CHEMICAL BASIS OF THE ANIMAL BODY. 



157 



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, fre- 

 quently aggregated in piles, but the successful obtaining of typical 

 crystals requires some attention to the concentration of the solution. 



FIG. 15. CRYSTALS OF 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 crystallises 



FIG. 16. CRYSTALS OF OXALATE OF UREA. (Krukenberg after Kiihne.) 



