WHAT USES DO WE MAKE OF WATER? 89 



Why Keep Clean? There are two reasons why we 

 should keep ourselves and our clothing clean. First 

 because we wish to be decent and attractive to others, 

 and second because good health demands that we keep 

 our clothing and bodies free from dirt and germs. 



What Makes Water So Useful? The uses of any kind 

 of matter are determined very largely by its properties. 

 Water is no exception. The form in which water exists, 

 whether solid, liquid, or gas, determines some of its uses. 

 We cannot wash clothes in ice nor can we skate on steam. 

 What do you suppose makes water sometimes liquid, 

 sometimes solid, and at other times a gas ? After a little 

 thought you will say correctly that heat determines the 

 state in which water exists. 



In general it is true that the warmer the water the more 

 solid the water can dissolve, but at any given temperature 

 there is a limit to the amount that it can hold. When 

 water has dissolved all that it can at a given temperature 

 it is said to be saturated. If a saturated solution is 

 cooled or if it loses water by evaporation some of the dis- 

 solved solid will separate from solution. With gases the 

 temperature effect is just the reverse. The warmer the 

 water the less gas it can hold in solution. Boiling the 

 water will remove all gases which are in solution. 



Demonstration 2. Water as a Solvent. 



Arrange six test tubes half full of water in a test-tube rack. 

 Add a gram of each of the following substances, each one in a 

 separate tube: (1) salt; (2) sugar; (3) oil or grease; (4) charcoal 

 or ashes ; (5) soap chips ; (6) baking soda. * Shake to see if each 

 substance will dissolve in the water. Tabulate the results. 



Practical Application. Why will water clean some dirt spots 

 more readily than it will others? 



When a small portion of salt or sugar is put into water 

 and stirred, the salt or sugar disappears. Water has 

 dissolved the solid. Neither an iron nail nor a silver 



