AGRICULTURE WITH CHEMISTRY. 



53 



forms gypsum, a salt which is very insoluble ; whilst 

 with magnesia arc! alkalis it forms Epsom salt, and vi- 

 triolated tartar, or Glauber salts : salts, whose beneficial 

 efFeds on the growth of plants have been fully ascer- 

 tained. 



The proportion of iron in most soils, is so very con- 

 siderable, tliat there can be no doubt but it was placed 

 there, by the Great Creator of all things, to answer some 

 wise purpose ; and, although it is only found in small 

 quantities in vegetable and animal substances, still its 

 effefts in j^romoting vegetation, may, in a chemical point 

 of view, be much greater than can possibly be accounted 

 for by the very small proportion of iron found in organic 

 bodies. 



The following is an attempt to explain how it ma^ 

 conduce to vegetation. 



Iron, as has been observed, is found in soils under 

 different modifications, changing from one itate to 

 another: when in that of pyrites it is changed, by the ab- 

 sorption of pure air or oxygen, to that of a metallic salt. 



When 



