one of the imperfect metals, of a dull white colour inclining to blue, the least ductile, the least elastic, and the least sonorous, of the whole, possesses a considerable degree of specific gravity, reaching from 11.3 to 11.479. It is found,

1. Native. Cronstedt and some other mineralogists have doubted whether native lead was ever found in the earth, but the matter is now decided by innumerable testimonies. It appears from the Philosophical Transactions for 1772, that some small pieces of native lead were found in the county of Monmouth in Wales. It is said also to be found in the Vivarais in France. Bomare mentions a curious specimen of native lead kept in the collection of the abbé Nolin at Paris, that had been found in the lead mines of Pompeii, near Rennes in Brittany. It was very malleable, could be cut with a knife without crumbling, and easily melted over the flame of a candle. It weighed about two pounds; was imbedded in an earthy lead ore of a reddish colour; and had a flaky vein that went through the middle of it.

2. Lead spar, is sometimes transparent, but generally opake, and crystallized in regular forms of a lamellar or striated texture. Lead ochre, or native cerusite, is the same substance, but in a loose form, or indurated and shapeless. Sometimes it is found in a silky form. Both contain some iron, calcareous earth, and clay; and both grow red or yellow when heated. They effervesc with acids, and afford from 60 to 80 or 90 per cent. of lead. They are found in Brittany, Lorraine, Germany, and England.

M. Sage, of the royal academy of Paris, pretended, that the white lead ore from Poulawen in the county of Bretagne in France, was mineralized by the marine acid; but his mistake was detected by the commissioners of that academy. This ore, according to the same academicians, is composed of striated crystals, of a whitish pale red or grey colour. There is a lead ore of this kind sometimes grey and sometimes yellow, which is very heavy. Its structure is either lamellated or fibrous, and its laminae can hardly be separated; but it is friable, and may be cut with a knife. Sometimes it is crystallized; and sometimes its fibres are extremely thin, semitransparent, and have a filky look. They effervesc with acids, decrepitate in the fire, and seem to lose the aerial acid by which the lead is mineralized.

The sparry lead ore has often a semitransparency like the sparry fluor; its crystals being generally terminated by hexahedral prisms, or cylindrical columns, striated, and apparently composed of a great number of filaments. These sparry crystals are always found in the same places with the galenas or sulphurated lead ores; and seem to be formed from their decomposition after the loss of their sulphur; so that it is not uncommon to find galenas which are beginning to pass into a state of white lead. There is a black ore of lead, which may be supposed to be in an intermediate state betwixt the white lead ore and galena, as it seems to be a true white lead tinged by the hepatic vapours of the sulphur on its parting from the galena. There is also a green transparent lead, having a more or less yellowish cast. It frequently has no regular form, and appears like a kind of moss. When this green ore is crystallized, it consists of hexahedral truncated prisms, terminated by six-sided pyramids, either entire or truncated near the base. Professor Brunniich tells us, that the green and the black lead ores from Saxony, and the Hungarian blue ores, are prismatic. According to Kirwan and Mongez, the green lead ores are either crystallized in needles as in Brittany, or in a loose powder as in Saxony; but mostly adhering to and involving quartz. They owe their green colour to iron, seldom containing any copper, and are very rare. Brunniich mentions a sapphire-coloured ore once found among some white lead spar at Wendish Lemen. It was easily melted by the blow-pipe. Natural red-lead or minium has been found in some Siberian mines. It is found either crystallized, or in shapeless masses, or in powder, in which it agrees with the brown or yellow ores. Dr J. R. Forster brought some of this crystallized red lead ore from Russia. The crystals were cubical, and the colour seemed rather pale. The red Siberian ores are perfectly rhombic; those from Bohemia have a cubical or rhomboidal form. Sulphur and arsenic have been found in the red ones, but the others have not been sufficiently investigated. Most of them effervesc with acids.

3. Artificial lead spar. Cronstedt says that he tried an ore of this kind from an unknown place in Germany, and found that no metal could be melted from it by means of the blow-pipe as could be done by other spars; but by doing it in a crucible, that part of the arsenic which did not fly off was likewise reduced, and found in the form of grains dispersed, and forced into the lead. Another ore similar to this, and which likewise was not easily reduced by means of the blow-pipe, always shot into polygonal, but chiefly hexagonal crystals, after being melted, having shining surfaces. Professor Brunniich observes, that these ores effervesc with acids, and contain 40 per cent. of lead.

