196 METALLOIDS. 



already, but its chemical appetite is only half satisfied 

 with that element. It is this gas, produced in the fire, 

 as before described, which converts iron ores into metal, 

 in the smelting furnace. It is itself converted into car- 

 bonic acid at the same time. 



SILICON. 



What is sili- 482. DESCRIPTION. Silicon is a dark 

 con ? gray substance, possessed of metallic lustre, 



but classed with the metalloids, because it resembles 

 them in its compounds. It is also called silicium. 

 It is prepared from silica, by the method hereafter de- 

 scribed for the production of calcium from lime. 



483. SILICIC ACID OR SILICA. Quartz 

 *icaf ^ Sll ~ or roc ^ crvsta lj i s nearly pure silica. Sea- 

 sand, opal, jasper, agate, cornelian, and 



chalcedony, are other forms of the same substance. 

 It forms also part of a very abundant class of rocks, called 

 silicates, and probably forms one-sixth of the mass of 

 the earth. 



484. SOLUBLE SILICA. Silica may be 



How can silica 



be made solu- dissolved in water, by first fusing it with 

 a large proportion of potash. On then ad- 

 ding acid, to neutralize the potash, the silica precipitates 

 in the form a jelly. By this circuitous process, the 

 most gritty sand is converted into a soft jelly. A sin- 

 gular application of this rock-jelly, in the adulteration 

 of butter, has recently been detected in England. Dis- 

 solved silica also occurs in nature, and hardens into 

 agates, onyx, and other precious stones. 



