70 AMERICAN MANURES. 



forming a storehouse of these substances for the 

 future use of plants. 



Sulphate of Iron is formed in soils that contain 

 the elements of sulphur and iron. This com- 

 pound, when present in large amount, is injuri- 

 ous to vegetation. And there are few soils that 

 do not contain some of it ; and it is often found 

 in low, marshy lands. Soils that contain it in 

 such quantity as to be injurious, are very much 

 benefited by the addition of lime, or marl ; the 

 lime uniting with the sulphuric acid of the sul- 

 phate to form gypsum." Iron pyrites, reduced 

 to a fine powder, may be applied in small quan- 

 tity very advantageously to some soils, when 

 iron and sulphuric acid are deficient, and the soil 

 abounds in carbonate of lime. But, should the 

 soil be deficient in lime, it should be applied at 

 the same time either as quicklime or marl. The 

 application of gypsum is not necessary to soils 

 that contain iron pyrites, as by the application 

 of lime to such soils it would be formed more 

 cheaply. 



POTASSIUM. 



Potassium is a solid; and was discovered by 

 Sir H. Davy, in 1807. It is silver-white in 

 color, and lighter in weight than water. If a 

 globule of potassium be dropped upon the surface 

 of water, it instantly takes fire, and burns with 



