a simple metal of a bluish-white colour, of the specific gravity 11.44; its chemical equivalent is 103.57, and its symbol Pb, from plumbum. It is so soft as to be cut by the nail, to take impressions, and to leave a streak on paper. Its ductility and tenacity are low, but it admits of being rolled into sheets, and drawn into wire. Its fusing point is 620° F. It contracts considerably in passing from the fluid to the solid state, and hence is not well fitted for castings. It is an inferior conductor of heat and electricity. By being repeatedly heated and cooled, it becomes permanently enlarged; whence the puckered appearance of the lead lining of sinks, &c., which are exposed to the action of hot and cold water.

There are four oxides of lead, only one of which, the protoxide, PbO, has basic properties.

Metallurgy of Lead.—The ore which supplies the greater portion of the lead produced in this country is galena, or the native sulphuret. The chief lead mines are in Derbyshire; but there are also mines at Allandale and other western parts of Northumberland; at Alston Moor, and other parts of Cumberland; in the western parts of Durham; in Swaledale, Arkendale, and other parts of Yorkshire; in Salop; in Cornwall; the Mendip Hills in Somersetshire; and in the Isle of Man. The Welsh mines are chiefly in Flint, Cardigan, and Montgomery shires; the Scotch in Dumfries, Lanark, and Argyll; and the Irish in Wicklow, Waterford, and Down.

Galena, when pure, consists of lead 86.55, and sulphur 13.45. It usually contains silver, and hence obtains the name of argentiferous galena. Galena crystallizes in the cubic system, and is deposited on a matrix of quartz, carbonatite of lime, fluor-spar, or baryta. In the West of England the lead mines occur in clay-slate; in Derbyshire, and other northern districts, in limestone.

Preparatory to smelting, the ore is picked, broken, and washed, to separate earthy and stony matters; it is next roasted at a moderate heat, so as to allow of oxygen being absorbed, whereby about one-half of the ore is converted into sulphate of lead; this is mixed up with the unaltered portions, and the temperature is rapidly raised, so as to run the two together, when sulphurous acid gas escapes, and pure metallic lead remains behind. In this process the sulphur of the unaltered portion of the ore unites with the sulphur and oxygen of the other portion.

The furnace employed is represented in vertical section (fig. 1). Its sole is made up of the fused slags of former operations, and the centre is hollowed, for the purpose of collecting the fused metal, which is drawn off by the tap-hole T, into a cast-iron pan on the outside. The arch of the furnace is depressed, so as to bring the flame of the fire into contact with the charge; this is let in by the hopper H, and is spread about and worked by means of iron paddles through the openings O, O, which also serve to supply air to the charge. At D is an opening for feeding the fire; C is the chimney; it is connected by means of flues, with condensing chambers, which prevent the poisonous lead fume from escaping into the surrounding district.

The charge varies from 12 cwt. in the north of England, to from 20 to 24 cwt. in Wales. It is spread evenly over the sole, and occasionally stirred for the purpose of bringing fresh surfaces to the air. After about two hours, some of the rich slags of former operations are thrown in. These quickly give up their metallic lead, and it is run out through the tap-hole. The heat is increased, and as the charge fuses, it is properly distributed over the sole. As the lead begins to collect at the lower part of the sole, quicklime Lead is thrown upon it, and, as the slags flow to the depression, they are pushed back to the fire-bridge. After from 3 to 3½ hours, the openings are closed, and the heat is urged for about three-quarters of an hour. After this the charge is again rubbed, to assist the flow of metallic lead into the hollow; the slags are pushed back, quicklime is added to set free a portion of the oxide of lead, and to reduce the liquidity of the slags, and allow of their being easily removed. The oxide reacts on any portion of the sulphuret not decomposed during the roasting; but it is now time to reduce the oxide, which is partly effected by the addition of powdered coal, and also by urging the heat for about 40 minutes, after which the furnace is tapped, and the slags, dried by a further addition of quicklime, are removed. From 7½ to 10 cwt. of coal are required for each ton of ore smelted, and the shaft of the furnace, including the casting of the lead into pigs, occupies from 6½ to 7 hours. If the lead contain antimony or tin, which often happens with Spanish ores, it has to be refined by an operation called improving. The lead is melted in a shallow cast-iron pan set in the bed of a reverberatory furnace, and kept in that condition until the antimony and tin, which are more oxidizable than lead, have been entirely removed in the pellicle of oxide, which continually forms on the surface, and is frequently raked off. A sample of the lead is examined from time to time, and when it exhibits a peculiar flaky crystalline appearance on the surface, the metal is run off and cast into pigs.

