INORGANIC SUBSTANCES. 



179 



Alluminum^ is a very rare metal. 



Allumina is very abundant, especially in clay soils. 

 It is soluble in acids, but not in water. The pro- 

 portion of it which plants absorb is exceedingly 

 small, and, from its abundance in the soil, would 

 lead one to suppose that it possessed some more 

 indirect and important quality, probably that of 

 the absorption of ammonia. 



Phosphate of alumina is present in the soil in very 

 small amounts. 



Sulphate of alumina exists in swampy, peaty soil. 



Calcium, in its combination with oxygen, forms 

 one of the most important of inorganic compounds. 



Lime. Many substances proceed very slowly in 

 their decomposition which is hastened by the ap- 

 plication of lime. 



Carbonate of lime forms a part of almost all plants, 

 and is very important to their growth. 



1 Johnston. 



