io8 Laboratory Arts 



made of conical shape, until the jet centres immediately over the 

 constriction. 



Finally, a side piece is sealed in the bulb at B. The complete 

 instrument is useful in either extracting air through B, or 

 injecting air through C by means of a water jet passing down D. 



The tubes at D and B may be constricted 

 slightly in order to allow stout rubber tubes to 

 be fastened to them by binding wire, the most 

 ff suitable shape being that shown in Fig. 98, which 



FIG. 98. permits wetted tubing being slipped easily over 



a diameter it would not otherwise encircle. 

 All ends of glass tubes should be bordered or "rounded," 

 to prevent damage to indiarubber junctions. 



EXERCISE 14. To make a eudiometer. 



Take a 15-13 mm. tube, close one end hemispherically, and 

 while still hot, heat a small portion of the tube more strongly, 

 touch with a thin glass rod, and pull out the glass to a fine point 

 (Fig. 99 (#)). Before breaking this open, repeat at a point 

 immediately opposite. 



Hold a piece of platinum wire about 2 cm. long in the centre, 

 and bend each of the ends into a circle round a small glass rod. 

 A piece of blue " enamel " glass rod is then drawn out, and wrapped 

 round the wire in such a way as to enclose the end of the wire and 

 a portion of the loop as indicated by the dotted line (Fig. 99). The 



enamel glass is heated very 

 strongly, until it closes upon 

 the wire like a "borax 

 bead." 



Cut the wire in the 

 centre, removing in addi- 

 tion any excess of wire, in 



FIG. 99.-Sealing wires into a eudiometer. view of the distance it has 



to bridge. Cut oft one of 



the drawn-out points from the long tube, insert one piece of wire, 

 and, holding the tube horizontally, the wire hanging down through 

 the hole, direct a fine flame upon the enamel until union with the 

 glass takes place. Pass round the junction with such a flame, 

 blowing into the tube as may be necessary in order to keep the 

 correct shape. 



Before cooling, when this is completed, insert the second wire 

 similarly, heat the whole top of the tube thoroughly before allowing 



