CHAPTER XXVII 



PHYSICAL EXPERIMENTS 



Evaporation and Condensation 



Nature study does not mean a study of plants and 

 animals exclusively, but also a study of the soil, air, 

 weather, and certain phenomena that touch our lives on 

 every hand. Indeed, we must know something about the 

 underlying principles of physics before we can understand 

 clearly how plants and soil and weather do their work. 



Water is the most familiar liquid that we know. 

 Water in the solid form (ice) is so common that we need 

 no experiment to prove it. Is it possible to change water 

 into a gas or vapor? 



Fill a measuring cup exactly half full of water. Pour 

 this into an ordinary tin cup or tumbler and set in a warm 

 place. This should be done several hours before the class 

 time, or even the day before. Fill a glass flask or test tube 

 half full of water, place it over the flame of the alcohol 

 lamp till it boils vigorously. What do you see coming out 

 of the mouth of the flask? Look in the flask above the 

 boiling water, can you see anything above the water in 

 the flask ? Where does the steam come from that is visible 

 at the mouth of the flask ? It is visible here because the 

 vapor has begun to change back into water. Is the true 

 vapor of water then visible or invisible? Watch the spout 



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