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The solubility equilibria of synthetic samples of hydroxylapatite, its arsenic isomorph, and a series of their solid solutions, spread over the entire compositional range, were investigated at 37 °C in the pH range 5.0 to 7.6 in buffered systems through microanalytical determinations of calcium, phosphorus, and arsenic in their saturated solutions. From the ionic products of the samples so determined their stoichiometric dissolution was established and their free energies of solution evaluated.

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Solubility equilibria of hydroxylapatite, chlorapatite, and a series of their solid solutions were investigated at 37 °C in the pH range 4.25 to 7.40 and their solubility products evaluated. Proof could be obtained for their stoichiometric dissolution.

To understand the toxic effects of vanadium on the human skeletal system, the solubility products of phosphate and vanadate apatites of calcium and eight of their solid solutions, spread over the entire compositional range, were investigated at 37°C in 0.165 M sodium chloride solution. They were found to increase with increase in the vanadium content, the dissolution being found to be stoichiometric. A theoretical interpretation based on changes in lattice and hydration energies resulting from isomorphous ionic substitution is advanced.

By appropriate modifications of existing precipitation methods, a sample of calcium vanadate apatite, Cal0(VO4)e(OH)2 was prepared at 11 0 ° C. It was characterized through X-ray, electron microscopic, infrared and thermoanalytical analyses in addition to chemical analysis. Equilibrating the sample in buffered aqueous media at 37 ° C, the solubility was measured using microanalytical techniques of Ca 2+ and VO 3-present in the saturated solutions after separating the colloidal component of the solute. Duration of equilibration for the attainment of saturation of the solution of the sample was obtained from a study on its dissolution kinetics. The pK~p of calcium vanadate apatite was found to be 1 07.09. The investigation showed that pK~p was independent of the presence of the common ions.

Reiner Chlorapatit wird durch die Festkörperreaktion Adargestellt und chemisch, röntgenographisch, elektronenmikroskopisch, IR‐spektroskopisch, durch TG und DTA charakterisiert.

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