Some friends and I were drinking from a jug of water that contained wedges of both lime and lemon. All the lemon wedges were floating, but all the lime wedges had sunk to the bottom of the jug.

There were enough pieces of both for us to infer this was not just coincidence, and all of us were pretty certain that we'd seen lime slices floating before. Can anyone offer an explanation?

Bladon Mooney, Leicester, UK

Thanks to the anonymous correspondent who sent a link to a page on the Steve Spangler Science site, where the answer is tested - Ed

(Image: tellgraf, stock.xchng)