when pure, 75 parts of silver united with 25 parts of chlorine. Good specimens of this ore exhibit, as its name implies, some resemblance to horn in appearance and softness. It is found abundantly in Chili and Peru, sometimes in large fragments, but more commonly in very small cubical crystals disseminated in a ferruginous rock. The butter-milk ore of the German miners contains chlo- ride of silver mixed with a large proportion of clay. Chloride of silver has been found, in small quantity, in Cornwall. Bromide and iodide of silver are also found in Mexico and Chili. In consequence of the high price of silver, it admits of being extracted with profit even from ores which contain a very small proportion of the metal, especially if some other useful metal can be extracted at the same time. Thus, 336 Metals: their Properties and Treatment. silver may be profitably obtained from galena containing only two parts of silver in a thousand, and even a smaller quantity than this is extracted from some copper ores. In these cases, the lead and copper respectively are extracted by the ordinary smelting processes, and are then subjected to special treatment for the extraction of the silver. It may be well to describe the principal methods in use for this purpose before considering the metallurgic treatment of the ores of silver with the sole object of extracting that metal. FIG. 99. English Cupel or Test. Extraction of Silver from Lead by Cupellation. Most of the silver produced in this country is extracted by this process from the rich lead obtained in Pattinson's desilver- ising process (p. 320). The process of cupellation, which is one of the most attractive metallurgic operations, derives its name either from the German kuppel, a cupola or dome, in allusion to the shape of the German cupellation furnace, or from a diminu- tive derived from the Latin cupa, a cup, referring to the concave hearth upon which the process is carried out. 337 The extraction of silver from lead by cupellation depends upon the facility with which the latter metal is converted into an oxide by the action of air at a high temperature, whilst silver is almost entirely unaffected ; the oxide of lead being easily melted, is partly removed from the surface in a liquid state, and partly absorbed by the porous hearth upon which the silver remains. In England, this hearth, which is called the cupel or test, is an oval frame of wrought iron (A, Fig. 99), 5 feet long and 2\ feet wide, which is crossed by five iron bars (a) 3^ inches in breadth. This frame is filled with finely-powdered bone ashes mois- tened with water, in which a little pearl- ash (carbonate of potash) has been dissolved ; this is well consolidated by beat- ing, and scooped out until it is about f of an inch thick over the cross bars, leav- ing a flat rirn of bone- ash all round, about 2 inches wide, except at one end (B), the front or breast of the cupel, where it is 5 inches wide ; through this a channel (F) is cut, to allow the melted oxide of lead to flo\v off without coming in contact with the iron, which it would corrode very seriously. This cupel rests upon a car, in order that it may be wheeled into its place under the reverberatory furnace (Fig. 100). of which FIG. loo. English Furnace for the cupellation of Lead. 338 Metals: tJicir Properties and Treatment. it forms the hearth (c), where it is arranged so that the flame of a coal fire (G) passes directly across it to the two rlues, which run into a chimney (B), about 40 feet high. A blast pipe or tuyere (N) enters the cupel at the end opposite to that through which the oxide of lead escapes, and throws a blast of air over the surface of the metal at the rate of about 200 cubic feet per minute. Opposite to the tuyere is a hood with a pipe (H) for carrying the fumes into the chimney. The cupel is very gradually heated nearly to redness, and almost filled with the lead to be treated, which is ladled in from an iron pot (P), in which it has been previously melted. From 500 to 600 Ibs. of lead are introduced at once. In a short time, the surface of the metal becomes covered with oxide of lead, or litharge* in a melted state ; the blast is then turned on, and drives the litharge in wavelets off the surface, through the channel made for its escape, into a cast- iron pot outside the furnace. When this channel is very much corroded, it is closed, and another is cut. In propor- tion as the lead upon the hearth diminishes, fresh portions are ladled in from the melting-pot, so as to keep the lead at about the same level. The process is continued for sixteen or eighteen hours, in which time four or five tons of lead will have been added, and an alloy containing about eight parts of silver in a hundred will be left in the cupel. A hole is then made in the bottom, through which the metal is run out and cast into pigs. A fresh charge is introduced, into the cupel, and the operation continued ; one cupel will often last for forty-eight hours, and is capable of treating 5 cwts. of lead per hour, with a consumption of i cwt. of coal. When about 3 -tons of the rich alloy (containing 8 per cent, of silver) have been obtained, it is again subjected to cupellation in the same furnace, but in a cupel which has a concavity at the bottom intended for the reception of the cake of silver, which will weigh about 500 Ibs. This second operation is * From two Greek words, signifying sune and silver. Cupellation. 339 necessary, because the litharge which is formed from this very rich alloy contains a considerable proportion of silver, so that the lead obtained by smelting it (p. 340) and by smelting the cupel, which absorbs a large proportion of litharge, contains 30 or 40 ozs. of silver in the ton, and must be treated for that metal. , - The appearance of the metal in the cupel as the last por- tions of lead are removed in the form of litharge and absorbed into the bone-ash, is very beautiful. When the film of oxide becomes so thin that the bright silver beneath can reflect the light through it, a decomposition of the light into its con- stituent colours takes place, and the most brilliant rainbow tints are seen upon the metal, their beauty being enhanced by the rapid rotation of the film. As soon as this film of oxide has been absorbed by the cupel, the splendid surface of the melted silver shines out (fulguration, coruscation, or brightening). During the cooling of the cake of silver, some very remarkable phenomena are observed. When a thin crust of metal has formed upon the surface, the silver beneath it assumes the appearance of boiling, and the crust is forced up into hollow cones about an inch high, through which the melted silver is thrown out with explosive violence, some of it being splashed against the arch of the furnace, and some solidifying into most fantastic tree-like forms several inches in height. This behaviour of silver has been shown to be due to its property of absorbing mechanically (occluding) oxygen, at a temperature above its melting-point, which it gives off as it approaches the point of solidification, the escaping gas forcing up the crust of solid silver formed upon the surface. A considerable proportion of lead and silver is carried off by the blast, in the form of vapour, and is partially recovered, as oxide, from the flues of the furnace. In some cupellation furnaces, instead of employing a blowing machine, a current of air is directed over the surface 34O Metals : tlieir Properties and Treatment. by means of a jet of steam issuing from a tube surrounded by a wider one through which the air is dragged by the mechanical action of the steam. This is said to hasten the operation, and to produce litharge of better quality. The litharge produced in the English cupellation furnace is reduced to the metallic state in a reverberatory furnace with a hearth measuring 8 feet by 7, which is lined with bituminous coal ; this soon becomes converted into a porous coke, which protects the clay hearth of the furnace from FIG. 101. German CnpeJlntion-ftirnace. being corroded by the melted litharge, and forms a filter through which the lead runs towards the opening from which it is tapped. About 3 tons of litharge mixed with 6 cwts. of small coal are charged at once ; the carbon of the coal removes the oxygen from the oxide of lead com- posing the litharge, and reduces the lead to the metallic state. The lead thus obtained usually contains 30 or 40 ozs. of silver in a ton, and is introduced into its appropriate place in a series of Pattinson's pans (p. 320). Cupellation. 341 The German cupellation-furnace($\. 101, 102) differs from the English in having a fixed instead of a moveablc hearth (A), covered with an iron dome (c) lined with clay, which is capable of being lifted off by a crane (G). The hearth is circular, about 10 feet wide, and is lined with marl, or with an intimate mixture of clay and lime well beaten and hollowed out like a saucer, with a circular cavity about 20 inches wide and \ inch deep, in the middle, for collecting the cake of silver. Wood ashes, previously washed and well beaten down, are sometimes employed instead of marl. Two tuyeres (a) direct the blast across the hearth, and are pro- FIG. 102. Section of German CupeUatKMi-furnace. vided with butterfly -valves for guiding the blast over the sur- face of the metal. The fire-place (F) is situated in a square furnace adjoining the hearth, and is supplied, when prac- ticable, with wood, which gives a longer and clearer flame than coal. Impure leads can be treated by the German pro- cess, whilst the English method of cupellation is adapted for those which are comparatively free from antimony and copper. From 4 to 17 tons of lead can be cupelled at once, accord- ing to the size of the hearth, the pigs being placed upon a thin layer of straw. The heat is gradually raised so as to melt the lead, no blast being employed for the first three hours. When the metal is in a state of tranquil fusion, the 342 Metals: their Properties and Treatment. surface is skimmed to remove the dross, and the bellows are worked at the rate of about four or five strokes a minute, in order to renew the air over the surface, so as to promote oxidation. In about two hours, a stronger fire is applied, and the crust of oxide and of various mechanical impurities is skimmed off the surface through the opening (o) provided for the escape of the litharge. About an hour and a half is occupied in thoroughly cleansing the surface of the lead. The blast is now freely directed upon the melted metal, so as to produce litharge abundantly, and to drive it in waves through the outlet ( an d treated withhot water containing a little sulphuric acid, until the liquor which runs off no longer becomes milky when mixed with common salt, showing it to be free from silver. The solution of sulphate of silver, thus obtained, is run into tubs containing copper, where the silver is precipitated, and is afterwards washed with diluted sul- phuric acid to remove adhering copper. The sulphate of copper in solution is decomposed by metallic iron, and the copper is employed for precipitating the silver. The copper matt of Freiberg is sometimes roasted, to convert the sulphuret of copper into oxide, and is then boiled in leaden tubs with diluted sulphuric acid, which 360 Metals : their Properties and Treatment. dissolves the oxide of copper in the form of sulphate of copper ; this salt is obtained in marketable crystals from the solution. The residue, which contains the silver and gold, is washed, mixed with half its weight of litharge, and made up into balls, which are dried and smelted together with more litharge and lead-slags, when the lead obtained con- tains all the silver and gold, which are recovered from it by cupellation. Very poor ores have sometimes been treated by melting them, either in cupola or reverberatory furnaces, with iron pyrites, which takes up the silver. By smelting this pyrites together with galena, the silver is obtained with the lead, which may be separated from it as usual (p. 320). A considerable quantity of silver is now extracted by Claudet's process from Spanish pyrites, after it has been calcined for its sulphur, in the manufacture of sulphuric acid. This process is described under COPPER. Applications of Silver. Pure silver is far too soft to resist the wear to which it is subjected in common use. It is therefore hardened by alloying it with copper, a consider- able quantity of which may be added without material altera- tion of colour. The hardest alloy is that which contains 4 parts of silver and i part of eopper. The standard silver used for coin and for silver articles in England contains, in 100 parts, 92^ parts of silver and 7^ parts of copper; the French silver coinage contains poparts of silver and 10 parts of copper. When the copper exceeds this amount, it is oxidised when the alloy is exposed to the air, whence the tarnished appearance of the silver coinage of Prussia, which contains one-fourth of copper. In English commerce, the purity or fineness of silver is generally expressed as so many pennyweights (dwts.) better or worse than the standard silver, of which the troy pound contains 1 1 ozs. 2 dwts. of pure silver and 18 dwts. of copper (commonly called alloy). Thus the French coin, which contains 24 dwts. of copper in the troy pound, would be Frosted and Oxidised Silver. 361 described as worse 6 dwts., because it contains that quantity less silver than the English coin. Mexican dollars contain 23^ dwts. of copper in the troy pound, being worse 5^ dwts. Indian rupees sometimes contain only 12 dwts. of copper in the troy pound ; hence they are better 6 dwts., that is, they contain 6 dwts. more silver than the English standard. The specific gravity of English silver coin is 10-3, and since all the alloys used to make counterfeits have tin for their chief constituent, they have usually a lower specific gravity, so that the best method by which to test whether a florin, for example, is good, without injuring it, is to ascer- tain its specific gravity, by weighing it first in the ordinary way, and afterwards when suspended in water, and dividing its weight in air by the loss of weight in water, when the quotient, for a genuine coin, would be io'3. Of course, if the coin be new, it will be sufficient to ascertain that it weighs just as much as a good florin, and is of exactly the same diameter and thickness, which are readily measured by cutting a slit in a piece of cardboard through which a new florin will exactly pass. Standard silver is whitened by being heated until the oxygen of the air has converted a little of the copper at the surface into oxide of copper, which is dissolved off by im- mersing the metal in weak vitriol (diluted sulphuric acid) or in ammonia, or by boiling it in a solution of cream of tartar and common salt. The film of nearly pure silver which then remains at the surface exhibits a want of lustre and is called dead or frosted silver. It is brightened by burnishing. Oxidised silver, as it is erroneously called, is made by immersing articles of silver in a solution obtained by boiling sulphur with potash, when the metal becomes coated with a thin film of sulphuret of silver. The tarnish which is produced upon the surface of silver when exposed to air is also due to the formation of a coating of sulphuret of silver by the action of sulphuretted hydrogen ; 362 Metals : their Properties and Treatment. the sulphuret of silver is itself black, but a thin film of it upon the surface of the metal often exhibits the rainbow colours caused by the decomposition of the light reflected through it. Tarnished silver is most readily cleaned with a solution of cyanide of potassium, but this salt is so fatally poisonous that its general use should be discouraged. Am- monia (hartshorn) will also remove the film of sulphuret of silver if assisted by friction. Plated articles are made of an alloy of copper and brass coated with silver. The brass having been melted with the requisite proportion of copper in a black-lead crucible, is cast into bars 3 inches broad, i|- inch thick and 18 or 20 inches long. The two faces of the bar are carefully smoothed with a file, and a plate of silver -^th inch thick, and some- what shorter than the bar, is laid upon each face and tied with iron wire. A little saturated solution of borax is allowed to run in round the edges, in order that this salt may melt and dissolve the oxide off the surface of the brass when heated in the furnace. The bar is now laid upon a coke fire and heated until the surfaces of brass and silver have contracted a firm adhesion, when the compound bar is ready for the rolling mill. After rolling, it is cleaned with diluted sulphuric acid. Sometimes the clean copper surface is washed over with solution of nitrate of silver before applying the plate of silver. A thin film of silver would then be chemically deposited upon the surface of the copper and would both prevent oxidation and favour the adhesion of the silver plate. The plated wire used for making toast-racks, &c., is made of copper coated with silver. The strip of silver is bent round into the form of a hollow cylinder, its edges somewhat over- lapping ; a red-hot cylinder of copper is thrust into this, and the edges of the silver are joined together by rubbing with a steel burnisher. The copper core is then withdrawn, the tube of silver thoroughly cleaned inside, and slipped upon a bright copper rod so as to fit closely, leaving the ends of the Electro-plating. 