NITRIFICATION 



35 



these investigations have been discounted on the grounds 

 that the cultures were contaminated with heterotrophs [35, 



percolating fluid 

 drawn up tube 

 by suction 



capillary 

 tube 



to suction 

 pump «. 



air or gas inlet 

 and sampling tube 



FIG. 3.1. — Lees' soil percolation apparatus, as modified 

 by Audus [3] 



12]. Quastel and Scholefield have pointed out that organic 

 inhibitors fall into two groups, those which inhibit in con- 

 centrations of 0-0 1 M. or less and those which inhibit only 



