246 Plant Physiology 



the power of ammonification. Place the cultures at a tempera- 

 ture of 28 to 30 C., and in two weeks test the inoculated and 

 uninoculated tubes for ammonia with Nessler's solution. 



The Nessler solution is prepared by dissolving 2 grams of 

 potassium iodide in 5 cc. of hot water, while warm add mercuric 

 iodide to excess of solution, cool, dilute with water to 25 cc., 

 shake, settle, filter, and then dilute the nitrate to 50 cc. with a 

 concentrated solution of caustic potash. This solution assumes 

 a yellow color when there is added to it a few drops of a solution 

 containing ammonia. 



Nitrification. A crude but simple demonstration of nitri- 

 fication phenomena, usually successfully carried out, may be 

 made with impure cultures as follows : 

 Prepare a solution containing 



Ammonium sulfate 5 gram 



Dipotassium phosphate 5 gram 



Sodium chlorid 2 gram 



Magnesium sulfate 2 gram 



Ferrous sulfate 05 gram 



Water 200 cc. 



Weigh out .5 gram of basic magnesium carbonate into each of 

 four small Erlenmeyer flasks, add to each 50 cc. of the above 

 salt solution, plug with cotton, and sterilize. When cool inocu- 

 late three of the flasks with a small quantity (about .1 gram) 

 of garden loam taken 5 or 6 inches below the surface of the soil. 

 Save the fourth flask as a control. Place all at a temperature 

 of 28 to 30 C. Once a week remove from the inoculated flasks 

 from 3 to 5 cc. of solution and make the following tests : 



1. For ammonia. Employ Nessler's solution. 



2. For nitrites. Acidulate with sulfuric acid about 2 cc. of 

 the solution, add a few drops of potassium iodide and starch 

 paste. If nitrates are present the starch is colored blue from the 

 reduced iodine. 



3. For nitrates. When from (2) it is evident that nitrites 

 are no longer present, dissolve a crystal of diphenylamine in 

 about 1 cc. of sulfuric acid in an evaporating dish. The addi- 



