RATE OF OXIDATION OF AMMONIUM SULFAT. 39 



BXBECISB XXL 



THE EATE OF OXIDATION OF AMMONIUM SULFAT IN SOLU- 

 TIONS AND IN SOILS IN THE PEESENCB AND 

 ABSENCE OF CaCOg. 



1. Measure off in 250 cc. Erlenmeyer flasks eight 100 

 cc. portions of "solution for nitrite formation," adding the 

 Caf'O,, required to only four of these portions. 



2. Plug and sterilize in the usual way. 



3. Weigh ofE eight 100 gram portions of air-dry, sieved 

 soil, in tumblers. 



4. Add 100 mgs. (NHJ„SO, to each. 



5. Add 1 gm. of CaCOg to four of these. 



6. Stir in thoroughly by means of a sterile spatula. 



7. Arrange thus : 



1, 2, 3 & 4—1100 cc. solution. 

 5, 6, 7 & .8—100 cc. solution -|- 1 gm. CaCO:,. 

 9, 10, 11 & 12—100 gms. soil -|- 100 mgs. (NHO^SO,. 

 13, 14, 15 & 10-100 gms. soil -f- 100 mgs. (NHJ.SO., + 1 gm. 

 CaCO,. 



H. Inoculate both soils and solutions with 10 cc. (=^ 5 

 gms. soil) of a 5-minute infusion of a fresh sample of the 

 soil employed. 



9. Add sterile water to the soil portions to bring the 

 moisture conditions up to the optimum an^ cover the tum- 

 blers with Petri dish covers. 



10. Place in the incubator at 20° C. 



11. Weigh every ten days and with sterile water replace 

 that lost by evaporation. 



