Usually refers to powder-like substances such as diatomaceous earth or volcanic ash used to coat a septum-type filter. Can also be used as an aid to sand filters.
Substance of low specific gravity which remains in suspension when mixed with the liquid to be filtered. It should be porous and must be chemically inert to the liquid being filtered. Increases filtering efficiency and maintains cake porosity.
A type of finely divided media usually diatomaceous earth, processed Perlite, or similar material used to coat a septum of diatomite type filter.