340 PHYSIOLOGICAL CHEMISTRY 



sulfite solution (to balance the sulfite 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 sulfite solution, containing 0.5 mg. of uric acid ; add 4 c.c. 

 of the cyanide solution 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 3 to 5 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 "day- 

 lite" glass) is better than day light for this color comparison. 



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. 



The discarded blue solution should be poured as directly as 

 possible into the drain pipes of sinks on account of the cyanide. 



Hippuric Acid. 



Hippuric acid may be estimated by the method of Folin and 

 Flanders which consists in hydrolyzing the hippuric acid and 

 estimating the benzoic acid liberated or by that of Kingsbury 

 and Swanson. 



Purine Bases. 



Purine bases may be estimated by a method similar in prin- 

 ciple to the Salkowski Method for isolating these compounds. 

 For details consult a larger work. 



40. Creatinine (Folin). 



The estimation of creatiniiie is a colorimetric method, based 

 on the Jaffe reaction already familiar to the student. Picric 

 acid is reduced to picramic acid and the red color produced by 

 the latter in alkaline solution is compared with a N/2 potas- 

 sium bichromate solution in a Duboscq colorimeter. 



Measure 10 c.c. urine into a 500 c.c. volumetric flask ,add 15 

 c.c. of a saturated solution of picric acid, and 5 c.c. W% NaOH. 

 Shake well and allow the mixture to stand 5 minutes. Employ 

 this interval to become familiar with the colorimeter. 



