Glass Working Exercises 



107 



Prepare a second piece, say of 5 -mm. bore, draw out to a 

 point, blow a bulb of 10 mm. diameter at the commencement of 

 the narrowing of the tube, and cut off the thin drawn out portion, 

 as shown in Fig. 96 (2). Heat both in the blowpipe flame until 

 almost softened, then introduce the jet and allow the bulb to rest 

 upon the flanges of the wider tube. Heat this junction strongly, 



FIG. 95. 



FIG. 96. 



maintaining the rotation of the tubes as before, and when glowing, 

 press together lightly, move to a vertical position, and blow into the 

 tubes. This will make the jet return to the direction of the axis 

 of the tube, and will finally seal the junction, while the extra 

 internal air pressure will restore the shape of the work (Fig. 96 (4) ). 

 A useful continuation of this exercise is to seal a jet through 

 the side of a tube of similar dimensions to that given above. 



EXERCISE 13. To make a filter pump.? 



This exercise is a combination of several preceding ones. 



A strong bulb 4 cm. diameter is blown at one end of a stout 

 8-6 mm. tube, about 30 cm. long, and a long jet is sealed into the 

 bulb in line with the axis of the tube. See Fig. 97. 



B 



FIG. 97. Filter pump. 



A constriction is then made on the tube opposite the jet, and two 

 or three acute bends made before the blowpipe, immediately below 

 this constriction. These bends serve to break the jet of water, and 

 so to make it carry away air in front of it. 



The lower portion of the bulb is then heated, and the bulb 



