This year in their early acceptance tubes, in honor of the 30th anniversery of the great balloon hack, the MIT admissions office sent a note encouraging us to hack our tubes. Since there were an number of balloons included in the tube, I decided to make my tube hack a tribute to the the great balloon hack. To fill the balloon, I built an electrolytic cell out of stainless steel washers. When the cell is placed in water (with baking soda added to increase its conductivity), the current splits the water into oxygen and hydrogen. This gas then fills the balloon. When the oxygen-hydrogen mixture in the balloon comes in contact with a flame, the oxygen and hydrogen very quickly combust back into water, producing a very satisfying explosion.
Adjacent plates are insulated from each other by plastic spacers, to prevent short circuits. I used stainless steel rather than steel or zinc coated washers because otherwise the metal would combine with the pure oxygen on the oxygen producing plates, causing them to rust very quickly.