[paul.fr]

If i pop a marshmellow in a vacuum chamber and remove the air, what will happen to it?
If i then let the air back in, what will then happen?
What will then happen if i remove the air again?

I know that's 3 questions, can i have 4?

How can i make a homemade vacuum chamber?

[Make it Lady]

Marshmellows in a true vacuum would explode. In a partial vacuum they get very, very big. The air inside them is not impeded by outside air pressure so it tries to fill the space in the vacuum causing the mms to swell. This is a good demo to show what would happen to Astronauts going out into space without a space suit on. As long as the mms stay in tact when the air is returned they shrink down again. You can repeat this with the same mms for quite a number of times. However after a while they start to crack and don't work so well.
The Kitchen science way to do this is to buy a vacuum storage container. They are available on Amazon and consist of a hard outer clear,colourless plastic container and a lid with a 'wine keep' valve on top. You pump the air out with a little hand pump that comes with it. If you can't do this get a wine bottle, pop in some mini mms and put in a wine keep cork. again pump the air out. You only get a partial vacuum but it is very visual and everyone loves it.
Otherwise we are talking bell jars and vacuum pumps. This is the expensive route.
I've seen deflated beach balls with the valve sealed, inflate in a vacuum. Have fun.

[syhprum]

If you have an upstairs room above about 10 meters and a length of reasonably strong hose you can siphon water out from a bowl covered with some bell jar like container, that will produce quite a good vacuum if the water is cold.

[keydetpiper]

The marshmallows will indeed inflate, and when removed from vacuum (or air is let back in) they shrink smaller more than the original size. As they expand some air leaks out, so when they contract there's not as much air to keep them originally sized.

This little demo is also a lot of fun to do with Peeps. They react the same, but the fact that they have a face makes it that much more disturbing.

[Seany]

Here is a video!!

http://www.youtube.com/watch?v=OHY9fFQhX68