Solubility relations In the CeCI-rlch region of the ternary system NaCI-CsCI-H20 have been determined at 25 °C by using the Isothermal method. These data together with the halite solubility data reported In part 1 of this series complete the solubility relations for the entire ternary system at 25 °C. A new compound, ß •2 ß •2 20, and a new solid-solution series, [Cs^tNa-H^jjCI with x ranging from 0 to 0.427, were found In this study. The new compound Is monocllnlc, belongs to space group /2/c, and has a = 13.620 (2), b = 5.831 (1), c = 10.709 (2) A, ß = 91.27 (1)°, Z = 4, V = 850.3 (1) A3;refractive Indices are = 1.520, ß = 1.540, = 1.552; density Dx = 2.509 g/cm3. The solid solution is cubic with the cell edge slightly larger than that of CsCI and the refractive index ntsD = -0.14638* + 1.8405.