IRIARTEA. 765 IRIDOSMINE. IRIARTEA, ir'i-ar'te-S (Xeo-Lat., named in honor of .liuin de Iriarte, a Spanish amateur bot- anist). A genus of South American palms which have lofty, smooth, faintly ringed stems, and pinnate leaves with somewhat triangular leaflets. The pashiuba or paxiuba palm (Iriartea exar- rhiza, by some botanists called Hocratea ex- orrhUa ) , common in low, wet grounds in the forests of the Amazon district, is remarkable fol its aerial roots, which e.tend from the stem obliquely downward, and often divide into many rootlets just before they reach the soil. As the tree grows it produces new roots from higher points. Since the older and more central ones die, a man may walk erect with a palm of 70 feet high supported as on legs rising straight above his head. The outer wood, which is very hard, is used for harpoons. It splits easily into straight laths, is excellent for floors, ceilings, shelves, etc., and is exported for umbrella-sticks. The leaves are extensively used in Brazil as thatch. IRIDACE.a!, ir'I-da'se-e (Neo-Lat. nom. pL, from Lat. iris, Gk. fpis, rainbow, sort of lily), or Iris F.mily. An order of monoeotyle<lonou3 plants, consisting mostly of herbaceous peren- nials, with tubers or rhizomes. The leaves are usually in two rows and equitant (i.e. so placed that one seems to fit over the back of the other) . The perianth is six-parted, colored, and in some kinds very beautiful. The stamens are three •with anthers turned outward. The ovary is infe- rior with one style and three stigmas, which are often petal-like and add much to the beauty of the flower. Tlie fruit is a three-celled capsule containing many seeds with small embryos in a hard endosperm. There are about 60 genera and 800 species kno^vn in temperate and tropical countries. South Africa and tropical America contain the greatest number. Some species, how- ever, range to rather high latitudes. Familiar examples of the order are the garden irises, crocuses, gladioli, etc. Some species have acrid properties, while the corms of others are edible, and others have medicinal properties of con- siderable value. The classification by Pax, with the principal genera, is as follows:" CrocoidefP, represented by Crocus and Romulea : Iridoideae, wth Iris, Moroea, Tigridia, and Sisyrinchium as the leading genera ; and Ixoidere, represented by Ixia, Tritonia, Gladiolus, and Freesia. See Col- ored Plates of Iris F.ini.T and Fleurs-de-Lis. IRIDESCENT GLASS (from Lat. iris. Gk. Tpis. in'.*, rainbow) . Glass containing a display of changing colors on the surface somewhat sim- ilar to the delicate hues of soap-bubbles. It is produi'ed by rendering the surface of the glass imperceptibly uneven, either by artificial means or by the natural process of incrustation and decay. One form of treatment consists in ap- plying to the surface of the glass to be treated a strong solution of hydrochloric acid under pressure in a closed vessel. Another method in use in many factories is to apply the fumes from chloride of tin or other chlorides volatilized in a reheatins furnace. Glass which has for manv years been submitted to the slowly disintegrat- ing influences of natural causes, svich as damp, successive heat and cold, light and darkness, will in many instances display an iridescent play of colors. The cause is due to a process of decom- position in the texture of the glass, resulting in the formation of minute scales. The action of water on glass has a tendency to extract the potash and soda which enter into its composition, together with a portion of the silica, the decom- position taking place with greater ease in pro- portion as the glass is richer in these alkalies, and more minutely divided, and the temperature of the water higher. The moisture in the atmosphere produces a similar alteration in the lapse of time. It separates the potash and soda, leaving the greater part of the silica with the lime on the surface of the glass. It is this decomposition which causes the prismatic colors. If subjected to heat, numerous fine scales will peel off and leave the surface dull, opaque, and wrinkled. Many attempts have been made to imitate by artificial means the singular display of changing hues, and varied success has attended the eff'orts. In Venice the workers succeeded in giving the surface of their glassware a peculiar kind of metallic iridescence, and a similar result was reached by certain Hungarian glass-workers. The beautiful Fairile Glass made by Tiffany of Xew York has a most striking iridescent play of color. See Glass. iridium: (Neo-Lat, from Gk.Tpis, iris, rain- bow; so called on account of its iridescence i . A metallic element discovered in 1803 by Smithson Tennant. It is found in platinum ores; as iridos- mine. a native alloy of iridium and osmium in varying proportions; and in the form of native alloys with the other platinum metals. The principal sources of these ores are various dis- tricts in the Ural Mountains, and on the Pacific Coast of the United States. The preparation of metallic iridium involves its separation from the accompanying metals by a long and com- plicated process. Iridium (svmbol Ir; atomic weight, 193.5) is a white steel-like metal, brittle when cold, and somewhat malleable at a white heat. In its ordinary, compact form, iridium is insoluble not only in the several mineral acids, but. also in aqua regia; the latter reagent, however, dissolves iridium powder, which may also be converted into the oxide IrjOj by heating in the air. Iridium has a specific gravity of 22.4. and it melts at 2300° C. It combines with ox-ygen to form an iridium sesquioxide and an iridium dioxide, which in turn give rise to iridious and iridic salts. The metal itself alloys with copper, gold, and lead, as well as with other platinum metals, and the alloy consisting of nine parts of plati- num with one part of iridium is extremely hard, as elastic as steel, perfectly unalterable' in the air, and capable of taking a high polish. It is of this alloy that the standard meter kept in Paris was made. Iridium is also used for the manufacture of standard weights, knife edges of balances, and for other articles which it is desired to preserve from the influence of the atmosphere. It has been used in .the United States to tip the edges of gold and other pens so as to produce a very hard surface. William L. Dudley of Cincinnati invented a process, in 1880. for the electrolvtic deposition of this material, and his process is now success- fully used for coating surgical instruments and other articles requiring an exceedingly hard sur- face. IR'IDOSIONE (from irirfium -f- osmium). A native alloy of iridium and osmium that
