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Air in mercury ?

  1. May 31, 2010 #1
    I was reading about the sprengel pump , And it uses falling mercury to trap air to evacuate a chamber to get the air out of it , http://en.wikipedia.org/wiki/Sprengel_pump you can look at the diagram of the pump , my question is when the mercury traps the air and pushes it down , why doesn't the air just rise back to the top like air bubbles coming out of a divers mask back to the surface of the ocean.
     
  2. jcsd
  3. May 31, 2010 #2

    Borek

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    Staff: Mentor

    It tries, but the diameter of the capillary tube is so small, and mercury surface tension so large, that air is trapped. It is just a matter of equilibrium of forces involved.
     
  4. May 31, 2010 #3
    sweet thanks for the answer , is there any other fluid that i could use besides mercury so that i could make my own , so this has a lot to do with the coulomb force.
     
  5. May 31, 2010 #4

    Borek

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    Staff: Mentor

    Will be difficult. Mercury is very good for two reasons - it has a very high density (hence can "suck" air much stronger than lighter liquids) and doesn't wet glass surface (which means it can't flow around the bubble on the glass walls).
     
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