354 SMITH'S INTERMEDIATE CHEMISTRY 



In subsequent chapters we shall return to the different classes 

 of organic substances, tabulated here and on pp. 347-50, and dis- 

 cuss their properties and industrial uses in greater detail. 



FLAME 



We have encountered a variety of flames, from the simple one 

 of hydrogen burning in air to the more complicated case of the 

 luminous flame of ethylene or acetylene. The subject will now 

 repay a somewhat closer study. 



The Simple Flame. The flame of hydrogen (giving water), 

 or of carbon monoxide (forming carbon dioxide) is very simple in 

 structure (Fig. 88). We find that there is a tapering column of 

 unburnt gas in the interior, surrounded by a layer of hot 

 gas the flame itself. The flame is therefore a hollow 

 cone. That the flame is hollow is easily shown by hold- 

 ing a wooden match across it. The match is charred at 

 the two points at which it crosses the flame, and remains 

 unheated in the middle. These flames are simple, be- 

 cause only one chemical change occurs in them. The 



r IG. oo 



flames are rather large, because sufficient oxygen to 

 burn all the gas does not reach the latter at once, and the gas 

 travels upwards and diffuses outwards a certain distance before 

 being all consumed. 



If oxygen is substituted for air, by lowering the jet into a jar 

 of that gas, the flame becomes much smaller. In the absence 

 of atmospheric nitrogen, there is now five times as much oxygen 

 within a given range of the center of the jet as before. This 

 chemical union, like any other, proceeds more rapidly with an 

 increase in the concentration of the interacting substances (p. 233). 

 It is therefore completed before the gas has time to 'diffuse very 

 far from the opening of the jet. 



The Candle Flame. A candle is made of a mixture of paraffin 

 and stearic acid (one of the higher members of the fatty acid 



