35 
Sodium nitrite (NaN0 8 ). _______1.00 gram 
Di-basic potassium phosphate (K 2 HP0 4 )_ __1.00gram 
Magnesium sulphate (MgSOj __0.30 gram 
Sodium carbonate (anhydrous) (Na 2 C0 3 )_1.00 gram 
Sodium chloride (NaCl). . ______0.50 gram 
Ferrous sulphate (FeS0 4 )_ trace 
Water-„. 1000 
1. Place in each of two clean bottles and a flask enough of the solution 
marked nitrite medium to form a layer one-fourth inch deep. Inoculate the 
bottles and flask as described in paragraph 3 above. 
2. Incubate all the cultures in the desk. 
3. Test the cultures once each week for: 
(a) Nitrites. 
(b) When Trommsdorf’s solution no longer gives a test for 
nitrites, test for nitrates. 
Note—To test for ammonia. —Place in a depression on a spot plate one 
drop of Nessler’s solution. Touch with a sterile glass rod carrying 
a drop of the solution to be tested. Do not stir. A test gives a 
brown color. 
To test for nitrites. —Place in a depression on a spot plate, 
Trommsdorf’s solution one or two drops and 1:3 sulphuric acid 
two or three drops. Mix. Touch with a drop of the solution to 
be tested. Do not mix. 
A test gives a deep blue color. 
4. 
To test for nitrates. —Place in a depression on a spot plate one 
drop of a solution of diphenylamine in concentrated sulphuric 
acid. Touch with a drop of the solution to be tested. 
A test gives a very dark blue color. Nitrites also give a blue 
color with diphenylamine, therefore before one can be certain 
nitrates are present, the solution must be tested for nitrites by 
the Trommsdorf reagent and the absence of nitrites shown. 
(a) What do you conclude regarding the nitrifying power of the 
two soils studied? 
( b ) What agricultural practice tends to promote the activity of 
these organisms in the soil? Why? 
(c) What is the purpose of the magnesium carbonate in the 
solution containing ammonium sulphate? 
(d) What use does the nitrite-forming organism make of the 
ammonium sulphate? 
(e) What use does the nitrate-forming organisms make of the 
sodium carbonate? 
(0 Why is plenty of air necessary for the growth of these 
organisms? 
(g) Who first isolated pure cultures of these organisms? 
(. h ) What are the names of the two species of organisms concerned 
in these processes? 
(j) Why is it not necessary to add magnesium carbonate to the 
solution containing sodium nitrite? 
