Steam boat

Break off the head of a match and drop some glue on to the end. If you place the match in a dish of water it moves jerkily forward.

The glue contains a solvent, which evaporates to give a vapour. It puffs out from the drop in invisible little clouds, giving the match a small push each time.

Eventually so much of the solvent has escaped that the glue becomes solid. In a dried drop of glue you can still see the residual solvent vapour as small bubbles.