138 CHEMISTRY. 



part, where the iminflamed gas is, there is no oxygen, and 

 the heated hydrogen and carbon are ready to unite with 

 oxygen, and so take it from the surface of the metal. Then, 

 too, in the bright part of the flame there is not a free access 

 of oxygen, and therefore the oxygen combined with the 

 metal is taken and used in the burning. The portions of 

 the flame, then, marked 2 and 3 in Fig. 52, are deoxidizing ; 

 that is, they take oxygen, de, from metallic oxides, while the 

 outer portion of the flame is oxidizing. The above experi- 

 ment is more satisfactory with a spirit-lamp than with a 

 candle, because in that there can be no trouble from soot. 

 A tarnished copper cent will answer for this experiment if 

 held with a pair of pincers horizontally in the flame. 



175. Combustion of Wood. The flame of burning wood 

 is essentially the same as that of the candle. It is not really 

 the wood that burns. As the tallow is turned into gas by 

 the heat before combustion occurs, so a part of the wood is 

 changed into gas, and this, burning, makes the flame. You 

 often see this illustrated in the kindling of wood. As it 

 lies with the bright coals beneath it, at first its under sur- 

 face smokes, but there is no flame. What is this smoke? 

 It is gas made visible by panicles of carbon, and perhaps 

 also by vapor from the water in the wood. Soon this smoke 

 takes fire, not from contact with the coals, but from their 

 heat radiated upward against it. We often see the same 

 thing in conflagrations. A wooden building, perhaps across 

 the street from the one that is on fire, begins to scorch and 

 smoke, and soon bursts into a flame. In these instances you 

 have clear illustrations of the fact that the formation of 

 gas and its combustion are two distinct processes. As an- 

 other example, we often see jets of gas blowing out from 

 some crevice in the wood, and set on fire by the heat. The 

 gas is generated in the wood by the heat, and comes out of 

 the crevice as from a gas-burner. If you hear the sound of 



