i6o 



THE POPULAR SCIENCE MONTHLY 



beauty, since the dense lead compounds have a tendency to sepa- 

 rate from the lighter silicates, and, consequently, if present in too 

 large amounts, they make the glass streaky and mottled. In gen- 

 eral, lead glass for domestic uses has a specific gravity of from 

 three to four — that is, it is from three to four times as heavy as 

 an equal bulk of water. The brilliancy given to the glass by its 

 increased density has attached the name crystal to this particular 

 product. 



It is essential that the several ingredients should be thoroughly 

 mixed, and to this end the operation is carried out mechanically. 



The materials are fed 

 into the upper end 

 of a slowly revolving 

 hopper, whose axis is 

 slightly inclined to 

 the horizontal, and 

 are thoroughly mixed 

 by the time they reach 

 the discharging end. 

 A dainty pink pow- 

 der falls into the re- 

 ceiving bins. Its sub- 

 sequent baptism by 

 fire transforms the 

 opaque into the trans- 

 parent. The furnaces 

 employed for this 

 purpose are of the 

 type common to other 

 glass-melting process- 

 es — simply a circular 

 and intensely heated 

 chamber, surmounted 

 by a stack, and pro- 

 vided with radial openings to permit the blowers to dip their blow- 

 pipes into the molten contents of the fire-clay crucible-pots. 



The scene around this industrial caldron is quite as busy as 

 that which has its center in the bottle furnace, and is even more 

 varied. The workers are fashioning objects of the most diverse 

 shape and for the most unlike purposes. Some are blowing lamp- 

 chimneys, others gaslight globes, or decanters or dishes. In the 

 center of the apartment a large press, with engraved steel dies, is 

 squeezing the plastic " metal " — for so the glass-blower designates 

 his still fluid glass — into decorative panels for car-windows and 

 transoms. As one passes from one end of the large room to the 

 other, he will see almost every conceivable shape in glass, suited 



Fig. 2.— The Process of Engraving on Glass. 



