URIN 393 



tube, dissolve the residue in dilute potassium hydroxide solution, and add very 

 dilute copper sulphate solution (see page 99). The purplish-violet color is due 

 to the presence of biuret which has been formed from the urea through the 

 application of heat as indicated. This is the reaction : 



NH 2 

 / NH 2 



Urea. C = 



\ c=o 



NH 2 i \ 



EM NH+NH 3 



H C=0 



Urea. C = O 



I NH 2 



NH 2 Biuret - 



6. Urea Nitrate. Prepare a concentrated solution of urea by dissolving 

 a little of the substance in a few drops of water. Place a drop of this solution on a 

 microscopic slide, add a drop of concentrated nitric acid, and examine under the 

 microscope. Compare the crystals with those reproduced in Fig. 124, page 391. 



FIG. 126. UREA OXALATE. 



7. Urea Oxalate. To a drop of a concentrated solution of urea, prepared as 

 described in the last experiment (6), add a drop of a saturated solution of oxalic 

 acid. Examine under the microscope and compare the crystals with those shown 

 in Fig. 126, above. 



8. Decomposition by Urease. To 5 c.c. of urea solution in a test tube add 

 i c.c. of urease solution or a little soy bean or jack bean powder. Allow the 

 tube to stand for ten minutes, heat the contents to boiling, holding moist red 

 and blue litmus papers at the mouth of the tube. What do you observe? 

 Note the odor. Explain. 



9* Decomposition by Sodium Hypobromite. Into a mixture of 3 c.c. of con- 

 centrated sodium hydroxide solution and 2 c.c. of bromine water in a test-tube 



