But what about the relative weights of the two gases in question? I read up on Dalton's law after the post. The example given is the hydrogen generation experiment with the inverted test tube in the water bath. Initially all the gas would be hydrogen - but then because the water is evaporating (inside and outside the tube - even at the same 1 atmosphere of pressure) then eventually it would reach equilibrium, and the gas in the tube would contain some water vapor as well as the hydrogen - BUT - in the tube itself - wouldn't the water vapor be stratified on the bottom?
In our practical example - yes, the pressure of the CO2 blanket and the air would be the same - but due to the geometry of the blow off tube in the carboy - the heavier CO2 would be trapped in the carboy. Assuming minimal agitation and thermal expansion - the CO2 wouldn't "fall out" of the tube and be displaced by the air. Even if a cycle of thermal expansion and contraction happened, and the headspace did contain a small amount of air - where would it be? Would it equally disperse throughout the volume? or would it float towards the top?
If I'm just a window licker - then so be it - but I can't see all of the CO2 dissipating - especially in the relatively short amount of time that imacoming was on vacation. Where's my helmet?!?!
Mylo
