CARBON. 



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FIG. 10. 



Flame is gas in the act of combustion. Of combustible gases, 

 have been mentioned : hydrogen, carbon monoxide, marsh-gas, and 

 olefiant gas. These four gases are actually those which are found 

 chiefly in any of the common flames produced by the combustion of 

 organic matter, such as paper, wood, oil, wax, or illuminating gas itself. 



These gases are generated by destructive distillation, the heat being 

 supplied either by a separate process (manufacture of illuminating 

 gas by heating wood or coal in retorts), or generated during the 

 combustion itself. 



In burning a candle, for instance, fat is constantly decomposed 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, i. e., have been 

 converted into carbon dioxide and water. 



An ordinary flame (Fig. 10) consists of three__rjarjbs 

 or cones. The inner or central portion is chiefly un- 

 burnt gas; the second is formed of partially burnt and 

 burning gas; the outer cone, showing the highest tem- 

 perature, but scarcely any light, is that part of the flame 

 where complete combustion takesj)lace. 



I 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 has carbon ; only a 

 limited amount of oxygen can penetrate into the flame, 

 and the hydrogen of the hydrocarbon will consume this 

 oxygen, the carbon being liberated momentarily until it 

 reaches the outer cone, where it finds sufficient oxygen with which to 



combine. 



jt 



If a sufficient amount of air be previously mixed with the illumi- 

 'nating gas, as is done in the Bunsen burner, no separation of carbon 

 takes place, and, therefore, no light is produced, but a more intense 

 heat is generated. 



Silicon or Silicium, Si = 28.3, is found in nature very abun- 

 dantly as silicon dioxide, or silica, SiO 2 (rock-crystal, quartz, agate, 

 sand), and in the form of silicates, which are silicic acid in which the 

 hydrogen has been replaced by metals. Most of our common rocks, 

 such as granite, porphyry, basalt, feldspar, mica, etc., are such sili- 

 cates, or a mixture of them. Small quantities of silica are found 

 in spring waters, as well as in vegetable and animal bodies. 



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