List of Colors starting with U
    The popular colors that start with the letter U are Ultramarine, Umber and United Nations blue
    List of colors A - Z

    UREA, or CARBAMIDE, 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. Wohler (Pogg. Ann., 1828, 12, p. 253) is of theoretical importance, since it was the first organic compound obtained from inorganic materials. Wohler 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: K4Fe(NC) — KCNO--sNH4CNO—>CO(NH2)2• 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., 188o, p. 393); by the action of 50 % sulphuric acid on cyanamide: CN•NH2+H20=CO(NH2)z; by the action of mercuric oxide on oxamide (A. Williamson) : (CONH2)z+HgO= CO(NH2)2+ Hg+C.O2; by decomposing potassium cyanide with a dilute solution of sodium hypochlorite, followed by adding ammonium sulphate (A. Reychler, Bull. Soc. Chim., 1893 [31, 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, decolorized by animal charcoal and saturated at 5o° C. with oxalic acid. The urea oxalate is recrystallized and decolorized and finally decomposed by calcium carbonate (J. J. Berzelius, Pogg. Ann., 183o, 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, decolorized 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 too° 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 adding 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. Pfluger and K. Bohland, Zeit. f. anal. Chem., 1886, 25, p. 599; K. A. H. Morner, ibid., 1891, 30, p. 389). Among the volumetric methods used, the one most commonly employed is that of W. Knop (ibid., 187o, 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. Pfluger, Zeit. f. anal. Chem., 188o, 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, 244, p. 30), melts at 5o° 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. Nitro-urea, 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 794 methyl derivatives of isocyanic acid, and nitramide, NH2NO2. Amidourea, or semicarbazide, NH2•CO•NH•NH2, is best prepared from hydrazine sulphate and potassium cyanate (J. Thiele and O. Stange, Ber., 1894, 27, p. 31). It may also be obtained by reducing nitrourea in acid solution with zinc dust. It crystallizes in prisms, which melt at 96° C., and are easily soluble in water. It reduces Fehling's solution in the cold. It reacts with carbonyl compounds, giving semi-carbazones, and in consequence is frequently used for characterizing such substances. Hydroxy-urea, NH2•CO•NH•OH, is produced from hydroxylamine and cyanic acid (W. F. Dresler and R. Stein, Ann., 1869, 15o, p. 242), or from ammonium hypo-chlorite and potassium cyanate (A. Hantzsch, Ann., 1898, 299, p. 99). It crystallizes in needles, which melt at 128-13o° C., and is decomposed on long heating. It is readily soluble in water and reduces warm silver solutions. Hyponitrous acid is formed by passing nitrous fumes into its methyl alcohol solution. Alkyl ureas are formed by the action of primary or secondary amines on isocyanic acid or its esters: CONH+NH2R= R.NHCONH2; CONR+NHR2=NR2•CO•NHR; by the action of carbonyl chloride on amines: COC12+2NHR2=CO(NR2)2+2HCI; and in the hydrolysis of many ureides. The tetra-alkyl derivatives are liquids, the remainder being solids. Hydrolysis by alkalis decomposes them into carbon dioxide, amines and ammonia. The symmetrically substituted ureas are generally tasteless, while the asymmetrical derivatives are sweet. For example, aa-dimethyl urea is sweet, a3-dimethyl urea is tasteless; p-phenetol carbamide or dulcin, N H2• CO • NH • C6H a• OC2H5, is sweet, while the di-p-phenetol carbamide, CO(NH•C6H4.0C2H5)2, is tasteless. The derivatives of urea containing acid radicles are known as ureides. Those derived from monobasic acids, obtained by the action of acid chlorides or anhydrides on urea, decompose on heating and do not form salts. Those containing more than one acyl group are formed by the action of carbonyl chloride on acid amides: COC12+2CH3CONH2 = CO(NHCOCHa)2+2HCI. Acetyl urea, NH2•CO•NH•000H3, formed by the action of acetic anhydride on urea, crystallizes in needles which melt at 212 ° C. and, on heating, strongly decomposes into acetamide and cyanuric acid. Methyl acetyl urea, CH2NH•CO•NH000H3, is formed by the action of potash on a mixture of bromine (1 mol.) and acetamide (2 mole.) (A. W. v. Hofmann, Ber., 1881, 14, p. 2725), or of methylamine on acetylurethane (G. Young, Jour. Chem. Soc., 1898, 73, p. 364). When heated with water it is decomposed into carbon dioxide, ammonia, methylamine and acetic acid. Bromural or a-bromisovaleryl urea, NH2•CO•NH•CO•CHBr•CH(CH3)2, has been introduced as an hypnotic; its action is mild, and interfered with by the presence of pain, cough or delirium. The ureides of oxy-acids and dibasic acids form closed chain compounds (see ALLANTOIN; ALLOXAN; HYDANTOIN; PURIN). Parabanic acid (oxalyl urea), CO[NH•CO]2, is formed by oxidizing uric acid ; or by condensing oxalic acid and urea in the presence of phosphorus oxychloride. It crystallizes in needles and is readily hydrolysed by