Galena always contains a small proportion of sulphuret of silver, the proportion being subject to considerable variation; an ore which yields 120 oz. of silver to the ton, or 0·86 per cent., is very rich. Formerly the silver was extracted in a cupel furnace, called a refinery, in which the process of cupellation, similar to that described under Assaying, was conducted on a large scale. Of late years, however, a simpler and more economical process has been adopted, based on the fact noticed by Mr Pattinson of Newcastle, that if fused argentiferous lead be briskly agitated during its slow cooling, a portion of the metal solidifies in the form of crystalline grains, which subside. These crystals consist of lead nearly free from silver, the fusing point of the argentiferous alloy being lower than that of pure lead. All, therefore, that is necessary, is to separate the crystals thus formed, and in proportion as this is done, the liquid mass left behind becomes rich in silver. In Mr Pattinson's process, eight or nine cast-iron pots, each containing about 5 tons of fused metal, are set in a row, with a separate fire beneath each. A charge is introduced into the middle pot, and when it is fused the fire is put out, and the metal is briskly stirred during the cooling. As the crystals subside, they are removed by means of a large perforated iron ladle, and transferred to the next pot on the right hand. When about ¼ths of the metal have thus been removed, the argentiferous alloy is ladled out into the next pot on the left hand, and a fresh charge is added to the centre pot, which is treated as before. When the pots on the right and on the left hand have received a sufficient charge, either of very poor or of very rich alloy, they are submitted to a similar process, the concentrated argentiferous portion is again passed on to the next pot on the left, while the crystalline, or poorer portion, is transferred to the next pot on the right. At length the last pot on the left may contain lead with 300 oz. of silver to the ton, and it has not been found desirable to concentrate it beyond this point; the last pot on the right may contain lead with not more than ½ oz. of silver to the ton. This is cast into pigs for the market, and the lead is found to be greatly improved in quality by the process. Lead which contains from 3 to 4 oz. of silver to the ton, admits of being profitably worked for the sake of the silver, while by the old method of cupellation, ores containing less than 20 oz. of silver per ton scarcely paid the expense of extracting the silver. The process of cupellation may, however, be profitably employed on the rich silver alloy contained in the extreme left-hand pot. This process is based upon the fact, that lead by exposure to a current of air at a high temperature absorbs oxygen rapidly, and becomes converted into a fusible oxide, whilst the silver remains unaffected. The oxide of lead, or litharge, fuses at a high temperature, and flowing off from the convex surface of the molten metal, constantly presents fresh surfaces to the action of the blast.

In Great Britain, cupellation is conducted in a reverberatory furnace with a moveable hearth or cupel, consisting of an oval shallow basin, made of a mixture of bone-ash and a small quantity of wood ashes; the two being slightly moistened, are beaten into an iron ring, about 4 feet by 2 feet; this cupel is supported in the furnace by means of bricks; when dry, the fire is lighted, the heat gradually raised, and the lead placed in the cupel; when melted, a blast of air from a tuyère is made to play over its surface; litharge forms in large quantity, fuses, and flows off through a gutter into an iron pot beneath the furnace. Lead is added from time to time to supply the place of the oxidized portions, until about 5 tons have been reduced to 2 or 3 cwt. The molten mass is run out through a hole made in the bottom of the cupel; the hole is then closed with fresh bone-ash, and another charge introduced. When sufficient metal has thus been collected to produce from 3000 to 5000 oz. of silver, the process is repeated in order to remove the last portions of lead. This separate process is found desirable, since towards the end of the process the litharge carries much silver with it, which litharge is reduced, and the silver obtained from it as before. The litharge obtained from the first process is sold as such, or it is reduced in a small reverberatory furnace by means of powdered coal or anthracite. The porous cupels are also passed through the furnace, in order to obtain the metal absorbed by them. In the earlier stages of the process, the litharge forms on the surface of the melted metal as quickly as it flows off; but when nearly the whole of the lead has been oxidized, the film becomes thinner and thinner, and at length thin enough to exhibit the beautiful iridescent tints of Newton's rings. The last film suddenly breaks up, and reveals the brilliant surface of the metallic silver, known as the fulguration of the metal, and this indicates the completion of the process.

