344 



Common Science 



What makes an auto- 

 mobile go. In all the 

 above cases the explo- 

 sions are caused by 

 chemical action. When 

 gasoline mixed with air is 

 sprayed into the cylinder 

 of an automobile, an 

 electric spark makes the 

 gasoline combine with 

 the oxygen of the air; 

 the gasoline suddenly 

 burns and changes to 

 steam and carbon dioxid. 

 As you already know, 

 when a liquid like gaso- 

 line turns to gases such 

 as steam and carbon 

 dioxid, the gases take 



much more room. But FIG. 180. Diagram of the cylinder of an 

 ji . 11 j/i A. r engine. The piston is driven forward by 



that IS not all that hap- th f ex plo S ion of the gasoline in the cylinder 



pens. Much heat is re- 

 leased by the burning of the gasoline spray, and heat 

 causes expansion. So the gases formed by the burn- 

 ing gasoline are still further expanded by the heat 

 released by the burning. Therefore they need a great 

 deal more room; but they are shut up in a small 

 place in the top of a cylinder. The only thing to hold 

 them up in this small space, however, is a piston 

 (Fig. 1 80), and the suddenly expanding gases shove this 

 piston down and escape. The piston is attached to the 



