228 UREA. 



means of cold alcohol. It crystallizes from the solu- 

 tion, when concentrated by distilling off a portion of 

 the alcohol. 2. Artificial preparation. Crude potassium 

 cyanate (prepared according to p. 212) is dissolved in 

 water without the aid of heat, and to the solution as 

 much ammonium sulphate is added as potassium ferro- 

 cyanide was employed ; the liquid is evaporated down 

 to a small volume, the potassium sulphate, that crystal- 

 lizes out on cooling, filtered off, and the filtrate evapo- 

 rated to dryness. The urea is extracted from the residue 

 by means of alcohol. 



Properties. Colorless, four-sided prisms, without odor, 

 of a cooling taste ; fuses at 130. Easily soluble in 

 water and alcohol. 



Heated above its fusing point, it is decomposed, am- 

 monia is given off, and, according to the duration of 

 the heating, the residue consists either of biuret (p. 221) 

 or cyanuric acid (p. 216). By heating with water in 

 fused tubes above 100 ; by boiling with alkalies ; by 

 heating with concentrated sulphuric acid ; by evapora- 

 tion of the solution, to which is added lead acetate, 

 urea is resolved into carbonic anhydride and ammonia, 

 water being assimilated. It suffers the same change in 

 foul urine. When heated for some time with alcoholic 

 carbon bisulphide, ammonium sulphocyanate and car- 

 bonic anhydride are formed. 



Urea combines with bases, acids, and salts, forming 

 crystallizing compounds. 



Urea nitrate, CHWO.HNO 3 , crystallizes from a 

 solution of urea on the addition of nitric acid. A salt 

 which is but slightly soluble in water, alcohol, and con- 

 centrated nitric acid. 



Urea hydrochlorate, CHWO.HC1, is produced by 

 the action of hydrochloric acid gas on urea. Yellow 

 oil, which soon congeals. An elevation of temperature 

 accompanies the action. Is decomposed by water, even 

 by lying in contact with moist air ; and, when heated, 

 it yields cyanuric acid and ammonium chloride. 



