1919] 



ALLEN — AZOTOBACTER CHROOCOCCUM 



15 



for nitrate determinations (Allen, '15, fig. 1), N/50 acid being 

 nsed in the receivers. Bumping was prevented by the addi- 

 tion of zinc. 



Extreme difficulty was experienced in carrying out the di- 

 gestions. Foaming was excessive and the cultures reported 

 "lost" in table i were those which foamed over. Only a very 

 low flame could be used and the rate of digestion was ex- 

 tremely slow. The large amount of carbonaceous material, 

 which formed from the decomposition of the mannite, was ex- 

 tremely resistant to digestion, and it was only after several 

 days of slow intermittent boiling that the mixtures cleared. 

 After the determinations or. these preliminary experiments 

 were completed, some studies on optimum conditions for di- 

 gestion were taken up. These are discussed separately. 



The results of the first of the preliminary experiments are 

 given in table i. The control cultures received, as stated 

 above, sodium chloride and cane sugar equivalent to the ferric 

 oxide and cane sugar in the remaining flasks. 



TABLE I 



EFFECT OF COLLOIDAL FERRIC OXIDE IN FIXATION OF NITROGEN BY 

 AZOTOBACTER CHROOCOCCUM IN DEEP AND SHALLOW LAYERS 



No. 



Additions to Ashby's 

 culture medium 



1 

 2 

 3 



4 

 5 

 6 



7 



8 

 9 



10 

 11 

 12 



300-cc. flasks 



T: "eat- 

 ment 



Control 

 Control 

 Control 



0.1 

 0.1 

 0.1 



mg 

 mg 

 mg 



FeA 



Fe,0, 

 Fe t O, 



Control 



Control 



Control 



1.0 mg. FeaOt 

 1.0 mg. FeiOi 

 1.0 mg. FeiO! 





Sterile 



Inoc. 



Inoc. 



Sttrile 



Inoc. 



Inoc. 



Sttrile 



Inoc. 



Inoc. 



St« rile 



Inoc. 



Inoc. 



N 

 found 

 (mgs.) 



Lost 

 3.23 

 2.84 



1.67 

 5.08 

 4.52 



1.34 

 2.33 

 1.80 



Lost 

 2.72 

 Lost 



N 

 fixed 



(mgs.) 



1.56* 

 1.17 



700-cc. flasks 



N 



found 



(mgs.) 



1.31 

 2.59 

 1.98 



1.34 

 7.94 



Lost 



1.45 

 2.60 

 3.99 



1.22 

 Lost 

 4.73 



N 



fixed 



(mgs.) 



1.28 

 0.67 



6.60 



1.15 



2.54 



3.51 



* Computed from No. 4 as blank. 



f Computed from No. 7 as blank. 



While the data are erratic and incomplete, they indicate 

 that the 0.1-mg. portion colloidal ferric oxide exerted a bene- 

 ficial effect on the growth of the microorganism. The growth 



