132 MANURE. 



2d. Those consisting chiefly of salts. 



3d. Mixed, or consisting of salts and geine. 



175. This seems to be a rational and practical mode of 

 classifying a vast amount of materials, and the explanation 

 of their action in classes, is preferable to a specific account 

 of each individual substance composing these classes. 



176. By far the greater part of manures belongs to the 

 third class. Such are all composts, all stable manure, and 

 all the usual products of the cow-yard and hog-pen. In dis- 

 cussing, therefore, this subject, there ought to be some start- 

 ing point, some standard common measure of value, to 

 which can be referred all manures, and by which their worth 

 can be determined. 



177. In selecting a manure for this purpose, if it can be 

 ascertained how much of geine, what salts, and in what pro- 

 portion these salts enter into its constitution, what gases it 

 evolves, what chemical action it induces upon silicates, it m ill 

 determine the relative value of all manures ; they will 

 approach or depart from the standard, in exact proportion to 

 the geine and kind of salts they contain. 



178. Manures, then, are the elements of fertility. They 

 contain besides the inorganic salts, the organic elements of 

 plants, oxygen, hydrogen, carbon, nitrogen. The quantity 

 of ammonia which each manure can afford, will be in direct 

 proportion to the quantity of nitrogen which each contains ; 

 and perhaps the only true and scientific view which should 

 be taken of manures is that which states their components 

 not as compounds, but as simple elements; a statement 

 which should give at a glance the exact quantity of the four 

 organic elements which enters into their composition. To a 

 limited extent this can be done, and in the attempts to illus- 

 trate this subject, this mode of stating the value of manures, 

 will be united with a more detailed account of their ingredients. 



