348 Common Science 



action which suddenly releases a great deal of heat and 

 combines solid things into expanding gases. But the 

 bursting of a steam boiler, or the " blow out " of an 

 automobile tire, or the bursting of a potato in the oven, 

 although not caused by chemical action, still are real 

 explosions. An explosion is the sudden release of a 

 confined gas. 



Application 77. Explain how gasoline makes a motorcycle 

 go, and why it goes " pop, pop, pop." Explain why a paper 

 bag will burst with a bang, when you blow it up and then 

 clap it between your hands; why a Fourth-of-July torpedo 

 " goes off " when you throw it on the pavement. 



Inference Exercise 

 Explain the following : 



491. The engine of an automobile is cooled by the water that 



passes over it from the radiator. 



492. When you light a firecracker, the flame travels down the wick 



until it reaches the gunpowder, and then the firecracker 

 bursts with a bang. 



493. If you light a small pile of gunpowder in the open, as you do 



when you make a squib by breaking the firecracker in two, 

 you merely have a blaze. 



494. Air-filled tires make bicycles ride much more evenly than 



solid tires would. 



495. When clay has once been baked into brick, you can never 



change it back to clay. 



496. A photographic negative turns black all over if it is exposed 



to the light before it is " fixed." 



497. The outside of a window shade fades. 



498. A vacuum electric lamp globe feels hot instantly when turned 



on, but if turned off again at once, it immediately feels cold. 



499. Coal gas is made by heating coal very hot in an air- tight 



chamber. 



500. White straw turns yellow when it is long exposed to the sun- 



light. 



