Abstract
An apparatus for measuring temperature dependence of equilibrium water-vapour-pressure has been developed in order to express states of water quantitatively in hydrous silicate minerals in terms of entropy values. A series of water vapour pressures can be measured by the apparatus at various temperatures and at variable water contents of zeolites or clay minerals. The entropy values obtained can be compared with those appeared so far in several investigations by means of low temperature adiabatic calorimeter. Although most of the entropy values lie between those of liquid water and of ice, the values obtained by the present method do not show those of average zeolitic water but those of water molecule at near surface layer equilibrated directly with H2O vapour.
