The gravity cell consists of a glass jar, in which a copper cathode sits on the bottom and a zinc anode is suspended beneath the rim. Copper sulfate crystals are scattered around the cathode and then the jar is filled with distilled water. As the current is drawn, a layer of zinc sulfate solution forms at the top around the anode. This top layer is kept separate from the bottom copper sulfate layer by its lower density and by the polarity of the cell.