22 



AGRICULTURAL CHEMISTRY 



and at the same time press outward with the thumbs. 

 This causes a square break of the tube. The cut ends of 

 the tubing should then be held in the outer portion of the 

 flame until the rough edges are annealed. 



25. Bending Glass Tubing. Place the wing-top at- 

 tachment on the burner. Hold the tube in the upper 

 part of the flame as shown in the illustration (Fig. 2), 



Fig. 2. Bending glass tubing. 



and rotate so that all parts are heated alike. When the 

 tubing becomes red and readily yields, it can be bent in 

 almost any form desired, but if overheated it becomes too 



soft and collapses. It is always 

 best to bend without removing 

 from the flame. A little prac- 

 tice with pieces of old tubing will 

 soon give the necessary experi- 

 ence. Avoid twisting or rapid bending of the tube. 

 Make all bends on the same plane and aim to make well 

 rounded joints as shown in Fig. 3. 



26. Perforating Works. Select a cork of suitable size 

 for the test-tube or flask used. New corks should always 



Fig. 3. Bent tube. 



