The "normalized absorbance" concept has been utilized in the continuous variations plot method of determining the composition of metal chelates and the corresponding extraction and formation constants. General equations for the calculation of conditional extraction and formation constants have been developed and the limiting parameters for the calculation of these constants have been delineated. The proposed method has been applied to the determination of the extraction constants for 6 metal chelates using dithizone or 8-quinolinol as the ligands.THE METHOD OF CONTINUOUS variations has been used frequently to determine the formulas and formation constants of complexes since its introduction by Ostromisslensky ( 1 ) and Job (2). The method is based on plotting measured absorbances, corrected for absorbances of reactants assuming no complexation, against mole fractions of the two constituents of a complex. Thus, a series of solutions is prepared by mixing different volumes of equimolar solutions of the two components and diluting to a constant volume to give solutions having identical total molar concentrations but different mole fractions. If a single, stable complex, one which is not appreciably dissociated, is formed, a plot of absorbance us. mole fraction of reactant gives a characteristic triangular plot. The mole fraction of the maximum of this plot, the apex of the triangle, indicates the composition of the complex. However, if a weak complex is formed, a very curved plot results. For a moderately stable complex, the composition of the complex can be obtained from the point of intersection of the tangents to the curve. This approximation is only valid for symmetrical plots (1 :1, 2 :2, etc.). A number of methods have been used to calculate the overall formation constant, once the formula of the complex has been determined. However, the formation constant of weak complexes cannot be determined very reliably using the continuous variations method as described by Job (2). Hagenmuller's method (3, 4 ) is only applicable to 1 :1 complexes because the solution of equations in (n + 1) powers, becomes very laborious. Other methods introduce either approximations or are limited in their applications (5-10).Cognizance of the inherent limitations of the continuous variations method in studying complexes formed in solution is necessary before attempting to determine either the composition of the complex formed or the corresponding formation and extraction constants. As indicated by Woldbye (11), valid data are obtained by the continuous variations method only when there is one predominant complex formed and the reactants and complex are not involved in concomitant equilibria.A new theoretical and generalized approach to the method of continuous variation in which no approximations are necessary is presented in this paper. General equations which do not contain molar absorptivities are given for describing the curved plots obtained when weak complexes are formed. Absorbance ratios are used in a manner similar to that pro...

This method has been developed for determining samples containing 0.01 gram of active oxygen to ±0.5%. The determination of peroxides other than benzoyl peroxide has not been tried; however, this method might well be used to determine other peroxides in organic media.No interference was noted in the samples containing unsaturated compounds on addition of the iodine to titrate the excess arsenious oxide. The arsenious oxide consumes the iodine instantly; most of the organic materials have been boiled off. Both these factors contribute to the lack of interference.In the case of benzoyl peroxide in polymers, not much peroxide was trapped in the polymer upon precipitation with ethanol. In amounts less than 3% it could be determined with no notice-able loss of peroxide in the precipitation. In polymer samples containing greater than 5% benzoyl peroxide, it is best, after precipitating'the polymer with the ethanol, to pour off the supernatant liquid, redissolve the polymer in benzene and reprecipitate it with ethanol, and then combine the two liquid portions before analysis. This achieves a more complete extraction of the peroxide.

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