During a series of comments here, it was suggested that taking dry ice into an airplane, the airplane gets lighter as the ice sublimes.
This was supported by the idea that when the dry-ice sublimes and CO2 is released in form of gas the pressure inside the plane rises, and as the airplane keeps the pressure at a certain level the 'extra pressure' would be released, releasing 'extra air' and thus making the airplane lighter.
I am not convinced with this idea, why would the sublimed CO2 gas rise the pressure if at the same time there is more volume available in the airplane? (the volume left behind by the dry ice which sublimed) My intuition tells me that the new volume available makes the pressure drop and the new gas makes the pressure rise, and that both drop and rise are equal.
Now, apart from some particularities the aircraft systems has with pressure and air, the more general question would be:
There is a box which you can fully close and no air escapes nor enters, you open the box and put inside dry-ice and close the door. The pressure inside the box would be equals to the room pressure, isn't it? Now, as time passes the dry ice fully sublimes, what is the pressure inside the box now?