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which have a sweetish taste. Its specific gravity is greater than that of any other earth. The base of yttria has been supposed to be a metallic substance, which would receive the name of yttrium ; but it has never been exhibited in a separate state. Yttria contains oxygen, and hence been inferred to be a metallic oxide.

GLUCINA.

Glucina, or Glucine, is an earth which has been procured only from the beryl, the emerald, and the euclase.

It derives its name from its forming salts which have a sweetish taste. It has no taste nor smell, is infusible by heat, but dissolves in the acids, and

It is insoluble in water. It is also supposed to be a metallic oxide.

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pure alkalies.

ZIRCONIA.

Zirconia is a very rare earth, found as yet only in the zircon or jargon of Ceylon, and the hyacinth. It is void of taste or smell ; is insoluble in water and pure alkalies; but is soluble in alkaline carbonates. Its base is supposed to be metallic.

THORINA.

This is another very rare earth, discovered by Berzelius, who extracted it from a species of gadolinite. It absorbs carbonic acid, and dissolves readily in acids. It is not soluble by the pure alkalies, but slightly so by the alkaline carbonates. It is supposed to be the oxide of a metal,

METALS.

We come now to treat of the last division of the metallic substances; those which, remaining in the air in the metallic state, have received the name particularly of metals.

Those metals whose combinations with oxygen form alkalies, as potassium, sodium, and lithium, as also those whose oxides form earths, as calcium, magnesium, barium, strontium, silicium, alumium, yttrium, glucinum, zirconium, and thorinum, have been already mentioned incidentally, in speaking of the alkalies and earths to which they give rise. But we shall now enumerate the general properties of this important class of bodies, including the above mentioned.

The metals are distinguished from all other substances by certain properties, particularly a peculiar lustre; and most of them have great weight, or specific gravity.

Several of them have been known to part of the world in very ancient times, while some savages in the present day are totally unacquainted with their use: but a considerable number of the metallic substances have been discovered only lately. The metals are so important in many mechanic arts, that mankind could never have attained their present state of civilisation without them.

Metals are, in general, solid bodies at the usual temperature: one only, mercury, is fluid.

They are opaque in the mass in its usual state; but gold, when beat into very thin leaves, transmits a faint greenish light, when held between the eye and the direct rays of the sun.

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The lustre by which they are distinguished, called the metallic lustre, is not easily described, but may be exemplified in that of silver, steel, lead, tin, &c., as distinguished from that of glass, diamond, &c. Mica has a lustre which approaches that called the metallic, but it loses this on being scratched, while the metals do not; on the contrary, they are more brilliant when fresh cut. This property of the metals renders them highly useful for ornamental purposes, and for reflecting light, as in mirrors.

Metals are the best conductors of heat, and also of electricity.

Some of the metals are capable of being extended under the blows of a hammer, which property is called malleability, and is peculiar to metals. Others, again, are brittle, on which account they were formerly called semi-metals. The malleable metals are, gold, platina, silver, palladium, potassium, sodium, mercury in its frozen state, copper, iron, lead, tin, zinc, and nickel. These differ much in their degrees of malleability. Gold may be beat into the thinnest leaves, and zinc is very little malleable, except when heated. The malleable metals are also ductile, or may be drawn out into wire. Gold and platina may be drawn into the finest wire.

One of the metals, iron, is capable of being made very elastic, which renders it fit for making springs.

Most of the metals are very fusible, or capable of being rendered fluid by the application of heat; on this account they may be cast into moulds, and formed into various utensils: some of the metals are volatile at a high degree of heat.

None of them are very hard naturally; but some

of them may be hardened by art: thus the moderns make cutting instruments of iron and steel, and the ancients made them of a combination of copper and tin.

All the metals are capable of combining with oxygen, and thus forming oxides; but they differ very much in the readiness with which they combine with it, which occasions their division into several classes.

The oxides of metals have none of the metallic brilliancy, and no malleability: their appearance and nature are totally different from that of the metals themselves.

The oxides of some metals, as potassium and sodium, are alcaline ; others are acid, constituting the metallic acids : the rest have neither acid nor alcaline properties, but are, as well as others, capable of being dissolved by the acids, thus forming salts.

Some of the metals attract oxygen so strongly, that they become oxidized almost immediately in the open air, and even take oxygen from all its combinations, so that they are, with great difficulty, preserved in the metallic state ; of this nature are metals that produce the alkalies and earths, which can only be kept in pure bitumen called naphtha, which has no oxygen in its composition.

Some of the metals do not experience any change on being kept in fusion by a strong heat with an access of air ; but others are by this means converted into oxides. The first have been called perfect metals, and comprehend gold, platina, silver, and palladium. The rest differ very much in the degree of heat necessary to oxidize them. Arsenic, manganese, and the bases of the earths and alkalies become oxides at the usual temperature of the atmosphere, even when perfectly dry. Lead

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and copper are oxidized slowly by moist air. Iron, zinc, copper, tin, &c., require to be heated to red

Although the perfect metals cannot be oxidized by any degree of ordinary heat, they may by the effect of electricity and galvanism. . All the metals, that are converted into oxides by atmospheric air, undergo this change still more rapidly in oxygen gas, as was shown in the burning of iron wire in oxygen.

Metals are also converted into oxides by the action of acids, but in different manners. Some acids which contain oxygen loosely combined part with it to the metal; while others, as the sulphuric and muriatic acids, do not act upon iron or zinc, except they are diluted with water, and then it is the water, and not the acid, which supplies the oxygen. Metals cannot be made to combine with all

proportions of oxygen, but are susceptible only of certain degrees or stages of oxidation. Thus iron has only two oxides; the black oxide composed of 29.5 parts

of

oxygen, and 100 parts metal ; and the red oxide of 43.5 parts of oxygen, and 100 parts of metal : and there are no intermediate degrees of oxidation, nor will iron combine with a larger or smaller proportion of oxygen. Metals differ in the number of oxides which they form : thus some have two, some three, and others four oxides : and, according to the law of the atomic theory, the different oxides of the same metal contain oxygen in proportions that are simple multiples of each other.

The different oxides of the same metals have different colours, which render them very valuable as pigments. They have also distinct chemical properties, and combine, in different proportions, with the acids, forming distinct salts.

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