T H E PHYSICAL CHEMISTRY O F COLOR LAKE FORMATION. 11. ADSORPTIOS OF TYPICAL DYES BY BASIC MORDANTS BY HARRY B . TVEISER A N D EVERETT E. PORTER
I n the first communication under the above title' a study was made of the influence of the hydrogen ion concentration on the adsorption of an inorganic anion, sulfatr, and an organic anion, oxalate, both separately and simultaneously by the hydrous oxides of iron, chromium, and aluminum, which are the most comnon basic mordants or lake bases. Some preliminary observations were also made on the effect of calcium ion on the adsorption of anions by the hydrous oxides at constant hydrogen ion concentration. The results of these observations which have been summarized at the conclusion of the paper, paved the way for a study of the mechanism of lake formation and the effect of the hydrogen ion concentration as well as the presence of other ions on the lake formation process. The results of this study will be reported in this and subsequent communications.
Experimental Procedures The general methods of procedure were the same as previously described in detail: A definite amount of dye solution was mixed with a definite quantity of a highly purified hydrous oxide sol which was precipitated. The same sols were used as in the earlier experiments. The adsorption was determined from the difference in the concentration of the solution before and after mixing with the sol. The hydrogen ion concentration was measured by means of the hydrogen electrode before and after precipitation. The variations in the hydrogen ion concentrations were accomplished by adding suitable amounts of alkali hydroxide or hydrochloric acid. The effect of the presence of the alkali cations and of the chloride ion was found to be negligible in comparison with the very much more strongly adsorbed hydrogen, hydroxyl, and dye ions. Analysis of Dyes. Considerable attention was given to the accurate quantitative estimation of the dyes whose adsorption was measured. I t was recognized at the outset that colorimetric methods would be unsatisfactory both because of errors inherent in colorimetric work and because of the marked influence on the colors of the dyes of minute changes in hydrogen ion concentration. Knecht's method2 of titrating the dye with titanous chloride was found to be quite satisfactory for the determination of varing concentrations of methylene blue, orange 11, and metanil yellow, the dyes used in this investigation. Methylene blue serves as its own indicator giving a reversible change a t the end point which is as clean cut as the starch-iodine indicator. Orange I1 and metanil yellow require an excess of titanous chloride for quantiJ. Phys. Chem., 31, 1383 (1927). Ber., 36, 1552 (1903); 40, 3819 (1907).
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tative reduction, necessitating back-titration with ferric salt and the use of an outside indicator. Special precautions are necessary to prevent the oxygen of the air from coming in contact with the reducing solution.
Adsorption of Orange 11. Adsorption by Hydrous Chromic Oxide at Constant Initial p H Values. Determinations of the adsorption of orange I1 anion were readily accomplished at all p H values but the determination of the pH in an orange I1 solution was found to be unsatisfactory unless the solution is slightly acid, or the concentration of the dye is low, since the dye undergoes reduction a t the electrode.
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