In the N. of England the galena is first roasted, and then reduced in a small square blast furnace or forge-hearth, known as the Scotch furnace. The rectangular cavity of masonry C (figs. 2, 3), is lined with cast-iron, and the sole-plate S is of the same material, furnished with an upright ledge at its back and two sides. The sole-plate is brought forward to the front of the hearth, or a separate cast-iron plate is attached to it, called the work-stone W (fig. 2). This also has a ledge, except towards the sole. The whole plate is set with a slope, so that the hinder ledge is about 4½ inches above the surface of the hearth. The reduced metal accumulates until it rises above the raised ledge, when it flows out by gutters g (fig. 3) in the work-stone, and is received into the melting-pot P. Above the hinder ledge of the sole is a block of cast-iron called the back-stone, and on this is the tuyère t; on this is another piece of iron called the pipe-stone, furnished with a cavity below for the passage of the tuyère. The back wall of the furnace is crowned by another piece of cast-iron, called the back-stone. The ledges of the two sides of the sole support bearers of cast-iron, above which, resting on fire-bricks, is another piece of cast-iron, called the fore-stone, while the space at each end of the fore-stone is closed by a cube of cast-iron, called a key-stone; two similar stones fill up the space between the fore-stone and the back part of the furnace. The front of the furnace is open for about 12 inches from the lower part of the front cross-piece or fore-stone, to the upper part of the work-stone, through which opening the workman operates. The flame is prevented from escaping into the smelting-house by means of a hood of masonry or brick-work.

The ore is first roasted on a long flat hearth, covered by a low arch, and heated by a fire at one end, the object being partly to oxidize and to get rid of sulphur. The roasting occupies from two and a half to three hours, on a charge of from 9 to 11 cwt., and the heat is managed so as not to fuse the galena; while the refuse of the ores, and other matters, are agglutinated so as not to be carried off by the blast. After a charge has been run out of the smelting furnace, a portion of imperfectly reduced ore remains behind; it is called browse, and is mixed with coke and clinkers, and used in the next charge. A quantity of peat, in blocks, is also built up in the furnace, near the front; this is ignited by means of a lighted peat, thrown before the tuyère t, a small portion of coal is next added, and then some of the browse. The matters on the hearth are next raked out upon the work-stone; the refuse of the ore, or gray slag, which is more resplendent than the browse, is removed and thrown outside to the right, while the browse is returned to the furnace with a small portion of coal. A peat is put before the tuyère to prevent it from choking, and also to diffuse the blast. Quicklime is added, if necessary, to solidify the slag of the browse, or to render more fusible any silica, alumina, or iron, which may be present in the ore. The gray slag is treated in a slag-hearth at a stronger heat. The browse being returned to the furnace, some of the ore is strewed over it, and in about a quarter of an hour the materials are again raked upon the work-stone, the gray slag is removed, while a quantity of metallic lead passes off by the channels g, into the pan. Another peat is put before the nozzle of the blast, coal and quicklime are added, and the browse is returned to the furnace, with a fresh quantity of ore. After another interval of about a quarter of an hour, the slag is once more separated, and another quantity of metallic lead flows into the pan. This mode of working is continued about fifteen hours, during which from 20 to 40 cwt. of lead, and upwards, are produced. The lead is of excellent quality, since, on account of the low temperature employed, metals of high fusing points, with which the ore may be contaminated, remain behind, and only the lead and silver escape into the pan. The furnace in which the slags are reduced is in the form of a rectangular prism 26 inches in length, 22 in breadth, 33 in height. The bottom inclines slightly from the tuyère towards the front, the fire-hearth is formed of two stout plates of cast-iron, 26 inches by 12 inches, supported by bearers at the sides. A space of about 5 inches is left between these plates, or stones, as they are called, and the bottom of the furnace, and there is also a row of fire-bricks between. Preparatory to working the furnace, the bottom is covered with cinders, beaten together, and the pot which receives the lead is filled with them. Peats are next added to the furnace and ignited, then comes a layer of coke, and when the heat is sufficiently strong the slags are added. The space is kept filled with alternate layers of coke and slag, and as the slag melts, the lead contained in it filters through the bed of peat cinders, while the more viscous slag remains behind. The slag is run out by perforating the coke bed with a bent iron rod, and after passing over the surface of the pot which receives the lead, it escapes into a large iron cistern, sunk in the earth, containing cold water, which causes the slag to fly to pieces, thus fitting it for washing and other mechanical processes for separating any metal which may yet remain in it. The high temperature necessarily employed in the slag-hearth deteriorates the quality of the lead produced. This furnace is also employed for reducing certain ores which are not rich in metal, and also for some of the carbonates in which silver is an object rather than lead.

