# Dispersion in Chromatography Columns - Alternative Equations for Peak Dispersion > The Knox Equation > Page 68

## The Knox Equation

During 1972
and 1973 Knox and his co-workers (18), (19), and (20) carried out a
considerable amount of work on different packing materials with particular
reference to the effect of particle size on the reduced plate height of a
column. The concept of *reduced plate height* (*h *) and *reduced
velocity* (n) was introduced
by Giddings (21) and (22) in 1965 in an attempt to form a basis for the
comparison of different columns packed with particles of different diameter.
The reduced plate height is defined as,

_{} (48)

In fact, the reduced plate height merely measures the normal plate height in units of particle diameters. It is also seen that the reduced plate height is dimensionless.

The reduced velocity is defined as,

_{} (49)

The reduced velocity compares the mobile phase velocity with the velocity of the solute diffusion through the pores of the particle. In fact, the mobile phase velocity is measured in units of the intraparticle diffusion velocity. As the reduced velocity is a ratio of velocities, like the reduced plate height, it also is dimensionless.