Laboratory behavior, standard operating procedure

No serious attempt has yet been made to standardize filtration tests and to categorize filtration behavior in generally accepted terms. A possibly useful measure of filterability, however, has been proposed by Purchas (1977 1981). The time in minutes required to form a cake 1 cm thick when the cell is operated with a differential of 500Torr (0.67 bar) is called the Standard Cake Formation Time (SCFT), tF. The pressure of 500Torr is selected because it is obtained easily with common laboratory equipment. The procedure suggested is to make a series of tests at several cake thicknesses and to obtain the SCFT by interpolation, rather than to interrupt a single test to make observations of cake thickness. A direct relation exists, of course, between the SCFT and resistivity a some examples are... 

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