Abstract
(1) Seven soil colloids rich in phosphoric acid, were treated with 100cc per one gram of dry colloid, of half normal solutions of Cl, SO_4,acetate, lactate, malate and citrate ions which were given in the form of potassium salt or the potassium salt plus the free acid, the latter being employed together with KOH for the pH regulation of the salt solutions. With the filtrates thus obtained, the amounts of phosphoric acid liberated, were colorimetrically determined. The pH values of the filtrates were also estimated. (2) The results indicated that the phosphoric acid liberation was lowest in amount at or near the point of pH7. In both sides of the neutral point, it ascended with fall and rise in pH. (3) Organic anions, especially oxyacid anions were found to have much greater power for the exchange-liberation than have inorganic anions. The liberation power of anion, whichever it may be organic or inorganic, seemed to increase with increase in valency. So far as the six anions concern, their liberation powers were found to be in the following order. citrate>malate>lactate>acetate>SO_4>Cl
