Dec. i6, 1918 



Nitrogefi-F Ixing and Nitrifying Organisms 



607 



until the soil became approximately air-dry. This was two days for the 

 first and second sets and six days for the third set. During this time, 

 in order to increase the surface exposed to air and also prevent contami- 

 nation, the bottles were left lying on their sides under a hood. 



After exposing the samples for the chemical to evaporate, another 

 series of cultures were made for Azotobacter. The water content of the 

 soil was then made up to one-half saturation and incubated at room 

 temperature. The water lost by evaporation was restored from time to 

 time. At the end of three months' incubation a third series of cultures 

 for Azotobacter were made and the nitrate content determined. 



The actual quantities of nitrogen fixed were not determined, for rea- 

 sons already given, the character of growth being considered a sufficient 

 index. The results are presented in Table IV. 



Table IV 



-Effect of carbon disidphid and toluol upon Azatobacter and nitrate accumu- 

 lation in soil 



W.ATER CONTENT OP SOIL, 3 PER CENT 



a I, 2, and 3 have reference to time at which cultures were made, i was made after chemical had remained 

 in soil three days, 2 was made after chemical was evaporated, and 3 was cultured after nine weeks' incuba- 

 tion. Nitrates and ammonia were determined after nine weeks' incubation. 



6 Nitrates in milligrams per 100 gm. of soil. 



