BULK DENSITY TESTER FOR POWDERS
THE SCOTT VOLUMETER
The bulk density of powders can be extremely difficult to measure since the slightest disturbance may result in a change in the result. This is the result of the relationship between the particles that constitute the powder bulk. This same relationship affects the ability of the powder to flow.
The bulk density of a powder may be described as the density of the powder ‘as poured’ into a measuring vessel. Tapped density, on the other hand, is the density attained after ‘tamping down’: this is normally measured using an instrument that lifts and then drops a measuring cylinder containing the powder through a fixed distance (see the Tapped Density Tester described on the opposing page).
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.
The Bulk Density Tester (Scott Volumeter) is described in USP Chapter <616> Method 2 and is designed for measuring the bulk density of fine powders and similar products.
The apparatus consists of: -
- A stainless steel top funnel having an integral ss 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 receiving cup having a capacity of 25 ml /- 0.05 ml
- A wooden stand to support the apparatus and to ensure that the cup when placed in position is exactly 19 mm from the bottom of the funnel
MODE OF OPERATION
- Weigh the empty receiving cup and place it in position
- Slowly pour the powder through the upper funnel until it overflows the receiving cup. (Note: Use a minimum of 35 cubic cm)
- 3) Level the top of the receiving cup with a spatula such that it is completely full being careful not to compress or shake the powder
- Re-weigh the receiving cup and its contents
- Calculate the bulk density in terms of grams per ml by dividing the weight of the powder by the volume of the cup.