CH. XXXVII.] 



UREA. 



549 



misled by seeing the names of the acids and metals separated. 

 The acids and the bases are combined to form salts, such as 

 urates, chlorides, sulphates, phosphates, &c. 



Urea. 



Urea, or Carbamide, CO(NH 2 )<j, is isomeric (that is, has the 

 same empirical, but not the same 

 structural formula) with ammo- 

 nium cyanate (NH 4 ) CNO, from 

 which it was first prepared syn- 

 thetically by Wohler in 1828. 

 Since then it has been prepared 

 synthetically in other ways. 

 Wohler's observation derives in- 

 terest from the fact that this 

 was the first organic substance 

 which was prepared synthetically 

 by chemists. 



When crystallised out from 

 the urine it is found to be readily 

 soluble both in water and alcohol: 

 it has a saltish taste, and is neutral to litmus paper, 

 of its crystals is shown in fig. 429. 



\Vhcn treated with nitric acid, nitrate of urea (CON 2 H4.HN0 3 ) 

 is formed ; this crystallises in octahcdra, lozenge-shaped tablets 



Fig. 429. Crystals of Urea. 



The form 



Fig. 4jo. Crystals of Urea nitrate. 



Fig. 431. Crystals of Urea oxalate. 



or hexagons (fig. 430). When treated with oxalic acid, flat or 

 prismatic crystals of urea oxalate (('(>N.jH v H 2 (' 2 ()4 + H 2 O) are 

 formed (fig. 431). 



These crystals may be readily obtained by adding excess of the 

 respective acids to urine which has been concentrated to a third 

 or a quarter of its bulk. 



I uder the influence of an organised ferment, the tornla or 

 micrococcus ureiu, which grows readily in stale urine, urea 

 taltes up water, and is converted into ammonium carbonate 



