Distance-time measurements in capillary penetration: Choice of the coordinate system

Washburn's equation is a useful tool for studying the penetration of liquid s in porous media because it predicts a relationship between the distance p enetrated by the liquid in the porous media, x, and the time spent in this process, t. Despite its extended applicability, some problems in the interp retation of the results obtained arise from its use in the linearized form of x(2) vs t. In this paper a careful mathematical analysis of Washburn's e quation shows that most of the discordance found from its application comes from inadequate use of Washburn's equation. To confirm this assessment, th e penetration of different liquids in plates used in thin-layer chromatogra phy was investigated. From that study it has been proved that the alien beh avior appearing when Washburn's equation is used in a linearized form disap pears when it is used in its polynomial expression. (C) 1999 Academic Press .