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IX.

*

BOOK short, connected with its history, would induce us to regard this fossil as a juice which once flowed from a tree, and which, buried in the earth by some natural convulsion, would be impregnated with mineral vapours, and acquire a certain degree of consistency. But as the copal, the only kind of known gum which resembles amber, is brought to us from Africa and the East Indies, it would appear, that the forests in which amber is produced, could not exist in the environs of the Baltic, unless a very elevated temperature prevailed. Thus, these small fragile crystals, which at first seem to be only an object of idle curiosity, become so many monuments of the revolutions which our planet has experienced.

443.

Fourcroy, Elémens d'Histoire Naturelle et de Chimie (édit. de 1789,) iii.

BOOK X.

Continuation of the Theory of Geography.

of the simple

substances which compose the solid part of the globe. Section Second: of Metals.

view of

THE only minerals which remain for us to consider, are General metals; substances whose brightness, weight, density, duc- metals. tility, and fusibility, engage the attention of mineralogists and crystallographers; substances which, forming sometimes the representative signs of the products of industry, and sometimes the useful or the formidable instruments of our arts, and our passions, ought to be carefully noticed in the description of political states; but they peculiarly deserve attention in the details of physical geography, from the intimate relation which they bear to the two great agents of nature, electricity and magnetism. Our knowledge of facts is too limited for enabling us to discuss with advantage the bold hypothesis of some Danish and German naturalists, who pretend to form from analogical conjectures a theory of the electrical and magnetic phenomena observed in metals, and who have even ventured to draw from it the conclusion, that the solid centre of the globe was a metallic mass, all the mineral substances in which were only oxides.* This theory, unsatisfactory and defective, notwithstanding all the attempts to support it by vague analogies, acquires, indeed, some interest, from its approximating to the results of Sir H. Davy's new experiments, which seem to indicate the metallic nature of a number of substances in appearance earthy and alkaline. We must wait the ulterior progress

* Steffens, Histoire Intérieure de la Nature. Schelling, Théorie de l'Univers. 1. Journal de Physique Spéculative, i. cah. 2. Ritter, le Sidérisme, etc.

X.

BOOK of these interesting researches, before we can apply them to explain the theory of the earth. But all philosophers should agree in considering the bearings and position of metals, as a subject worthy our most careful and persevering researches. Physical geography indispensably requires that a subject of this nature should constitute one of its departments; and if we devote to it a certain portion of our pages, our readers will perceive, in the progress of our work, the advantages which are thus afforded us, even in the study of political geography. We shall class metals according to their specific gravity.

Platina,

Property of
Platina.

Platina remained unknown, or neglected, until 1735. Don Ulloa, a Spanish geometrician, who accompanied Condamine and Bouguer, in their voyage, to measure a degree at Peru, having found this metal there, announced the discovery of it in the relation of his voyage. Platina as yet has been found only in the gold mines of America,* particularly in those of Santa Fé, near Carthagena, in Castille. d'Or, and in the mines of Choco, in Peru. It is brought to us in little grains, mixed with gold dust, ferruginous sand, and some particles of mercury. That which has been brought into Europe, contains three or four extraneous minerals. It is the least fusible of all the metals.

To melt it into ingots, it is mixed with arsenic, a substance which renders the platina very fusible, and from which it is afterwards easily separated by roasting. But this process exposes the workmen to vapours, the danger of which is unfortunately too well known. It is of platina that those rods are made, that have been employed in measuring the base of the chain of triangles, whence has been deduced the length of the arc of the meridian which traverses France, and by consequence, the distance from the equator to the northern pole.

This metal has been chosen for such purposes, because it is little susceptible of dilating, or contracting from the va

It is also found in Estramadura in Spain.-T.

