21 



EXPERIMENT 11. GLASS MOLDING 



( I ) To make a stirring rod or a medicine dropper. 



Hold a glass tube, about a foot long, in the Bunsen 

 burner (Fig. 12), and 

 slowly rotate it in 

 order that it may be 

 uniformly heated. 

 When the glass be- 

 gins to soften, sepa- 

 rate the hands, draw- 

 ing out the glass into 

 the shape shown in 



(Fig. 13). Then cut the tube at c. The cutting of glass 

 tubes should be done as follows. 



\ 



a, _ 



FIG. 13. Drawing out the tube. 



By means of a strong file make a short, but deep scratch 

 on the glass where it is desired to make the cut, then 



grasp the tube so that 

 the thumbs are together 

 behind the scratch (Fig. 

 14), and push with the 

 thumbs. The tube will 

 break at the scratched 



FIG. 14. Breaking a tube. point. 



The cutting of the glass tube leaves us with two stirrers, 

 each of which has a sharp edge at the narrow end. These 

 sharp edges can be rounded and smoothed off (Fig. 15) 

 by slowly rotating the sharp end of the glass in the flame 



