Glass Working Exercises 



in 



The supporting strip of paper is now removed, and the open 

 end may be drawn out by softening about 3 cm. past the end of 

 the inner tube, and drawing out in the usual way after thickening. 

 Instead of sealing off, however, a straight piece of thin tubing 

 should be joined in at this end in order to complete the apparatus. 

 Finally, border all sharp edges (Fig. 102 (4) ). 



Corks maybe used to close up any unnecessary openings during 

 blowing, and if the inner tubes be too wide to blow into comfort- 

 ably, they may be closed with a cork through which passes a narrow 

 tube. Immediately they are completed joints should be wrapped 

 in cotton-wool, which may be held in place by a few strands of 

 cotton while the work is being completed. As far as possible a 

 joint should be heated thoroughly all round after it has been 

 successfully made, as this will tend to equalize all strains from the 

 unequally heated patches, and lessen the liability to cracking. 



EXERCISE 17. To make a Hoffmann 's voltameter. 



Several types of this instrument are in vogue, the simplest in 

 construction being described below. 



Select a straight length of 15-13 mm. glass tube, and cut off 

 two 5o-cm. lengths, and two lo-cm. lengths. Also a 4o-cm. length 

 of 26-24 mm. glass tube. 



Join the two lo-cm. pieces at right angles, as described in Exer- 

 cise 7. Attach the wider 4o-cm. tube - to the side piece in the 

 T, as in Exercise 4. Join the 

 two 5o-cm. pieces to the ends 

 of the lo-cm. cross piece 

 about 5 cm. from the ends 

 (see Fig. 103). This latter 

 portion of the work will pre- 

 sent the only difficulty, which 

 may be considerably lessened 

 by mounting the glass upon 

 a board, and binding round 

 with copper wire, or by hold- 

 ing the various portions se- 

 curely by means of retort 

 stands and clamps, closing 

 all openings but one, into 

 which a cork carrying a tube 

 is fitted, and the tube connected with rubber tubing to a mouth- 

 piece for blowing. In this case the blowpipe should be removed 



JL 



FIG. 103. Stages in the construction of 

 Hoffmann's voltameter. 



