188 AMERICAN MANURES. 



vious state of combination. For example; the 

 two gases, nitrogen and hydrogen, the elements 

 of ammonia, may be mechanically mixed, but no 

 chemical combination will ensue. But should 

 nitrogen be present when water is being decom- 

 posed, the hydrogen being in the nascent state, 

 actual ammonia will at once be formed. 



As sulphate of lime or land plaster which is 

 a compound of sulphuric acid, lime and water 

 is present in the heap, the carbonate of ammonia 

 formed, decomposes the above compound, pro- 

 ducing carbonate of lime and sulphate of am- 

 monia, which is a stable compound, very soluble 

 in water. The formation of this salt prevents 

 loss from the volatilization of the ammonia. 

 This is the object in applying it in the heap. 

 From this the farmer can realize the importance 

 of applying plaster to his compost heap. Still, 

 it must be added with discretion, and not in 

 larger quantity than we have recommended ; if 

 too much is added, it will check the fermenta- 

 tion, and thus defeat the object to be attained by 

 composting; 100 Ibs. of ordinary unburnt ground 

 gypsum will fix nearly 20 Ibs. of ammonia. 

 The sulphuric acid of the gypsum will also act 

 beneficially, in decomposing the mineral sub- 

 stances contained in the vegetable remains. 

 The ammonia formed in the compost heap often- 

 times undergoes another change, which may be 



