This really does not sound as bad as you would think. I have seen this done somewhere and it is really impressive. All you need is a bottle of carbonated (fizzy) water, some raisins, food coloring and a torch.
Pour the fizzy water into a good sized see through jug or vase. Pour in a good handful of raisins and a little food coloring. The each raisin will rise and fall in the water for ages. Shine a torch through the vase for the full effect.
