Glass Working Exercises 115 



These lie side by side. They are to be cut off with a single stroke 

 of the file, and one of the curves heated until the two ends so 

 produced come into exact line and touch each other at some con- 

 veniently accessible place, such as X. The apparatus is clamped 

 in a stand, and the blowpipe flame is then projected against a 

 small portion of the junction, and a thin glass rod held ready to 

 touch the junction, should the glass tend to separate. As heating 

 proceeds, the glass will fuse and usually fall together, when a puff 

 of air will prevent collapse. Then another portion of the circle is 

 dealt with, and similarly until the joint is completed all round. 

 It should not be necessary to draw the ends together by the fused 

 rod, but it is well to be prepared. 



Glass Rod is worked as may be necessary much in the 

 same way as tubing, but of course it cannot be blown. Two 

 pieces to be joined are heated strongly, pressed firmly together, 

 and while still strongly heated are gradually drawn out until 

 the original diameter (or 



that required) is reached. [T| , ^n ti -fj t 



A distension on a rod ^T~ 

 (Fig. 109, (b)) may be made (a} Fia log . (b] 



by heating and pressing 



together, and an end (Fig. 109, (a)) may be formed by heating 

 and pressing upon a block of charcoal. 



Lead Glass. This material has largely fallen into disuse, 

 though in some ways it was more easy to work than soda-glass, 

 being less liable to crack on cooling. Soda-glass has, however, 

 been so much improved recently that almost all the advantages 

 of lead glass are secured without its drawbacks of which the 

 principal is discolouration in the usual (reducing) blowpipe 

 flame. 



Lead glass is worked in a roaring or " brush " flame, as 

 distinguished from the quiet flame used for soda-glass. Much 

 more air is required to produce this oxidizing flame, and the 

 same blowpipe rarely produces both flames correctly at will. 

 A special blowpipe is thus required capable of giving a small 

 oxidizing flame, and under these circumstances all the exercises 

 described above may be performed with lead glass. 



Jena Glass Tubing is very hard, and is recognized by a 



