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The alcaline solution distilled with muriatic acid gave a volatile metallic oxide dissolved in water, which from the peculiar smell, Mr. Tennant called osmium. The pure metal may be obtained by shaking mercury in the solution of the oxide, and distilling the mercury from the amalgam so formed; the metal is white, very infusible and fixed. With tincture of galls its solutions afford a blue precipitate.

The acid solution contained another metal called iridium, on account of the various colours exhibited by its oxide.

Dr. Wollaston principally turned his attention to the solution remaining after the precipitation of the platinum by sal ammoniac. This may contain iron, copper, lead, gold, platinum, and two new metals. These different substances are separable by a plate of iron, which, when immersed in their solution, throws down every thing except iron. This precipitate is digested in weak nitric acid, which dissolves the lead and copper; then in nitro-muriatic acid, which takes up the platinum, and the remaining two metals. The addition of common salt forms triple compounds with each of them. Alcohol dissolves two of these, and leaves a triple salt of a metal which produces red saline compounds, and which Dr. Wollaston thence called rhodium.

The alcoholic solution contains the salt of platinum, which we may set aside, and another salt, containing the remaining new metal palladium, which is separable by prussiate of mercury; or palladium may be at once precipitated, by adding prussiate of mercury to the solution remaining after the precipitation of platinum by sal ammoniac. Rhodium is a white. metal, its specific gravity 11. Palladium is a little heavier. Palladium alloyed with gold has been employed, at the suggestion of Dr. Wollaston, for the graduated part of the great astronomical circle, erected at the Royal Observatory, by Mr. Troughton.

A separate ore, consisting of iridium and osmium, has been discovered by Dr. Wollaston among the grains of crude platinum. Its specific gravity 19,5; it is hard, not malleable, and very brilliant.

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I have thus endeavoured to describe, and as far as their nature admits, to exhibit the analytic processes by which the various substances existing in crude platinum are separable, as well as the characters which enable us to recognise them as distinct and peculiar bodies. The separation of the new metals from this complicated mixture, may be considered as one of the great triumphs of modern analysis, and sets the skill and dexterity of the discoverers in the strongest light; for they had not merely to disunite a compound of known elements, but were further perplexed by the unknown characters of the new and unexamined metals.

The case before us will also serve to give those who know chemistry by name only, some notion of the difficulties which beset the chemical analyst, and of the patience and knowledge required to overcome them; for these persons often imagine, that making a chemical analysis is a very simple process; they have been in the habit of looking at results, but have neglected the steps that led to them; forgetting, as Lord Bacon has somewhere said, "that in philosophy as in husbandry, a few hands suffice to measure out and fill into sacks, that corn which requires very many more labourers to sow, and reap, and bind, and bring into the barn."

We now pass on to another metal-mercury or quicksilver, of which there is but one ore of any consequence: the sulphuret called also cinnabar or vermillion. It occurs crystallized, and massive; light and dark red, and often sprinkled with globules of metallic mercury. This ore has been found in France, in the department of Mont Tonnerre, and in other parts of the kingdom; but the most celebrated European mines are those of Almaden, in Spain.

The Spanish dominions in America are also very rich in quicksilver, and large portions are annually prepared for the purposes alluded to in my last lecture. In the kingdom of New Granada, a large vein was discovered by shodeing, that is, by traceing the fragments of ore washed down by currents to their source. Quicksilver, geologically speaking, stands among the newest metals. In primitive countries it occurs only in

small quantities, and is rare; but in bituminous slate, shell lime-stone, sand-stone, and breccias, the great repositories

exist. It has been found by Dolomieu among volcanic products, doubtless sublimed by subterranean fires.

There are two leading processes by which quicksilver is obtained in its metallic state. In France, cinnabar is distilled with lime and iron, by which it is decomposed, and the quicksilver passes over. In Spain, it is procured by roasting the ores: of these, and indeed of most other metallurgic processes, an excellent account will be found in Aikin's chemical dictionary.

This ore of mercury is easily known by being wholly dissipated with a sulphureous smell before the blowpipe. It is used as a pigment, and for colouring red sealing wax.

Quicksilver is a metal presently recognised by its fluidity. It boils at +660°, and freezes at-40°. It forms two oxides; the protoxide is black, and contains 190 metal + 7,5 oxygen: the peroxide is red, and consists of 190 metal and 15 oxygen.

