CHAPTER VI 



CHANGES IN STATE OF MATTER 



Three states of matter. It is a familiar fact that 

 water may exist in three different forms. It may be a 

 solid, a liquid, or a gas. When a solid it is called ice; 

 when a liquid, water; and when a gas, steam. 



It is not so well known that many other substances 

 also exist in three forms. The chief reason for this 

 lack of knowledge is the fact that few substances are 

 as useful as water, in all three forms in which they 

 exist. Few substances, therefore, have been studied 

 as carefully as water. 



Most of us know many substances which exist both 

 as solids and as liquids. Iron and lead we know can be 

 melted ; paraffin can easily be melted and thus changed 

 from the solid to the liquid state. Many substances 

 require extremely high or extremely low temperature 

 to change from one of these states to another. Most 

 metals, for instance, assume the gaseous state only at 

 very high temperature, and many common gases 

 become liquid and solid only at very low temperature. 

 Air has been known in the liquid and the solid states 

 only within the last twenty-five years. 



So far as is known, all substances become solids when 



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