Glass Working Exercises 103 



point at which it resumes its full diameter, and pull off a second 

 portion, if necessary, so producing a blunt end. Heating this for 

 about 5 mm. up the stem, blow as soon as possible better too soon 

 than too late, and never permit the glass to accumulate at the 

 heated end, nor the bore to collapse beyond the amount necessary 

 to keep the small bulb concentric with the outside contour of the 

 glass. Once the first bulb is correctly produced, no difficulty will 

 be experienced in the completion of the exercise, which is carried 

 out in exactly the same way as that indicated previously. 



EXERCISE 7. To make a right-angled junction. 



Take a piece of 6-4-mm. tube, 20 cm. long, draw apart at 

 14 cms. from one end, and set aside to cool. When quite cool, 

 heat the longer portion at one spot in its side without rotating or 

 moving in any way, until it shows signs of collapse. A very fine 

 flame should be used for this purpose. Blow down the tube, and 

 expand it where it is softened ; reheat until it collapses and expand 

 a second time, the object being to build up on the side of the tube 

 a cylindrical attachment, to which the incoming tube may be 

 joined. This is a matter requiring some care. The tube should 

 not be allowed to form into a thin bulb (or it will open out on the 

 next reheating) until the junction is satisfactorily formed on the 

 tube (Fig. 92 (5)). When this stage is reached, the top of this side 

 tube is removed with a sharp puff of air or the stroke of a file, and the 

 opening so produced, together with the rim of the incoming tube, is 

 heated in the flame. Rotate the incoming tube, and take care that 

 the contraction or recession of the heated glass of the longer tube 

 takes place evenly, i.e. that the tube is evenly heated. When both are 

 evenly and equally red hot, place the two portions carefully and 

 slowly together, press together for one second, then pull apart while 

 blowing down the open end of the tube. This will secure the equal 

 thickness of glass at the junction necessary for a reliable joint, 

 and the junction itself will be barely visible, as a circle round the 

 smaller tube. Such joints should withstand any reasonable pulling 

 upon any two parts just as much, in fact, as one would give to 

 a straight piece. 



Frequently an airtight joint is made which is very unsightly. 

 This should be reheated at the junction, first in the direction A, 

 until a portion of each tube is softened and shows signs of collapse 

 a puff of air then restoring the shape. Several reheatings may 

 be necessary, and it should not be left until an evenly curved joint 

 is secured, though the whole junction must meanwhile be kept well 



