ACTION OF LIME. 405 



originally derived. Exported in the form of grain, or 

 milk, or beef, it returns to the soil in some distant re- 

 gion or is poured into the rivers and the sea through 

 the drains of populous cities. New supplies of potash 

 and other material, are, therefore, demanded by the 

 vegetation of every successive year. 



1015. A large part of the materials re- 



How docs it . 



accomplish the ferred to are locked up in hard grains of 

 object ? granite, or other silicates which are found 



in the soils. Being insoluble in water and the other 

 solvents of the soil, they are inaccessible to the plant. 

 Lime has the property of forcing itself into the rocky 

 prison of every such insoluble grain, and setting part 

 of its inmates at liberty. At the same time it opens 

 the door to the action of other agencies which liberate 

 the rest. They are then floated away in the water 

 which penetrates the soil, and being in due season ab- 

 sorbed, are built into the substance of the plant. 



1016. ACTION OF LIME ON MINERAL MATTER 



Give the chem- ......,, , ... . 



ical explana- EXPLAINED. The actlOll of lime, Which 



tfon US a ~ nas J ust b een mentioned, is a simple conse- 

 quence of its basic properties. It takes 

 possession of part of the silicic acid of the alkaline 

 silicate in the rocky grains. Their potassa and soda 

 being now combined with this acid in small proportion, 

 are soluble in the water which penetrates the soil. 



10 17. The water of the soil always con- 



What other . . /--. j 



decomposing tains a certain proportion 01 carbonic acid. 

 a s % s t / xist ' sin This acid being itself material for vege- 

 table nutrition, has also the property of 

 dissolving those mineral substances which the plant 



