DRINKING WATER 139 



DEMONSTRATIONS 



61. Show that all water contains mineral matter by evaporating a 

 few drops of pure spring water upon a piece of clean glass. A little 

 white spot will be left by each drop. Boil some water and notice the 

 absence of taste. Cool it and shake it in a can, and notice its natural 

 taste again. Set aside some pure water containing a few bread crumbs 

 or a shred of meat, and notice the unpleasant odor of decay developed 

 in a few days. 



62. A rough test for the purity of water is to stir in a little pure 

 sugar and set it aside. If it contains any organic matter, it will turn 

 yellowish in a few days, but otherwise it will remain colorless. Collect 

 some rain water from a dirty building, or mud-puddle water, or water 

 from a barnyard well, and note the color and the odor. After keeping 

 it a few days, note the deepened color and worse odors, showing decay 

 within the water. 



63. Doubtless the class will ask to be shown " animalculae" in water. 

 Water has to be almost turpid and putrid before living beings are pres- 

 ent in sufficient numbers to be easily detected with a microscope. If a 

 drop of very stagnant water is examined under the microscope with a 

 power of 100 to 400 diameters, many strange beings will be seen moving 

 about. Place a little hay in a bottle of water and examine a drop of the 

 water every day, and notice the changing forms of the living beings as 

 one kind dies and another is produced. 



REVIEW TOPICS 



1. Describe the appearance and taste of pure water. 



2. State what substances are found in all water ; what in 



mineral water ; and the difference between hard and 

 soft water. 



3. State the most dangerous impurity in water. 



4. Give three ways in which nature purifies water. 



5. Show how to avoid pollution of a well. 



6. Show how to render impure water safe for use. 



