136 EXPERIMENTAL GENERAL SCIENCE 



9. Why is the water in shallow wells, especially in cities, usually unfit 

 to drink? 



10. Explain how coffee is made by pouring hot water over the coffee 

 in a percolator. 



11. Make a saturated solution of nitrate of soda or sal ammoniac and 

 water and put a few drops on a clean sheet of glass, draining off all that 

 does not cling to the glass. What happens to the solute as the solvent 

 evaporates? 



12. With a simple lens, examine the material left on the glass. What 

 is the shape of the crystals? 



13. Make a dilute solution of table salt and water and place in a 

 broad flat dish to evaporate. How does the shape of the salt crystals 

 compare with those made in the previous experiment? 



14. How do you account for the diffusion of gases by the molecular 

 theory of matter? 



15. Heat some ammonia water in a florence flask stopped with a one- 

 hole stopper through which is thrust a glass tube. Hold a test-tube 

 over the end of the glass tube and catch some of the ammonia gas 

 driven off. When the tube is full, plunge it, mouth down, into a dish of 

 water. Explain the disappearance of the gas. 



16. Could aquatic animals live in water that had first been boiled and 

 then cooled? Why? 



17. The "flat" taste of boiled water may be removed by exposing the 

 water to the air for a time, or by shaking it up in a jar with air. Explain. 



18. Carbonated water, such as is used at soda fountains, consists of 

 carbon dioxide in solution in the water. Should the water be hot or 

 cold to take up as much carbon dioxide as possible? 



