  Non-equilibrium and equilibrium thermodynamics of an interacting component in
a special-relativistic multi-component system is discussed by use of an entropy
identity. The special case of the corresponding free component is considered.
Equilibrium conditions and especially the multi-component Killing relation of
the 4-temperature are discussed. Two axioms characterize the mixture:
additivity of the energy momentum tensors and of the 4-entropies of the
components generating those of the mixture. The resulting quantities of a
component and of the mixture, energy, energy flux, momentum flux, stress
tensor, entropy, entropy flux, supply and production and their Newtonian limits
in zeroth approximation are derived.
