. Radioactive transformations . ation,and reaches a maximum about three hours after the introductionof the emanation. After barium platinocyanide has been exposedfor some time to the action of a large amount of the emanation,the crystals change to a reddish tinge, and the luminosity ismuch reduced. This has been shown to be due to a permanentchange in the crystals by the action of the rays. By re-solutionand crystallization, the luminosity again returns. THE KADIUM EMANATION 79 Curio and Debierne early showed that glass hecomes luminousunder the action of the rays from the emanation. This effe
. Radioactive transformations . ation,and reaches a maximum about three hours after the introductionof the emanation. After barium platinocyanide has been exposedfor some time to the action of a large amount of the emanation,the crystals change to a reddish tinge, and the luminosity ismuch reduced. This has been shown to be due to a permanentchange in the crystals by the action of the rays. By re-solutionand crystallization, the luminosity again returns. THE KADIUM EMANATION 79 Curio and Debierne early showed that glass hecomes luminousunder the action of the rays from the emanation. This effectis most marked in Thuringian glass, hut as a rule the luminosityis feehle compared with that produced in willemite or zinc sul-phide. The glass hecomes colored under the action of the rays,and with strong emanation is rapidly blackened. The sharpness of the temperature of volatilization of theradium emanation was very clearly illustrated by some experi-ments made by Rutherford and Soddy, using the electric method. VOCTI-IETCK. Fig. 21. Determination of the temperature of condensation of the radium emanationby the electric method. The emanation collected in the gasometer, B, was condensed ina long spiral copper tube, S, (see Fig. 21) immersed in liquidair, and a slow steady stream of air after passing through thetube entered a small testing vessel, T. After condensation thecopper spiral was removed from the liquid air and allowed toheat up very slowly. The temperature was deduced frommeasurements of the resistance of the copper spiral. Just be-fore the point of volatilization was reached, very little effectwas observed in the testing vessel. Suddenly a rapidly increas-ing movement of the electrometer needle was noted, and by 80 RADIOACTIVE TRANSFORMATIONS using a large quantity of emanation the rate of movement in-creased in a few moments from several divisions to severalhundred divisions per second. The rise of temperature ob-served between the point at which there was practi
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