Simple device with a multitude of demonstration possibilities. The rod responds to changes in density of a liquid by sinking or rising in the liquid. As the density of the liquid is changed, the rod moves up or down accordingly. It sinks in warm water but floats in cold water. A temperature gradient in a column of water will find the rod held in suspension somewhere in the middle. Put the rod in alcohol and it will sink. Add different amounts of salt to water and the rod will rise or sink as the density changes. Comes with instructions and detailed explanation of density theory.