336 ANALYSIS OF URINE. [CH. XIII. 



(v.) Into E (or the flask shewn in fig. 45) measure 20 cc. of the 

 standard sulphuric acid, fit the stopper and connect up E to D. 



(vi.) Immerse the tube B in a beaker or can of water at a 

 temperature of about 45 C., and leave it undisturbed for 10 to 12 

 minutes. 



(vii.) Remove the tube from the bath, connect up E to the 

 pump, and B to the wash bottle A, and send a strong air current 

 through the apparatus for i minute to sweep over any ammonia 

 that may have escaped from the fluid and be present in the air 

 of B. 



(viii.) Stop the air current and disconnect the entry and exit 

 tubes of B. Remove the stopper with these tubes and place it on 

 the bench in such a way that the small amount of fluid on the end 

 of the entry tube is not lost. 



(ix.) Add 4 to 5 grams, of pure dry potassium carbonate to B, 

 roughly measuring it with a suitable spoon, immediately replace the 

 stopper and connect up the apparatus. Send a slow air current 

 through for 2 minutes and then a rapid current for 12 minutes. 



(x.) Proceed as described in Ex. 399 (iv.), 



Calculation. Determine the percentage of nitrogen in the form of 

 ammonia and urea as described for Kjeldahl's method, p. 323. The result 

 thus obtained is the mgms. of (urea + ammonia) N. in 0-5 cc. urine = Ua. 



So mgms. of (urea + ammonia) N. in 100 cc. = 200 x Ua. 



From Ex. 399, the mgms. of ammonia N. in 100 cc. = 20 A. 



So mgms. of urea N. in TOO cc. = (200 x Ua) - 20 A = U. 



Since 60 grams, of urea contain 28 grams, of nitrogen, the grams, of urea in 



60 i 

 joo cc. urine = U x x ^^ = U x 0-00214 (log. 3*33 10 )- 



E. Creatinine and Creatine. 



The methods that are universally adopted are based on Jaffe's test for 

 creatinine (Ex. 227) as applied by Folin for colorimetric estimation. Creatine 

 does not reduce picric acid, but" is converted to creatinine either by heating 

 with hydrochloric or picric acid. The combined (creatinine + creatine) is 

 then estimated colorimetrically. Folin and Doisy* have recently pointed out 

 that considerable errors may occur if impure picric acid is used, especially in 



* Folin and Doisy, Journ. Biol. Chem., xxviii., p. 349. 



