Thermogravimetric analysis of silica gel has shown that the loss in weight between 30° and 910°C can be quantitatively explained
on the basis of water being lost from three distinct and different populations of sites on the silica gel surface. The results
indicate that the site energies of the three different populations are randomly distributed and, consequently, the resulting
weight loss steps from each population can be described by the integral of a simple normal distribution with temperature.
The calculated weight loss obtained by assuming three different site-groups having randomly distributed adsorption energies
is, within experimental error, coincident with the experimental data. It is also shown that the water evolved from the second
population of sites originates from strongly bound water and may also contain water generated by the condensation of (geminal)
silanol groups contained in the overlapping and neighbouring population.