QUALITATIVE AND QUANTITATIVE ANALYSIS 63 



ammonia-free water, namely: 0.0, 0.1, 0.3, 0.5, 0.7, 1.0, 1.4, 1.7, 

 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, and 6.0. 



2. These will contain 0.01 milligram of ammonia nitrogen for 

 each cubic centimeter of the standard solution used. 



3. Nesslerize the standards and also the distillates by adding 

 approximately 2 cubic centimeters of Nessler's reagent to each 

 tube. 



4. Do not stir the contents of the tubes. 



5. After Nesslerizing, allow the tubes to stand for 10 minutes. 



6. Compare the color produced in these tubes with that in 

 the standards by looking vertically downward through them at 

 a white surface placed at an angle in front of a window, so as to 

 reflect the light upward. 



3. Aeration Method.' — Place in a Kjeldahl flask 100 grams of 

 soil to be analyzed, 4 grams of sodium carbonate, 0.5 cubic 

 centimeter paraffin oil, and about 300 cubic centimeters of 

 ammonia-free water. Apply suction, bubbling the air first 

 through weak (10 per cent) sulphuric acid solution, to remove 

 any ammonia that might be present in the air; the air is bubbled 

 through the solution containing the soil and then is bubbled 

 through a bottle or long tube containing standard sulphuric acid 

 0.2N, O.IN, or 0.05N depending on the amount of ammonia 

 present), where the ammonia is absorbed. The flasks containing 

 the soil are placed in a water bath, the temperature of which is 

 maintained at 75 to 80°C. Aeration is continued for 2 to 3 

 hours. In the case of liquid cultures, 30 to 50 cubic centimeter 

 portions of the culture solution are placed in Folin aeration tubes, 

 5 cubic centimeters of 20 per cent sodium carbonate solution, 

 1 gram NaCl and 0.5 cubic centimeter petroleum oil are added 

 to each and aeration continued for 3 hours, tubes being placed in 

 thermostat at 60 to 65°C. 



QUANTITATIVE (COLORIMETRIC) METHOD FOR DETERMINING 



NITRATES 



Evaporate to dryness in a porcelain dish on a water bath a 

 convenient quantity of unknown nitrate solution, depending 

 upon the amount of nitrate present. 



1 GiBBS, W. M., et at, Soil Sci., 15 : 261-267, 1923. 



