Question

Why we call hemihydrated calcium sulphate as plaster of paris

Answer 1

Plaster is the common name for calcium sulphate hemi hydrate(CaSO4 . 1/2H2O) made by heating the mineral gypsum, the common name for sulphate of lime. Plaster was first made about 9000 years ago, and has been used by ancient Egyptian, Greek and Roman civilizations. However, it wasn't used on a large scale until 1700s, when it was required to be used in all construction in Paris. In 1666, a fire raged across London, destroying many parts of it. In its aftermath, the king of France ordered that all walls made of wood in Paris be immediately covered with plaster, as a protection against such fires. This resulted in large-scale mining of gypsum which was available around Paris in huge quantities. Thus, during the early 18th century, Paris became the centre of plaster production, and hence the name, plaster of Paris.