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Rh was one of the chief centres for the production of majolica, especially the towns of Gubbio and Castel Durante. Most of the finest pieces of Urbino ware were made specially for the dukes, who covered their sideboards with the rich storied piatti di pompa. Among the distinguished names which have been associated with Urbino are those of the Ferrarese painter and friend of Raphael, Timoteo della Vite, who spent most of his life there, and Bramante, the greatest architect of his age. The Milanese sculptor, Ambrogio, who worked so much for Federigo, married a lady of Urbino, and was the progenitor of the Baroccio family, among whom were many able mathematicians and painters. Federigo Baroccio, Ambrogio's grandson, was a very popular painter, some of whose works still exist in the cathedral and elsewhere in Urbino. This city was also the birthplace of Pope Clement XI., of several cardinals of the Alban family, and of Bernardino Baldi, Fabretti, and other able scholars. An interesting view of Urbino, in the first half of the 16th century, occurs among the pen drawings in the MSS. Arte del vasajo, by the potter Piccolpasso, now in the Victoria and Albert Museum.

See also E. Calzini, Urbino e i suoi monumenti (1897); G. Lipparini, Urbino (Bergamo, 1903).  URBS SALVIA (mod. Urbisaglia), an ancient town of Picenum, Italy, about 8 m. S. of the modern Macerata, and 10 m. S. of Ricina. It was the meeting-point of several ancient roads; the road leading south from Ancona through Ricina and Falerio to Asculum was crossed here at right angles by that from Fanum to Tolentinum, Septempeda (S. Severino) and Nuceria Camellaria, while another led north-east from Urbs Salvia to Pausulae and the coast at Potentia (near mod. Porto Recanati). It seems to have been also called Pollentia. The date of its foundation is unknown, but it became a colony in the time of Trajan, and its importance seems to begin from this period. It was utterly destroyed by Alaric, and both Procopius (B.G. ii. 16, 17) and Dante (Paradiso, xvi. 73) speak of its desolation. The arx is occupied by the modern village; below it considerable remains of the city walls and of the buildings within them, alike of brickwork of the imperial period, are preserved—an amphitheater 328×249 ft., with an arena 190×112 ft., a theatre, baths, tombs, &c. A subterranean aqueduct and a number of inscriptions have been found on the site. Close by is a little chapel with paintings of the early 16th century. The Romanesque abbey church of the Fiastra, about 3 m. to the north, is noticeable. The territory of Urbs Salvia probably extended as far as the old Romanesque church of S. Maria. di Rambona, 8 m. to the north-west.  URDŪ, the name of that variety of Hindostani which borrows a great part of its vocabulary from Persia and Arabic, as contrasted with “Hindi,” the variety which eschews such words, but borrows from Sanskrit instead. It is spoken by Mussulmans and those Hindus who have come under Mussulman influences, and has a considerable literature. See and .  UREA, or, CO(NH2)2, the amide of carbonic acid, discovered in 1773 by H. M. v. Rouelle, is found in the urine of mammalia, birds and some reptiles; human urine contains approximately 2-3%, a grown man producing about 30 grammes daily. It is also a constituent of the blood, of milk, and other animal fluids. Its synthesis in 1828 by F. Wöhler (Pogg. Ann., 1828, 12, p. 253) is of theoretical importance, since it was the first organic compound obtained from inorganic materials. Wöhler oxidized potassium ferrocyanide to potassium cyanate by fusing it with lead or manganese dioxide, converted this cyanate into ammonium cyanate by adding ammonium sulphate, and this on evaporation gives urea, thus:—

It may also be prepared by the action of ammonia on carbonyl chloride, diethyl carbonate, chlorcarbonic ester or urethane; by heating ammonium carbamate in a sealed tube to 130-140° C.; by oxidizing potassium cyanide in acid solution with

potassium permanganate (E. Baudrimant, Jahresb., 1880, p. 393); by the action of 50% sulphuric acid on cyanamide: CN⋅NH2+H2O = CO(NH2)2; by the action of mercuric oxide on oxamide (A. Williamson): (CONH2)2+HgO = CO(NH2)2+Hg+CO2; by decomposing potassium cyanide with a dilute solution of sodium hypochlorite, followed by adding ammonium sulphate (A. Reychler, Bull. Soc. Chim., 1893 [3], 9, p. 427); and by oxidation of uric acid. It may be obtained from urine by evaporating to dryness on the water bath, taking up the residue in absolute alcohol and evaporating the alcoholic solution to dryness again. The residue is then dissolved in water, decolonized by animal charcoal and saturated at 50° C. with oxalic acid. The urea oxalate is recrystallized and decolonized and finally decomposed by calcium carbonate (J. J. Berzelius, Pogg. Ann., 1830, 18, p. 84). As an alternative method, A. N. E. Millon (Ann. chim. phys. [2], 8, p. 235) concentrates the urine and precipitates the urea by nitric acid. The precipitate is dissolved in boiling water, decolonized by potassium permanganate and decomposed by barium carbonate. The solution is then evaporated to dryness and extracted by alcohol.

