. Conduction of electricity through gases and radio-activity; a text-book with experiments . num tube be heated toa white heat, a remarkable change takes place. At this hightemperature the emanating power is greatly decreased and oncooling the thoria does not regain its emanating power, but itis permanently reduced to only a small fraction of its originalvalue. This de-emanating, as it is called, of the compound ispermanent, but its original power of emitting emanation maybe restored by dissolving the compound and then separating itfrom the solution. Radium compounds may also be de-emanatedand
. Conduction of electricity through gases and radio-activity; a text-book with experiments . num tube be heated toa white heat, a remarkable change takes place. At this hightemperature the emanating power is greatly decreased and oncooling the thoria does not regain its emanating power, but itis permanently reduced to only a small fraction of its originalvalue. This de-emanating, as it is called, of the compound ispermanent, but its original power of emitting emanation maybe restored by dissolving the compound and then separating itfrom the solution. Radium compounds may also be de-emanatedand afterwards restored by a similar process. 200 EMANATIONS 131. Condensation of the Emanations.—These emanationsact in all respects like gases. One of the most conclusiveproofs of their gaseous nature lies in the fact that they may becondensed by very low temperatures. Rutherford and Soddywere the first to show this experimentally and used the fol-lowing method: The radium emanation is stored in a reservoirR (Fig. 66) and may be forced out of the reservoir by raising HiIHamaaa^ \J\7 \\7. Fig. 66. the level of the liquid. This is connected through the stop-cock S to the horizontal tube above through which a steadystream of gas may be sent from a gasometer and on its waypasses through a bulb B containing drying material. CDEis a spiral made from a copper tube of a total length of 310cm. and internal diameter of 2 mm. FH is a cylindrical test-ing vessel of the usual form containing an insulated electrodeK, so that by connecting this electrode to the electrometer andthe cylinder to a battery any ionization current produced in thecylinder may be measured. If the stopcock 5 be opened andthe liquid in R be raised while a slow stream of gas is passedalong the horizontal tube the emanation will be carriedthrough the spiral D and into FH, where an ionizationcurrent will be produced. If the copper spiral D be im-mersed in liquid air the emanation will not reach the ves- CONDENSATION OF E
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