274 PHYSIOLOGICAL. CHEMISTRY. 



EXPERIMENTS ON URIC ACID. 



1. Isolation from the Urine. Place about 200 c.c. of filtered 

 urine in a beaker, render it acid with 2-10 c.c. of concentrated 

 hydrochloric acid, stir thoroughly and stand the vessel in a cold 

 place for 24 hours. Examine the pigmented crystals of uric acid 

 under the microscope and compare them with those shown in Fig. 

 101, p. 347 and PI. V., opposite p. 273. 



2. Solubility. Try the solubility of pure uric acid, furnished by 

 the instructor, in the ordinary solvents (see p. 23) and in alcohol, 

 ether, concentrated sulphuric acid and in boiling glycerol. 



3. Crystalline Form of Pure Uric Acid. Place about 100 c.c. 

 of water in a small beaker, render it distinctly alkaline with potas- 

 sium hydroxide solution and add a small amount of pure uric acid, 

 stirring continuously. Cool the solution, render it distinctly acid 

 with hydrochloric acid and allow it to stand in a cool place for crys- 

 tallization. Examine the crystals under the microscope and com- 

 pare them with those reproduced in Fig. 89, below. 



4. Murexide Test. To a small amount of pure uric acid in a 

 small evaporating dish add 2-3 drops of concentrated nitric acid. 

 Evaporate to dryness carefully on a water-bath or over a very low 



FIG. 89. 



PURE URIC ACID. 



flame. A red or yellow residue remains which turns purplish-red 

 after cooling the dish and adding a drop of very dilute ammonium 

 hydroxide. The color is due to the formation of murexide. If po- 

 tassium hydroxide is used instead of ammonium hydroxide a pur- 



