ADVANCED AND QUANTITATIVE 

 METHODS 



CHAPTER XVIII 

 QUANTITATIVE EXAMINATION OF URINE 



Estimation of Total Nitrogen by Kjeldahl Method. Pipette off 5 c.c. of 

 the urine into a 300 c.c. combustion flask, add 10 to 15 c.c. N.-free 

 H 2 SO 4 and a small piece of copper foil (2-3 mm. square). Heat this 

 mixture in a fume chamber, carrying on the combustion until the 

 solution is colourless, then allow to cool. Now transfer the cold colour- 

 less solution to a 1,000 c.c. distilling flask of hard glass, washing out the 

 combustion flask thoroughly with distilled water until the total volume 

 in the distilling flask is about 500 c.c. Add a drop or two of alizarin red 

 solution (a 1 per cent, solution in water of sodium alizarin sulphonate) 

 and then almost neutralise the contents with strong (40 per cent.) 



NaOH solution, cool. Measure 50 c.c. of r^ H 2 SO 4 into an Erlen- 



meyer or other suitable flask of about 500 c.c. size, add a few drops of 

 alizarin red solution and place below the condenser, taking care that the 

 connecting tube dips below the surface of the acid. (Indicator is added 

 at this stage so that if too little acid has been taken to neutralise the 

 NH 3 distilled over early evidence may be obtained and more acid can 

 be added.) Now make the contents of the distilling flask distinctly 

 alkaline by a further addition of caustic soda, care being taken not to 

 add a huge excess, and immediately connect with the condenser. The 

 bunsen below the distilling flask is now lighted and the distillation 

 continued until all the ammonia has distilled over : this requires about 

 half an hour. The addition of a few pieces of porous earthenware or of 

 granulated zinc to the distilling flask before it is finally made alkaline 

 assists materially in the prevention of bumping. When the distillation 

 is ended the distilling flask is removed and the condenser tube is well 



N 

 washed down with distilled water into the flask containing the y^ H 2 SO 4 . 



N 

 When cool this acid is titrated with y^ NaOH and the difference 



N 

 between the amount of =r~ alkali in c.c. required to neutralise com- 



N N 



pletely the J-Q acid remaining and the amount of y~ sulphuric acid 



279 



