NITRIFICATION 65 



41. Nitrification of Ammonium Compounds, 



the 



100 c.c. of this solution are placed in two small flasks, 

 which are closed with plugs of cotton-wool, and the 

 contents then boiled gently for fifteen minutes. The 

 flasks and contents are allowed to cool, the plugs removed, 

 and to each is added about -5 gram of calcium carbonate, 

 free from nitrates, which has been previously sterilised 

 by heating. To one flask only is also added about 

 one-fifth of a gram of ordinary arable soil. The two 

 flasks, one containing the original solution and the 

 other inoculated with active soil, are again closed with 

 the cotton-wool plugs and placed in a dark cupboard in 

 a warm room. (The optimum temperature of nitrifica- 

 tion is if C.) 



Every three or four days 5 c.c. of solution are 

 removed from each flask and tested for nitrites by 

 means of naphthylamine and sulphanilic acid (see 217, 

 p. 224), and for nitrates with diphenylamine and 

 sulphuric acid (40 {c\ p. 63). By this means the course 

 of nitrification can be readily traced. 



The experiment can be rendered quantitative by 

 estimating the nitrites and nitrates by the methods 

 described under Water Analysis (p. 223), or in 48 {d), 

 p. 70. If this is done the results should be plotted 

 graphically. 



E 



