PURINE BASES 63 



purpose about 15 to 25 c.c. of water. Add 5 c.c. of 10 per cent 

 sodium sulphite solution (to balance the sulphite in the standard 

 uric acid solution). Dilute to a volume of about 50 c.c. 



Transfer to another 100 c.c. flask 5 c.c. of the standard uric 

 acid sulphite solution, containing 0.5 mg. uric acid. Add 4 c.c. 

 of the cyanide solution from a burette and dilute to about 50 c.c. 

 Then add 20 c.c. of saturated sodium carbonate solution to each 

 flask, mix, and finally add with shaking, 2 c.c. of the uric acid 

 reagent. Let stand for three to five minutes, fill to the mark, 

 mix, and make the color comparison in the usual manner, never 

 omitting to first read the standard against itself. Artificial light 

 (with "daylite" glass) is better than daylight for this color com- 

 parison. 



Calculation. With the standard set at 20 mm., 10 divided 

 by the reading of the unknown (in mm.) gives the amount of 

 uric acid (in mg.) in the volume of urine taken. 



Remarks. The discarded blue solution should be poured as 

 directly as possible into the drain of sinks on account of the cyanide. 



PURINE BASES 



Kriiger and Schmidt's Method 1 



Principle. This method serves for the determination of both 

 uric acid and the purine bases. The principle involved is the 

 precipitation of both the uric acid and the purine bases in com- 

 bination with copper oxide and the subsequent decomposition of 

 this precipitate by means of sodium sulphide. The uric acid is 

 then precipitated by means of hydrochloric acid and the purine 

 bases are separated from the filtrate in the form of their copper 

 or silver compounds. The nitrogen content of the precipitates 

 of uric acid and purine bases is then determined by means of the 

 Kjeldahl method (see page 33) and the corresponding values for 

 uric acid and purine bases calculated. 



Procedure. To 400 c.c. of albumin-free urine in a liter flask, 

 add 24 gms. of sodium acetate, 40 c.c. of a solution of sodium 

 bisulphite, and heat the mixture to boiling. Add 40 to 80 c.c. 



1 Kriiger and Schmidt: Zeit. f. physiol. Chem., 1905, 45, 1. 



