THE JOURNAI. OF PHARMACOLOGY. 203 



If carefully executed this method yields very trustworthy results. 

 J, Method of Hay craft [titrimetric.) 



This method is based on the principle that uric acid in the presence of 

 magnesium salts is precipitated by ammoniacal silver nitrate, i molecule 

 of uric acid corresponding to i atom of silver. 



The quantity of silver used is ascertained by titrating back with solution 

 of ammonium or potassium sulphocyanate. 



From the quantity so used the quantity of uric acid is calculated. 



If albumin is present it must be first removed. 



Sohitions required : 



' {a) Ammoniacal solution of silver nitrate : 



{b) Magnesia mixture : These may be the same as those employed in 

 the Salkowski-Ludwig method. 



[c) Jq or y^o normal solution of ammonium or potassium sulphocyanate, 

 which has been carefully standardized with solution of silver nitrate of 

 the same strength. 



Execution of the method (modification of Herrmann) : 50 cubic centi- 

 meters of urine are decomposed with 5 cubic centimeters each of ammoni- 

 acal silver nitrate solution and magnesia mixture. Allow the precipitate 

 which forms to settle and decant the clear liquid upon a filter. Then dis- 

 tribute 4 grammes of sodium bicarbonate (in coarse powder) upon the sur- 

 face of the filter and transfer the entire precipitate to the filter. Now wash 

 with water to which a small quantity of ammonia water has been added, 

 until the washings are free from chlorides and silver. The precipitate on 

 the filter is then dissolved by means of 20-30 per cent, nitric acid, and the 

 filter well washed with water, incorporating the washings with the filtrate. 

 The combined liquids are then titrated with 5V or y^^ normal solution of 

 ammonium or potassium sulphocyanate in the same manner as indicated 

 under chlorides. 



I Cc. 5V KCNS or NH4CNS v.s. =0.00336 uric acid 

 I Cc. y^o KCNS or NH4CNS v.s. =0.00168 uric acid. 



The results obtained by this method are usually high. 



^. Method of Czapek. 



This method is very similar to that of Haycraft. Instead of, as in the 

 latter method, estimating the silver in the precipitate, the silver in the fil- 

 trate is estimated. The quantity so found is deducted from the total 

 quantity of silver used. The difference represents the quantity of silver in 

 combination with uric acid. 



High results are the rule with this method. 



Albumin if present must first be removed. 



