These flat bottomed filtration funnels are particularly well suited for rhodium purification and refining applications. When combined with a vacuum pump, Buchner funnels are the fastest, most efficient means of filtering most liquids [for standard filtration, see aspirator vacuum pump, for high volume filtration, see ARVT pump]. Shor Buchner filter funnels have a flat, perforated plate at the base of each funnel that is eminently suited for very rapid filtration (especially when combined with a vacuum pump [see the very inexpensive Shor aspirator vacuum pump below]). Shor Buchner funnels are designed to accept filter paper that is the same diameter as the inside diameter of the funnel. However, we recommend that, when using them to filter precious metals, use a filter paper of one size larger than the funnel's diameter. All Shor Buchner funnels, except the 5" diameter, sit flat on a tabletop.