TJRBINO. 756 TJREA. the Metauro and the Foglia, 25 miles southwest of Pesaro ( Jlap : Italy, G 4 ) . The streets are narrow and tortuous, but gorgeous views are ob- tained of the mountains and the Adriatic. The house in which Raphael was born is now fitted up as a niuseunij and belongs to the 'Reale Ac- cademia Raft'aello.' The new cathedral is inter- esting for its paintings. In the Church of Santo Spirito are noteworthy pictures by Luea Signo- relli, and in the San Domenico are good reliefs by Luea della Robbia. The Oratorio della Con- fraternitn di San Giovanni Battista is a splen- did structure. The famous ducal palace was erected in the fifteenth century. It is rich in in- teresting sculptures and decorations, and has a collection of Roman inscriptions and a biblical picture gallery. The city has a free universit}', founded in 1671, and an academy of fine arts. The celebrated library has been removed to Rome. Urbino manufactures silks, majolica, bricks, lime, oil, and cheese. There are in the vicinity sulphur and travertine quarries. Population (commune), in 1881, 16,812; in 1901, 1S,.307. Urbino, the ancient Urbinum, was an impor- tant city under the Romans. It became very prosperous in the fourteenth century. Federigo da Montefeltre, who ruled from 1444 to 1482 and who was elevated by the Pope to the dignity of Duke of Urbino in 1474, maintained a magnificent court, built the palace, and made the city a centre of science and art. During the sixteenth century, under the Della Rovere family, Urbino was im- portant in the manufacture of majolica. It was a Papal possession from 1626 to 1860. TJRDANETA,, oor'da-na'ta. A town of Lu- zon, Phili])pines, in the Province of PangasinSn/ situated 27 miles southeast of Lingayen (Map: Luzon, D 3). Population, about 16.600. UKDU, oBr'dno. The speech of the ^Nloham- medan population of Central Hindustan, and a sort of lingua franca for almost all the peninsula. See Hindustani Language and Literature. URE, Andrew (1778-1857). A Scotch chemist, born at Glasgow. He studied at Glasgow and Edinburgh. In 1802 he became professor of chemistry and natural philosophy in the Ander- sonian Institution at Glasgow: took an active part in the establishment (1809) of the Glasgow Observator}'. and was appointed its first di- rector. In 18.30 he removed to London, and in 18.34 he was appointed analytical chemist to the Board of Customs. He published a number of valuable works, his two dictionaries remaining for many years the standard books of reference: viz. his Dictionary of Chemistry (2 vols. 1821), and .1 Dictionary of. Arts, Manufactures, and Mines (1837 and .several later editions). Among his other works may be mentioned the Systematic Table of the Materia Mrdica (1813): A ?few System of Qeology (1829); the Philosophy of Manufactures (1835); and The Cotton Manu- facture of Great Britain Compared with That of Other Countries (1836 and 1861). tTREA (Neo-Lat.. from Gk. otipov, ovron, urine), or Carbamide, COfXH,),. An organic substance which derives its name from its hav- ing been originally discovered in urine, of which it forms the most important and characteristic ingredient. Pure urea, which has been allowed to crystallize slowly, occurs in white, glistening. streaked, four-sided prisms; but when the crj-s- tallization is rapid or disturbed, it separates in small white silky needles. It is devoid of smell, has a coolish, bitter taste, like that of salt- petre (which it closely resembles in its external form), and is very slightly deliquescent. It is readily soluble in water and alcohol, but only slightly in ether. Pure urea melts at 132° C. ; dry urea may be sublimed without decomposition by heating in vacuo between 120° and 130° C. If heated, under ordinary pres- sure, above these temperatures, it is decompo.sed with formation of ammonia, cyanuric acid, biuret, and carbonic acid ; the formation of biuret is represented by the following chemical equation: 2CO(NH2)„ = NHjCONHCONHj+NHj TJrea Biuret Ammonia. The formation of cyanuric acid (CjHjNjOa) takes place indirectly, probably through the combina- tion of biuret with cyanic acid. If heated with water at 120°, or if boiled with dilute mineral acids, urea combines with water, yielding am- monia and carbonic acid according to the follow- ing equation: CO ( NH, ) J -f 2H,0 = ( NH, ) ,00, Urea Carbonate of .ramonia. A similar change takes place at ordinary tem- peratures in urine exposed for some time to the air. Here the transformation is eflfected through a process of fermentation caused by certain micro-organisms producing, when killed, an enzyme that hydrolyzes urea with great rapidity. This enzyme is probably secreted also by the mucous membrane of the bladder in certain in- flammatory conditions, the fermentation then taking place while the urine is still in the bladder. The following are some of the most important of the compounds of urea: Nitrate of urea. C0(NH,),.HN03, and oxalate of urea, 2C0- (NH2),.H2C;0,, are readily crystallizable salts, formed by the direct addition of the respective acids to a moderately strong solution of urea. As nitrate of urea requires eight parts of cold water, and is still more insoluble if an excess of free nitric acid is present, and the oxalate is more insoluble than the nitrate, while urea dis- solves in its own weight of water, these salts may be employed to test for and approximately deter- mine the quantity of urea. Among the com- pounds of urea with metallic oxides, those which it forms with the oxides of mercury are especially interesting, and have been completely examined by Liebig. A result of his researches is his celebrated method, which is now in universal use, of determining the amoint of urea volumetrical- ly. The following are other accurate methods of determining urea quantitatively: (I) Knop-Hiif- ner's method consists in decomposing urea into nitrogen and carbonic acid, with sodium hypo- bromite. and determining the volume of nitrogen produced from which the amoint of urea can be readily calculated. (2) An excellent method de- vised by Bunsen consists in heating urea in a sealed glass tube with barium chloride, which breaks up urea into carbonic acid and ammonia, the former combining with barium chloride to give the insoluble barium carbonate which is readily isolated, dried and weighed : the weight of barium carbonate gives the weight of carbonic
