Write down the preparation,properties,and uses of Calcium sulphate $(CaSO_{4} \cdot \frac{1}{2} H_{2} O)$ (Plaster of Paris).

(N/A) Preparation: It is a hemihydrate of calcium sulphate. It is obtained when gypsum $(CaSO_{4} \cdot 2 H_{2} O)$ is heated to $393 \ K$.
$2(CaSO_{4} \cdot 2 H_{2} O) \rightarrow 2(CaSO_{4}) \cdot H_{2} O + 3 H_{2} O$
Above $393 \ K$,no water of crystallisation is left and anhydrous calcium sulphate $(CaSO_{4})$ is formed. This is known as 'dead burnt plaster'.
Properties: It has a remarkable property of setting with water. On mixing with an adequate quantity of water,it forms a plastic mass that sets into a hard solid in $5$ to $15$ minutes.
Uses: $(i)$ The largest use of Plaster of Paris is in the building industry as well as in plasters. $(ii)$ It is used for immobilising the affected part of an organ where there is a bone fracture or sprain. $(iii)$ It is also employed in dentistry,in ornamental work,and for making casts of statues and busts.