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dom, approaches nearer than any of the metals which have been mentioned, to those metallic bases which form the great mass of the crust of the earth, silicium and aluminum. It is found everywhere associated with them, sometimes in veins traversing the older rocks, sometimes in beds manifestly deposited from a fluid 'medium, sometimes in nodules imbedded in deposites of clay, and sometimes in combination with other substances, in the crystalline state. It has been everywhere mingled with the matter of the soil, from which it is taken up by the roots of growing plants; and sometimes it is deposited by them again, as in bog-iron ore, in such quantity as to form considerable deposites, even in the newest formations.
This metal is widely diffused, existing in the organic as well as in the mineral kingdom, and the ores which contain it are numerous. Some of these are binary combinations of manganese with another body, as oxygen, and some of them are salts, having an oxide of manganese for the base, or part of the base. Of these ores, the most abundant are the oxides. From these the metal may be obtained by forming the oxide into a paste with oil, and exposing it to a violent heat in a covered crucible lined with charcoal, by which process several times repeated, the metal is de-oxidated, and remains in the crucible in the form of a semi-globular mass.
Manganese thus obtained, has a grayish-white colour somewhat lighter than cast iron. It is hard and brittle, so that it may be reduced to powder. It is doubted whether it is attracted by the magnet, when perfectly pure. It requires for its fusion the most intense heat of a wind furnace. It soon oxidates on exposure to the air, and when heated to redness attracts oxygen rapidly, the result being the protoxide. At common temperatures it decomposes water, though slowly, but at a red heat the decomposition is very rapid.
The specific gravity of this metal has been variously computed from 7.05 to 8.013. Its combining weight has been computed to be 27.72 or nearly that of iron. It has some of the characters of zinc, but all its essential properties connect it with iron.
Iron and the allied substances exhibit an increasing affinity for oxygen over the bodies that precede them. They pass into the next group to be considered, of which the
type is aluminum, and which latter metals have a yet increased affinity for oxygen, and are never found in nature pure. They form the basis of the earths, commonly so called, and pass into the bases of the alkaline earths, and these again into the bases of the true alkalies, which have the greatest affinity of all known bodies for oxygen.
None of these groups of bodies, however, is unconnected with another, nor can they be represented in a strictly linear series. They rather form reticulations than chains. Tracing, indeed, a series of bodies from nitrogen downwards, we find the connexion wonderfully perfect; but this series is not insulated but passes into others. We have the sulphur group passing gradually by antimony and bismuth into copper and the more perfect metals, and in like manner the siliceous group becomes connected with iron, but still more directly with aluminum, and the bodies we are now to review. These latter bodies arranged nearly in the order of their affinities for oxygen, are
Aluminum is the type of the series, and the others, all rare bodies in nature, are chiefly interesting as shewing the passing of aluminum, on the one hand, into the iron series of bodies, and on the other into the bases of the alkaline earths.
XLII. CERIUM AND LANTANUM.
Cerium was first obtained from a mineral, found in the copper mine of Bastnäs, in Sweden, and it has been found in one or two other rare minerals, derived from the north of Europe and Greenland. It exists in the natural state only as an oxide, always associated with silica, alumina, yttria, and other substances. It may be obtained by forming a chloride of cerium by the same process as is employed in the cases of aluminum, glucinum, and yttrium, to be referred to. It is procured in the form of a gray powder, having a metallic lustre. Its properties may be said to be unknown. Its oxide resembles the earths, commonly so called, and it is manifestly in the same class of natural bodies.
Lantanum has been recently added to the list of simple bodies, by the discovery of its oxide in the same mineral from which oxide of cerium was first procured. Nay, it appears that this new oxide forms two-fifths of what was regarded as oxide of cerium, so that the cerium, hitherto described as a simple body, is really a compound one. The new element, it is said, alters little the properties of cerium, and therefore the former has been termed lantanum, as being concealed, as it were, in cerium. It is described by M. Mossander, its discoverer, as being a gray powder with metallic lustre, which undergoes oxidation in water, and is changed into a white hydrate.
Now, nothing can be less satisfactory than these experiments, in so far as they are designed to establish the existence of a new body, to be termed simple. The intimate alliance of this rare substance with another from which it can scarcely be distinguished, should refer us to some common origin for both, rather than to a distinct origin for each, In truth, the two bodies are so similar, that it is almost ridiculous to regard them as essentially and radically distinct from one another. We frequently find a much greater difference in the characters of the same body under different circumstances, than in those which we thus assume to be distinct. Shall it be said, that having been unable to decompose the metallic base of lantanum, we are bound to hold it to be simple? Such a conclusion should of itself shew that our rule is unsound. The negative evidence that a substance so rare as lantanum has not been decomposed, and is therefore to be regarded as simple, cannot, it is manifest, be weighed against the evidence supplied by analogy, that such a substance must be derivative and not simple. The discovery of twenty such substances, instead of shewing that twenty new elements should be added to the list of simple bodies, should lead us to the conclusion, that the reasoning had been illogical by which so many had been already admitted.