NITKOGEN J?ISATION BY SOILS. 43 



GROUP V. NON-SYMBIOTIC NITROGEN 

 FIXATION. 



Exercises XXXII. to XLIII. 



EXEECISE XXXII. 



NITROGEN- FIXATION BY SOILS IN MANNITE SOLUTIONS. 



1. Measure ofl! four 100 cc. portions of mannite solution 

 and place in 500 cc. flasks. 



2. Plug and sterilize in the autoclave as usual. 



3. Inoculate duplicate portions with 20 cc. of a freshly 

 prepared 5-minute infusion of two soils of different types. 



4. Incubate for 10 days at 20° C. 



5. Make transfers for the isolation of pure cultures in the 

 succeeding experiment. 



6. Eemove plugs, add 0.7 gm. Hg. and 80 cc. of HgSO^ 

 and determine the nitrogen present by the regular Kjeldahl 

 method. 