4. The blue glanz of the Germans contains lead mineralized with sulphur alone, and of this there are two or three varieties. At Villach in Austria there is said to be found a potters lead-ore containing not the smallest portion of silver.

5. Lead mineralized by the vitriolic acid, is generally in the form of a white mass, soluble in 18 times its quantity of water. Sometimes it is blackish, and crystallized in very long strata, or in friable stalactites; this last variety effervesces in the air, and is converted into Lead into a true vitriol of lead. According to Mr Kirwan, it does not effervescence nor is soluble in other acids, but may be reduced by laying it on a burning coal. It originates from the decomposition of sulphurated lead ores. Dr Withering informs us, that it is found in great quantity in the island of Anglesey; but united to iron, and not reducible by the blow-pipe or charcoal.

6. Lead mineralized by the phosphoric acid, was lately discovered by Mr Gahn. It is of a greenish, yellow, or reddish colour, and does effervescence with acids. After solution in nitrous acid, the lead may be precipitated from this ore by the vitriolic acid. An hundred grains of lead are produced from 137 of this precipitate washed and dried. The decanted liquor evaporated to dryness affords the phosphoric acid, from which the inflammable compound may be produced by distillation with charcoal. Seven ounces of this lead ore from the neighbourhood of Friburg, treated in the manner just mentioned, yielded by distillation 144 grains of phosphorus. A compound similar to this ore may be obtained by mixing pure phosphoric acid (that is, such as is combined with the volatile alkali, for the fossil alkali in the microcosmic salt hinders the operation) with red lead.

7. Galena, or potters ore, in which the metal is mineralized by sulphurated silver. According to Mr Kirwan it is the most common of all the lead ores, of a bluish dark lead colour, formed of cubes of moderate size, or in grains of a cubic figure, whose corners have been cut off; its texture is lamellar, and its hardness varying in different specimens. That which is formed into grains is supposed to be the richest in silver; but even this contains only about one or one and a half per cent.; that is, about 12 or 18 ounces per quintal; and the poorest not above 60 grains. Ores that yield about half an ounce of silver per quintal are barely worth the extracting. Different specimens also vary in the quantity of sulphur they contain, from 15 to 25 per cent., and that which contains the least is in some degree malleable. The proportion of iron in this ore is very small, but the lead is from 60 to 85 per cent. M. Monnet asserts, that galena is insoluble in the nitrous acid; but Dr Watson has shown, that it is completely dissolved by the acid when diluted. The specific gravity of galena is from 7,000 to 7,780. It yields a yellow flag when melted.

M. Fourcroy distinguishes several varieties of this ore. 1. Cubic galena, the cubes of which are of various sizes, and found either single or in groups; it is often found with the angles truncated, and is common at Freyberg. 2. In masses, without any regular configuration; very common at St Maire. 3. With large facets. It does not compose regular crystals, but is entirely formed of large laminae. 4. With small facets, appearing like mica, composed of white and very brilliant scales. It is called white silver ore, because it contains a considerable quantity of that metal. 5. Small grained galena, so called because it has a very close grain. It is likewise very rich in silver, and is found with the foregoing ore. No galena, excepting that of Carinthia, is known to be without silver; but it has been observed, that those which afford the most silver have the smallest facets. 6. Galena crystallized like lead spar, in hexagonal prisms or cylindrical columns, contains little silver, and seems to be merely spathose lead, mineralized without having lost its form. Crystals of pure spathose lead entirely covered with a very fine galena, are sometimes found in the same piece, together with others which are changed into galena throughout.

8. Antimonial lead-ore, in which the metal is mineralized by sulphur with silver and regulus of antimony. This is of the same colour with galena, but its texture is different, being radiated, filamentous, or striated. When heated, it yields a white smoke; and it affords from 40 to 50 per cent. of lead, and from half an ounce to two ounces of silver per quintal.

9. Pyritous lead-ore, mineralized by sulphur with silver and a large proportion of iron. This is of a brown or yellowish colour; of an oblong or stalactitic form; friable; and of a lamellar, striated, or loofe texture; affording 18 or 20 per cent. of lead at most, which is obtained merely by melting it, the iron detaining the sulphur. It is only a mixture of galena with the brown pyrites.