There are also two chlorides. The one commonly called calomel, and composed of 190 quicksilver and 33,5 chlorine. The other is corrosive sublimate, and contains 190 quicksilver, +67 chlorine. The modes of forming these two very important compounds were exhibited; and Mr. Brande took the opportunity which was thus afforded, of shewing the fallacy of the notions which some have entertained respecting the compound nature of chlorine.

After shewing the nature of the salts of mercury formed by the two oxides, Mr. Brande proceeded to the metal copper, of which the ores were more numerous, and the processes of reduction more complicated than those of the metals before noticed. It is found native, combined with oxygen and with chlorine; in the state also of carbonate, arseniate, and phosphate; and lastly, united to sulphur. Specimens of these ores were shewn, and their mineralogical and chemical characters were dwelt on at some length.

The ores of copper are mostly peculiar to the old or primitive rocks. In this country, Cornwall not only furnishes profusion

of the useful ores, but the most select and scarce cabinet specimens-such as native copper, black sulphuret of copper, and arseniate of copper.

Blue carbonate of singular beauty is found at Chessy, in France. Malachite, or green carbonate of copper, in Siberia. It is used in China as a common green paint, and for ornamental purposes. The most considerable mines in the world are those of Cornwall and Anglesea. Russia, Austria, and Sweden, are also rich in this metal.

There is no metal, the presence of which is of more easy detection than copper. The suspected mineral is to be powdered, and boiled in dilute nitric acid, when it either affords a blue solution, or one which becomes so by the addition of ammonia. Solutions of copper furnish a precipitate of metallic copper, when a plate of clean iron is immersed in them.

The ores of lead met with in the cabinet of the mineralogist are very numerous; but those which are really useful as

sources of the metal are few.

Those ores of lead which are not of a metallic appearance, have a vitreous or greasy looking fracture; and they are easily reducible by the blowpipe, when mixed with charcoal and some proper flux. The evidence respecting the existence of native lead, is by no means good. Mr. Rathkié is said to have found it in Madeira, but it has been there considered as of volcanic origin.

Native oxide of lead is also a very scarce ore; it is of a red colour, and generally associated with sulphuret, from the decomposition of which it probably results. It has been found in Yorkshire, and in some of the German lead mines.

Chloride of lead, called also horn-lead, has been found in Derbyshire, Germany, and in the United States by Dr. Meade; it is a very rare ore.

Carbonate of lead commonly occurs crystallized in 4 and 6sided prisms, and in long acicular and capillary crystals, aggregated into a columnar form. It is a soft, brittle, and heavy ore, and easily furnishes a metallic globule by the blowpipe.

It generally contains about 90 per cent. of carbonate of lead, and 10 per cent. of silica, alumina, and oxide of iron. Greywacke, slate, and lime-stone rocks, are the usual containers of this ore; other lead ores and copper ores usually accompanying it. It is found in Lanarkshire, Durham, Cumberland, Shropshire, and in Cornwall, of singular beauty in Pentire glaise, in the parish of St. Minver. The mines of Saxony, Siberia, and of Chili in America, have also produced splendid specimens. Its chemical character is solubility in nitric acid, with effervescence. The solution affords a precipitate of metallic lead by the immersion of a plate of zinc.

Phosphate of lead, or green lead ore is crystallized in six-sided prisms, and short diverging acicular crystals. Before the blowpipe it melts into a polyhedral globule. Yorkshire, Scotland, Germany, and Siberia, afford fine specimens. One variety is brown, and occurs massive and crystallized; it is found in Hungary, Saxony, and very fine in Huelgot, and Poullouen, in Brittany; also in Mexico.

Arseniate of lead is a rare mineral. There are two varieties, the filamentous and reniform; it has a brownish colour. Before the blowpipe it exhales arsenic and leaves lead. Hitherto it has been found only in France and Siberia.

Sulphate of lead has a grey colour, and when crystallized assumes the forms of octohedra and four-sided prisms. It decrepitates under the blowpipe, and gives metallic lead. It is found in Anglesea, Scotland, Cornwall, the Hartz, and Siberia.

Molybdate of lead, or yellow lead ore, crystallizes in modified octohedra, and tables. It was analysed by Mr. Hatchett, in the year 1796. It is found in Carinthia, the Tyrol, and Mexico.

Chromate of lead, or red lead of Siberia, crystallizes in foursided prisms, &c. It is of a fine reddish yellow colour, and has lately been artificially prepared by Dr. Bollman, and advantageously employed in the arts.

These ores of lead are chiefly to be recognized as chemical and mineralogical varieties; they are highly interesting and

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