9 8 



Laboratory Arts 



Care must be taken throughout this, and other exercises, to 

 rotate the tube gently and continuously, and to arrange that the 

 rotation be of one complete revolution, neither more nor less. 



EXERCISE 4. -Joining two tubes \ end to end. 



In this exercise it will be well for a beginner to close the end 

 of one of the tubes, either with a small cork, or a plugged india- 

 rubber tube. The two pieces of tube are then held in a fairly large 

 flame facing the blast (Fig. 86), in such manner as will secure equal 

 heating for the extreme rim of each, and rotated 

 slowly and evenly as before. When the respective 

 rims are red hot, and begin to close in slightly, 

 the two tubes are pressed together gently, and 

 after adhesion is secured, pulled apart slightly, 

 not sufficiently to narrow the tube, but to 

 counteract any swelling at the junction that may 

 have occurred when pressing the tubes together. 

 At the instant immediately before solidification, 

 the tube should be gently blown into, which will 

 help to keep the junction of correct bore. 



The first few attempts may not be very suc- 

 cessful, from some of the following reasons : 



1. Too great hurry to place the hot rims 

 together, resulting in a displacement of the axis 

 of one piece relative to that of the other. 



2. Too great delay in pulling apart after 

 joining. 



3. Too great delay in blowing. 



4. Undue softening of the glass, causing a side collapse of 



the joint. 



5. Unequal softening of the 

 glass. 



In order to reduce the likelihood 

 of these errors being made, the 

 tubes may be separately heated, 

 and when hot, expanded by a twist 

 of the carbon cone (Fig. 87 (i) ), 

 afterwards proceeding exactly as 

 indicated above. This, giving 

 greater diameter to the tubes, re- 

 duces the prospect of error, but the joint so made is not likely to 

 be so sightly as the first, owing to the greater amount of glass 



FIG. 86. 



FIG. 87. Stages in the joining of 

 two tubes end to end. 



