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. 



BY air is generally understood, the medium in which 

 terrestrial animals move and .breathe. It is possessed of 

 weight or gravity, is capable of compression : without 

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

 tained, or heat generated. 



f . 



--^ --. * ^ V i 



Part only of atmospheric air serves for the support of 

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



oxygen. 



