OF AGRICULTURE. 217 



muriatic acid it forms common table salt, with the 

 taste of which every one is familiar ; with sulphuric 

 acid it forms Gluaber's salts, or sulphate of soda. 

 All the salts of soda are soluble in water. When 

 applied to the soil it immediately combines with -the 

 acids, and forms soluble salts, 



MAGNESIA, 



Magnesia is a common substance, existing in most 

 soils. It is a white, light, and odorless powder, and 

 slightly soluble in water. It forms soluble salts with 

 nitric, muriatic, or sulphuric acids. According to 

 11 Bergmann," magnesia forms an important ingredient 

 of some of the most important soils, and of the mud 

 of the river Nile, in Egypt, Jlagnesia is present in 

 almost all soils, in sufficient quantities for plants, and 

 is found in the seeds of most plants. It can be pro- 

 cured in large quantities from magnesian lime -stone, 

 which abounds in various sections of the world. 



IRON. 



Iron is sometimes found in its natural state, but 

 very seldom. The ores of this metal are very 

 numerous, and some of them very beautiful and 

 interesting. They are chiefly sulphurets and oxydes, 

 but the oxydes are the only ores from which the 

 metal is obtained. Iron combines with carbon, sul- 

 phur, iodine, phosphorus, and the different acids. It 

 is present in most all the soils, and is a constituent of 

 the blood of all animals, including man. 



SULPHUR. 



Sulphur is a well known brittle solid, of a greenish- 

 yellow color. It is chiefly interesting in agriculture 

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