Water 51 



tential energy which is released as the water flows against the 

 turbine wheels at the base of the falls. 



To show the dissolving property of water, stir salt in a glass 

 of water. What happens? Boil the water until it evaporates, 

 and the salt will be found to remain in the bottom of the dish. 

 This illustrates the solvent power of water. Most water has sub- 

 stances in solution. It often has lime, which is sometimes seen 

 deposited in the bottom of the family teakettle. Beautiful rock 

 formations, resembling icicles, are sometimes found hanging from 

 the roofs of caves. These were made by the evaporation of water 

 holding lime in solution as it trickled from above. 



To show that water quickly rises in porous substances, those 

 full of small spaces, place one end of a strip of blotting paper in 

 a dish of colored water. Observe what happens. This ability 

 to fill the spaces in porous materials is known as capillarity. It 

 accounts in part for the rise of sap in trees. It is also capillarity 

 that makes it possible for us to dry our hands with a towel. 



To show that water seeks its own level: Cut a hole in the 

 side of a can near the bottom. Insert in the hole one end of a 

 glass tube which is bent at right angles. Turn the other end 

 upwards. To prevent leakage, seal the opening around the con- 

 nection with wax. Fill the can with water. Observe how high 

 water rises in the upright arm of the tube. This rising of the 

 water in the tube is due to the downward pressure caused by the 

 weight of the water in the can. Because of this tendency of water 

 to rise to the level of its source, a water reservoir is placed higher 

 than the homes it supplies. From it water flows down through 

 underground mains and rises again in the house pipes. 



The Home Water Supply. The source of the water used 

 in the home may be a well, a spring, a river or a lake. From 

 whatever source it comes, great care should be taken to make 

 sure that all water used for drinking is free from disease germs. 

 This can be assured only by microscopic examination of the 

 water by an expert. The clearest water may contain germs of 

 some dangerous disease. On this account, it is vitally important 

 that all water mains, pumps, pipes and faucets be kept free from 

 organic matter and as clean as possible. 



