URINE 341 



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 

 the remaining three provided they do not vary more than 0.2 mm. 



Exactly at the close of the 5 minutes, dilute the unknown 

 solution to the 500 c.c. mark shaking the flask during the 

 addition of the water to insure complete mixing. Stopper care- 

 fully and thoroughly mix the solution. Pour out the bichro- 

 mate from the right hand cylinder, rinse carefully first with 

 water and then with the solution to be analyzed, and fill the 

 cylinder half full of the liquid. Match the color by moving the 

 prism in the unknown solution, making three or four rapid 

 readings. 



Ordinarily 10 c.c. of urine is used for this determination, but 

 if the content of creatinine is above 15 mg. or below 5 mg. the 

 determination should be repeated with a volume of urine con- 

 taining an amount of creatinine between 5 and 15 mg. This is 



