  The properties of the two-dimensional exactly solvable Lieb and Baxter models
in the critical region are considered based on the thermodynamic method of
investigation of a one-component system critical state. From the point of view
of the thermodynamic stability the behaviour of adiabatic and isodynamic
parameters for these models is analyzed and the types of their critical
behaviour are determined. The reasons for the violation of the scaling law
hypothesis and the universality hypothesis for the models are clarified.