363 copper somewhat projecting. Grooves are made in these ends, into which the silver is forced down, so as to exclude the air from the copper surface inside. The cylinder is made red hot and well rubbed with a steel burnisher, until the silver thoroughly adheres to the copper, which is then drawn into wire. Electro-plating is now very generally employed for coating articles of baser metal with a film of silver. This art consists in decomposing a solution containing silver, with the aid of a galvanic battery, in such a manner that the metal may be deposited upon the surface of the article to be plated ; German silver (p. 298) is generally employed as the material Process of Electro-plating. for the latter, the articles being then said to be electro-plated on white metal. They must be thoroughly cleaned by boiling them with soda, washing with water, and dipping into very weak aquafortis (dilute nitric acid) to take off the film of oxide ; they are afterwards washed, scoured with sand, again dipped in the weak acid, and finally rinsed in water. The articles to be electro-plated are suspended by stout copper wires (Fig. in) in a vessel of wood or earthenware containing a solution of cyanide of silver in cyanide of potassium, of which every gallon contains an ounce of silver. The suspending wires are connected by stout copper wires writh the last zinc plate of a galvanic battery consisting of 364 Metals : tJieir Properties and Treatment. alternate plates of zinc and copper immersed in diluted sulphuric acid ; the last copper plate of this battery is con- nected with a series of silver plates suspended in the silvering liquid opposite to the articles to be coated. The galvanic influence (or current) transmitted from the battery causes the decomposition of the cyanide of silver in the solution, the silver being deposited upon the articles to be plated, and the cyanogen, which was combined with the silver in the liquid, uniting with the silver upon the plates of that metal and forming a fresh quantity of the cyanide of silver equal to that which has been decomposed ; this dissolves in the liquid and always maintains it of the same strength. The articles are weighed before and after plating, in order to ascertain the amount of silver which has been deposited upon them ; it usually amounts to about an ounce and a half upon a square foot of surface. In order to secure the perfect adhesion of the film of silver, the objects to be plated are sometimes dipped into a solution of nitrate of mercury until they are covered with a thin coating of that metal, before they are immersed in the silvering-bath. They are then struck by placing them in the silvering liquid and connecting them with the zinc of a strong battery for a short time, after which they are brushed with fine sand to show that the coating is perfect, and the process of silvering is then proceeded with. To preserve the silvering solution of uniform strength, the articles to be plated are sometimes kept in motion by attaching the connecting rods to a frame furnished with wheels which travel along a rail on the edge of a vat, and are moved by clock-work or steam-power. The deposit of silver is without lustre and requires bur- nishing. It is dried by immersing the article in boiling distilled water, and allowing it to dry by its own heat when removed. When a lustrous deposit is required, one gallon of the silvering liquid is mixed with six ounces of a liquid called bisulphide of carbon and set aside for twenty-four Dry Silvering. 365 hours. Two ounces of this solution are added to twenty gallons of the silvering liquid, and left for twelve hours before use. The action of the bisulphide of carbon in causing a lustrous deposit has not yet received a satisfactory explanation. Silvering for merely Ornamental Purposes. Where a very chin film of silver only is required, as for articles not sub- jected to much wear, advantage is taken of the great malleability of this metal, in which it is surpassed only by gold, to beat it out into exceedingly thin leaves, which are applied to the surface to be silvered. The silver leaf is manufactured in the same manner as gold leaf, to which the reader may refer. It is applied to non-metallic objects with some adhesive liquid, such as gum or size. In covering metallic objects with silver leaf, they are heated to remove grease, and plunged into weak aquafortis to dissolve off the oxide. The surface is next scoured with wet pumice stone, warmed, and again dipped in weak aquafortis, to roughen it, so that the silver leaf may more readily cling to it. If necessary, the surface is further roughened by hatching with a graving tool. The metal is then carefully heated till a thin film of oxide causes it to assume a bluish tint, the leaves of silver applied in successive layers, and well fixed by a burnisher of steel, the object being heated again before every application of the silver. The process of dry silvering upon copper and brass, which is now seldom followed, consisted in applying to the clean surface an amalgam of silver from which the mercury is afterwards expelled by heat. A pasty amalgam is made by dissolving silver in about six times its weight of mercury. The amalgam is applied with a brush made of brass wire dipped into a solution of nitrate of mercury, which, being decomposed by the copper and zinc of the brass, deposits a coating of mercury upon the brush to which the silver- amalgam then readily adheres. The article is then mode- rately heated to expel the mercury in vapour, when a dead 366 Metals : their Properties and Treatment. film of silver is left upon the surface, which is afterwards burnished. For silvering flat surfaces, such as the scales of barometers, the chloride of silver is employed. To prepare this, a piece of standard silver is dissolved in a glass or earthen vessel, with the aid of heat, in aquafortis (diluted nitric acid). II any dark powder remains undissolved, it consists of finely divided gold, which is often found in old silver. The solu- tion, which contains nitrate of silver and nitrate of copper, is mixed with common salt dissolved in water. The chloride of sodium (common salt) decomposes the nitrate of silver, forming nitrate of sodium, and chloride of silver, which separates as a white curdy precipitate. The liquid is well stirred, the chloride of silver allowed to settle down, the liquid poured off and replaced by fresh water ; after this has been repeated several times, the washed chloride of silver is dried in an oven, and finely powdered. One part of the powder is mixed with three parts of pearlash, one part of chalk, and one-and-a-half of salt. The surface of the copper or brass to be silvered is rubbed with a wet cork or leather dipped in this mixture, when the metal decomposes the chloride of silver, forming chloride of copper, and, in the case of brass, chloride of zinc, and metallic silver is deposited. A mixture of the chloride of silver with ten parts of cream of tartar is said to answer the same purpose. Silvering on glass is effected by precipitating silver from a solution, in contact with the glass, by certain chemical agents, and being a purely chemical process, will not be considered here. Looking-glasses are silvered with an amalgam of tin (see Mercury). Occurrence of Gold in Nature. 367 GOLD. There is no positive evidence that gold exists in Nature in any other than the metallic state, though it is believed by some to exist as a sulphuret in some varieties of pyrites. There are few regions in which small quantities of this metal cannot be discovered, though in the great majority of cases its quantity is too small to pay for the labour of separating it from the other matters with which it is associated. In England, small quantities of gold are found in the Cornish alluvial deposits which furnish the stream tin ore. In Wales, it has been found near Dolgelly. Ireland has furnished gold from Wicklow, where it is found scantily distributed through sands in the form of gold-dust, and very rarely in small rounded fragments or nuggets. In Scotland, the precious metal has been traced in Perthshire, and, very recently, considerable quantities of it have been extracted in Sutherlandshire. On the continent of Europe, the gold mines of Hungary and Transylvania are the most important. At Konigsberg, the metallic gold is disseminated through sulphuret of silver. In Sweden, gold is found associated with pyrites at Edelfors in Smoland. The sands of the Rhine contain minute quantities of gold for which they are sometimes washed when work is scarce, although about eight million parts of sand must be washed for one part of gold. In Spain, the province of Asturias formerly furnished a considerable quantity of gold, but the workings are now neglected. Italy is by no means destitute of gold. Veins of pyrites containing gold are found in a granitic rock at the foot of Monte Rosa. The sands of some of the rivers on the southern slopes of the Alps also furnish gold. Siberia yields gold distributed through 'fwrnstone, a variety of quartz. The sands of Siberian rivers are not considered 368 Metals: tncir Propei ties and Treatment. to be worth washing if they contain less than one part of gold in a million. The Ural mountains contain some rich gold districts, the metal being found in pyrites, in clay, and in the sands of rivers. Japan, Ceylon, Borneo and Thibet also contribute to the supply of gold. Africa seems to have been the oldest and richest of the sources of gold. Sofala, on the coast of Caffraria, has sands abounding in gold-dust, and is reputed to have been the Ophir of the ancients. To the south of the great desert of Sahara, the negroes dig out earth rich in gold-dust to a con- siderable depth. In modern times, down to about the year 1850, Brazil, Chili, Peru and Mexico purveyed most of the gold employed throughout the world. Minas Gera'es in Brazil was a cele- brated auriferous district But the discoveries of gold in California and Australia, which are yet fresh in the memory of the present generation, have immensely increased the supplies of the metal. In California, the gold is chiefly alluvial gold, being found in the alluvial deposits formed by the Sacramento and other rivers. In Australia, gold-quartz is more common, the metal being disseminated in thin plates, and in branch-like frag- ments, through lumps of quartz-rock. It is also abundant, in the form of gold-dust and nuggets, in the alluvial forma- tion produced by the crumbling down of the rocks containing gold, under the influence of torrents which have carried the gold, together with clay and other matters, into deep gullies, at the bases of the rocks, where the alluvium has been de- posited upon a bed of pipe-clay, being richest in gold at the lower part of the deposit, on account of the great weight of the metal Native gold always contains silver, and generally copper, but in very variable proportions, though the gold from the same district has commonly the same composition. Aus- tralian gold is remarkably pure. Gold-washing. 369 The simplest method by which gold is extracted is that of washing the alluvial deposits, the sands of rivers, Scc. There ^ are various modes of effecting this, according to the resources of the gold-washers, but in all cases the separation of the gold from the earthy matters depends upon the high specific gravity of the gold (ig'3), the lighter earthy matters being carried off by the water. In Africa, the deposits containing gold are washed by the negroes in the shells of gourds, being well stirred up with water, which is poured off with the earthy matters suspended in it, leaving the gold dust in minute flattened grains at the bottom. The gold is kept in tubes made from the quills of the ostrich or vul- ture. In South America, the washing is conducted in shallow iron or zinc pans FIG. 112. Goid-wahing Pan. (Fig. 112, Sometimes the deposits are thrown upon the top of a sloping plank with shallow grooves cut across it, when the grains of gold settle down into the grooves, and the earthy matters are carried on by the stream. Long shallow troughs of wood are employed by some gold-washers, lined at the bottom with coarse baize, or with tanned skins with the hair upwards. The grains of gold become entangled in these, and when the earthy matters have been washed away, the linings are well beaten over a tank of water to remove the gold. At the Californian and Australian gold-diggings, a cradle (Fig. 113) has been extensively employed. This is a wooden trough about six feet long, resting upon rockers. At the head of it is a grating upon which the alluvial deposit to be washed is thrown. This end of the cradle is about four inches higher than the other, so that a stream of water enter- ing it flows through and escapes at the lower end, left open for this purpose, carrying the earthy matters with it, leaving 37O Metals : tJieir Proper-tics and Treatment. the particles of gold, with a small quantity of earthy matter, in the trough. These are swept out into a pan, dried in the sun, and freed from the lighter matters by blowing upon tli em. In the gold washings of the Ural Mountains, the sands are thrown into boxes the bottoms of which are made of perforated iron plates. These boxes are placed under a fall of water, in which the sands are stirred up with a shovel. The fine sand and gold dust are washed through on to s'oping boards covered with baize, a workman being engaged in sweeping the deposit up the inclined plane with a heather broom. After a second washing on a smaller inclined table, the particles of magnetic iron ore are extracted by a magnet, and the gold dust is melted in a plumbago crucible, when the earthy matters remain upon the surface of the melted gold. At some of the Russian works, the sifting of the sands is effected in cylinders of perforated sheet iron, which are placed in a sloping position above the washing tables, and made to rotate upon an axis. A stream of water being let in at the upper end, carries the sand and gold dust through Extraction of Gold. 371 the perforations on to the sloping tables, while the large pebbles pass out at the lower end of the cylinder. The boxes in which the more tenacious alluvial deposits are mixed with water are sometimes provided with agitators worked by horse or steam power, and having knives attached for breaking up and mixing the deposits. When the gold is disseminated through quartz or some similar rock, this must be crashed in order to extract the gold, an operation attended with great expense, on account of the hardness of the rock. Where it is possible, the rock is rendered more brittle by being heated to redness and quenched with water. The crushing is effected either by passing the gold-quartz between chilled cast-iron rollers, or by means of stampers similar to those employed in the Cornish tin-works. From the stamped ores, as well as from the auriferous sands which have been concentrated by washing, the gold is sometimes extracted by a process of amalgamation similar to that employed in the case of silver. As practised by the Mexican gold-washers, the process of amalgamation consists in shaking the damp gold-dust, still mixed with foreign matters, with metallic mercury which dissolves the gold. The impurities having been washed away, the amalgam is squeezed in a cloth, when about half the mercury flows out, and the solid amalgam remaining in the cloth is placed in a small iron dish, covered up with green leaves and set over a charcoal fire ; a good deal of the merrury vapour is condensed in the leaves, which are re- newed from time to time as they get dry. In the Tyrol, particles of gold exist disseminated through iron pyrites, from which they are extracted by amalgamation. The amalgamating mill (Fig. 114) is a large cast-iron dish (e) firmly fixed upon a wooden table. In this dish there is a heavy cone of hard wood (ni) of the same shape as the dish, and just large enough to leave an interval of half-an-inch between them ; several projecting iron ribs are fixed to the under side of this> cone, which nearly touch the bottom of B B 2 372 Metals : their Properties and Treatment. the pan, and the upper surface of the cone is hollowed out so as to form a shallow funnel. The wooden cone is con- nected with an axle (a), so that it may be made to revolve at the rate of about twenty turns a minute. About 50 Ibs. of mercury having been poured into the iron pan, the auriferous pyrites, previously stamped or ground to a fine powder, is brought into the mill by a stream of water from the spout (G), when it is thoroughly stirred with the mercury by the projecting ridges at the bottom of the wooden cone. In order that no gold may escape being dissolved by the mercury, the pyrites which has been treated in one mil 1 FIG. 114. Mill for amalgamating Pyrites containing Gold, r r 1 ', Toothed wheels for transmitting motion to the axle a. b. flows out through a spout (G) into the next, and so on through an entire series. After about a month, the mercury is drawn off and squeezed through wash-leather, which allows the liquid portion to pass through, and retains a soft solid amalgam containing about one-third of its weight of gold, from which the mercury is separated by distillation in the apparatus represented in Fig. 115. For the extraction of gold from gold-quartz, lead has been employed with great advantage, since this metal, when melted, will dissolve gold just as mercury will at the ordinary temperature. The crushed quartz is fluxed by an addition of lime and clay (see Iron), with which is added either Extraction of Gold. 373 metallic lead or galena (sulphuret of lead), or even rich iead slags, with some coal or charcoal to reduce the lead to the metallic state. The lead containing gold (and silver) is then subjected to the process of cupellation (p. 336). In Hungary, gold is extracted from iron pyrites associated with quartz, by taking advantage of the property of dissolv- FIG. 115. Apparatus for distilling the Amalgam of Gold, a, Dishes for re- ceiving the amalgam, attached to the pillar b. A, Iron cylinder heated by a fire on the grate c. d, Iron dome, e, Iron cover of the furnace. /, Tube for vapour of mercury, g. Cylinder in which the mercury condenses, closed by an iron plate h and a wooden plug i. k. Water- tank. /, Vessel for collecting the mercury, m. Chimney. ing gold possessed by sulphuret of iron. The pyrites is roasted in heaps with brushwood, to convert a part of the bi- sulphuret of iron into oxide of iron, and a part into sulphuret of iron. The roasted ore is fused with an addition of lime, when a slag is formed by the combination of the silica (quartz), the oxide of iron, and the lime, whilst the sulphuret of iron fuses, dissolves the gold, and forms a matt beneath the slag. This sulphuret of iron is roasted so as to convert it into 374 Metals : their Properties and Treatment, oxide, and fused with a fresh quantity of the auriferous pyrites and the requisite proportion of lime, when a fresh quantity of the matt will be obtained, containing the gold from the two charges of pyrites. This operation is repeated until a sufficient quantity of gold has accumulated in the matt of sulphuret of iron, which is then melted down with lead ; this metal extracts the gold from the sulphuret of iron, and the latter remains in a melted state upon the surface of the lead. The lead is afterwards cupelled in order to extract the gold, and since lead containing silver is generally employed, this metal is left on the cupel alloyed with the gold. Whenever ores of copper, lead, or silver contain gold, the latter is always present in the metal extracted from them, and is recovered from those metals by the processes de- scribed in the article on Silver. In order to separate the gold from the silver with which it is commonly alloyed, whether it has been obtained by wash- ing, or by any of the above processes of extraction, the alloy of silver and gold is heated with sulphuric acid, which con- verts the silver into sulphate of silver, capable of being dis- solved by water, and leaves the gold untouched. Parting by Sulphuric Add. The alloy of silver and gold, in which, of course, the former metal always predominates, is melted either in wrought-iron or plumbago crucibles, and poured into water in order to granulate it or divide it into a flaky condition, exposing a large surface to the action of the acid The granulated metal is dried, weighed, and boiled with oil of vitriol (concentrated sulphuric acid). When the alloy is rich in gold, the operation is performed in platinum alembics or stills, but in the more common case, where the silver contains only a few grains of gold in the pound, cast- iron pans are employed ; each pan (about two feet wide) has an iron lid, from which a bent pipe passes down into an air- tight leaden tank, where the vapour of sulphuric acid which escapes during the boiling may be condensed. A large quantity of sulphurous acid gas passes off during the opera- Parting by Sulphuric Acid. 375 tion, and this is conducted, from the leaden tank, by a pipe of the same metal, into a large leaden chamber, 30 feet long by 10 feet wide, and 6 feet high, in which it is reconverted, by an appropriate chemical process, into oil of vitriol, which is used over again. One fire is made to heat two of the iron pots, in which the granulated silver is placed, together with twice its weight of concentrated sulphuric acid, which is gently boiled until the silver is entirely converted into sulphate of silver, forming a pasty mass consisting of minute crystals. This is taken out by cast-iron ladles, and thrown into leaden cisterns, where it is stirred up with water, and boiled by passing steam into it through perforated leaden pipes connected with a boiler. The boiling water dissolves the sulphate of silver, and the finely-divided gold is left as a black powder, which, when accumulated in sufficient quantity, is well washed and dried. It still retains a small proportion, varying from ^th to ^th of its weight, of silver. The solution of sulphate of silver is drawn off, by leaden siphons, into leaden troughs, where it is left in contact with shavings of copper. This metal enters into solution, form- ing sulphate of copper, and separating the silver in a finely- divided state, as a grey powder ; this is allowed to settle down, the solution of sulphate of copper run off into another cistern, and the silver washed with fresh water, drained, and compressed by hydraulic pressure, in a square cast-iron box, which makes it into cakes of 60 Ibs. each. These are dried, melted in plumbago crucibles, and cast into ingots. Cast- iron crucibles strengthened by shrinking hot iron hoops upon the cold crucibles are sometimes employed, but since they become impregnated with silver, the latter must be extracted by melting some lead in them when they are worn out. The solution of sulphate of copper formed in displacing the silver by copper is evaporated in shallow leaden pans, to a proper strength, and the sulphate of copper allowed to crystallise out on cooling. The liquid remaining after the 376 Metals: their Properties and Treatment. last crystals have separated contains the excess of sulphuric acid which has been employed in the process, very little sulphate of copper being left in it, because this salt is almost insoluble in moderately strong sulphuric acid. This liquor is boiled down in a platinum still, until the water has boiled away, and the concentrated sulphuric acid is left in the still, ready to be employed for the treatment of a freoh quantity of silver. The sulphate of copper (blue vitriol) obtained in this pro- cess is a salt for which there is a considerable demand ; it is largely used for dressing grain intended for seed, to prevent smut. It is also employed in dyeing and calico-printing, and in many other branches of industry, as well as in several forms of galvanic battery. When there is no market for the sulphate of copper, the solution of the salt is decomposed by scrap iron, as in the case of the blue water at Anglesea (p. 248), to recover the metallic copper. In such works for the refining of gold and silver, the pro- cesses can be conducted economically only when great care is taken to avoid the loss of any particles of the precious metals. Thus all the old crucibles are ground and treated with mercury in the amalgamation mill, and after as much gold and silver as possible have been thus extracted, the residues are sold to the sweep-washers, who extract a little more by melting with lead. The very dust off the floors is collected and treated in a similar manner. One part of gold can be profitably extracted from 2,000 parts of alloy by this process of parting by sulphuric acid. Its introduction has affected the metallurgy of gold in the same way as Pattin- son's process did that of silver, much old silver plate having been treated by it for the sake of the gold which had not been found worth extracting by the older and more expensive method of parting by nitric acid. When the alloy contains copper as well as silver and gold, it may also be treated in the same way, the copper being re- moved, with the silver, as a soluble sulphate ; but the pro- Parting by Nitric Acid. 377 cess does not succeed well with an alloy containing more than 75 parts of copper in i,coo, so that, if it be richer, it is either melted with more silver, or is cupelled with lead (p. 336), in order to reduce the copper to the right propoi- lion. Nor should the alloy contain more than one-fifth of its weight of gold, or the sulphuric acid will not extract the silver. When platinum stills are employed for parting by sulphuric acid, it is necessary that the alloy should be free from lead and tin, which are apt to melt upon the bottom of the still and seriously to corrode the platinum. Parting of Gold and Silver by Nitric Acid. Silver is easily dissolved by nitric acid and converted into nitrate of silver, but this acid, if pure, does not attack gold. If the nitric acid contains chlorine, however, it will dissolve some of the gold, so that it is always necessary to test it by adding a little solution of nitrate of silver, which will render it milky, from the separation of the insoluble chloride of silver, if any chlorine be present. An alloy containing more than one part of gold to three parts of silver is very little affected by nitric acid, so that it becomes necessary to fuse very rich alloys with so much silver that the gold shall form only one- fourth of the alloy; this is the origin of the term inquartation or quartation, used in speaking of this process. The alloy, in a granulated state, is heated with twice its weight of moderately strong nitric acid (sp. gr. 1-32) in a still made of platinum, glass, or earthenware, connected with an apparatus for condensing the vapours of nitric acid which pass off. Whilst the silver is being dissolved, a large quan- tity of red gas is evolved, resulting from the action of the silver upon the nitric acid, and when this is no longer per- ceived, the silver is known to be dissolved. The still is then cooled, the solution of nitrate of silver drawn off, and the undissolved gold boiled with a little more nitric acid to extract any remaining silver. It is then washed with water, dried, melted, and cast into an ingot. In order to recover the silver from the nitrate, hydro- 3/8 Metals: their Properties and Treatment. chloric acid is cautiously added, so as to separate the bulk of the silver as the insoluble chloride, leaving the nitric acid in the solution, which may be used again, if care be taken to leave a little nitrate of silver undecomposed in the solution, so as to ensure the absence of chlorine. The separated chloride of silver is washed with water, moistened with sul- phuric acid, and some bars of zinc placed in it, when chloride of zinc is formed and dissolved, the silver being left in the finely-divided metallic state. The rest of the zinc is then taken out, the silver allowed to remain in contact with dilute sulphuric acid to dissolve any particles of zinc, then thoroughly washed with water, dried, melted, and cast into ingots. Refining of Gold. The gold obtained by parting with sul- phuric acid is refined by mixing it with one-fourth of its weight of dried sulphate of soda, and treating it, in an iron pan, with oil of vitriol, to the amount of three parts for even' five parts of sulphate of soda. Heat is applied as long as any vapours of sulphuric acid escape. This is repeated a second time, but without driving off the whole of the sulphuric acid. The mass is then boiled with sulphuric acid, when the gold alone is left, and is melted with a little saltpetre, which extracts a little platinum, before casting it into an ingot At the Russian mint, the re-melting is effected in a small reverbera- tor)' furnace, with a cavity in which the gold collects. The explanation of this process is simply that the sulphuric acid combines with the sulphate of soda, and may then be raised to a higher temperature without vaporising than is possible with uncombined sulphuric acid. The higher temperature employed enables the sulphuric acid to attack the remainder of the silver. Extraction of Gold from Gotd-qnartz in the wet way.- -It has been proposed to avoid the expensive process of amal- gamation, by digesting the pulverised gold-quartz with y^th part of black oxide of manganese and some muriatic acid, in an earthen vessel, for twelve hours, when chlorine is generated, which dissolves the gold in the form of chloride of g9ld, from Extraction of Gold in the wet way. 379 which the metal may be separated in a finely-divided state by adding to the liquid a solution of copperas (sulphate of iron). The dark powder of gold thus separated is washed with water, dried, and melted down. 'UTien the gold con- tains much silver, common salt is employed to dissolve the chloride of silver, which would otherwise protect the gold from the action of the chlorine. Planner's Process, which was employed with economy foi the extraction of gold from the abandoned residues of roasted pyrites at Reichenstein, in Upper Silesia, containing less than T oz. of gold per ton, is rather a chemical than a metallurgical process, and consists in treating the fine powder, in a moist slate, with chlorine gas, which converts the gold into a soluble chloride ; this is washed out with water, and treated with sulphuretted hydrogen, which separates the gold as an insoluble black sulphuret, leaving the iron, &c., in the solu- tion. The sulphuret of gold is heated to expel a part of the sulphur, dissolved in a mixture of hydrochloric and nitric acids, and separated from the solution in the pure metallic state by sulphate of iron. The precipitated gold is washed, and melted down with a little borax and saltpetre. Gold dust and nuggets of gold never consist of the pure metal, but always contain silver, and sometimes copper and small quantities of other metals, such as antimony and bis- muth. Grains of platinum and its allied metals are also very commonly found in alluvial gold. The purest native gold has been found at Giron, in New Grenada, containing only 7-^th part of silver. Some Californian gold contains as much as nine parts of silver and nearly one part of copper in a hun- dred parts. Californian gold also sometimes contains small grains of an extremely hard alloy of osmium and iridium, which occasion great injury to the die in coining, since they remain unchanged when the gold is cast into ingots. At the American mint, the Californian gold, which con- tains about ToVoth of its weight of the osm-iridium alloy, is melted with thrice its weight of silver, which lowers its specific gravity, and allows the osm-iridium to settle to the 380 Metals: their Properties and Treatment. bottom. The greater part of the melted metal is ladled out, leaving the rest very rich in osm-iridium at the bottom. This is repeatedly melted with silver, by which the proportion of gold is still further diminished, and ultimately the mixture of osm-iridium with silver and a little gold is boiled with sul- phuric acid, which extracts the silver, leaving the osm- iridium mixed with some powdered gold, which may be removed by washing. When gold contains platinum or palladium, it is very much lighter in colour. These metals cannot be separated by the ordinary refining processes. The presence of lead or antimony, even in very minute proportion, is found to render gold extremely brittle. Australian gold is frequently brittle from the presence of lead or antimony. It is sometimes refined by