Chapter 8

H. v. Kap-Herr,Die abendländische Politik des Kaisers Manuel(Strassburg, 1881).

IRETON, HENRY(1611-1651), English parliamentary general, eldest son of German Ireton of Attenborough, Nottinghamshire, was baptized on the 3rd of November 1611, became a gentleman commoner of Trinity College, Oxford, in 1626, graduated B.A. in 1629, and entered the Middle Temple the same year. On the outbreak of the Civil War he joined the parliamentary army, fought at Edgehill and at Gainsborough in July 1643, was made by Cromwell deputy-governor of the Isle of Ely, and next year served under Manchester in the Yorkshire campaign and at the second battle of Newbury, afterwards supporting Cromwell in his accusations of incompetency against the general. On the night before the battle of Naseby, in June 1645, he succeeded in surprising the Royalist army and captured many prisoners, and next day, on the suggestion of Cromwell, he was made commissary-general and appointed to the command of the left wing, Cromwell himself commanding the right. The wing under Ireton was completely broken by the impetuous charge of Rupert, and Ireton was wounded and taken prisoner, but after the rout of the enemy which ensued on the successful charge of Cromwell he regained his freedom. He was present at the siege of Bristol in the September following, and took an active part in the subsequent victorious campaign which resulted in the overthrow of the royal cause. On the 30th of October 1645 Ireton entered parliament as member for Appleby, and while occupied with the siege of Oxford he was, on the 15th of June 1646, married to Bridget, daughter of Oliver Cromwell. This union brought Ireton into still closer connexion with Cromwell, with whose career he was now more completely identified. But while Cromwell’s policy was practically limited to making the best of the present situation, and was generally inclined to compromise, Ireton’s attitude was based on well-grounded principles of statesmanship. He was opposed to the destructive schemes of the extreme party, disliked especially the abstract and unpractical theories of the Republicans and the Levellers, and desired, while modifying their mutual powers, to retain the constitution of King, Lords and Commons. He urged these views in the negotiations of the army with the parliament, and in the conferences with the king, being the person chiefly entrusted with the drawing up of the army proposals, including the manifesto called “The Heads of the Proposals.” He endeavoured to prevent the breach between the army and the parliament, but when the division became inevitable took the side of the former. He persevered in supporting the negotiations with the king till his action aroused great suspicion and unpopularity. He became at length convinced of the hopelessness of dealing with Charles, and after the king’s flight to the Isle of Wight treated his further proposals with coldness and urged the parliamentto establish an administration without him. Ireton served under Fairfax in the second civil war in the campaigns in Kent and Essex, and was responsible for the executions of Lucas and Lisle at Colchester. After the rejection by the king of the last offers of the army, he showed special zeal in bringing about his trial, was one of the chief promoters of “Pride’s Purge,” attended the court regularly, and signed the death-warrant. The regiment of Ireton having been chosen by lot to accompany Cromwell in his Irish campaign, Ireton was appointed major-general; and on the recall of his chief to take the command in Scotland, he remained with the title and powers of lord-deputy to complete Cromwell’s work of reduction and replantation. This he proceeded to do with his usual energy, and as much by the severity of his methods of punishment as by his military skill was rapidly bringing his task to a close, when he died on the 26th of November 1651 of fever after the capture of Limerick. His loss “struck a great sadness into Cromwell,” and perhaps there was no one of the parliamentary leaders who could have been less spared, for while he possessed very high abilities as a soldier, and great political penetration and insight, he resembled in stern unflinchingness of purpose the protector himself. By his wife, Bridget Cromwell, who married afterwards General Charles Fleetwood, Ireton left one son and three daughters.

Bibliography.—Article by C. H Firth inDict. of Nat. Biog.with authorities there quoted; Wood’sAth. Oxon.iii. 298, andFasti, i. 451; Cornelius Brown’sLives of Notts Worthies, 181;Clarke Paperspublished by Camden Society; Gardiner’sHistory of the Civil War and of the Commonwealth.

