3/2 PHYSIOLOGICAL CHEMISTRY. 



III. Uric Acid. 



i. Folin-Shaffer Method. Introduce 100 c.c. 1 of urine into a 

 beaker, add 25 c.c. of the Folin-Shaffer reagent 2 and allow the mix- 

 ture to stand, 3 without further stirring, until the precipitate has 

 settled (5-10 minutes). Filter, transfer 100 c.c. of the filtrate 

 to a 200 c.c. beaker or Erlenmeyer flask, add 5 c.c. of concentrated 

 ammonia and allow the mixture to stand for 24 hours. Transfer 

 the precipitated ammonium urate quantitatively to a filter paper, 4 

 using 10 per cent ammonium sulphate to remove the final traces 

 of the urate from the beaker. Wash the precipitate approximately 

 free from chlorides by means of 10 per cent ammonium sulphate 

 solution, 5 remove the paper from the funnel, open it and by means 

 of hot water rinse the precipitate back into the beaker in which 

 the urate was originally precipitated. The volume of fluid at this 

 point should be about 100 c.c. Cool the solution to room temper- 

 ature, add 15 c.c. of concentrated sulphuric acid and titrate at once 

 with IQ- potassium permanganate, K 2 Mn 2 O 8 , solution. The first 

 tinge of pink color which extends throughout the fluid after the ad- 

 dition of two drops of the permanganate solution, while stirring 

 with a glass rod, should be taken as the end-reaction. Take the 

 burette reading and compute the percentage of uric acid present in 

 the urine under examination. 



Calculation. Each cubic centimeter of ^ potassium permangan- 

 ate solution is equivalent to 3.75 milligrams (0.00375 gram) of 

 uric acid. The 100 c.c. from which the ammonium urate was pre- 

 cipitated is equivalent to only four-fifths of the 100 c.c. of urine 

 originally taken, therefore we must take five-fourths of the bur- 

 ette reading in order to ascertain the number of cubic centimeters 

 of the permanganate solution required to titrate 100 c.c. of the 

 original urine to the correct end-point. If y represents the num- 

 ber of cubic centimeters of the permanganate solution required, we 

 may make the following calculation : 



y X 0.00375 = weight of uric acid in 100 c.c. of urine. 



1 It is preferable to use more than 100 c.c. of urine if the fluid has a specific 

 gravity less than 1.020. 



3 The Folin-Shaffer reagent consists of 500 grams of ammonium sulphate, 5 

 grams of uranium acetate and 60 c.c. of 10 per cent acetic acid in 650 c.c. of 

 distilled water. 



3 The mixture should not be allowed to stand for too long a time at this point, 

 since uric acid may be lost through precipitation. 



*The Schleicher and Schiill hardened papers or the Baker and Adamson 

 washed, ashless variety are very satisfactory for this purpose. 



5 This washing may be conveniently done by decantation if desired, thus retain- 

 ing the major portion of the precipitate in the beaker or flask. 



