242 PHYSIOLOGICAL CHEMISTRY 



black specks are present, remove the flask from the flame and 

 by careful shaking, rinse them down. Do not attempt to rinse 

 them down by adding water. 



Note: Injurious fumes are given off during the heating 

 in the Kjeldahl analysis, so that it should never be carried 

 out in the open laboratory, but in a well drawing hood, or 

 other arrangement for carrying off the fumes. 



When digestion is complete, allow the liquid to cool and 

 about half fill the flask with distilled water. The nitrogen now 

 is in solution in the form of ammonium sulphate. It must be 

 set free as ammonia and driven over by distillation into a 

 known volume of standard acid. 



Arrange apparatus (condenser, connections, etc.) to distill 

 off the ammonia. The most satisfactory receiving flask is a 

 Woulff bottle. Connect the delivery end of the condenser with 

 one neck of the Woulff bottle by means of rubber and glass 

 tubing, and a stopper. In the other neck of the Woulff bottle 

 fix a cork through which passes the narrow tube of a CaCl 2 

 tube. Charge the bulb of the CaCl 2 tube with glass pearls. 



Prepare the Woulff bottle by running into it over the glass 

 pearls in the calcium chloride tube, 50 c.c. N/10 hydrochloric 

 acid measured with a pipette, add 2-3 drops alizarine red and 

 connect the bottle by the other neck with the delivery tube of 

 the distilling apparatus. Set the digestion flask on a ring over 

 the flame and make sure that all connections fit properly. Add 

 a small quantity of talcum powder to prevent irregular boiling 

 (bumping) but not more than the amount that can be taken up 

 on the tip of a knife blade. Add a drop of alizarine and then 

 about 50 c.c. of sat. NaOH to neutralize the sulphuric acid. 

 In adding the alkali, the flask should be tilted somewhat and 

 the sodium hydrate poured down the side of the tube so that 

 it will form a layer underneath the acid. This is to avoid 

 possible loss of ammonia. Stopper the flask immediately, make 

 sure that the stopper fits tightly, and rotate the flask gently 

 so as to mix the contents thoroughly. If the liquid does not 



