GLASS BLOWING 493 



brass on the joint while applying a very intense blast lamp 

 flame. The brass melts and passes into all the crevices 

 between the adjoining pieces of iron. When the parts are 

 cooled a very firm joint should be formed. 



Glass Blowing. Only two of the most common operations 

 need be mentioned here, for the making of complicated 

 articles of glass requires great skill and long practice and 

 training. It is, however, often almost imperative for the 

 instructor or mechanic to be able to make a few things from 

 glass tubing. These articles are usually cannulas, and tubes 

 which are bent in various directions. Very fine pointed 

 cannulas are so easily broken and are so frequently needed 

 that it is a matter of special importance for the simpler 

 forms to be made in the laboratory. Figs. 378, 379, and 380 

 show essentially the processes involved. Very fine can- 

 nulas, as those needed for Wharton's duct or the thoracic 

 duct, should be made of small tubing (about 3/16 inch out- 

 side diameter). The glass is heated up slowly at first (best 

 in a smoky flame) to avoid cracking. A very small flame 

 is then used to heat a short length (14 to y 2 inch) of the 

 tube. When the glass softens (the tube is rotated con- 

 stantly) the heated part is then drawn out for a distance of 

 two or three inches, depending on the size of the point 

 desired for the cannula, The glass is then allowed to cool 

 enough to harden. The flame is then made exceedingly 

 small and is directed against one of the "shoulders" of 

 the drawn out portion of the tube. The tube is kept rotating 

 and as soon as the glass in the "shoulder" begins to be- 

 come fairly soft it is quickly drawn out a little and a 

 "neck" is thus made for the cannula as shown in Fig. 379. 



The process is repeated for the other "shoulder" and two 

 cannulas are thus formed but are held together by a nar- 

 row length of the drawn out tubing. With the sharp corner 

 of a file a scratch is made a little beyond the point where the 

 tip of each cannula should be. The tube is snapped off at 

 each of the scratches and then the points of the cannulas are 

 carefully rounded by heating in a very small yellow flame. 



