240 



GENERAL SCIENCE 



Light in the House. In recent years a great deal of 

 attention has been given to the problem of proper light- 

 ing for different kinds of buildings. The manufacture 

 of cheap glass has made it possible to have sunlight in 

 abundance in all rooms with an outside exposure. It is 

 quite important from the standpoint of health that we 

 have plenty of sunlight in our homes and working places, 



since darkness fosters the 

 collection of dirt and filth 

 and the growth of disease 

 germs. 



A few generations ago 

 sunlight in the home was 

 a luxury because of the 

 scarcity of transparent 

 materials which could be 

 used in windows. 



How Glass is Made. 

 It is quite certain that 

 the Egyptians and Phoe- 

 nicians knew how to 

 make glass long before 

 the Christian Era, but 

 it was not until the six- 

 teenth century that win- 

 dow glass was first used ; and then for many years it 

 was used only by the most wealthy. 



Glass commonly is made by melting together the sili- 

 cates of calcium and sodium, or we may say by melting 

 together a mixture of sand, limestone, and soda. The 

 mixture is melted in pots of fire clay. This is the soft 

 glass which is used in making windows and ordinary 

 glass dishes. If potassium silicate is used instead of 



Copyright by Underwood & Underwood, N. Y. 

 FIG. 215. Glass Bottle Making. 

 Blowing a bottle and shaping bottom 

 of carboy base. 



