318 Common Science 



to combine with the filament ; so the lamp does not 

 burn out. 



What flames are. When you look at a flame, it seems 

 as if fire were a real thing and not merely a process of 

 combining something with oxygen. The flame is a 

 real thing. It is made up of hot gases, rising from the 

 hot fuel, and it is usually filled with tiny glowing parti- 

 cles of carbon. When you burn a piece of wood, the 

 heat partly separates its elements, just as heating sugar 

 separates the carbon from the water. Some of the 

 hydrogen gas in the wood and some of the carbon too are 

 separated from the wood by the heat. These are pushed 

 up by the cooler air around and combine with the oxygen 

 as they rise. The hydrogen combines more easily than 

 the carbon; part of the carbon may remain behind as 

 charcoal if your wood does not all burn up, and many 

 of the smaller carbon particles only glow in the burning 

 hydrogen, instead of burning. That is what makes the 

 flame yellow. If you hold anything white over a yellow 

 flame, it will soon be covered with black soot, which is 

 carbon. 



What smoke is. Smoke consists mostly of little 

 specks of unburned carbon. That is why it is gray or 

 black. When you have black smoke, you may always 

 be sure that some of the carbon particles are not com- 

 bining properly with oxygen. 



Yellow flames are usually smoky ; that is, they 

 usually are full of unburned bits of carbon that float 

 off above the flame. But by letting enough air in with 

 the flame, it is possible to make all the little pieces of 

 carbon burn (combine with the oxygen of the air) before 





