86 



GENERAL SCIENCE 



longer to cook potatoes on top of Pikes Peak than at 

 Chicago. Why? In the city of Quito, Ecuador, water 

 boils at 90 C., and on top of Mt. Blanc it boils at 84 C. 

 At the Dead Sea water will not boil until its tempera- 

 ture is over 100 C. In a steam engine in which the 

 pressure of the steam is 100 pounds per square inch on 

 the surface of the water, the boiling point is 155 C. 



The change of boiling point according to the pressure 

 on the water can be illustrated by the following experi- 

 ment. Take a flask of about 

 400 cc. capacity. Fill it about 

 half full of water and heat to 

 the boiling point. While the 

 water is still boiling, close the 

 flask with a rubber stopper, 

 being careful to remove it 

 from the fire as soon as closed. 

 Invert the flask on a ring- 

 stand and pour over it some 

 cold water. The cold water 

 cools the glass and causes the 

 steam inside to condense. This 

 CHANGING PRESSURE condensation reduces the pres- 



Showing how pressure influences sure on the water in the flask, 



boiling point. . , ' 



and the steam pressure in the 



water becomes equal to the steam pressure on the water 

 and so steam bubbles escape. The escaping of these 

 bubbles is boiling. This cooling of the flask and the 

 boiling of the water in it can be continued until the 

 water can be made to boil by holding the flask in the 

 hand. The author has made water boil in a flask 

 when its temperature was 19 C., by placing ice on top 

 of the flask. 



