Answer
For torque to be generated, forces need to be applied on a point at a particular distance away from center. In this case, although mercury is much heavier, it does not matter, because the buoyant force are perpendicular to all of the surfaces, so it is not possible for the cylinder to rotate. So I would not invest money in this.
Work Step by Step
For torque to be generated, forces need to be applied on a point at a particular distance away from center. In this case, although mercury is much heavier, it does not matter, because the buoyant force are perpendicular to all of the surfaces, so it is not possible for the cylinder to rotate. So I would not invest money in this.