code: def get_element_mfr(self, element):
          
  
          result = 0.0
          for compound in self.material.compounds:
              formula = compound.split('[')[0]
              result += self.get_compound_mfr(compound) *\
                  stoich.element_mass_fraction(formula, element)
          return result
docs: Determine the mass flow rate of the specified elements in the stream.
  
          :returns: Mass flow rates. [kg/h]