This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
This filter (European make) consists of a cast-iron plate, in which is fitted an iron cylinder closed by an iron cover plate. 00 is a hollow cylinder of porous sandstone. The water, entering at W under pressure, penetrates the pores of the sandstone cylinder 0 and flows out clear on top. When the pores of cylinder 0 are clogged up and the filter lacks efficiency, another stone cylinder has to be put in. The old one may be saved for further use by turning or grinding off its outsides with the clogged pores.
Fig. 29. - Gaber's Sandstone Filter.