98 PHYSIOLOGICAL AND PATHOLOGICAL CHEMISTRY. 



/ 



OC( 



\ 



/ 

 OC< 



> 

 OC< 



\ 



NH 



x 2 



OC< \NH 2 



X NH 2 



Biuret gives a characteristic reaction. Dissolve the 

 fused mass in water with the addition of some caustic soda, 

 then add cautiously dilute copper sulphate solution; the 

 copper hydroxide resulting dissolves, forming a reddish-violet 

 fluid (biuret reaction). 



2. Repeat the fusing of the urea, but continue the heating 

 until the entire mass has again solidified; after cooling dis- 

 solve in water containing some caustic soda, and acidify 

 cautiously with hydrochloric acid: precipitation of cyanuric 

 acid, CgOgNsHg (cyanic acid is first formed; this, however, 

 polymerizes at once to cyanuric acid). 



3. Dissolve a few crystals of urea on a watch-glass in a 

 drop or two of water, and add a little concentrated oxalic acid 

 solution: precipitation of urea oxalate (OCN 2 H 4 ) 2 -C 2 H 2 4 + 

 H 2 0. Examine under the microscope. 



4. Repeat this experiment, using nitric acid instead of 

 oxalic acid: urea nitrate, OCN 2 H 4 -HN0 3 , (see Fig. 7). 



5. Heat some urea with caustic soda solution : strong evo- 

 lution of ammonia with the formation of sodium carbonate : 



OC < -h 2NaOH = OC < + 2NH 3 . 



6. Warm a small drop of mercury with nitric acid in a 

 test-tube and then add a little urea: marked foaming due 

 to the development of a colorless, odorless gas, a mixture of 

 carbon dioxide and nitrogen. The reaction is due to the 

 action of nitrous acid on urea* 



OCN 2 H : + N 2 3 = C0 2 + 2N 2 + 2H 2 0. 



