@staticmethod
def __map_conc_to_species(tag):
    """ Creates dict mapping the species to concentration where tag is
        either a <reactants> or <products> XML tag.
        """
    result = {}
    for item in tag.text.strip().split():
        species, conc = item.strip().split(':')
        conc = int(conc)
        species = species.upper()
        result[species] = conc
    return result
