NITRIFICATION 145 



the development of a violet blue colour shows the presence of a 

 nitrate. Since the same colour is given with a nitrite, this test, 

 if intended for detecting nitrates, can only be applied when a 

 previous test for a nitrite has failed. 

 Note the time 



(1) Taken for the complete disappearance of ammonium 



reaction. 



(2) When nitrite first appears. 



(3) When nitrate first appears. 



(4) When the nitrite disappears. 



Repeat the above experiment, using soil from 



(1) An ordinary arable field. (3) A peat bog. 



(2) An old pasture. (4) A wood or forest. 

 Also with soil from 



(1) The surface of the ground. (3) 12 inches below ground. 



(2) 6 inches below ground. (4) 3 feet 



Ex. 75. To test the influence of temperature on nitrification, 

 repeat Ex. 74, keeping some of the flasks 



(1) In a cool place. 



(2) At a temperature of 20 C. 



(3) At a temperature of 30 to 35 C. 



(4) Add to one of the flasks soil which has been heated to 



a temperature of 100 C. for half an hour. 



Ex. 76. To test the inhibiting effect of soluble organic com- 

 pounds on nitrification, repeat Ex. 74, adding to a series of 

 flasks .01, .03, .3, i, and 3 per cent, of 



(1) Dextrose, 



(2) Peptone, 



(3) Urea 

 respectively. 



Ex. 77. Take six or eight conical flasks with bases about 

 4 or 5 inches in diameter : pour into each 50 c.c. of the 

 solution given in Ex. 74, and add .5 gr. of basic magnesium 

 carbonate. Inoculate one of the flasks with about i gram of 



K 





