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  1. #1
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    Default alcohol and chemistry

    Having made the switch to an alcohol stove, I've noticed what I think is a strange property of stove alcohol. I carry HEET in a 20 oz soda bottle. I've noticed that if I leave it capped for any length of time (say a day), the pressure inside the bottle appears to be lower than the air pressure outside the bottle. That is, the bottle appears to be sucked inwards by the alcohol. This happens even when the bottle is sitting in my apartment, so it isn't caused by a change in the ambient air pressure. The effect appears to be increased if there is a change in ambient temperature.

    While I've formulated a few ideas on what might cause this effect, my chemisty knowlege is far too lacking to form a good opinion. Does someone with more knowlege that I know the reason for the pressure change (if, in fact, that is what it is)?

  2. #2
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    Default

    Well, are you sure you have high quality alcohol, or LOW quality alcohol? Low quality alcohol sucks.

    The Weasel
    "Thank God! there is always a Land of Beyond, For us who are true to the trail..." --- Robert Service

  3. #3
    2005 Camino de santiago
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    Default Pressure

    Now that is wierd. I suspect as you heat it, alcohol molecules begin to boil off surface,[actually, a component gas of the complex mlecule] is boiling off and pressure begins to build up within the sealed, air-tight container, increasing pressure with increase in temperature. Everyone knows this is what happens..

    Now, if you put your hot alcohol into a hot vessel on a hot day, seal it, I would comfortably suspect that the inverse is true. The molecules , as temperature dropped, would revert back from vapor to liquid, since alcohol is a liquid at room temperature. But so much would be converted back to liquid as to begin pulling a vacumn in the air-tight container of alcohol?...

    I have carried various containers of denatured ethyl alcohol and don't recall it happening to me. If it did the vacumn pull was so slight as to not notice it.

    Chris, can we safely assume the alcohol was not Tennessee sippin' whiskey and that you were not imbibing?

  4. #4
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    Default

    The alcohol in question was HEET, the stuff you put in your car so that something or other doesn't happen. I think it is just pure alcohol of some flavor. I have noticed the effect both when sober and during high tea when camped for the day. Of course, high tea usually consists of me sitting in the dirt, under a tree or by a creek somewhere, drinking a concoction of Earl Grey tea mixed with Jim Beam.

    I like the reverse cooling theory. I'm heading back into the Smokys in a few weeks and will try to make some observations.

  5. #5
    2005 Camino de santiago
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    Default Heet

    I looked HEET (and ISO-HEET) up. They are gas-line antifreeze. The yellow bottle HEET version has been sold for about 50 years and contains methanol. ISO-HEET comes in the red bottle and contains isopropanol. Neither product is widely sold in Florida! Both products prevent gas line freeze-up but remove water in different ways.

    I have never tried it because I cant get it here. What is purchased here is either methyl or ethyl [denatured] alcohol, depending on which product is added to the ethanol to denature[poison] it. What a waste!

    You can get it at any hardware store. But I sure would like to try some HEET for once, just to see if there is any difference.

  6. #6
    Section Hiker 180 AT miles
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    Default

    well i dont know if youve ever tried to blow up a ballon into a flask before, but its not easy, due to the fact that the air inside has nowhere to go. but there is a way. and that way is to place the balloon over the mouth of the flask and seal it, then place the flask over a heat source, the gas molecules within the container will become excited and the preasure will increase inflating the balloon outside the flask. if you then take the flask off the heat remove the baloon deflate the air out of it and place it back on the flask as the flask cools the balloon will be sucked into the flask by negative preasure and seem to inflate within the flask. same as what highway said. that may be the reason. perhaps there are other properties of HEET that were not aware of, its possible that for some reason it is a very reactive solvent to air, which would mean that it would draw the air out of the space at the top of the bottle leaving a vacuum, but i dont think thats likely. its probably just temperature.
    "Do what you Love, Love what you do"

  7. #7
    First Sergeant SGT Rock's Avatar
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    Default

    Alcohol tends to expand and contract quite a bit based on temperature. Since their is also air in the bottle, you will have bottles bulge and shrink. I see it all the time with my fuel bottle. We are't used to seeing it with water, so it is a little different. White Gas can actually do the same, but since it's stored in metal bottles, you don't notice it.
    SGT Rock
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