You can observe how lipids organize themselves. Have you ever seen cold soup with a film of fat on top? Or do this: shake up a bottle of water that has some oil in it. If you let the water stand undisturbed for a few hours, you will see the oil rise to the top and form a film all by itself. 

 

Using vessels like those shown on the right, we can collect oil separate from water by draining off the lower liquid compartment. Membrane lipids can be extracted by homogenizing tissue in water and letting the lipid separate. More efficient is to use an organic solvent, like hexane (see toxic hazards in protein unit). Such solvents can produce purer separations of oil from water.