Mingling of Molecules 



289 



pressed on so hard by 

 the air above it. And as 

 in the case of the ris- 

 ing warm air, the water 

 vapor condenses when it 

 cools, and forms the mist 

 that you see. This mist, 

 like all clouds and fog, 

 consists of thousands of 

 extremely small droplets. 



Experiment 89. Hold a 

 saucer of ice just below 

 your mouth. Open your 

 mouth wide and breathe 

 gently over the ice. Can 

 you see your breath? 



Now put the ice into 



half a glass of water and FIG. 158. If you blow gently over ice, you 



cover the glass. Be sure can see your breath ' 



the outside of the glass is thoroughly dry. Set it aside and 



look at it again in a few minutes. 



What caused the mist when you breathed across the ice ? 



Where did the water on the outside of the glass of ice 

 water come from ? What made it condense ? 



Application 66. Explain why clouds are formed high in 

 the atmosphere; why we have dew at night instead of in 

 the daytime ; why clothes dry more quickly in a breeze than 

 in still air ; why clothes dry more quickly on a sunny day than 

 on a foggy one. 



Inference Exercise 

 Explain the following : 



411. A gas-filled electric lamp gets hotter than a vacuum lamp. 



412. You can remove a stamp from an envelope by soaking it in 



water. 



