ESTIMATION OF URIC ACID. 675 



it to .about 15 cc., add a few drops more of hydrochloric acid, and allow 

 it to stand for twenty-four hours. The uric acid which has crystallized 

 is collected on a small weighed filter, washed with water, alcohol, ether, 

 and carbon disulphide, dried at 100-110 C., and weighed. For each 

 10 cc. of aqueous filtrate we must add 0.00048 gram uric acid to the 

 quantity found directly. Instead of the weighed filter-paper a glass 

 tube filled with glass wool as described in other handbooks may be sub- 

 stituted (LUDWIG). Too intense or too long continued heating with 

 the alkali sulphide must be prevented, otherwise a part of the uric acid 

 may be decomposed. 



SALKOWSKI deviates from this procedure by first precipitating the 

 urine with a magnesium mixture (50 cc. to 200 cc. urine), filling up to 

 300 cc., and filtering. Of the filtrate, 200 cc. are precipitated by 10-15 

 cc. of a 3-per cent silver-nitrate solution. The silver precipitate is shaken 

 with 200-300 cc. of water acidified with a few drops of hydrochloric 

 acid, decomposed by sulphuretted hydrogen, heated to boiling, the 

 silver-sulphide precipitate boiled with fresh water, filtered, the filtrate 

 concentrated to a few cubic centimeters, treated with 5-8 drops of hydro- 

 chloric acid, and allowed to stand until the next day. 



HOPKINS' method is based on the fact that the uric acid is com- 

 pletely precipitated from the urine as ammonium urate on saturating 

 with ammonium chloride. The uric acid can either be weighed after 

 being set free by hydrochloric acid or it can be determined in several 

 ways by titration with potassium permanganate or by the KJELDAHL* 

 method. Several modifications of this method have been worked out 

 by FOLIN, FOLIN and SCHAFFER, WORNER, and JoLLES. 1 The last 

 named converts the uric acid into urea by oxidation with potassium 

 permanganate in sulphuric-acid solution and then determines the quan- 

 tity of this by sodium hypobromite. Of these methods we shall describe 

 only that suggested by FOLIN-SCHAFFER. 



Folin-Schaffer Method. Treat 300 cc. urine with 75 cc. of a solu- 

 tion containing 500 grams of ammonium sulphate, 5 grams of uranium 

 acetate, and 60 cc. of 10-per cent acetic acid in a liter, and filter after 

 five minutes. This removes an unknown constituent of the urine (a 

 protein substance) which would otherwise contaminate the uric acid. 

 Take 125 cc. of the filtrate (corresponding to 100 cc. of the urine) and 

 add 5 cc. of concentrated ammonia. After twenty-four hours the pre- 

 cipitate is filtered off and washed free from chlorine on the filter by means 

 of an ammonium-sulphate solution. The precipitate is washed off the 

 filter b}^ water (total 100 cc.) into a flask, treated with 15 cc. of con- 

 centrated sulphuric acid, and titrated at 60-63 C. with N/20 potassium- 

 permanganate solution. Each cubic centimeter of this solution cor- 

 responds to 3.75 milligrams uric acid. Because of the solubility of the 

 ammonium urate a correction of 3 milligrams must be added for every 

 100 cc. of the urine. 



In regard to the numerous other methods for estimating uric acid, 

 we must refer to special works on the subject, and especially to HUPPERT- 

 NEUBAUER. 



1 Hopkins, Journ. of Path, and Bact., 1893, and Proceed. Roy. Soc., 52; Folin,. 

 Zeitschr. f. physiol. Chem., 24; Folin and Schaffer, ibid., 32; Worner, ibid., 29; Jolles, 

 ibid., 29, and Wien. med. Wochenschr., 1903. 



