This seems to be a relatively simple question, yet I'm not sure of the answer. A balloon filled with helium gas floats in air. If I submerged a balloon or container in a liquid (e.g. water), is there a liquid with which I can fill the container so as to make it float to the surface. What kind of a liquid would this be? What kind of properties must it have in relation to the water? Specifically this liquid should be the reason the container floats - without the liquid the container sinks. Looking forward to your responses.