PRODUCTS OF DECOMPOSITION. 35 



great sources of loss in the decomposition of farm- 

 yard manure is due. If the temperature of the 

 manure-heap be permitted to rise too high, the car- 

 bonate of ammonia volatilises. It is probable, also; 

 that a not inconsiderable portion of the nitrogen 

 escapes into the air in the free state. The last of the 

 most important gaseous products of decomposition are 

 sulphuretted and plwsphoretted hydrogen. It is to these 

 gases that much of the smell of rotting farmyard 

 manure is due. 



2. The second class of substances formed are soluble 

 organic acids, such as Jiumic and ulmic acids. The 

 function performed by these acids is a very important 

 one. They unite with the ammonia and the alkali 

 substances in the mineral portion of the manure, 

 forming humates and ulmates of ammonia, potash, &c. 

 It is these ulmates that form the black liquor which 

 oozes out from the manure-heap. 



In very rotten farmyard manure traces of nitric 

 acid may be found, but it must be remembered that 

 the formation of nitrates is practically impossible 

 under the ordinary conditions of active fermentation 

 of farmyard manure, except perhaps in its very last 

 stages. 



3. The third class of changes taking place have to 

 do with the mineral portion of the manure. The 

 result of the formation of so much carbonic and other 

 organic acids is to increase the amount of soluble 

 mineral matter very considerably. 



