Temperature. Thermometers 



139 



softened, blow as before, and the small bulb should 

 become somewhat larger. These processes should be 

 repeated till the bulb obtained is about \" in diameter, 

 and its wall is of even thickness. The latter point 

 may be tested by gently knocking various parts of the 

 bulb upon the top of the bench, when the bulb has 

 cooled down. The nature of the sound produced 

 will vary if different parts of the wall are of different 

 thicknesses. The production of a good bulb requires 

 some care and it may be found that two or three 

 attempts will have to be made before a really satis- 

 factory one is obtained. Special attention must be 

 paid to the direction to continue the heating till the 

 glass is thoroughly softened, as it is useless to attempt to 

 blow a bulb from insufficiently heated glass. 



Next draw out the other end of the tube at a point 

 about 2" from the end in the manner already described. 

 Cut off the thin tube close to the shorter piece of tubing. 

 Bend the thin tube near its junction with the thick- walled 

 part by heating it at this 

 point carefully, removing it 

 as soon as it shows signs 

 of softening, and gently 

 bending it into the shape 

 indicated in Fig. 41. Ar- 

 range the apparatus as in 

 the figure. The bulb is im- 

 mersed in a beaker of water, 

 while the open end of the 

 tube dips into a small beaker 

 containing freshly distilled 

 alcohol to which sufficient 

 colouring-matter, such as 



Fig. 41, 



litmus, has been added to render it more clearly visible 



