62 LABORATORY MANUAL OF MICROBIOLOGY 



capacity of the soil as well as the moisture content of the par- 

 ticular soil can be calculated from these data. 



QUANTITATIVE METHODS FOR AMMONIA DETERMINATION 

 1. Direct Distillation : 



Sulphuric acid solution N/14 



Sodium hydroxide solution N/14 



Methyl-red. 



Magnesium oxide. 



1. Transfer the culture to be analyzed to an 800-cubic centi- 

 meter Kjeldahl or a copper flask, using about 200 cubic centi- 

 meters of distilled water. 



2. Add 5 grams of magnesium oxide and some shavings of 

 paraffin to prevent foaming. 



3. Connect to a condenser, the lower end of which is in iV/14 

 acid contained in an Erlenmeyer flask. 



The period of distillation will vary with the amount of ammonia 

 present. As a rule, 1 hour is long enough to drive off all ammonia 

 nitrogen. 



4. If methyl-red is used as an indicator, the distillate should be 

 boiled for a few minutes, cooled to 15 or 20°C., about 5 drops of 

 methyl-red added, and the solution titrated. 



5. The distillate is titrated with standard alkali, and from the 

 number of cubic centimeters of standard acid neutralized by 

 the distillate the weight of nitrogen liberated as ammonia is 

 calculated. 



2. Nesslerization. — Ammonia-free water should be prepared 

 by adding sodium hydroxide and potassium permanganate to 

 laboratory water and redistilling. Discard the first portion of 

 the distillate. After about one-fourth of the water has been 

 evaporated, the subsequent distillate will be free of ammonia. 



Standard Ammonium Chloride Solution. — Dissolve 3.82 grams 

 of ammonium chloride in 1,000 cubic centimeters of distilled 

 water; dilute 10 cubic centimeters of this to 1,000 cubic centi- 

 meters with ammonia-free water. One cubic centimeter of this 

 solution contains 0.01 milligram of nitrogen. 



1. Prepare a series of 16 Nessler's tubes which contain the 

 following number of cubic centimeters of the standard ammonium 

 chloride solution, and dilute to 50 cubic centimeters with 



