fluor spar or fluate of lime during the chemical changes occurring in the calcination of the ore. [See OP. II.] The property of fluoric acid to act on silica is well known, and probably if the contents of the flue from the calciner's were accurately examined, silicated fluoric acid gas and hydrofluoric acid would be formed. The mechanical impurities consist of the fine particles of the ore carried over by the draught of the furnaces. They may contain a portion of copper, but the quantity of this is unquestionably very small." In some of the works, lofty stacks have been erected to carry the smoke so high as to become greatly diluted with the air before it reached the ground; but it is stated that the effect of this plan was to increase the evil by diffusing the smoke over a wider area. The plan of passing the smoke through showers of water, as recommended by Sir Humphry Davy and others, has also been abandoned, and it is stated that all the plans hitherto devised for rendering the smoke innocuous, are so expensive, that if adopted it would be impossible to carry on the trade. The prosperity of the town depends so much on the copper-works, that the inhabitants are content to put up with a positive inconvenience rather than by indicting the proprietors, compel them to seek another locality, and take away a trade which has so greatly benefited the town and neighbourhood. The total annual weight of ores smelted in South Wales amounts to about 200,000 tons, from which about 46,000 tons of sulphur is expelled to waste, and this produces about 92,000 tons of sulphurous and sulphuric acids. Every day the Swansea works project into the air 188 tons of these acid gases, the noxious influence of which extends to a considerable distance: the aspect of the country proves that the fertility of the soil is thereby considerably diminished, especially in the direction of the prevailing winds. The action on animal life, although not so evident, is no less certain. Where the smoke is so diluted by diffusion that grasses can grow, the cattle that feed on them and the sheep pastured on them are subject to luxations and enlargements of the joints, and a metallic coating is given to their teeth. The gases given off from the numerous chimneys of the works form a white cloud, so thick as greatly to diminish the transparency of the air, and when the gases are beaten down by the wind it is sometimes scarcely possible to discern objects a few yards distant. The SECOND OPERATION.-The object of the second clouds continue for a long time before they are dis-operation is to separate the ore from its gangue, and sipated in corrosive rain, and they may sometimes be seen after having been driven 3 or 4 miles from the works. Their opacity is probably due to the mutual condensation of the two transparent gases and the aqueous vapour of the atmosphere. The flues of the various calciners discharge their contents into a gallery, g, Fig. 614, where the smoke, being somewhat cooled, deposits some of its solid matter, which, to a certain extent, diminishes the evil. But the smoke of the copper works contains other ingredients besides the principal ones above named. In a tract on this subject, Mr. Vivian gives the following particulars :-" Copper-smoke, or what may be properly considered under that head, as being peculiar to the operations in a copper-work, may be said to consist of the following substances or chemical compounds, formed during the calcining processes by the evolution of substances contained in the ore :1, Sulphurous acid; 2, sulphuric acid; 3, arsenic; 4, arsenious acid; 5, fluoric compounds, and chemical impurities. Of the above substances, the first two are formed by the combustion of the sulphur. The sulphurous acid, which is by far the most abundant, is evolved in the state of a pungent and penetrating gas. The sulphuric acid, which is composed of sulphur combined with more oxygen than exists in the sulphurous acid, and water, appears as a dense white vapour. The arsenical contents of the copper ores expelled by heat, appear partly as arsenic, in the metallic state, partly as combined with oxygen, forming arsenious acid or white oxide of arsenic in both cases it assumes the form of vapour. The fluoric compounds are produced by the decomposition of the to get rid of a portion of the oxide of iron which abounds in poor calcined ores. The action of a very high temperature upon the charge is to separate its component parts into three distinct portions: 1, the whole of the copper, or nearly so, is collected in a matt, consisting essentially of sulphuret of copper and sulphuret of iron; 2, a scoria or slag in which the earthy matters, oxide of iron, and other fixed products are collected; 3, gaseous compounds composed essentially of sulphurous acid and other volatile matters, formed by the mutual reaction of the substances employed under a high temperature. The most difficult and also the most important part of this operation is to concentrate all the copper in the matt, for as the scoria which is produced is thrown away as worthless, any portion of copper contained in it is thus lost. The charge is composed of calcined ore from Op. I., and of some of the scoria rich in copper from Or. IV. V. and VII. which contain substances of easy fusibility, such as silicate of iron, whereby the fusion of the quartz and of the oxide of iron which abound in the ores is greatly promoted, and which, but for this, would react with difficulty on each other. Fluor spar is also added as a flux, and there are also certain earthy matters produced by the action of