CHAPTER VI 



POTASH AND PHOSPHORUS 



LET us burn a plant, no matter what kind. The 

 first effect of the heat is to produce carbon, 

 which, mixed with other substances, constituted the 

 plant. If combustion continues, this carbon is dissi- 

 pated in the air in the form of carbonic acid gas, and 

 there remains an earthy residue which we call ashes. 

 Here then are two kinds of material, carbon and 

 ashes, which without exception enter into all plant- 

 life. The plant did not create them, did not make 

 them out of nothing, since it is impossible to obtain 

 something from nothing. It must, then, have de- 

 rived them from some source. "We shall take up be- 

 fore long the subject of coal and its origin, and shall 

 find that it comes chiefly from the atmosphere, 

 whence the leaves obtain carbonic acid gas, which 

 they decompose under the action of the sun's rays, 

 retaining the carbon and throwing off the air in a 

 condition fit for breathing. The vegetation of the 

 entire earth thus finds its principal nutriment in the 

 atmosphere, an inexhaustible and increasingly abun- 

 dant reservoir, because the respiration of animals, 

 putrefaction, and combustion are continually giving 

 forth as much carbonic acid gas as the combined 

 plant-life of the earth can consume, To maintain 



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