1 8 GENERAL SCIENCE 



On the inside the flame begins where the kindling tempera- 

 ture of the supply of gas or vapor has been reached, and 

 where oxygen is available for combustion. The candle flame 

 has the form of a hollow cone, enclosing a cone of vapor that 

 is not burning. The blowpipe flame is hot because the same 

 amount of combustion occurs within a smaller space. 



The color of different lights is largely due to the kind of 

 material that is incandescent (light giving), and to the tem- 

 peratures to which this material is heated. In the common 

 electric bulb there is no combustion, the bulb having no 

 oxygen inside of it. The temperature of the filaments 

 caused by the electric current is sufficiently high to produce 

 incandescence. 



SUMMARY 



The term combustion in opular usage means a case of oxidation 

 where the heat liberated causes burning material to become so hot as 

 to give off light. 



The products of oxidation are known as oxides. They may be gases 

 as carbon dioxide, or liquids as water, or solids as iron rust. 



A flame is a gas or vapor that is burning. The combustion may be 

 slow and under control, or it may be instant and explosive in violence. 

 The size of a flame is determined by the distance outward to which 

 the mixture of the gaseous material with air extends. 



In a candle flame the inner dark cone consist of vapor not burning 

 because of lack of oxygen, and because its temperature is below the 

 point for ignition. The hollow luminous cone is burning vapor, the 

 outermost limits of which are almost colorless by reason of an almost 

 completed combustion. 



Carbon dioxide gas from the air is used by plants in the manufacture 

 of such materials as sugar, starch, and wood fibre. But it must not 

 be overlooked that plants, like animals, must have a supply of oxygen 

 to maintain their life, and to provide the energy necessary for their 

 growth. The amount of carbon dioxide given off as a product of this 

 plant breathing is, however, insignificant in comparison with the 

 amount converted by the plant into wood, starch, and sugar. 



