The Archimedean principle is applied for determining the specific gravity of a solid with this measuring device:
A solid immersed in a liquid is subjected to the force of buoyancy. The value of this force is the same as that of the weight of the liquid displaced by the volume of the solid.
With a hydrostatic balance which enables you to weigh a solid in air as well as in water, it is possible to: determine the specific gravity of a solid if the density of the liquid causing buoyancy is known