A study has been made at 25" of the influence of pH upon the relative quantum yields for the consumption of oxalate and the production of carbon dioxide, carbon monoxide, and uranous ion by light of 254 nm absorbed by the uranyl oxalate actinometer system. The uranyl ion was at 0.01 F , the oxalate at 0.06 F , and initial pH was at 0-6. About 12% of the oxalate was decomposed. The quantum yields for the consumption of oxalate were found to be independent of the pH between 1 and 5 but to decrease outside this range. The reaction at all values of pH was found to consume acid. The moles of carbon dioxide produced in all forms (COZ, H&Oa, HCOa' , COa2-and the uranyl carbonate complexes) per mole of oxalate consumed very nearly equalled unity at pH 0 to 5. The moles of carbon monoxide produced per mole of oxalate consumed were always less than unity; they decreased with increase in pH abruptly between pH 1 and 2, and became negligible above pH 3. The mole ratio of uranous ion produced to oxalate consumed increased slowly from about 0.03 between pH 1.5 and 4 to about 0.08 at pH 6. The mechanisms of the reactions are discussed.

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