CHEMICAL AND PHYSICAL CHANGES 45 



or boiling of water. The color of some materials is altered 

 by heat or dampness, but returns to its original tint or shade 

 when the temperature is lowered or the dampness driven off. 



References : 



1. 1703 : 2-4. Relation between Chemistry and Physics, 



a. 1701 : 2-3. Chemical and Physical Changes. 



6. 1702 : 1-3. Physical and Chemical Changes. 



c. 1704 : 7-8. Chemical and Physical Changes. 



d. 1705 : 3-5. Physical and Chemical Changes. 



e. 1706 : 1-2. Physical and Chemical Changes. 

 /. 1707 : 2-3. Chemical and Physical Changes. 

 g. 1708 : 2. Physical and Chemical Changes. 

 h. 1709 : 1-2. Physical and Chemical Changes. 

 i. 1711 : 23-27. Physical and Chemical Changes. 

 j. 1712 : 13-14. Physical and Chemical Changes. 



Experiment 19. Physical and Chemical Changes. 

 Apparatus : Burner, tweezers, test tube, 6" X J", test-tube 

 holder. 



Materials: Mercuric oxide, strips of copper 6"x|". 



a. Barely cover the bottom of a test tube with mercuric 

 oxide, and heat gently. Note change in color. What is it an 

 example of ? Let the test tube cool a little and see if what you 

 expect happens. 



b. Heat the test tube strongly for several minutes and tell 

 what happens to the mercuric oxide. The material on the 

 sides of the test tube is mercury. Examine it. Mercuric 

 oxide is a compound of mercury and oxygen. Where is the 

 oxygen? What kind of a change has taken place? 



c. Heat one end of the copper strip until the other end is too 

 hot to hold in the hand. Let it cool. Is this a chemical 

 change or physical change ? 



d. Hold one end of the copper strip by the tweezers and put 