the charge on the sole and walls of the furnace. The fuel used is a mixture of 0.68 anthracite, and 0.32 of bituminous coal. Each furnace is served by two men, who work 12 hours each: each charge is in the furnace 4 hours, so that 3 charges are made during the 12 hours. The successful working of the furnace depends on the skill and attention of the men, and the older 42 mns mercasts the stof. If there be too The two more fue de senery a a £vide the charge of coal Dude and add a portion fremary A anspeare is fatal to the success ʼn de menorm for the charge under SUL PLUS nes becomes fised to the scie, and it 1 TELL The ire af the same fen ut innret The twe of his & T ressure the masste of fusion Indeed, the management of the feats operation requires tart and judgmess the scly of air must be carefully regated fie a excess a short flame will be produced not sufiont to reach to the extremity of the fucce The mense caquary of the furnace is about 3 times less then that of the calcing farmace, Or. L, nevertheless a very much larger quantity of fuel is consumed. The granty of coal consumed in 12 hours amounts to 1477 tons, to burn which requires 1.665 son of oxygen or 7.96 tons of atmospheric air. The results of the ece bustion are therefore :Combusthie gas, procured by the distillatio Fig. 617. PLAN OF COARSE METAL MELTING-FURNACE Fig. 618. COARSE-METAL FURNACE. the process, and he usually estimates its success by the intensity of the light. If this diminishes, the fire has too much or too little solid fuel upon it, or the gases which issue from it are not in the proper proportion to form the highest attainable temperature. If there be too much fuel on the fire (as would be the case if the charge of fuel were not added after the proper interval, but were heaped up at a later period,) the man rakes out some of the clinker, and 8.783 tom The chimney is of large size, and the gases pour into it at a very high temperature. There is no lateral opening in the flue to cool the current, as at g, Fig. 614, and the single opening through which the charge is drawn out, is carefully closed during the operation. A door, at the extremity of the furnace, allows the workmen to elaborate the charge by means of a long | rake, and the effect of opening this door is not to I cool the furnace, because, although the draught is thereby suspended, yet the cool air rushing in to supply the fire, escapes not into the furnace, but into a side opening. The second charge is introduced immediately after the first is withdrawn; the calcined ore, OP. L. and the flux are poured into the hopper above, and so let down into the furnace; the scoria, which is in large lumps, is thrown in through the door. The composition of the charge varies with the nature of the ores; the scoria from OP. IV. V. and VII. accelerate the fusion, and the metal-calciner men are consequently very eager to get it. This kind of slag has increased in quantity during the last 20 years, in consequence of the importation of the rich foreign ores. The weight of refractory matter in each charge usually varies from 1.05 ton to 1.20 ton, and the weight of scoria assisting the fusion 0.15 to 0.20 ton. The following is an average composition of a charge: Calcined ore Crude ore........ Tons. Tons Tous 0.8961 1.000 Total 1.300 The workman begins by letting fall on the sole 1.051 tons of ore and flux; he then closes the funnel and the damper of the flue, and by means of a rake rapidly spreads the charge in a uniform layer over the sole. Then taking in his hand the largest pieces of scoria heaped up near the furnace door, he throws them in, scattering them about with tolerable regularity; he then lowers the door, and carefully excludes all access of air thereby by luting it to the wall. The charge is then left for 3 hours to the influence of the heat, and the man devotes his time to the management of the fire, and the conveyance the different materials required for the use of the furnace. He detaches from time to time fragments of clinker which fall into the ash-pit, and he keeps open, by means of a pointed iron, the central channel of the fire, which has a tendency to become choked up; a fresh supply of fuel, weighing 0.168 ton, is added about every 72 minutes, and this charge is twice the thickness of the charge in Or. I. VOL. I. of yy Yards where slags are sorted. r Rubbish heaps of slags raised up the inclined plane 1 by means of the small engine e. c Canal by which coals, &c. are brought. b Canal basin. pp Quays for landing Coals, &c. The men of 4 furnaces usually unite in bringing the ore, flux, &c. to the furnaces. It is to the interest of the men, who are paid by the charge, to pass as many charges as possible through the fire within a given time, and if left to themselves, they would take a short supply of the refractory minerals, and lessen the weight of the charge. A foreman is therefore stationed near the weighing-out scales, who makes an entry of every charge. About half-an-hour after the charge has been introduced, the superficial layer of scoria begins to fuse, and forming liquid furrows among the powdered materials of the charge gradually filters through them, or collects in little ponds. The quantity of fluid silicate rapidly increases, and it soon begins to foam in consequence of the formation of gases below it, and escaping up through it; this agitation brings into more intimate contact the fluid silicate, and the FF substances which compose the scoria in process of formation, assisting at the same time in reducing it to a fluid state, while the elements of the matt are by