These PYREX® Hirsch funnels have a 20mm or 30mm diameter and medium or coarse porosity fritted disc. These fritted disc funnels are very useful in preparative work, or in making separations where it is necessary to wash the precipitate and redissolve with chemicals which would attack filter paper. The angle of the funnel body facilitates the removal of precipitates. Porosity is controlled in manufacture, and discs are individually tested and graded into these classifications. The porosity for the pore diameter of the filter is determined in the same manner as specified in ASTM E-128 “Maximum Pore Diameter and Permeability of Rigid Porous Filters for Laboratory Use.” For more information on fritted products, please check the Technical Information Listing for the Guide to Selecting and Using Fritted Glassware.