THE URINE. 187 



Determination of the Total Nitrogen in Urine. 

 (Kjeldahl Method.) 



1. Apparatus. A Kjeldahl digestion-flask (250 cc.), an 

 Erlenmeyer flask (1 liter), two accurate Schellbach burettes, 

 a Reitmeyer bulb-tube, a Liebig's condenser, and the neces- 

 sary stands. 



2. Reagents. Pure concentrated sulphuric acid, specific 

 gravity 1.84, an alcoholic solution (10 per cent.) of phenol 

 phthalein, a strong solution of sodium hydroxide free from 

 carbonates, pure crystallized copper sulphate (CuS0 4 +5H 2 0), 

 pure crystallized potassium sulphate, a fifth-normal solution 

 of hydrochloric acid, a tenth-normal solution of ammonia, a 

 dilute solution of cochineal, and some granulated zinc. 



3. The Digestion. Place 0.7 to 3.5 g. of the substance 

 (5 cc. of urine or milk accurately measured from a burette), 

 accurately weighed, in a 250-cc. Kjeldahl digestion-flask, 

 add 20 cc. of pure concentrated sulphuric acid, specific gravity 

 1.84, and about half a gram of crystallized copper sulphate. 

 Place the flask in an inclined position on a stand in the hood 

 and heat over a low flame until frothing ceases and the black- 

 ened material begins to wash down the sides of the flask. 

 Lower the flame and, when the contents of the flask have 

 cooled somewhat, add from a 20-cc. test-tube 10 g. of crys- 

 tallized potassium sulphate. Raise the heat gradually till 

 the acid boils briskly, and continue to boil the solution till 

 the acid becomes clear and has a pale-blue or green color. 

 Then let cool. 



4. The Distillation. When the contents of the digestion- 

 flask are cold add cautiously about 100 cc. of distilled water 

 and transfer the mixture by means of a 10-cm. funnel to a 

 one-liter Erlenmeyer flask. Rinse the digestion-flask three or 

 more times with 50 cc. portions of distilled water, so as to 

 make the contents of the distillation-flask about 350-400 cc. ; 



