CHANGES IN STATE OF MATTER 



43 



Water is boiled in a flask until the air has been 

 expelled by the steam. It is then quickly closed with 

 a tight cork and inverted. If cold water is then 

 poured over the flask, the water within it boils vio- 

 lently. The cold 

 water condenses some 

 of the steam in the 

 flask, thereby dimin- 

 ishing the pressure 

 in the flask, and as 

 a result the water 

 boils. 



From these experi- 

 ments we learn that 

 the boiling point of 

 water is lowered if 

 the pressure is dimin- 

 ished. 



T)^~ ~f +1, j: Fig. 22. Water is boiling in the 



Because Ot the dl- flask while cold water is being poured 

 . . , , , over it 



mmished atmospheric 



pressure at high altitudes, the boiling point of a liquid 

 is considerably lower upon a mountain than it is 

 near sea level. On Pike's Peak water boils at 

 about 86C. 



On the other hand, experiments have shown that 

 water will not boil even at a temperature of 100 C., 

 if the pressure is increased above normal at sea level. 



A change in pressure also affects the melting points 

 of substances. A decrease in pressure will usually 



