Hard pelletised materials tend to vary little in bulk density, generally settling to a closer re-orientation of particle structure under vibration than under compacting stresses, which in any case reach a limiting value in a deep silo due to the Janssen effect. Soft pellets will deform at point of loaded contact without serious change of bulk density, so meaurments taken in tapped condition are likely to reflect stored values within close industrial requirements. The bulk density will reduce on discharge as the bulk dilates to flow and attain a value according to the prevailing stress conditions; unlike fine products that are also affected by their stress history. ■