296 PHYSIOLOGICAL CHEMISTRY 



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 

 an essential point, as the method is accurate only within these 

 limits. 



By experiment it has been determined that 10 mg. of pure 

 creatinine gives a color of such strength that 8.1 mm. of such a 

 solution exactly matches 8.0 mm. of bichromate under the 

 above conditions. From the reading obtained with the unknown 

 solution it thus is possible to calculate the amount of creatinine 

 present in the volume of urine used. Remember that the larger 

 the amount of creatinine, the deeper will be the color, and the 

 shorter the column of liquid necessary to match the color of 

 the standard. If a reading of 8.1 mm. corresponds to a creat- 

 inine content of 10 mg., calculate the amount of creatinine cor- 

 responding to the reading of your solution, not forgetting that 

 the proportion will be inverse. Calculate the amount of creat- 

 inine in the volume of urine used and in the 24-hour specimen. 



From the formula of creatinin calculate what per cent of 

 nitrogen it contains, and then the amount of creatinine nitro- 

 gen present in the 24-hour sample. Calculate the per cent of 

 the total nitrogen which this represents. 



10. Indican. 



By applying the qualitative test for indican, already per- 

 formed by the student, and comparing the color produced with 



