50 METHODS FOR THE ANALYSIS OF URINE 



tion 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 N/20 potassium per- 

 manganate solution is equivalent to 3.75 mg. (0.00375 gm.) 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 

 burette reading in order to ascertain the number of cubic centi- 

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

 of the original urine to the correct end point. If y represents 

 the number of cubic centimeters of the permanganate solution 

 required, we may make the following calculation: 



yX 0.00375 = weight of uric acid in 100 c.c. of urine. 



Because of the solubility of the ammonium urate a cor- 

 rection of 3 mg. should be added to the final result. 



Calculate the quantity of uric acid in the twenty-four hour 

 urine specimen. 



URIC ACID 



Microchemical Colorimetric Method 



Benedict and Hitchcock Modification of the Folin-Macallum- 

 Denis Procedure. 1 Principle. The principle of the method de- 

 pends upon the fact, first noted by Folin and Macallum and further 

 investigated by Folin and Denis, that uric acid gives, with phospho- 

 tungstic acid and alkali, a deep blue color the depth of which is pro- 

 protional to the amount of uric acid present. Since certain other 

 substances present in urine produce a similar blue color with the 

 phosphotungstic acid, it is necessary to separate the uric acid 

 from them. This is accomplished by precipitation as the silver 

 salt. The silver urate is subsequently dissolved and treated with 

 the uric acid reagent. 



1 Folin and Macallum: Jour. Biol. Chem., 1912, 12, 363. Folin and 

 Denis: Jour. Biol. Chem., 1913, 14, 95; ibid., 1913, 13, 469. Benedict and 

 Hitchcocit: Jour. Biol. Chem., 1915, 20, 619; Benedict: ibid., 1915, 20, 629. 



