Japan To examine the propriety of the so-called "modern filtration theory", porosity variations in constant-pressure filtration cakes are measured electrically by means of filter equipment having six pairs of disk-type electrodes. Experimental results show good agreement with the theoretical values predicted by filtration theory on the basis of compression-permeability data. The so-called "retarded packing compressibility" phenomena previously presented by Rietema et a/, are not recognized through all runs attempted in this study.