260 FLUIDITY AND PLASTICITY
From the above equation we see that this distance is propor-
tional to the square root of the fluidity, the surface tension, the
ladius of the capillary and the time.
It is generally assumed that the material of the pore walls is
immaterial so long as the walls are wet by the liquid. Adhesion
"between solid and liquid may come into play in certain cases
making such an assumption fallacious, as already pointed out.
Experiments on the impregnation of fabrics, belting, wood et
cet. with oils, gums, paints et cet. have shown that thorough dry-
ing of the former materials has an extraordinary effect upon the
penetration of the latter. This may be due to increasing adhe-
sion although it may be explained in some other way.