+ Fourcroy et Vauquelin, Annales du Muséum, tome iii. p. 149; tome iv. p. 77.800.

is only ter, or

X.

riations of temperature. Its dilatation, according to Borda, BOOK 30 for one degree of the centrigrade thermomefor a degree of Reaumur. Whilst a rod of iron dilates for a centesmial degree, and 733 for a degree of Reaumur.*

Gold is only found in its native state, that most pure. It exists in all kinds of earth.

is to say, al- Gold, its It is found in position.

little beds in the primitive mountains of gneiss, and of micaceous schist, in the country of Salzbourg, and in Carniola; it occupies veins in the mountains of sienite and porphyry near Kremnitz in Hungary, in the secondary rocks of argillaceous-quartzous schist, or even of sandstone, (grès,) at Zalatna in Transylvania, and in an argillaceous free stone, (grès argileux†) not far from Ekaterinbourg in Siberia; thus, says Werner, this metal has been formed in very different periods. It is also proved by the experiments of Sage, Berthollet, Rouelle, Darcet and Deyeux,§ that there are particles of gold existing in vegetables. Berthollet has extracted about 2 grammes,, or 40 grains T of gold, from 489 hectogrammes, or a quintal of ashes. Werner assures us, that at Zalatna, native gold has been found in half petrified wood, or rather, says he, in bituminous wood.

cal situa

The mine of gold which is in Norway is poorer than Geographithat in Sweden; those of the north produce altogether tion of scarcely the twentieth part of the quantity furnished by gold. that of Nagyag in Transylvania, or that of Kremnitz in Hungary. But what indeed are all the gold mines of Europe, taken together, in comparison of one single mine in Peru or Brazil? In going from La Paz, towards Potosi, and Tucuman, all the beds of clayey schist are found pene

Or about I

32323 according to the scale of Fahrenheit. One degree of Reaumur being supposed equal to 2 1-4 of Fahrenheit.-T.

† Gris sometimes means fliut or silicious substances, and sometimes is translated free-stone. The context must determine which it designates.-T.

Werner, Nouvelle Théorie des Filons, 77.

Chaptal, Elémens de Chimie, tom. iii. p. 401.
Theorie des Filons, loc. cit.

X.

BOOK trated with veins of auriferous quartz; and the fall of a shelf of rock discovers masses of gold from 2 to 300 pounds in weight. The islands of Borneo, of Celebes, or Macassar, and of Sumatra, situated under the equator, contain very rich mines of gold, though badly worked.†

Sands pro

ducing gold.

Quality of gold.

Europe has also rivers, which carry along with them some grains of gold; but in Africa, in searching along the rivers, we find almost every where auriferous sand. In Nigritia, the natives are regularly employed every year in this golden harvest, after having finished that of the corn. Near Akim, upon the coast of Guinea, one person may pick up several ounces a day. This increasing abundance of one of the most weighty and dense metals, as we approach the equator, presents to us a question, as interesting as it is difficult to solve.

The valuable qualities of gold render it worthy of the rank which opinion has assigned to it amongst metals. Less brilliant than platina, it has a colour more agreeable to the eye. Thus, the poets have not failed to give golden locks to Apollo; to Jupiter a throne of gold; Vulcan employs gold to forge a buckler for Achilles; in short, in the form of an adjective, the words gold and beauty are synonymous amongst the Greeks. Tractable in the hands of art, from its great ductility, gold assumes every form which we wish it to acquire. The goldsmith, the jeweller, the embroiderer, and the gilder, employ it with equal facility. It is capable of the most astonishing superficial extension, thus making up, in some measure, for its scarceness, by its ductility. A quantity of gold, of the weight of one grain (53 milligrammes) can be beaten out into a sheet, the surface of which will cover 50 square inches, or 3% square decimetres; and when used in the gilding of silver wire, its extension is nearly sixteen times greater. The tenacity of gold is such, says Hauy, that one thread of this metal, of 2 millimetres, or of an inch

65

*Helm, Journal d'un Voyage de Buenos-Ayres à Lima, (en All.)

+ Mem. de la Société de Batavia, ii, 166, iv. 589, etc.

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