URINE 275 



2. Organic Constituents. 



(a) UREA. 



(1) Preparation from Urine. Evaporate 500 c.c. of urine on 

 the water bath to the consistency of a thin syrup. Cool and add 

 twice the volume of nitric acid (50%). Allow to stand in a cool 

 place over night. Filter off the crystals (dry between filter 

 papers,), remove crystals from the filter, and dissolve them in a 

 small amount of hot water. Add a little potassium permanga- 

 nate solution to this urea nitrate solution, stirring constantly, 

 until the nitrate solution is nearly colorless. Bring the solution 

 to a boil, and add first solid sodium carbonate and then solid 

 barium carbonate until C0 2 ceases to come off, and the solution 

 is neutral. Evaporate over the water bath to dryness, powder the 

 residue and extract it with 95% warm alcohol. Filter and set the 

 filtrate aside to cool. Examine the crystals under the micro- 

 scope. 



(2) Reaction of Urea. 



i. Test solubility of urea in alcohol. 



ii. Heat a few crystals of urea gently in a dry test tube. 

 Add a small volume of water and perform the biuret test. Since 

 biuret is formed when urea is heated dry, a positive test should 

 result. 



iii. Dissolve a few crystals of urea in a few drops of water. 

 Add 2 drops of cone. HN0 3 . Observe the crystals of urea nitrate 

 under the microscope, and draw. Repeat with oxalic acid and 

 observe the urea oxalate. 



iv. Dissolve a few crystals of urea in a few cubic centimeters 

 of water and add sodium hypobromite solution. 



Note : Sodium hypobromite is prepared by adding bro- 

 mine water to sodium hydrate solution. 



Note effervescence. This is due to the liberation of free nitro- 

 gen in the decomposition of urea by the hypobromite. 



(b) URIC ACID. 



(1) To a liter of urine add 25 c.c. cone, hydrochloric acid. 

 Allow to stand in the ice chest over night. Decant carefully from 



