SECOND CHAPTER, 



THE ORGANIC ELEMENTS. 



i^F THE four elements which constitute the bulk 

 ^^ of vegetable substances, and which are torn 

 away from this combination and allowed to escape 

 into the air by exposure to heat (rapid combustion, 

 or burning), carbon deserves to be named 

 first, as it forms nearly one- half, by 

 weight, of all the dry substance of our farm crops. 

 In charcoal we have the most common and best 

 known, though an impure form of carbon. Other 

 organic forms of this element are soot, lamp-black, 

 etc. , and in an inorganic condition it appears in the 

 diamond, which is pure carbon, in graphite, petro- 

 leum, etc. 



Oxygen forms about one-third, by weight, of the 

 dry substance of vegetable matter. It is a most re- 

 markable, ever-present, gaseous body, responsible 

 for the great changes that occur, and especially 

 powerful in destroying. We may call it 

 ^^^*°' omnivorous (all devouring), as it is 

 always ready to pounce upon and combine with 

 other substances, tearing them away from other affil- 

 iations, and thus ever changing their forms and 

 conditions. It has a particular appetite for carbon 

 and other combustible substances, and when once 



