CHEMICAL effects produced by roentgen radiation have been studied during the past years by several investigators. Changes have been produced in a number of compounds, as has been pointed out in a recent article by Clark and Pickett (1). As a rule, very minute quantities are changed chemically by the roentgen dose which can be applied in a reasonable length of time. It is, therefore, not surprising that some of the substances irradiated seem to have been unaffected. Whether no change at all took place, or whether the methods for detecting the change were not delicate enough, remains to be determined. The studies to be described here may lead to a delicate method for detecting chemical effects of the radiation and a method which may perhaps be applied to a great number of substances. Our investigations were at first aimed mainly at finding a simple method for measuring roentgen-ray dosage. Considering that some color change might be found that would be satisfactory for this purpose, we started to investigate the effect of radiation on solutions of a number of chromatic substances. Color changes produced by roentgen rays have long been utilized as a means of measuring radiation quantitatively. The Sabouraud-Noiré (2) dosimeter is based on this principle. Solids of fairly high average or effective atomic weights are used in this as well as in other similar dosimeters. Aqueous solutions should be better for two reasons: (a) water absorbs and scatters roentgen rays to about the same extent as tissues, and (b) the color change in solutions can be measured accurately by means of colorimeters, or, still better, by spectrophotometers. Fricke and Morse (3) have described how the oxidation of ferrous sulphate in a 0.8 N sulphuric acid solution can be used for measuring dosage, and we have used this method to find out how much roentgen radiation was absorbed in the different solutions we examined. The main practical objection to this method is that the amount of FeSO4 oxidized has to be determined in a rather complicated way. Recently Wyckoff and Baker (4) have found that the action of roentgen rays on Eder's solution [HgCl2 (NH4)2 C2O→HgCl] may be utilized for measurements of dosage. It is, however, rather questionable whether this method can be made practical, though attempts in this direction have been made (5). Fricke found that the amount of FeSO4 oxidized per cubic centimeter of solution was directly proportional to the dose, and independent of the concentration. The same relation was found by Clark and Pickett (1) to hold for the reduction of potassium nitrate to nitrite. We have obtained similar relations for tyrosine (5) and phenol. As very small amounts are changed it is evident that at least for certain compounds it is best and often necessary to use very dilute solutions in order that it may be possible to measure the effect of the radiation. We consequently used only substances which gave a strong color in weak solutions.
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Stenström et al. (1931) studied this question.