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)?