We report the first calorimetric characterization of isothermal glass transitions on a so called ‘‘fragile’’ liquid and introduce the notion of the entropic relaxation consecutive to annealing effects in the compressed glass at P≳Pg. The piezothermal method involves measurements of the heat of compression of a sample enclosed in a hydrostatic pressure cell under isothermal and reversible conditions. Approximate relaxation times and relaxation functions near the glass transition are reported.