AGRICULTURE WITH CHEMISTRY. 15 



EARTH OF IRON 



Exists in ground in a metallic state, in the state of 

 an earth, and in the state of a mineral salt. It is the only 

 metallic earth thought necessary to define, in this Trea- 

 tise on Agriculture. An attempt will hereafter be made 

 to explain the manner in which it promotes vegetation. 



AIR. 



Bv air'^is generally understood, the medium in which 

 terrestrial animals move and breathe. It is possessed ot 

 weight or gravity, is capable of comj)rcssion : without 

 it neither animals could live, nor could fire be main- 

 tained, or heat generated. 



Part only of atmospheric air serves for the support of 

 animal life and combustion, called vital air, pure air, or 



oxygen. 



