Photochemical Reduction with X-Rays and Effects of Addition Agents

Abstract

Ceric sulfate solution was reduced by exposure to x‐radiation. In order to follow this reaction a very accurate method was developed for the determination of ceric sulfate in dilute solutions by the use of orthophenanthroline indicator. The amount of reduction of ceric sulfate by x‐rays was found to be practically independent of concentration. Reduction was shown to be directly proportional to time of exposure up to 50 percent and slightly less efficient beyond that point. Silver perchlorate and silver nitrate decreased the amount of reduction of ceric sulfate by x‐rays. Mercuric nitrate and acetic acid increased the amount of reduction caused by x‐rays. Curves are also presented to show the effect of changing the concentration of these addition agents. Indications are that the mercuric nitrate was truly a catalyst to the reduction of ceric sulfate by x‐rays and that the acetic acid increased the amount of reduction by direct action on the ceric sulfate under the influence of x‐rays. Perchloric and nitric acids increased the reduction of ceric sulfate appreciably but not to as great an extent as did Hg(NO₃)₂. Sodium nitrate, perchlorate and sulfate showed no effect. Various organic substances were tried and found to increase the reduction by varying amounts. Experiments were carried out with various combinations of the catalysts and inhibitors to determine their relative efficiencies. The reduction of potassium permanganate by x‐rays proceeded to manganese dioxide for low acid concentrations and to manganous ion at higher acidity. The reaction was greater than for ceric sulfate but not as nearly proportional to dosage. The effect of addition agents was similar to that for ceric sulfate. X‐rays did not produce the same reaction in solutions of uranyl sulfate‐oxalic acid as does ultraviolet radiation. Solutions of potassium iodate were reduced by x‐rays but to a less degree than ceric sulfate or potassium permanganate. Hydrogen peroxide was formed in samples during radiation but did not effect the potassium iodate. Solutions of potassium bromate were not reduced by x‐rays but even larger amounts of hydrogen peroxide were formed. Calculations were made for: ions reduced per r unit absorbed, r units necessary for reduction of one equivalent, ions reduced per ion pair formed by x‐rays, and calories of absorbed energy necessary for reduction of one equivalent, by two independent methods. A mechanism was proposed for the formation of hydrogen peroxide by x‐rays in the presence of dissolved oxygen.