LIBERATION OF NITROGEN. 309 



of soda ; otherwise a serious loss of nitrogen will result. This 

 injurious action is, however, not limited merely to such fields as 

 have been artificially manured with nitrate, since (as we shall see 

 in Chapter xxxvi. ) the ammonia salts in the soil are, under favour- 

 able conditions, oxidised into nitrates by the activity of a special 

 group of bacteria, such nitrates then forming a welcome food for 

 the organisms dealt with in the present paragraph. That it is 

 a question of more than merely insignificant quantities will be 

 evident from the discovery reported by PAUL WAGNER (I.) a 

 discovery which led to the aforesaid researches of Burri and 

 Stutzer viz., that out of 100 parts by weight of nitrogen applied 

 in the form of stall-manure to the soil, only 25 parts are, on an 

 average, recovered in the crop, whilst the remaining 75 parts are 

 entirely lost. These figures do not fully represent the extent of 

 the loss occasioned in the soil and manures by the activity of the 

 de-nitrifying bacteria, and there still remains another phenomenon 

 for consideration. We must recall that the fission fungus known 

 as Bacillus denitrificans (and probably also a number of allied 

 species not hitherto investigated) separates nitric oxide as well as 

 nitrogen from nitrates. This oxide then escapes into the outer 

 layers of the manure heap or soil, where it is brought into contact 

 with oxygen, and combines therewith to form nitrogen trioxide 



2NO + = N 2 3 . 



This latter then reacts on the ammonia and ammonia deriva- 

 tives (urea, &c.) in the soil, in such a manner as to liberate both 

 the nitrogen of the trioxide and that of the ammonia as well 



N 2 3 + 2NH 3 = 2N 2 + 3H 2 O. 



Consequently the nitrogen compounds insusceptible to the direct 

 action of the microbes in question are also included in the wasteful 

 reaction set up. It was on this account that the production of 

 ammonia during the decomposition of manure was casually re- 

 ferred to at the commencement of this paragraph. The present 

 is a fitting opportunity for referring to the statements of several 

 workers e.g. H. B. GIBSON (I.) who, like Reiset, thought they 

 had observed a liberation of nitrogen in their researches on putre- 

 faction. Their results were all obtained by the use of complex 

 bacterial mixtures, and therefore cannot be considered as reliable. 

 In this case, also, those experiments alone are decisive in which 

 pure cultures have been employed. 



By the activity of these bacteria an enormous quantity of com- 

 bined nitrogen is daily set at liberty in the soil. To replace this 

 loss, and to restore the continuity of the nitrogen cycle, is the task 

 of a separate group of bacteria, which will be dealt with in 

 Chapter xxxiii. 



The reduction of nitric acid by bacteria does not always stop 

 short at the liberation of free nitrogen, but in many instances 