10. Lead mineralized by arsenic, was lately discovered in Siberia. It is of a pale colour externally, but internally of a deep red. It is for the most part crystallized in rhomboidal parallelopipeds, or irregular pyramids. Lehman says, that it contains sulphur, arsenic, and about 34 per cent. of lead; and Mr Pallas says, that it contains some silver also. It was found near Catherineburg in Siberia; and Lehman says, that on being reduced to powder, it resembled the best carmine. A specimen examined by Mongez was of a yellow-greenish colour, and was found among quartz in the same country, and contained some arsenic. Both these, according to M. Magellan, may be easily reduced by means of a blow-pipe.

11. Stony or sandy lead-ores, consist either of the calciform or the galena kind, intimately mixed and diffused through stones and earth, chiefly of the calcaceous or barytic genus. To this species Mongez refers the earthy lead ore, falsely called native mafficot, found in the lead mines of Pompeian in Brittany, principally in solid pieces. These are either yellowish or grey; they appear bright like glass when broken, and effervesce with acids; whence it appears that the ore contains fixed air. Sometimes it is mixed with clay.

12. The mine of Morgenstern at Freyberg has a peculiar variety of lead-ore containing silver, and which deserves to be noticed on account of its yellowish-brown colour, and likewise on account of its singular figure, which consists of slender cylinders. Sometimes it is found in dendritical forms, like the knit colalt.

Most of the ores of lead contain silver; and those kinds of galena which do not, are very scarce. In Hungary and Transylvania, the lead ore contains a quantity of gold as well as silver. Sometimes the potters' ores are found so poor in silver, that it is not worth the expense of extracting it. These, when free from mixtures of the rock, are employed without any fusion to glaze earthen ware; and a considerable trade is carried on in the Mediterranean with such ores from the mines of Sardinia and France.

Lead, exposed to heat, melts long before it is ignited. By a strong heat it becomes volatile, and flies off in vapours. If suffered to cool very slowly, and the melted portion be poured off from that which is become come solid, it is found to be crystallized in quadrangular pyramids. When melted with the contact of air, it soon becomes covered with a grey dull pellicle, which by proper management is converted into minium, as explained under the article Chemistry; and by this operation it becomes heavier by about ten pounds in the hundred, though it is said that at Nuremberg it gains twice as much. By too much heat minium loses its beautiful red colour, and assumes that of a pale yellow: by a heat still more violent, it melts into a transparent glass, fusible, that it penetrates the crucible and escapes. But if one part of sand be added to three parts of calx of lead, the sand melts, by the assistance of the calx, into a beautiful amber-coloured glass. With two parts of lead and one of sand, it resembles a topaz. A similar quantity of the calx of lead, added to common glass, does not alter its transparency, but gives it a greater degree of weight, and more especially a kind of unctuousness, which renders it capable of being cut and polished more easily without breaking. This glass is very proper for making achromatic lenses; but is subject to veins, and to have a gelatinous appearance. "The English (says M. Fourcroy) call it flint glass; our workmen find great difficulty in selecting pieces of any considerable magnitude, exempt from striæ, in that which is imported from England." This great imperfection seems, in Macquer's opinion, to depend on the principles of the glass not being uniformly combined: for that purpose it is necessary that it should be kept in fusion for a long time; but as the lead would by that means be dissipated, the flint glass would lose a part of its density and unctuousness, which are its chief merit.

M. Magellan tells us, that it is the purest calx of lead called minium, made immediately from the metal, and the most pure quartzous sand, with pure mineral alkali, or rather with good nitre, that produce, when properly melted, the best flint-glass. The greater the proportion of red-lead, the heavier is the glass, and of course its refraction the greater; an essential requisite for such glass as is employed for the lenses of achromatic telescopes. It must, however, be observed, that glasses made with lead has the defect of being of unequal density, for want of a perfect mixture of all its parts; so that it is extremely difficult to find pieces of a few inches diameter among hundred weights of this glass, that shall be quite free from filaments and striæ. By chance the late Mr Dollond procured a pot of pure flint glass, from which he made the admirable triple object lenses of three feet and a half focus, which have been so much admired; but no such other glass has yet been found, though very considerable premiums have been offered for the method of producing the best kind of glass for optical instruments.

