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XXIV. TITANIUM.

This metal was first obtained from a black sand found in Cornwall, resembling gunpowder, composed of titanic acid and protoxide of iron, and it has since been discovered in a few other minerals. It has likewise been found in crystals of titanic acid, taken from the bottom of the smelting furnaces of large iron works.

Titanium may be procured by subjecting the acid along with charcoal to the most powerful heat of a wind-furnace, which reduces the acid, but does not fuse the metal. It may likewise be procured from the chloride, in the state of a deep blue-coloured powder, which burns when exposed in a heated state to the air. But after it has been subjected to a high temperature, it becomes incombustible, harder, and denser, and is no longer acted upon by acids. These are the characters of silicium, which this substance further resembles in its combinations. Its combining weight has been calculated at 24.33. It combines with oxygen, chlorine, and sulphur, and doubtless with many other bodies; but its compounds have been only partially examined. Its combinations with oxygen are—

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The latter substance is a white powder, which acquires a yellow tint by heat. It is insoluble in water, and infusible; but, like silica, it may be obtained in the state of a white gelatinous precipitate, which is soluble in diluted hydrochloric acid. When this precipitate is dried and heated, it glows, and is then no longer soluble in any acid.

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From this account of titanium, no doubt can exist that it is closely allied to silicium. Further, it so nearly resembles zirconia that the two bodies are with difficulty distinguished, and is thus seen to be one of the links which connect the siliceous group of bodies with the aluminous.

These three substances, then, silicium, boron, and titanium, may be said to constitute the siliceous series of undecomposed bodies. They are few in number, but of vast extent with relation to other mineral products, since one of them, silicium, forms the basis of the greater part of the matter existing on the globe.

The other bodies regarded as simple are all metals. They may be conveniently arranged, nearly in the order in which they combine with oxygen, placing at the head of the scale gold, which is the most electro-negative, and exhibits the least affinity for oxygen, and at the bottom of the scale potassium, which has the greatest affinity for oxygen, and may be regarded as electro-positive with relation to all the others. The manner in which the sulphur and siliceous groups are related to them may be illustrated thus:—

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Bismuth, it was seen, passes into copper, copper passes into zinc, zinc into tin, tin into lead, and so on to iron and the alkaligenous metals. The whole members of the group are thus connected with one another, and with the other bodies termed simple, exhibiting a concatenation of parts, which can be accounted for only by a common derivation.

XXV. GOLD.

Gold, although not the most useful, has in every age been regarded as the most precious, of the metals; a distinction which it owes to its rarity, its beauty, its indestructibility, and other properties. It occurs in the metallic state, either pure, or alloyed with silver, or other metals, and frequently with iron pyrites. It occurs crystallized in the cubic or allied forms, in veins and threads, but is often so disseminated in the mass of rock as to be only detected by pounding and washing. It is, however, most abundantly found in the sand of rivers and other alluvial deposites, into which it has been carried. In this condition it is found in Brazil, Mexico, and Peru, in Africa, and in the river sands of many countries. The chief supplies of it are derived. from Mexico and South America, from the mines of Hungary, and more recently from the Oural Mountains.

Gold is easily separated from the alloys and extraneous bodies with which it is found. When pure, it is of a yellow colour, which distinguishes it from the other simple metallic bodies. Its lustre is considerable, but even when burnished, it is inferior in brilliancy to silver, steel, or mercury. Its specific gravity is from 19.4 to 19.6. It is soft, and very

flexible. It is of all the metals the most ductile and malleable. It may be beaten into leaves of surpassing tenuity. It melts at the temperature of about 2016° F., and when in the melted state, assumes a bluish-green colour. It expands more in the act of fusion, and consequently contracts more in cooling, than most other metals, and hence it is not well fitted for forming casts from moulds. It is in no way altered by water or air, and hence it may be exposed for ages to moisture and the atmosphere without having its surface

corroded. It is not oxidated by being kept in a state of fusion in open vessels; but it may be ignited by the powerful action of electricity or the oxyhydrogen blow-pipe, and then it burns brilliantly with a greenish-blue flame, and is dissipated in the form of a purple powder. It is not oxidated and dissolved by any of the pure acids. But chlorine combines with it, and hence it is dissolved by nitro-hydrochloric acid, which supplies chlorine, and this acid, on account of its dissolving gold, was distinguished by the older chemists as aqua regia.

The combining weight of gold is estimated by some at 199.2, by others at one-half. It combines with oxygen, chlorine, sulphur, and other substances, and forms alloys with bodies of its own class.

Gold, regarded in all ages as the noblest of the metals, is yet connected with the others of the class, by characters which place it beyond dispute, in the same natural group. It passes through platinum, silver, and mercury, into copper, and through copper, into tin, lead, and other metals. Copper, it has been seen, is connected by the closest relation with bismuth, antimony, arsenic, and these again with sulphur, and so on to nitrogen and oxygen. Gold, therefore, with all its beauty and perfectness of metallic characters, is no other than a sequence of a chain of bodies; and what we believe of any one of them, with respect to its essential constitution, we must believe of gold.

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