stirring a little corrosive sublimate (chloride of mercury) into the melted gold, when the chlorine combines with the base metals, forming chlorides which are expelled in the form of vapour, together with the liberated mercury. F. B. Miller has intro- duced an improved process for refining such gold by forcing into the melted metal a current of chlorine gas, through the stem of a tobacco-pipe. The chlorine converts the silver present in the gold into chloride of silver, which collects, in a melted state, upon the surface of the gold, whilst any arsenic, antimony, bismuth, lead, or zinc, is also converted into chloride, and driven off in the form of vapour. The silver is afterwards easily extracted from its chloride. Perfectly pure or fine gold is nearly as soft as lead, far too soft therefore to resist the wear to which it would be sub- jected in coinage and gold plate. The alloy used for coin, in England, consists of 1 1 parts of gold and i part of copper, which is harder and more fusible than pure gold. Formerly, the gold was alloyed with silver, or with silver and copper, and this latter alloy is still employed by goldsmiths. The guinea was composed of 1 1 parts of gold, \ part of silver, and part of copper. The specific gravity of sovereign Testing of Gold. 381 gold is 1 7 -15 7 (that of pure gold being 19 -3). The safest method of ascertaining whether a sovereign is genuine consists, as in the case of silver coin (p. 361), in showing that it has the same size and weight as a sovereign known to be genuine. A new sovereign weighs 123^ grs., but it is a legal tender as long as it is not less than 122^ grs. in weight So hard is the alloy, that with proper wear, a sovereign will circulate for eighteen years without falling below the legal standard. The gold coin of the United States and of France con- tains only 9 parts of gold to i part of copper. The fineness or purity of gold is commonly expressed by stating how many carats of gold are present in 24 carats of the alloy. Thus pure gold would be 24 carats fine ; sovereign gold, 22 carats fine. Fractions of a carat are expressed in grains (4 grains are equal to i carat) and eighths of a grain ; thus French gold coin would be styled of 21 carats 2| grs. fine, or -worst O carat if grs., implying that it contained so much less gold than the English standard. The fineness may of course be judged of, as in the case of sovereign gold, from the specific gravity, since the specific gravities of silver and copper (respectively, 10-5 and 8-9) are so much lower than that of gold (i9'3). But this test has been found fallacious in a case where bars of platinum (sp. gr. 21-5) were coated with gold and sold as solid ingots of that metal, which is more than twice the price of platinum. Gold of 1 8 carats fine has the specific gravity i6'8. The goldsmith or pawnbroker generally tests the gold by touching its surface with a stopper wetted with aquafortis (nitric acid), which produces a green stain upon the metal when a very large proportion of copper is present, nitrate of copper being then produced. This is, at best, a rough test, and would of course fail altogether if the surface only of the base alloy were coated with fine gold. The use of the touchstone admits, in practised hands, of a 382 Metals: their Properties and Treatment. far more exact determination of the value of the alloy, and unless it be pretty thickly coated with richer metal, decep- tion is more easily detected. The touchstone is a piece of black basalt, or even of black slate, over which the gold to be tested is drawn so as to leave a streak of fine particles of the metal upon the surface ; this streak of course remains untouched when moistened with nitric acid, but if a streak of any base alloy (of copper and zinc for example), made to imitate gold, be made upon the surface of the touchstone, the nitric acid will immediately dissolve it. The acid employed in this test is generally mixed with a minute proportion of hydrochloric acid (98 parts by weight of nitric acid, of sp. gr. 1*34, 2 parts of hydrochloric acid, of sp. gr. ri73, and 25 parts of water). The streak is not apparently affected by the acid if the gold is not below 1 8 carats fine; by making several streaks in succession, or by grinding off a part of the surface upon the touchstone, any error arising from a thin external coating of fine gold may be avoided ; the feather of a pen, or a glass rod, serves for moistening the streaks with the acid. In order to determine by the touchstone the proportion of gold which is present in the alloy, the streak is compared with that made by a series of touchnecdlcs composed of alloys containing gradually diminishing quantities of gold. In experienced hands, the quantity of gold may thus be ascertained with an error of not more than one part in a hundred. The exact assay of the FIG. n6.-Cupel. allo 7 S f S ld is an imlta - tion, on the small scale, of the metallurgic processes of inquartation, cupellation and parting. A weighed quantity of the alloy, say 6 grs., is wrapped in a piece of thin paper together with three times its weight of pure silver, and added to twelve times its weight of pure lead already melted in a bone-ash cupel Assay of Gold. 3*3 FIG. 117. Muffle, (Fig. 116), heated in a muffle (Fig. 117) or arched clay oven, with slits for admitting air, which is placed in a brisk fire (Fig. 1 1 8). The lead and copper are both converted into oxides, the oxide of copper dissolving in the oxide of lead, and both being absorbed by the bone-ash. After the brightening (P- 339) tne alloy of silver and gold which is left on the cupel is hammered flat, annealed by heating to redness, rolled out thin, coiled up into the form of a tube, and boiled, first with weak nitric acid (sp. gr. i'i8), and then with a stronger acid (sp. gr. 1-38) in order to extract the silver; the gold is left in the form of a little tube (cornette) having much the appearance of red earthenware. It is well washed with water, carefully transferred to a small crucible without breaking it, dried, and heated to redness in the muffle, when it shrinks, and assumes the ordinary appearance of gold. Its weight is ascertained by a very accurate balance, and multiplied by four (six grains having been assayed) to ex- press the fineness of the gold. To avoid errors, the exact assayer commonly passes a proof or weighed quantity of FIG. n8.-A pure gold through the same process, at the same time, with the addition of a proportion of copper about equal to that in the alloy, and corrects his assays by deducting from the weight of the gold finally obtained the increase which the pure gold was found to have experienced in . consequence of its having retained traces of lead, silver and copper. iy by Cupellaiion. a, Iron castors on which the furnace moves. b. Ash-pit, c, Damper. whilst the last twelve ascend a corresponding inclined plane the centre aludel of the series being perforated in the lower side, so that the condensed mercury may run out into a gutter which conducts it into receiving basins (;//, n, Fig. 120) underneath the furnace. The vapour of mercury which escapes condensation in the aludels passes, together with the sulphurous acid gas, into a chamber (i, Fig. 119) in which a further considerable quantity of the mercury is condensed to the liquid state. The sulphurous acid gas eventually escapes through the chimney. The imperfect character of this condensing apparatus is evident ; the loss of mercury vapour through the leakage of the numerous joints, and through the openings in the lowest aludels, must be very great, so that it is not surprising that only 10 parts of mercury should be extracted from a hundred parts of rich ore. Each roasting lasts about twelve hours, and the furnace requires three or four days to cool before receiving a fresh charge, affording a striking contrast to the system of nearly continuous working adopted in the metal- lurgic processes of this country. The mercury mines at Idria in Austria, which are now probably more important than those at Almaden, were formerly worked by state prisoners and criminals, on account of the unhealthy nature of the occupation. In these mines the ore is found both in limestone and in a bituminous slate, and contains a considerable proportion of bituminous matter. Previously to the year 1794, the aludel furnace just described was also employed at Idria, but it was then superseded by a very large brick structure containing a series of condensing chambers. The roasting furnace (Fig. 122) consists of a grate upon which wood is burnt, surmounted by three perforated arches (n p r) of fire-brick, for receiving the ore, the large fragments being placed upon the lowest arch, the smaller pieces on the next, whilst the uppermost supports a number 394 Metals : their Properties and Treatment. of shallow earthen dishes (j) containing the dust of the ore and the mercurial soot from former operations. Air is ad- mitted to the heated ore through small passages in the walls, FIG. 122. Extraction of Mercury at Idria. G H, Passages from which air enters through tiues into the space occupied by the ore. c, Condensing chambers. and the sulphurous acid and vapour of mercury are drawn by the two chimneys, through six condensing chambers (CD, Fig. 123) on each side of the furnace, so connected by nar- row openings that the vapours are forced to pervade one FIG. 123. Section of Idrian Furnace and Condensing Chambers. A, Fire- place. B, Arches upon which the ore is placed. CUE, Condensing chambers. G H, Air channels. chamber before entering another. In the last chamber (D) of each series, which is surmounted by the chimney, the last \ ortions of mercury are condensed by a cascade of water. The Extraction of Mercury at Idria. 395 greater portion of the mercury is condensed into the liquid form in the first three chambers of each series, and is collected in an underground gutter which conveys it into a tank, from which it is ladled out to be filtered through cloth, and put into the wrought-iron bottles, containing about 60 Ibs. each, in which it is imported into this country. The three last of each series of condensing-chambers receive the remainder of the mercury chiefly in the form of dust or soot, consisting of finely-divided mercury, with some sulphuret of mercury which has escaped in vapour, and some carbon from the bituminous matter in the ore. About a week is required to complete the distillation, including the time required for cooling the furnace. Only about 8i parts of mercury are obtained from 100 parts of ore. In 1803, a fire broke out in the mines at Idria, and the combustion was sustained by the bituminous matter in the ore, so that it became necessary to flood the workings with water. The vapours of mer- cury evolved proved very injurious to the health of the neighbourhood. A process similar to that employed at Idria is followed at New Almaden, in California, for the extraction of the mercury. Within the last few years, a greatly improved apparatus nas been employed at Idria. The ore, in fragments as large as a fist, is thrown through a hopper into a deep cylindrical fire-place, upon which a little wood and coal are burnt. The mercurial vapours are conducted into six condensing chambers covered with iron plates and kept cool by a stream of water. The draught through the chambers is maintained by a chimney, where terraces are constructed over which water is allowed to flow. Fresh charges of 7 cwts. of ore and 28 Ibs. of charcoal are introduced every three-quarters of an hour, and the spent ore is raked out from below through the moveable bars of the grate. A still more scientifically constructed apparatus is em- ployed at Idria for the treatment of small ores containing 3Q3 Metals : their Properties and Treatment. one-hundredth or less of mercury, in which the ore is heated on the hearth of a reverberatory furnace (a, Fig. 124), the mercurial vapour being passed i, through a condensing chamber (d) ; 2, through a wide sloping iron pipe (/) kept cool by the constant trickling of water over it, from the perforated gutter (e) ; 3, into a second condensing chamber (g) ; 4, through a second iron pipe (//), similar to the first, into a chimney (). The hearth of the reverberatory furnace is divided into three compartments, the ore being first FIG. 124. Modern Idiian Mercury-furnace. thrown, through a hopper (b), upon that farthest from the grate, being raked out into each of the other compartments in succession, so as to be exposed to a gradually increasing temperature until it is drawn out in a spent condition through a channel near the fire-bridge, whilst fresh ore is charged at the other end of the hearth. Wood is the fuel employed. Beside the liquid mercury which is run out into proper receptacles, a large proportion of mercurial soot, containing finely-divided mercury, is collected in the con- densing pipes and chambers. This is dried, raked over on Distillation of Cinnabar witli Lime. 397 an inclined plane as long as any mercury runs out, and afterwards distilled to obtain the last portions of the metal. On the west bank of the Rhine there are several small mercury mines which yield sulphuret of mercury associated with sandstone. These ores are made to yield their mercury by distilling them with lime, a process generally resorted to in the smaller mercury works. The distillation is effected in cast-iron pear-shaped vessels (A, Fig. 125), thirty of which are heated by the same fire, in a gallery furnace (M), the grate of which runs through its entire length, and is fed with coal, which does not come into contact with the iron vessels, these being arranged in the upper part of the furnace, on each side of the grate, in two rows, one above the other, so that the flame may circulate around them before escaping through the openings into the chim- ney. The ground ore is mixed with about one-fourth of its weight of quicklime, and about 70 Ibs. of the mixture are intro- duced into each of the cast-iron bottles, which are then about two-thirds full. The neck of each bottle fits into a stone bottle (B) half full of water, placed outside the fur- nace, to receive the mercury. The water above the metal becomes filled with black mercury containing undecomposed sulphuret and finely-divided mercury; this is dried and distilled again with more lime. In this process, the lime, or oxide of calcium, composed of calcium and oxygen, decomposes with the sulphuret of mercury, yielding sulphuret of calcium, which remains in the FIG. 125. Extraction of Mercury in the Palatinate. 398 Metals : tJieir Properties and Treatment. iron bottle, mercury which passes over in vapour, and oxygen which converts a part of the sulphuret of calcium into sulphate of lime. This operation in the gallery furnace is obviously attended with waste and inconvenience. The trouble of charging and discharging so many small bottles and of cementing the joints is very considerable, and has led to the introduction, in some places, of another arrangement which allows the mercury to be extracted on the same principle but with much greater economy. In place of the bot- tles, cast-iron retorts (a, Fig. 126) are em- ployed, resembling those used in distilling coal for gas. These are about seven feet long and one foot square in sectional area, so that they may be charged with 700 Ibs. (instead of 70) of the mixture of the ground cinnabar with lime, in- troduced at the back of the retort, which is then closed with an iron plate. The front end is also closed with an iron plate (a, Fig. 127), which is provided with a sloping cast-iron pipe (b), 4 inches in diameter, having a door through which it may be cleared with a wire. This pipe dips into water contained in a condenser (c] resembling the hydraulic main of the gas works, being an iron pipe, 1 8 inches wide, and 20 feet long, which runs along the front of the range of nine retorts, and receives the mercury condensed from them, being itself kept cool by a stream of water running through a wooden trough around it. This pipe is a little inclined Extraction of Mercury from Grey Copper Ore. 399 towards one end, so that the condensed mercury may run down into a pipe (D) which conveys it into a locked cistern (oft metal and therefore ill-adapted to resist ordinary wear. It is easily corroded and rendered brittle by carbon and silica, both of which are present in coal, coke, and charcoal, for which reason platinum crucibles are never allowed to come into direct contact with the solid fuel, but are heated either in the flame of a gas or spirit lamp, or in a muffle (p. 383), or enclosed in a clay crucible lined with magnesia to prevent the platinum from sticking to the heated clay. Metals must never be melted in platinum crucibles, since most of the metals are capable of forming alloys with it. Caustic alkalies and saltpetre in a melted state also act upon the metal, and phosphorus and arsenic combine with and corrode it very rapidly at moderately high temperatures. Neither sulphuric, hydrochloric, nitric or hydrofluoric acid separately has any action upon platinum, but a mixture of hydrochloric with nitric acid dissolves it, though more slowly than it dissolves gold. An alloy of platinum, iridium and rhodium is sometimes employed for crucibles, which are harder and less easily corroded than those made of pure platinum. To obtain the alloy, the ore of platinum (which contains the two other metals) is mixed with a quantity of lime equal to that of the iron contained in the ore, and fused by the oxy-hydrogen blowpipe in a furnace made of lime (p. 408). The iron and copper are converted into oxides which form a fusible slag with the lime, whilst the gold, palladium and osmium are expelled in the form of vapour, and the alloy of platinum, iridium and rhodium remains. Small tubes, &c., may be easily extemporised with platinum wire and foil, by taking advantage of the readiness with which surfaces of this metal unite when hammered at a high temperature. Platinum vessels are cleaned by smearing them with a paste containing equal bulks of borax and cream of tartar Separation of Gold and Platinum. 