. Carnegie Institution of Washington publication. IN MIXTURES OF ACETONE AND WATER. 113 parallel to those for the conductivity of potassium sulphocyanate in solution in the same mixtures. The fluidity curve for acetone has a minimum between per cent and 50 per cent; and the fluidity for the rubidium halides and nitrate has its minimum in approximately the same position (fig. 46). The conductivity curves, however, of the rubi- dium salts have their minima corresponding to a much greater per- centage of acetone (fig. 47). As has been shown by previous workers, this minimum in fluidity occur
. Carnegie Institution of Washington publication. IN MIXTURES OF ACETONE AND WATER. 113 parallel to those for the conductivity of potassium sulphocyanate in solution in the same mixtures. The fluidity curve for acetone has a minimum between per cent and 50 per cent; and the fluidity for the rubidium halides and nitrate has its minimum in approximately the same position (fig. 46). The conductivity curves, however, of the rubi- dium salts have their minima corresponding to a much greater per- centage of acetone (fig. 47). As has been shown by previous workers, this minimum in fluidity occurs at the position where the breaking down of association of one solvent by the other is greatest. The con- ductivity depends upon the velocities of the ions and the degree of dissociation. The dissociation is least when the association of the solvent is least, and the speed of the ions is least when the fluidity is greatest. Therefore, if these were the only determining factors, the conductivity minima always correspond to the fluidity minima. 240 220 200 180 160 140 120 100 80 60 \ \ \ \ \ Solv< •nt \ \V \\ Soh V ition \ \ // X Sy J*" t£ / ^*^ -=±r i^*" 110 100 90 100 75 50 25 0 Percentage acetone FIG. 46.—Fluidity of rubidium bromide, solution and solvent. 70. 75 50 25 Percentage acetone FIG. 47.—Conductivity and viscosity of rubid- ium iodide in acetone-water at 25°. Curve I, ordinates, molecular conductivity. Curve II, ordinates, fluidity. Potassium sulphocyanate has a considerable solubility in pure ace- tone (about 20 grams in 100 grams of acetone at 20°), whereas the rubidium salts studied are only slightly soluble in pure acetone. There- fore, in the same concentrations, the rubidium salts are nearer satura- tion than potassium sulphocyanate. The percentage dissociation is, therefore, lower in the case of rubidium salts than in that of potassium sulphocyanate. A possible explanation of the shifting of the minimum
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