URIC ACID, CREATINE, CREATININE, AND ALLANTOIN 241 



sodium tungstate in 600 ml. water. Add 50 g. pm'e arsenic pent- 

 oxide followed by 25 ml. 85% phosphoric acid and 20 ml. cone, 

 hydrochloric acid. Boil for 20 min., cool, and dilute to 1 liter. 

 Folin's Stock Uric Acid Standard Soln. Place 1 g. uric acid, weighed 

 to 1 mg., in a 1 1. volumetric flask. Add 150 ml. water to 0.6 g. 

 lithium carbonate in a 250 ml. flask and shake until dissolved. 

 Filter, and heat the filtrate to 60°. Warm the flask containing the 

 uric acid in running hot water and pour the warm lithium carbon- 

 ate soln. into the volumetric flask containing the uric acid; wash 

 down crystals adhering to the neck. Shake until the uric acid has 

 dissolved (about 5 min.), cool under the tap, add 20 ml. 40% 

 formaldehyde, and half fill the flask with water. Add a few drops 

 of methyl orange and then pipette in slovdy, with shaking, 25 ml. 

 1 A^ sulfuric acid. Dilute the pink soln. to 1 1. Store the reagent in 

 v/ell-stoppered bottles and keep in the dark. Diluted standards 

 made from this soln. will keep for several days, but do not use 

 them sooner than 1 hr. after they are made. 



PROCEDURE 



1. Pipette 1-2 ml. of sample, 1 ml. water, and 0.05 ml. 2.5% 

 zinc chloride into a Pyrex test tube ( 125 X 9 mm. inside) provided 

 with a ground-glass stopper. Mix well by inversion several times. 



2. Add 0.4 ml. 10% sodium carbonate and again mix by inver- 

 sion. 



3. Centrifuge the test tube, pour ofT the supernatant, and take 

 up the last drop from the lip of the tube with filter paper. 



4. Add 0.5 ml. N/14: hydrochloric acid, 1.5 ml. water, and 1 ml. 

 cyanide soln. 



5. Stopper the tube and shake well to dissolve all precipitate 

 and leave a clear colorless soln. 



6. Add 0.2 ml. arsenophosphotungstate soln. and again mix well 

 by inversion. 



7. Place the stoppered tube in a 37° water bath for 40 min., and 

 then in an ice water bath for 15 min. 



8. Centrifuge, transfer some of the supernatant to an absorption 

 cell, and determine the color spectrophotometrically at 610 mix. 



9. In a parallel manner, treat four standard solns. covering the 

 range to 1.0 milligram per cent uric acid in order to obtain a 

 calibration. 