IRIARTE(orYriarte)Y OROPESA, TOMÁS DE(1750-1791), Spanish poet, was born on the 18th of September 1750, at Orotava in the island of Teneriffe, and received his literary education at Madrid under the care of his uncle, Juan de Iriarte, librarian to the king of Spain. In his eighteenth year the nephew began his literary career by translating French plays for the royal theatre, and in 1770, under the anagram of Tirso Imarete, he published an original comedy entitledHacer que hacemos. In the following year he became official translator at the foreign office, and in 1776 keeper of the records in the war department. In 1780 appeared a dull didactic poem insilvasentitledLa Música, which attracted some attention in Italy as well as at home. TheFábulas literarias(1781), with which his name is most intimately associated, are composed in a great variety of metres, and show considerable ingenuity in their humorous attacks on literary men and methods; but their merits have been greatly exaggerated. During his later years, partly in consequence of theFábulas, Iriarte was absorbed in personal controversies, and in 1786 was reported to the Inquisition for his sympathies with the French philosophers. He died on the 17th of September 1791.

He is the subject of an exhaustive monograph (1897) by Emilio Cotarelo y Mori.

IRIDACEAE(the iris family), in botany, a natural order of flowering plants belonging to the series Liliiflorae of the class Monocotyledons, containing about 800 species in 57 genera, and widely distributed in temperate and tropical regions. The members of this order are generally perennial herbs growing from a corm as inCrocusandGladiolus, or a rhizome as inIris; more rarely, as in the Spanish iris, from a bulb. A few South African representatives have a shrubby habit. The flowers are hermaphrodite and regular as inIris(fig. 1) andCrocus(fig. 3), or with a symmetry in the median plane as inGladiolus. The petaloid perianth consists of two series, each with three members, which are joined below into a longer or shorter tube, followed by one whorl of three stamens; the inferior ovary is three-celled and contains numerous ovules on an axile placenta; the style is branched and the branches are often petaloid. The fruit (fig. 2) is a capsule opening between the partitions and containing generally a large number of roundish or angular seeds. The arrangement of the parts in the flower resembles that in the nearly allied order Amaryllidaceae (Narcissus,Snowdrop, &c.), but differs in the absence of the inner whorl of stamens.

1. Flower, from which the outer petals and the stigmas have been removed, leaving the inner petals (a) and stamens.

2. Pistil with petaloid stigmas.

3. Fruit cut across showing the three chambers containing seeds.

4. A seed. 1-4 about ½ nat. size.

The most important genera areCrocus(q.v.), with about 70 species,Iris(q.v.), with about 100, andGladiolus(q.v.), with 150.Ixia,Freesia(q.v.) andTritonia(includingMontbretia), all natives of South Africa, are well known in cultivation.Sisyrinchium, blue-eyed grass, is a new-world genus extending from arctic America to Patagonia and the Falkland Isles. Onespecies,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, andRomulea 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 inaqua 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 (seePlatinum), 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 inaqua 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 andaqua 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 thesesquioxide, Ir2O3, and thedioxide, 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 inaqua 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. Thesesquisulphide, 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. Thedisulphide, 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).

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 theIliad, but never in theOdyssey, 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, theXyrisor 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 germanicaof 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 ofIris florentinaa 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, asI. reticulataandI. 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 inI. Pseudacorus,germanica,florentina, &c. Some botanists separate these bulbousirises from the genusIris, and place them apart in the genusXiphium, the Spanish iris, including about 30 species, all from the Mediterranean region and the East.

The iris flower is of special interest as an example of the relation between the shape of the flower and the position of the pollen-receiving and stigmatic surfaces on the one hand and the visits of insects on the other. The large outer petals form a landing-stage for a flying insect which in probing the perianth-tube for honey will first come in contact with the stigmatic surface which is borne on the outer face of a shelf-like transverse projection on the under side of the petaloid style-arm. The anther, which opens towards the outside, is sheltered beneath the over-arching style arm below the stigma, so that the insect comes in contact with its pollen-covered surface only after passing the stigma, while in backing out of the flower it will come in contact only with the non-receptive lower face of the stigma. Thus an insect bearing pollen from one flower will in entering a second deposit the pollen on the stigma, while in backing out of a flower the pollen which it bears will not be rubbed off on the stigma of the same flower.

