182 Transformation of Nitrogen 



Mechanism of Nitrite Oxidation. The oxidation of nitrite to 

 nitrate takes place according to the following reaction: 



NaNOa + ^Oa = NaNOg 



This was demonstrated by measuring the nitrite and oxygen con- 

 sumption. With optimum concentration of the nutrients and proper 

 aeration of the culture, the nitrate-forming organisms, in liquid 

 culture, may oxidize 4-5 gm NaNOo per liter in 24 hours. 



Winogradsky observed the interesting phenomenon that am- 

 monium salts injuriously affect the growth of nitrate bacteria. This 

 seemed rather strange in view of the fact that the nitrate bacteria 

 are active side by side with the nitrite bacteria which use the am- 

 monium salt as a source of energy. It was then suggested that 

 the two processes follow in two successive periods in the soil, nitrate 

 formation beginning only after all the ammonium salt is converted 

 into nitrite. On decreasing the amount of NaoCOs, which would 

 lead to a lower alkalinity, Boulanger and Massol found that the 

 injurious effect of ammonium salt is less, and concluded, therefore, 

 that the growth of nitiate bacteria is not injured by the salt but by 

 free ammonia. This was confirmed by Meyerhof, who established 

 that the injurious influence of ammonia and its derivatives ( aliphatic 

 amines) consists in the penetration of the base into the cell (which 

 does not take place in the case of ammonium salt) and in a specific 

 action of the NH3 and NHo groups. Lipoid-insoluble amines, like 

 the diamines, are not injurious. The injurious effect of amines and 

 cations depends upon their ability to penetrate into the cell and 

 upon the reaction of the media; respiration is usually less affected 

 than growth. The intermediary products of the oxidation of sulfur 

 ( hyposulfite ) are a decided deterrent to the process of nitrate forma- 

 tion in soil; the nitrifying bacteria as such are not injured, since the 

 process is resumed as soon as these intermediary products have dis- 

 appeared. 



Schloesing compared the formation of nitrates from various am- 

 monium salts added to the soil and fouud that the following relative 

 amounts of nitrogen (in milligrams) are nitrified per day: NH4CI, 

 3.4; (NH4),S04, 9.0; (NH4)2CO:i, 4.0. Ammonium salts of organic 

 acids are also nitrified rapidly. 



It was thought at first that organic matter can be nitrified directly. 

 Miintz has shown, however, that organic matter has to be decom- 

 posed first, and ammonia liberated, before nitrates can be formed. 

 Omeliansky later obtained negative results also for urea, asparagine, 