The neighbourhood of lead works is liable to contamination from the escape of lead fume. Professor George Wilson states that, in 1851, he had within five months to make a series of analyses with reference to the deaths of thirteen horses and several cows, which were supposed to have been poisoned by compounds of lead, transferred by the air or the water to the fields in which they were pastured. The grass of such fields was found to be impregnated with carbonate of lead; and in two cases the water drunk by the animals was found to be contaminated with the water used in washing the ore. Lead was found in several of the organs of the animals, especially the spleen, which, from its small size, spongy texture, and comparative freedom from fatty matter, admits of being rapidly and satisfactorily examined; and lead being found in this organ, it would not, in general, be necessary to seek for it in other organs. At some works attempts are made to condense the fume, by making the flues of the furnaces communicate with chambers in which cold water showers down from the roof; at other works, the gases from the flues are drawn through cold water. At the Duke of Buccleuch's works at Wanloch, in Dumfriesshire, the condensing apparatus, constructed about 100 yards from the smelting furnaces, consists of a rectangular block of masonry about 30 feet high, divided by a partition into two chambers, the first of which, the condensing chamber, receives the fumes from the furnaces through a large pipe; while the second, called the exhausting chamber, communicates with a lofty chimney. The condensing chamber is formed into two distinct compartments, by means of a pair of vertical walls, placed 2 feet from each other so as to form a kind of flat pipe, open at the top, and running the whole width of the chamber, into which water falls in drops, produced by passing the water through a filter of pounded coal, situate in the upper part of the flat pipe. The condensing chamber is further divided into five compartments, each 6 feet high, by means of four horizontal floors, the last compartment corresponding to a bed of coals which forms a filter for the smoke. When the smoke enters the condensing chamber, it has to pass in zig-zags through the five compartments, and then through the bed of coal, on its way to the exhausting chamber. The opening which conducts the smoke from the exhausting chamber to the chimney is situate in its lower part, so that the smoke has to pass through the whole of the exhausting chamber where it

meets with an abundant shower of rain. This shower is regulated by a contrivance in the upper part of the chamber, where the top is covered with a large iron lid with twelve grooves about an inch wide. This lid is furnished with a slide, with openings of the same size, and moving upon it so as to open or close the grooves, while a current of water, being conducted from the upper part of the chamber, falls at intervals through the openings, and produces a copious shower in the chamber. "The atmospheric pressure acts on each movement of the slide with a force resembling that of a blast of an iron furnace, and produces an action sufficiently powerful to mix the impure vapours with the water, so that smoke at length passes into the atmosphere deprived of its injurious properties. The saturated water proceeding from these chambers is afterwards conducted into a reservoir, where it deposits the particles of lead salts that the fumes had carried off." In the Great Exhibition, specimens of flume, thus recovered, were shown, containing 33 per cent. of pure lead, and about 4 oz. 17 dwt. 7 grs. of silver per ton. It is stated that the results of the above arrangement are most beneficial to the surrounding district. Formerly the noxious fumes poisoned the neighbourhood, burnt up the heather, destroyed the vegetation, and rendered it impossible for a beast to graze, or a bird to feed, near the spot. The heather now grows in luxuriance close to the works, sheep graze within a stone's throw of the chimney shaft, and game seek cover on all sides.

