DENITRIFICATION. 69 



(k) Nitrification is stopped if the amount of ammonium 

 carbonate present exceeds 400 parts of nitrogen per 

 million, but 1000 parts of nitrogen as ammonium chlo- 

 ride do not prevent the action. Warington* found 

 that the presence of gypsum effectively prevented the 

 inhibitory effect of too large a quantity of ammonium 

 carbonate by producing ammonium sulphate. The 

 presence of gypsum would thus be advantageous in 

 all cases where rapidly decomposing animal nitro- 

 genous matter (e.g., urea) has to be nitrified, for it 

 would prevent the danger of the too -rapid formation 

 of ammonium carbonate, and consequent stoppage of 

 nitrification (or even in some cases the destruction of 

 the nitrifying organism). 



(1) Potash compounds added to soils rich in humus have a 

 favouring action upon nitrification, especially if the 

 carbonate be employed, or if calcium carbonate be 

 simultaneously applied.! Some of their results are 

 given below : 



Moor soil Soil +4-5% Soil + 2'5% Soil +5% Soil+2'5% CaCO s 

 only. K 2 CO : >. CaCO ;! . K 2 S() 4 . +5% K 2 SO 4 . 



Amount of nitric\ 



a^VS 25 438 30 18t 25 189 

 day s, per million J 



Denitrification. A chemical change involving the libera- 

 tion of free nitrogen from nitrates takes place under certain 

 circumstances in soils and in manure heaps. This process is 

 effected by the agency of micro-organisms, several species of 

 which appear to exist. The loss of nitrogen consequent upon 

 this reaction is of serious importance and the subject has, of 

 late, attracted considerable attention in France and Germany, 

 as well as in England. 



Breal in 1892 :[ showed that straw always contains micro- 

 organisms which, in the absence of air, can produce free 

 nitrogen, and to a small extent organic nitrogenous compounds, 



* J.C.S. Trans. 1885, 758. 



t Dtunont and Crochotelle, Compt. Rend. 118, G04; Jour. Chem. Soc. 1894, alst. ii., 248. 

 t Compt. Rend. 114, 681 ; J.C.S. 1892, 1259. 