The hardier bulbous irises, including the Spanish iris (I. Xiphium) and the English iris (I. xiphioides, so called, which is also of Spanish origin), require to be planted in thoroughly drained beds in very light open soil, moderately enriched, and should have a rather sheltered position. Both these present a long series of beautiful varieties of the most diverse colours, flowering in May, June and July, the smaller Spanish iris being the earlier of the two. There are many other smaller species of bulbous iris. Being liable to perish from excess of moisture, they should have a well-drained bed of good but porous soil made up for them, in some sunny spot, and in winter should be protected by a 6-in. covering of half-decayed leaves or fresh coco-fibre refuse. To this set belongI. persica,reticulata,filifolia,Histrio,juncea,DanfordiaeRosenbachianaand others which flower as early as February and March.The flag irises are for the most part of the easiest culture; they grow in any good free garden soil, the smaller and more delicate species only needing the aid of turfy ingredients, either peaty or loamy, to keep it light and open in texture. The earliest to bloom are the dwarf forms ofIris pumila, which blossom during March, April and May; and during the latter month and the following one most of the larger growing species, such asI. germanica,florentina,pallida,variegata,amoena,flavescens,sambucina,neglecta,ruthenica, &c., produce their gorgeous flowers. Of many of the foregoing there are, besides the typical form, a considerable number of named garden varieties.Iris unguicularis(orstylosa) is a remarkable winter flowering species from Algeria, with sky-blue flowers blotched with yellow, produced at irregular intervals from November to March, the bleakest period of the year.The beautiful JapaneseIris Kaempferi(orI. laevigata) is of comparatively modern introduction, and though of a distinct type is equally beautiful with the better-known species. The outer segments are rather spreading than deflexed, forming an almost circular flower, which becomes quite so in some of the very remarkable duplex varieties, in which six of these broad segments are produced instead of three. Of this too there are numberless varieties cultivated under names. They require a sandy peat soil on a cool moist subsoil.What are known asOncocyclus, or cushion irises, constitute a magnificent group of plants remarkable for their large, showy and beautifully marked flowers. Compared with other irises the “cushion” varieties are scantily furnished with narrow sickle-shaped leaves and the blossoms are usually borne singly on the stalks. The best-known kinds areatrofusca,Barnumae,Bismarckiana,Gatesi,Heylandiana,iberica,Lorteti,Haynei,lupina,Mariae,meda,paradoxa,sari,sofaranaandsusiana—the last-named being popularly called the “mourning” iris owing to the dark silvery appearance of its huge flowers. All these cushion irises are somewhat fastidious growers, and to be successful with them they must be planted rather shallow in very gritty well-drained soil. They should not be disturbed in the autumn, and after the leaves have withered the roots should be protected from heavy rains until growth starts again naturally.A closely allied group to the cushion irises are those known asRegelia, of whichKorolkowi,Leichtliniandvagaare the best known. Some magnificent hybrids have been raised between these two groups, and a hardier and more easily grown race of garden irises has been produced under the name ofRegelio-Cyclus. They are best planted in September or October in warm sunny positions, the rhizomes being lifted the following July after the leaves have withered.

The flag irises are for the most part of the easiest culture; they grow in any good free garden soil, the smaller and more delicate species only needing the aid of turfy ingredients, either peaty or loamy, to keep it light and open in texture. The earliest to bloom are the dwarf forms ofIris pumila, which blossom during March, April and May; and during the latter month and the following one most of the larger growing species, such asI. germanica,florentina,pallida,variegata,amoena,flavescens,sambucina,neglecta,ruthenica, &c., produce their gorgeous flowers. Of many of the foregoing there are, besides the typical form, a considerable number of named garden varieties.Iris unguicularis(orstylosa) is a remarkable winter flowering species from Algeria, with sky-blue flowers blotched with yellow, produced at irregular intervals from November to March, the bleakest period of the year.

The beautiful JapaneseIris Kaempferi(orI. laevigata) is of comparatively modern introduction, and though of a distinct type is equally beautiful with the better-known species. The outer segments are rather spreading than deflexed, forming an almost circular flower, which becomes quite so in some of the very remarkable duplex varieties, in which six of these broad segments are produced instead of three. Of this too there are numberless varieties cultivated under names. They require a sandy peat soil on a cool moist subsoil.

What are known asOncocyclus, or cushion irises, constitute a magnificent group of plants remarkable for their large, showy and beautifully marked flowers. Compared with other irises the “cushion” varieties are scantily furnished with narrow sickle-shaped leaves and the blossoms are usually borne singly on the stalks. The best-known kinds areatrofusca,Barnumae,Bismarckiana,Gatesi,Heylandiana,iberica,Lorteti,Haynei,lupina,Mariae,meda,paradoxa,sari,sofaranaandsusiana—the last-named being popularly called the “mourning” iris owing to the dark silvery appearance of its huge flowers. All these cushion irises are somewhat fastidious growers, and to be successful with them they must be planted rather shallow in very gritty well-drained soil. They should not be disturbed in the autumn, and after the leaves have withered the roots should be protected from heavy rains until growth starts again naturally.

