INORGANIC SUBSTANCES. 181 



Sulphuret of iron exists in some undrained soils, 

 and although not itself injurious, yet, when exposed 

 to the air. it produces the sulphate of iron, or green 

 vitriol, which is decidedly hurtful to plant-life. 



If the land is thoroughly pulverized and drained, 

 this will become the per-oxide, which is so beneficial 

 a compound. 



Carbonate of magnesia exists in many soils, and 

 has great powers of absorbing moisture. 



Chloride of magnesium has been applied with 

 benefit to lands, but great care must be exercised 

 on account of its remarkable solubility. 



Phosphate of magnesia is present in urine, and in 

 many of our most valuable fertilizers. 



Manganese resembles iron in its action and char- 

 acter, and in forming several combinations with 

 oxygen. 



Phosphorus, when combined with other substances, 

 forms many valuable compounds — such as phos- 

 phate of lime, phosphate of potash, etc. 



Silica produces many valuable substances in its 

 combination with potash, soda, etc. It is present 

 in all vegetable matter, and is distributed very lib- 

 erally through the soil. It is insoluble in water, 

 and dissolves very slowly in alkalies. 



Carbonate of potash exists in the sap of almost all 

 plants, and the good results following the applica- 

 tion of wood ashes are produced by its presence. 



Chloride of potassium is also found in the ashes 

 16 



