  The Coulomb sum rule for inclusive quasielastic electron scattering in
$^{12}$C, $^{40}$Ca and $^{56}$Fe is analyzed based on scaling and superscaling
properties. Results obtained in the relativistic impulse approximation with
various descriptions of the final state interactions are shown. A comparison
with experimental data measured at Bates and Saclay is provided. The
theoretical description based on strong scalar and vector terms present in the
relativistic mean field, which has been shown to reproduce the experimental
asymmetric superscaling function, leads to results that are in fair agreement
with Bates data while it sizeably overestimates Saclay data. We find that the
Coulomb sum rule for a momentum transfer $q\geq 500$ $MeV/c$ saturates to a
value close to 0.9, being very similar for the three nuclear systems
considered. This is in accordance with Bates data, which indicates that these
show no significative quenching in the longitudinal response.
