140 THE WATERS OF THE EARTH 



ocean from top to bottom is practically uniform in 

 composition. 



Water is the greatest of all solvents. It dissolves to a 

 greater or less extent almost all substances with which it 

 comes in contact. There are, however, substances which it 

 dissolves but slightly if at all. When it is necessary to get 

 these substances into solution, other solvents must be used. 



MONTEZUMA'S WELL 



A famous water hole due to the dissolving power of water on rock- 

 forming substances. 



Gasoline, for example, dissolves grease ; turpentine dissolves 

 fresh paint, and alcohol dissolves grass stain. 



Experiment 61. Fill a small beaker with fresh water. Heat it 

 slowly. Bubbles collect on the bottom and sides. When the 

 water becomes cold these bubbles do not disappear immediately. 

 If these were bubbles of water vapor, they would condense to water 

 when the temperature was lowered. What are they? Where 

 did they come from ? 



We have learned that all air has water vapor diffused 

 through it. Experiment 61 showed that there was also 



