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The marked tendency of the cobaltic ion to combine with ammonia and similar unsaturated molecules is evidently responsible for the existence of the numerous, variegated and frequently very stable cobaltammines. It appeared to us of interest to determine the actual magnitude of this tendency toward complex formation and to examine how it varies among the different ammines. b r AT'direct and elegant method of accomplishing this purpose, since we can be sure that the concentration of the simple cobaltic ions is minute undeiany experimental conditions, is to determine the ratio of the cobaltic and cobaltous ion concentrations by measurements of the oxidation potentials of solutions containing known concentrations of cobaltous ions and of the cobaltammines. From these ratios we at once know the actual cobaltic ion concentrations, and these in turn are an inverse measure of the stabilities, since evidently the more stable the complex ion the less the equilibrium concentration of the cobaltic ion in its solutions.This method has entailed certain subsidiary determinations. Thus, it has been necessary to determine the cobaltous ion concentrations in ammoniacal solutions of cobalt salts; also since the existing data on the normal oxidation potential of the cobaltic-cobaltous electrode are very meager, additional determinations of this potential in solutions containing known concentrations of the respective ions have been required.Attempts were first made to measure the oxidation potential in neutral and slightly acid solutions of the ammines, but definite and reproducible results could not be obtained under these conditions. Satisfactory results were, however, obtained in concentrated ammoniacal solutions, the observed potentials varying normally with changes in the cobaltic-cobaltous ion concentrations. Nevertheless, the use of such solutions involved much inconvenience since they had to be scrupulously protected from contact with the air.Preparation of Ammines.The 6 ammines studied were prepared and carefully purified by the most recent methods of J6rgensen11 and were in general used promptly after preparation. These precautions as to purity and freshness are necessary, since it was found that with certain ammines small amounts of impurities have a noticeable effect on the potential, while with other ammines, and in particular the aquo-tetrammine chloride, changes occur on standing even in the dry state which produce marked effects on the potential.

Weinland and Koch' have recently disclosed some interesting facts regarding the precipitability of the chlorine in the green

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