52 METHODS FOR THE ANALYSIS OF URINE 



reagent gives to uric acid an intense color, the depth of which is 

 compared with the standard solution of uric acid also treated with 

 this reagent. 



Solutions needed. 1. Standard uric acid solution. Before 

 starting to prepare the uric acid solution a 20 per cent filtered 

 solution of sodium sulphite should be available. Dissolve 1 gm. 

 of uric acid in a 125 to 150 c.c. of 0.4 per cent lithium carbonate 

 solution and dilute to a volume of 500 c.c. Transfer 50 c.c. 

 corresponding to 100 mg. of uric acid, to each of a series of volu- 

 metric liter flasks. Add about 300 c.c. of water and then add 

 500 c.c. of clear 20 per cent sodium sulphite solution, mix, dilute 

 to volume, and mix thoroughly. Fill a series of 200 c.c. bottles, 

 and stopper very tightly. The reason why a series of small 

 bottles is used as containers is, of course, to reduce the absorption 

 of oxygen from the air. 



2. A 10 per cent sodium sulphite solution, kept like the uric 

 acid solution, in small tightly stoppered bottles. 



3. A 5 per cent sodium cyanide solution. 



4. A solution containing 5 per cent of silver lactate and 5 

 per cent of lactic acid. 



5. The uric acid reagent of Folin and Denis. To prepare 

 this boil 100 gms. of sodium tungstate with 80 c.c. of phosphoric 

 acid (85 per cent) and 700 c.c. of water, for not less than two 

 hours, and dilute to 1 liter. 



Procedure. Transfer from 1 to 3 c.c. of urine to a 15 c.c. 

 centrifuge tube and mix with enough water to make a volume 

 of about 6 c.c. Add 5 c.c. of the acid silver lactate solution and 

 stir with a very fine glass rod (diameter 1 to 2 mm.), rinse off 

 the rod with a few drops of water and centrifuge. If enough silver 

 solution has been added the precipitate settles very quickly. Add 

 a drop of silver lactate solution so as to be certain that an excess 

 is present; if a precipitate forms add more (2 c.c.) of the silver 

 lactate solution and centrifuge again. In point of fact the first 

 5 c.c. addition of silver lactate is usually sufficient but it is not 

 safe to omit the test. Pour off the clear supernatant liquid as 

 completely as possible. 



To the precipitate in the centrifuge tube add, from a burette, 

 4 c.c. of 5 per cent sodium cyanide solution, and stir until a per- 

 fectly clear solution is obtained. Pour the contents into a 100 c.c. 

 volumetric flask and rinse the tube and stirring rod, using for this 



