ESTIMATION OF URIC ACID. 711 



the same beaker by the aid of a glass rod and a wash-bottle, without 

 destroying the filter. Now heat to boiling 10-20 cc. of the alkali- sulphide 

 solution, which has previously been diluted with an equal volume of 

 water, and allow this solution to flow through the above filter into the 

 beaker containing the silver precipitate; wash with boiling water, and 

 warm the contents of the beaker on a water-bath for a time, stirring 

 constantly. After cooling, filter into a porcelain dish, wash the filter 

 with boiling water, acidify the filtrate with hydrochloric acid, evaporate 

 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. According to 

 SALKOWSKI and KASHIWABARA 1 the precipitation with zinc salts can also 

 be used in the estimation of uric acid. 



Hopkins' methcd 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. 2 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 



1 Zeitschr. f. physiol. Chem., 4. 



, 8 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. 



