The separation of three immiscible liquids(mercury, oil and water) by a separating funnel depends on the differences in their densities. The mixture of three immiscible liquids is put in a separating funnel and allowed to stand for sometime. the mixture separates into three layers according to the densities of the liquid in it. The heavier or denser liquid forms the lower layer whereas the lighter liquids forms the middle and upper layers. On opening the stop cock of separating funnel, the lower layer of Mercury(heavier liquid) comes out first and collected in a beaker. When the lower layer of heavier liquid is completely run off, the stop cock is closed. The water in the medium layer is collected in a separate beaker by opening the stop cock again. Finally oil with lighter density than water and mercury will remain in funnel and can be connected in a separate jar.