The internal energy is given by the energetic equation of state, u − − C u = ∫ ∫ c v ( v , T ) d T + ∫ ∫ [ T ∂ ∂ p ∂ ∂ T − − p ( v , T ) ] d v = ∫ ∫ c v ( v , T ) d T + ∫ ∫ [ T 2 ∂ ∂ ( p / T ) ∂ ∂ T ] d v where C u is an arbitrary constant of integration.