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a crackling sound. It has considerable malleability, and is beaten for certain purposes of the arts, into leaves, termed tin-foil, of about ioooth part of an inch thick. When at the temperature of boiling water, it can be drawn into wires of considerable fineness. But it is inferior in tenacity to other of the more perfect metals, a wire of .078 of an inch in diameter being capable of supporting a weight of only 34.7 lb. It fuses at a temperature of 442° F.; but a violent heat is required to raise it in vapour. When heated to whiteness it takes fire, and burns with a white flame, very much like antimony, being converted into the peroxide, which may be obtained in octahedral crystals. Tin, though soon tarnished when exposed to the air, does not undergo much further change, and is not even sensibly affected by being kept under water, and hence its use in culinary vessels, as a coating to the more oxidable metals. But when water is passed over a surface of red-hot tin, the water is decomposed and the tin oxidated, and when tin is exposed for a time to the atmosphere in a state of fusion, it is partially oxidated, and assumes irridescent colours in the manner of copper. The density of pure tin is about 7.3. Its combining weight is calculated at 58.92. It enters into combination with oxygen, chlorine, sulphur, arsenic, and other bodies, and with other metals forms alloys, some of which are of important uses in the arts. Its bisulphuret is a beautiful substance so like gold in appearance, that the alchymists termed it aurum musivum or mosaic gold, and, as if further to delude them, it was found to possess, likewise, the property of being soluble in no acid except aqua regia. Peroxide of tin resembles alumina, in forming insoluble compounds with colouring matters, so that it is employed in dyeing as a base or mordant,

XXXVII. LEAD.

Lead is one of the most plentiful of the malleable metals, and the knowledge of it, like that of gold, silver, copper, tin, seems to have been possessed in the infancy of human societies. Of the ores of lead mineralogists enumerate upwards of 30 species, many of them very beautiful. They are found usually in veins, in the primary, transition, and lower secondary formations. Of these ores, greatly the most abundant, and that from which nearly all the lead of commerce is derived, is the sulphuret, termed likewise galena or lead glance. From this ore the lead is obtained by the action of heat in a reverberatory furnace. The sulphur and the metal are both oxidated, and the sulphur is driven off as sulphuric and sulphurous acids. A portion of the sulphuric acid combines with the oxidated metal, and forms sulphate of lead, to reduce which quick-lime and coal are added during the process, the lime combining with the sulphuric acid, and the carbon of the coal abstracting the oxygen of the oxide. The metal being reduced, is collected in vessels, from which it is cast into ingots, which form the subject of commerce.

Lead possesses a bluish-gray colour, and when newly melted or recently cut, is very bright, but it becomes tarnished by exposure to the air, its surface becoming oxidated, and the oxide combining with the carbonic acid of the atmosphere. Lead has little taste, but emits a peculiar smell on being rubbed, and it stains paper and the skin of a bluish colour. It is a soft metal, very flexible and inelastic. It is exceedingly malleable, and may be reduced to thin plates, by pressure or the hammer. It may be drawn into wires, but its ductility is not very great, and its tenacity is less than that of any other of the ductile metals, a wire off of an inch diameter being capable of supporting only 18.4 lb. It fuses at the temperature of 612°, contracts on becoming solid, and if slowly cooled, forms octahedral crystals. It may be heated to whiteness in close vessels, without subliming. When exposed to the air, it becomes quickly tarnished by the oxidation of the metal, but the oxide further combines with carbonic acid, which preserves the metal for a long time from the further action of the air. At a high temperature, however, lead absorbs oxygen quickly, and when kept in a state of fusion, its surface is covered with a gray film; and when strongly heated, it is dissipated entirely in fumes of the protoxide. Water has, of itself, no action upon lead, but its presence facilitates the action of air in corroding it. In distilled water, and in close vessels, lead suffers no sensible change; but in open vessels it is oxidated, yielding minute white crystalline scales of carbonate of the protoxide.

The specific gravity of lead is 11.357, and it is not increased by hammering. Its combining weight is calculated at 103.73. It combines with oxygen, chlorine, sulphur, and other bodies, and it forms alloys with the other metals.

This metal although found only in the older rock formations, yet in its abundance, exhibits an approach to iron and the metallic bases generally diffused. It is found chiefly as a sulphuret, but largely too as a carbonate, and its salts form numerous mineral species.

XXXVIII. COBALT.

Cobalt is contained in minute quantity in aërolites. The ores of the metal are few, and, like nickel, it occurs for the most part associated with arsenic and sulphur. The ore from which it is usually procured is a native arseniet. It may be extracted from this substance by a process analogous to that employed in the case of nickel. It may be procured in the state of powder, and by the action of intense heat be fused into a mass. It is of a reddish-gray colour, and feeble metallic lustre. It is a brittle metal, and fuses at a heat somewhat lower than iron. It has hitherto been supposed to be magnetic; but M. Faraday states that, when perfectly pure, it is not susceptible of this property. It is little, if any thing, affected by exposure to the air ; but it attracts oxygen when heated in open vessels, and at a red heat decomposes water. It has the property of communicating a colour, generally blue, to many of its compounds. Its density is about 7.834, and its combining weight is calculated at 29.57. This metal is manifestly allied, in its essential characters, to nickel and iron.

XXXIX. NICKEL.

This metal is found in a few minerals, and chiefly in combination with sulphur and arsenic. It is derived, too, from those remarkable metallic substances termed aërolites, which, from time to time, have fallen from the atmosphere, sometimes in masses of prodigious weight, and which have at all times excited, by their appearance, the wonder of mankind. A remarkable circumstance attending these bodies is, their uniform composition, denoting a common origin in them all. Many hypotheses have been formed to account for their origin and fall. The most probable is, that they are the result of some vast electric action, by which the elements of bodies already existing in the atmosphere, have formed new combinations. If metallic matter is formed of simpler elements, as is now contended for, we may conceive, perhaps, how a power as intense as the electricity of the clouds has been able to fix these elements in new combinations. All the äerolites, it is believed, contain nickel along with iron.

Nickel is generally obtained from the native arseniet of nickel, which is found both in the primary and older secondary rock formations, and from an arseniet obtained in the smelting of cobalt. The process is very complicated; but the result is, that an oxalate of nickel is obtained, and that from this salt the oxalic acid is expelled by heat and the action of carbon, and the metal obtained in the form of an ash-coloured powder, which fuses at a high temperature.

Nickel is of a fine white colour, intermediate between silver and tin. It is somewhat softer than iron. It is malleable, and may be hammered into plates, not exceeding ito part of an inch thick. It is ductile,

It is ductile, and may be drawn

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