42 LABORATORY LESSONS IN GENERAL SCIENCE 



Grasp a handful of sand. Try to do the same with water, 

 and explain the difference in results. Explain why liquids 

 at rest have a smooth upper surface rather than a rough 

 heaped-up form. 



VAPORIZATION AND CONDENSATION 



1. What change occurs in the quantity of water (a) when 

 a little is left in an open dish exposed to the air for some 

 time; (6) when a wet piece of cloth, as a handkerchief, is 

 hung up exposed to the air? After some water has been 

 boiled for a time in an open dish, what is true of the quan- 

 tity of it? 



In all these cases what becomes of the water? At what 

 temperatures does this change of vaporization of the water 

 go on most rapidly? Name other conditions that favor a 

 rapid vaporization of water from the earth's surface. Name 

 several sources whence the supply of moisture in the air is 

 maintained. Whence comes the heat? 



2. Over the mouth of a test tube in which water is boil- 

 ing hold an inverted wide-mouthed bottle whose sides are 

 dry and cool. Describe what takes place. What relation 

 is there between the processes of vaporization and con- 

 densation? What causes condensation of the moisture 

 present in the atmosphere? In what ways (two or more) 

 does this come about ? 



3. How is it that in some regions of earth a sudden and 

 extreme fall in temperature may cause no precipitation 

 either of rain or snow ? What is true of the general character 

 of a region, and its fitness for habitation, where the atmos- 

 phere is commonly destitute of moisture ? In regions that 