About 55,000 tons of lead are annually raised in England, from which about 150,000 oz. of silver are produced. In the year ending 31st Dec. 1855, the quantity of lead exported from the United Kingdom amounted to 22,353 tons, of the declared value of L.512,426. In 1854, 19,005 tons, and in 1853, 16,242 tons, were exported.

In Germany, and some other parts of Europe, where poor ores of lead are treated, the sulphurates are reduced by means of granulated metallic iron; the iron combining with the sulphur of the lead forms a fusible sulphide of iron, and the lead is set free. This method is useful where the ores are largely mixed with silica, which, under the English method, would combine with oxide of lead, and form a fusible slag.

Metallic lead is used in the arts in the form of sheets for covering roofs and pipes for conveying water; also in the manufacture of shot, type-metal, solder, &c.

When lead is exposed to the action of air and pure water, it is partly corroded, and hence lead pipes and lead vessels for conveying or containing water for culinary purposes may act as sources of poison. By such exposure the lead becomes converted at the surface into an oxide which the water dissolves; the solution absorbs carbonic acid, and a film of hydrated oxy-carbonate of lead is deposited in silky scales; a fresh portion of oxide is then formed and dissolved by the water; and so on. This action is greatly modified by the presence of different salts in the water, although the quantity may not exceed 3 or 4 grains to the gallon; the corrosive action being increased by the chlorides and nitrates, and diminished by the sulphates, phosphates, and carbonates, so much so, that oxide of lead is scarcely soluble in water containing these salts. Bicarbonate of lime exerts a remarkable preservative influence, and as it is a very common impurity in water, few spring waters exert much action on lead. In such cases a film of insoluble carbonate of lead is formed upon the surface, which serves as a protection to the metal. Rain water which pours into cisterns from the roofs of houses, is usually sufficiently impure, especially in towns, to reduce its action on the metal. The hydrated oxy-carbonate of lead is the least soluble among the salts of lead; pure water not taking up more than about \( \frac{1}{10} \)th of a grain per gallon. By exposure to the air, a solution of oxide of lead, by absorption of carbonic acid, forms silky crystals of the hydrated oxy-carbonate, and in a few hours, only a very minute portion of the metal will remain in solution; but water highly charged with carbonic acid may dissolve lead to a dangerous extent, from the solubility of carbonate of lead in excess of carbonic acid; but, by boiling, the gas is expelled, and the carbonate subsides. Traces of lead may generally be found in water that has been stored in leaden cisterns, so that slate ones are to be preferred. Lead is corroded in the presence of moisture by contact with sulphate of lime; hence, in using it for building purposes, the contact of stucco or plaster should be avoided.