the separation of the materials of the slags brought together, and begin in their turn to react upon each other, leading to the production of gaseous compounds. By degrees, the fusion and consequent separation of the slag and of the matt are accomplished, the matt occupying the lower surface of the sole, and the lighter and more bulky scoria floating on its surface. In 3 hours, the metallurgic reactions appear to have ceased; a few bubbles of gas rise here and there on the surface and burst; around the edge of the sole may also be seen floating foam-like masses which have escaped liquefaction; the man observing these, opens the door and rabbles the charge, detaching these masses, which fall into the fluid scoria and dissolve. The rabbling being completed, the man closes the door, lets fall some clinker, and arranges his fire so as to produce the maximum of heat. He then prepares for the casting of the scoriæ or slags, for which purpose he spreads out a quantity of sand, which has been heaped up on the ground before the door, and having levelled its surface, he digs in it 4 rectangular cavities 1, 2, 3, 4, Fig. 617, in which the scoria is received and moulded. The matt is drawn by the channel p, Fig. 617, and the slags by the door at o. These are allowed to pour out first into No. 1; when this is full it pours over by a side channel into No. 2, and then into No. 3, and when these are full, No. 1 begins to pour into No. 4, by passing over a channel a little more elevated than the others. A quarter-of-an-hour after the rabbling, the man prepares for the casting of the matt by cautiously tapping with a pointed iron the orifice communicating with the lower part of the sole. A thin stream of liquid matt issues out and falls into a cylindrical iron vessel immersed in a well, w, supplied with cold water by the pipe t, the effect of which is to granulate the metal, and to divide it into portions of about the size of hempseeds, the largest not exceeding that of a bean. The man then opens the door of the furnace, and draws out the slags into the mould already described; this part of the process requires considerable care, in order to separate the slags from the matt. The basis of this scoria is a silicate of iron, which in itself is very fusible, but its fluidity is greatly diminished by the presence of several fragments of quartz and quartzose rock entangled with it. It is too viscid to flow out spontaneously, but must be got out by a rake. To prevent it as much as possible from mixing with the matt, the soles of the furnace is so arranged as to incline towards a sort of basin, h, Fig. 617, on one side of the furnace, and occupying scarcely d of the area of the sole. At the end of the operation, the scoria covers the matt only in this basin, in all the other parts it rests on the sole. The scoria nevertheless contains a considerable portion of copper, and it is for the purpose of recovering this copper that the scoria is cast into bricks. The granulated copper having a tendency to fall to the bottom of the mass of slag, it is chiefly collected in the mould, No. 1; the 3 other moulds being supplied by the overflowing of No. 1, contain a very much less quantity of copper. The men mark the bricks of slag in the order in which they were cast. The scoriæ are at a white heat when they are cast, and their temperature is kept up as long as possible, to facilitate the subsidence of the copper; hence, during the casting, iron plates are set up on edge near the moulds to keep off the cool air, and when the casting is complete, the bricks are covered over with sand. In the meantime, the matt continues to flow, its surface in the furnace being protected by the coating of slag, a portion of which has not been disturbed. A certain portion of slag is also left on the sole to protect it from the corrosive action of the slags formed by the next charge, which is introduced while the matt is still flowing off. The volume of fluid matt produced by each charge does not exceed 12 gallons, and the yield of two contiguous furnaces, (Nos. 2, Fig. 620,) is collected into one pit. With new varieties of ore, the work is a little more laborious, and requires the supervision of the inspector of the foundry; or should the supply of certain ores which are usually employed, fail, the proportions of the charge require modification. In such cases, the flux is not added to the charge at once, and many successive rabblings are required to ascertain the progress of the fusion, the flux is then added as occasion requires. In this way, much practical knowledge is gained which contributes greatly to the success of the work. The metallurgic re-actions in OP. II. are simple. The oxides and sulphurets are combined in the charge in such proportions that the oxygen lost by the oxides whose metals pass into the matt, and the oxygen lost by the ferric oxide which passes in the shape of ferrous oxide into the scoria, combine with the sulphur of the sulphurets, and form sulphurous acid, the disengage ment of which keeps up a certain agitation which favours greatly the progress of the re-actions. The action of the fluoride of calcium, or fluor spar, is somewhat complex. In the gangue of the copper ores alumina and magnesia are more common than lime; the portion of calcium, which, under the influence of oxygen and silica, passes into the state of lime, contributes to the fluidity of the silicates. About one half of the fluor spar remains undecomposed, and the fluor silicate which is formed, adds to the fluidity of the scoria. The fluoride of calcium, which is at first dissolved