730 



EXPEEIMENT STATION RECORD. 



other words, onlj" about two-tenths of the total nitrogen in the medium 

 was converted into ammonia." 



The ammonia produced was determined by distilling with calcined 

 magnesia. It was found that the uninoculated bouillon gave 3.4 mg. 

 of ammonia per 100 cc. by this treatment, and consequently this cor- 

 rection was made in the results obtained with the diti'erent cultures. 



To determine the effect of an abundant supply of air upon the deni- 

 trifying action of soil bacteria Bacillus j)ulvmatHSV7iis grown in peptone 

 solution containing 0.1 gm. of nitrate of soda per liter in a flask abund- 

 antly supplied with purified sterile air and also in a flask without 

 aeration. "At the end of 5 days 7 mg, of nitrite of soda per 100 cc. 

 were found in the aerated culture and 30 mg. in the nonaerated. At 

 the end of 10 days 20 mg. of nitrite of soda were found in the aerated 

 and -40 mg. in the nonaerated culture." 



The denitrifying action of a number of soil organisms was studied. 

 The various organisms were grown in a neutral 1 per cent Witte peptone 

 broth containing 0.1 gm. of nitrate of soda per liter, in Erlenme3"er 

 flasks plugged with cotton wool and kept at room temperatures. 

 Nitrite was determined by the Griess colorimetric method. The 

 results were as follows: 



Nitrite in cultures of soil bacteria. 



The organisms studied were found to grow best in neutral or slightly 

 alkaline media. In media containing carbohydrates the organisms 

 produced considerable amounts of acid, including acetic, formic, 

 propionic, butvric, and lactic acids. "All soils containing larger or 

 smaller quantities of vegetable matter are liberally supplied with car- 

 boh\^drates in one form or another, hence all soils have a tendenc}^ to 

 become acid as a result of the development of soil microbes." 



The following table shows the amounts of free acid stated in the 

 number of cubic centimeters of tenth-normal sodium hydroxid re- 



