What is plaster of paris ? Write a short note on it ?

1) Hemihydrate calcium sulphate is called plaster of paris.
2) The formula of plaster of paris is ${\mathrm{CaSO}}_4\frac{1}{2}{\mathrm{H}}_2\mathrm{O} \left(\mathrm{or}\right) 2{\mathrm{CaSO}}_4\cdot {\mathrm{H}}_2\mathrm{O}$
3) When gypsum is heated at 120°c to form plaster of paris.
${\mathrm{CaSO}}_4\cdot 2{\mathrm{H}}_2\mathrm{O}\stackrel{{120}^{\circ }\mathrm{C}}{\to }C{\mathrm{aSO}}_4\cdot \frac{1}{2}{\mathrm{H}}_2\mathrm{O}+\frac{3}{2}{\mathrm{H}}_2\mathrm{O}$
4) When plaster of paris mixed with water to form a paste which sets to hard mass on standing. This process is called setting.
5) In setting of plaster of paris, it converts into gypsum, the mass become hard and the volume increase.
${\mathrm{CaSO}}_4\frac{1}{2}{\mathrm{H}}_2\mathrm{O}+\frac{3}{2}{\mathrm{H}}_2\mathrm{O}\stackrel{\text{ setting }}{\to }\underset{ }{\underset{\left(\mathrm{orthorambic}\right)}{{\mathrm{CaSO}}_4\cdot 2{\mathrm{H}}_2\mathrm{O}} \stackrel{\mathrm{hardening}}{\to } \underset{\left(\mathrm{monoclinic}\right)}{{\mathrm{CaSO}}_4\cdot 2{\mathrm{H}}_2\mathrm{O}}}$
Uses:
1) It is used in manufacture of statues, toys.
2) It is used in setting of broken bones and teeth.