ERLENMEYER and Gartner1 have reported that interchange of hydrogen isotopes takes place when hexammine cobaltic nitrate, [Co(NH3)6] (NO3)3, is dissolved in heavy water, all the hydrogen atoms being replaceable. Bankowski2, however, has stated that the hydrogen in complex ammines is only partially replaceable, one atom being interchanged in [Co(NH3)4(H2O)2]Cl3, and three atoms in [Co(NH3)4C03]Cl.