FERMENTATIVE ACTION OF SOILS 209 



Add to watch-glasses or small beaker the following amounts of 

 the third solution : 



1 c.c. (which corresponds to .005 gr. of Nitrogen). 



2 c.c. .01 

 4 c.c. .02 

 6c.c. .03 

 8 c.c. .04 



10 c.c. .05 



15 c - c - -75 



20C.C. .10 



and evaporate all to dryness over a water bath. 



Then pour over the dry matter on each glass i c.c. of a 

 solution of 



4 gr. phenol in 



36 gr. sulphuric acid. 



Dilute with 5 c.c. of water, and wash off each into separate 

 narrow colorimetric cylinders with 15 c.c. of a 5 per cent, 

 solution of ammonia, and fill up to the 50 c.c. mark. 



Add to the series a cylinder of distilled water. 



After preparation of the standard colour scale take the nitrified 

 solution to be tested, and filter it. Wash the sediment in the 

 filter with distilled water, and make up the volume of the filtrate 

 to 100 or 150 c.c. Of this solution take 50 c.c., evaporate to 

 dryness, and treat as indicated in the preparation of the scale. 



Make up the solution of ammonium picrate obtained to 50 c.c., 

 and place it in a cylinder alongside those of the scale for com- 

 parison of tint. 



From the result. calculate the amount of nitrate present in the 

 nitrified solution. 



(v) Test the nitrogen-fixing power of the soil. 



Place the following solution in a large Erlenmeyer flask : 



Dextrose . . . . . 4 gr. 



Di-potassium phosphate . . .2 gr. 



Sodium chloride . , , , .2 gr. 

 



