CHLORIDE. NITROGEN AND AMMONIA 283 



When a crucible oven is available, first heat to about 300° for 10 

 min. and then continue to heat over the flame. Employ the coolest 

 flame that will burn away the brown tar which forms. 



2. Add 50 /xl. 0.10 N nitric acid with a hand pipette. 



3. Titrate the liquid in the tube with the titration soln. keeping 

 the galvanometer circuit closed and closing the titration circuit by 

 bringing the liquid in contact with the burette tip. Observe the 

 deflection each time the tip touches the liquid and a little of the 

 titration soln. runs out. Close the titration circuit only momentarily 

 to prevent polarization. When the deflection changes direction, the 

 end point has been reached. 



NITROGEN AND AMMONIA 



A discussion of various methods for the titrimetric determination 

 of total nitrogen and ammonia has been included in the section 

 dealing with the colorimetric methods (page 233). Since the method 

 developed at the Carlsberg Laboratory is the most precise (0.005 

 ixg. nitrogen) and has had its worth established by the most critical 

 trial over many years, the procedure finally recommended, and 

 given by Briiel, Holter, Linderstr0m-Lang, and Rozits ( 1946) , will 

 be the only one presented. In its present form the range of the method 

 is 0.1-1 fig. nitrogen, but larger quantities may be determined by 

 increasing the concentration of the reagents. The digestion of the 

 sample by the method of these investigators has already been de- 

 scribed on pages 234-236). To avoid the use of alkaline solutions 

 in the microburette, standard acid is employed for the titration 

 after an excess of dilute alkali has been added to the acid used to 

 absorb the ammonia. 



Briiel, Holter, Linderstr^m-Lang, and Rozits Method for 

 Nitrogen and Ammonia 



SPECIAL MATERIALS 



Paraffin Block. Smooth the surface of a block of paraffin by scrap- 

 ing with a knife. Store the block under distilled water, and dry 

 with filter paper when removed from the water for use. 



SPECIAL REAGENTS 



18 N Sodium Hydroxide. 

 0.015 N Sulfuric Acid. 



