276 I R I I R K by reducing ammonium iridichloride, (NH 4 ) 2 IrCl 6 and potassium iridichloride, K 2 IrCl , by heating in a current of hydrogen, and finds as the mean of fifteen accordant experiments Ir=192 74 (Berichte d. deut. chem. Gesellsch. zu Berlin, 1878, 1767). * This result justifies the placing of iridium before platinum in the table in vol. v. p. 543. The alloy used in the construction of the international geodesic standard was prepared by fusing together pla tinum and iridium in a lime crucible by a powerful blast of oxygen and coal gas ; it has the following composition : Analysis 1. Analysis 2. Platinum 89-40 89-42 Indium 10 16 10"22 Rhodium 0-18 16 Ruthenium . 0*10 o-io Iron 06 06 It is almost indestructible, and has extreme rigidity, especi ally in the tube form ; its coefficient of elasticity is very great ; it has a high density, and a most beautifully polished surface can be obtained upon it (com p. Deville, Ann. Chim. Phys. 1879 [5] xvi. 506). An iridio-platinum alloy containing about 20 per cent, of iridium has also a very high coefficient of elasticity (22-20), whilst its malleability and ductility are almost without limit. A 25 per cent, alloy can only with great difficulty be worked into sheet and wire when heated at a low temperature, 30 and 40 per cent, with great difficulty only at a temperature little below melting; it is brittle when cold, but has a grain of great beauty and fineness (Matthey). IRIS, the rainbow, was personified as one of the second ary deities of Olympus, and occurs very frequently both in art and in literature. 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. According to Hesiod (Theog. 260) she is the daughter of Thaumas and Elactra and sister of the Harpies, the stormwinds. With the swiftness of the wind (de AAoTros, TroS^i/e/xos) she pene trates everywhere, bearing the messages of heaven. She often carries the caduceus, the herald s staff of Hermes. An epithet frequently applied to her is " golden- winged " (XpwoTrrepos), and in painting and sculpture she is always represented with wings. In the absence of other criteria, it is sometimes difficult to distinguish her from Nike. The latter is more frequently attendant on Athene, while Iris oftener accompanies Hera. IRIS. The iris flower belongs to the natural family Iridaceae, of the class monocotyledons, and to the petaloid division with inferior ovary and only three stamens (the outer series), being thus distinguished from the Amaryllis family, which has six stamens. They are handsome showy- flowered plants, the Greek name iris having been applied on account of the hues of the flowers. Two of the species are British, /. Pseudacorus, or yellow flag, and the /. foetidissima, the fcetid iris or roast-beef plant, with blue- purple rarely yellow flowers. The former species is widely distributed ; the latter is English, although naturalized in Scotland and Ireland. The roasted seeds of I. Pseud- acorus have been used as a substitute for coffee. 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. From the flowers of Iris florentina a 1 Quite recently (Liel)ig s Annalen, ccvii. 1), Seubert has corrected the atomic weight of platinum also, which he finds to be 194 34. 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 /. reticulata and /. 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 is tuberous and not a rhizome as in /. Pseudacorus, florentina, &c. Modern botanists separate these bulbous irises from the genus Iris, and place them apart in the genus Xiphium, the Spanish iris, /. Xiphium of the older botanists being now known as Xiphium vidgare. As defined by Baker, Xiphium includes 15 species, all from the Mediterranean region and the East, and Iris 81 species, mostly from the northern temperate region. Remains of three species of Iris have been met with in a fossil state, in rocks of Tertiary age. IRISH MOSS, or CAEEAGEE^ (Irish carraiyeen, " moss of the rock "), is a sea-weed (Chondrus crispus) which grows abundantly along the rocky parts of the Atlantic coast of Europe and North America. It is collected for commercial purposes on the west and north-west of Ireland, and in very large quantities on the coast of Plymouth county, Massachusetts, United States. In its fresh con dition the plant is soft and cartilaginous, varying in colour from a greenish-yellow to a dark purple or purplish- brown ; but when washed and sun-dried for preservation it has a yellowish translucent horn-like aspect and consistency. The principal constituent of Irish moss is a mucilaginous body, of which it contains about 55 per cent. ; and with that it has nearly 10 per cent, of albuminoids and about 15 per cent, of mineral matter rich in iodine and sulphur. When softened in water it has a sea-like odour, and from the abundance of its mucilage it will form a jelly on boiling with from 20 to 30 times its weight of water. The jelly of Irish moss is used as an occasional article of food, and is a popular remedy in cases of chest disease. It may also be used as a thickener in calico- printing, and in America it is used for fining beer. In the neighbourhood where it is obtained it is utilized for feeding cattle. As found in commerce, Irish moss is fre quently mixed with Gigartina mammillosa, G. acicularis, and other sea-weeds with which it is associated in growth. IRKUTSK, a government of Asiatic Russia, extending over an area of 272,140 square miles of eastern Siberia, and bounded by the Yenissei and Yakutsk governments, the Trans-Baikal region, and the Chinese frontier. It is divided into the districts of Kirensk, Nizhne-Udinsk, Irkutsk, Verkholensk, and Balagansk. The surface of the government is mountainous, espe cially in the south-west. While the greater part lies at a level of from 1200 feet to nearly 3000 feet above the sea, the range of the Sayanski mountains reaches from 6000 feet to between 7000 and 8000 feet (the highest point, Mungu Sarduik, is in Chinese territory). Other mountains of note are the Gurbi Daban and Tunkinski Byelki ranges and the massif of the Khamar Daban. All the rivers of the government belong either to the system of the Yenissei (as the Angara and the two Tunguskas) or to that of the Lena (as the Kirenga, the Tchaya, the- Tchuya, the Kuta, the Ilga). Of the geological features of the country the most remarkable is the wide distribution of volcanic products basalts, dolerites, tuffs, obsidians even, and pumice. The mountain chains consist in the main of crystalline rocks. Iron is obtained in considerable quan tities; coal-beds exist in various parts, especially in the basin of the Angara ; graphite is wrought in several places ; and salt-springs form the object of a considerable exploitation.
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