80 THE MANURE HEAP AND SEWAGE 
especially subject to this destructive fermentation; a fact due 
partly to the large amount of hay that it contains and partly 
to its loose and porous nature, which allows a free access of air. It 
suffers more loss for this reason than most other types of manure— 
a loss that may be lessened by mixing with it some of the moister, 
denser cow manure. Liquid manure also is subject to heavy losses, 
because it so rapidly undergoes the ammoniacal fermentation. 
There are two general methods of controlling and reducing these 
losses. The first is by chemical means. Since the ammonia is 
volatile and a strong base, the addition to the manure of some 
chemical to combine with it will produce salts that will be more 
likely to be retained in the manure. For this purpose quite a list 
of substances has been recommended, of which gypsum, sulphuric 
acid and phosphates are of most importance. Mosi of them are too 
costly to be economical; but certain phosphate fertilizers have 
proved of considerable practical value. Their value is not wholly 
because they fix the ammonia, but also because farm manure is de- 
ficient in phosphorous and the use of phosphates reinforces it in this 
particular. The losses due to ammonia vaporization may be pre- 
vented by these chemicals; but the losses caused by the liberation 
of free nitrogen cannot be checked by any means short of stopping 
bacterial growth, and this would check the beneficient as well as 
the injurious fermentations. 
The second method is mechanical and is more efficient. It is 
based upon the facts already emphasized, viz., that the destructive 
fermentations take place most vigorously in the presence of a large 
supply of oxygen and that the volitilization is much more rapid 
from a partly dry than from a wet mass. Hence manure that is 
loosely piled loses much more nitrogen than that which is firmly 
compacted. The practice of firmly compacting manure into con- 
ical heaps with smooth sides is best calculated to reduce the losses 
to a_ minimum. Experiment has shown that a lot of manure 
firmly compacted may lose 15 per cent. of its nitrogen during stor- 
age, while a similar lot loosely stored loses 35 per cent.; a very 
