Solubility determinations on two particle sizes of crystalline gibbsite, from both undersaturation and supersaturation in the acid pH range, gave a K SO of −34.03 ± 0.05. Using the same gibbsite in the alkaline pH range and extrapolating values from supersaturation to infinite time, a *K S4 of −15.30 ± 0.05 was obtained. From these values a ΔG f 0 (gibbsite) of −274.20 ± 0.06 kcal/mole of Al(OH) 3 and a ΔG f 0 [Al(OH) 4 ‐ aq] of −310.03 ± 0.07 kcal/mole were calculated. The value for gibbsite confirms previous work on the stability of gibbsite and the new Al(OH) 4 ‐ value eliminates a discrepancy between gibbsite stabilities derived from solubility measurements in the acid and in the alkaline pH range.
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J. A. Kittrick (1966) studied this question.