338 ANALYSIS OF URINE. [CH. XIII. 



acid and soda as before and mix, noting the time. After the 

 flasks have each stood for 10 minutes they are separately filled to 

 the mark with distilled water and the contents well mixed. The 

 solutions are then compared in a colorimeter (see p. 384), the 

 standard being set at 15 mm. 



Should " U " read below 10 mm., the determination must be 

 repeated, using i cc. of an accurately diluted urine, say I in 2 or 

 i in 3. Should " U " read above 22 mm. the determination must 

 be repeated with 2 cc. or more of the urine. In such cases there 

 is no necessity to make another standard, the colour being 

 quite permanent for hours. 



Calculation. 



Mg. in i cc. urine Reading of " S " 15 



Mg. in i cc. standard "~ Reading of " U " Reading of " U " 



M S- in ' cc ' = Reading'of "U" = Cn " 



If more or less than i cc. of urine have been taken, this must be divided 

 by the volume of urine used. 



Grams, of creatinine in 100 cc. = Cn x o-i. 



Since 129 grams, of creatinine contain 42 grams, of nitrogen, grams, of 



creatinine- N in 100 cc. = Cn x o-i x - - Cn x -0325 (log. 2-5126). 



403. The estimation of creatine and creatinine (Folin). 



(i.) Weigh a 200 cc. Erlenmeyer flask of " Duro " glass. 



(ii.) Into it measure the amount of urine that contains between 

 0-7 and 1-5 mgm. of creatinine, as determined by the previous 

 exercise. 



(iii.) Add 20 cc. of saturated picric acid and about 130 cc. of 

 water and a few pieces of broken porcelain. 



(iv.) Boil gently over a micro-burner for i hour. 



(v.) Increase the heat and boil down to rather less than 20 cc. 



(vi.) Weigh the flask and add water, if necessary, to make the 

 total weight of the contents equal to 20-25 grams. 



(vii.) Cool in running water. 



