THE PLANT. 27 



CHAPTER IY. 



EAKTHY MATTER. 



WE will now examine the ashes left after burning 

 vegetable substances. This is earthy matter ; and it 

 is obtained from the soil. Atmospheric matter, al- 

 though forming so large a part of the plant, we 

 have seen to consist of four different substances. 

 The earthy portion, on the contrary, although 

 forming so small a part, consists of no less than nine 

 or ten different kinds of matter. These we will 

 consider in order. In their relations to agriculture 

 they may be divided into three classes alkalies^ 

 acids, and neutrals* 



Alkalies and acids are of opposite properties, and 

 when brought together they unite and neutralize 

 each other, forming compounds which are neither 

 alkaline nor acid in their character. Thus, carbonic 

 acid (a gas) unites with lime a burning, caustic 

 substance and forms marble, which is a hard, taste- 

 less stone. Alkalies and acids are characterized by 

 their tendency to unite with each other, and the com- 

 pounds thus formed have many and various proper- 

 ties, so that the characters of the constituents give 

 no indication of the character of the compound. 

 For instance, lime causes the gases of animal manure 



* This classification is not strictly scientific, but it is one which 

 the learner will find it well to adopt. These bodies are called 

 neutrals because they have a less decided alkaline or acid charac- 

 ter than the other. 



