Equilibrium in liquid mixtures has been studied for a large number of ternary systems, but no detailed study of a quaternary system such as will be considered in this paper has, so far as we are aware, been reported.The choice of liquids to be used was based on the ease of purification and analysis, the particular system studied being composed of acetone, acetic acid, chloroform, and water at a temperature of 25°C. PURIFICATION OF THE FOUR COMPONENTSPure glacial acetic acid crystals were prepared by equilibrium melting, and the resultant acid was freed from water by distillation with the addition of ethylene dichloride. The ethylene dichloride was found to be stable in boiling acetic acid solution, no chlorine derivatives being formed.Analar acetone was dried over calcium chloride, filtered, and fractionated. The fraction distilling at 56.0°C. at 760 mm. was employed.Distilled water was treated with solid barium hydroxide, filtered, and redistilled.Analar chloroform was fractionated and the fraction boiling at 61.1°C. at 760 mm. was employed.All solutions were stored in clean dry Winchester bottles, fitted with soda lime tubes and hand pumps for transfer of reagents. Air in the storage bottles was previously displaced by nitrogen.METHODS OF ANALYSIS 1. Chloroform A method was developed for the estimation of chloroform, based upon the formation of potassium chloride by treatment with alcoholic potassium hydroxide, the potassium chloride formed being titrated with silver nitrate. About 5 ml. of chloride-free normal alcoholic potassium hydroxide was weighed in a small stoppered glass tube. A few drops of chloroform were 683