SILICON BORON. 



83 



FIG. 6. 



These gases are generated by destructive distillation, the heat 

 being either supplied by a separate process (manufacture of 

 illuminating gas by heating wood or coal in retorts), or gener- 

 ated during the combustion itself. 



In a burning candle, for instance, the fat is constantly de- 

 composed by the heat of the flame itself, the generated gases 

 burning continuously until all fat has been decomposed, and the 

 products of decomposition have been burned up or converted 

 into carbon dioxide and water. 



An ordinary flame (Fig. 6) consists of three parts or cones. 

 The inner or central portion is chiefly unburnt gas; 

 the second is formed of partially burnt and burning 

 gas; the outer cone, showing the highest tempera- 

 ture, but scarcely any light, is that part of the 

 flame where complete combustion takes place. 



The light of a flame is caused by solid particles 

 of carbon heated to a white heat. The separation 

 of carbon in the flame is explained by the fact that 

 hydrogen has a greater affinity for oxygen than 

 carbon ; only a limited amount of oxygen can pene- 

 trate into the flame, and the hydrogen of the hydro- 

 carbon will consume this oxygen, the carbon being 

 liberated momentarily until it reaches the outer 

 cone, where it tinds sufficient oxygen with which 

 to combine. 



If a sufficient amount of air be previously mixed 

 with the illuminating gas, as is done in the Bunsen 

 burner, no separation of carbon takes place and no light, but a 

 more intense heat is generated. 



Silicium or Silicon, Si = 28, and Boron, B = 11, are elements 

 which, in many respects, resemble carbon. Both, like carbon, 

 are infusible, non-volatile, and insoluble in all common solvents. 

 Like carbon, they are known in the amorphous state, and as 

 crystals which resemble diamond or graphite. Silicium is, like 

 carbon, quadrivalent; boron, however, is trivalent. 



Silicium is found in nature very abundantly as silicium di- 

 oxide, or silica, Si0 2 (rock-crystal, quartz, agate, sand), and in 

 the form of silicates, which are silicic acid, H 4 SiO 4 , in which the 

 hydrogen has been replaced by metals. Most of our common 