4 1 1 with a little water, drying and heating them till the mixture melts, and immersing them for several hours in diluted sulphuric acid. Heating in contact with fused bisulphate of potash, or with powdered sal-ammoniac, is also employed for the same purpose. The platinum vessels are finally well washed with water and burnished with agate. Platinum is sometimes employed for the touch-holes of small-arms, and for the vents of cannon, on account of its resistance to corrosion. The circumstance that it expands less than any other metal when heated, enables it to be cemented into glass, by fusing the latter, whilst other metals which differ much from glass in their rate of expansion by heat, would crack it as they cool. This renders platinum of great importance in the fabrication of various philosophical instruments. Though pure platinum is unaffected by nitric acid, it may be rendered soluble in that acid by previously alloying it with ten or twelve times its weight of silver, which is taken advantage of in order to separate platinum from gold in the process of assaying the latter metal with which platinum is frequently associated. If the platinum be present in small proportion (not exceeding 3 or 4 per cent) in the alloy of gold and silver obtained by cupellation (p. 383), the whole of it will be dissolved together with the silver, in parting by nitric acid; but when the quantity of platinum is larger, which is indicated by the difficult fusibility of the button on the cupel, and by the blanched appearance of the gold eventually obtained, the latter must be again fused with at least three times its weight of pure silver, the alloy rolled very thin, and boiled for half an hour, and a quarter of an hour, respectively, with the two strengths of nitric acid mentioned at page 383, in order to remove the whole of the silver and platinum. An alloy of silver with one-third of its weight of platinum is employed by dentists on account of its great elasticity. The remarkable property of platinum, especially in the 4 1 2 Metals : tJieir Properties and Treatment. finely-divided states of spongy platinum and platinum black, to condense gases into its pores and thus to promote their chemical action upon each other, is not suited for descrip- tion in a metallurgic treatise. PALLADIUM is generally found in small quantity, not exceeding i per cent, associated with the ore of platinum, from which it is extracted by a process which is purely chemical. Formerly there existed a pretty abundant source of this metal in the form of an alloy with gold found in the mines of Brazil, but of late years this has failed, and pal ladium has risen to an extremely high price. In appearance it resembles platinum, but is much harder, though it pos- sesses considerable malleability and ductility. It is quite unchanged by air at the ordinary temperature, but assumes a bluish colour, from the formation of a thin film of oxide, at a moderately high temperature, becoming bright again at a .higher temperature, the oxide being decomposed. Palladium fuses at a somewhat lower temperature than platinum, but cannot be fused in a furnace. It is only half as heavy as platinum, its specific gravity being 11-5, so that it is much better adapted for making very accurate balances and other philosophical apparatus. The graduated scales of astro- nomical instruments are often made of palladium, and au alloy of this metal with -^th of silver has been sometimes employed by dentists. Ores of A ntimony. 4 1 3 ANTIMONY. Though antimony is far too brittle to be employed in its pure state for any useful purpose, it has been shown to be of great service in hardening the softer metals lead and tin, so that the history of this metal is not devoid of interest for the metallurgist. Antimony is occasionally found in Nature in the metallic state, as at Andreasberg in the Hartz, where it is alloyed with small quantities of silver, iron, and arsenic. The only ore from which it is largely extracted is the grey antimony ore, a sulphuret of antimony, containing, when pure, 7 if parts of antimony combined with 28^ parts of sulphur. It is found in Cornwall, Auvergne, Hungary and Borneo, associated with galena and iron pyrites, and with quartz and heavy spar, in veins traversing rocks of granite or slate. The ap- pearance of grey antimony ore is very characteristic ; it commonly resembles a compact bundle of dark grey metallic needles converging towards one point, and often exhibiting a blue iridescence due to a thin film of oxide. It is very heavy (sp. gr. 4 '63), and melts easily even in the flame of a candle. This fusibility is taken advantage of in order to separate it from the earthy matters, to effect which the ore is heated on the concave hearth of a reverberatory furnace, the hearth being lined with charcoal to prevent oxidation of the sulphuret, which melts and is run out into moulds, where it is cast into the form of the cakes sent into com- merce as crude antimony, which contains, in addition to the sulphuret of antimony, sulphurets of arsenic, iron and lead. The oxide of antimony occurs in Algeria, and is smelted in France. Red antimony, a compound of oxide and sulphuret of antimony, is found in Tuscany, and smelted at Marseilles. 414 Metals: their Properties and Treatment. of antimony, or metallic antimony, is extracted from the sulphuret by melting it upon the hearth of a rever- beratory furnace in contact with metallic iron (clippings from the tin-plate works), which removes the sulphur, form- ing sulphuret of iron ; this collects above the melted antimony, which is run out into moulds. It contains a con- siderable quantity of iron. Sometimes the regulus is extracted directly from the rich antimony ore, without previous production of crude anti- mony. For this purpose the ore is broken into pieces as large as an egg, and introduced into red-hot crucibles, together with a little alkaline slag ; some scrap-iron is placed on the top and pressed down when the mass has fused. After about two hours, the melted antimony and sulphuret of iron are poured into conical iron moulds, where they separate into two layers. A purer metal is obtained by the following process. The sulphuret of antimony, or the rich original ore, is crushed, and roasted, without being melted, for six hours, in a rever- beratory furnace, when most of the sulphur is expelled as sulphurous acid gas, and most of the arsenic as arsenious acid, whilst part of the antimony is converted into vapour, and combines with oxygen to form the oxide of antimony, which is carried into the flues of the furnace. The roasted ore, which has a red-brown colour, contains the oxide and sulphuret of antimony. It is ground to powder, mixed with about one-fifth of its weight of charcoal, some chloride of sodium, carbonate of soda, sulphate of soda, and slags from a former operation. The mixture is thrown upon the hearth of a reverberatory furnace, and well stirred, when the oxide of antimony in the roasted ore is reduced to the metallic state by the charcoal, whilst the sulphuret of antimony exchanges its sulphur for the oxygen of the soda, yielding oxide of antimony, which is also reduced by the charcoal, and sulphuret of sodium, which forms a slag with the sulphurets of other metals present, and with the Antimony. 415 chloride of sodium. The metal and slag are run off into an outer basin. The fumes of oxide of antimony are conden ed in long flues. The poorer ores, after being roasted, are smelted in cupola furnaces with coke. The antimony is refined by melting it, in quantities of 60 or 70 Ibs., with i or 2 Ibs. of American potashes (car- bonate of potash) and 10 Ibs. of the slag. It is then allowed to solidify quietly under a layer of slag, in order that it may assume the beautiful fern -like crystalline markings on its surface which have gained for it the name si star-antimony. The above process for extracting the metal is far from economical, little more than one-half of the antimony present being obtained in the metallic state. Antimony can easily be distinguished from ever)' other metal by its hardness, brittleness and crystalline structure ; a slight tap with a hammer suffices to break an ingot of antimony, and the broken surface exhibits large shining plates;* it is so brittle that it may be easily reduced to a fine powder in a mortar. It is comparatively a light metal, its specific gravity being only 67. It melts at 800 F., and at a higher temperature it gives off much vapour, which produces a thick white smoke of oxide of antimony. Its applications have been noticed in the preceding pages. * The addition of a minute proportion of tin to antimony causes it to crystallise more readily and in larger crystals. 4 1 6 Metals : tJieir Properties and Treatment BISMUTH. Bismuth, or marcasite* as it was formerly termed, is a comparatively rare metal which is found associated with the ores of nickel, cobalt, copper and silver, chiefly in Saxony, Transylvania and Bohemia. It also occurs in smaller quantity in Cornwall, Cumberland, Stirlingshire, Norway, Sweden, and the United States, and has lately been found in Peru, Bismuth is always extracted from the ores which contain il FIG. 130. Extraction of Bismuth. in the uncombined metallic state, by taking advantage of the readiness with which it fuses (507 F.) and drains away from the other constituents of the ore. It is extracted chiefly at Schneeberg in Saxony, from an ore containing from seven to twelve parts of bismuth in a hundred, associated with a compound of arsenic and cobalt This is broken into pieces about the size of a nut, and introduced, in charges of about 5olbs., into sloping cast-iron cylinders (Fig. 130) heated by a wood fire. The lower opening (b) of each cylinder is closed with a file-clay stopper having an aperture through which the melted bismuth may run out The upper open- * A term sometimes applied also to iron pyrites. Extraction of Bismuth. 417 ings are closed by an iron door ( i 0009 I344-0 Silver Ag 108 10-53 1873 i -002 1 6573 lS-2 Tin . Sn 118 7-29 442 1-0023 455'i 2-Ot03-5* Zinc* Zn 65 7-14 773 i 0029 445-7 3-3108-3* NOTE. (i) The figures in the tables must be looked upon only as approximately true : no two pieces of metal would give precisely the same result. (2) < is used to signify less than, = equal / greater than. * Signifies that the figures refer to wrought metal, t Maximum. The minima are sp. gr. 7-5, tensile strength 16. J Total expansion. For the same kind of metal, the greater its density, the greater its expansion for a given increase in temperature. 4 25 Tables. TABLE II., showing the Specific Gravity, 6-v. of some of the Non-metallic Materials employed in works. r~ Name of Substance Sp., Gr. Weight of one cub. ft. ID Ibs. No. of cub. ft. in one ton Crushing strain in Ibs. per sq. in. Brickwork, common . { I -6 to 20 100 tO 125 22-4 to 17-9 ,, London stock . 1-84 "s 19-4 red . i 2-16 134 167 808 ,, Stourbridge fire 2-2 137 16-3 1,717 Welsh fire 2'4 150 14-9 Cement .... 17 106 31*1 5,000 Chalk, in lumps. 2-0 125 17-9 ,, powder . 2-6 4 165 13-6 I'O 1 " I IQ 188 ,, fire- (Newcastle) . 2-52 * L y 157 14-2 _ Concrete . . ' . 1-9 119 18-8 Granite, Aberdeen . . 2-62 163 137 10,900 ,, Cornish 2-66 1 66 I3-5 6,300 Limestone, blue Lias . 2-47 154 14'S ,, compact . 2-58 161 13-8 8,000 Masonry (mean) . 2-1 131 17 i Mortar . { 1-38 to 1-9 86 to 119 26 to iSS - Quartz . . . | 2-55 to 277 159 to 173 14-1 to 12-9 - Sand, coarse 1-61 IOO 22-4 ,, fine .... 1-52 95 23-6 Sandstone, Arbroath pave- 1 inent . . . J 2-47 155 14-4 7,884 Sandstone, Bramley Fall . 2-5 156 I4-3 6,050 ,, Caithness . . 2-64 165 13-6 6,490 Craigleith. -. 2-45 153 ir6 5,287 ,, Derby grit . 2-4 150 14-9 3,100 red (Cheshire) . 2-15 133 16-9 2,185 ,, Yorkshire paving 2-51 157 14-2 5,7'4 Slate, Cornish . 2-51 157 14-2, 10,000 Welsh . 2-88 i So ia-4 ; tO 21,000 Tables. 427 IHH >P,0 -25! 5: % ure H i & b MESTO 5S jb|^v| ? fl I J ^ureg 1 "!? ?l II" i: n 1 . M . M J-*? ^ ^'S, * f | Sv* "i M ei # b ptrej o^o o o *S co "o * B H -UOJ M S H M i S m Cl >I b I xog S>g"g | O PI 8K 5 2 v*a S; N M M l *> 2 2" MM V. b -suouy iplc-l 1 g? |f 1 =2 b 3 1N ^ b jj ^* %5= <$ ? u,^. 1 | " ? Cl Vl 1 b | s S2J OKR'O-I 1 ri | ft ^ ! 1 55 anois K^S^vS 1 5 * B *" * ?? - b Z UOJtK> X * s- 1 * I 1 sl II 1 b Q M 50 moo is. O\ Ov CO -^ ^ i UO PP 3 H Si ""1 1 B s v 1 b c3 =>i*a o* i S'S ss E | X3[JBQ ^0 M I ap. J M'PI " - 1 ^ 1 1 > fl \ I ^ I 2 O j 1 a 1 - P g N 3 C < "* ' IJronze for bearings - - - - 6 - - ~ - 17 2 77 orw ee oxes. Dutch-m^tal . Electrum . __ _ _ 51''- _ _ _ 25-8 _ _ 22'6 Fusible metal Lich- tenberg's . 20 JO 3 Fusible metal Rose's' JO 25 25 Wood's 50 I2'J 23 1 2"; German silver - - otc 60 - - Otn 20 - 3010 (plate) . . - 55 _ 2 24 3 16 Gold coinage . . - ^3: g.-66 Gun-metal . . Muntz's metal - - - 9 64 - ~ ~ ~ '- 40 to 35 Pewter, plate 7 2 a 85 triple 15 6 79 ley 20 80 Silver coinage 7'5 9**5 Solder fine . 33'3 66'C ,, common . 50 50 coarse . 66' f 33'3 for aluminium brazinjr 6 -' 4 - - - ~ 90 y , glaziers' _ - - - - 25 _ 75 5 gold 22' 66'6 in ' pewterers' II' 2 9'4 5 s-s silver - an - - - 335 29-2 Speculum-metal . Sterro-metal . - - - - crfo fa JtO., - - - 33'3 It02 34 to 44 Tutenag 45'7 - i?'4 36-9 Type-metal . . . OS - - 75 - - 5 5 QUESTIONS FOR EXAMINATION. FUEL. 1. How are the relative quantities of heat given out during the combustion of different bodies ascertained and computed ? 2. Define the terms calorific power and calorific intensity, and compare carbon and hydrogen in this respect when burnt in (a) oxygen, (&) air. 3. What are the conditions favourable to a high calorific intensity? 4. Why is less heat given out by the combustion of carbon to carbonic oxide than when the latter is burnt to carbonic acid ? 5. What is the effect of increased pressure during combustion ? 6. Define the term dissociation, 7. Can the commercial value of a given coal be ascertained by analysis alone? If not, by what would you be guided in forming' an opinion? 8. What is the approximate composition of (a) wood, (6) charcoal ? Has charcoal any advantages over wood as a fuel? 9. State briefly the general methods of manufacturing charcoal, enumer- ating any special precautions which it is necessary to take. 10. What is peat? How is it prepared for use? What are its properties as a fuel ? IT. Classify the various kinds of coal, and state the purposes for which each is more particularly suited. 12. In what respect does caking coal essentially differ in composition from non-caking coal? 13. Is more heat generated by the combustion of anthracite than by the combustion of caking coal ? 14. What deleterious substance is always present in greater or less quantity in coal? 15. Explain and compare the most important methods of coking coaL 1 6. Why is coke preferable to coal for certain purposes ? 17. Describe the construction of a gas-producer. t8. Describe the Siemens' regenerative system, and explain the advaa- 432 Questions for Examination. tages and disadvantages attending the use of gaseous fuel as compared with solid fuel 19. Sketch and describe (a) Cowper's stove, (i) Whitwell's stove. REFRACTORY MATERIALS. ^o. By what circumstances would you be guided in the selection of suit- able refractory materials for the construction of the various parts of furnaces and other metallurgical appliances ? 