10 



CHAPTER II. 



GROWTH OF PLANTS AND MOLES OP IMPROVING. 



In discussing the subject of Agricultural Chemistry we will 

 consider the three systems under which the growth of plants 

 may be classified. 



1st. The natural, or normal system. 



2d. The system whereby the natural or normal yield is main- 

 tained. 



3d. The system called " high-farming," whereby it is sought 

 to double or even treble the natural yield. 



In all these systems certain conditions, such as soil, moisture, 

 air, heat, light, electricity, must be constant ; any great excess 

 or deficiency in these physical conditions rendering plant life 

 impossible. 



Soils are the result of the disintegration of rocks, and are, 

 therefore, as variable in chemical composition as are the rocks 

 from which they are derived. The way in which the disinte- 

 gration is accomplished is this : 



No rock, however compact, is impervious to water. Water, 

 as rain, therefore, holding in solution carbonic acid and oxygen, 

 coming in contact with a rock penetrates it, and yielding up 

 these gases to the elements for which they have an affinity, 

 renders them soluble in the water ; thus the rock breaks up from 

 having some of its particles continually removed, so that if we 

 should suppose a block of granite to be exposed to these condi- 

 tions for an indefinite time, we would have it at first solid, 

 then gradually disintegrated, next the mica and feldspar, pul- 

 verulent and fine, while the quartz remains massive, and lastly, 

 all in solution but the clay and sand. 



There is a property of soils which is of great importance in 

 agriculture, and without which plant life would be difficult. 

 This is the "absorptive power;" by this the soil absorbs and 

 stores in itself nutritious substances both from aqueous solu- 

 tions and from the atmosphere; and more, it even effects de- 

 composition, so as to retain the useful and eliminate the useless 

 material. 



Thus if we apply to a soil a soluble chloride or sulphate, as 

 potassic chloride or sulphate, a decomposition will take place ; 

 for if we pour on water we will find that the hydrochloric or 

 sulphuric acid will leach out combined with lime, while the 

 potash will be retained. 



In geaeral the soil absorbs the base and sets the acid free. 

 Phosphoric acid is, however, a striking exception, for this acid 



