Experimentalists usually estimate kinetics parameters by measuring the progress curves for the product of the indicator reaction or the rate of its product formation. The mass action equation for the rate of product formation 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0. Fig. The inner solution (66a) (dashed blue curve) provides a good approximation to the mass action equations (7a)-(7d) (solid black curve) when t ≤ t * * s 2 , while the outer solution (66b) (dashed red curve) provides a good approximation when t > t * * s 2 . The dashed/dotted vertical line corresponds to t * s 2 and the dashed vertical line corresponds to t * * s 2 . Time has been mapped to the t∞ scale: t∞(t) = 1 -1/ ln(t + e).