A YEAE IN SCIENCE 43 



Heat the water to about 60 C. Then remove the 

 llask and place it on the receiver of the air pump. 

 Rub the edge of the belljar with vaseline and then 

 lower it over the flask. Exhaust the air- from under 

 the belljar. What happens to the water? What is 

 the temperature at which water boils under ordinary 

 conditions? How can you explain the results of this 

 exercise? 



If the belljar is sufficiently high, the thermometer 

 should be left in the flask. Repeat the experiment 

 several times, each time recording the temperature at 

 which the water boils. 



B. Again half fill the flask with water and heat it 

 until it boils. After it has boiled about two minutes, 

 insert the rubber stopper. Allow the flask to cool a 

 few minutes and then invert it on the ring of the ring- 

 stand. Pour cold water over the flask. What happens 

 to the water? Why? Will the boiling point of water 

 be above or below 100C. on top of a mountain? Why? 

 It is impossible to cook potatoes by boiling on top of a 

 very high mountain. Why ? 



Exercise 20. How Water is Distilled. 



Object: To determine how substances dissolved in 



water may be separated from it. 

 Apparatus 



I' lask Bunseii burner 



One-bole rubber stopper Ring stand 



Delivery tube \Yire jjauze 



Test tube Salt 



Beaker 



