KlDUCftOtf PROCESSES IN THE SOIL 540 



mental evidence. However, the more recent ideas concerning the proc- 

 esses involved in the reduction of nitrates can be best presented as 

 follows: 268 



OH 

 / /OH 



N=0 +2H^N{ +H 2 

 \ ^0 



O 



nitrate nitrite 



/OH 1 



N< +2 H 

 ^O N— OH 



il + 2H 2 



/OH i N— OH 



N/ +2H 



^O J hyponitrite 



NOH N v 



|| - ||>0 + H 2 



NOH N/ 



N v N 



||>0 + 2H->|||+H 2 



To explain the formation of hydroxylamine and ammonia, in the reduc- 

 tion of nitrates, by the above theories, the following reactions may be 



suggested : 



2 H 2 NOH 



N— OH + 2 HI 



H 



N— OH + 2 HJ 



H 2 NOH + 2 H -> NH 3 + H 2 



With the exception of the organisms capable of oxidizing sulfur and 

 the Bac. amylobacter group, all denitrifying bacteria reduce nitrate to 

 nitrogen gas and N 2 0, in varying proportions, Bac. nitroxus being par- 

 ticularly active in the process. A 5 to 12 per cent solution of nitrate 

 inoculated with soil gives, at 20° to 37°, a current of gas which is eighty 

 per cent N 2 0. Various other denitrifying bacteria, like Bad. pyocy- 

 aneum and Bad. stutseri, give in solutions of nitrate (particularly 

 NH4NO3) a gas rich in N 2 0. Out of one hundred cultures of bacteria 

 tested by Maassen, 27 thirty-one were found capable of reducing nitrate 



* 6a Kluyver and Donker, 1926 (p. 526); Blom, J. Studier over Nitrat, Nitrit 

 og Hydroxylamin. N. J. F. Kongr. Oslo. 1926; Joss, E. J. The action of metals 

 on nitric acid. Jour. Phys. Chem., 30: 1222-1275. 1926. 



27 Maassen, 1901 (p. 181). 



