Before 1959 both the IUPAP and IUPAC used oxygen to define the mole; the chemists defining the mole as the number of atoms of oxygen which had mass 16 g, the physicists using a similar definition but with the oxygen-16 isotope only.
Pred rokom 1959 IUPAP a IUPAC používali pre definíciu molu kyslík, chemici definovali mol ako počet atómov kyslíka s hmotnosťou 16 g, fyzici používali podobnú definíciu, ale iba s izotopom kyslík-16.