we can calculate the refractive index of liquids like water using a converging lens and mirror by the standard method . r.index of water is less than that of lens(glass) . now taking mercury, whose r.index is > glass, can we do the same experiment and find its r.index ? i believe the answer is no.. coz there the rays get diverged and hence no real image is formed. but i dont think it will always diverge ?? any in sight ?