. Radio-activity . r. Itwas found, however, that hydrogen peroxide is not radio-active,and that its action on the plate is a purely chemical one, whileit is the radiation from the emanation and not the emanation itselfthat produces ionizing and photographic effects. 140. Experimental arrangements. The emanation fromthorium is given off in minute quantity. No appreciable loweringof the vacuum is observed when an emanating compound is placedin a vacuum tube and no new spectrum lines are observed. For an examination of the emanation, an apparatus similar inprinciple to that shown in Fig. 51 is co
. Radio-activity . r. Itwas found, however, that hydrogen peroxide is not radio-active,and that its action on the plate is a purely chemical one, whileit is the radiation from the emanation and not the emanation itselfthat produces ionizing and photographic effects. 140. Experimental arrangements. The emanation fromthorium is given off in minute quantity. No appreciable loweringof the vacuum is observed when an emanating compound is placedin a vacuum tube and no new spectrum lines are observed. For an examination of the emanation, an apparatus similar inprinciple to that shown in Fig. 51 is convenient. The thorium compound, either bare or enclosed in a paperenvelope, was placed in a glass tube C. A current of air from agasometer, after passing through a tube containing cotton-wool toremove dust particles, bubbled through sulphuric acid in the vesselA. It then passed through a bulb containing tightly packed cotton-wool to prevent any spray being carried over. The emanation. From Gasometer To Electrometer. Fig. 51. mixed with air, was carried from the vessel G through a plug ofcotton-wool D, which removed completely all the ions carried withthe emanation. The latter then passed into a long brass cylinder,75 cm. in length and 6 cm. in diameter. The insulated cylinderwas connected with a battery in the usual way. Three insulatedelectrodes, E, F, H, of equal lengths, were placed along the axis ofthe cylinder, supported by brass rods passing through ebonitecorks in the side of the cylinder. The current through the gas,due to the presence of the emanation, was measured by means of VIl] RADIO-ACTIVE EMANATIONS 241 an electrometer. An insulating key was arranged so that any oneof the electrodes E, F, H could be rapidly connected with one pairof quadrants of the electrometer, the other two being always con-nected with earth. The current observed in the testing cylindervessel was due entirely to the ions produced by the emanationcarried into the vessel by the current of air. O
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