APART from the results of a series of studies dealing with complexes of copper, little is known of the stability of internal complexes. Calvin and his collaborators1 have found wide variation in the stability of complexes of copper formed from a series of I diketones and o-hydroxy-aromatic aldehydes. It is a matter of interest to determine whether a similar wide variation of stability occurs with complexes formed by the co-ordination of a series of metals with one chelating molecule. For this reason and also because stability constants may eventually help to throw some light on the inactivation of essential trace metals in biological systems2, we have begun an investigation of complexes formed by a variety of metals.