CHAPTER II. 



METALS, METALLOIDS, AND ORGANIC ELEMENTS OF 

 SOILS. 



SILICON.* 



SILICON is one of the most abundant and widely distributed 

 substances, constituting probably one sixth of the entire mineral 

 weight of the globe. It is never found pure or in an uncom- 

 bined state, but always combined with oxygen, forming oxide 

 of silicon, or silicic acid. The vast mountains of granite, gneiss, 

 porphyry and sandstone, mica, feldspar, crystal quartz, nearly 

 all precious stones, -the sands of the sea shore and desert, and 

 all stones that emit sparks on being struck by steel, are mainly 

 silicon. 



It is contained in a crystaline state in the outside bark of 

 many plants, particularly in cane, bamboos and the grasses. It 

 is with difficulty separated from its oxygen, but when sepa- 

 rated and pure, it is a fine whitish powder, destitute of taste 

 or odor: it undergoes no change, except becoming darker and 

 denser, by any common degree of heat, but melts before the 

 blow pipe into colorless glass ; it has no affinity for pure water, 

 so that it is not dissolved in it in the smallest degree ; it absorbs 



* Recent investigations appear to show that silicon is neither a metal 

 nor a metalloid. 



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