code: def get_element_mass(self, element):
          
  
          result = numpy.zeros(1)
          for compound in self.material.compounds:
              result += self.get_compound_mass(compound) *\
                  numpy.array(stoich.element_mass_fractions(compound, [element]))
          return result[0]
docs: Determine the mass of the specified elements in the package.
  
          :returns: Masses. [kg]