ABSTRACT
This chapter introduces the third law of thermodynamics which concerns the properties of systems, and which to a large degree is about the behavior of entropy. An effective method of cooling at low temperatures involves the adiabatic demagnetization of paramagnetic materials, a discussion of which requires knowledge of the thermodynamics of magnetic substances. The Nernst theorem is not based on theoretical reasoning, however, but on a detailed study of chemical reactions using electrochemical cells. Boltzmann-Planck's version of the third law is the assertion that the ground state of every system is nondegenerate. The F. E. Simon statement applies to processes not involving factors that are not in internal equilibrium, the third law applies to processes during which internal constraints remain in effect. It is impossible by any procedure to reduce the temperature of a system to absolute zero in a finite number of operations.
