The structure of paper

The flow of liquid in porous material can be described in first instance by means of two constants: the mean pore radius r and the pore density N. To determine these two constants two mutually independent equations are needed, such as the equation of Lucas—Washburn for the height of rise, that of Poiseuille for the rate of flow, that for the capillary volume, etc. This structure description is inadequate: a. to explain the striking-away phenomenon; b. to explain the height of rise when the capillary pressure and the hydrostatic pressure are in equilibrium, and c. to calculate the weight of liquid risen.