COMBUSTION. 



135 



into the lime-water. There it will form a milky cloud, 

 wjiich on settling is found to be calcium carbonate or chalk, 

 proving that the gas produced by the burning of the can- 

 dle is carbonic anhydride. It is just as we prove carbonic 

 anhydride to be discharged from the lungs, as described in 

 125. 



172. Structure of the Candle's Flame. The flame of a can- 

 dle is quite a complex affair. You can see that it is not sim- 

 ply one thing, for some of it is dark, 

 and that which is bright is not all 

 equally so. It is really a shell of burn- 

 ing gas, containing within it a body of 

 gas that is not on fire. The shell itself 

 is not one thing, as you will see when 

 we describe Fig. 52, which is a sort of 

 map of the whole. At 3 we have the 

 gas that is not yet on fire. This is the 

 melted tallow which has come up the 

 wick, and is now vaporized by the heat. 

 Around this interior dark cone is a 

 very bright envelope, at 2 in the figure, 

 formed by active combustion of the 

 hydrocarbons, and containing the lit- 

 tle red-hot particles of carbon which, 

 sparkling brightly, give to this part of 

 the flame its strong light. Then at 1, 

 the outer part of the shell, the fine car- 

 bon is finishing its burning by uniting 

 thoroughly with the oxygen of the air 

 to form carbonic anhydride. This out- 

 side portion of the shell is called the 

 mantle, and this is the hottest part of the flame. Observe 

 why the gas at 3 is not on fire. It is shut in by the shell 

 of flame around it from the oxygen of the air, and there can 



Fier. 52. 



