MANURE. 125 



what o-ases it evolves, what chemical action it induc- 

 es upon silicates, it will 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, beside the inorganic salts, the organic 

 elements of plants, oxygen, hydrogen, carbon, nitro- 

 gen. The quantity of ammonia which each manure 

 can afford, will be in direct proportion to the quan- 

 tity of nitrogen which each contains ; and perhaps 

 the only true and scientific view, which should be 

 taken of manures, is that, which states their compo- 

 nents 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 illustrate this subject, 

 this mode of stating the value of manures, will be 

 united with a more detailed account of their ingre- 

 dients. 



179. And first, for the choice of some substance 

 which shall form the type of manures, and be con- 

 sidered the standard of value. Let it be pure fresh 

 fallen cow dung, and what is its composition ? Water, 

 hay, and bile, with a few salts. The author has re- 



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