How is bleaching powder prepared? Why does bleaching powder $(i)$ not dissolve completely in water?

(N/A) Bleaching powder is prepared by the action of chlorine gas $(Cl_{2})$ on dry slaked lime $[Ca(OH)_{2}]$.
The chemical reaction is as follows:
$Ca(OH)_{2} + Cl_{2} \rightarrow CaOCl_{2} + H_{2}O$
$(i)$ Bleaching powder does not dissolve completely in water because it contains some amount of unreacted lime $[Ca(OH)_{2}]$,which is insoluble in water. Due to the presence of this unreacted lime,the solution appears milky or leaves a residue when dissolved in water.