The isoplethic sections in the diagram of the quaternary system Na+ , Mg2+ //Cl– , SO2–4 –H2 O were established at 25 and 30oC by analytical and conductometric measurements. Three compounds can be observed in the isoplethic
sections: NaCl, Na2 SO4 and MgNa2 (SO4 )2 4 H2 O. Seven fields are determined, relating to the precipitation of one, two or three salts. The solubility range of MgNa2 (SO4 )2 4 H2 O is wide, while the liquidus curve of Na2 SO4 is very short. The compositions, expressed in Jnecke coordinates, at the eutonic and peritonic points, respectively, were:
42.70% Cl– and 745% H2 O; 79.47% Cl– and 787% H2 O; 71.6% Cl– and 744% H2 O at 25C; and 48.80% Cl– and 715% H2 O; 80.20% Cl– and 778% H2 O; 70.14% Cl– and 707% H2 O at 30C.