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osmium and iridium. Many methods have been devised for the separation of these metals (see PLATINUM), one of the best being that of H. St. C. Deville and H. J. Debray (Comptes rendus, 1874, 78, p. 1502). In this See also:

PROCESS

process the osmiridium is fused with See also:

ZINC

zinc and the excess of zinc evaporated; the residue is then ignited with See also:

BARIUM (symbol Ba, atomic weight 137'37 [0=16])

barium nitrate, extracted with See also:

WATER

water and boiled with nitric See also:

ACID (from the Lat. root ac-, sharp; acere, to be sour)

acid. The iridium is then precipitated from the See also:

SOLUTION (from Lat. solvere, to loosen, dissolve)

solution (as See also:

OXIDE

oxide) by the addition of baryta, dissolved in aqua regia, and precipitated as iridium ammonium chloride by the addition of ammonium chloride. The See also:

double chloride is fused with See also:

NITRE

nitre, the melt extracted with water and the residue fused with See also:

lead, the excess of lead being finally removed by solution in nitric acid and aqua regia. It is a brittle See also:

metal of specific gravity 22.4 (Deville and Debray), and is only fusible with See also:

GREAT

great difficulty.

It may be obtained in the spongy form by igniting iridium ammonium chloride, and this variety of the metal readily oxidizes when heated in See also:

air. Two oxides of iridium are known, namely the sesquioxide, Ir203, and the dioxide, Ir02, corresponding to which there are two See also:

SERIES (a Latin word from serere, to join)

series of salts, the sesqui-salts and the iridic salts; a third series of salts is also known (the iridious salts) derived from an oxide IrO. Iridium sesquioxide, Ir203, is obtained when See also:

POTASSIUM [symbol K (from kalium), atomic weight 39.114 0=16)]

potassium iridium chloride is heated with See also:

SODIUM [symbol Na, from Lat. natrium; atomic weight 23.00 (0=16)]

sodium or potassium See also:

CARBONATES

carbonates, in a stream of See also:

CARBON (symbol C, atomic weight 12)

carbon dioxide. It is a bluish-See also:

black See also:

POWDER (through O. Fr. puldre, modern poudre, from Lat. pulvis, pulveris, dust)

powder which at high temperatures decomposes into the metal, dioxide and See also:

OXYGEN (symbol 0, atomic weight 16)

oxygen. The hydroxide, Ir(OH)3, may be obtained by the addition of See also:

CAUSTIC (Gr. rcavvraubs, burning)

caustic potash to iridium sodium chloride, the mixture being then heated with See also:

ALCOHOL

alcohol. Iridium dioxide, IrO2, may be obtained as small needles by See also:

HEATING

heating the metal to See also:

bright redness in a current of oxygen (G. Geisenheimer, Comptes rendus, 1890, IIo, p. 855). The corresponding hydroxide, Ir(OH)4, is formed when potassium iridate is boiled with ammonium chloride, or when the tetrachloride is boiled with caustic potash or sodium carbonate. It is an See also:

INDIGO (earlier indico, from Lat. indicum, the Indian sub-stance or dye; the Sans. name was niti, from nila, dark blue, and this through Arab. al-nil, annil, gives " aniline ")

indigo-See also:

BLUE (common in different forms to most European languages)

blue powder, soluble in hydrochloric acid, but insoluble in dilute nitric and sulphuric acids. On the oxides see L. See also:

WOHLER, FRIEDRICH (1800-1882)

Wohler and W.

Witzmann, Zeit. anorg. Chem. (1908), 57, p. 323. Iridium sesquichloride, IrC13, is obtained when one of the corresponding double chlorides is heated with concentrated sulphuric acid, the mixture being then thrown into water. It is thus obtained as an See also:

OLIVE (Olea europaea)

olive See also:

green precipitate which is insoluble in acids and alkalis. Potassium iridium sesquichloride, KalrCl6'3H20, is obtained by passing See also:

SULPHUR

sulphur dioxide into a suspension of potassium chloriridate in water until all dissolves, and then adding potassium carbonate to the solution (C. Claus, Jour. prak. Chem., 1847, 42, p. 351). It forms green prisms which are readily soluble in water. Similar sodium and ammonium compounds are known.

Iridium tetrachloride, IrCl4, is obtained by dissolving the finely divided metal in aqua regia; by dissolving the hydroxide in hydrochloric acid; and by digesting the hydrated sesquichloride with nitric acid. On evaporating the solution (not above 4o° C.) a dark See also:

mass is obtained, which contains a little sesquichloride. It forms double chlorides with the alkaline chlorides. For a bromide see A. Gauthier and M. Riess, Ber., 1909, 42, p. 3905. Iridium sulphide, IrS, is obtained when the metal is ignited in sulphur vapour. The sesquisulphide, Ir2S3, is obtained as a See also:

brown precipitate when sulphuretted See also:

HYDROGEN [symbol H, atomic weight x-oo8 (0=16)]

hydrogen is passed into a solution of one of the sesqui-salts. It is slightly soluble in potassium sulphide. The disulphide, IrS2, is formed when powdered iridium is heated with sulphur and an alkaline carbonate. It is a dark brown powder.

Iridium forms many ammine derivatives, which are analogous to the corresponding platinum compounds (see M. Skoblikoff, Jahresb., 1852, p. 428; W. See also:

Palmer, Ber., 1889, 22, p. 15; 1890, 23, p. 3810; 1891, 24, p. 2090; Zeit. anorg. Chem., 1896, 13, p. 211). Iridium is always determined quantitatively by See also:

CONVERSION (Lat. conversio, from convertere, to turn or ,change)

conversion into the metallic See also:

state. The atomic weight of the element has been determined in various ways, C. Seubert (Ber., 1878, It, p.

1770), by the See also:

ANALYSIS (Gr. avci and Meta, to break up into parts)

analysis of potassium chloriridate obtaining the value 192.74, and A. Joly (Comptes rendus, 189o, IIo, p. 1131) from analyses of potassium and ammonium chloriridites, the value 191.78 (0 =15.88).

End of Article: IRIDIUM (symbol Ir.; atomic weight 193.1)

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