Induced reactions involving sulphate radicals

Reaction between iron(II) and peroxydisulphate ions, if the iron(II) is added rapidly, occurs according to 

On the other hand, Kolthoff et established that the ratio [Fe(II)] reacted/ [S2O8 ] reacted in acidic, neutral and alkaline medium is the same but much less than 2, if iron([f) is added at very low speed. The decrease in the oxidizing capacity can be explained by the induced decomposition of peroxydisulphate, though the detection of oxygen as a product was not successful. 

In the presence of organic compounds, according to the observations of Merz 

According to this mechanism the value of the consumption ratio 

Dilution of the reaction mixture with water or acid results in a decrease in the consumption ratio. This result cannot be interpreted by the above mechanism because the induced oxidation depends on the relative and not on the absolute concentrations. But assuming that reaction (109) is reversible we obtain for the consumption ratio 

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