Building Materials, Their Use and Origin 421 



fire clay, or pottery clay ; what materials, if any, are mixed with the 

 clay, and for what purposes. Find out the temperature at which 

 clay products are baked in the kiln. Note also the machines and 

 motive power employed in the different stages of mixing, molding, 

 transferring of molded products to kiln, and so on. Is the clay bed 

 near the factory, or is clay transported from a distance? If the 

 latter, find out what conditions led to the location of the factory away 

 from the clay beds. 



201. Other clay products. By mixing different materials 

 with ordinary clay, and by making use of clays of different kinds 

 and grades, all sorts of brick and tile and the like are produced. 

 Ordinary clay mixed with sand makes the glazed brick ; a clay 

 with a very high point of fusion is made into fire brick and fire 

 proofing tile ; and by a variation of the materials and processes, 

 waterproof brick and tile, vitrified, paving, clinker, and fancy 

 colored bricks, drain pipes and tile, architectural terracotta, 

 and very many other varieties of clay products are now available 

 for all sorts of building and construction purposes. 



With necessary modification of process and variation of 

 materials, earthenware, pottery, and chinaware are made in 

 large quantities. Porcelain articles often used in the kitchen, 

 and for parts of electric appliances are made from a mixture of 

 pure white clay and powdered felspar, which is heated to such 

 a high temperature that the felspar is melted and made to fill 

 the minute pores that occur in the clay products. The value 

 of the output of the finer clay products is about $30,000,000 a 

 year. The industry employs more than two thousand indi- 

 viduals, and with its allied branches of decorating and mining, 

 employs several thousand more. 



202. Glass. Glass is indispensable to-day. For windows 

 there is no satisfactory substitute for glass, although oiled 

 paper, mica, and other substances have been utilized. For 

 lenses and laboratory apparatus of many kinds glass has no 

 competitor, while for the commonest articles such as bottles 

 and dishes glass is the cheapest and most suitable known ma- 

 terial. Glass is readily manufactured and molded into any 



