URINE 531 



Procedure. 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 (silver lactate 5 per cent., lactic acid 5 per cent) and stir with a 

 fine glass rod. Rinse the rod with a few drops of water. Centrifuge the 

 counterbalanced tube for 2-3 minutes. Add a drop of silver lactate solution 

 so as to be sure that 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 buret, 4 c.c. of a 5 per 

 cent sodium cyanide solution (poisonous 3 c.c. may be fatal dose). Stir the 

 mixture until a perfectly clear solution is formed. Rinse the stirring rod, collect- 

 ing the rinsings in a 100 c.c. volumetric flask ; pour the contents of the tube into 

 the same flask and rinse the tube 3 times with about 5 c.c. of 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 1 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 2 to each flask and 

 finally add with shaking 2 c.c. of the uric acid reagent. 3 Let stand 3-5 minutes, 

 fill to the mark, mix and compare the two colored solutions in a colorimeter. 



Calculation. Since the standard is 0.5 mg., if the standard is set at 20 mm. 

 divide 10 by the reading of the unknown (in mm.) to obtain the amount of uric 

 acid (in mg.) in the amount of urine taken. 



Interpretation. For adults on a mixed diet the average excretion of 

 uric acid is about 0.7 gram. It arises from the purines of ingested food 

 (exogenous uric acid) and from purines. derived from the body tissues 

 by disintegration of nuclein material (endogenous uric acid). Exoge- 

 nous uric acid depending entirely upon the diet is greatly increased 

 by the ingestion of purine-rich foods (meat, liver, sweetbreads, etc.) and 

 reduced to a very low level on purine-free foods, e.g., milk, eggs, etc. 

 (see Chapter XXVIII) . Endogenous uric acid is influenced by exercise 

 and by the diet (protein foods particularly giving rise to increases). 

 It appears to be partly the result of gastro-intestinal secretory activity. 

 On a purine-free diet the average excretion is 0.1-0.5 gram. On a high 

 purine diet the uric acid output may be 2 grams per day. 



1 Preparation of Standard Uric Acid Solution. In a 500 c.c. flask dissolve exactly i g 

 of uric acid in 150 c.c. of water by the help of 0.5 g. lithium carbonate. Dilute to 500 c.c. 

 and mix. Transfer 50 c.c. to a liter flask, add 500 c.c. of 20 per cent sodium sulphite 

 solution, dilute to volume and mix. Each c.c. of this solution is then "equal to o.i mg. of 

 uric acid. Transfer to small bottles (cap. 200 c.c.) and stopper tightly. This standard 

 uric acid solution keeps almost indefinitely in unopened bottles, because the sulphite pre- 

 vents the spontaneous oxidation of the uric acid. In used bottles the standard usually 

 remains good for 2-3 months. 



2 Sodium Carbonate Solution. Dissolve 200 grams of anhydrous sodium carbonate in 

 warm water, cool and dilute to i liter. 



Preparation of Uric Acid Reagent. Introduce into a.flask 700 c.c. of water, 100 g. 

 of sodium tungstate, and 80 c.c. of phosphoric acid (85 per cent HsPO^. Partly close 

 the rnguth of the flask with a funnel and a small watch glass and boil gently for 2 hours. 

 Dilute to i liter. 



