Classical thermodynamics of states with negative absolute temperature or with negative absolute pressure

Traditionally thermodynamics considers pressure defined by other disciplines, or the simple kinetic definition is accepted. Negative pressure states are often considered as impossible ones by thermodynamicians. In this paper we would like to show, that classical thermodynamics gives a good approach to investigate the properties of negative pressure states. Such kind of state is not just possible but in spite of the metastability it can be observed experimentally.