By using the '' simultaneous Q-DTA, Q-TG measuring technique '' elaborated recently, conditions near to the requirements of thermodynamics can be created, thus the '' normalized '' course of curves taken by this method, their characteristic temperatures or the values measured for the enthalpy change can be considered to be near to the theoretical values. For testing this new method, CuSO(4)(.)5H(2)O, MnSO4.5H(2)O, Mg(NO3)(2)(.)6H(2)O and Na(2)SO(4)(.)10H(2)O have been investigated. These model substances can be prepared in stoichiometric composition free of impurities, their decomposition mechanism is well-known, thus the effect of the altered experimental conditions by the simultaneous Q-DTA, Q-TG method on the course of their dehydration can be calculated. (c) 2005 Elsevier B.V. All rights reserved.