# Dispersion in Chromatography Columns - Dispersion Processes that take Place in an LC Column > Longitudinal Diffusion > The Diffusion Process > Page 19

and
_{}

Therefore, dividing by l to obtain the variance per unit length,

In the same manner as the constant (l) introduced by Van Deemter into the function for multipath dispersion, Van Deemter also introduced a constant (g) into the Longitudinal Dispersion contribution to variance to account for some packing inhomogeneity. As a consequence, the expression for the Diffusion contribution to the variance per unit length of the column became,

(8)

To be precise,
there should be a second longitudinal diffusion contribution to the overall
variance that would arise from the *stationary *phase. The same method of
derivation can be used but the time the solute spends in the stationary phase
is now, is now a function of the capacity ratio of the column, (k').