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This assumption is the more tempting because the compound H 2 N 2 2 

 could easily be imagined to split off water, hereby yielding nitrous oxide : 



(6) H 2 N 2 2 -> N 2 + H 2 



Moreover, a continued hydrogenation of the dimer might well yield 

 gaseous nitrogen: 



(7) H 2 N 2 2 + 2 H -> N 2 + 2 H 2 



In the meantime the possibility cannot be excluded that the hydro- 

 genation takes place only after the water has been split off, and there- 

 fore consists in a hydrogenation of the free nitrous oxide : 



(8) N 2 0+2H -> N 2 +H 2 



The question arises, therefore, in how far experimental evidence in 

 favour of the postulated reactions can be adduced. 



It is clear that much would be gained, if we could arrive at an iden- 

 tification of the compound H 2 N 2 2 . The most plausible hypothesis is 

 that here we are dealing with hyponitrous acid, in itself a far from 

 stable compound, but of which various salts can be prepared without 

 serious difficulties. 



Until now, however, all attempts to demonstrate the presence of 

 hyponitrite in denitrification media have failed. Still more important 

 is that it has neither been possible to induce denitrifying bacteria to 

 convert an added hyponitrite preparation either into nitrous oxide or 

 into gaseous nitrogen (Allen and Van Niel, 1952). If, therefore, the 

 preparations in question, indeed, represent the symmetrical configu- 

 ration which is ascribed to them, hyponitrous acid has to be rejected 

 as an intermediate in dissimilatory nitrate reduction. This situation has 

 led Allen and Van Niel to accept that the compound H 2 N 2 2 should 

 have a different configuration, and as such they have postulated nitra- 

 mide : H 2 NN0 2 . This compound differs from hyponitrous acid in the first 

 place by its asymmetrical configuration which - it may be remarked by 

 the way - does not facilitate the explanation of its origination from ni- 

 troxyl. In the meantime we owe to Allen and Van Niel the experimental 

 proof that Pseudomonas stutzeri is able to bring about a dehydrogenation 

 of nitramide to gaseous nitrogen. This observation certainly adds to the 

 probability that we should specify the reactions (5) and (7) as follows: 

 (5a) 2HNO -> H 2 NN0 2 



(7a) H 2 NN0 2 +2H -> N 2 +2H 2 



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