Watch a drop of mercury pulsate like a heart when touched with iron The pulsation of the mercury drop takes place because of a change in the surface tension. In the acid solution, the mercury is oxidized, and the surface tension decreases. The mercury drop comes into contact with iron, and iron reduces the mercury ions to metal because it has a more negative electrochemical potential. The surface tension of the mercury drop increases, and the drop contracts. The contact of mercury and iron is br