Universality class of criticality in the restricted primitive model electrolyte

The 1:1 equisized hard-sphere electrolyte or restricted primitive model has been simulated via grand-canonical fine-discretization Monte Carlo. Newly devised unbiased finite-size extrapolation methods using loci in the temperature-density or (T, rho) plane of isothermal rho(2-k) vs pressure inflections, of Q = [m(2)](2)/[m(4)] maxima, and of canonical and C-V criticality, yield estimates of (T-c, rho(c)) to +/-(0.04, 3)% . Extrapolated exponents and Q ratio are (gamma, nu, Q(c)) = [1.24( 3), 0.63(3); 0.624(2)] , which support Ising (n = 1) behavior with (1.23(9), 0.630(3); 0.623(6)), but exclude classical, XY (n = 2), self-avoiding walk (n = 0) , and n = 1 criticality with potentials phi(r) > Phi/r(4.9) when r --> infinity .