U R E 



U R E 



the prefeiit time. Berzelius appears to have been the firft 

 who obtained it in a feparatc It ate, but the account he has 

 given of it does not feem to have much attraded the atten- 

 t\oii of chemiih, for the more recent defcrlption of it by 

 Thenard is much lefs correcl. M. Vauquchn is faid to have 

 procured it very lately in the pure ilatc in which we are 

 about to delcribe it, which defcription we adopt from Dr. 

 Prout, who has juft pubhfhed an account of this Angular 

 principle in tlic Tranfadioiis of the Medico-chirurgical So- 

 ciety of London. 



To obtain urea in any quantity is no eafy talk. This 

 arifes from the care with which it is decompofed, and the ob- 

 ilinacy with which the colouring matter, and other urinary 

 principles, adhere to it. Dr. Prout recommends that urine 

 fhould be carefully evaporated to the confiltence of a fyrup ; 

 that nitric acid fliould be llowly added to it in this (late, 

 which combines with the urea, and thus feparates it from 

 many other principles. The nitrate of urea is then to be 

 decompofed by carbonate of potafh, and after the nitre 

 formed has been feparated by cryftallization, animal char- 

 coal is recommended to be added to the coloured folution 

 of urea, which feparates moll of the colourinj;; matters : 

 laftly, the folution of urea is again ordered to be evaporated 

 to drynefs, and heated with llrotig alcohol and heat ; the al- 

 coholic folution thus formed is then to be concentrated by 

 evaporation, and on cooling the urea feparates from it in a 

 pure cryftalline (late. Thus obtained, urea has the follow- 

 ing properties : 



" Urea moil frequently alTumes the form of a four-fided 

 prifm. Its cryftals are tranfparent and colourlefs, and have 

 a flight pearly ludre. It leaves a fenfation of coolnefs on 

 the tongue like nitre. Its fmell is faint and peculiar, but 

 not urinous. It does not affeft litmus or turmeric papers. 

 It undergoes no apparent change on expofure to the air, 

 except in very damp weather, when it flightly deliquefces, 

 but does not feem to fuffer decompofition. Expofed to a 

 ftrong heat it melts, and is partly decompofed and partly 

 fublimed apparently unaltered. The fpecitic gravity of its 

 crydals is about 1.350. 



" Water at 60^ dilfolves more than its own weight of 

 urea, and the folution expofed to the air for feveral months 

 underwent no change. Boiling water diCTolves any quantity 

 of it whatever, and the urea does not appear to undergo 

 any change at this degree of temperature. 



"Alcohol ((p. gr. .816) at a mean temperature diffolvcs 

 about 20 per cent., and at a boiling temperature more than 

 its own weight, and the urea feparates on cooling in the 

 form of cryltals. It is very fparingly if at all foluble in 

 fulphuric ether, or the effential oil of turpentine, though 

 thefc fluids are rendered opaque by it. 



" The pure alkalies and alkaline earths dccompofe it, 

 efpecially when afiilled by heat, and the refult is chiefly 

 carbonate of ammonia. It unites with moft of the metallic 

 oxyds. The combination with filver is greyifh, and de- 

 tonates on being heated, and the filvcr ia reduced. It does 

 not feem however to be alone capable of dccompoiing any 

 metallic fait, but in order to effeft the union in queflion the 

 aid of double decompofition is neccffary. 



" It combines with nitric acid, and forms a cryftaUine 

 compound but fparingly foluble in water. It forms alio a 

 fimilar compound with oxahc acid. In neither of thcfe 

 compounds are the properties of the acids neutralized." 



Urea has the remarkable property of changing the cryf- 

 talline forms of thofe falts with which it is in folution. Thu» 

 the cubical form of the muriate of foda is changed into an 

 oftohcdron, while the oftohedral form of the muriate of 

 ammpnia is converted into a cube. The prifmatic fonn of 



nitre alfo is liable to be varioudy modified. Thefe changes 

 do not appear to take place unlefs the urea be in excgfs in a 

 folution, and the proportional quantities of the different 

 falts be fuch as to cryftallize (lowly. 



Urea fubmitted to analyfis, by combuftion with the oxyd 

 of copper, was found to confid of 



2 atoms or z volumes of hydrogen 2.5") 'o f hydrogen 6.66 

 I atom or i volume of carbon 7.5 I ^ J carbon 19.99 

 I atom or ^volume of oxygen 10. o f A^ J oxygen 26.66 

 I atom or I volume of azote I7-5J o (.azote 46.66 



37-5 



100.00 



The nitrate of urea, the cryRalline compound before- 

 mentioned, confifts, according to Dr. Prout's analyfis, of 



Nitric acid 47.37 or one atom. 

 Urea S^-^S O"" ^^'^ atoms. 



100.00 



Hence wc are enabled, by means of this analyfis, to efti- 

 mate the quantity of urea in a given fpecimen of urine. 



Urea fometimes exifts fo abundantly in urine, as to cryf- ^ 

 tallize fpontaneoufiy on the addition of nitric acid. In fuch 

 inftances it is ufually accompanied by an excefs of the phof- 

 phates. A remarkable relation was found by Dr. Prout to 

 fubfift between urea and the faccharine principle, which, in 

 his opinion, fatisfaftorily explains the phenomena of diabetes, 

 a difoafe in which fugar is known to be prefent in the urine, 

 in the proportion in which urea is abfent. Another re. 

 markable circumflance is, its compofition being in con- 

 formity to the atomic theory, or theory of definite propor- 

 tions. This however is not pecuhar to urea, but was found 

 by Dr. P. to hold good in other urinary principles. Sec 

 Uric Acid. 



URECOURT, in Geography, a town of France, in 

 the department of the Vofges ; 6 miles NN.W. of J_,a 

 Marc he. 



UREDEN, a town of Germany, in the bifiiopric 

 of Munfter, on the Berckel ; 26 miles W.N.W. of 

 Munder. 



UREDO, a word ufed by fome of the chemical writers 

 to exprefs the virtues of metals communicated to them from 

 the fun. Pliny ufes the fame word to exprsfs the fmut af- 

 fcfting fruits ; and fome medical writers have expreffed by 

 it a very violent and excruciating pain in the head : and 

 others an extreme itching or burning in the (kin. Sec 

 Smut, Blast, and Blight. 



Uredo, in Botany, an old Latin name, from itro, to burn, 

 or parch, applied to thofe occafional difcolorations on the 

 furfaces of plants, which were attributed to blafts, or inju- 

 ries of the atmofphcrc or heavenly bodies, but wliich are 

 now generally found to be parafiticalyi;nf< ; at lead fuch is 

 the date of thefc appearances, when they come under our 

 obfcrvation, whatever injury or difcafe, in the plant which 

 bears them, may have favoured their produftion. The 

 above name is now applied to one particular genus of this 

 kind of vegetable. — Perf. Obf. Mycol. fafc. 2. 23. Syn. 



Fung. 214 Clafs and order, Cryptogamia Fungi. Nat. 



Ord. Fungi. 



EIT. Ch. Coat none. Powder naked, deciduous. Seeds 

 uniform, generally globofe. 



Such IS Perfoon's generic charaAer, by which the dif- 

 ference between this genus and another of the fame author's, 

 named Puccinia, feems to be, that in the latter what he 

 terms, with a mark of doubt, SporuU, feeds, are faid to be 

 3 S 2 cluftercd 



