A study of the extinction coefficient for ferric and ceric ions.

Ferric Species Standard ferric sulfate solutions were prepared by dissolving spectrographically pure iron rod (Johnson Matthey) in sulfuric acid and oxidizing with hydrogen peroxide. The decadic molar extinction coefficient of ferric ion in 0.8 N sulfuric acid at 24.9?C was found to be 2199 ? 4 liters mole-' cm-l at 304 m,/. The effect of a decrease of acidity and of added ferrous and cupric sulfates at this temperature is shown in Table I. Values of the ratio of observed extinction coefficient to the extinction coefficient in 0.8 N sulfuric acid are given. The temperature coefficient was measured in the range 20? to 30?C. for solutions of ferric ion in 0.8 N and 0.1 N sulfuric acid and in 0.01 N acid containing 0.01 M cupric ion. The results are given in Table II.