CLASS BLOWING 



495 



A special form of emery wheel or a file may be used to 

 slant tlie end of the cannula before the point is rounded. 

 The danger here is that the points may be heated too hot 

 and become sealed off. The outer edge of a very small 

 yellow flame is employed for this work. Each eannula as 

 a whole is then cut off from the main length of the glass 

 tube by scratching a ring around the tube with a file and 

 snapping the eannula off at the ring. The rough ends thus 

 formed are rounded by heating gently in the flame and the 

 eannula is made. It should be cooled slowly. 



Position of nails 



Cut off ends with 

 nippers after wire 

 is bent. 



Board held in vise 

 or nailed to table 



wire wrapped as shown 

 by arrows 



No 18 spring brass wire 



Fig. 383. Process for making frog clips. 



For the purpose of bending, glass tubes should be heated 

 in the flame from a fish tail burner (the tube is constantly 

 rotated) as shown in Fig. 381. As the glass softens over 

 a sufficient length of the tube the two ends of the tube are 

 bent upward and brought to the proper angle as shown in 

 Fig. 382. This is the method used for bending manometer 

 tubes, etc. The danger usually is that not a long enough 

 length of the tube may be heated before the bend is at- 

 tempted. The bent tube should be cooled very slowly to 

 avoid cracking. 



Frog Clips. These can be made cheaply and easily by the 

 method shown in Fig. 383. The seven small nails driven 



