Subject: Building a submarine

My assignment is to make a submarine out of objects found around the house. It 
doesn't have to look like a submarine, but it must behave like one (goes and 
touches bottom and rises back to the surface). It can't make a mess (no 
pollutants) and it can't be connected to anything (tubes, hands). I know I need 
a ballast. I was trying to figure out a way to use Alka Seltzer or something 
that would dissolve and fill the ballast with gas to make the submarine rise.

Re: Building a submarine