BY MANURES. 283 



rectly under the notice of tlie farmer, than any other pertain- 

 ing to his employment. It is one which may derive the most aid 

 from science. In fact it is the most important branch of 

 Agricultural Chemistry, to point out the best and cheapest 

 modes of preparing manures in sufficient quantities ; of ap- 

 plying them to different soils, and for different crops ; and to 

 explain the theories of their action both in the soil and in 

 vegetation. 



Manures contain all the elements of fertility. They are 

 composed of decaying vegetable and animal matter (humus 

 or geine), which constitutes the largest portion of them ; of 

 a small quantity of silicates, such as silicate of potash ; and 

 of salts, such as phosphates, nitrates, sulphates, carbonates 

 and muriates. 



Manures have been variously classified. A very ancient 

 division is into animal, vegetable and mineral ; thus indicat- 

 ing the source from which they are derived. 



The classification proposed by Dr. Dana* appears to be 

 the most scientific as well as practical. His classes depend 

 upon the quantity of geinef and salts. This arrangement, 

 with some modifications, will be adopted in this work. 



1. Mixed manures, or those which consist of salts and 

 geine. 



2. Manures which consist mostly of salts, derived from ani- 

 mal and vegetable bodies. 



• 3. Manures which consist mostly of geine. 



4. Saline manures, or those which are composed of inor- 

 ganic salts. 



The points most worthy of attention, both in a scien- 

 tific and practical view, are the nature and composition of the 



* Muck Manual, p. 124. 



t The term geine is used here not as synonymous with huviic acid, 

 but with humus ; and wherever it is used, in treating of this subject, 

 it is intended to include the organic portions of manures, or the de- 

 caying organic matter. 



