CHANGES IN STATE OF MATTER 49 



together. This can be brought about in two ways: 

 first, by reducing the temperature of the substances, 

 and second, by increasing the pressure upon them. 



It is only by the combination of a great increase in 

 pressure and a great decrease in temperature, that it 

 has been possible to convert some gases into liquids, 

 and the resulting liquids into the solid state. 



Questions 



1. In what three forms may a substance exist ? 



2. Name two solids which cannot be changed to 

 liquids. Why is it impossible to convert them into 

 liquids ? 



3. At what temperature does water boil? Freeze? 



4. How many calories of heat are required to 

 change one gram of ice to water? 



5. What are the sources of heat for melting ice 

 in a refrigerator? 



6. Is it warmer or cooler near a body 'of melting 

 ice than it is at some distance away? Why? 



7. Why is salt mixed with chopped ice for use in 

 ice cream freezers? 



8. What effect does water which is melting have 

 upon the surrounding temperature ? 



9. How many calories of heat are given off when 

 10 grams of water are changed to ice ? 



10. What is the melting point of ice? Alcohol? 

 Mercury ? 



11. Why is it impossible to melt iron in a glass 

 dish? 



12. What is the boiling point of water? Alcohol? 

 Ether? Mercury? Copper? 



