may be dissolved completely, in a mixture, by measure, of two parts muriatic acid with one of nitric.

The lead appears preferable, as it is reduced, by evaporation, to an insoluble muriate. The muriate of rhodium then exhibits the rose colour, from which the name of the metal was given.

.

SECTION VII.

OF IRIDIUM.

Experiment 1. Mr. Tennant obtained iridium in the following manner: introduce a quantity of the black powder, remaining after the solution of the ore of platinum in nitro muriatic acid, into a silver crucible, with a large portion of soda, and fuse the mixture for some time. The alkaline mass, according to Mr. Tennant, will acquire, when dissolved in water, a deep orange, or brownish yellow colour, but much of the powder remains undissolved. This powder, on being digested in muriatic acid, afforded Mr. Tennant a dark blue solution, which afterwards became of a dusky olive green, and finally, by continuing the heat, of a deep red colour Part of the powder being yet left undissolved by the muriatic acid, was again heated with alkali, and by the alternate application of the alkali and acid a complete solution was at last obtained. The alkaline fluid, containing the oxyd of a volatile metal (osmium) not yet noticed, but which shall be described presently, was put aside. The acid solution contained the metal iridium, (and also a small portion of osmium.) To obtain the muriate of iridium, free from the other metal, the solution was evaporated to dryness; the dry mass was again dissolved in water, and suffered to crystallize. It yielded distinct octahedral crystals. These crystals, on being dissolved in water, gave a deep red coloured solution, inclining to orange. With an infusion of galls, no precipitate was

formed, but the colour was instantly and almost entire ly taken away. Muriate of tin, carbonate of soda, and prussiate of potash, produced nearly the same effect. Ammonia precipitated the oxyd, but retained a part, and acquired a purple colour. The alkalies also precipitated the greater part of the oxyd, and if added in excess, a portion of the oxyd became again dissolved, which imparted to the solution a yellow colour. All the metals, except gold and platina, produced a dark or black precipitate, when mingled with the muriatic solution of iridium, and rendered it at the same time colourless. To obtain the iridium in a pure state the octahedral crystals of muriate of iridium need merely be exposed to heat; both the muriatic acid as well as the oxygen are driven off, and the metal is obtained pure.*

Mr. Smithson Tennant discovered this metal in 1803; Descotils, Vauquelin and Fourcroy afterwards investigated it. Iridium has the appearance of platinum. It resists the action of all acids, even the nitro muriatic almost completely; much more than three hundred parts being necessary to dissolve one of iridium. The affinity between this metal and oxygen is very weak; but, like other metals, it unites with it. It combines with two doses of oxygen, and forms two oxyds. This is inferred from the phenomena of its solution in muriatic acid.f

Iridium does not combine with arsenic; but it readily unites with lead. The latter is separated by cupellation, leaving the iridium upon the cupel, as a coarse black powder.§

* See Tennant's paper in the Phil. Trans. for 1804, or Nicholson's Journal, No. 37, 1805, p. 24.

+ Fourcroy and Vauquelin. Ann. de Chim.

Thomson, i. 199.

§ For the experiments on this subject, consult Tennant's paper already quoted.

SECTION VIII.

OF OSMIUM.

*

Experiment 1. Osmium may be obtained by fusing any quantity of the black powder which is mixt with the ore of platinum, or which remains after dissolving the ore in nitro-muriatic acid, with at least four or six times its quantity of soda, or potash, dissolving the alkaline mass in water, and simply distilling the solution previously mingled with an acid. The oxyd of osmium is thus taken up by the water, and passes over in the receiver. The sulphuric acid being the least volatile, is the most proper for this purpose. But as even of this acid a little is liable to pass over, a second slow distillation should be had recourse to, to obtain the oxyd of osmium in a pure state. The solution of the oxyd of osmium thus procured is colourless; it has a sweetish taste, and strong odour.

Another mode of obtaining the oxyd of osmium consists in distilling the black powder procured from the ore of platinum with nitrate of potash. By this means the oxyd of osmium is obtained in a more concentrated state. See Tennant's paper, on two new metals found in the black powder after the solution of platina. Philos. Trans. 1804; and Nicholson's Journal, No. 37, 1805, p. 24.

Remark. This metal was discovered by Mr. TenMessrs. Fourcroy and Vauquelin discovered

nant.

* Mr. Tennant noticed that the oxyd of osmium even escapes in part by the mere affusion of water upon the dry alkaline mass, as is manifested by the pungent peculiar colour, from which property its name has been derived.

some of its properties. Its colour is of a dark gray, or blue. When heated in the open air it evaporates with a peculiar smell; but in close vessels, when the oxydizement is prevented, it does not appear in the least volatile. It is not acted upon by any acid, not even the nitro-muriatic, after exposure to heat; but with potash, as before noticed, it unites, and forms with it an orange yellow solution. One of the most singular characters of this metal, is the facility with which it unites with oxygen, and becoming oxydized, when heated in the open air, or when fused with potash, though it resists the action of acids. Considering the great volatility of this oxyd, its smell, taste, solubility in water, and the peculiar colour which it assumes with potash, is sufficient to distinguish it from every other metal.

The solution of osmium stains the skin of a dark colour, which cannot be effaced. With the infusion of galls it produces a purple colour, which gradually assumes a vivid blue. A mixture of iridium and osmium may be easily detected. On adding the infusion the red colour of the iridium is instantly taken away, and soon after the purple or blue colour of the esmium appears. Alcohol or ether mixed with the solution of oxyd of osmium in water, becomes black, the oxyd is reduced, and the osmium appears in black films. This oxyd is decomposed by all the metals, except gold and platinum. Silver immersed into the solution acquires a black colour. Copper, zinc, tin, and phosphorus produce a black or gray powder, and deprive the solution of its smell, and the power of giving a blue colour with galls. This black powder contains osmium in a metallic state, and the oxyd of the metal employed to precipitate it. It is soluble in nitro-muriatic acid, and then becomes blue with infusion of galls.

Osm'um unites with some of the metals. As this metal, like the preceding, is but little known, for further information on it, the reader is referred to Mr. Tennant's paper in the Philosophical Transactions.

SECTION IX.

OF COPPER.

Experiment 1. In order to obtain copper from its ores, if they contain much sulphur, after being pounded and washed, they are roasted in the open air. After the roasting has been continued, the ore is melted in the open fire into a mass, called a mat of copper. After roasting it again, the metal acquires a certain degree of purity, and is called black copper. In order to get rid of some impurities, the copper is hastily fused with three times its weight of lead. As the black copper contains sulphur, iron, and some other foreign bodies, the lead acts by uniting with the copper, and expelling the iron or other impurity. By keeping the copper heated in crucibles, it is further purified, as the foreign bodies are disengaged in the form of scoriæ. Its purity is judged by immersing iron rods from time to time, into the melted metal. As these rods become coloured with a small quantity of copper, the brilliancy of which indicates the goodness of the copper.

Rationale. The roasting separates the sulphur in part, and, by fusion with lead, iron, if it be present, is disengaged; the copper is afterwards separated by fusion, and the other metals are thrown up in the form of scoriæ. If the ore of copper should contain oxygen, as in the calciform ores, the ore, for obtaining the metal, must be fluxed with some carbonaceous matter. An enumeration of the ores of copper, may be seen in the classification of ores.

Experiment 2. If copper be dissolved in muriatic acid, and precipitated by a polished plate of iron; or the black oxyd of copper obtained by decomposing cuprated ammonia, melted with its own weight of pounded glass and pitch, will afford pure copper.*

* Thomson.