ADVANCED CHEMICAL PHYSIOLOGY 283 



The uranium precipitate has then settled and the clear supernatant fluid 

 may be removed by decantation (filtration if necessary). 100 c.c. 

 ( = 80 c.c. urine) of this fluid is measured into a beaker, 5 c.c. of strong 

 ammonia added, and the mixture allowed to stand overnight. The 

 precipitate is then filtered off, washed with 10 per cent, ammonium 

 sulphate solution until chloride free. The filter paper is removed from the 

 funnel, unfolded, and the precipitate washed back into the beaker with 

 water, the filter paper and enough water to make about 100 c.c. added. 

 The precipitate is now dissolved by the addition of 15 c.c. concentrated 



N 



H 2 SO 4 and at once, whilst warm, titrated with ^n potassium per- 

 manganate solution. The end point is the first appearance of a 

 permanent pink colour. (Note this colour will disappear within about 

 half a minute.) 



N 

 1 c.c. -oTT potassium permanganate = 3-75 mgms. uric acid. 



A correction of + 24 mgms., due to the solubility of ammonium urate, 

 is added to the result. 



Folin and Wu Colorimetric Method. Transfer 1-3 c.c. of urine, 

 according to concentration, to a centrifuge tube and add water to a 

 volume of about 6 c.c. Add 5 c.c. of a silver lactate solution (5 per cent, 

 silver lactate and 5 per cent, lactic acid) and stir with a fine glass rod. 

 Rinse off the rod with a few drops of water. Centrifuge hard for two to 

 three minutes. Add a drop of silver lactate solution to make sure an 

 excess is present ; if a precipitate (of AgCl) is formed add 2 c.c. more of 

 the silver solution and centrifuge again ; if no precipitate forms pour off 

 the liquid as completely as possible. 



To the precipitate in the centrifuge tube add, from a burette, as it is 

 very poisonous, 4 c.c. of a 5 per cent, sodium cyanide solution. Stir the 

 mixture until the precipitate is completely dissolved. Rinse the stirring 

 rod, collecting the rinsings in a 100 c.c. graduated flask ; pour the 

 contents of the centrifuge tube into the same flask and rinse the tube 

 three times with about 5 c.c. water. Add 5 c.c. of a 10 per cent, sodium 

 sulphite solution (to balance the sulphite in the standard uric acid 

 solution) and dilute to a volume of about 40 c.c. In another 100 c.c. 

 flask place 5 c.c. of a standard uric acid sulphite solution containing 

 0-5 mg. of uric acid ; add 4 c.c. of cyanide solution and about 35 c.c. of 

 water. Then add 20 c.c. of 20 per cent, sodium carbonate solution to 

 each flask and finally add with shaking 2 c.c. of the uric acid phospho- 

 tungstic reagent. 1 Allow to stand three to five minutes, fill to the 

 mark and mix. 



Set the standard uric acid solution at 20 mm. in both colorimeter cups 

 and adjust the colorimeter until the two fields are exactly alike. Then 

 empty one of the cups, rinse it out with the urine sample to be tested, fill 

 and compare against the standard uric acid solution. 



Calculation : Since the standard is only 0-5 mg., 10 divided by the 

 reading of the unknown (in mm.) gives the amount of uric acid (in mg.) 

 in the volume of urine taken. 



Be careful to pour the discarded blue uric acid cyanide mixtures 



1 Preparation of uric acid reagent. Into a litre flask introduce 750 c.c. 

 water, 100 gms. sodium tungstate and 80 c.c. phosphoric acid (85 per cent. 

 H 3 PO 4 ). Put a small funnel with a watch glass in the mouth of the flask 

 to act as a condenser, then boil gently for two hours. Cool and dilute to 

 1,000 c.c. 



