

NITRIFICATION. 



which appear to differ in their susceptibility of undergoing 

 nitrification and also in their behaviour towards alkalis and 

 acids. * All animal and vegetable refuse contains combined 

 nitrogen, probably mainly in the form of proteid substances ; 

 as these undergo putrefaction in the soil and become converted 

 into humus, carbon dioxide is evolved, and the nitrogen is 

 probably converted into bodies of simpler constitution, amides,! 

 ammonium carbonate, and in some cases, free nitrogen. As 

 has been already shown, the form in which nitrogen occurs 

 associated with humus is not known. It probably exists 

 mainly as somewhat complex compounds, possibly of an amide 

 character, or as amido-acids,:j: but of this, little knowledge has 

 been acquired. These organic compounds are probably broken 

 down in the soil, yielding first, ammonium compounds, e.g.: 



CO |NH! + H * 2NH * + co, 



Carbamide (urea). Water. Ammonia. Carbon dioxide. 



In this case the ammonia and carbon dioxide in the presence 

 of water would yield ammonium carbonate (NH 4 ). 2 CO 3 . This 

 change takes place very readily (as is show r n by the smell of 

 ammonium carbonate in stables, &c.) and is in all probability 

 effected under the influence of a micro-organism. Indeed, 

 according to experiments made by Miintz and Condon, and 

 especially by Marchal, a large number of different bacteria 

 and moulds are possessed of the pdwer of converting the 

 nitrogen of albumen into ammonia. Moulds probably do a 

 large portion of the work in the case of manure heaps, humus, 

 and very peaty soils ; but in ordinary arable soils bacteria, of 

 which Bacillus myco'ides appears to be the most important, 

 predominate. The bacterium just named is very widely dis- 

 tributed, constantly occurs in surface soils, in the air, and in 

 natural waters. In decomposing albumen it produces ammo- 

 nium carbonate with small quantities of formic, HCOOH, 

 propionic, C. 2 H,-COOH, and butyric acids, C 8 H 7 COOH. No 



* Andre, Compt. Rend. 1898, 414. 



t An amide is a substance derived from an organic acid by the replacement of the 

 OH group by NHo. Thus from acetic ac i d {c0()H is derived acetamulel pQ 3 NH 



f O TT / "V T-T "^ * 



from carbonic acid CO-! ^g carbamide (urea) CO-j ^^ &c., &c. 



} Sestini J.C.8. 1899, abst. ii., 120. Jour. Chem. Soc. 1894, abst. ii., 248. 



F 