White Lead.—There is an enormous consumption of lead in the manufacture of white lead, which forms the basis of all ordinary oil paints, constituting at least \( \frac{3}{5} \)ths of their composition. There are various methods of manufacturing white lead, the two most important of which may be briefly noticed. In the Dutch method, as it is called, which was introduced into England about 1780, and is still carried on at Newcastle-upon-Tyne, and other places, a number of small glazed earthen pots, of the shape shown in fig 4, contain in the lower part a quantity of weak malt vinegar V, and above this is placed a spiral of thin sheet lead l; the pots are arranged in rows, with a plate of lead over each, and then in tiers to a height of 18 or 20 feet, and covered up with fermenting tan, partly new and partly spent, or with decomposing stable manure; the moderated warmth thus produced causes the vinegar to evaporate, and, under the united action of the air and the acid fumes, an oxide of lead is formed on the surface of the metal, which oxide, combining with the acetic acid, forms a basic acetate of lead; the carbonic acid from the decomposing hot-bed converts this salt into carbonate of lead, whilst the neutral acetate again combines with a fresh portion of newly-formed oxide and forms the sub-acetate, which is again decomposed; in this way decompositions and recompositions take place in succession, the neutral acetate dissolving the oxide and forming the sub-acetate, while this is again decomposed under the influence of carbonic acid. In this process the quantity of vinegar required is very small, the function of the acid vapour being to act as a sort of carrier between the carbonic acid evolved from the hot-bed, and the oxide of lead formed under the influence of the acid vapour and the oxygen of the air. One part of pure acetic acid to 100 parts of lead, is sufficient for carrying on the process. The carbonate of lead slowly forms a compact layer on the surface of the coils, and it breaks off in flakes on unrolling them, forming the dead white colour which is so much in request, notwithstanding its poisonous properties. Before it is ready for the painter it is ground up with water into a thin paste, and is then reduced, by successive washings and subsidences, to an impalpable powder, which is collected in earthen pans, and dried at about 190°. When dry the powder gives no signs of crystalline structure, even under the microscope.

During the pulverization, particles of the powder escape

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1. Jury Report of the Exhibition of 1851, Class I. 2. Professor Miller's Elements of Chemistry, part II., 1856. 3. The innocuous oxide of zinc has been introduced as a white paint, in the place of white lead, but it has failed from the circumstance of its being partially transparent, so that it does not possess the covering properties, or body, of white lead. Moreover, the oxide of zinc will not combine with oil to form a plaster as oxide of lead does; hence it is a long time in drying. Lead. into the air, to the great injury of the health of the work-people. The formation of the carbonate is also very slow, from four to six weeks being required for the complete coating of the coils. These circumstances led the French chemist Thenard, to substitute for the foregoing process, the direct decomposition of a solution of sub-acetate of lead, by means of a current of carbonic acid; in this way the carbonate is quickly formed in a state of extreme division, but unfortunately the white is less opaque, in consequence of the crystalline character of the powder, than that obtained by the Dutch method.

M. Payen describes a method of grinding and sifting white lead which is less injurious to the health of the work-people than the common method. The dried cakes are put into a hopper h (fig. 5), through which they fall upon an endless band e, the motion of which conveys them to a mill mm, which grinds the cærule to powder. The powder falls upon a sieve bb, furnished with brushes, attached to the axis of the mill; the larger particles which do not pass through the sieve, escape by the side openings n into a close receiver. The powder which passes through the top sieve, falls upon a second sieve, and from thence down an inclined plane into a vessel oo, which may contain oil, if the white lead is to be mixed therewith, or it may be collected in this vessel dry. The mills are surrounded by a chamber C, at the upper part of which is a pipe R, opening into a shaft, the draught of which carries off the dust from the chamber, but a large portion of this dust is condensed by means of the jets of steam S, thus preventing loss of the white lead by way of the chimney.

Carbonate of lead is often largely adulterated with sulphate of baryta. What is called Venice white is a mixture of equal parts white lead and sulphate of baryta. Hamburg white consists of 1 part white lead and 2 baryta; while Dutch white is 1 part white lead, and 3 baryta. Krems or Kremnitz-white, silver-white, and Clichy-white, consist of pure white lead. There is a tendency in white lead to a yellow tinge, to correct which a minute quantity of indigo, charcoal, or sulphuret of lead, is commonly added.

Red Lead, or minium, largely used by the glass-maker, the paper-stainer, and the red sealing-wax maker, is a compound of protoxide of lead with the peroxide of the metal. Leadhills It is obtained by heating the metal in a reverberatory furnace, with a double hearth, one above the other, the heat being greatest in the lower; here the lead, which should be nearly pure, is converted into the protoxide, or massicot, care being taken not to fuse it. This is levigated, washed, and deposited to get rid of metallic particles, and is then placed on the upper hearth, which derives its heat from the lower. It is placed in iron trays, and, at a temperature of about 600°, it gradually absorbs the additional quantity of oxygen. The colour is improved by making the red lead in large quantities, but its brilliancy suffers by exposure to light.