126 THE ATMOSPHERE AND ITS SERVICE TO MAN 



FIGURE 69 



In this experiment the steam was condensed by the sud- 

 den lowering, of the temperature. The condensation of the 



steam relieved the pressure on 

 the surface of the water, and 

 the water in the flask began to 

 boil again although it had be- 

 come considerably cooler than 

 when it was first boiled. Thus 

 it appears that if the pressure 

 on the surface of water is de- 

 creased, the water will boil at 

 a lower temperature. Advan- 

 tage is taken of this in condens- 

 ing milks and sirups. The 

 liquids are heated under hoods 

 from which air is continuously 



exhausted. The water is thus "boiled away" at so low 



a temperature that there is no danger of scorching the 



sirup or the milk. 

 On high mountains 



where the air pressure is 



considerably less than at 



sea level, water boils at 



less than 100 C. In 



Denver it boils at 95 



C.; in the City of 



Mexico, at 92 C.; in 



Quito, Ecuador, at 90 



C. Because water boils 



in such places at a lower 



temperature, it takes 



longer to boil food Until PRESSURE COOKER 



