  The relativistic effective mass $M^*$, and Fermi momentum, $k_F$, are
important ingredients in the determination of the nuclear equation of state,
but they have rarely been extracted from experimental data below saturation
density where translationally invariant nuclear matter becomes unstable against
clusterization into the existing atomic nuclei. Using a novel kind of
superscaling analysis of the quasielastic cross section electron scattering
data involving a suitable selection criterion and $^{12}$C as a reference
nucleus, the global scaling properties of the resulting set of data for 21
nuclei ranging from $^2$H to $^{238}$U are then analyzed. We find that a subset
of a third of the about $20000$ data approximately scales to an universal
superscaling function with a more constrained uncertainty band than just the
reference $^{12}$C case and provides $M^*$ as a function of $k_F$.
