SUBSTANCES AND PEOPERTIES 11 



Whenever memory fails to give a perfectly clear report of the 

 matter in hand, the text must be read and re-read until the essen- 

 tial point can be repeated from memory. 



Use the same method in all future chapters. A useful prac- 

 tice is to employ a pencil as you read and to underline systematic- 

 ally all the important facts and statements, and then to go back 

 and apply to each marked place the process described above. 



8. Define the following terms : Specific gravity, tenacity, melt- 

 ing-point, specific physical property, pure body, vacuum. 



9. Is it logical to say " pure substance? " 



10. Why do we decide that granite is a mixture and iron a 

 single substance? 



11. What weight of oxygen would be required to convert 25 

 grams of lead into oxide of lead? 



12. Make a list of the technical words we have defined, and 

 place the definition opposite to each. 



