4-5] 



THE BLOWPIPE 



to produce a continuous blast. This is acquired by first 

 inflating the cheeks with air from the lungs, keeping them 

 inflated until the lungs are exhausted of 

 air ; then when inhaling — i.e. refilling the 

 lungs — the air in the cheeks should be ex- 

 pelled gradually, and thus keep the blast 

 continuous. After a little practice the stu- 

 dent will be able to breathe through the 

 nose during blowpipe-work, whilst he is 

 employing his cheeks and lungs to keep up 

 a steady blast. 



4. For heating large vessels to a high 

 temperature the table blowpipe is usually 

 used. In this blowpipe the air is forced 

 through the flame by means of a. foot-bellows. 

 Since both hands are at liberty it is usually 

 used in glass -working (paragraphs 5, 6, 

 and 7). 



5. Cutting and Bending Glass Tube and 

 Rod. — Glass tube (or rod) may readily be cut by first 

 making a deep cut with a sharp triangular file, then holding 

 the tube on either side of the cut, and finally applying a 



Fig. 3 



strain partly between a pull and a break. The rough edges 

 should either be filed or held for a short time in the Bunsen 

 burner, so as to fuse the edges, and thus prevent the jagged 

 edges from cutting the hands. 



Glass tube (or rod) is readily bent by holding the tube 

 in the upper part of a fish-tail burner (fig. 5), constantly 



a 2 



