GLASS-BLOWING AT A PENNSYLVANIA PLANT 



In this picture are shown most of the operations of blowing glass by hand methods. The 

 first man on the left of the picture is the "blower." The glass has been gathered on the end 

 of the blowpipe for him and he is shaping it. The next workman is cooling the shaped ball. 

 More glass is then gathered on the ball and the third workman is enlarging it. The fourth 

 workman is the final blower. Standing on the "blower's block," he blows the glass until it 

 assumes the shape of the mold inside the block. The making of window glass by hand 

 methods is a variation of the process shown (see text, page 395). 



endeavor where glass does not play an 

 essential role. 



It was Pennsylvania that fostered the 

 manufacture of this commodity in Amer- 

 ica, and it is from Pennsylvania today 

 that the American people get a third of 

 their supply. 



The processes of manufacturing glass 

 are extremely interesting. To see sand, 

 soda, and lime mixed, subjected to heat, 

 and turned into glass as transparent as 

 the clearest water, or even as the very 

 air itself, shows what liberties man has 

 learned to take with Nature. Now as 

 free-flowing as water, now as sticky as 

 warm taffy, now as hard as flint, it lends 

 itself to the manipulation of human 

 hands and the purposes of man with as- 

 tonishing versatility. 



The mixed materials, technically known 

 as the "batch," consist of white sand and 

 such bases as potash, soda, lime, and lead. 

 Small quantities of other materials are 

 added as auxiliaries to change the color 

 or nature of the glass. Manganese and 

 arsenic are among the agents employed to 

 make it colorless. For window glass a 

 batch may be made up of 8,000 parts 

 sand, 2,200 of soda sulphate, 2,500 of 

 lime, 50 of arsenic, and 40 of powdered 

 coal ; or the amount of lime may be cut 

 down and carbonate of soda substituted. 



Window glass is of two kinds — cast 

 and blown. The cast is the plate-glass of 

 commerce. In making it the process is 

 not dissimilar to the rolling of dough on 

 a dough-board. A huge flat table with a 

 rim around the edge is filled with a pile 



392 



