A common problem that you may face in doing extractions is trying to determine which one of the two layers in the separatory funnel is the aqueous layer and which one is the organic layer. The heavier layer (i.e., the more dense liquid) is the lower layer, of course, but some organic liquids (e.g., benzene, diethyl ether, ethyl acetate) are lighter than water and some (e.g., chloroform, dichloromethane) are heavier than water, so, depending on the solvents being used, the organic phase might be the upper or the lower layer in the separatory funnel. You could look up the densities of the two liquids to determine which is greater, but sometimes a high concentration of dissolved substances in the aqueous phase can cause it to be more dense than expected and to be found as the lower layer in the separatory funnel, even when extracting with an organic solvent with a density greater than water’s. If you are unsure about which layer is which, carry out a simple test: mix a small sample of each layer with a few drops of water in a test tube and see if the two liquids are miscible; the aqueous solution will dissolve the water drops but the organic solution will be immiscible with the added water.