EXAMINATION OF THE URINE. 99 



7. Add to a little bromine-water in a test-tube an ex- 

 cess of caustic soda solution. Sodium hypobromite, NaBrO, 

 is formed. If some urea solution is added to this mixture 

 nitrogen is evolved, causing marked effervescence, while the 



FIG. 7. Urea Nitrate. 



carbon dioxide formed at the same time is absorbed by the 

 excess of caustic soda present: 



OCN 2 H 4 + SXaBrO = C0 2 + N 2 + 2H 2 + 3XaBr. 



IV. PREPARATION OF URIC ACID, C 5 H 4 X 4 3 . 



(a) From Urine. Add 50 cc. of hydrochloric acid to 500 cc. 

 of urine and let stand for twenty-four hours in a cool place, 

 filter, and wash with water. Examine the crystals of uric 

 acid under the microscope. Nearly neutralize the nitrate 

 with ammonia, then add magnesia mixture, filter, and add to 

 the filtrate some silver nitrate solution: precipitate of a 

 double compound of silver and magnesium with that part of 

 the uric acid which was not precipitated by the hydrochloric 

 acid. Filter off the precipitate, wash, suspend in water, 

 decompose by means of hydrogen sulphide, filter from the 

 silver sulphide, evaporate to a small volume, and add hydro- 



