PROPERTIES OF UREA. 653 



in an equal weight of water and in five parts alcohol; it requires one 

 part boiling alcohol for solution; it is insoluble in alcohol-free anhydrous 

 ether, and also in chloroform. If urea in substance is heated in a test- 

 tube, it melts, decomposes, gives off ammonia, and finally leaves a non- 

 transparent white residue which, among other substances, contains 

 cyanuric acid and biuret, which latter dissolves in water, giving a beautiful 

 reddish-violet liquid with copper sulphate and alkali (biuret reaction). 

 On heating with baryta-water or caustic alkali, also in the so-called 

 alkaline fermentation of urine caused by micro-organisms, urea splits 

 into carbon dioxide and ammonia with the addition of water. The 

 same decomposition products are produced when urea is heated with 

 concentrated sulphuric acid. An alkaline solution of sodium hypobromite 

 decomposes urea into nitrogen, carbon dioxide, and water according 

 to the equation 



CON 2 H 4 + 3NaOBr = 3NaBr + CO 2 + 2H 2 O + N 2 . 



With a concentrated solution of furfurol and hydrochloric acid urea 

 in substance gives a coloration passing from yellow, green, blue, to violet, 

 and then after a few minutes beautiful purple-violet (SCHIFF'S reaction). 

 According to HUPPERT 1 the test is best performed by taking 2 cc. of a 

 concentrated furfurol solution, 4-6 drops of concentrated hydrochloric 

 acid, and adding to this mixture, which must not be red, a small crystal 

 of urea. A deep violet coloration appears in a few minutes. 



Urea forms crystalline compounds with many acids. Among these 

 the one with nitric acid and the one with oxalic acid are the most 

 important. 



UREA NITRATE, CO(NH 2 )2.HNO 3 . On crystallizing quickly this 

 compound forms thin rhombic or six-sided overlapping tiles, or colorless 

 plates, with an angle of 82. When crystallizing slowly, larger and 

 thicker rhombic pillars or plates are obtained. This compound is rather 

 easily soluble in pure water, but is considerably less soluble in water 

 containing nitric acid; it may be obtained by treating a concentrated 

 solution of urea with an excess of strong nitric acid free from nitrous 

 acid. On heating this compound it volatilizes without leaving a residue. 



This compound may be employed with advantage in detecting small amounts 

 of urea. A drop of the concentrated solution is placed on a microscope slide and 

 the cover-glass placed upon it; a drop of nitric acid is then placed on the side 

 of the cover-glass and allowed to flow under. The formation of crystals begins 

 where the solution and the nitric acid meet. Alkali nitrates may crystallize 

 very similarly to urea nitrate when they are contaminated with other bodies ; 

 therefore, in testing for urea, the crystals must be identified as urea nitrate by 

 heating and by other means. 



1 Huppert-Neubauer, Analyse des Harns, 10. Aufl., 296. 



