512 PHYSIOLOGICAL CHEMISTRY 



treatment with an ammonium sulphate-uranium acetate solution is for 

 the purpose of removing interfering organic substances. The method 

 gives accurate results. 



Procedure. Introduce 100 c.c. 1 of urine into an Erlenmeyer flask, add 

 25 c.c. of the Folin-Shaffer reagent 2 and after shaking the flask to thoroughly 

 mix the fluids allow the mixture to stand, 3 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 ammo- 

 nium urate quantitatively to a filter paper, 4 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, 5 remove the paper from the funnel, open it, and by means of hot water 

 rinse the precipitate 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 O 8 , 

 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/2O potassium permanganate solu- 

 tion 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 

 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 : 



yXo.oo375 = weight of uric acid in 100 c.c. of urine. 



Because of the solubility of the ammonium urate a correction of 3 mg. should 

 be added to the final result. 



Calculate the quantity of uric acid in the 24-hour urine specimen. 



4. Heintz Method. This is a very simple method and was the first one in 

 general use for the quantitative determination of uric acid. It is less accurate than 

 the methods just described. The procedure is as follows: Place 100 c.c. of filtered 

 urine in a beaker, add 5 c.c. of concentrated hydrochloric acid, stir the fluid thor- 

 oughly, and stand it away in a cool place for 24 hours. Filter off the uric acid 

 crystals upon a washed, dried and weighed filter paper and wash them with cold 

 distilled water, a few cubic centimeters at a time, until the chlorides are removed. 



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

 than i. 020. 



2 The Folin-Shaffer reagent consists of 500 grams cf 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. 



4 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 decantation if desired, thus retaining the 

 major portion of the precipitate in the flask. 



