NITRIFICATION IN SOLUTION 47 



Exercise 13 



NitrijBication in Solution 



A. Nitrite Qualitative: 



1. Prepare five 150-c.c. Erlenmeyer flasks with 20-c.c. 

 portions each of nitrite solution (m. 26). 



2. Inoculate two of the flasks. 



(a) Add approximately o.i gram of field soil. 

 (&) Add approximately o.i gram of garden soil. 



3. Incubate at 28° C. 



4. At regular intervals of four to six days remove, with 

 a sterilized platinum needle, i drop of the solution from 

 each flask and test as follows: 



(a) Presence of nitrites — ^Trommsdorf's reagent (see page 136). 

 Q}) Absence of ammonia — ^Nessler's reagent (see page 135). 



Use the spot plate for this test. Record the date and 

 results of test in the table on p. 48. 



5. As soon as the culture shows the presence of nitrites 

 and absence of ammonia, make loop subinoculations into 

 a sterile flask of the same medium. 



6. If it is desirable to study the nitrite bacteria in enrich- 

 ment cultures, repeated subinoculations may be made. 



B. Nitrate Qualitative: 



1. Prepare five 150-0.0. Erlenmeyer flasks with 20-c.c. 

 portions each of nitrate solution (m. 28). 



2. Inoculate two of the flasks. 



{a) Add approximately o i gram of field soil. 

 Q)) Add approximately 0.1 gram of garden soil. 



