54 A TREATISE ON THE CONNECTION OF 



When alkalis, calcareous matter, or magnesia, are added 

 to soils containing snch metallic salts, they are decom- 

 posed; the acid combining with these substances in pre- 

 ference to the earth of iron, which is separated in the 

 state of yellow ochre, or iron combined with fixable air. 



By the addition of animal, vegetable substances, or 

 carbonaceous matter, to lands containing iron in this 

 state, it is brought towards a metallic state, and fixable 

 air is disengaged. Ground, containing much iron in the 

 state of ochre, is of a yellowish tinge, or colour ; but as 

 it receives d\mg or inflammable matter, the soil, together 

 with the iron contained in it, -will change to a brown or 

 dark colo u . 



Iron thus reduced to a metallic state is capable of com- 

 bining with pure air or oxygen, in which case fixable 

 air would be generated by the combination thereof 

 with the carbonaceous matter of the iron. The fixable 

 air thus generated, may be disengaged from the earth 

 of H-on by a fresh application of inflammable matters. 

 Nothing is at rest in this world ; all bodies are under- 

 going successive changes from one state to another. 



I On 



