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.

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.

Das mit Ca",(PO4)6(OH)2 isomorphe Ca",(AsO4)"(OH)2 (1) wird bei der Einlagerung von AsOi′ ins menschliche Skelett durch POf‐Austausch gebildet.