72 THE MANURE HEAP AND SEWAGE. 
This loss occurs in several ways. i. Liberation of ammonia. 
Since the ammonia resulting from decomposition is a gas, it will, to a 
considerable extent, dissipate itself at once into the atmosphere. 
Such portions of it as unite with carbon dioxid to form ammonium 
carbonate are less volatile, but this, too, is partly volatilized. The 
odor of ammonia common around a manure heap plainly demon- 
strates this loss. 2. Denitrification. If by this term we refer only 
to the reduction of nitrates so as to set nitrogen free, the process is 
not very important in a manure heap, since there is present only a 
little nitrate, none, indeed, at first, when the fermentations are 
greatest. If nitrates are present, denitrification will cause a loss, and 
in the later stages of the rotting of manure, after nitrates are formed, 
this loss might be considerable. But it seems that loss from this 
cause is not so great as was formerly supposed. 3. Destruction of 
ammonia. There seems to be a direct " burning" of ammonia 
compounds in the manure heap by which the nitrogen is set free 
from it as free nitrogen. Little is known concerning this factor at 
present. 
The extent of the nitrogen losses from these sources may be 
considerable. Various estimates of the amount have been made, 
and it seems not beyond the mark to say that, in the ordinary condi- 
tions on the farm, at least 50 per cent, of the nitrogen is lost to the 
manure. It is sometimes considerably more than this, 50 per cent, 
being a fair average. When the farmer remembers the high cost of 
nitrogen fertilizers he may perhaps realize the very poor economy of 
allowing this loss to continue. Not all the loss is avoidable, for 
under the best conditions, perhaps 15 per cent, is lost; but even if this 
is true, 35 per cent, may be saved by proper care. It is possible for 
a farmer to know when this loss is becoming excessive by two means : 
i. The appearance of a strong odor of ammonia tells its own story; 
and while some such odor may always be expected, a strong odor 
indicates a too rapid loss. 2. The heating of the manure indicates 
rapid aerobic fermentations and this is always accompanied by a 
large nitrogen loss. Properly kept manure will not show a great 
rise in temperature and never a rapid one. The farmer may be 
confident that a noticeable heating of his manure pile means a large 
