AGRICULTURE WIT^ CHEMISTRY. 51 



MAGNESIA, CONSIDERED AS A MANURE, 



Is contained in steatities or soap rock, and in a variety 

 of otiier earths and stones. It combines with acids, 

 forming neutral sahs, all of which are very soluble, and 

 the greater part of them promote, in a very considerable 

 degree, the growth of plants. Magnesian earths may 

 be applied with peculiar advantage to soils generally, 

 and not improperly called sour soils, containing green 

 vitriol, arising from the decomposition of pyrites. It 

 will decompose the metallic salt by superior affinity, 

 and form with the acid, Epsom salt, known in a high 

 degree to promote vegetation ; while the earth of iron 

 will be separated in the state of an ochre, or iron com- 

 bhied with fixable air. 



G a IRON". 



