absorbs (molar absorptivity ε = 2.76 × 104 L mol−1 cm−1),
iodine only weakly (ε = 189 L mol−1 cm−1), and iodide not at
all,5−7 as is the case with persulfate. This spectrophotometer
had no ancillary temperature controller for the cell-holder, but
the surplus mixed solution was measured and remained close to
20 °C throughout the scanning period.