How could you tell if a liquid has a higher or lower density than water?
If a liquid does not mix with water and you pour a little water on the liquid, then if the water sinks, the water has a higher density than the liquid; otherwise, the liquid has a higher density. If a drop of the water dissolves in the liquid, then you weigh an equal volume of both liquids. The heavier one has the higher density.
A substance will float in a liquid if its density is lower than that of the liquid. Density is defined as the mass per unit volume. If an object sinks it means that its density is higher than the density of the liquid. Objects that appear to be suspended within the liquid near the surface have density that is very close to the density of the liquid.