E. J. Russell and E. H. Richards 553 



5. In the only heap where we were satisfied that the conditions 

 were anaerobic there was no accumulation of ammonia. 



6. There is no loss of nitrogen during the process: the whole of 

 the initial nitrogen being recovered within the error of the experiment. 



The aerobic changes are as follows : 



1. The loss of dry matter is greater and the temperature rises 

 higher than under anaerobic conditions. The gases evolved contain 

 no hydrogen or marsh gas. 



2. The loss of dry matter shows some relationship to the aggregate 

 rise of temperature. 



3. There is almost always a larger decomposition of complex 

 nitrogen compounds than under anaerobic conditions. There is not 

 usually an accumulation of ammonia in the laboratory, and in the heap 

 there is invariably a loss. 



4. Nitrate is found in the dry outer portions of the heap, but not 

 in the moister interior, nor was it found in the laboratory experiments 

 where the manure remained moist: the necessary conditions appear 

 to be dryness and sufl&cient air. 



5. Under ordinary conditions of incomplete aeration there is an 

 evolution of gaseous nitrogen, though this is not observed when the 

 conditions are wholly aerobic without any local anaerobic action. 



6. The loss of ammonia shows some relationship to the maximum 

 temperature attained. 



7. The loss of dry matter is greater from exposed heaps than from 

 sheltered heaps and so is the loss of ammonia, unless this is already 

 at a minimum ; but the loss of total nitrogen is not always greater. 



8. The loss of nitrogen is not wholly dependent on that of dry 

 matter, since as already stated it does not occur under purely aerobic 

 or purely anaerobic conditions, although other constituents are lost. 

 But the loss of nitrogen that occurs in the mixed aerobic and anaerobic 

 conditions occurring in practice varies under comparable conditions, 

 with the loss of dry matter, all constituents of the heap apparently 

 breaking down simultaneously. An exception occurs when the tem- 

 perature has risen high, e.g. to 70° C. after which decomposition of 

 nitrogen compounds and loss of nitrogen proceed more slowly than loss 

 of dry matter : an actual concentration of nitrogen in the heap therefore 

 occurs. A second exception is seen in exposed heaps, when the loss 

 of dry matter is usually proportionally greater than that of nitrogen. 



9. The loss of nitrogen might occur by 



(a) washing away of soluble nitrogen compounds, 