A closely allied group to the cushion irises are those known asRegelia, of whichKorolkowi,Leichtliniandvagaare the best known. Some magnificent hybrids have been raised between these two groups, and a hardier and more easily grown race of garden irises has been produced under the name ofRegelio-Cyclus. They are best planted in September or October in warm sunny positions, the rhizomes being lifted the following July after the leaves have withered.

IRISH MOSS,orCarrageen(Irishcarraigeen, “moss of the rock”), a sea-weed (Chondrus crispus) which grows abundantly along the rocky parts of the Atlantic coast of Europe and North America. In its fresh condition 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%; and with that it has nearly 10% of albuminoids and about 15% 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. It may also be used as a thickener in calico-printing and for fining beer. Irish moss is frequently mixed withGigartina mammillosa,G. acicularisand other sea-weeds with which it is associated in growth.

IRKUTSK,a government of Asiatic Russia, in East Siberia, bounded on the W. by the government of Yeniseisk, on the N. by Yakutsk, on the E. by Lake Baikal and Transbaikalia and on the S. and S.W. by Mongolia; area, 287,061 sq. m. The most populous region is a belt of plains 1200 to 2000 ft. in altitude, which stretch north-west to south-east, having the Sayan mountains on the south and the Baikal mountains on the north, and narrowing as it approaches the town of Irkutsk. The high road, now the Trans-Siberian railway, follows this belt. The south-western part of the government is occupied by mountains of the Sayan system, whose exact orography is as yet not well known. From the high plateau of Mongolia, fringed by the Sayan mountains, of which the culminating point is the snow-clad Munko-sardyk (11,150 ft.), a number of ranges, 7500 to 8500 ft. high, strike off in a north-east direction. Going from south to north they are distinguished as the Tunka Alps, the Kitoi Alps (both snow-clad nearly all the year round), the Ida mountains and the Kuitun mountains. These are, however, by no means regular chains, but on the contrary are a complex result of upheavals which took place at different geological epochs, and of denudation on a colossal scale. A beautiful, fertile valley, drained by the river Irkut, stretches between the Tunka Alps and the Sayan, and another somewhat higher plain, but not so wide, stretches along the river Kitoi. A succession of high plains, 2000 to 2500 ft. in altitude, formed of horizontal beds of Devonian (or Upper Silurian) sandstone and limestone, extends to the north of the railway along the Angara, or Verkhnyaya (i.e.upper) Tunguzka, and the upper Lena, as far as Kirensk. The Bratskaya Steppe, west of the Angara, is a prairie peopled by Buriats. A mountain region, usually described as the Baikal range, but consisting in reality of several ranges running north-eastwards, across Lake Baikal, and scooped out to form the depression occupied by the lake, is fringed on its north-western slope by horizontal beds of sandstone and limestone. Farther north-east the space between the Lena and the Vitim is occupied by another mountain region belonging to the Olekma and Vitim system, composed of several parallel mountain chains running north-eastwards (across the lower Vitim), and auriferous in the drainage area of the Mama (N.E. of Lake Baikal). Lake Baikal separates Irkutsk from Transbaikalia. The principal rivers of the government are the Angara, which flows from this lake northwards, with numerous sharp windings, and receives from the left several large tributaries.as the Irkut, Kitoi, Byelaya, Oka and Iya. The Lena is the principal means of communication both with the gold-mines on its own tributary, the lower Vitim, and with the province of Yakutsk. The Nizhnyaya Tunguzka flows northwards, to join the Yenisei in the far north, and the mountain streams tributary to the Vitim drain the north-east.

