URIC ACID 99 



running water, and add 2 c.c. 1 of colloidal iron solution (Merck's 

 " Dialyzed Iron," 5 per cent solution) while the flask is being 

 gently rotated. Filter the mixture through a small folded filter 

 into a 100 c.c. Jena Florence flask, and wash the residue twice 

 with distilled water. The filtrate obtained here should be as clear 

 and colorless as distilled water. Boil the solution down to a volume 

 of from 1 to 2 c.c. (care being taken in the early stages to prevent 

 bumping), then carefully pour into a small centrifuge tube and 

 wash out the flask with three portions of water (1 or 2 c.c. each), 

 heating each to boiling in the flask and shaking thoroughly prior 

 to transferring it to the centrifuge tube. The volume of liquid 

 in the tube at this point should be from 5 to 10 c.c. Cool the 

 liquid, add 20 drops of the ammoniacal silver magnesium solution. 

 Mix the contents of the tube with a small stirring rod and centri- 

 fuge the tube for one or two minutes. Pour off the supernatant 

 liquid, as completely as possible, by inverting the tube, allowing 

 it to drain a moment, and then touching the inside of the lip of 

 the tube with a towel or piece of filter paper. Add to the residue 

 in the tube two drops of a 5 per cent solution of potassium cyanide 

 to dissolve the silver urate, stir the mixture thoroughly with a 

 thin rod, for half a minute, add a few drops (0.5 to 1.0 c.c.) of 

 water, and stir again. 2 Two c.c. of the uric acid reagent are 

 added and the mixture stirred again, after which 3 add 10 c.c. 

 of 20 per cent sodium carbonate solution, transfer quantitatively 

 to a 50 c.c. flask, and at the end of about one -half minute, dilute 

 to mark. Compare this solution in the Duboscq colorimeter with 

 a simultaneously prepared solution obtained by treating 5 c.c. of 

 the standard uric acid solution, contained in a 50 c.c. flask, with 

 2 drops of the potassium cyanide solution, 2 c.c. of the uric acid 



1 With old samples of blood it may be necessary to add 3 or 4 c.c. of the 

 iron solution and a little 10 per cent sodium chloride solution. When the 

 precipitate separates in large flocculent masses the right amount of iron has 

 been added. Any excess of iron must be avoided, as it would oxidize some 

 of the uric acid later on in the process. 



2 At this point perfectly clear solutions are obtained with pure uric acid 

 solutions in phosphate mixture or in pyridin. With urines some magnesium 

 ammonium phosphate is precipitated with the uric acid, which does not 

 dissolve in the cyanide. After adding the two subsequent reagents, however, 

 a perfectly clear solution is obtained. 



3 Bogert (Jour. Biol. Chem., 1917, 31, 1651 advocates transferring the 

 mixture to the volumetric flask by washing with 20 to 30 c.c. of water before 

 adding the sodium carbonate, as a means of preventing turbidity. 



