154 BASIC BODIES. 



action on vegetable colours. Its concentrated aqueous solution is 

 not changed by boiling or by long keeping, but a dilute solution 

 suffers change. 



At about 120 urea fuses without suffering change, but at a 

 little above that temperature it begins to develope ammonia, to 

 become pulpy, and to change into cyanuric acid (3C 2 H 4 N 2 O 2 = 

 3H 3 N + C 6 HN 3 O 4 .2HO) ; when rapidly heated it also yields 

 cyanic acid which is produced from the previously formed cyanuric 

 acid (C 6 HN 3 O 4 .2HO=3C 2 NO.HO). On heating urea very slowly, 

 it becomes converted (according to Wohler and Liebig*) into a 

 glistening white body, insoluble in water but soluble in acids and 

 alkalies, carbonic acid and ammonia being evolved during the 

 process. This body=C 4 H 6 N 4 O 2 , for 3C 2 H 4 N 2 O 2 - (2CO 2 + 

 2H 3 N)=zC 4 H 6 N 4 O 2 . If, on the other hand, urea be kept for some 

 time in a state of fusion at from 150 to 170, not only are the 

 above-named compounds formed, but also (according to Wiede- 

 mannf) the biuret, C 4 H 5 N 3 O 4 , whose production is explained by 

 the equation, 2C 2 H 4 N 2 O 2 -H 3 N=C 4 H 5 N 3 O 4 . 



If chloride of sodium or hydrochlorate of ammonia be present 

 in a solution of urea, the former will crystallise in octohedra and 

 the latter in cubes ; if, however, the crystals be again dissolved in 

 water, and allowed to crystallise anew, they separate in the ordinary 

 manner, namely, the chloride of sodium into cubes, and the 

 hydrochlorate of ammonia into octohedra or feathery forms. 



Urea will combine only with certain acids and a few bases; 

 neither the metallic salts, tannic acid, nor any other re-agent, can 

 precipitate it from its solutions. 



On heating a concentrated solution of urea with nitrate of 

 silver, cyanate of silver separates, while nitrate of ammonia re- 

 mains in solution. (C 2 H 4 N 2 O 2 + AgO.NO 5 = AgO.C 2 NO + 

 H 3 N.HO.NO 5 ). 



By nitrous acid urea is decomposed into nitrogen, water, and 

 carbonic acid; (C 2 H 4 N 2 O 2 + 2HO + 2NO 3 =6HO + 2CO 2 + 4N ;) 

 by chlorine into nitrogen, carbonic acid, and hydrochloric acid ; 

 (C 2 H 4 N 2 2 + 2 HO + 6C1 ^ 6HC1 + 2C0 2 + 2N.) 



On boiling urea either with strong mineral acids or with caustic 

 alkalies, it takes up 2 atoms of water and is decomposed into 

 ammonia and carbonic acid (C 2 H 4 N 2 O 2 + 2HO = 2H 3 N + 2CO 2 .) 



If organic matters, either putrefying or capable of undergoing 

 putrefaction, be mixed with an aqueous solution of urea, the latter 

 is soon converted into carbonic acid and ammonia. 



t Ann. d. Ch. u. Pharm. Bd 54, S. 3? I. 

 J Journ. f. pr. Ch. Bd. 43, S. 271-280. 



