COMBUSTION 



215 



perceive in the forms of light and heat. In the rusting 

 of iron we do not perceive it; it is too small in amount at 

 any given time to be perceptible to our senses, yet it is 

 measurable by means of instruments of precision which 

 are used in physical laboratories. In the case of our own 

 bodies, combustion releases energy which is manifested 

 both by the heat of our bodies and by the motions of our 

 muscles. 



It may occur to you that this energy release should in 

 some way confuse the results obtained by weighing the 

 substances which result from combustion and comparing 

 their weight with that of the original substance. But 

 let us remember that energy is not a substance and cannot 

 be weighed. Let us also note that we speak of the re- 

 lease of this energy rather than of its production, for energy, 

 as you know, cannot be produced; it can only be trans- 

 formed. So combustion is a process of energy transforma- 

 tion as well as of substance alteration. The energy which 

 was confined or "stored up" in the combustible substance 

 is released, and we may perceive it as light, heat, or motion. 



QUESTIONS 



1. What is combustion? 



2. What is rusting? 



3. Does rust weigh more or less than the iron which formed it? 



4. What are clinkers? 



5. What are smoke and soot ? 



6. Is smoke necessary? 



7. What chemical elements are involved when a candle burns? 



8. What transformation of energy takes place when wood burns? 



