  In titration experiments with NaOH we have determined the full phase diagram
of charged colloidal spheres in dependence on the particle density n, the
particle effective charge Zeff and the concentration of screening electrolyte c
using microscopy, light and Ultra Small Angle X-Ray Scattering (USAXS). For
sufficiently large n the system crystallizes upon increasing Zeff at constant c
and melts upon increasing c at only slightly altered Zeff. In contrast to
earlier work equilibrium phase boundaries are consistent with a universal
melting line prediction from computer simulation, if the elasticity effective
charge is used. This charge accounts for both counter-ion condensation and many
body effects.