All the calces of lead, especially minium, have a great attraction for fixed air. If therefore we should desire a calx of lead in perfect purity, it must be kept defended from the contact of air, or slightly calcined before it is used, in order to separate the fixed air it may have absorbed. When exposed to the air, it tarnishes in proportion to the dampness of the air, and contracts a white rust, which is not a pure calx, but combined with the fixed air imbibed from the atmosphere. It is not altered by pure water; and therefore we must conclude, that the whitish crust with which the internal part of lead pipes through which water runs is usually covered, must be owing to the saline substances contained in the water.

"All the phenomena of the calcination of lead (says M. Magellan), and of its reduction to the metallic state, show that it has the smallest adhesion to phlogiston; as appears by the simple action of fire, which separates both, whilst their attraction is equally quick in its reduction to the metallic state. A common wafer, which owes its colour to red-lead, by being burned in the flame of a candle, immediately exhibits pure globules or little drops of the metal. The readiness with which lead parts with its phlogiston is shown by the curious experiment lately performed at Paris by Doctor Luzuriaga pensioner of the court of Spain. He put four ounces of lead-shot wetted with water into a pint bottle filled with atmospheric air, and closed with a stopple. Having shaken it several times, a black powder was produced, which soon turned white: on opening the bottle at the end of 24 hours, the air was found to have lost a fifth part of its bulk, and to have become phlogisticated. Dephlogisticated air was still more reduced in bulk; but the contrary took place when inflammable air was employed."

Caustic alkaline lixivia, boiled on lead, dissolve a small quantity of it, and corrode more. It has been observed, that plants do not thrive so well in leaden as in earthen vessels.

In Holland, and perhaps in other places, it has been customary to correct the most offensive expressed oils, as that of rape-seed and rancid oils of almonds or olives, by impregnating them with lead. This dangerous abuse may be discovered by mixing a little of that oil with a solution of orpiment made in lime-water: for, on shaking them together, and suffering them to rest, the oil, if it has any saturnine tint, will appear of an orange red; but if pure, of a pale yellowish one. A similar abuse has also been practised with acid wines, which dissolve as much of the lead as communicate a sweetish taste. This is discovered in a similar manner; and upon this principle is founded the liquor probatorius, or test-liquor. This liquor is nothing else than a solution of orpiment or liver of sulphur in lime-water. If a few drops of this solution be put in a glass of the suspected liquor, it will exhibit a precipitation like a dark-coloured cloud. This is owing to the attachment of the lead to the sulphur in the orpiment. If lead, or its calces, in powder, be mixed with a solution of hepatic sulphur, a decomposition ensues, but the alkali is not thus deprived of its sulphur. Instead of this, it is reconverted into vitriolated tartar; the lead seizes the phlogiston of the sulphur, and allows the vitriolic acid to unite with the alkali.

Lead unites with most other metals. It cannot, however, be united with iron; but if both are exposed to the fire in a proper vessel, the lead scorifies the iron by seizing on its phlogiston; after which it melts with the calx into a dark-coloured glass. This property which lead possesses, of reducing all the imperfect metals to a glass, is the reason of its being used in the purification of gold and silver; neither of which can be touched by it, but remain pure in the bottom of the cupel. This process is the more complete by reason reason of the great efficacy of lead in dissolving earthy bodies. In this respect it is so powerful a flux, that no earthen vessel or crucible can contain it when fused, of whatever materials the vessel be made. A mixture of raw and burned clay stands the action of lead for the greatest length of time; but at last this also gives way, and is corroded in the sides.

Litharge, a sort of refuse of lead, is employed in the composition of all the finer glasses called palets, which are designed as imitations of precious stones. The addition of litharge renders them more solid and brilliant. The principal ingredients are the purest of flint, purified alkali, borax, and litharge; the other additions, chiefly of metallic calces, are added, merely for the sake of tinging them with various colours.

