Bulk density and Tapped density are importanta parameters to measure the flow properties, compressibility index of pharmaceutical raw materials. The difference between bulk density, tapped density and true density can simply understand from its definition.

As per British Standard Institution Definition of Density:

  • Apparent density: The mass of a powder divided by its apparent volume.
  • Bulk density: The apparent powder density under defined conditions.
  • Tap density: The apparent powder density obtained under standard conditions of tapping.
  • True density: The mass of a particle divided by its volume, excluding open and closed pores.

The bulk density of a material is the ratio of the mass to the volume (including the interparticulate void volume) of an untapped powder sample. Where the tapped density is obtained by mechanically tapping a graduated cylinder containing the sample until little further volume change is observed. in this case, the container is tapped to accommodate more samples and the process above is repeated. And the true Density is the measure of the mass per unit TRUE volume of the grains which does not include pore spaces in between the samples.

Apparent density is also called bulk density measured by pouring the material through a funnel into a cylinder of known volume. It provides the mass per unit volume of loose packed powders.

Apparent density formula

 ρ (0) = m/v

Where,  'ρ (0)' is the apparent density (g/cm3 or kg/m3); 'm' is the mass, (g or kg); 'v' is the volume in loose packed condition (cm3 or m3).

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