40 PHOPERTIES OF ELEMENTS OF SOIL. 



cornelian. All these are silicon, acidified by oxy- 

 gen, hence called silicic acid. It is this acid which 

 forms with potash, the hard coat of the polishing 

 rush ; the outer covering of the stalks of grasses. 

 Wheat, rye, oats, barley, owe their support to this 

 covering of silica. It cases the bamboo, and rattan 

 with an armor of flint, from which may be struck 

 sparks. Entering into the composition of all soil, 

 and hard and unyielding as it appears, forming not 

 only the solid rock, but the delicate flower, which 

 that supports ; forming combinations with the metals 

 of soil whose gradual decomposition is the birth of 

 fertility, silicon demands a detail of its properties, 

 commensurate with the high functions it performs. 



68. Silicon, in the purest state, yet obtained, is a 

 dull, brown powder, soiling the fingers. It dissolves 

 in fluoric acid, and in caustic potash. Heated in air 

 or oxygen gas, it burns vividly, and is partly con- 

 verted into silica. Heated in a closed crucible, it 

 shrinks very much, but does not vaporize. Heat 

 has altered all its properties. It has become a deep 

 chocolate color. It sinks in oil of vitriol, one of the 

 heaviest of fluids — it will dissolve in no acid, except 

 a mixture of nitric and fluoric ; caustic alkali has no 

 action on it, nor will it burn, in the intensest flame 

 of air or oxygen gas. No other simple substance is 



