URINE 295 



8. 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. 



9. Creatinine (Folin.) 



The estimation of creatinine 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. 10% NaOH. 

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

 this interval to become familiar with the colorimeter. 



Before putting any liquid into the cups put them in place 

 and run both prisms down until they touch the bottoms of the 

 cylinders. Read both sides of the instrument. Both readings 

 should be 0.0. If they are not, record the readings carefully 

 and take them into consideration in making readings during the 

 analysis. Be careful about spilling liquid upon the instrument. 

 In case any liquid is spilled upon the instrument, wipe it off 

 carefully. 



Pour a little N/2 potassium bichromate into each of the 

 cylinders of the Duboscq colorimeter. Adjust the depth of the 

 solution in the left hand cylinder exactly to the 8 mm. mark. 

 (If the reading on this side was not 0.0 when the prism was run 

 to the bottom of the cup, make the necessary correction so that 

 the distance between the prism and the bottom of the cylinder 

 is exactly 8.0 mm.) Practice matching the color in the two 

 halves of the field in order to insure greater accuracy in the 

 examination of the' unknown. Since the two bichromate solu- 

 tions are of equal strength, the readings should be identical, no 

 two readings differing by more than 0.1 to 0.2 mm. from the 

 true value (8 mm.). Always make four readings. Disregard 

 the first, which is apt to be inaccurate, and take the average of 



