There have been no isothermic phase-rule studies on acetic acid, as a single solvent, reported in the literature; though Davidson ad co-workers have studied many binary and several ternary systems by the synthetic or freezing-point method. The binary sustem PBAc₂ - HAc has been studied by Davidson and Chappel (J.A.C.S. 52. 507. 1930) and later (J.A.C.S. 55. iii. 4524. 1933) by the freezing-point method, using anhydrous hemi-solvate crystals of lead acetate to see the solution. Analysis of the solid phase gave Pb AC₂ ½HAc as the solid phase. Davidson and McAllister (J.A.C.S. 52. 507. 1930) investigated the binary system NH₄Ac - HAc confirming a solvate NH₄Ac. HAc.