Hydrostatic Weighing

a method of measuring the density of liquids and solids, based on Archimedes’ law. The density of a solid is determined by weighing it twice—first in air and then in a liquid whose density is known (usually distilled water). During the first weighing the weight of the object is determined. The difference between the results of the two weighings determines the volume of the object.

In measuring the density of a liquid an object—usually a glass float whose weight and volume are already known—is weighed in the liquid. Depending on the degree of accuracy required, hydrostatic weighing is done on technical, analytical, or standard balances. For weighing massive objects less accurate balances are widely used, which facilitate quicker measurement (for example, the Mohr balance).