pyknometry

Pyknometry is the method and science of determining the density and related properties of substances by means of a pycnometer, a device that provides a known, fixed volume. In practice, pyknometry can be conducted using liquid methods (liquid pycnometry) or gas methods (gas pycnometry), each suitable for different classes of materials.

The basic principle is to relate mass to true volume. For solids, a sample is weighed and then placed into a pycnometer filled with a liquid of known density at a controlled temperature. The pycnometer is weighed empty, filled with the liquid, and with the sample inside. From these masses and the liquid’s density, the true volume of the sample is calculated, and its density is obtained by dividing the sample mass by that volume. Gas pycnometry uses the displacement of a known-volume chamber by a test sample and applies gas laws to infer the sample’s true volume, avoiding issues with liquid wetting and capillary effects.

Applications span materials science, geology, and related fields. Liquid pycnometry is common for polymers, metals, ceramics, and carbon materials, while gas pycnometry is favored for highly porous or delicate samples. The technique provides skeletal or true density, enabling porosity calculations when bulk density is known, and it supports quality control and material characterization.

Standards and methodologies for pycnometry are published by bodies such as ASTM and ISO, covering instrument calibration, temperature control, and data interpretation. The term derives from Greek roots meaning dense or compact, reflecting its focus on measuring volume and density.