A gas pycnometer is a laboratory device used for measuring the density—or, more accurately, the volume—of solids, be they regularly shaped, porous or non-porous, monolithic, powdered, granular or in some way comminuted, employing some method of gas displacement and the volume:pressure relationship known as Boyle's law.
Resulting changes in pressure can be read by means of a transducer, or nullified by adjustment of a third ancillary, graduated variable-volume chamber.
Therefore, the volume measured considering the finest scale of surface roughness will depend on the atomic or molecular size of the gas.
Adsorption of the measuring gas should be avoided, as should excessive vapor pressure from moisture or other liquids present in the otherwise solid sample.
Gas pycnometers are used extensively for characterizing a wide variety of solids such as heterogeneous catalysts, carbons,[5] metal powders,[6][7] soils,[8] ceramics,[9] active pharmaceutical ingredients (API's) and excipients,[10] petroleum coke,[11] cement and other construction materials,[12] cenospheres/glass microballoons and solid foams.