  A systematic analysis of the multifragmentation (MF) in fully reconstructed
events from 1A GeV Au, La and Kr collisions with C has been performed. This
data is used to provide a definitive test of the variable volume version of the
statistical multifragmentation model (SMM). A single set of SMM parameters
directly determined by the data and the semi-empiricalmass formula are used
after the adjustable inverse level density parameter, $\epsilon_{o}$ is
determined by the fragment distributions. The results from SMM for second stage
multiplicity, size of the biggest fragment and the intermediate mass fragments
are in excellent agreement with the data. Multifragmentation thresholds have
been obtained for all three systems using SMM prior to secondary decay. The
data indicate that both thermal excitation energy $E_{th}^{*}$ and the isotope
ratio temperature $T_{He-DT}$ decrease with increase in system size at the
critical point. The breakup temperature obtained from SMM also shows the same
trend as seen in the data. The SMM model is used to study the nature of the MF
phase transition. The caloric curve for Kr exhibits back-bending (finite latent
heat) while the caloric curves for Au and La are consistent with a continuous
phase transition (nearly zero latent heat) and the values of the critical
exponents $\tau$, $\beta$ and $\gamma$, both from data and SMM, are close to
those for a 'liquid-gas' system for Au and La. We conclude that the larger
Coulomb expansion energy in Au and La reduces the latent heat required for MF
and changes the nature of the phase transition. Thus the Coulomb energy plays a
major role in nuclear MF.