21. State what you know of the composition of clays. To what does clay owe its great value as a constructive material ? 22. What is the object of mixing with raw clay used for making refractor) bricks, &c. one of the following substances: burnt clay, coke dust, graphite, or silica? 23. Why is iron pyrites so objectionable in clay for crucibles ? 24. Describe the manufacture of crucibles. 25. How are silicious bricks made, and for what purposes are they used? 26. What is bauxite ? 27. What is dolomite, and what are its properties as a furnace material ? How is it prepared for use ? GENERAL PROPERTIES OF METALS. 28. What is meant by the tenacity of a metal ? Compare tin, steel, and copper with respect to this quality. 29. Why are metals annealed during the process of rolling them intc Sheets? 30. Explain why iron, though less malleable than lead, is more ductile. 31. The specific gravity of mercury is given as 135 ; what does this signify? 32. Spirit of wine burning in an earthern saucer is extinguished when poured upon an iron plate ; how is this accounted for? 33. If expense were no object, what metal would be best adapted for telegraph wires ? 34. Which of the metals in common use can be melted in a ladle placed upon an ordinary fire ? IRON. 35. What is meteoric iron! By what metal is it always accompanied? 36. Which of the ores of iron are most abundant in England and Scot- land respectively ? Are these the only iron ores smelted in this country ? 37 Why are some iron ores calcined or roasted previously to smelting them? Questions for Examination. 433 38. By what considerations is the pressure of the blast from the twyers of a blast-furnace regulated ? 39. Explain the principles upon which the flux for iron ores is selected. 40. Mention the chief chemical operations which take place in the blast^- furnace. 41. What is the nature of the gas issuing from the blast-furnace, and how is it turned to account ? 42. Point out the chief ingredients of the blast-furnace cinder. What does a black slag indicate? 43. Name the principal constituents of cast iron, and explain their presence. 44. Explain the difference between graphite and combined carbon, and state how their proportions influence the properties of cast iron. 45. What is the effect of casting in chills, and how can it be accounted for? 46. By what process can hard castings be softened externally ? 47. Under what circumstances does the blast-furnace yield white iron? 48. Which of the varieties of pig-iron contains the largest proportion of silicon ? 49. What quality of cast iron is best suited for fine castings ? 50. Why is the yield of iron from a given furnace greater in winter than in summer? 51. What is the mode of proceeding to obtain a mottled iron from a given furnace ? 52. What is the effect of phosphorus on cast iron ? 53. Describe a cupola furnace, and its use. 54. For what purpose is lime introduced into a cupola furnace ? What evil results from using an excess of lime? 55. State how chilling may be avoided when casting in sand. 56. Describe \hzfinery-hearth. 57. How is the composition of pig-iron affected by the process of refining ? 58. Compare the composition of finery cinder with that of blast-furnace cinder. 59. Explain the principle of the puddling process. 60. Mention the essential particulars in the construction of a puddling furnace. 61. Point out the difference between dry puddling and pig-boiling. 62. State the composition of tap-cinder. 63. Mention the principal defects of the puddling process. 64. What are the characters of mill bar, and how is it converted into merchant and best bar ? 65. In what particulars does the reheating furnace differ from other furnaces ? 434 Questions for Examination. 66. What explanation can be given of the improvement of bar iron by piling? 67. Explain the meaning of the terms hot-short and ccld-short, as applied to iron. 68. By what physical properties is steel distinguished from iron ? 69. Enumerate the most essential points to be attended to in the manu- facture of puddled steeL 70. Point out the best materials for making permanent and temporary magnets respectively. 71. How may iron bars be converted into steel ? 72. State the peculiar features of the cementation furnace. 73. What is the influence of the duration of the cementing process upon the character of the steel ? 74. Point out the defects of blister steel, and describe its conversion into shear steel. 75. How is cast steel produced? What advantages are secured by adding Spiegel-eisen to it ? 76. Is any chemical difference observable between hard and soft steel ? 77. By what process can the highest degree of hardness be conferred upon steel ? 78. Why is oil sometimes employed for hardening steel ? 79. Describe the process fur reducing the hardness of steel. 80. What is the object in bluing steel articles, and how is it effected ? 81. Describe and explain the process of case-hardening. 82. What descriptions of articles are usually case-hardened ? 83. By what mode of treatment may small castings be converted into malleable iron ? 84. What is meant by the Catalan process for the extraction of iron ? Why is it not practised in England ? 85. How would you explain the carburisation of the iron in the cementa- tion process ? BESSEMER PROCESS. 86. Describe and illustrate by sketches the apparatus necessary in the Bessemer process. 87. What means have been devised to enable the converter to be rapidly changed ? What advantage is thus gained ? 88. What kind of pig-iron would you use for this process ? Give your reasons. 89. Explain how the process is carried out. 90 In what respect does the Thomas-Gilchrist or 'basic' Bessemer process differ from the Bessemer or ' acid ' process : (a) in the nature of the plant ; (b) in the pig-iron used ; (c) in the earning out of the process ; () the Ponsard furnace. What are the probable advantages and disadvantages cf these furnaces? 95. What is the effect of the following elements on iron, individually, and also in the presence of one another : carbon, silicon, phosphorus, sulphur, copper, chromium, and tungsten ? COPPER. 96. Where is copper chiefly found in the metallic state? 97. Give the composition of the most abundant of the English ores of copper. 98. Name the chief seat of British copper smelting, and state the reasons for its selection. 99. What is the composition of fluor spar, and why is it useful in copper smelting ? ico. Enumerate the chie'" stages of the process for smelting copper ores, with the objects to be attained by each. 101. Explain the management of the clinker grate in the roasting-furnace. 102. What is the nature of copper-smoke ? 103. Point out the chief differences between metal slag and ore-furnace slag. 104. What advantage is secured by air-channels in the fire-bridge of the roasting-furnace ? 105. Give an explanation of the terms underpoled and overpoled copper. 106. What is the reason for scorifying copper with lead before rolling? 107. Why does the process adopted at Mansfeld differ from the Welsh process of copper smelting ? 108. Describe the process for refining the rosette copper at Mansfeld. 109. How is cement copper obtained, and what is its quality? 1 10. What is bean-shot copper used for, and how is it preparcyl ? in. Is impure copper more inclined to hot-shortness or to cold-shortness ? 112. Which of the uses of copper is most seriously interfered with by the presence of small quantities of foreign matter ? 113. Describe the process of obtaining precipitate copper from Spanish pyrites. How is the silver recovered ? r F 2 436 Questions for Examination. TIN. 114. What is the composition of tinstone, and where is it chiefly founi? 115. Explain the meaning of stream-tin. 116. Give an outline of the mechanical treatment of tin ores. 117. Describe the smelting process, pointing out the precautions against loss of tin in the slag. 118. How is tin refined by liquation ? 119. What are the objects of boiling and tossingl 120. How does the process followed in the Saxon tin-works differ from the English process? 121. What useful compound is prepared from the wolfram occasionally associated with tin ores ? 122. By what physical peculiarity may tin be immediately recognised ? 123. How is tin-plate made ? 124. Point out the difference between charcoal-plate and coke-plate. 125. Why is a kettle of block-tin so much more expensive than a common tin kettle? 126. How is copper cleaned previously to tinning it ? 127. Should alloys be regarded as merely mechanical mixtures, or as chemical compounds ? 128. Mention the chief useful alloys of copper and tin. 129. State the composition of the current bronze coin. 130. What is the method of hardening and tempering bronze? ZINC. 131. Enumerate the chief ores of zinc, stating their composition. 132. In what respect does the process of extracting zinc differ from those employed for most metals ? 133. What is the commercial name for zinc? Is any other substance ever called by it ? 134. By what rather rare metal is zinc usually accompanied in its ore ? 135. Under what conditions may zinc be rolled into sheets ? 136. Hosv can zinc be purified from lead ? 137. What is meant by burned zinc ? 138. Corrugated iron is used for building ; what is it ? 139. What impurity is especially objectionable in the zinc employed far making brass ? 140. State the composition of Dutch leaf gold. 141. For what reason is a little lead sometimes added to brass ? 142. How is brass lacquered ? Questions for Examination. 437 143. By what process are pins coated with tin ? , 144. State the composition of sterro-metal. For what purpose has it been employed ? 145. What is aluminium-bronze ? N'ICKEL AND COBALT. 146. Describe the physical properties of these metals. 147. Which are the principal ores of nickel and cobalt, and what is their usual compos 1 tion? 148. Give the principle of the methods employed in extracting nickel and cobalt from their ores. 149. For what purposes are these metals useful in the arts ? 150. By what means are nickel and cobalt rendered malleable? LEAD. 151. Give the name and composition of the most abundant ore of lead. 152. What other metals are generally found in lead ore ? 153. Point out the peculiar features of the reverberatory furnace for lead- smelting. 154. In what respect does the process of smelting galena resemble that adopted for copper pyrites? 155. Why is iron sometimes added to the charge in thesmelting-furnace? 156. In what respect does the economico-furnace differ from the re- verberatory furnace for smeitmg lead ores ? 157. What is the nature of the improving process ? 158. How may a poor argentiferous lead be rendered fit for cupellation ? 159. Point out the distinction between the high and low systems of con- centrating silver-lead. 160. By what method can leaden pipes be protected from the corrosive action of water ? 161. Of what material are metallic pencils composed? 162. State the composition of type-metal. 163. Why does antimony unfit lead for rifle-bullets? 164. How is the spherical form given to small shot? 165. Describe the mode of constructing the leaden chambers for the titriol-works. 166. What is the nature of the change by which lead is converted into an earthy mass, easily crumbling ? 167. State the composition of pewter. Why is the standard proportion of lead fixed at one-filth only ? 168. What is the difference between pewterers' solder and common solder ? 438 Questions for Examination. 169. Why is zinc dissolved in the muriatic acid which is used for soldering? 170. Give the composition of hard Bolder. What is the effect of adding silver to it ? SlLVfc-R. 171. Explain the principles of the process of cupellation. 172. What is litharge ? How is it obtained ? 173. Why does melted silver sprout in solidifying? 174. Mention the principal differences between the English and German cupellation processes. 175. Describe the extraction of silver from the black copper at Mansfeld. 176. What is the principle of the extraction of silver by amalgamation? 177. Why is this process carried on so differently in Mexico and Saxony? 178. Describe a process in which common salt is employed for extracting silver from the ore. 179. What is the composition of silver coin ? Why is not pure silver circulated ? 180. What is understood by the assayer's statement that a sample of silver is worse 5 diets. ? 181. How can the genuine character of a shilling be tested without injuring it ? 182. Why does silver tarnish so quickly where coal-gas is employed ? How may it be cleaned ? 183. Point out the difference between old silver plate and electro-plate. 184. What solution of silver is best adapted for electro-plating? 185. In what respect does the mode of occurrence of gold in nature differ from that of most other metals ? 186. Describe the washing of auriferous sand in the cradle. 187. How is gold extracted from pyrites in the Tyrol ? 188. Describe the process of parting by sulphuric acid. How is the silver recovered in the metallic form ? 189. Is native gold absolutely puie ? 190. .What is meant by fine gold, and by gold 0/18 carats fin el 191. By what rough test is gold commonly tried? Show when it is fallacious. 192. Explain the use of the touchstone. 193. What is meant by inquartation in the assay of gold, aac* why is i necessary ? 194. Describe the manufacture of gold-leaf. 195. How are buttons coated with gold? Questions for Examination. 439 MERCURY. 196. In what forms is mercury met with in the mineral kingdom ? 197. What is the nature of the process employed for extracting mercury a; the works in Idria? 198. Is there any more economical process than this? 199. Give a ready method for ascertaining the purity of quicksilver. 200. Why is mercury selected for filling thermometers ? 201. What is an amalgam ? 202. How are looking-glasses usually made ? PLATINUM. 203. What is the condition of platinum in the ore ? 204. Point out the chief differences between the old and new processe* for treating platinum ores. 205. How is platinum melted in considerable quantities ? 206. In what branch of manufacture is platinum largely employed ? 207. Why should platinum vessels never be heated in a coal fire ? ANTIMONY, &c. 208. What is the difference between crude antimony and regulus of antimony ? 209. By what peculiarities is antimony distinguished from all othei metals ? 210. What is remarkable in the process of extracting bismuth from it* ores? 21 r. Mention the impurities commonly found in the bismuth of com- merce. 212. Upon what peculiarities do the uses of bismuth depend ? 213. Where is aluminium met with ? Does its high price depend upon its scarcity ? 214. What useful applications have been found for aluminium? 215. From what circumstance does magnesium derive importance? INDEX. AFF BAR BLA AFFINITY, chemi- cal, i After-blow (basic process), Anodes, nickel, 300 Anthracite, 27, 34 Anthracitic coals, 34 Bar-iron, 176 -, fibrous, 157 , manufacture of, 161 211 Antimony, 413 Basic-Bessemer process, Agitator, Bessemer's, 204 Aich-metal, 293 , alloy of, 294 and lead, alloy of, 320 209 lining, 85, 210 Air, action of upon heated , crude, 413 for Siemens-Martin carbon, 5 , grey ore of, 413 process, 213 composition of, 5 Alloy, fusible, 419 in coal, 37 in lead ores, 309 process, value of phos- phorus in, 2 i Alloys, 269 , native, 413 Barometer, 401 of copper and tin, 269 Alluvial tin-ore, 251 ore, 413 oxide, 413 Barvtes, sulphate of, 302 Bauxite, 83, 420 Almaden, extraction of , properties of, 415 composition of, 83 mercury at, 390 - , red, 413 extraction of alumi- Altenau, improvement of regulus, 413 nium from, 420 lead at, 320 , star-, 415 Bean-shot copper, 249 Altenberg tin-works, 262 Aludels, 392 sulphuret, 413 Apatite, 100 Bee-hive coking oven, 40 Bell-metal, 270 Alumina : a refractory Appolt coking oven, 42 Bessemer's agitator, 204 substance, 83 Aquafortis test for gold, converter, 199 , silicate of, 77 Aluminum, 419 and silver, alloy of, 421 381 Argillaceous iron ores, 102 Arguzoid, '-199 pressure furnace, 9 process, 198 Bessemer blow, 202' bronze, ^94, 421 , extraction of, 420 Armour plates, 214 Arsenic, 230 , duration of, 209 casting-ladle, 202 -gold, 421 in coal, 37 converter, bricks for, Amalgam, 402 in lead shot, 330 81 , dentists', 403 sulphuret, 331 piocess,use of spectro- for electrical machines, , white, 2 3 o ; 33I scope in, 209 403 Arsenical pyrites, 224 value of silicon in, , magnetic, 403 Arsenide of nickel, 295 207 of gold, 371 Arsenious acid, 230, 331 steel, 198 of silver, 349 Ash of coal, 36 - for cutlery, 222 Amalgamating, 88 Amalgamation, 345 of peat, 19 of wood, ii Best selected copper, 237 ' Binding ' coal, 36 -floor, 346 Assay of gold by cupella- Bismuth, extraction of, , hot, 349 tion, 382 416 , Mexican process, 346 Augustin's process for in tin, 262 , , reactions in, 347 extracting silver, 357 Bituminous coal, 27, 31 of gold ores, 371 of silver ores, 345 , Saxon process, 350 Autogenous soldering, 332 Axes, tempered, 216 Azurite, 225 wood, 30 Blackband, 103 Black brush ore, 102 , Washoe process, 350 copper, 237, 245 Amalgams, 402 , refining of, 245 Anglesea copper, 248 BANCA TIN, 260 Blacking, ironmouldtiSj Anglesite, 30} BarfTs process for 160 Annealing, 91 protection of iron, 126 Black-jack, 273 442 Index. BLA CAR CAS Black plates, 265 Britannia metal, 272 i Carbon, action of carbonic Blast-furnace, 128 Bronze, 272 acid on red-hot, s , boshes of, 138 aluminium-, 294 and iron, 215 , charging of, 146 _ , annealing of, 272 , chemical changes in, coin, 272 , calorific intensity of, 4 , power of, 2 132 founding, 272 , combustion of, i , conditions in, 132 nails, 272 , graphitic, in pig-iron. , construction of, 138 powder, 291 151 - , dimensions of, 143 pump-valves, 272 in iron, i. 2is gases, 69, 135 j sockets, 272 Carbonic acid, 2 , composition of, 69 , lining of, 138 stop-cocks. 