NITKATE FORMATION" IN SOLUTIONS. 25 



GROUP II. NITRIFICATION. 

 Exercises XVIII. to XXIV. 



EXEECISE XVIII. 



NITRfTE FORMATION IN SOLUTIONS. 



1. Measure ofE twelve 100 cc. portions of "solution for 

 nitrite formation" into 250 cc. Erlenmeyer flasks. Plug 

 and sterilize as usual. 



2. Inoculate in duplicate with 20 cc. portions (= 10 

 gms. soil) of 5-niinute infusions of the two soils to be 

 tested. 



3. Incubate 7-8 days at 20° C. 



4. Test qualitatively for the presence of nitrites by the 

 Griess colorimetric method. 



5. If nitrites are found, by means of a platinum loop, 

 inoculate from the growth in each flaslc into other flasks of 

 the same solution. 



6. Incubate these new cultures 7-8 days. 



7. Test again for the presence of nitrites, and if positive 

 results are obtained repeat the inoculation, using still other 

 flasks of solution. 



8. After 7-8 days"' incubation, filter and wash and de- 

 termine the nitrites present by the Griess colorimetric 

 method. 



9. Calculate the per cent, of the original ammonia nitro- 

 gen changed to nitrite. 



