# Dispersion in Chromatography Columns - Experimental Validation of the Van Deemter Equation > Page 83

Although a
good fit is obtained to the Giddings equation, the value of (E) is shown to be
numerically equal to zero. This is further evidence that the Van Deemter
equation can be considered to be a special case of the Giddings equation,
where, at the linear velocities employed (*i.e.* those normally employed
in practical LC), the constant (E) was zero or tended to zero. It is quite
probable, however, that if mobile phase velocities are considered outside the
range studied, the Giddings equation would be more appropriate. There does not
appear to be sufficiently precise data available at this time to test
this possibility. In any event, the Van Deemter equation and the Knox equation
are the two that must be further considered as they do describe the
experimental data accurately.

The Van Deemter equation in explicit form is,

_{}(61)

and that of Knox,

_{} (62)

where, (g) and (g') are constants

and the other symbols the meanings previously ascribed to them.