9-1- Mr. F. G. Hopkins. [June 16, 



It lias long been known that ammonia, and salts of ammonia, will, 

 after long standing, so completely precipitate the uric acid from 

 urine that subsequent treatment with acids produces no further pre- 

 cipitate (Wetzlar, ' Beitrage zur Kenntniss des menschlichen 

 Haras,' Frankfurt a.M. 1821, p. 19). Fokker, moreover, observed 

 that when a solution of any urate is made alkaline, and then mixed 

 with a solution of ammonium chloride, the uric acid slowly separates 

 out as the biurate of ammonia. Upon this observation the well- 

 known Fokker- Salkowski process is based. 



But the crucial fact that saturation with the ammonium chloride 

 renders the separation rapid and absolutely complete does not seem 

 to have been previously observed. The importance of this fact in 

 any attempt to estimate uric acid by means of its separation as 

 ammonium urate will be seen when it is remembered that, hitherto, 

 in all such processes a large correction has to be made to allow for 

 incomplete separation, even after long standing. In the Fokker- 

 Salkowski process, for instance, the factor which has to be added to 

 the result amounts to, at least, 25 per cent, of the total variable dealt 

 with, a necessity which would seem to render the process of little 

 scientific value (vide Fokker, Pfluger's 'Archiv,' vol. 10, p. 157, 

 1875; Salkowski, Virchow's ' Archiv,' vol. 68, p. 401, 1876). In 

 the method about to be described no such correction is necessary. 



The following experiments with pure urates will show the complete 

 separation of ammonium urate which occurs after saturation with the 

 chloride. 



In each case pure uric acid, prepared by means of the sulphate, 

 was used. The ammonium salt precipitated was decomposed by 

 means of HC1, and the uric acid subsequently washed and weighed, 

 due allowance being made for washings : 



Uric acid 

 recovered. 



(1.) One decigramme of uric acid dissolved in 

 ammonia, solution made up to 250 c.c., 

 saturated with ammonium chloride, and 

 filtered after 30 minutes 0'0994 



(2.) Fifty milligrammes dissolved as above 

 and made up to 150 c.c. Filtered after 

 15 minutes 0'0502 



(3.) One decigramme dissolved in Na 2 Co 3 , 

 solution made up to 100 c.c. Filtered 

 after 3 hours 0*0986 



(4.) One decigramme dissolved as in (3). 



Filtered after 4 hours 0'0990 



The presence of excess of bases, other than ammonia, delays the 



