The PERLITE 23-S is a unique filter aid made from volcanic rock which is expanded and milled to specific grades by Silbrico's stringently controlled processing techniques. Purity is maintained by and exclusive procedure for removing grit and other foreign substances. The resulting filter aid is an extremely pure, inert, white, light weight material having a unique interlocking structure with myriads of microsscopic channels. Due to the light weight, 20--50% density advantage, the PERLITE 23-S offers twice as much filtration, pound for pound, than diatomaceous earth. A PERLITE 23-S filter cake density is only 9 pounds per cubic foot. The microphotos of the Perlite 23-S shows the myriads of microscopic channels which afford optimum flow rates.