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Latest comment: 10 years ago1 comment1 person in discussion
Some knowledgeable person should say how big the pores are in these filters. They played an important role in the discovery of viruses, which were originally called "filterable viruses" because liquids containing them remained infectious, even passing through these filters, whose pores were too small for bacteria to pass through.CharlesHBennett (talk)
The filters have different grades of porosity. Berkefeld Filters, made from kieselguhr, have three grades: V (viel) the coarsest, W (wenig) the finest and N (normal) in between these. Chamberland Filters, which are unglazed porcelain, are graded L1 the most porous, and L1a, L2 and L3, which correspond to Berkefeld V, N and W. I doubt that the inventors knew the average pore size, but the British Pharmaceutical Codex required filters to be able to trap Serratia marcescens, which indicates and average pore diameter of 0.5 microns and less than 0.75 microns. Later filters became more refined and up until the 1960s, the sizes of viruses were estimated by using filters that had pores measured in millimicrons. Graham Colm (talk) 10:05, 13 March 2014 (UTC)Reply
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