The Bulk Density Tester (Scott Volumeter) is described in USP Chapter <616> Method 2 and is used to measure the bulk density of fine powders and similar products.
The apparatus consists of:
- A stainless steel top funnel with an integral stainless steel 18-mesh screen
- A baffle box containing four glass baffle plates over which the powder slides and bounces as it passes
- A stainless steel bottom funnel to direct the powder into the receiving cup
- A cylindrical or square receiving cup
- A stand to support the apparatus and to ensure that the cup is exactly 19mm from the bottom of the funnel when placed in position
The bulk density of a powder may be described as the density of the powder ‘as poured’ into a measuring vessel.
The bulk density of powders can be extremely difficult to measure since the slightest disturbance may create a change in the result. This is caused by the relationship between the particles that constitute the powder bulk. This same relationship affects the ability of the powder to flow.
A comparison of the bulk and tapped densities of powders can give an indication of the type of interaction present between the various particles making up the powder mass and hence provide an index of powder flowability (Hausner Ratio and Compressibility Index).
The unit is very simple to use. Weigh then place the sample receiving cup at the base of the unit. Carefully pour the powder into the top of the unit until the cup overflows, then level off the powder using a flat edge. Reweigh the cup and calculate the density.
The USP procedure states:
Allow an excess of powder to flow through the apparatus into the sample receiving cup until it overflows, using a minimum of 25 cm3 of powder with the and 35 cm3 of powder with the cylindrical cup. Carefully scrape excess powder from the top of the cup bysmoothly moving the edge of the blade of a spatula perpendicular to and in contact with the top surface of the cup, taking care to keep the spatula perpendicular to pre-vent packing or removal of powder from the cup. Remove any material from the sides of the cup, and determine the weight, M, of the powder to the nearest 0.1%.