428 Introduction to the Study of Science 



7. From what are bricks made? 8. What is the origin of clay? 

 9. Why are clay beds so abundant and frequent? 10. What is the 

 commercial importance of bricks? 11. Describe how bricks are 

 made. 12. What other products besides bricks are made of clay? 

 13. Of what materials is porcelain ware made? How? 



14. What are the most important uses of glass? 15. What evi- 

 dences are there that the ancients made glass? 16. What countries 

 are notable for glass making? 17. What are the chief glass making 

 centers in the United States? Why? 18. Of what materials is 

 glass made? 19. Describe process of making (a) lamp chimneys, 

 (6) window glass, (c) plate glass, (d) cut glass. 20. Why has cheap 

 glass often a greenish tint? Red? 



21. What is sand? 22. Mention several uses of quartz. Upon 

 what characteristics do these uses depend? 23. Give the chemical 

 name of quartz or silica. What does the name suggest as to its com- 

 position? 24. Give an account of the distribution of silica in nature. 

 25. What is the relative abundance in the earth's solid crust of silicon? 

 Oxygen? Aluminum? Iron? 26. Of what materials is carborun- 

 dum made ? For what is it used ? 



