294 PHYSIOLOGICAL CHEMISTRY 



let stand for 48 hours. Filter cautiously through a hard filter, 

 using a glass rod to avoid loss of liquid. Rinse out the beaker 

 several times with 10% ammonium sulphate solution, each time 

 pouring the rinsing liquid onto the filter after it has drained 

 completely, thus rinsing both beaker and precipitate with the 

 same liquid. This rinsing should be repeated 5 or 6 times. 



Carefully remove the filter paper from the funnel, open it 

 and rinse the precipitate into the beaker from which it was 

 just removed, taking care that all the crystals are transferred 

 to the beaker. It is most satisfactory to use hot water for the 

 rinsing. No color should remain on the filter paper. (Note. 

 Do not heat the water in a thick glass wash bottle. Heat in a 

 beaker and pour into the wash bottle). The total volume of the 

 rinsings should be as close as possible to 100 c.c. Cool to room 

 temperature. 



Add 15 c.c. of cone. H^SO^ and titrate the hot liquid at once 

 with N/20 potassium permanganate. The liquid should be 

 shaken or stirred continuously. At first the color of the per- 

 manganate will disappear instantly without diffusing through 

 the liquid. The first instantaneous pink color throughout the 

 entire liquid is taken as the end point of the titration. This 

 color will disappear very quickly, but the addition of another 

 drop also will cause a pink color to diffuse for a very brief time 

 throughout the entire liquid. Each c.c. of N/20 permanganate 

 = 3.76 mg. uric acid. Calculate the amount of uric acid in the 

 volume of urine used (100 c.c.). From this calculate the 

 amount of uric acid in your 24 hour specimen. 



From the formula of uric acid calculate the percentage of 

 nitrogen it contains. From this and the results obtained above, 

 calculate the amount of nitrogen in the total uric acid. Calcu- 

 late the per cent of the total nitrogen present as uric acid nitro- 

 gen. 



7. Hippuric Acid. 



Hippuric acid may be estimated by the method of Folin and 

 Flanders which consists in hydrolyzing the hippuric acid and 

 estimating the benzoic acid liberated. 