The post-Tertiary formations are represented by glacial deposits in the highlands and loess on their borders. Jurassic deposits are met with in a zone running north-westwards from Lake Baikal to Nizhne-udinsk. The remainder of this region is covered by vast series of Carboniferous, Devonian and Silurian deposits—the first two but slightly disturbed over wide areas. All the highlands are built up of older, semi-crystalline Cambro-Silurian strata, which attain a thickness of 2500 ft., and of crystalline slates and limestones of the Laurentian system, with granites, syenites, diorites and diabases protruding from beneath them. Very extensive beds of basaltic lavas and other volcanic deposits are spread along the border ridge of the high plateau, about Munko-sardyk, up the Irkut, and on the upper Oka, where cones of extinct volcanoes are found (Jun-bulak). Earthquakes are frequent in the neighbourhood of Lake Baikal and the surrounding region. Gold is extracted in the Nizhne-udinsk district; graphite is found on the Botu-gol and Alibert mountains (abandoned many years since) and on the Olkhon island of Lake Baikal. Brown coal (Jurassic) is found in many places, and coal on the Oka. The salt springs of Usoliye (45 m. west of Irkutsk), as also those on the Ilim and of Ust-Kutsk (on the Lena), yield annually about 7000 tons of salt. Fireclay, grindstones, marble and mica, lapis-lazuli, granites and various semi-precious stones occur on the Sludyanka (south-west corner of the Baikal).The climate is severe; the mean temperatures being at Irkutsk (1520 ft), for the year 31° Fahr., for January −6°, for July 65°; at Shimki (valley of the Irkut, 2620 ft.), for the year 24°, for January −17°, for July 63°. The average rainfall is 15 in. a year. Virgin forests cover all the highlands up to 6500 ft.

The climate is severe; the mean temperatures being at Irkutsk (1520 ft), for the year 31° Fahr., for January −6°, for July 65°; at Shimki (valley of the Irkut, 2620 ft.), for the year 24°, for January −17°, for July 63°. The average rainfall is 15 in. a year. Virgin forests cover all the highlands up to 6500 ft.

The population which was 383,578 in 1879, was 515,132 in 1897, of whom 238,997 were women and 60,396 were urban; except about 109,000 Buriats and 1700 Tunguses, they are Russians. The estimated population in 1906 was 552,700. Immigration contributes about 14,000 every year. Schools are numerous at Irkutsk, but quite insufficient in the country districts, and only 12% of the children receive education. The soil is very fertile in certain parts, but meagre elsewhere, and less than a million acres are under crops (rye, wheat, barley, oats, buckwheat, potatoes). Grain has to be imported from West Siberia and cattle from Transbaikalia. Fisheries on Lake Baikal supply every year about 2,400,000 Baikal herring (omul). Industry is only beginning to be developed (iron-works, glass- and pottery-works and distilleries, and all manufactured goods are imported from Russia). The government is divided into five districts, the chief towns of which are Irkutsk (q.v.), Balagansk (pop., 1313 in 1897), Kirensk (2253), Nizhne-udinsk and Verkholensk.

(P. A. K.; J. T. Be.)

IRKUTSK,the chief town of the above government, is the most important place in Siberia, being not only the largest centre of population and the principal commercial depot north of Tashkent, but a fortified military post, an archbishopric of the Orthodox Greek Church and the seat of several learned societies. It is situated in 52° 17′ N. and 104° 16′ E., 3792 m. by rail from St Petersburg. Pop. (1875) 32,512, (1900) 49,106. The town proper lies on the right bank of the Angara, a tributary of the Yenisei, 45 m. below its outflow from Lake Baikal, and on the opposite bank is the Glaskovsk suburb. The river, which has a breadth of 1900 ft., is crossed by a flying bridge. The Irkut, from which the town takes its name, is a small river which joins the Angara directly opposite the town, the main portion of which is separated from the monastery, the castle, the port and the suburbs by another confluent, the Ida or Ushakovka. Irkutsk has long been reputed a remarkably fine city—its streets being straight, broad, well paved and well lighted; but in 1879, on the 4th and 6th of July, the palace of the (then) governor-general, the principal administrative and municipal offices and many of the other public buildings were destroyed by fire; and the government archives, the library and museum of the Siberian section of the Russian Geographical Society were utterly ruined. A cathedral (built of wood in 1693 and rebuilt of stone in 1718), the governor’s palace, a school of medicine, a museum, a military hospital, and the crown factories are among the public institutions and buildings. An important fair is held in December. Irkutsk grew out of the winter-quarters established (1652) by Ivan Pokhabov for the collection of the fur tax from the Buriats. Its existence as a town dates from 1686.

IRMIN,orIrminus, in Teutonic mythology, a deified eponymic hero of the Herminones. The chief seat of his worship was Irminsal, or Ermensul, in Westphalia, destroyed in 772 by Charlemagne. Huge wooden posts (Irmin pillars) were raised to his honour, and were regarded as sacred by the Saxons.

