A rate equation for the total path of decomposition of aqueous Na2S204 in the p H range 3.5-5.0 at 23 "C was determined, taking into account the rapid autocatalytic decomposition as well as the "induction" period. The kinetic data were determined by a continuous polarographic method. The form of the rate equation was found by studying the decomposition of aqueous Na2S204 at various values of p H and at various initial concentrations. Rate constants were calculated from the data using the integrated form of the rate equation. The rate equation, with certain limitations, was found to be where kl = 1.67 x 10-l l mole-' s-l and k, = 5.83 x 10312 molew2 s-' at 23 "C; C and C, being dithionite concentration at time t and initial concentration, respectively. The integrated form of the rate equation was used to generate decomposition curves, which are in reasonable agreement with the experimental data.

The decomposition of dilute aqueous sodium dithionite has been studied in unbuffered solutions by means of continuous polarography, accompanied by recorded p H values. The decomposition-time curve began with a slow "induction" period followed by an S-shaped rapid phase. The p H values decreased slightly during the induction period and increased considerably during the rapid phase. The addition of a solution of fresh decomposition products eliminated the induction phase. The addition of sulfide also eliminated the induction period and catalyzed the reaction. The accepted stoichiometry (2)

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