Add salt to oil floating on water and watch convection that looks like a lava lamp.
To Do and Notice
Fill the clear container 2/3 full of water.
Add a layer of oil on top of the water about 1 cm thick.
Shake some salt on the top of the oil layer.
Notice that when salt is added on top of the oil the bottom of the oil layer bulges down and then a drop of salted oil breaks free and falls to the bottom of the container. With time the oil on the bottom begins to bulge upward, after some time a drop breaks free and floats back up to join the layer of oil at the top surface.
What's Going On?
Salt crystals fall through the oil. The oil adheres to the salt and the oil plus the salt crystals is denser than water. The salt-oil mixture falls through the water. At the bottom, the oil slowly flows away from the salt crystals making a layer of pure oil which gathers and rises through the water.
Scientific Explorations with Paul Doherty
18 August 2005