ANALYSIS OF URINE 561 



Estimation of Uric Acid. 



The estimation of uric acid is effected by colorimetric comparison with a 

 standard solution treated in the same way. The uric acid is isolated from 

 urine by either of the methods (a) or (b) : 



(a) After Evaporation. 



2-5 c.c. of urine are measured into a TOO c.c. beaker, a drop of 

 saturated oxalic acid solution is added and they are carefully evaporated to 

 dryness on a water-bath or over a free flame. The evaporation is continued 

 until the upper parts of the beaker are dry. 



10-15 c - c - f a mixture of 2 parts of pure ether and i part of methyl 

 alcohol are added to the dry residue. After 5 minutes they are carefully 

 poured off and another 10 c.c. of the mixture added; they are poured off 

 when the insoluble matter has settled. This mixture dissolves the phenols, 

 but leaves the uric acid. There are two slight errors which balance them- 

 selves : the uric acid is not absolutely insoluble and the phenolic substances 

 are not entirely removed if there are large residues from the urine. 



For ordinary routine work 90 per cent, alcohol may be used. 



5-10 c.c. of water and a drop of saturated sodium carbonate solution are 

 added to the washed residue which is stirred till it passes into solution. 



2 c.c. of the reagent + 20 c.c. of saturated sodium carbonate solution are 

 added. The blue solution after 15- minutes is transferred to a 100 c.c. 

 measuring flask and diluted to the mark. 



At the same time the number of c.c. of the uric acid standard, containing 

 i mgm. of uric acid, is treated with 2 c.c. of reagent and 20 c.c. of carbonate 

 solution and transferred to a 100 c.c. flask after 15 minutes. 



This standard will serve for several estimations which are carried out at the 

 same time. 



(ft) By Precipitation. 



i or 2 c.c. of urine are measured into a centrifuge tube with a Ost- 

 wald pipette and water is added to make the volume = 5 c.c. : 6 drops of 

 3 per cent, silver lactate solution, 2 drops of magnesia mixture and 10-20 

 drops of -880 ammonia (to dissolve silver chloride) are added. The tubes are 

 centrifuged for 1-2 minutes at 2000 revolutions. The supernatant liquid is 

 poured off and to the precipitate are added 6 drops of fresh saturated hydrogen 

 sulphide solution and a drop of concentrated hydrochloric acid. The tube is 

 placed in a boiling water-bath until the hydrogen sulphide has disappeared. 

 This may be tested for by adding a drop of lead acetate solution after 5 minutes. 

 The heating is continued if hydrogen sulphide be present. The tube is 

 allowed to cool and 2 c.c. of reagent and 20 c.c. of saturated sodium 

 carbonate solution are added. After 15 minutes the solution is transferred to 

 a 50 c.c. flask and diluted to the mark. 



A standard with i mgm. of uric acid is prepared at the same time. 



If the urine contain albumin, there is a brown colour after adding the 

 hydrogen sulphide. After removing the gas, 2 or 10 drops of 10 per cent 

 acetic acid are added to the hot solution to remove it. 



