ICE, WATEK, AND STEAM 



105 



is it on the Falirenheit scale? After a mass of water has 

 reached the boiling point, its temperature does not rise as 

 long as any of the water remains in the liquid form. In your 

 experiment you will find the boil- 

 ing point somewhere near 100 C., 

 but it is not probable that it will 

 be exactly that. 



The most common cause for vari- 

 ation in the boiling point above or 

 below 100 C. is difference in air 

 pressure. If the air pressure is 30 

 inches on the barometer, the boiling 

 point of pure water will be 100 C. ; 

 if the pressure is greater, the boiling 

 point will be higher ; and if the pres- 

 sure is lower, water will boil before 

 it is as hot as 100 C. To most of 

 us this makes little difference, but 

 to people who live on the moun- 

 tains it is sometimes a serious matter. 

 Since the air pressure grows less as 

 one goes higher up, of course the 

 air pressure in elevated places is 

 less than that near the sea level. 

 Likewise the boiling point is lower. 

 On the top of Mont Blanc the boil- 

 ing point of water is only 84 C. ; 

 at the city of Quito, Ecuador, it is 

 90 C. ; and at many places in our 

 own country, particularly in the 

 West, the same condition exists 



(fig. 57). When you boil eggs Or Note the bubbles rising through 

 ... ,, , .,. ,, the water and the steam issu- 



potatoes it is not the boiling that ing from the tube . The steam 



COoks them, it is the heat. If yOU is transparent when it is in the 

 i ,t rv/-vn /-X flask, and also when it issues 



cannot get water hotter than 90 C., f rom the end of the tube 



FIG. 56. How water boils 



