CHEMICAL BASIS OF THE ANIMAL BODY. 1255 



not readily observed, but rather that of irregular dendritic 

 crystals. 



Urea is very soluble in cold water, distinctly less soluble in 

 cold alcohol, readily so in hot ; it is insoluble in anhydrous 

 ether and in petroleum-ether. It possesses a somewhat bitter, 

 cooling taste, resembling saltpetre. 



Urea readily forms compounds with acids and bases ; of 

 these the following are important as a means of detection and 

 identification. 



Nitrate of urea. (NH 2 ) 2 CO . HNO 3 . 



Obtained by the addition of a slight excess of pure colourless 

 nitric acid to a moderately concentrated solution of urea. The 

 nitrate should separate out rapidly in the form of six-sided or 

 rhombic tables, frequently aggregated in piles, but the success- 

 ful obtaining of typical crystals requires some attention to the 

 concentration of the solution. 



FIG. 209. CRYSTALS OP NITRATE OF UREA. (Krukenberg after Kiihne.) 



The crystals are but slightly soluble in nitric acid, or alcohol, 

 more soluble in cold water and much more so in hot water. 

 They are insoluble in ether. 



Oxalate of urea. [(NH 2 ) 2 CO] 2 . H 2 C 2 O 4 + H 2 O. 



Obtained by the addition of concentrated aqueous solution 

 of oxalic acid to a concentrated aqueous solution of urea. 

 This salt crystallizes out in rhombic tables closely resembling 

 those of the nitrate, but they are frequently aggregated into a 

 characteristic prismatic form. As in the case of the nitrate 

 some care is required with respect to the concentration of the 

 respective solutions during its preparation. 



The crystals are less soluble in oxalic acid than in water, 



