Liquid pyknometry

There are several British Standards that deal with liquid pyknometry applied to specific materials12-13-141516. A pyknometer bottle of up to 50 ml volume is usually sufficient for fine powders but coarse materials may require larger calibrated vessels. BS 1377 1975, for example, requires the use of a 1 litre cylindrical gas jar, closed by a ground plate, to measure the density of soils that contain particles coarser than 2 mm BS test sieve (but not coarser than 37.5 mm). 

If distilled water is not suitable because it dissolves, reacts with or is absorbed by the solid, another liquid must be used. 

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Quoted density values in standard reference works are of the materials true density. If density is determined using a gas pyknometer, the volume measured would include closed pores but exclude open pores i.e. the measured density would be the apparent density. If the suspending liquid penetrates all the cracks and fissures on the particle surface, the measured volume would be the same as that determined by gas pyknometry but the total mass would be greater due to the included liquid that will remain with the particle as it falls in the liquid, hence its sedimentation density will be intermediate between the apparent density and the true density and greater than the effective density. These differences are usually not highly significant for coarse particles unless they are highly porous. 

The apparent particle density (or if the particles have no closed pores, also the true particle density) can be measured by fluid displacement methods, i.e. pyknometry, which are in common use in industry today. The displacement can be measured with either liquids or gases and there are, therefore, two groups of techniques and instruments available, as follows. 

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