IRNERIUS(Hirnerius, Hyrnerius, Iernerius, Gernerius, Guarnerius, Warnerius, Wernerius, Yrnerius), Italian jurist, sometimes referred to as “lucerna juris.” He taught the “free arts” at Bologna, his native city, during the earlier decades of the 12th century. Of his personal history nothing is known, except that it was at the instance of the countess Matilda, Hildebrand’s friend, who died in 1115, that he directed his attention and that of his students to theInstitutesandCodeof Justinian; that after 1116 he appears to have held some office under the emperor Henry V.; and that he died, perhaps during the reign of the emperor Lothair II., but certainly before 1140. He was the first of the Glossators (seeGloss), and according to ancient opinion (which, however, has been much controverted) was the author of the epitome of theNovellaeof Justinian, called theAuthentica, arranged according to the titles of theCode. HisFormularium tabellionum(a directory for notaries) andQuaestiones(a book of decisions) are no longer extant. (SeeRoman Law.)

See Savigny,Gesch. d. röm. Rechts im Mittelalter, iii. 83; Vecchio,Notizie di Irnerio e della sua scuola(Pisa, 1869); Ficker,Forsch, z. Reichs- u. Rechtsgesch. Italiens, vol. iii. (Innsbruck, 1870); and Fitting,Die Anfänge der Rechtsschule zu Bologna(Berlin, 1888).

IRON[symbol Fe, atomic weight 55.85 (O = 16)], a metallic chemical element. Although iron occurs only sparingly in the free state, the abundance of ores from which it may be readily obtained led to its application in the arts at a very remote period. It is generally agreed, however, that the Iron Age, the period of civilization during which this metal played an all-important part, succeeded the ages of copper and bronze, notwithstanding the fact that the extraction of these metals required greater metallurgical skill. The Assyrians and Egyptians made considerable use of the metal; and in Genesis iv. 22 mention is made of Tubal-cain as the instructor of workers in iron and copper. The earlier sources of the ores appear to have been in India; the Greeks, however, obtained it from the Chalybes, who dwelt on the south coast of the Black Sea; and the Romans, besides drawing from these deposits, also exploited Spain, Elba and the province of Noricum. (SeeMetal-work.)

The chief occurrences of metallic iron are as minute spiculae disseminated through basaltic rocks, as at Giant’s Causeway and in the Auvergne, and, more particularly, in meteorites (q.v.). In combination it occurs, usually in small quantity, in most natural waters, in plants, and as a necessary constituent of blood. The economic sources are treated underIron and Steelbelow; in the same place will be found accounts of the manufacture, properties, and uses of the metal, the present article being confined to its chemistry. The principal iron ores are the oxides and carbonates, and these readily yield the metal by smelting with carbon. The metal so obtained invariably contains a certain amount of carbon, free or combined, and the proportion and condition regulate the properties of the metal, giving origin to the three important varieties: cast iron, steel, wrought iron. The perfectly pure metal may be prepared by heating the oxide or oxalate in a current of hydrogen; when obtained at a low temperature it is a black powder which oxidizes in air with incandescence; produced at higher temperatures the metal is not pyrophoric. Péligot obtained it as minute tetragonal octahedra and cubes by reducing ferrous chloride in hydrogen. It may be obtained electrolytically from solutions of ferrous and magnesium sulphates and sodium bicarbonate, a wrought iron anode and a rotating cathode of copper, thinly silvered and iodized, being employed (S. Maximowitsch,Zeit. Elektrochem., 1905, 11, p. 52).

In bulk, the metal has a silvery white lustre and takes a high polish. Its specific gravity is 7.84; and the average specific heat over the range 15°-100° is 0.10983; this value increases with temperature to 850°, and then begins to diminish. It is the most tenacious of all the ductile metals at ordinary temperatures with the exception of cobalt and nickel; it becomes brittle, however, at the temperature of liquid air. It softens at a red heat, and may be readily welded at a white heat; above this point it becomes brittle. It fuses at about 1550°-1600°, and may be distilled in the electric furnace (H. Moissan,Compt. rend., 1906, 142, p. 425). It is attracted by a magnet and may be magnetized, but the magnetization is quickly lost. The variation of physical properties which attends iron on heating has led to the view that the metal exists in allotropic forms (seeIron and Steel, below).

