342 ANALYSIS OF URINE. fCH. XIII. 



The uric acid is rapidly and quantitatively precipitated as ammonium urate. 

 This is filtered off, washed with ammonium sulphate to remove the greater 

 part of the chlorides, dissolved in hot sulphuric acid and titrated with standard 

 potassium permanganate. The end point is reached when a momentary pink 

 flush is seen over the whole body of the fluid. This marks a stage when the 

 rate of oxidation of the uric acid suddenly decreases. Up to this point i cc. 

 of 0-05 N. permanganate is found empirically to correspond to 3-7 mg. of uric 

 acid. The chemical changes involved in the oxidation have not yet been 

 determined. 



Solutions and reagents required. 

 (i.) Colloidal (dialysed) iron, 0-6 per cent, 

 (ii.) Pure, dry, recrystallised ammonium chloride. 



(lii.) Washing fluid. 100 grams, of pure ammonium sulphate are dissolved 

 in about 800 cc. of distilled water, 10 cc. of strong ammonia are added 

 and the volume made up to i litre with water. It is convenient 

 to use this from a wash bottle with a fine jet. 



(iv.) 45 per cent, sulphuric acid (by volume) . To 500 cc. of distilled water in 

 a large flask cautiously add 450 cc. of pure concentrated sulphuric 

 acid, cooling at intervals. Cool thoroughly under the tap and 

 make up the volume to 1,000 cc. 



(v.) 0-05 N. potassium permanganate. Dissolve 1-58 gram, of the pure 

 salt in distilled water and make the volume up to 1,000 cc. Care 

 must be taken to see that the whole of the solid has dissolved before 

 the solution is used. It can be titrated against pure ammonium 

 oxalate as described on p. 132. If Ox. be the weight of the oxalate 

 taken in grams, (about 0-15) and P the volume of permanganate 



required, then the normality is p x O-O7IOS = Pn ' 



i cc. of 0-05 N. permanganate "3-7 mgms. uric acid. 



_ 3-7 x Pn 

 i cc. of PnN. permanganate ^7 mgms. 



Method. Measure 1 50 cc. of the urine into a 200 cc. beaker, 

 marking the 100 cc. level by means of a label. Add 30 cc. of the 

 colloidal iron, stirring well during the addition. Filter through two 

 dry papers into two dry flasks (two being used to save time) . When 

 at least 100 cc. of the nitrate has been collected, carefully measure 

 the amount taken and transfer it to the marked beaker, which has 

 been previously washed and drained. It is convenient to take 100 cc. 

 but with dilute urines it is better to take 120 or 150 cc. For every 

 10 cc, of the filtrate taken weigh out 2 grams, of the solid ammonium 

 chloride ; add this to the beaker and stir well. When it has dis- 

 solved add 3 cc. of concentrated ammonia and stir again. Stir at 

 intervals for 20 minutes, then remove the rod and let it rest on the 

 rim of the beaker. When the bulk of the precipitate has settled 



