Building Materials, Their Use and Origin 427 



Concrete, or artificial stone, is made of a wet mixture of cement, 

 sand, and gravel, or crushed rock, and may be reinforced with steel 

 rods. 



Brick, tile, and other clay products produced annually in the United 

 States have a value of about $140,000,000. Their production is an 

 example of the use of heat in manufacturing. 



From finer clays and related materials, with a better control of 

 temperature, are made earthenware, chinaware, and porcelain. 



The wide use of glass makes it practically indispensable. 



The art of glass making was known to the ancient Egyptians and 

 others. 



Bohemia, Italy, and Belgium are notable for their glass manufac- 

 ture. Pennsylvania leads in the production of glass in the United 

 States 



The chief varieties of glass are crown, flint, and hard glass. 



Crown or soda glass is used for making window glass, tumblers, 

 and bottles. 



Flint glass, a lead glass, is used in cut glassware and lenses. 



Bohemian or hard glass, one variety of which is Jena glass, is used 

 for scientific apparatus. 



Glass is made by melting a mixture of sand and other materials, 

 and is shaped by blowing, molding, rolling, and grinding. 



The colors of glass are due to small traces of certain minerals. 



In general the larger the proportion of silica in glass, the harder 

 the glass is and the more resistant to the effect of chemicals and high 

 temperatures. 



Sand is mostly quartz, which is a compound of silicon and oxygen, 

 and called silicon dioxid or silica. 



Silica is very widely distributed in nature and is the most abundant 

 mineral. 



Many precious stones such as the amethyst, opal, and agate are 

 silica with traces of coloring matter. 



Carborundum, made from carbon and silica fused at the tempera- 

 ture of the electric furnace, is next to the diamond in hardness and is 

 used for grinding tools. 



REVIEW QUESTIONS 



1. Recall in detail the observations made when lime was slaking. 

 2. Of what advantage is the knowledge of chemistry in lime manu- 

 facture and use? 3. What is the value of the cement manufactured 

 annually in the United States ? 4. Mention some of its uses. 5. Ex- 

 plain the setting of cement. 6. What is reinforced concrete? 



