METHODS. 85, 



IV. Humus Determination. 



1. 10 gms. of the sample are placed in a Gooch crucible 

 and extracted with 1% HCl until the filtrate gives no re- 

 action with ammonia and ammonium oxalate. 



2. The acid is removed by washing with water. 



3. The contents of the crucible are then washed into a 

 glass stoppered cylinder with 500 cc. of 4% NH^OH. Stand 

 24 hours with occasional shaking. Stand 12 hours to permit 

 settling. 



4. The supernatant liquid is filtered and an aliquot evap- 

 orated, dried at 100° C. and weighed. 



5. The residue is then ignited and weighed. 



6. The humus is calculated from the difference in weight 

 between the dried and the ignited residues. 



V. Ammonia Determination. 



10-15 gms. of heavy MgO and a piece of paraffin are added 

 to the solution to be tested, the NHg distilled off, collected 

 in standard acid, and titrated against standard alkali. 



VI. Some Qualitative Tests. 



1. Nitrates. 



A small portion of the solution to be tested is treated with 

 a solution of diphenylamine in H2SO. The presence of ni- 

 trates is indicated by the appearance of a blue color. 



2. Acetic acid. 



Treat a little of the solution to be tested in a test tube with 

 a mixture of HjSO^ and ethyl alcohol. The presence of 

 acetic acid may be detected by the ethyl acetate odor which 

 is quite distinctive. 



