SALICYLIC ACID AND SALIC YLATES. 723 



URIC ACID DETERMINATIONS (FOLIN's MODIFICATION OF HOPKINS'S METHOD)." 



In order to precipitate the uric acid and to remove the small amount 

 of mucoid substance which is always present the following reagent is 

 employed: 500 grams of ammonium sulphate and 5 grams of uranium 

 acetate are dissolved in 650 cc of water, to which 60 cc of a 10 per 

 cent solution of acetic acid are further added. 



Seventy -five cubic centimeters of this reagent are added to 300 cc of 

 urine. After standing five minutes the mixture is filtered through 

 two folded filters, the filtrate is divided into two portions of 125 cc 

 each, representing 100 cc of the original sample, and /) cc of concen- 

 trated ammonia added. The solution, after stirring, is set aside until 

 the next day. 



The precipitated ammonium urate settles to the bottom of the 

 beaker during this time. The supernatant liquid is poured through a 

 filter (Schleicher and Schull, No. 575), a hardened filter being found 

 the most serviceable, and the precipitate is collected and washed by a 

 small amount of a 10 per cent solution of ammonium sulphate. 



After washing three or four times on the filter with the 10 per cent 

 ammonium sulphate solution the precipitate is washed back into the 

 same beaker in which the precipitation was made, using about 100 cc of 

 water. Fifteen cubic centimeters of concentrated sulphuric acid are 

 then added and the solution titrated immediately with one-twentieth 

 normal potassium permanganate. The first trace of a rose color 

 throughout the entire fluid is taken as the end point. Each cubic 

 centimeter of the standard permanganate N/20 is equivalent to 

 0.00375 gram of uric acid. Owing to the solubility of ammonium 

 urate, a final correction of 0.003 gram for each 100 cc of urine 

 employed is necessary. 



KREATININ DETERMINATIONS (FOLIN's METHOD). & 



In this work kreatin was determined along with and calculated as 

 kreatinin. The method is based on the reaction of kreatinin with 

 alkaline picric acid solution. The red colored solution produced by 

 this reaction has, when in proper dilution, the same shade of color as 

 potassium bichromate solution. 



The solutions required are: Half normal potassium bichromate; 10 

 per cent caustic soda; saturated (1.2 per cent) picric acid solution and 

 normal hydrochloric acid where kreatin and kreatinin are determined 

 together. 



The determination is carried out in the following manner: Ten cc 

 of urine are placed in a 500 cc graduated flask, 5 cc of normal h} T dro- 

 chloric acid added and the mixture heated on the water bath for three 



Zts. physiol. Chem., 22 : 552. & Zts. physiol. Chem., 1904, 41 : 223. 



