Density value P calculated from the crystal cell and contents,
               expressed as per cent solvent.
               P = 1 - (1.23 N MMass) / V
               N     = the number of molecules in the unit cell
               MMass = the molecular mass of each molecule (gm/mole)
               V     = the volume of the unit cell (A3)
               1.23  = a conversion factor evaluated as:
                       (0.74 cm3/g) (1024 A3/cm3)
                       --------------------------------------
                            (6.02*1023) molecules/mole
                       where 0.74 is an assumed value for the partial specific
                       volume of the molecule