In a previous paper, a thermodynamic examination of magnetic fluids was conducted and the obtained relations were compared with the relations usually applied to fluids. Three independent variables were considered in the general formulation. The aim of this paper is to examine, in a similar way, dielectric systems (gases, liquids and solids) considering three independent variables in the general case. The independent variables can be assumed as only two, when the volume is practically constant. In some ranges of temperature, various dielectrics present a dependence of the electric field strength upon temperature, similar to that of magnetization (Curie's law); this case also is studied. Quasi-static irreversible processes with uniform intensive properties are considered.