def get_size_class_mass(self, size_class):
return self.size_class_masses[self.material.get_size_class_index(<EOL>size_class)]<EOL>
Determine the mass of the specified size class in self.

:param size_class: The formula and phase of the size class,
  e.g. 'Fe2O3[S1]'

:returns: [kg] The mass of the size class in self.