Urea crystallizes in long needles or prisms which melt at 132° C. and sublime when heated in vacuo. It is readily soluble in water and in alcohol, but is insoluble in chloroform and ether. When heated above its melting-point, it yields ammonia, cyanuric acid, biuret and ammelide. On warming with sodium, it yields cyanamide. Dry chlorine gas passed into melted urea decomposes it with formation of cyanuric acid and ammonium chloride, nitrogen and ammonia being simultaneously liberated. Alkaline hypobromites or hypochlorites or nitrous acid decompose urea into carbon dioxide and nitrogen. It is also decomposed by warm aqueous solutions of caustic alkalis, with evolution of ammonia and carbon dioxide. When heated with alcohol in sealed tubes, it yields carbamic esters; with alcohol and carbon bisulphide at 100° C., carbon dioxide is liberated and ammonium sulphocyanide is formed. Acid potassium permanganate oxidizes it to carbon dioxide and nitrogen. It acts as a monacid base.

Urea may be recognized by its crystalline oxalate and nitrate, which are produced on addin oxalic and nitric acids to concentrated solutions of the base; by the white precipitate formed on adding mercuric nitrate to the neutral aqueous solutions of urea; and by the so-called “biuret” reaction. In this reaction urea is heated in a dry tube until it gives off ammonia freely; the residue is dissolved in water, made alkaline with caustic soda, and a drop of copper sulphate solution is added, when a fine violet-red coloration is produced. Several methods are employed for the quantitative estimation of urea. R. Bunsen (Ann., 1848, 65, p. 875) heated urea with an ammoniacal solution of barium chloride to 220° C., and converted the barium carbonate formed into barium sulphate, which is then weighed (see also E. Pflüger and K. Bohland, Zeit. f. anal. Chem., 1886, 25, p. 599; K. A. H. Mörner, ibid., 1891, 30, p. 389). Among the volumetric methods used, the one most commonly employed is that of W. Knop (ibid., 1870, 9, p. 226), in which the urea is decomposed by an alkaline hypobromite and the evolved nitrogen is measured (see A. H. Allen, Commercial Organic Analysis). J. v. Liebig (Ann., 1853, 85, p. 289) precipitates dilute solutions of urea with a dilute standard solution of mercuric nitrate, using alkaline carbonate as indicator. In this process phosphates must be absent, and the nitric acid liberated during the reaction should be neutralized as soon as possible. Chlorides also prevent the formation of the precipitate until enough of the mercury solution has been added to convert them into mercuric chloride (see also E. Pflüger, Zeit. f. anal. Chem., 1880, 19, p. 378). E. Riegler (ibid., 1894, 33, p. 49) decomposes urea solutions by means of mercury dissolved in nitric acid, and measures the evolved gas.

Urea chlorides are formed by the action of carbonyl chloride on ammonium chloride (at 400° C.), or on salts of primary amines. They are readily hydrolysed by water, and combine with bases to form alkyl ureas, and with alcohols to form carbamic esters. Substituted urea chlorides are formed by the direct action of chlorine (F. D. Chattaway and D. F. S. Wunsch, Jour. Chem. Soc., 1909, 95, p. 129). Urea chloride, NH2⋅CO⋅Cl (L. Gattermann, Ann., 1888, 24, p. 30), melts at 50° C. and boils at 61-62° C. In the presence of anhydrous aluminium chloride it reacts with aromatic hydrocarbons to form the amides of aromatic acids. Nitrourea, H2N⋅CO⋅NH⋅NO2, prepared by adding urea nitrate to well-cooled concentrated sulphuric acid (J. Thiele and A. Lachmann, Ann., 1895, 288, p. 281), is a crystalline powder, soluble in water, and which decomposes on heating. It is a strong acid and is stable towards oxidizing agents. Diazomethane converts it into the