alkalis. It behaves as a monobasic acid and forms unstable salts. When heated with urea, it forms oxalyl diureide, H2N•CO•CO•NH•CO•NH•CO•NH2. Dimethylparabanic acid (cholesterophane), CO[NCH3•CO]2, is formed by oxidizing caffeine or by methylating parabanic acid. It crystallizes in plates, which melt at 145.5° C., and is soluble in cold water. Hydrochloric acid at 200° C. decomposes into oxalic acid, carbon dioxide and methylamine, whilst an alcoholic solution of a caustic alkali gives dimethyl urea and oxalic acid. Barbituric acid (malonyl urea), CH2[CO•NH]CO.2H2O, formed by condensing malonic acid with urea (E. Grimaux, Bull. Soc. Chem., 1879, 31, 146), crystallizes in prisms, which decompose on heating. It yields a nitroso derivative, is nitrated by nitric acid to dilituric acid and brominated by bromine. It is a dibasic acid. Veronal (q.v.) is diethyl malonyl urea. For isobarbituric acid see T. B. Johnson and E. V. McCollum, Jour. Biol. Chem., 1906, 1, p. 437. Tartronyl urea (dialuric acid), CO[NH•CO]CH•OH, formed by the reduction of alloxan (J. v. Liebig and F. Wohler, Ann., 1838, 26, p. 276), or of alloxantin (A. Baeyer, Ann., 1863, 127, p. 12), crystallizes in needles or prisms and possesses a very acid reaction. It becomes red on exposure, and in the moist condition absorbs oxygen from the air, giving alloxantin. Allophanic acid, NH2•CO•NH•CO2H, is not known in the free state, as when liberated from its salts, it is decomposed into urea and carbon dioxide. Its esters are formed by passing the vapours of cyanic acid into alcohols
URI, one of the cantons of central Switzerland, and one of the earliest members of the confederation. The name is probably connected with the same obscure root as Reuss and Ursern, and is popularly derived from Urochs or Auerochs (wild bull), a bull's head having been borne for ages as the arms of the region. The total area of the canton is 415.3 sq. m., of which 184.3 are reckoned as " productive " (forests covering 43.9 sq. m.), while of the rest 44.3 are occupied by glaciers and 71 sq. m. by the cantonal share of the Lake of Lucerne. The highest summit in the canton is the Dammastock (11,920 ft.). The canton is composed of the upper valley of the Reuss, a mountain torrent that has cut for itself a deep bed, save in case of the basin of Ursern, near its upper end, and the plain of Altdorf, just before it forms the Lake of Lucerne. Hence, save in these two cases, the canton is made up of a wild Alpine valley, very picturesque in point of scenery, but not offering much chance of cultivation. Through nearly the whole of this savage glen runs the main line of the St Gotthard railway (opened in 1882), the part (281 m.) in the canton being that between Sisikon, on the Lake of Lucerne, and Goschenen, at the northern mouth of the great tunnel (91 m.) through the Alps, and at the lower end of the wild SchBllenen gorge that cuts it off from the basin of Ursern. The most remarkable engineering feats are near Wassen. There is also an electric tramway from Altdorf to its port, Flifelen. On the other hand, several magnificent carriage roads are within the borders of the canton, leading to or over the mountain passes that give access either to Glarus (the Klausen Pass, 6404 ft.), or to Ticino (St Gotthard Pass, 6936 ft.), or to the Grisons (Oberalp Pass, 6719 ft.), or to the Valais (Furka Pass, 7992 ft.). Owing to the physical conformation of the canton, it was difficult for it to extend its rule save towards the south (see below), but since very early days it has held the splendid pastures of the Urnerboden, on the other slope of the Klausen Pass, as well as the Blacken Alp, at the head of the Engelberg valley, though the northernmost slope of the St Gotthard Pass still belongs to Ticino. In 1900 the population of the canton was only 19,700, of whom 18,685 were German-speaking, 947 Italian-speaking (this number varied much during the construction of the St Gotthard railway, mainly by Italian navvies), and 24 French-speaking, while 18,924 were Romanists, 793 Protestants, and z a Jew. The capital is Altdorf (q.v.), indissolubly connected with the legend of William Tell (q.v.). The only other important villages are Erstfeld (2416 inhab.), a great railway centre, where the mountain engines are put on, and Silenen (1892 inhab.). The population is all but exclusively pastoral, natural causes limiting much effort in the way of agriculture, save near Altdorf. In the canton there are 102 " alps " or mountain pastures, capable of supporting 10,354 cows, and of an estimated capital value of 5,771,000 fr. Till 1814 Uri formed part of the diocese of Constance (save Ursern, which has always been in that of Coire), while since that date it is administered by the bishop of Coire, though legally in no diocese. The inhabitants are very industrious and saving, though not rich in worldly goods, as their land is so barren. They are extremely conservative, and passionately attached to their religion. Wooden sandals are still commonly worn in the Alpine glens. Of