The grain density and porosity is measured on cleaned and dried plugs by a helium porosimeter.
The He-porosimeter measures the grain volume Vg of the sample. The empty sample container of the porosimeter has a volume VS before the sample is inserted.
A reference volume Vr is filled by helium and the pressure Pr is recorded. The gas is expanded from the reference volume to the sample container and the resulting pressure PX is recorded. The grain volume is determined by applying Boyles low: PIVI = P2V2 or PrVr = PX(Vr+Vs-Vg).