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Thursday, 22 July 2021

Chemistry Practicals For Class IX (Science Group) - Experiment No. 1: To cut and bend a glass tube and draw a Jet.

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EXPERIMENT NO. 1
TO CUT AND BEND A GLASS TUBE AND DRAW A JET

APPARATUS:
  • Glass Tube
  • Small Triangular file
  • Knife
  • Match Box
  • Meter stick
  • Glass marking pencil
  • Bunsen burner / Spirit lamp

CUTTING OF A GLASS TUBE
METHOD:
  • Place a glass tube horizontally on a table (or any solid support) as given in the figure.
  • Measure the desired length by the meter stick.
  • Mark the length with a glass marking pencil.
  • Make a single sharp transverse scratch with a triangle file at the mark.
  • Hold the tube with both hands in a way that thumbs remain below (opposite to) the mark.
  • Exert a little force to break the tube into two pieces with a quick jerk.
  • Keep the tube away from your face.
  • The tube breaks evenly at the scratched place.
  • Round the rough edges of cut tubes by rotating in flame (fire-glazing).
  • Allow the tube to cool by placing it over an asbestos sheet.


BENDING OF A GLASS TUBE
METHOD:
  • Hold a tube horizontally in your both hands over a Bunsen flame at the ptace where it is to be bent as shown in the figure.
  • By rolling and moving the tube back and forth, heat the 2 inches part of the tube evenly, that has to be bent.
  • Keep it rotating until it softens.
  • When glass becomes soft.
  • Bend it at the desired angle, keeping it a bit up from the tip of the flame.
  • Hold until the glass hardens.


MAKING OUT A JET
METHOD:
  • Hold the tube in your both hands as given in the figure.
  • Put it over the flame in a way that only one and half inch of the tube remains in the flame.
  • Slowly rotate the tube about its axis, keeping it in the flame until it softens.
  • When soft, remove it from the flame and immediately draw the two ends apart carefully till it forms a fine capillary of desired diameter.
  • After cooling, cut the tube to separate the two ends by means of a knife.
  • Round the rough edges of cut tubes by rotating in flame (fire-glazing).
  • Each piece of the tube has a jet.


PRECAUTIONS:
  • The scratch on the tubes should be sufficiently deep.
  • Pressing of thumbs should be with a uniform force.
  • Avoid too much heating, it may cause poor bends.
  • The tube should be continuously rotated while heating.
  • Do not keep the hot tube on the table.
  • Pull the ends of the tube by taking it out of the flame.
  • Heat the tube in the upper portion of the flame and continue rotating.
  • While drawing a jet the pulling apart of the glass tube should be immediate and carefully.
  • Never try to break the tube with simple bare hands.


Special Thanks to Sir Sajjad Akber Chandio


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