species, S. angustifolium, an arctic and temperate North American species, is also native in Galway and Kerry in Ireland. Other British representatives of the order are: Iris Pseudacorus, (yellow iris), common by river-banks and ditches, I. foetidissima (stinking iris), Gladiolus communis, a rare plant found in the New Forest and the Isle of Wight, and Romulea Columnae, a small plant with narrow recurved leaves a few inches long and a short scape bearing one or more small regular funnel-shaped flowers, which occurs at Dawlish in Devonshire.
IRIDIUM (symbol Ir.; atomic weight 193.1), one of the metals
of the platinum group, discovered in 1802 by Smithson Tennant
during the examination of the residue left when platinum ores
are dissolved in aqua regia; the element occurs in platinum
ores in the form of alloys of platinum and iridium, and of 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 process the osmiridium is fused with zinc
and the excess of zinc evaporated; the residue is then ignited
with barium nitrate, extracted with water and boiled with nitric
acid. The iridium is then precipitated from the solution (as
oxide) by the addition of baryta, dissolved in aqua regia, and
precipitated as iridium ammonium chloride by the addition of
ammonium chloride. The double chloride is fused with nitre,
the melt extracted with water and the residue fused with lead,
the excess of lead being finally removed by solution in nitric
acid and aqua regia. It is a brittle metal of specific gravity
22.4 (Deville and Debray), and is only fusible with 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 air.
Two oxides of iridium are known, namely the sesquioxide, Ir2O3, and the dioxide, IrO2, corresponding to which there are two 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, Ir2O3, is obtained when potassium iridium chloride is heated with sodium or potassium carbonates, in a stream of carbon dioxide. It is a bluish-black powder which at high temperatures decomposes into the metal, dioxide and oxygen. The hydroxide, Ir(OH)3, may be obtained by the addition of caustic potash to iridium sodium chloride, the mixture being then heated with alcohol. Iridium dioxide, IrO2, may be obtained as small needles by heating the metal to bright redness in a current of oxygen (G. Geisenheimer, Comptes rendus, 1890, 110, 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 indigo-blue powder, soluble in hydrochloric acid, but insoluble in dilute nitric and sulphuric acids. On the oxides see L. Wöhler and W. Witzmann, Zeit. anorg. Chem. (1908), 57, p. 323. Iridium sesquichloride, IrCl3, 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 olive green precipitate which is insoluble in acids and alkalis. Potassium iridium sesquichloride, K3IrCl6·3H2O, is obtained by passing 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 40° C.) a dark mass is obtained, which contains a little sesquichloride. It forms double chlorides with the alkaline chlorides. For a bromide see A. Gautbier 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 brown precipitate when sulphuretted 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. 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 conversion into the metallic state. The atomic weight of the element has been determined in various ways, C. Seubert (Ber., 1878, 11, p. 1770), by the analysis of potassium chloriridate obtaining the value 192.74, and A. Joly (Comptes rendus, 1890, 110, p. 1131) from analyses of potassium and ammonium chloriridites, the value 191.78 (O = 15.88).
IRIGA, a town of the province of Ambos Camarines, Luzon,
Philippine Islands, on the Bicol river, about 20 m. S.E. of Nueva
Cáceres and near the S.W. base of Mt. Iriga, a volcanic peak
reaching a height of 4092 ft. above the sea. Pop. (1903) 19,297.
Iriga has a temperate climate. The soil in its vicinity is rich,
producing rice, Indian corn, sugar, pepper, cacao, cotton, abacá,
tobacco and copra. The neighbouring forests furnish ebony,
molave, tindalo and other very valuable hardwoods. The
language is Bicol.
IRIS, in Greek mythology, daughter of Thaumas and the
Ocean nymph Electra (according to Hesiod), the personification
of the rainbow and messenger of the gods. As the rainbow
unites earth and heaven, Iris is the messenger of the gods to men;
in this capacity she is mentioned frequently in the Iliad, but never
in the Odyssey, where Hermes takes her place. She is represented
as a youthful virgin, with wings of gold, who hurries with the
swiftness of the wind from one end of the world to the other,
into the depths of the sea and the underworld. She is especially
the messenger of Zeus and Hera, and is associated with Hermes,
whose caduceus or staff she often holds. By command of Zeus
she carries in a ewer water from the Styx, with which she puts
to sleep all who perjure themselves. Her attributes are the
caduceus and a vase.
IRIS, in botany. The iris flower belongs to the natural order
Iridaceae of the class Monocotyledons, which is characterized
by a petaloid six-parted perianth, an inferior ovary and only
three stamens (the outer series), being thus distinguished from
the Amaryllidaceae family, which has six stamens. They are
handsome showy-flowered plants, the Greek name having been
applied on account of the hues of the flowers. The genus contains
about 170 species widely distributed throughout the north
temperate zone. Two of the species are British. I. Pseudacorus,
the yellow flag or iris, is common in Britain on river-banks,
and in marshes and ditches. It is called the “water-flag”
or “bastard floure de-luce” by Gerard, who remarks that
“although it be a water plant of nature, yet being planted in
gardens it prospereth well.” Its flowers appear in June and July,
and are of a golden-yellow colour. The leaves are from 2 to 4 ft.
long, and half an inch to an inch broad. Towards the latter part
of the year they are eaten by cattle. The seeds are numerous
and pale-brown; they have been recommended when roasted as
a substitute for coffee, of which, however, they have not the
properties. The astringent rhizome has diuretic, purgative
and emetic properties, and may, it is said, be used for dyeing
black, and in the place of galls for ink-making. The other
British species, I. foetidissima, the fetid iris, gladdon or roast-beef
plant, the Xyris or stinking gladdon of Gerard, is a native
of England south of Durham, and also of Ireland, southern
Europe and North Africa. Its flowers are usually of a dull,
leaden-blue colour; the capsules, which remain attached to
the plant throughout the winter, are 2 to 3 in. long; and the
seeds scarlet. When bruised this species emits a peculiar and
disagreeable odour.
Iris florentina, with white or pale-blue flowers, is a native of the south of Europe, and is the source of the violet-scented orris root used in perfumery. Iris versicolor, or blue flag, is indigenous to North America, and yields “iridin,” a powerful hepatic stimulant. Iris germanica of central Europe, “the most common purple Fleur de Luce” of Ray, is the large common blue iris of gardens, the bearded iris or fleur de luce and probably the Illyrian iris of the ancients. From the flowers of Iris florentina a pigment—the “verdelis,” “vert d’iris,” or iris-green, formerly used by miniature painters—was prepared by maceration, the fluid being left to putrefy, when chalk or alum was added. The garden plants known as the Spanish iris and the English iris are both of Spanish origin, and have very showy flowers. Along with some other species, as I. reticulata and I. persica, both of which are fragrant, they form great favourites with florists. All these just mentioned differ from those formerly named in the nature of the underground stem, which forms a bulb and not a strict creeping rhizome as in I. Pseudacorus, germanica, florentina, &c. Some botanists separate these bulbous