272 , tempering of, 272 , action of red-hot carbon on, 5 , modern, 139 weapons, 272 , composition of, 2 - slag, 146 wheel-boxes, 272 , temperature of dis- , tapping, 139 , twyers of, 142 Blast-furnaces, Styrian Bronzing, 292 Brown blaze, 278, 424 haematite, 101 sociation of, 9 oxide, 5 , calorific intensity and Carinth an, 128 Browse, 312 of, 7 Blast main, 131 Brunton's calciner, 255 , calorific power of, 6 , pressure of, 131 regulator, 131 Brush-ore, 102 Buddie, 254 , composition of, 6 , formation of from Blauofen, 128 Bull-dog, 170 carbon and carbonic Bleiberg, extraction of Bullets, rifle, 329 acid, 5 lead at, 309 , shrapnel, 330 , reduction of iron Blende, 273 Burden of furnace, 128 ores by, 105 Blister copper, 238 - steel, 114 Burning-house, 254 Burnt clay, addition of to , temperature of dis- sociation of, 9 Block tin, 268 fire-clay, 79 Carinthian blast-furnaces, Bloodstone, 100 Burra-Burra copper, 250 128 Bloom, 161 Butter-milk ore, 335 Carnallite, 422 Bloomery, 161 Blooming-mill, 177 Blowing-cylinders (blast- Buttons, gilding of, 388 Bye-products of coke manufacture, 52 Carves' coking oven, 54 Case-hardening, 122 Castilian furnace (lead), furnace), 130 -engines, 130 Castings, iron, chilling of, -house, 261 Blue, cobalt, 297 pADMIA, 279 V_x Cadmium, 273, 424 , , influence of cool- malachite, 225 extracted from zinc ing upon, 155 metal (copper), 236 steel, 216 vitriol, 244 ores, 278 Caking coal, 27, 32 CaJamme, 273, 274 , , influence of crys- tallisation upon, 155 , , protection of from water, 248 , electric, 274 rust, 160 Boil (Bessemer process), Calcination of iron ores, Casting-ladle, Bessemer, 203 144 185 Boiler-plate iron, 189, 214 Calciner, 228 Casting of iron in sand. -plates, by open-hearth Calcining, 143 '59. processes, 189 furnaces, 144 Cast-iron, 141) Boiling process (iron), Calc-spar, 302 , composition of, 149 173 Calomel, native, 390 , con version of into bar- Boshes of blast-furnace, Calorific intensity, 3 iron, 161 138 , influence of pres- , grey, 153 Bottle-slag, 259 sure upon, 7 , malleable, 122 Bottoms (copper), 237 limited by disso- , manufacture of, 128 Brasque, 83 ciation, 8 , mottled, 152 Brass, 289 of carbon, 4 , phosphorus in, 149, for engraving, 292 of carbonic oxide, 7 founding, 290 of hydrogen, 4 , remelting of, 158 , malleable, 293 power, 3 , silicon in, 149 , manufacture of, 290 Braunkohle, 29 of carbon, 2 of carbonic oxide, 6 , specific gravity of, 153 , sulphur in, 152 Brazing, 334 of cellulose, it , varieties of, 151 Breeze, 14 Bricks, silicions, 8r of hydrogen, 2 Candles, puddlers', 174 , white, 153 Cast-steel, 118 , slag, 148 Cannon, casting of, 271 , silicious, 220 Brightening, 339 Carat, 381 1 Casting iron, 158 Index. 443 CAT CON COP Catalan process, 107 Coal, arsenic in, 37 Conducting power of Cawk, 302 Cellulose, ii , ash of, 36 , copper in, 37 metals for electricity, 94 of metals for heat, , calorific power of, n , employment of, in Cementation, 112 making malleable iron, Considere's process, 206 -furnace, 112 1 168 Continuous working of powder, 113 , first use of in blast- iron ores in India, 106 , theory of, 123 furnace, 130 Converted steel, 119 Cement copper, 248 -gas, 51 Converting-furnace, 112 -, slag-, ,48 , iron in, 37 -vessel ( Bessemer's), Charcoal. !2 , lead in, 37 '99 , absorbing power of, -measures, 27 Cooling, irregular, of iron 18 -measures, ironstones castings, 155 -burning, 13 of the, 103 Coppe'e coking oven, 46 , circular pile for, 14 , rectangular piles , phosphorus in, 36 -slack, 49 Copper, 223 , alloys of, 289 for, 1 6 , sulphur in, 36 and arsenic, 250 from peat, 26 -, valuation of, 10 and iron, 221 , inflaming point of, 13 , weathering of, 37 and nickel, 298 -plates, i 66, 264 -refined iron, 166 Coals, anthracitic, 34 -, classification of, * 7 , 28 and silver, 360 and tin 269 Charge for blast-furnace, , composition of, 28, 29 and zinc, 289 146 Coarse copper, ,37 , Anglesea, 248 Chemical affinity, i metal, 231 , antimony in, 249 Cherry-coal, 32 Chessy copper, 248 Chill-casting, 154 , calcination of, 235 Cobalt, 294 , malleable, 299 , arsenic in, 249 ' , barilla, 223 , bean-shot, 249 Chills, 154 China clay, 77 , ores of, 295 , separation from nickel, , best selected, 237 -, bismuth in, 249 Chinese cannon, 293 297 -, blister, 238 Chisels, tempered, 216 Chrome steel, 221 , specific gravity of, 295 Coin-bronze, 272 , cement, 248 cleaned, 268 Chromium and iron, 221 Coin, gold, 380 - dry, 241 in pig, 151 -, silver, 360 , effect of impurities on pig, 151, 222 , testing of, 361, 381 249 steel, 221 Coke, 37 , of phosphorus on, Cinder, 105 bui ned in piles, 37 250 , finery, 163 from blast-furnace, 146 , definition of, 31 , desulphurisationof, 50 , of sen-water on, 250 , electric conductivity Cinnabar, 390 , kilns for preparing, 38 of, 250 Classifications of coals, manufacture, bye-pro- , extraction of, 226 27, 28 ducts of, 52 , - of, at Mansfcld. Claudet's process, 360 , percentage of from 242 Clausthal, extraction of coals, 28 , of silver from, 343 lead at, 317 -plates, 16', 264 , feathered shot, 249 Clay, 77, 419 , washing of to remove glance, 225 -band, 102 pyrites, 51 , impurities in, 249 , causes influencing fu- sibility of, 78 , china, 77 oven, Appolt, 42 , Bee-hive, 40 , Carves, 54 in coal, 37 , indigo, 225 _ , Lake Superior, 223 , composition of, 76 , Coppe'e, 46 , lead in, 241 crucibles, manufacture , Pernolet, 52 , moss, 237 of, 79 Cold-shortness in iron, , effect of the impurities produced by phos- , nickel in, 249 in, 78 phorus, 220 ore, bituminous, 243 , fire-, 78 in iron, produced , black, 225 ironstones, 102 by silicon, 217 , grey, 224 , Stourbridge, 78 Combined carbon in iron, , red, 225 , testing of, tor resist- 15' , variegated, 224 ance to heat, 79 Combustion, heat of, x , yellow, 224 Cleveland blast-furnace, Common tin, 260 ores, 224 Clinker, 36, 229 Composition of blast-fur- nace gases, 69 , calcining of, 227 , fusion 01, fot Coal, 26 of coals, 28, 29 coarse-metal, 231 , antimony in, 37 Concrete, slag, 148 , roasting of, 227 444 Index. COP ECO FUE Copper ores, treated for silver, 343 Cupellation of platinum, 408 Electrical amalgam, 403 , overpoled, 241 , oxides of, 224 on large scale, 336 on small scale, 383 Electric calamine, 274 conductivity ot metals, , oxygen in, 241 , peacock-, 224 , phosphorus in, 250 Cupola furnace, 158 Cyanogen, influence of in steel making, 114 Electro-gilding, 389 Electro - metallurgical plates, cast, 248 Cymbals, 270 treatment of 2inc ores, , poling, 240 288 precipitate, 247 Electro-plating, 363 , precipitated, 248 Electro-silvering, 363 pyrites, 224 , recovery of from DAM - PLATE of blast-furnace, 139 Electrum, 298 Eliquation, 343 hearths of furnaces, 242 Dam-stone of blast-fur- Elongation of steel, 210 refining, 239 at Mansfeld, 245 nace, 138 Danks' furnace, 180 Expansion of steel during hardening, 217 , rose, 248 Dannemora iron, 100 , rosette, 248 Dead-head, 271 sand, 223 scale, 249 Decarburisation of iron, 122 -C-AHLERZ, 399 J. Fallow-ore, 399 schist, 242 Density of coke, 54 Ferro-manganese, 150 separated from silver, Desilvering lead, 320 Fettling, 170 343 by Parkes' process, Fibre in iron, 138 smelting, 226 3 2 7 destroyed by vibra- smoke, 230 by zinc, 327 tion, 158 -, Spanish, 249 Diffusion, influence of on Fibrous bar-iron, 157 sulphate, 376 cementation, 124 structure, 157 sulphur in, 249 tin in, 249 Dinas brick, 67 Dissociation, influence of, Fine-metal (copper), 236 (iron), 165 tinning of, 268 in cementation, 116, 123 Finery, 161 tough-cake, 240 , influence of, on heat of cinder, 163 tough-pitch, 240 underpoled, 241 combustion, 8, 67 , temperature of, for for making steel, 167 furnace, 161 vessels for cooking, carbonic acid, 9 hearth, 161 , of, for carbonic Fire-bridge, 170 c u8 oxide, 9 of reverberatory , blue, 376 , of, for water furnace, 56 Cornette, 383 Corrugated iron, 288 Coruscation, 339 Distillation of lignite, 31 of wood, 12 Fire-clay, 78 Fire, the Hollow, 166 Fleitmaun's method for Cowper stove, 70 Dolly, 254 producing malleable , dimensions of, 73 Cradle for gold-washing, 37 Dolomite, 85 as furnace lining 85 Double shear steel, 117 nickel, 299 Flexibility of steel, 219 Flue - bridge (puddling Crucible of blast-furnace, Doubles (tin-plate), 168 furnace), 170 138 ' Down-comer ' of blast- Fluor-spar, 227 Crucibles, firing of, 80 for distilling zinc, 276 for melting steel, 118 machine-made, 80 furnace, 70, 141 of gas producer, 58 Dowson's gas producer, 63 Flux, 103 Fore - hearth (blast-fur- nace, 139 Forest of Dean iron, 102 manufacture of, 79 plumbago, 83 Cryolite, 419 ' Dry * copper, 240 Dry puddling, 173 Ductility, 92 Forge, Catalan, 107 train, 175 Fork handles, German Crystalline iron, 155 Dust, removal of, from silver, 298 Crystallisation, influence of, on ron castings, Cowper stoves, 73 , of, from Whitwell Forks, Gorman silver, 298 Formation of coal, 26 Cup and cone for blast- stoves, 75 Dutch gold, 291 Fossil wood, 30 Fracture of bar-iron, 158 furnace, 135 metal, 291 ' Free-burning ' coal, 36 Cupel, 336 Freiberg, extraction of for assaying, 382 silver at, 350, 359 furnace, 382 Fuel, i Cupellation, German me- thod, 341 ECONOMICO-FUR- NACE, 315 , calorific intensity of, 3 , hot-blast, 343 Elasticity of steel, 216 , power of, 3 Index. 445 FUE GOL HOR Fuel for blast-furnace, 130 Gilders' wax, 388 Gold, white, 404 , gaseous, advantages Gilding, 387 Gongs, 270 of, 55 -, dead, 388 Grain nickel, 297 Fuels, patent, 50 , electro-, 389 tin, 260 Fuel, valuation of, 10 iron and steel, 389 Graphite in iron, 151 Figuration, 339 Gjers pneumatic lift, 136 Gravity, specific, 92 Furnace, Bessemer s pres- Gold, 367 Green malachite, 225 sure, 9 , alluvial, 368 Greillade, 108 , blast, 128 -, calcining, (lead), 318 , amalgam of, 371. 387 and copper, alloy of, Grey cast-iron, 153 , theory of its , Catalan, 107 380 production, 151 , cementation, 112 and platinum sepa- iron, conversion of. , cupola, 158 rated, 411 into white, 163 , Banks' puddling, 180 and silver, alloy of, copper ore, 2^5 , finery, 161 , improving, (.lead), 318 334 separated, 37 i slag, 312 Guineas, composition of, , mill, J77 assay by cupellation, 380 , Pernot's revolving, 195 382 -beaters' skin, 385 Gun-metal, 270 Guns, casting of, 271 , Ponsard, 213 -beating, 384 , puddling, 170 , Californian, 379 , regenerative, 63 , re-heating, 177 , reverberatory, 56, 228 carats, 381 , chloride of, 388 cleaned from mercury, HAEMATITE, 100 , brown, 101 , roasting, 228 402 , red, loo , Siemens', for direct coin, 380 Hammer-scale, 170 production of malleable iron, 192 , colouring of, 384 , Dutch, 291 Hammer-slag, 170 for puddled balls, , Siemens' regenera- , effect of antimony 175 tive, 63 on. 380 Hardening by chilling, , Stirling's regenera- , ofleadon, 3 8o '54 tive, 63 extracted by amalga- in oil, 217 Fusibility, 95 mation, 371 of steel, 216 Fusible alloy, 419 from old silver, 374 Hard head, 260 from pyrites, 371 metal, 271 from quartz, 371 Hearth for refining cast GALENA, 301 , argentiferous, with lead, 372 extraction in the wet iron, 164 of blast-furnace, 138 302 way, 378 Heat, bright red, 96 , roasting of, 303 , fine, 380 , cause of intensity of, , smelting of, 303 , fineness of, expressed, in Bessemer process, Gallery furnace, 397 381 207 Galvanised iron, "287 lace, 386 , cherry red, 96 Gangiie, 147 leaf, 384 , conducting power of Canister, 82 Gas coke, 53 for dentists, 384 , manufacture of, metals for, 93, 94 of combustion, i Gaseous fuel, 55 384 , red, 96 Gases from blast-furnace, , Mosaic, 292 -, white, 96 69, 135 , native, 368 Heath process, addition Gas-furnace for puddling, pens, 405 of manganese to steel, 172 quartz, 368 1 20 , Siemens' regenera- -, red, 388 for making steel tive, 64 , refining, 378 by fusion, 185 Gas-producers, analysis of gas from, 60 , removal of mercury from, 402 Heavy spar, 302 Heliotrope, 100 Gas-producer, Dowson's, 63 separated from silver and copper, 374 Helve-hammers, 175 Hollow fire, the, 166 , Siemens', 57, 61 standard, 380 Honeycombed ingots of , use of steam in, 59 . testiner of. with aaua- steel, 119 , Wilson's, 63 Gedge's metal, 293 fortis, 381 , of, with touchstone, Honeycombing, preven tion of, in Bessemer German silver, 298 381 castine. 206 castings, 298 thread, 386 Horn-silver, 335 Gerstenhoffer's furnace, , transparency of, 386 Hornstone, 367 230 washing, 369 Horseshoe main. -.41 446 Index. HOT KN1 LEA. Hot-blait. -.31 Iron, malleable, produc- Knives, tempered, 2:6 Twyers. 142 Hydrogen, calorific in- tion of, 105, 161, 190 Konesberg, treatment of , use of manganese, in silver ores at, 345 tensity of, 4 , power of, 2 221 Kryolite, 419 , meteoric, 98 Kupfernickel, 295 , mottled, IS', '5' -moulders' blacking, IDRIA, extraction of 160 T ACQUER, 292 mercury at, 393 Indigo-copper, 225 , native, 98 I ^ Lacquering, 292 ores, 98 Ladle, Bessemer casting-, Inflaming point of char- , calcination of, 144 ; 185 coal, 13 -- -.reduction of, by ! Lake ores. 102 of wood, 12 carbonic oxide, 105 Lamination, 91 Inquartation, 377 ore, sparry, 102 Lancets, tempered, 216 Iridium and osmium, al- , oxide of, 99 Lead, 301 loy of, 379, 405 partitions, use of in , action of acids on, Iron, 97 regenerators, 68 331 , action of air on, 126 and zinc, alloy of, , phosphorus in, 154 plates cleaned, 265 and antimony, alloy of, 320 287 rolled, 265 and tin, alloys of, 332 , antiquity of, 104 , bar-, 176 , protection of from rust, BarfTsand Bower's pro- , argentiferous, 320 , calcining of, 317 bloom, 161 cesses, 126 carbonate, 302 , Burmese method of pyrites, 104 -coated projectiles, 329 extraction of, 106 m coke, 50 containing silver. 320 , carbonate of, 102 , raw, 162 , corrosion of, 332 , cast, 149, 158 red oxide of 100 desilverised, 320 , casting of, in sand, , red-short, 188 -, English, 317 159 refinery, 163 , Extraction of in ore- , castings, influence of , remelting of cast, 158 hearth, 310 cooling upon, 155 , influence of crys- tallisation upon, 155 , casting, value of phos- , removal of phos- phorus from, in bloom- ery, 163 san-1, 100 , hard, 317 , hardened, 329 improving process, 317 phorus in, 221 scales, 170 in brass, 292 , combustion of, 203 silicate, 170 in coal, 37 , copper in, 22 1 smelting, 128 in copper, 241 , corrugated, 288 , steely, 109 , native, 301 , decarburisation of, stones, 102 ore, preparation of, 122 of the coal mea- 303 , direct production of sures, 103 ores, 301 malleable, by the Siemens process, 100 sulphide, 104 , sulphur in, 152 poisoning, 328 , pressed, 309 , early methods of ex- , tinned, 264 , silver extracted from. traction of. 105 , effect of carbon on, 2 ' 5 , useful properties ol, 97 336 slags smelted, 313 , of chromium upon, 221 , white, 153 - -works of the Pyre- smelting, 303 smelling in Carinthia , of phosphorus nees, 107 39 upon, 220 , wrought, direct ex- - in reverberator? , of silicon upon, 217 traction of, 105, 191 , direct manufacture of, furnace 303 , softening, 317 , of sulphur upon. 105, 161, 190 , Spanish, 317 220 sulphate, 303 , of tungsten on, 222 sulphide, 301 , extraction of, 104 , hbre in, is? JAPAN copper, 248 Johnstone's malleable , permeation of cru- cibles by, 80 -, galvanised, 287 "ickel, 299 sulphuret, 301 glance, 101 pipes, tinned, 329 , grey, 153 , uses of, 328 in coal, 36 , Indian mtthod of ex- KIEVE, 254 Kilns for calcining , virgin, 309 , white, 332 traction of, 106 , magnetic oxide of, gy, iron ores, 144 Knife-handles, German Leaden chambers, 33: cisterns, 328 126 silver, 298 coffins, 334 Index. 