422 Introduction to the Study of Science 



form. It is also tough, hard, and strong, as may be seen from 

 the fact that it is not easily scratched and marred and that it 

 sustains hard usage and heavy weights. 



Exercise : Uses of glass. For what purposes other than those 

 mentioned have you seen glass utilized? Have you noticed glass 

 reinforced with wire net ? What is the purpose of this ? Modern 

 factory buildings are largely made of glass. What kinds of glass have 

 you seen used in this way? How is glass strengthened when it is used 

 for practically the entire sides of buildings? What are some of the 

 popular devices for this purpose? Consult advertising pages of 

 periodicals, and note qualities claimed for the devices advertised. 



To what extent do you think the* world could get along without 

 glass? In what ways do you think the increased use of glass would 

 be advantageous? Can too much light be admitted into a building? 



Glass manufacturing past and present. Glass making is 

 a very old industry. The earliest known examples are some 

 blue glass beads brought to England between 3000 and 2000 

 B.C. by traders who distributed their wares throughout Europe 

 and told tales of ships plying the waters of the Nile and the ad- 

 jacent seas. The art of glass manufacture was developed in 

 Egypt, learned later by the Babylonians and by some of the 

 Etruscan tribes in the northern part of Italy. In Greek and 

 Roman art and during the Middle Ages in Europe glass making 

 was highly developed for decorative and useful purposes. 



To-day some of the most beautiful glass is made in Bohemia, 

 where quartz sand is plentiful and well adapted to the purpose. 

 The glass is colored by adding small quantities of minerals 

 found in the mines of the country. Italy is also noted for its 

 fine glass. 



In the United States, Pittsburgh is the center of plate glass 

 manufacturing, largely because deposits of sand especially 

 suitable for this glass are found near the city. Pennsylvania, 

 Indiana, Ohio, Illinois, and West Virginia are the chief manu- 

 facturing states, partly because of the supply of cheap fuel, 

 and partly because of the abundance of sand of good glass- 

 making quality. 



