ORGANIC CONSTITUENTS OF THE URINE. 



91 



residue into two portions, using one for the preparation 01 

 nitrate, and the other for oxalate of urea. 



4. Urea Nitrate, CH 4 N 2 O, HNO 3 . 



(a.) To the concentrated urine add strong, pure nitric 

 acid = a precipitate of glancing scales of urea nitrate, which, 

 being almost insoluble in HNO 3 , separate out in rhombic 

 plates or six-sided tables, with a mother-of-pearl lustre, and 

 often imbricate arrangement. 



(b.) Examine the crystals microscopically (Fig. 21). 



-)/- b 



Fig. 21. a, Urea; b, hexagonal plates; and c, smaller scales, or rhombic 

 plates of urea nitrate. 



(c.) If only traces of urea are present, concentrate the 

 fluid supposed to contain the urea, place a drop on a slide, 

 put into the drop one end of a thread, apply a cover-glass, 

 and put a drop of pure nitric acid on the free end of the 

 thread. The acid will pass into the fluid, and microscopic 

 crystals of urea nitrate will be formed on the thread. After 

 a time examine the preparation microscopically. 



