I have long wanted to build a baking powder submarine from commonly available materials. I had one of these in the 1950s when Kellogg's gave them as a prize in cereal boxes. Those were a little over two inches in length. A couple of years later l saw a much longer one in a store window. Mr_o_uk
got me thinking about it again with his Baking Powder Diving Submarine Instructable
, but his is a concept submarine he has not actually built. There are some practical problems I had to solve before my concept would be a working bathtub submarine that goes to the bottom, rests there, rises, discharges a bubble of CO2
, and sinks to the bottom again in endless cycles until the baking powder is depleted. I have done that in a way someone reading this Instructable can replicate.