Density is an essential parameter for the evaluation of the best uncertainty values of reference standard weights and volume standards.

However it is also a parameter of importance to many different industries, whose requirements extend beyond artefacts of standard shape, size and material.

In many cases, the basic principle for the determination of solid density has changed little since Archimedes leapt out of his bath shouting “Eureka”. Uncertainty demands have, however, increased and the methods for achieving them have therefore been refined.

Measurements are carried out by comparing the weight of the artefact in air and in pure water of known density. Alternatively, the weight of the artefact in water can be directly compared with that of a primary volume standard. NPL has a series of apparatus providing solid density measurements for artefacts ranging in mass from 5 g to 20 kg. These are available for both regular and non-regular shaped artefacts.

An increasing requirement, however, is for the density determination of porous materials that cannot be placed in water. NPL’s facilities for vacuum weighing allow their density to be determined by weighing in an inert gas over a small pressure range.

The density of liquids can be determined by weighing a solid volume standard in the liquid under test. Alternatively, where only a smaller volume is available, a vibrating cell density meter can be used.

See also: The Weighing Panel of the Institute of Measurement and Control (InstMC)