286 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



period, again weighed and analyzed. The following are some of 

 the results : 



Exposure to rain certainly involves a considerable loss of 

 fertility. 



Fermentation. 3 Two classes of bacteria take part in the fer- 

 mentation of manure ( I ) Aerobic, which live only in the presence 

 of oxygen, (2) Anaerobic, which live only when oxygen is ex- 

 cluded. On the outer surface of the heap, the aerobic bacteria 

 are active, while the anaerobic ferments act in the interior of the 

 heap where the supply of air is limited. The anaerobic bacteria 

 are less vigorous in their action than the aerobic. They often 

 produce foul smelling gases. The fermentation also varies ac- 

 cording to circumstances. It depends on the temperature, the 

 supply of air, the moisture, the composition of the material, and 

 the preservatives used. 



The optimum temperature for manure fermentation is about 

 131 F. The temperature may rise high enough to set the mass 

 on fire, if it is dry enough. The temperature of the interior of 

 the heap, where anaerobic fermentation is in progress, rarely 

 rises over 95 F. 



The supply of air is determined by* the compactness of the heap. 



1 Bulletin 150. 



2 Bulletin 183. 



3 Herbert, Exp. Sta. Record 5, p. 146. 