Iron is very reactive chemically. Exposed to atmospheric influences it is more or less rapidly corroded, giving the familiar rust (q.v.). S. Burnie (Abst. J.C.S., 1907, ii. p. 469) has shown that water is decomposed at all temperatures from 0° to 100° by the finely divided metal with liberation of hydrogen, the action being accelerated when oxides are present. The decomposition of steam by passing it through a red-hot gun-barrel, resulting in the liberation of hydrogen and the production of magnetic iron oxide, Fe3O4, is a familiar laboratory method for preparing hydrogen (q.v.). When strongly heated iron inflames in oxygen and in sulphur vapour; it also combines directly with the halogens. It dissolves in most dilute acids with liberation of hydrogen; the reaction between sulphuric acid and iron turnings being used for the commercial manufacture of this gas. It dissolves in dilute cold nitric acid with the formation of ferrous and ammonium nitrates, no gases being liberated; when heated or with stronger acid ferric nitrate is formed with evolution of nitrogen oxides.

It was observed by James Keir (Phil. Trans., 1790, p. 359) that iron, after having been immersed in strong nitric acid, is insoluble in acids, neither does it precipitate metals from solutions. This “passivity” may be brought about by immersion in other solutions, especially by those containing such oxidizing anions as NO′3, ClO′3, less strongly by the anions SO″4CN′, CNS′, C2H3O′2, OH′, while Cl′, Br′ practically inhibit passivity; H′ is the only cation which has any effect, and this tends to exclude passivity. It is also occasioned by anodic polarization of iron in sulphuric acid. Other metals may be rendered passive; for example, zinc does not precipitate copper from solutions of the double cyanides and sulphocyanides, nickel and cadmium from the nitrates, and iron from the sulphate, but it immediately throws down nickel and cadmium from the sulphates and chlorides, and lead and copper from the nitrates (see O. Sackur,Zeit. Elektrochem., 1904, 10, p. 841). Anodic polarization in potassium chloride solution renders molybdenum, niobium, ruthenium, tungsten, and vanadium passive (W. Muthmann and F. Frauenberger,Sitz. Bayer. Akad. Wiss., 1904, 34, p. 201), and also gold in commercial potassium cyanide solution (A. Coehn and C. L. Jacobsen,Abs. J.C.S., 1907, ii. p. 926). Several hypotheses have been promoted to explain this behaviour, and, although the question is not definitely settled, the more probable view is that it is caused by the formation of a film of an oxide, a suggestion made many years ago by Faraday (see P. Krassa,Zeit. Elektrochem., 1909, 15, p. 490). Fredenhagen (Zeit. physik. Chem., 1903, 43, p. 1), on the other hand, regarded it as due to surface films of a gas; submitting that the difference between iron made passive by nitric acid and by anodic polarization was explained by the film being of nitrogen oxides in the first case and of oxygen in the second case. H. L. Heathcote and others regard the passivity as invariably due to electrolytic action (see papers in theZeit. physik. Chem., 1901 et seq.).

Compounds of Iron.

Oxides and Hydroxides.—Iron forms three oxides: ferrous oxide, FeO, ferric oxide, Fe2O3, and ferroso-ferric oxide, Fe3O4. The first two give origin to well-defined series of salts, the ferrous salts, wherein the metal is divalent, and the ferric salts, wherein the metal is trivalent; the former readily pass into the latter on oxidation, and the latter into the former on reduction.

Ferrous oxideis obtained when ferric oxide is reduced in hydrogen at 300° as a black pyrophoric powder. Sabatier and Senderens (Compt. rend., 1892, 114, p. 1429) obtained it by acting with nitrous oxide on metallic iron at 200°, and Tissandier by heating the metal to 900° in carbon dioxide; Donau (Monats., 1904, 25, p. 181), on the other hand, obtained a magnetic and crystalline-ferroso-ferric oxide at 1200°. It may also be prepared as a black velvety powder which readily takes up oxygen from the air by adding ferrous oxalate to boiling caustic potash. Ferrous hydrate, Fe(OH)2, when prepared from a pure ferrous salt and caustic soda or potash free from air, is a white powder which may be preserved in an atmosphere of hydrogen. Usually, however, it forms a greenish mass, owing to partial oxidation. It oxidizes on exposure with considerable evolution of heat; it rapidly absorbs carbon dioxide; and readily dissolves in acids to form ferrous salts, which are usually white when anhydrous, but greenish when hydrated.

