The invention relates to laboratory equipment for chemical laboratories and more specifically to vacuum filter funnels of the shape typically referred to as a buchner funnel.
A buchner funnel typically has an upper cylindrical portion which holds the liquid and solids to be filtered which upper portion terminates in a lower perforated plate. A filter medium such as filter paper is placed on the upper surface of the perforated plate and typically a vacuum is drawn on the lower side of the perforated plate to increase the flow rate of filtrate through the filter medium.
If the filter medium does not conform closely to the perforated plate, it is possible that solids will pass around the outside of the filter medium and through the relatively large perforations in the bottom plate. Such bypassing can be highly detrimental to many chemical laboratory procedures. Although this problem does not occur with frequency with common filter paper, it can be a substantial problem with rigid filter materials such as fritted glass.