Various mixtures of synthetic apatite

magnesium oxide and silica oxide in various proportions have been fused at 1400℃

for thirty minutes. The citric acid solubility of the products has been determined. At SiO2/MgO ratios of 1 to 2.6 by weight

the percentage of synthetic apatite in the mixtures corresponding to the highest citric acid solubility of the products

has been found to be within the range of 40% to 46%. It has been found that

if the SiO2/MgO ratio in the mixtures is greater than 3

the citric acid solubility of the products decreases suddenly. If the R2O3 content in the mixtures is not too high

for example

5% R2O3

the citric acid solubility of the product is slightly higher than that in the absence of R2O3.