There's an experiment called "six density tower" .You need to put 6 kinds of liquids into a bottle and it will according to the density to have 6 s according to the densities .The lower the density the higher the liquid will be in the bottle .So the higher the density the lower the liquid will be in the bottle .

　　First we should put some soy sauce into the bottle .Then we should put a little vegetable oil into the bottle .You will find that the soy sauce and the oil won't mix they will separate .The soy sauce is on the top the oil is on the bottom .It's very strange.

　　Then we need to put some alcohol into the bottle you will find that the alcohol will be on the top and the oil will sink to the middle between the soy sauce and the alcohol.

　　You will ask  what makes it like this .It's because of density .As I say the higher the density the lower the liquid will be .