PAKT II. WATER AND ITS USES 



CHAPTER X 

 ICE, WATER, AND STEAM 



116. The three states of matter. In previous work we have 

 seen that the same substance may occur in either solid, liquid, 

 or gaseous form. This is noticed more frequently in the case 

 of water than with any other common substance, but it will 

 be worth while, in the following study of water, to remember 

 that many of the things which are true of it are true of other 

 substances also. We need to be clear about the names which 

 are used for the different states of water. The liquid form 

 is most commonly found, and to this form the name " water " 

 is especially applied. It must be remembered that when liquid 

 water evaporates (thus passing into the form of gas) or when 

 it freezes (becoming a solid) it does not cease to be water. 

 For instance, we may speak of the water that is contained in 

 the air although it is a gas, and if we calculate the amount of 

 water in the ocean, we include also the ice. The word "water," 

 therefore, may refer either to the liquid state or to the sub- 

 stance, without regard to whether it is solid, liquid, or gas. 

 " Ice " is the name of the solid form, and " steam " is the name 

 of the gas. Sometimes the latter is called water vapor. 



117.. When water freezes. What happens when water 

 freezes ? Perhaps most of us have observed nothing more 

 than that when water gets cold it changes into a solid, and 

 perhaps we have also been compelled to notice that when it 

 becomes a solid it frequently breaks the containing vessel. 

 But that is not the whole story. 



103 