447 LEA MET MJG Leaden pipes, 328 Lignite, 26, 29 , distillation of, 31 Malleable iron, conversion of pig-iron into, 161 , direct production of, Mexican process for ex- tracting silver, 346 _ , reactions in, 347 Lime as a flux for iron 106, 107 Micaceous iron ore, JOT ores, 145 , of, by the Mild steel, 119 as refractory material, Siemens process, 190 Mill, blooming-, 177 84 nickel, 299 -furnace, 177 , composition of, 146 Manganese and iron, 221 (puddling process), 175 , use of in the blast-fur- in cast iron, 150 Mine, 108 nace, 14; in iron ores, 102 tin ore, 251 Limestone for basic lining, in pig-iron, 150 Mirrors, manufacture of, 210 , magnesian, use of, as in steel, 120, 220 , use of, in Catalan pro- 402 Mispickel (arsenical py- cess, no rites), 224 Lining, basic, 85, 210 of blast-furnace, 138 , use of, in open-hearth steel making, 188 Moire' me'taliique, 268 Mona copper, 248 of converter, basic pro- , use of, in preventing Mortar, slag-, 148 cess, 210 red-shortness in steel, Mosaic gold, 292 Liquation, 215 -hearth, 216 188 Mansfeld copper process, Moss copper, 237 Mottled cast-iron, 151, of tin, 139 List on tin-plate, 267 242 , extraction of silver 152 Muffle, 281, 383 -pot, 267 at, 343 furnace, 383 Litharge, 338 , flaky, 343 Manure, slag-, 149 Marcasite, 416 Mundic (iron pyrites), 104 , green, 342 Market-pot (lead), 321 Muntz-metal, 293 , red, 342 , reduction of, 340 Lloyd's spray twyer, 142 Loadstone, 99 Lodej ico Masse', 108 Matt, 233 Mechanical puddling, 179 Melting-points of metals, 96 NAILS, bronze, 272 for sheathing, 293 Nassau, extraction of lead Looking-glasses silvered, Mercury, 389 in, 309 402 and silver, 334 Native copper, 223 Lustre, metallic, 88 , black, 397 iron, 98 extracted from grey New Caledonian nickel copper ore. 700 ore, 295 MACHINE, Banks' , extraction'of, 390 puddling, 180 , impurities in, 400 Newton's fusible alloy, 419 , puddling, 179 , Withams puddling, nitrate, 387 , properties of, 401 Nickel, 294 and copper, alloy of, 179 , purification of, 400 298 Machinery for crucible , removal of, from gold, ami zinc alloy, 300 making. So 402 , arsenide of, 295 Magistral, 347 sulphide, 390 , extraction of, 296 Magnesian limestone for sulphuret, 390 , grain-, 297 basic lining, 210 : , uses of, 401 , malleable-, 299 , use of, as furnace Metal, 87 , , for anodes, 300 lining. 84 Metals, 87 ore, smelting of. in Maguesite, 422 , characteristics of, 88 [ blast-furnace, ^297 Magnesium, 422 , conducting power for , ores of, 295 , extraction of, 422 electricity of, 95 , separation of, from , properties of, 422 ' , for heat of, 94, cobalt, 297 Magnetic iron-ore, 99 95 , silicate of, 295 oxide of iron, 126 ; , ductility of, 02 -silver, 298 Magnetism, power of steel , fusibility of, 96 , specific gravity of, 295 to retain, increased by , heat conducted by, -speise. 296 tungsten, 222 93 ; Non-caking coal, 27, 32 Magnetite, 99 , lustre of, 88 > Northamptonshire iron Malacca tin, 260 . malleability of. 01 ore. IOA Malachite, 225 , specific gravity of, 93 ' Nose ' of slag (blast-fur- , blue, 225 , strength of, oo nace\ 152 Malleability, gi , tenacity of, 89 Noses of tuyeres, 132, Malleable brass, 293 1 Metal-slag, 234, 237 315 cast iron, 122 j Meteoric iron, 98 ' Nova Scotia iron, ror cobalt, 299 Meteorite of Lenarto, 98 ' Nuggets, gold, 367 448 Index. OCH PNE RED OCHRES, ioa Oil, cooling of steel Phosphorus, elimination of, from iron, 129 Poling, 240 Polishing, 89 in M 9 , hardening in, 217 , of, in basic process, 209 Potash, prussiate of, for case-hardening, 122 Oolitic iron ore, 104 of, in Bloomery, Pots (cementation pro- Open-hearth process for 163 cess), 113 steel making, 186 in bar iron, 220 Ponsard furnace, 213 Ore-furnace, 231 in cast iron, 149, 220 Precipitate copper, 247 slag, 234 in coal, 36 Pressure furnace, Besse- hearth, 310 in iron, 154 mer's, 9 Ores, 98 , use of, in iron casting. , influence of, on calori- Orpiment, 331 221 fic intensity, 7 Osmiridium, 379 Osmium and iridium, , value of, in basic pro- cess, 211 Prince's metal, 292 Proof-bar (steel), 113 alloy of, 379, 405 Oven. Appolt coking, 42 , Bee-hive coking, 40 , Carves' coking, 54 Pickling iron plates, 265 Pig-boiling, 173 , chromium-, 222 -iron, 149 Proof in assaying, 383 Protection of iron from rust, BarrTs process, 126 Prussiate of potash for ' Oven ' coke, 53 , chromium, 151 case-hardening, 122 Oven, Coppee coking, 46 , impurities in, 150, Puddled bars, piling of, , Pernolet coking, 52 176 Over-melting, effect of on , silicon in, 149 - steel, x8 4 steel, 217 , tungsten, 151 Puddlers' candles, 174 Overpoling of copper, 241 Oxide of iron, 99 Oxyhydrogen furnace,4o8 Piling bar-iron, 176 Pimple metal, 236 Pinchbeck, 292 Pins, tinned, 292 mine, 171 Puddling, dry, 173 furnace, 170 , Danks', 180 , whitened, 293 , Witham's, 179 PADDLE, 170 Paint, metallic, 286 Pittsburg, Siemens' rota- tors at, 195 machine,Witham's,i7g , mechanical, 179 Palladium, 412 Plane-irons, tempered, 216 i process of, 168 and silver, alloy of, 412 Plasticity of clay, 77 rolls, 175 Parkes' process, 327 Parting of gold by nitric Plate-metal, 165 Plated goods, manufac- Pyrenees, iron-works in, 107 acid, 377 ture of, 362 Pyrites, arsenical, 224 by sulphuric acid, 374 wire, 362 Platina, 404 , copper, 224 , effect of, on clay for Patera's process for ex- tracting silver, 358 , muriate of, 292 Platinum, 404 crucibles, 79 , extraction of silver Patent fuels, 50 Pattinsonising, mechani- ammonio-chloride, 405 and gold separated, from, 360 in coke, 50 cal, 326 : . 411 , iron, 104 Pattinson's process, 320 and silver, alloy of, 411 Pyroligneous acid, 12, 17 high system, 324 black, 412 low system, 324 Pauwels and Dubochet, cleaned, 410 corroded, 410 QUARTATION, 377 coking oven, 52 crucibles, 409 Quartz, 227 Peacock copper, 224 , extraction of, by the -, gold in, 368 Pea iron ore, 101 dry method, 407 Quicksilver, 389 Peat, 18 , by wet method, 405 charcoal, 26 , fusion of, 406 cutting machine, 20 , specific gravity of, 19 -iridium alloy, 410 , nuggets of, 404 T) ABBLE, 172 IN. Rabbling, 171 Pencils, metallic, 329 Penknives, tempered, 216 Permeation of crucibles ore, 404 , soldering of, 409 , spongy, 405 Rack, 254 Rails, Bessemer steel, 209 Railway bars, 214 by sulphide of lead, 80 Pernolet coking oven, 52 stills, 409 touch-holes, 411 Rain-chamber, 311 Raw iron, 162 Pernot's furnace, use of, in Scotland, 197 , uses of, 409 , welding of, 406 Razors, tempered, 216 Recovery of copper from Pernot revolving furnace. Planner's process for ex- hearths cf furnaces, 242 Pewter, 332 tracting gold, 379 Plumbago crucibles, 83 Red coppsr ore, 225 heat, 96 Phosphorus and iron, 220 Pneumatic lift for charg- haematit:, 100 as a fuel, 2 ing blast-furnace, 137 -shortness, 188 Index. 449 RED SIL SLA Red - shortness in iron, [ Scintillation of white iron caused by sulphur, 220 i in pouring, 153 , produced by sil- ' Scona, 241 Silver and palladiuni.alloy of, 412 and platinum, alloy of. bcorincation, 241 4:1 -short steel, 188 silver ore, 335 Scotch furnace for lead- smelting, 310 and zinc alloy, 327 , applications of, 360 zinc ore, 273 Refinery, 163 Serpentine as refractory material, 83 blackened by air, 361 bromide, 335 slag (copper), 241 Refining basi (tin), 259 Refining cast iron, 163 Shear-steel, 116 Shears, tempered, 216 Ship-plates by open- chloride, 335 cleaned, 362 coin, 360 copper, 239 hearth processes, 189 , dead, 36! Refractory materials, 75 Sh t, 330 extracted by Augus- Regenerative furnace, Siemens', 63 , cast-iron, 155 Siemens' gas-producer, t's process, 357 by Patera's process, , Stirling's 63 57, 61 358 steel furnaces, 121 Siemens-Martin process, by Ziervogel's pro- stoves, 63 186 cess, 358 Regule, 237 , basic lining for, from bismuth, 417 Regains, 933 . 2 '3 from copper, 343 of antimony, 414 Siemens* open-hearth from copper-matt. Reheating furnace, 177 steel melting furnace, 356 Remeltmg of cast iron. 64 from copper ores, 158 , pig and ore process, 343 Retorts for charcoal-burn- 186 from its ores, 345 ing, 17 Reverberatory furnace, process for direct pro- duction of malleable from lead, 336 extraction by amal- 56 Revolving furnace, Banks', 180 iron, 190 regenerative furnace, 63 gamation, 345 by lead, 345 , fineness of, expressed, , Pernot's, 195 rotating furnace, 191 36 Richardson's furnace steel, 189 , frosted, 361 (lead), 315 for cutlery, 222 , German, 298 Roaster-slag, 238 -melting furnace, glance, 355 Roasting, 143 bricks for, 81 in lead, 320 furnace, 228 Silica, 75, 227 in lead-ore, 302 in heaps, 144 , composition of, 162 iodide, 335 of iron ores, 144 Silicate of alumina, 77 - leaf, 365 -stalls, 244 of iron, 170 , native, 334 Rocks, weathering of, 77 Rolling-mills, 175 of nickel, 295 Silicates, formation of, 75 ore, brittle, 335 , red, 335 iron. 175 j Silicious bricks, 81 metals, pt cast-steel, 220 oxidised 361 Rolls, puddling-, 175 j iron, detection of, 218 plate, 362 Rosette copper, 248 pig iron, 149 Rotators, Siemens', iqo Silicium (see Silicon) Roughing-down (pud- Silicon and iron, 217 dling process), 175 as a fuel, 2 refining, 343, 350 solder, 334 , standard, 360 sulphuret, 335 Rust, 99 in iron, 217 , tarnished, 361 , protection of iron in pijj-iron, 149 , whitened, 361 castings from, 160 } in steel, 217 , proiection of iron i , use of, in Bessemer Silvering, 363 -, dry, 365 from, 126, 160 process, 207 mirrors, 402 Rusting, 85 use of, in iron-casting, Slack of coal, 49 SAL-AMMONIAC, 268 218 Silver, 334 amalgam, 334, 349 and aluminum, alloy Slag, 105 , blast-furnace, 146 as manure, 149 composition, 146 Salmons of lead, 322 Sand, casting of iron in, of, 421 and copper, alloy of, , utilisation of, 148 , bottle-, 259 159 360 j use of, in welding and gold, alloy of, 334 iron. 178 separation of, -bricks, 148 from blast-furnace, characters of, 147 Scale, hammer-, 170 374 -hearth, 313 Schmollnitz copper, 248 and mercury, 334 in bar-iron- 105. 176 G G 450 Index. SI.A STR THE Slag, iron-finery, 163 -lead, 315 Steel, 109 . annealing of, 217 Stream tin ore, 151 Strength of metals, &^ metal-, 231, 237 Bessemer, 198 Stuckofen, 128 ore-furnace, 234 blistered, 114 Styrian blast-furnace, 128 puddling-fumace, 170 carbon in, 127 Sulphide of iron, 104 refinery (copper), 241 cast, 118 of lead, permeation of roaster-. 238 -wool, 148 cementation, 112 colours of, 216 crucibles by, 80 Sulphur and iron, 220 Slimes, 253 Slurry, 85 containing chromium, as a fuel, a , behaviour of, in basic Smalt, 301 cooling of, in oil, 219 process, 211 S melting-house, 257 double-shear, 117 Sulphuretted hydrogen, Smelting iron ores, 129 , effect of Tungsten on, by action of water on Sodium, 423 222 hot coal, 50 amalgam, 350, 403 , extraction of, 423 , flexibility of, 219 , hardening of, 216 Sulphur from pyrites, 104 in coal, 36 Solder, 333 , braziers', 334 , coarse, 333 , Hindoo, in , impurities in, 215 , influence of man- in iron, 152 in steel, 220 , removal of, from coke, , common, 333 , fine, 335 ganese on, 120 , phosphorus on, 120 Sulphuric acid chambers, for aluminium, 421 in the Catalan forge, 33 , pewterers', 333, 419 110 Sump, 286 >, silver-, 334 Soldering, 333 , magnetism of, 97, 222 making. Heath's pro- Sweating-furnace, 345 Sweating stage of char- , autogenous, 331 , hard, 333 , use of sal ammoniac in, 333 cess for, 185 making in open hearth, 1 86 , manufacture, 111,112, coal-burning, 15 Swedish iron ore, 100 Sweep-washers, 576 Swords, tempered, 216 Sovereign gold, 380 184 Sovereigns tested, 381 , manufacture of, by Sow (iron casting), 161 Spanish copper, 249 - lead, 317 the Hindoos, in melting, 118, 185 , mild, 119 TABLE of conducting power, 94 of copper ores, 224 pyrites, extraction of ore, 102 of ductility, 92 silver from, 360 -, polished, 89 of electric conduc- Sparry iron ore, 102 Spathic iron ore, 102 , production of, 185 , , in finery, 167 tivity, 05 of fusibility, 96 Specific gravities of me- , puddled. 184 of iron ores, 99 tals, 92 rails, 209, 214 of malleability, 92 gravity, 92 , determination of, , shear, 116 , Siemens-Martin, 186 of specific gravities, 93 of tenacity, 90 361 , silicious cast, 220 Tap-cinder, 170 of peat, 19 Spectroscope in the , tempering of, 216 , tensile strength of, -hole, 139 Tapping of blast-furnace. Bessemer process, 209 219 *39 Specular iron ore, 101 Speculum-metal, 270 , tilted, 116 , toughened, 216 of slag, 107 Teeming of steel, 119 Speise, 296 united 10 iron, 220 Temper, 119 Spelter, 378 Spence's calciner, 330 Spiegeleisen, 119, 150 Spiegel, use of, in Bes- , use of the term, 214 , working of, 215 Steely iron, 109 Sterro-metal, 293 Temperature judged by colour, 96 Tempering, 216 bronze, 272 semer process, 203 Sti rling's regenerative fur- , colours in, 216 Splint-coal, 32 Spongy platinum, 405 nace, 63 Stirrer, Bessemer's, 204 in oil, 217 of steel, 216 Spoons, German silver, Stopper-hole (puddling Temper-pot, 321 298 furnace), 171 Tempers of steel, 216 Spray twyers, Lloyd's, 142 Sprouting of silver, 409 Stourbridge clay, 78 Stove, Cowper, 70 Tenacity, 89 , effect of heat on, 90 Stamp-chest, 252 Stamps (iron finery), 166 Star antimony, 415 Steam, use of, in gas pro- , dimensions of, 73 -, Whitwell, 73 , , dimensions of, 75 , hot-blast, 70 Terne-plate, 334 Test, 336 Thermo-electric-piles, 418 Thermometer, mercurial. ducer, 59 Straits tin, 251 401 Index. 451 THO VVEA ZIN fhomas Gilchrist pro- cess, 209 Tungstate of baryta, 262 soda, 262 Weathering of rocks, 77 Weber's method for treat- Tiers-argent, 421 Tilted steel, 116 Tungsten, 251 and iron, 222 ing peat, 23 Weight of metals, 92 Tilt-hammer, 117 Tin, 250 in pig-iron, 151 in steel, 222 Welding, 97, 106 Wheelswarf, 114 , alloys of, 293 , amalgam of, 402 and copper, alloys of, Tungstic acid, 251 Tuyere (see Twyers). Twyer-house, blast fur- White heat, 96 iron, 153 , conversion of grey 269 nace, 141 iron into, 163 and lead, alloys of, 332 Twyers, 106 , theory of its pro- , Banca, 260 of blast-furnace, 142 duction, 151 -, black, 257 , Lloyd's spray, 142 lead ore, 301, 302 , block, 268 Tymp-plate of blast-fur- metal, 236 , boiling of, 259 nace, 138 for electroplating, , casting of, 261 -stone of blast-furnace, 363 , common, 260 138 Whitening of iron, 163 , dropped. 260 Type-metal, 329 of pins, 293 , foil, 264 Whitwell stove, 73 , grain, 260 , impurities of, 259 in brass, 292 in type-metal, 329 UCHATIUS process, 185 , dimensions of, 75 Whitworth s process, 206 Wilson's gas-producer, 63 Wire-drawing, 92 , liquation of, 259 , Malacca, 260 Umbers, 102 Underpoling of copper, w'itham's ' puddling ma- -ore, 250 241 chine, 179 , calcining of, 254 Utilisation of waste heat Wolfram, 251 containing tung- of blast-furnace gases, Wood, ii sten, 262 69 , bituminous, 30 , dressing of, 251 , mechanical prepa- Utilisation of slag, 148 , destructive distillation of, 12 ration of, 251 Wooden sleepers sup- , prepared, 257 , roasting of. 254 plate, 264 VALUATION of coal, Vegetable matter, com- planted by steel, 214 Wood, fossil, 30 , inflaming point of, la Wool, slag, 148 , properties of, 264 , refined, 260 position of. 2 Vegetable origin of coal, Wootz, in Working-pot, 321 refining. 259 26 Wrought iron, manufac- slags, 258 Vein-stone, 224 ture of, 105, 161, 190 smelting, 257 in Saxony, 261 Vermilion, 390 Vibration, influence of, spots, 272 stone, 250 straits, 251 on iron, 157 Villacher lead, 309 Vitriol chambers, 331 Y^e^Io^sneathing. , test of purity of, 260 293 , tossing of, 260 Tinned iron, 264 lead pipes, 329 Tinning copper, 268 iron, 266 YyASH-GILDINO, Washing of coke, 51 yiERVOGEL'S pro- Z-* cess for extracting silver, 358 of pins, 292 Washoe amalgamation Zinc, 273 Titanic acid, 100 process, 350 , action of air on, 288 iron, 160 Waste gases of blast-fur- and copper, alloys of. Titanium, 100 nace, utilisation of, 135 209 Tools, tempered, 216 Watch-springs tempered, and iron, alloy of, Tossing. 260 216 287 Tossing-tub, 254 Touch-needles, 382 Water vapour, tempera- ture of dissociation of, 9 and nickel alloy, 300 and silver alloy, 327 Touchstone, 381 Weakness of ircii -listings -, burned, 287 Tough-cake copper, 240 due to crystallisation. carbor.ate, 273, 274 Toughening copper, 240 Tough-pitch, 240 1'roughs (cementation Weathering, effect of, on caking of coal, 37 chloride, 333 , combustibility of, 387 , distilled. 275 process), n 3 of coal, 37 dust, 284 452 Index. ZIN Zinc, extraction of, 274 at Bleiberg, 284 at Stolbcrg, 284 at Vieille Mon- tagne, 281 , Belgian method, , of by electricity of, 288 , English method, vjd ZIN Zinc extraction, Silesian method, 281 furnace, Belgian-Sile- sian, 283 - -, English, 27? , iron in, 286 , lead in, 286 ores, 273 , calcination of, 275 treated in blast- fur- nace, 284 ZIN Zinc, oxide of, 273 , refined, 286 , removal of, lead from, 286 , rolling of, 285 , silicate of, 274 , sulphide of, 273 , sulphuret of, 273 , uses of, 286 white, 287 works, 274 PRINTED BY SPOTTISWODDE AND CO., NEW-STREET SQUARE LONDON UNIVERSITY OF CALIFORNIA AT LOS ANGELES THE UNIVERSITY LIBRARY This book is DUE on the last date stamped below , i APR 5 193b ^3 1938 I 193$ WY s 1 I94 g Aue OCT I* W OCT 28 1947 W/rYi APR 2 8 1953 1AY8 1962 Form L-9-15m-3,'34 ^ REFD L r O.^ fiQLjUN2J31976 LIBRARY 001 188 045 7