Those hygroscopic solids which absorb moisture from the air up to such an extent that they become wet and turn into liquids are called deliquescent substances and this phenomenon is called deliquescence. the water of crystallization may be defined as the certain number of water molecules which are associated as the part of the constituent per molecule of solids. A unit cell in a crystal lattice having the lattice points only at its corner is known as a primitive or simple unit cell. In covalent crystals, atoms or molecules of crystals are linked to one another by covalent bonds. For example diamond, silica, carborundum.