124 MANURE. 



is capable of simplification. Manures are generally 

 considered and treated of, under the division of ani- 

 mal and vegetable. This common and ancient di- 

 vision, indicating little of the nature of manures, 

 actually confounds those, whose elements are es- 

 sentially alike. Manures are to be divided by their 

 elements," into three classes : — 



1st. Those consisting chiefly of geine. 



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 pref- 

 erable to a specific account of each individual sub- 

 stance 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 discussing therefore, this subject, 

 there ought to be some starting point, some standard 

 common measure of value, to which can be referred 

 all manures, and by which their worth can be deter- 

 mined. 



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

 can be ascertained, how much of geine, what, and 

 in what proportion salts enter into its constitution, 



