WHAT IS WATER? 



85 



What Is Evaporation ? When ice is left in a hot kitchen 

 uncovered, it absorbs heat and soon changes its state 

 from solid to liquid, and if it is left exposed to the air for 

 a short time, some of it will pass off into the air. Evap- 

 oration is the changing of water to a gas when the change 

 is at the surface of 

 the liquid. Some 

 water evaporates 

 into the air when- 

 ever air and water 

 are in contact. The 

 warmer it is, the 

 faster it evaporates. 



The Water Cycle 

 in Nature. Air, soil, 

 and living , things 

 play an important 

 part in the ceaseless 

 changes of water on 

 our earth. The at- 

 mosphere receives 

 water in the form of water vapor and gives it back in a 

 variety of ways. Evaporation of water from all surface 

 bodies of water, from wet rocks and soil, and even from 

 snow and ice charge the air with moisture. To this must 

 be added the moisture given off from the burning of fuels, 

 by the breathing of animals, and from trees and other 

 plants. A single tree sometimes gives off almost half a 

 ton of water in a day. This water vapor in the air is an 

 invisible gas. When air that has become saturated with 

 moisture is cooled, some of the water separates out into 

 minute particles. Continued cooling increases the size 

 of the particles. The particles may make dew drops, fog, 

 clouds, and rain, or if the temperature is very low, frost 

 or snow will result. The great bulk of this condensed 



Read the text and then explain this diagram of the 

 water cycle. 



