556 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



MICRO-METHODS FOR THE ANALYSIS OF THE 

 NITROGENEOUS CONSTITUENTS OF URINE. 



Folin and his co-workers, who have adapted and devised methods for 

 analysing the soluble non-protein nitrogenous constituents of blood, have shown 

 that these methods can be used for the analysis of the same constituents in urine 

 if smaller quantities of urine be taken, or if the urine in some of the analyses 

 be considerably diluted. It has since been shown that the urea can be 

 estimated by means of urease using smaller quantities of urine. By thus 

 reducing the amount of urine the time taken to effect the analyses is consider- 

 ably shortened. These methods are particularly useful for the analysis of 

 the urine of fish and small animals where only small quantities of urine are 

 obtainable. 



The analyses are made colori metrically : ammonia by comparison with 

 a standard ammonium sulphate with Nessler's reagent, uric acid with the 

 phosphotungstic acid reaction, creatinine with picric acid and caustic soda. 

 The ammonia analyses can, however, be made by titration with -02N alkali. 

 In all cases the ammonia is liberated by the aeration method, as used in the 

 estimation of ammonia and urea by the urease method (p. 136). Jena 

 glass test tubes 20 cm. long and 2-3 cm. wide are employed. The ammonia 

 is either removed by suction with a good water-pump and water supply or 

 by blowing with an air blast. The arrangement of the apparatus is shown in 

 Figs. 76 and 77. 



FIG. 76. (After Folin.) Fio. 77. (After Folin.) 



Old pipettes of 20-30 c.c. capacity serve well as the traps ; to prevent 

 splashing over a piece of rubber is cut to shape, put through a hole upon the 

 entry tube and fitted below the exit tube. 



The other apparatus required is : 



A Duboscq colorimeter. 



A micro-burner. 



Accurate i c c. pipettes of the Ostwald pattern. Their contents are 

 delivered by allowing the pipette to drain against the sides of the vessel for 

 10 seconds and then blowing out clean. 



Glass tubes sealed at the end and perforated with about 6 small holes. 



50 c.c. and 100 c.c. measuring flasks. 



The reagents required are : 