Lead is employed in making of various vessels, as cisterns for water, large boilers for chemical and other purposes, &c. It is frequently mixed with tin by the pewterers; a practice which M. Fourcroy sets forth as very dangerous, and gives the following process for detecting it: "Dissolve two ounces of the suspected metal in five ounces of a good pure nitrous acid. The calc of tin is to be washed with four pounds of distilled water, and dried, and the water evaporated by the heat of a water-bath. By this evaporation nitre of lead is procured; which being calcined, the weight of the residue shows the quantity of metal contained in the tin, allowing a few grains for the augmentation of weight arising from calcination, as well as the other metallic substances, such as zinc and copper, which the tin under examination may contain. Bayan and Charlard by this method ascertained, that fine wrought tin or pewter contains about 10 pounds of lead in the 100; and that the common tin sold in France under that name, often contains 25 pounds in the same quantity; an enormous dose, sufficient to expose those who use vessels made of this composition to the greatest danger."

There are several methods used by pewterers to discover the fineness of tin. This is done in some cases by simple inspection, the judgment being assisted by the weight and noise produced in bending the metal. But the best method is by trying the specific gravity of the metal; which will discover a very small quantity of lead, the difference between the two metals being so considerable.

Lead, when taken into the human body, is productive of various disorders, particularly a dangerous kind of colic terminating in a palsy; and as all the common earthen ware is glazed with minium, the use of it cannot be supposed to be void of danger in all cases. Fountains, or vessels of lead which contain water, often communicate a noxious quality to it when suffered to remain long full. Its vapour is dangerous to the workmen who melt it, and the fumes falling upon the grass render it poisonous to the cattle who eat it; the fish who inhabit the waters near smelting houses soon die, nor is it safe for any animal to drink of it. In cases of poisoning by lead, antimonial emetics are recommended. Navier prescribes liver of sulphur and hepatic waters. The internal use of lead is certainly dangerous, though it is often prescribed in medicine; and even the external use of it is not altogether safe. Certain it is, that all workmen who deal much in lead, are subject to the choleric above mentioned from the habitual contact of the metal or its calces, even though they neither take it internally, nor are exposed to its fumes.

Black-Lead (Plumbago), a genus of inflammable substances, frequently confounded with molybdena; the appearance of which is nearly the same, though the qualities are very different. Black-lead, when pure, is extremely black; but when fresh cut, appears of a bluish white, and shining like lead. It is micaceous, and minutely scaly; easily broken, and of a granular and dull appearance when broken. Its tract on paper is much darker than that of molybdena, which has a fine silvery appearance; by which means they are easily distinguished from one another. Black-lead is too soft to strike fire with steel: it is insoluble in acids; but in a very strong fire, when exposed to the air at the same time, it is entirely volatile, leaving only a little iron and a small quantity of siliceous earth. It may be decomposed by deflagration with nitre; but the common fluxes are not capable of procuring its fusion. Its specific gravity is from 1.987 to 2.267. According to Scheele, this substance consists of phlogiston combined with aerial acid; but M. Pelletier has shown, that when pure it neither produces fixed nor inflammable air; both which, when found, are entirely owing to the substances that are mixed with it. Mr Scheele says, that one part of plumbago requires ten of nitre to decompose it, but charcoal only five. The conclusion drawn from hence, viz. that plumbago contains twice as much phlogiston as charcoal, however, is by no means just; for the phlogiston may be defended from the action of the nitre, by means we cannot possibly know, in the one and not in the other. Dr Priestley's experiments on the distillation of charcoal into inflammable air also show, that charcoal is little or nothing else than mere phlogiston, so that no substance whatever can contain more. From these experiments Mr Kirwan concludes, that 100 parts of plumbago contain 67 of phlogiston; because 100 grains of nitre contain 33 of real nitrous acid; all of which are decomposed when it receives as much phlogiston as is necessary to convert it into nitrous acid, or a little more. But 33 grains of nitrous acid are converted into nitrous air by 67 grains of phlogiston; the remaining 33 parts may be water, or other volatile substance. By the experiments of Messrs Gahn and Hielm, it appears, that 100 grains of plumbago, calcined in a muffle, lost 90 grains in weight; the remainder being a ferruginous earth, and the sulphureous smell showed that it contained some pyrites, both which were accidental to the black lead. M. Pelletier, however, as has already been hinted, affirms, that plumbago is volatilized in a strong fire, without producing any aerial vapour whatever; whence we must conclude, that the plumbago used by Scheele had not been quite pure. In close vessels, however, all agree, that black-lead sustains a vehement fire for a long time without any sensible diminution of weight. This is similar to charcoal; which for a long time was supposed to be indestructible in close vessels; but Dr Priestley has shown, that in a very violent fire, in close vessels, charcoal begins to emit inflammable air, and continues to do so without any end of the process that he could perceive; whence it is probable, that in this way also charcoal might be entirely dispersed, provided we could find vessels capable of of sustaining such a long and vehement heat. No experiments have been made with black-lead in this way, either with the solar heat in vacuo, or with a violent heat in an iron or other vessel capable of resisting a long continued heat.

