Abstract: | The precipitation of different calcium phosphates in gelatine gels was studied by diffusion of disodium hydrogen phosphate solutions into ten percent gels containing calcium cation at liquid gel pHs from 6 to 11. At pHs 6.0 to 7.5, calcium hydrogen phosphate dihydrate (CaHPO4 · 2 H2O) was deposited as a continuous precipitate and then as rings of precipitate (the Liesegang phenomenon): their spacing coefficients varied with the reciprocal initial anion concentrations according to the Packter-Matalon relation. At liquid gel pHs 8.0, 8.5, tretacalcium phosphate (Ca4H(PO4)3) was deposited as a continuous precipitate. At liquid gel pHs from 8.5 to 11, hydroxyapatite (Ca10(PO4)6(OH)2, Ca/P ratios = 1.50 to 1.67) was deposited as a continuous precipitate. The mechanisms of precipitation of the different calcium phosphates (in gelatine gels) is briefly discussed. |