124 



SCIENCE OF AGRICULTURE. 



We have then three great natural divisions of the 

 ingredients of soil : 1, geine, 2, salts, 3, granitic 

 sand, or silicates. Let us glance at these three di- 

 visions: 



1. Geim, — Geine enters vegetables either as geine 

 or as an alkaline, earthy or metallic geate dissolved 

 in water or alkali. The acids and salts of the plant 

 decompose these varied forms. The elements of 

 geine, its oxygen, hydrogen, and carbon, play their 

 usual parts in vegetable economy. The earthy and 

 alkaline bases of the geates form the bases of the 

 various salts which plants afford. 



2. Salts. — This class includes, first, compounds of 

 geine, second, alkaline, salts, potash, soda, ammonia, 

 and all their combinations known by the names of 

 carbonates, sulphates, phosphates, nitrates, muri- 

 ates, &-C. 



3. Silicates., or granitic sand. 



Table of the constituents of the elements of gra- 

 nitic sand. 



100 parts of 



Argillite, 

 Quartz, 

 Mica, Isinglass 

 Felspar, 

 Hornblend, 



Oxyd of 

 Mansa- 



1 to 2 



0.5 



0.25 



Argillite, a soft rock of the consistence of common 

 slate, contains carbon. Sulphuret of iron abounds. 

 Its decomposition produces with the silicates, sul- 

 phates of alkalies, earths, and oxyds. These with 

 the muriates and phosphates, give the inorganic ele- 

 ments of plants. Burning reduces these to two 

 classes, ashes and soluble salts. The last are found 

 in soot. The ashes are formed of salts and silicates 

 as the following analysis shews: 



Analysis of Wood Ashes. 

 Ashes are divided by the simple process of leech- 



