80 Our Surroundings 



27. Name three materials so alike that labels are advisable for quick iden- 

 tification. 



28. What property of hydrogen makes it good for use in airships, and 

 what property makes it bad? 



29. Suggest several ways in which the solvent power of water is of 

 value to us. 



30. Is it true or false that the mercury column of a barometer rises as 

 a storm approaches? Why? 



31. Why is scientific progress more rapid now than a century ago? 



32. Explain: 



Soft water requires less soap to make a lather than hard water. 



33. Suggest an original experiment to show that matter occupies space. 



34. Is it true or false that much-used stone stairs wear down by chemi- 

 cal change? Why? 



35. Suggest several reasons why early settlers made their homes beside 

 water. 



36. Is it as necessary to-day to live near water as it used to be? Why? 



37. Was it safer for the early settler to drink from running streams than 

 it is for us to do so? Why? 



38. Is it true or false that your arm has both potential and kinetic energy? 



39. Is it true or false that cold days are better drying days than warm 

 ones? Why? 



40. Why do air cushions and air-filled tires lessen shocks? 



41. Why is it wise to lower a lighted candle or a lantern into a vault 

 before descending into it? 



42. Name six basic elements of matter. 



43. If an uncorked bottle of water is inverted, why does not the liquid 

 flow out smoothly? 



44. Why is a labeled diagram better than an unlabeled one? 



45. Is it true or false that water taken from wells is often hard? Why? 



46. Is it true or false that burning produces water? Why? 



47. Two of the following devices depend on the atmosphere for their 

 action: air gun, automobile tire, lift (suction) pump, sand blast, medi- 

 cine dropper. 



a. Select one of these two devices and describe an experiment illustrat- 

 ing how it works. 



b. Make a labeled drawing of the device selected. 