rapidly in the silicates, for which it has a great affinity, is then decomposed gradually under the influence of the fragments of silica suspended in the mass; the silica yields oxygen to the calcium, and the resulting silicum, which is the exact equivalent of the fluorine of the fluor spar, combines therewith. This disengagement of fluoride of silicum forms a sort of natural rabbling of the charge at the period when sulphurous acid is no longer disengaged, and this mechanical action is one of the essential advantages of the fluor spar flux. The following statement will show the results of air. The charge is weighed out, and conveyed in OP. II: An examination of the scoria produced in OP. II. will always show whether the metal calciner men have done their duty. The scoria are inspected in a courtyard, yy, Fig. 620, where the men deposit it in regular order, under the number of each furnace. Each brick is broken with a hammer, and the fracture examined; the lower part of the brick is minutely inspected, especially that of the brick No. 1: the small grains of matt, mechanically mixed with the slag, exhibit a clear bronze colour, and a metallic lustre on the black, dull surface of the fracture. The value of the copper in the slags is thus judged of very accurately: if the proportion be from to an experienced eye can tell within or the quantity of copper contained therein. In breaking up the bricks the inspector forms the fragments into two heaps; the larger heap contains those which are to be thrown upon the rubbish heap, r, Fig. 620, the other heap contains those fragments which are to be returned to the furnace. Each new charge contains 0.071 tons of this rich scoria; a larger proportion than this would be injurious, but as a larger quantity than can be used is produced, the surplus is melted down once a-week or fortnight, for which service the men receive no pay. The iron cylinder containing the coarse metal, as it is called, produced by two contiguous furnaces, is hauled up by means of a crane, Fig. 618, and conveyed in wheelbarrows to the dépôt, Fig. 620. Sunday is to the men engaged in OP. I. and II., what it ought to be to every one, a day of rest from worldly occupation. The fires, however, require to be kept up, and this service is performed by one man, who has the charge of 4 furnaces, and he must so arrange that the furnaces be at the full heat for the reception of the charges on Monday morning at 5 o'clock. THIRD OPERATION.-The coarse metal obtained in the last operation is in very small fragments, externally of a deep brown colour; they are easily crushed by a blow, and the surface of the fracture is of a brownish red. The metallic copper forms about 3d of the total weight; it is, in fact, very similar to copper pyrites free from gangue. It is, therefore, in the first part of OP. III. simply calcined with access of atmospheric wheelbarrows to the hoppers over the calcining furnaces, which are similar to those used in OP. I. Each of these is served by two men, who relieve each other alternately. One man must work on Sunday, because each operation extends over a period of 36 hours. The most important part of this operation consists in the management of the fire; it is the same in principle as in OP. I., but more fuel is consumed, and the heat requires to be greatly increased towards the end of the operation; 0.043 tons of coal per hour is burnt, whereas in OP. I. it was only 0.035 tons. The charge having been spread over the sole, the temperature is kept up to the highest that it will bear without fusing. Two hours after the doors have been closed it emits abundant fumes of sulphurous acid, and it is rabbled every two hours in order to expose a fresh surface. The charge must be gradually raised during the first 12 hours to an incipient red heat; by the 24th hour the charge and the walls of the furnace must be at a cherry-red heat, and by the 36th hour at a lively red. The effect of rabbling is not only to expose new surfaces, but also to break up any masses which tend to agglutinate. The coarse metal is the only solid product of this operation; the sulphur passes off in the form of sulphurous and sulphuric acids, while a proportion of oxygen combines with the matt nearly equal to that of the sulphur expelled. Omitting the sulphuric acid, the following tables will show the difference between the substances before and after the operation : 0.804 0.196 1.000 0.783 0.217 1.000 The product of this operation may be bad either from the result of too high or too low a temperature. There is not much chance of too high a temperature being produced, for this would agglutinate the charge, and give the workman much extra labour in rabbling. The danger is the other way, and in order to keep the men to their work 4 inspectors are appointed to 15 furnaces, whose duty it is to see that the heat is gradually and properly raised, and that the rabblings are attended to every two hours. The physical and chemical properties of the coarse metal are greatly altered by calcination: the fragments are much reduced in size, the general colour is a deep black, with light brown reflections; many of the grains are friable; others are encased in a friable envelope, the nucleus being hard and compact; this, when broken, has a lustre of various colours; other fragments are formed by the incipient fusion of several particles together. FOURTH OPERATION.-White metal, the object of this operation, is produced by associating with the calcined coarse metal those ores of copper which are almost entirely free from sulphuret of iron, and consist |