THE URINE. 191 



for the solubility of the uric acid; however, this is permissible 

 only when the quantity of uric acid is not abnormally small 

 and the quantity of the filtrate and wash-water does not 

 exceed 60 cc. It is customary to add 0.5 mg. of uric acid 

 for every 10 cc. of the filtrate plus the wash- water. The 

 product of the amount obtained by 0.75 gives the percentage 

 of uric acid in the urine. 



The above-described method, though exact, is undeniably 

 involved and somewhat difficult to carry out. The Hop- 

 kins method, in which the uric acid is precipitated as the 

 ammonium salt and then titrated, gives apparently just as 

 exact results. According to Folin 1 the following is the best 

 procedure : 



To 100 cc. of the urine (according to Worner it is best to 

 heat the urine previously to 40-45 C.) add 20 to 30 g. of 

 powdered ammonium chloride or 30 g. of ammonium sulphate, 

 and dissolve this by shaking. Filter off the precipitate after 

 two hours and wash free from chlorine with a concentrated 

 solution of ammonium sulphate and rinse into a flask with 

 hot water. When cold add 15 cc. of concentrated sulphuric 

 acid and titrate to a permanent rose-color with one-twen- 

 tieth normal potassium permanganate solution (1.581 g. 

 potassium permanganate to one liter; the solution is to be 

 tested as to its correctness with one-twentieth normal oxalic 

 acid or with iron ammonium sulphate). The temperature 

 of the fluid titrated should be 60 to 63. If it is higher, 

 wait until it cools to this temperature. The number of cubic 

 centimeters of potassium permanganate used multiplied by 

 3.75 2 gives the quantity of the uric acid in milligrams. 



Worner 3 recommends the following procedure for the 

 determination: 150 cc. of the urine are heated in a beaker 



1 Zeitschr. f. physiol. Chemie, 24, 224. 



2 Ibid. 



3 Ibid. 29, 70. 



