IV. THE EEACTIONS OCCURRING IN SOILS 63 



00 (NH: + H * 2NHa + c 2 



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 shown by the smell of ammonium car- 

 bonate in stables, etc.) and is in all probability effected under the in- 

 fluence of a micro-organism. Indeed, according to experiments made 

 by Miintz and Condon, and especially by Marchal, 1 a large number of 

 different bacteria and moulds are possessed of the power of converting 

 the nitrogen of albumin into ammonia. Moulds probably do a large 

 portion of the work in the case of manure heaps, and very 

 peaty soils ; but in ordinary arable soils, bacteria, of which Bacillus 

 mycoides appears to be the most important, predominate. The bac- 

 terium just named is very widely distributed and constantly occurs in 

 surface soils, in the air and in natural waters. In decomposing 

 albumin, it produces ammonium carbonate with small quantities of 

 formic, HCOOH, propionic, C 2 H 5 COOH, and butyric acids, C 3 H 7 COOH. 

 No hydrogen nor nitrogen is evolved in the free state. It requires the 

 presence of oxygen, or if nitrates be present they are reduced to 

 nitrites or even ammonia. Its action nearly ceases at 5 C., is 

 greatest about 30 C., and stops at 42 C. It acts upon other nitro- 

 genous organic compounds, e.g., leucine, CH 3 .(CH 2 ) 3 .CH(NH 2 ).COOH, 

 tyrosine, HO.C 6 H 4 .CH 2 .CH(NH 2 ).COOH, creatine, C 4 H 7 N 4 O 3 , or aspar- 

 agine, C 4 H 8 N 2 3 , but not upon urea, CO(NH 2 ) 2 . 



The ammonium salts thus formed from the nitrogenous organic 

 matter of the soil usually quickly oxidise again under the influence of 

 a micro-organism, with the production of nitrous acid, or rather a 

 nitrite, and finally, by additional oxidation, a nitrate. The ultimate 

 chemical reactions are simple : 



(i) (NH 4 ) 9 C0 3 +30., = C0 2 +2HN0 2 +3H 2 

 (ii) 2HNO 2 +0 2 = 2HNO 3 



These changes, effected by the oxygen of the air, were shown in 

 1877 by Schloesing and Miintz - to be produced only under the in- 

 fluence of micro-organisms. Since then the subject has been carefully 

 studied by Winogradski, Deherain, Warington, Frankland and many 

 others. 



The general conclusions arrived at may be stated as follows : 

 1. The nitrogen of organic matter and humus is converted into 

 nitrates by passing through the intermediate stages of ammonium com- 

 pounds and nitrites, the successive steps being the work of different 

 organisms. Karerer, 3 however, states that some soils contain an or- 

 ganism, Bacillus nitrator, which can, in one operation, effect the 

 conversion of ammoniacal nitrogen into nitrates. The production of 

 ammonium compounds may be brought about by quite a number of 

 bacteria and moulds, but the changes of nitrogen from the state of am- 



Uour. Chem. Soc., 1894, Abstracts, ii. 248. 



2 Compt. Rend. 84, 301 ; Jour. Chem. Soc., 1877, 215. 



-Jour. Chem. Soc., 1907, Abstracts, ii. 381. 



