IO4 Common Science 



why you hang clothes in the sun or by the stove 

 to dry. 

 Try these experiments : 



Experiment 33. Read a thermometer that has been ex- 

 posed to the room air. Now dip it in water that is warmer 

 than the air, taking it out again at once. Watch the mer- 

 cury. Does the thermometer register a higher or a lower 

 temperature than it did at the beginning? What is taking 

 up the heat from the mercury? 



Experiment 34. Put a few drops of water in each of two 

 evaporating dishes. Leave one cold; warm the other over 

 the burner, but do not heat it to boiling. Which evaporates 

 more quickly? 



Why the sea is salt. You remember various fairy 

 stories about why the sea is salt. For a long time the 

 saltness of the sea puzzled people. But the explanation 

 is simple. As the water from the rains seeps through 

 the soil and rocks, it dissolves the salt in them and con- 

 tinually carries some of it into the rivers. So the waters 

 of the rivers always carry a very little salt with them 

 out to sea. The water in the ocean evaporates and 

 leaves the salt behind. For millions of years this has 

 been going on. So the rivers and lakes, which have only 

 a little salt in them, keep adding their small amounts 

 to the sea, and once in the sea the salt never can get 

 out. The oceans never get any fuller of water, because 

 water only flows into the ocean as fast as it evaporates 

 from the ocean. Yet more salt goes into the ocean all 

 the time, washed down by thousands of streams and 

 rivers. So little by little the ocean has been growing 

 more and more salty since the world began. 