recent years the canton has been much visited by travellers, who have brought much money into it. It forms a single administptive district, which comprises twenty communes. The legislature of the canton is the time-honoured primitive democratic assembly, called the Landsgemeinde, composed of all male citizens of 20 years of age, and meeting once annually near Altdorf on the first Sunday in May. It has retained many curious antique ceremonies and customs. It elects the single member of the Federal Standerat, as well as the cantonal executive of seven members (holding office for four years), two of whom are the highest officials, the Landammann and his deputy. There is also a sort of standing committee, called the Landrat, which is charged with the administration and minor legislative matters. It is composed of members elected for four years by a popular vote in the pro-portion of one to every 400 (or fraction over 200) inhabitants, though each commune, even if not attaining this standard of population, is entitled to a member. The single member of the Federal Nationalrat is elected by a popular vote. The constitutional details, apart from the Landsgemeinde, are settled by the cantonal constitution of 1888 (since revised slightly). Uri is first mentioned in 732 as the place of banishment of Eto, the abbot of Reichenau, by the duke of Alamannia. In 853 it was given by Louis the German to the nunnery (Frauenmunster) at Zurich which he had just founded, and of which his daughter, Hildegard, was the first abbess. Hence the "abbey folk" in Uri enjoyed, as such, the privilege of exemption from all jurisdictions save that of the king's Vogt or " steward of the manor " at Zurich, this Vogtei being cut off from the country of the Zurichgau. The rule of the abbess was mild, so that the other inhabitants of Uri either became her. tenants or obtained similar privileges. Little by little the gathering together of all the inhabitants for the purpose of regulating the customary cultivation of the land created a corporate feeling and led to a sort of local government. On the extinction of the Zaringen dynasty (1218), the Vogtei reverted to the king, who gave it to the Habsburgs. But in 1231 King Henry bought Uri from them, and thus it became again immediately dependent on the king, the purchase being perhaps due to the rising importance of the route over the St Gotthard Pass (first distinctly mentioned in 1236). As early as 1243 Uri had a common seal, and in the confirmation of its privileges (1274) granted by Rudolf of Habsburg mention is made of its " head-man " (Amman) and of the " commune " (universitas). Uri therefore was quite ready to take part, with Schwyz and Unterwalden, in founding the " Everlasting League " (germ of the later Swiss confederation) on the 1st of August 1291, defending its liberty in the fight of Morgarten(1315) and renewing the League of the Three at Brunnen (2315). Later it took part in the victory of Sempach (1386). In 1403, with the help of Obwalden, it won the Val Leventina from the duke of Milan, but it was lost in 1422, though in 1440 Uri alone reconquered it and kept it (winning the bloody fight of Giornico in 1478) till 1798. In 1419, with Obwalden, Uri bought Bellinzona, but lost it at the battle of Arbedo (1422), though, with Schwyz and Nidwalden, it won it back in 1500, keeping it also till 1798. In 1512 Uri shared in the conquest of Lugano, &c., by the Confederates, her natural position forcing her to extend her rule towards the south, though many attempts on and temporary occupations of the Val d'Ossola (1410-1515) ultimately failed. In 1410 a perpetual alliance was made with the valley of Ursern or Val Orsera, the latter being allowed its own head-man and assembly, and courts under those of Uri, with which it was not fully incorporated till 1888. Ursern originally belonged to the great Benedictine monastery of Disentis, at the head of the Vorder Rhine valley, and was most probably colonized in the 13th century by a German-speaking folk from the Upper Valais. At the Reformation Uri clung to the old faith, becoming a member of the " Christliche Vereinigung " (1529) and of the Golden League (1586). In 1798, on the formation of the Helvetic republic, Uri be-came part of the huge canton of the Waldstatten and lost all its Italian possessions. In September 1799 Suworoff and the Russian army, having crossed the St Gotthard to Altdorf, were forced by the French to pass by the Kinzigkulm Pass into Schwyz, instead of sailing down the lake to Lucerne. In 1803 Uri became an independent canton again, with Ursern, but without the Val Leventina. It tried hard to bring back the old state of things in 1814-15, and opposed all attempts at reform, joining the League of Sarnen in 1832 to maintain the pact of 1815, opposing the proposed revision of the pact, and being one of the members of the Sonderbund in 1845. Despite defeat in the civil war of 1847, Uri voted against the Federal constitution of 1848, and by a crushing majority against that of 1874.