194 Miracles Ahead! 



her and quantity of materials that go into each mixture, or 

 batch. Different chemicals and minerals are added to give the 

 glass certain properties. And these "alloy glasses" are as supe- 

 rior to ordinary glass as alloy steels are to ordinary cast iron. 



Since Corning brought out its Pyrex glass in 1915, tre- 

 mendous strides have been made in the manufacture of flame- 

 proof glass. Ordinary glass has a high "coefficient of expan- 

 sion" that is, it varies sharply with changes in temperature 

 and it is a poor conductor of heat. Thus a thick piece of 

 ordinary glass will crack when heated, because the outside 

 expands more than the inside. The low "coefficient of expan- 

 sion" of Pyrex prevents it from cracking when exposed to a 

 flame. 



Coming's latest Pyrex-type glass is said to be "so new that 

 industry hasn't yet caught up with it." The discovery of this 

 glass called Vycor has been rated one of the outstanding 

 scientific achievements of the century. Vycor glass is 96 per 

 cent silica thereby approaching the characteristics of quartz, 

 which is pure silicon dioxide with a very low coefficient of 

 expansion and with high resistance to chemicals. Vycor is 

 made by giving the glass a chemical treatment which removes 

 one-third of the mass. Little but silica remains and it is in a 

 porous state. This is reheated and the glass "shrinks" until all 

 the minute holes are closed and a transparent, nonporous glass 

 is produced. According to Dr. W. W. Shaver, head of the 

 production-development department of Corning, this 96 per 

 cent silica glass has the property of used sand. To answer any 

 questions about Vycor's toughness, Dr. Shaver heated a cup 

 of this glass red-hot and then plunged it against a cake of ice. 

 The glass was not damaged. 



Another glass which is similar to Vycor has been made by 

 the Pittsburgh Plate Glass Company and other glass manufac- 

 turers. A quick-cooling process balances the forces of expan- 

 sion and contraction in the glass, making it more than four 



