532 PHYSIOLOGICAL CHEMISTRY 



In gout the uric acid content of the urine is low preceding an attack 

 and increases during the attack, this fall and rise being more or less 

 characteristic. The excretion rises after atophan administration ap- 

 parently due to increased kidney activity. In leukemia the excretion 

 is extremely high due to nuclear destruction. The uric acid content 

 of the urine is of importance in relation to the formation of uric acid 

 calculi. The administration of alkali carbonates and citrates by de- 

 creasing the acidity of the urine increases its solvent power for uric 

 acid, and decreases the liability of the formation of this type of calculus. 



2. Folin-Shaffer Method. 1 Principle. The uric acid is precipitated as am- 

 monium urate by the addition of ammonia, the precipitate filtered off, washed 

 and titrated with potassium permanganate. A preliminary treatment with an 

 ammonium sulphate-uranium acetate solution is for the purpose of removing 

 interfering organic substances. The method gives accurate results. 



Procedure. Introduce 2 100 c.c. of urine into an Erlenmeyer flask, add 25 c.c. 

 of the Folin-Shaffer reagent 3 and after shaking the flask to thoroughly mix the 

 fluids allow the mixture to stand, 4 with or without further stirring, until the 

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

 200 c.c. Erlenmeyer flask, add 5 c.c. of concentrated ammonium hydroxide and allow 

 the mixture to stand for 24 hours. Transfer the precipitated ammonium urate 

 quantitatively to a filter paper, 5 using 10 per cent ammonium sulphate to remove 

 the final traces of the urate from the flask. Wash the precipitate approximately 

 free from chlorides by means of 10 per cent ammonium sulphate solution, 6 remove 

 the paper from the funnel, open it, and by means of hot water rinse the precipi- 

 tate back through the funnel into the flask 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 temperature, add 15 c.c. of concentrated sulphuric acid and 

 titrate at once with N/20 potassium permanganate, K 2 Mn 2 O8, solution. The 

 first tinge of pink color which extends throughout the fluid after the addition 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 permanganate solution 

 is equivalent to 3.75 mg. (0.00375 gram) of uric acid. The 100 c.c. from which 

 the ammonium urate was precipitated 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 centimeters of the perman- 

 ganate solution required to titrate 100 c.c. of the original urine to the correct 



1 Folin and Shaffer: Zeit. physiol. Chem., 32, 552, 1901. 



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

 than i 020. 



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

 uraniu.m acetate and 60 c.c. of 10 per cent acetic acid in 650 c.c. of distilled water. 



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

 acid may be lost through precipitation. 



6 The Schleicher and Schiill hardened papers or the Baker and Adamson washed, askless 

 variety are very satisfactory for this purpose. 



6 This washing may be conveniently done by Recantation if desired, thus retaining the 

 major portion of the precipitate in the flask. 



