140 FIRST YEAR COURSE IN GENERAL SCIENCE 



nation takes place rapidly, noticeable quantities of heat and 

 light are given off, and the process is called combustion or 

 burning. If the change takes place slowly without any 

 flame, the process is called simply oxidation or slow combus- 

 tion. The compounds formed in both cases are oxides. 



The burning and the decay of wood are both oxidation 

 and form the same compounds. In the case of burning, 

 the heat is intense for a short time. In decay, the change 

 in temperature is too slight to be detected by ordinary ob- 

 servation, and the process may take many years. 



150. Spontaneous Combustion. The slow oxidation of 

 oily rags or paper is often the cause of accidental fires. The 

 oil slowly unites with the oxygen of the air and heat is pro- 

 duced. If the rags are loosely placed, the heat may be given 

 off as fast as it is made and no harm is done. If the matter 

 is packed closely or is in a small space like a closet where 

 there is little change of air, the temperature rises until it is 

 high enough to set the combustibles on fire. This is called 

 spontaneous combustion. 



151. Explosions. A little gunpowder spread upon a 

 stone and set on fire burns quickly but quietly, making a 

 large amount of smoke. A smaller quantity of gunpowder 

 in a firecracker burns quickly and bursts the firecracker, 

 making a loud noise. In both cases the powder burns; in 

 the second case it results in an " explosion." The noise pro- 

 duced in this way and the bursting are both called explosions. 

 In both cases of burning, a large amount of gas is formed 

 quickly; in the second case the gas is confined and makes 

 room for itself by pushing away the confining walls. 



Explosives are made for the purpose of pushing the pro- 

 jectile from a gun, the rocket from its fastening, the rock 

 from the side of a mountain. An explosive always contains 

 two things: (1) a substance which, on being struck or 

 heated, sets free oxygen to insure rapid combustion; and 

 (2) a combustible material which, when united with oxygen, 



