URINE 325 



Organic Constituents. 

 UREA. 



8. 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. 



Reaction of Urea. 



9. Test solubility of urea in alcohol. 



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

 Add a small volume of water and perform the biuret test, Ex- 

 plain. 



11. 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. 



12. 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. 



13-14. URIC ACID. 



To a liter of urine add 25 c.c. cone, hydrochloric acid. Al- 

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

 the reddish brown crystals and collect them on a small filter. 



