168 PHYSIOLOGY OF PURIN METABOLISM 



tives has been directly observed in experiments with tissue 

 pulp. 60 



Quantitative Estimation of Uric Acid. In concluding 

 the present lecture a few words may be devoted to enumera- 

 tion of recent advances in the analysis of the urinary 

 purins. 



Besides the time-honored method of E. Ludwig and 

 Salkowski, which, as is well known, depends upon precipitat- 

 ing the uric acid by magnesia mixture and ammoniacal silver 

 solution, the method of Hopkins has met with the most 

 popularity. In the latter the uric acid is thrown down by 

 ammonia and ammonium chloride as ammonium urate. The 

 uric acid, freed from the urate by hydrochloric acid, may be 

 weighed or determined by the Kjeldahl method. Folin and 

 Schaffer have modified this method, by titration of the acid 

 in sulphuric acid solution with permanganate. According 

 to Bonchese the uric acid separated by the Hopkins method 

 may readily be titrated with a solution of iodine in an 

 alkaline medium, employing starch paste as an indicator. 61 

 Kowarski 62 proposes to free the uric acid from the urate of 

 ammonium precipitated as in the Hopkins method, by means 

 of hydrochloric acid, then to wash with water and alcohol 

 until the reaction becomes neutral, and finally to titrate with 

 n/50 piperidin solution against phenolphthalein. According 

 to Kriiger and Schmid 63 precipitation of uric acid and the 

 purin bases with copper sulphate and acid sulphite of sodium 

 has proved useful; after breaking up the precipitate with 

 sodium sulphide the uric acid may be caused to crystallize 

 out by rendering the solution acid with sulphuric acid; by 

 which means it may be separated from the purin bases. 

 His's method of uric acid estimation consists in acidifying 



w Brugsch, Pincussohn and Schittenhelm, cited in Handb. d. Biochem., 

 4', 528; Y. Kotake, Zeitschr. f. physiol. Chem., 57, 378, 1909; J. Schmid 

 (Breslau), ibid., 67, 155, 1910. 



A. Ronchfcse, C. R. Soc. de Biol., 60, 504, 1906. 



61 A. Kowarski, Deutsche med. Wochenschr., 1906, 997. 



68 J. Kruger and J. Schmid, Zeitschr. f . physiol. Chem., 45, I, 1905. 



