values calculated by each method, It was shown that AKOH at any pH was equal to a function containing the hydrogen and hydroxide ion concentrations, dissociation constants, the stoichiometric concentrations of ligand and acid, and the concentration of potassium hydroxide in the ligand-metal titration.
Comparison of A values calculated by the two methods gives a check on the validity of the data and for the concentration of ligand.
It was pointed out that calculations for tetracycline analogs a t a high pH would be inaccurate since a dissociable hydrogen on a complexed molecule, but remote from the site of coordination, will have a larger dissociation constant than the same hydrogen on a free ligand.
The thermodynamic dissociation and stoichiometric stability constants were calculated for five tetracycline analogs with cupric ion and these values were compared with the data of previous workers. Contrary to the conclusions of Doluisio and Martin, the biologically inactive analogs, 4-epi-chlortetracycline and 4-epi-anhydrotetracycline, were found to form 2: 1 complexes, which were quite insoluble and which precipitated a t W values just above 1. 987 Methods for the calculations of the biligand stability constants were discussed.
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