in addition the solubility of the calcium phosphate compounds is affected by the ph of the solution used for dissolution for example hydroxyapatite is more soluble in acidic solution and less soluble in alkaline solution because the acid reacts with the hydroxide ions thus reducing the hydroxide concentration in solution and causing the equilibrium between the solid and the ions in solution to shift toward the ions in solution this phenomenon occurs in order to replace the hydroxide ions in solution lost upon reaction with the acid the opposite shift occurs in alkaline solution thus the equilibrium shifts toward the solid and the solubility of the hydroxyapatite is decreased as illustrated in fig1 the calcium phosphate body may be hollow and or porous in general the size of the void depends on the amount of calcium in the glass and the shape of the starting soluble glass body for example when the water soluble glass body is a sphere the alkali metal oxide component is li 2 o and the glass former is b 2 o 3 a cao content of less than about 40 wt results in a hollow calcium phosphate sphere generally decreasing amounts of calcium tend to increase the size of the hollow cavity within a calcium phosphate body without being bound by theory it is presently believed that the calcium oxide in the water soluble glass reacts with the phosphate solution to produce calcium phosphate and thus the amount of calcium in the water soluble glass body limits the amount of calcium phosphate formed as the amount of calcium oxide in the water soluble glass increases therefore it is believed that more calcium phosphate is formed which can deposit on the.