404 ORGANIC CHEMISTRY. 



nia, which is the rarest and most expensive one, in 

 much larger proportion. 



1012. USE OF THE CLAY. The clay in 



What purpose . 



does day sub- soils serves to retain the ammonia and 



e certam otner valuable materials, which 

 would, otherwise, be washed away by 

 descending rains. It seizes not only upon that which 

 comes from the decaying humus, but finds particles in 

 the drops of every shower, which it stores safely away 

 for the future use of the plant. It serves also to retain 

 moisture in the soil, and to impart to it the tenacity 

 by which the roots are enabled to gain a firm hold upon 

 the earth. Soils which contain but a small proportion 

 of clay are for these reasons improved by its addition. 



1013. USES OF THE SAND. Sand, where 



What is the 



office of sand it exists in due proportion, gives the proper 

 tn wist degree of porosity to the soil, and thus 

 ensures the entrance of the air and fertilizing liquids, 

 and the draining away of all excess of water. Access 

 of air is important, because it brings with it fertilizing 

 ammonia and carbonic acid, and by accelerating the 

 decay of vegetable matter, produces more of these 

 valuable substances. 



1014. USES OF THE LIME. The lime in 



What is the -, . , , -, -, 



office of lime soils, beside serving directly as building 

 on the soil? mater ial for all forms of vegetation, is the 

 key which unlocks other treasures of the soil and sup- 

 plies them, also, to the growing plant. The building 

 material which is furnished, as before explained, by 

 the decay of previous plants, is not sufficient. A por- 

 tion of it never reaches the fields from which it was 



