Test Tubes:

• Material:
  Test tubes are typically made of glass, although plastic test tubes are also available for certain applications.

• Shape and Size:
  They are cylindrical in shape, rounded bottom and come in various sizes. The common sizes include small, medium, and large, with diameters ranging from a few millimeters to a few centimeters.
• Small Test Tubes:
  Length:           75 mm to 100 mm
  Diameter:       10 mm to 16 mm
• Medium Test Tubes:
  Length:           100 mm to 150 mm
  Diameter:       16 mm to 20 mm
• Large Test Tubes:
  Length:           150 mm to 200 mm
  Diameter:       20 mm to 25 mm
• Extra-Large Test Tubes:
  Length:           200 mm and above
  Diameter:       25 mm and above
• Heat Resistance:
  Glass test (Borosilicate) tubes are generally heat-resistant and can withstand exposure to flame. This makes them suitable for various laboratory experiments that involve heating substances.
• Graduations:
  Some test tubes may have graduations (measurement markings) to allow for precise volume measurements.

• Uses:
  

  Mixing and Stirring: Test tubes are often used for mixing small quantities of substances. They can also be used for stirring solutions.
  Heating: They are suitable for heating substances over a Bunsen burner or in a water bath due to their heat-resistant nature.
  Chemical Reactions: Test tubes are commonly used to perform small-scale chemical reactions. They provide a controlled environment for observing reactions.
  Storage: Test tubes can be used to store small amounts of liquids or substances for short durations.
  Culturing Microorganisms: In microbiology, test tubes are used for culturing and growing microorganisms.
  Qualitative Analysis: Test tubes are often employed in qualitative analysis to test for the presence or absence of certain substances in a sample.

• Caring for Test Tubes:
  

  Cleaning: Clean test tubes thoroughly after each use. Use appropriate cleaning agents and brushes to remove residues.
  Drying: Allow test tubes to dry completely before storing them. Invert them on a drying rack to ensure proper drying. Before using sterile the tube at 160 ^oC for one hrs. in a hot air oven.
  Storage: Store test tubes in a designated area, away from direct sunlight and potential breakage.
  Handling: Handle test tubes carefully to avoid breakage. Use tongs or a tube holder when heating them.
  Avoiding Extreme Temperature Changes: Avoid exposing glass test tubes to extreme temperature changes, as this can lead to breakage.