THERMODYNAMICS AND STATISTICAL PHYSICS 127The ideal gas law gives
Substituting(S.4.33.4) and (S.4.33.5) into (S.4.33.3)gives
4.34 Modified Joule–Thomson (Boston)
The work done by the piston goes into changing theinternalenergy of the
part of the gas ofvolume that enters the plug andinto the work done
by the gas to enter containerBoccupying volume So we maywrite
where is theconstant-volume heat capacity for onemolecule and is
the number ofmolecules in thevolume On theother hand, before and
after theplug, wehave, respectively,