144 NITRIFICATION 



solution of ferrous sulphate to prevent coagulation : sterilize at 

 100 C. Inoculate with pure cultures of 



(a) Bs. mycoides ; 



(b) Bact. fluorescens liquefaciens ; 



(c) Bact. (Proteus) vulgare ; 

 and incubate at 30 C. for ten to fifteen days. 



(1) Test for ammonia with Nessler's solution. 



(2) Heat with calcined magnesia and test the gases evolved 



with litmus paper. 

 Compare with uninoculated sterilized control tubes. 



Ex. 74. Prepare the following solution : 



Ammonium sulphate . . ... 2 gr. 



Di-potassium phosphate . . . i gr. 



Sodium chloride . . . . . 2 gr. 



Magnesium sulphate . . , . .5 gr. 



Ferrous sulphate . . . . . .4 gr. 



Distilled water , . . . . i litre. 



Pour 50 c.c. into three or four conical flasks and to each add 

 .5 gr. of basic magnesium carbonate. Then add to each about 

 i gram of garden soil taken 4 or 5 inches below the surface of 

 the ground, and keep at a temperature of 30 C. Withdraw 

 5 c.c. from each flask every three or four days and test one-third 

 of each 5 c.c. : 



(1) For ammonia with Nessler's solution. 



(2) For nitrites by means of zinc iodide or cadmium iodide 



starch paste and sulphuric acid. 



Dissolve a small quantity of starch in water by heating ; cool 

 and add a crystal of Cdl and heat till dissolved, then add 

 i to 2 c.c. of dilute H 2 SO 4 (^ per cent.) : a blue colour indicates 

 the presence of a nitrite. 



(3) For nitrates after the nitrites have disappeared with 



diphenylamine and sulphuric acid. 



Dissolve a small crystal of diphenylamine in i or 2 c.c. of 

 strong H 2 SO 4 , then add a few drops of the nitrifying solution ; 



