4 PRACTICAL AGRICULTURAL CHEMISTRY [6-7 



rotating the tube so as to heat it uniformly. When the 

 glass becomes soft it may be bent at any desired angle. 



Fig. s 



When cold the soot may be wiped off with a duster. If 

 bent as described the bend will be rounded and of uniform 

 bore throughout. If bent in a Bunsen flame the tube is 

 usually flattened out at the bend and very liable to break. 



6. Making Closed Tubes.— Select a piece of glass 

 tube about 6 in. long and -^ in. internal diameter. Heat 

 it in the middle portion by means of the blowpipe flame. 

 When quite soft draw it out, as shown, fig. 6. Next heat 

 the portion (a) in the tip of the flame, so that on drawing 



Fig. 6 



a 



Fig. 7 



out again a tube closed at one end (fig. 7) is formed. The 

 closed end of the tube may then be rounded by heating it 

 strongly and blowing gently into the open end, so as to 

 slightly expand the softened portion. Or, if required, a 

 bulb may be formed by again heating the closed end and 

 blowing into the tube more strongly. 



7. Mounting Platinum Wire.— For a number of 

 purposes (paragraphs 26 and 27) a piece of platinum wire, 

 about two inches long, and fused into a piece of glass tube 

 to act as a holder, will be required. Draw out a piece of glass 



