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I recently purchased a Vacmaster VP215C chamber sealer, and have noticed that when I place a small container of water into the chamber, and pull a vacuum for just over 25 seconds, the water begins to boil. This is very well understood, and also very interesting to watch.

My question is:

If I were to put a small mason jar into the chamber, half filled with water, and the lid loosely placed on top, and then pull a vacuum until well after the water begins to boil - and then hit the cancel button to force the air back into the chamber, if enough of the vacuum remains in the jar as the lid is sucked down, will the water continue to boil?

I tried it with a hermetic jar, and although the water boiled, as soon as the sealer stopped, and let the air back in, the jar did seal up but the water stopped boiling.

Was this because water will not continue to boil unless the vacuum is increasing, or is it because when the air was let back into the chamber, the vacuum inside the jar was lessened a bit before the lid sealed onto the jar?

Hypothetically, if I were to create a large vacuum chamber in which I had a robotic arm, and in this chamber I placed a jar capable of withstanding the pressure of a high vacuum, put some water into it, brought it to a boil and then used the robotic arm to afix a perfectly sealed lid to the jar before re-pressuring the chamber... would the water inside the jar continue to boil indefinitely?

Thank you for any help. I know my question is probably not phrased very scientifically, but I'm not a scientist or a physics major - just a curious layman.

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  • $\begingroup$ If this worked you would have a version of a perpetual motion machine which we know is impossible in this universe. $\endgroup$
    – CJ Dennis
    Commented May 15, 2015 at 10:49
  • $\begingroup$ Out of curiosity, are you sure the water is actually boiling, or are the bubbles dissolved gases precipitating out due to the lowered pressure? Have you tried keeping the vacuum on until the water has completely evaporated/boiled away? $\endgroup$
    – Reinstate Monica -- notmaynard
    Commented May 15, 2015 at 16:43

1 Answer 1

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The boiling water is converting liquid water to gas. Unless this gas is continually removed by the pump, it quickly increases the pressure inside the vessel. This increased pressure will stop the boiling.

Setting a lid on the jar gives it a one-way valve. Gas can still escape. If you instead put on a full seal so that gas cannot escape, then it will stop boiling even with the vacuum maintained in the outer chamber.

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    $\begingroup$ Thank you for helping me understand this. Your answer was clear and to the point.. There goes my dream of having a jar of water boiling on my bookshelf for all eternity... :( $\endgroup$
    – BBagi
    Commented May 15, 2015 at 7:51
  • $\begingroup$ @BBagi, The problem now is how to put water back into the jar while it's vapor is being pumped out. One day...we will all have jars of boiling water on our desks! (Never give up hope) $\endgroup$
    – Mark N
    Commented May 15, 2015 at 13:55
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    $\begingroup$ @BBagi Try putting something like CPU cooler to the metal lid and warm the bottom of the jar over a lamp to create a temp gradient. With vacuum inside, a 40-60W bulb may be enough keep small amount of water boiling. Just like lava lamp : ) $\endgroup$
    – Agent_L
    Commented May 15, 2015 at 14:52

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