Cronstedt, when treating of this mineral, observes, that "Mr Pott examined it in clole vessels, and Mr Quist in an open fire; from which difference in the mode of treatment, different notions had arisen: because the black-lead, when treated in clole vessels, or when immediately put into a strong charcoal fire, is almost unalterable; but in a calcining heat, becomes almost entirely volatile. This is the case with several of the other mineral phlogitons; and from this we may in general learn, how necessary it is to examine the mineral bodies by many and different methods, and to endeavour to multiply the experiments more than has hitherto been done."

With regard to the reduction of metallic calces, which ought to be accomplished by this phlogistic substance, M. Pelletier affirms, that it cannot be done unless the black-lead be mixed with fixed alkali, in the same manner as when charcoal is employed in such circumstances. It cannot be combined with iron, as Bergman asserts; nor with any other metal, though it may be simply interspersed betwixt its particles. M. Pelletier indeed owns, that there is a kind of plumbago found swimming over the melted iron in large furnaces where iron-ores are smelted; but he thinks, that this must have been naturally mixed with the mineral. It is also the only known plumbago of a very distinct lamellar form; as he observed in the pieces obtained from the iron works at Vallancy in the French province of Berry.

Black-lead is found of different kinds; viz. 1. Of a steel-grained and dull texture; naturally black, but when rubbed affording a dark-lead colour. 2. Of a granulated and scaly appearance at the same time. It is found in different countries, as Germany, France, Spain, the Cape of Good Hope, and America; but generally in small quantities, and of very different qualities. The best sort, however, and the fittest of all for making pencils, is that met with in the county of Cumberland in England. It is found in such plenty at a place called Borrowdale in this county, that hence not only the whole island of Britain, but the whole continent of Europe, may be said to be supplied. "I have seen (says M. Magellan) various specimens from different countries; but their coarse texture and bad quality cannot bear any comparison with that of Borrowdale; though it sometimes, but seldom, contains pyritaceous particles of iron. It is but a few years ago, that this mine seemed to be almost exhausted; but by digging some few yards through the strata underneath, according to the advice of an experienced miner, whose opinion had been long unattended to, a very thick and rich vein of the best black-lead has been discovered, to the great joy of the proprietors and advantage of the public."

The principal use of black-lead is for making pencils for drawing; which have the advantage of marking paper very distinctly for a time, though their traces may afterwards be entirely rubbed out by soft bread or elastic gum. To form the pencils, the lead is cut into thin parallelopipeds, and put into quadrangular grooves cut in pieces of cypress wood; and a slit being glued over, they are worked into small cylinders like quills. A coarser kind are made by working up the powder of black-lead with sulphur, or some mucilaginous substance; but these answer only for carpenters, or some very coarse drawings. One part of plumbago with three of clay, and some cows hair, makes an excellent coating for retorts, as it keeps its form even after the retorts have melted. The famous crucibles of Ypsen are formed of plumbago mixed with clay. They are known in Britain by the name of Hessian crucibles; but a manufacture of the same kind is now established at Chelsea in the neighbourhood of London, where crucibles are manufactured nearly of the same quality with the foreign ones. The powder of black-lead serves also to cover the straps for razors; and it is with it that the cast-iron work, such as stoves, &c., receive a glost on their surface. An application, however, perhaps as useful as any other, is that of black-lead to smooth the surfaces of wooden work which are subjected to much friction, as wooden screws, packers, &c.; neither greasy nor oily substances, nor foamy ointments, produce such a good effect upon them.

Milled Lead. See Chemistry, no 1219. Poison of Lead. See Poison. Sheet-Lead. See Plumbery.