Ferric oxideor iron sesquioxide, Fe2O3, constitutes the valuable ores red haematite and specular iron; the minerals brown haematite or limonite, and göthite and also iron rust are hydrated forms. It is obtained as a steel-grey crystalline powder by igniting the oxide or any ferric salt containing a volatile acid. Small crystals are formed by passing ferric chloride vapour over heated lime. When finely ground these crystals yield a brownish red powder which dissolves slowly in acids, the most effective solvent being a boiling mixture of 8 parts of sulphuric acid and 3 of water. Ferric oxide is employed as a pigment, as jeweller’s rouge, and for polishing metals. It forms several hydrates, the medicinal value of which was recognized in very remote times. Two series of synthetic hydrates were recognized by Muck and Tommasi: the “red” hydrates, obtained by precipitating ferric salts with alkalis, and the “yellow” hydrates, obtained by oxidizing moist ferrous hydroxide or carbonates. J. van Bemmelen has shown that the red hydrates are really colloids, the amount of water retained being such that its vapour pressure equals the pressure of the aqueous vapour in the superincumbent atmosphere. By heating freshly prepared red ferric hydrate with water under 5000 atmospheres pressure Ruff (Ber., 1901, 34, p. 3417) obtained definite hydrates corresponding to the minerals limonite (30°-42.5°), göthite (42.5°-62.5°), and hydrohaematite (above 62.5°). Thomas Graham obtained a soluble hydrate by dissolving the freshly prepared hydrate in ferric chloride and dialysing the solution, the soluble hydrate being left in the dialyser. All the chlorine, however, does not appear to be removed by this process, the residue having the composition 82Fe(OH)3·FeCl3; but it may be by electrolysing in a porous cell (Tribot and Chrétien,Compt. rend., 1905, 140, p. 144). On standing, the solution usually gelatinizes, a process accelerated by the addition of an electrolyte. It is employed in medicine under the nameLiquor ferri dialysati. The so-called soluble meta-ferric hydroxide, FeO(OH)(?), discovered by Péan de St Gilles in 1856, may be obtained by several methods. By heating solutions of certain iron salts for some time and then adding a little sulphuric acid it is precipitated as a brown powder. Black scales, which dissolve in water to form a red solution, are obtained by adding a trace of hydrochloric acid to a solution of basic ferric nitrate which has been heated to 100° for three days. A similar compound, which, however, dissolves in water to form an orange solution, results by adding salt to a heated solution of ferric chloride. These compounds are insoluble in concentrated, but dissolve readily in dilute acids.

Red ferric hydroxide dissolves in acids to form a well-defined series of salts, the ferric salts, also obtained by oxidizing ferrous salts; they are usually colourless when anhydrous, but yellow or brown when hydrated. It has also feebly acidic properties, formingferriteswith strong bases.

Magnetite, Fe3O4, may be regarded as ferrous ferrite, FeO·Fe2O3. This important ore of iron is most celebrated for its magnetic properties (seeMagnetismandCompass), but themineral is not always magnetic, although invariably attracted by a magnet. It may be obtained artificially by passing steam over red-hot iron. It dissolves in acids to form a mixture of a ferrous and ferric salt,1and if an alkali is added to the solution a black precipitate is obtained which dries to a dark brown mass of the composition Fe(OH)2·Fe2O3; this substance is attracted by a magnet, and thus may be separated from the admixed ferric oxide. Calcium ferrite, magnesium ferrite and zinc ferrite, RO·Fe2O3(R = Ca, Mg, Zn), are obtained by intensely heating mixtures of the oxides; magnesium ferrite occurs in nature as the mineral magnoferrite, and zinc ferrite as franklinite, both forming black octahedra.

Ferric acid, H2FeO4. By fusing iron with saltpetre and extracting the melt with water, or by adding a solution of ferric nitrate in nitric acid to strong potash, an amethyst or purple-red solution is obtained which contains potassium ferrate. E. Frémy investigated this discovery, made by Stahl in 1702, and showed that the same solution resulted when chlorine is passed into strong potash solution containing ferric hydrate in suspension. Haber and Pick (Zeit. Elektrochem., 1900, 7, p. 215) have prepared potassium ferrate by electrolysing concentrated potash solution, using an iron anode. A temperature of 70°, and a reversal of the current (of low density) between two cast iron electrodes every few minutes, are the best working conditions. When concentrated the solution is nearly black, and on heating it yields a yellow solution of potassium ferrite, oxygen being evolved. Barium ferrate, BaFeO4·H2O, obtained as a dark red powder by adding barium chloride to a solution of potassium ferrate, is fairly stable. It dissolves in acetic acid to form a red solution, is not decomposed by cold sulphuric acid, but with hydrochloric or nitric acid it yields barium and ferric salts, with evolution of chlorine or oxygen (Baschieri,Gazetta, 1906, 36, ii. p. 282).

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