68 



LABORATORY MANUAL OF MICROBIOLOGY 



B. Total Nitrogen Including Nitrates in Aqueous Solu- 

 tions (Davisson-Parsons Method) 1 



In addition to the usual apparatus for Kjeldahl analysis, pre- 

 pare absorbing towers as shown in Fig. 2. Place 35 cubic centi- 

 meters of sulphuric acid in each glass bead tower (concentrated 

 H2SO4 4 parts and water 1 part). 



Take 100 cubic centimeters of the liquid to be analyzed, e.g., 

 soil extract (if rich in nitrogen a suitable 

 aliquot may be used). Place the 100 

 cubic centimeters in an 800-cubic centi- 

 meter Kjeldahl flask and add sufficient 

 strong sodium hydroxide to make the 

 solution approximately 0.1 N NaOH. 

 Now add 4 drops of paraffin oil and 

 one gram of Devarda's alloy (60-mesh, 

 made free of ammonia by heating to 

 about 200°C. for 30 minutes) and im- 

 mediately connect to the glass bead 

 tower. Heat with a rose top burner 

 (high flame) until boiling, boil gently 

 for 20 minutes (during this time the acid 

 in the tower should about reach the 

 boiling temperature). Remove the 

 flame, allow the acid to suck back into 

 the flask, and again bring the solution 

 in Kjeldahl flask to the boiling tempera- 

 ture. Boil for a few minutes. Wash 

 the tower with small quantities of dis- 

 tilled water and allow the water to suck 

 back into the flask. About four wash- 

 ings of 25 cubic centimeters each will 

 be found sufficient to remove all of the 

 ammonia from the tower. Place on Kjeldahl digestion shelf and 

 heat with a low flame until the organic matter begins to char. 

 Now add 5 grams of potassium sulphate and continue digestion 



1 Davisson, B. S. and J. T. Parsons, /. Ind. Eng. Chetn., 11: 306-311, 

 1919. Jacob, K. D. and W. J. Geldard, /. hid. Eng. Chem., 14: 1045- 

 1047, 1922. 



S 



Fig. 2. — Apparatus for 

 measuring total nitrogen in 

 the presence of nitrates. 



