22 



FIG. 





stirring rod can 

 be smoothed off. 



until a yellow color appears. When the edge has been 

 smoothed off, the tube should be slowly moved in and out 

 of the flame to prevent sudden cooling, 

 since any sudden heating or cooling of 

 glass is apt to crack it. A hot tube 

 should never be removed from a flame 

 suddenly, nor laid on a cold surface. A 

 cold tube should never be put into a flame suddenly, 

 but should be moved in and out until moderately warm, 

 when it can be held in the flame permanently without 

 danger of cracking. 



(2) To make a closed tube. 



Put the end to be closed into the flame, and rotate it 

 slowly; allow the glass to remain in the flame until it be- 

 comes molten and runs together, closing the open end. 



(3) To make a curved or bent tube. 



Hold the tube in the flame as before; but in addition to 

 rotating it, move it slowly from right to left, so that a few 

 inches of the rod are heated. As soon as the heated por- 

 tion becomes soft, re- 

 move the tube from the 

 flame and bend it slightly 

 (Fig. 1 6); put it in the 



flame again, 



and when it has 



again become 



soft bend it fur- 

 ther as before. 



Continue this 



until the desired 



~" curve has been 



FlG ; 



A bent 



tube. made(Fig. 17). 



FIG. 16. Bending glass. 



