196 RADIUM. 



ting the material nature of the emanation, this expression tnay be 

 employed to designate the special radio-active energy stored in the 

 gas. "■ 



Air charged with the emanation provokes phosphorescence in bodies 

 which are immersed in it. Glass (especially Thuringian glass) gives 

 a beautiful white or green phosphorescence. Sidot's sulphide of zinc 

 becomes excessively brilliajit under the action of the emanation.* This 

 experiment may be tried with the apparatus shown in fig. 8. The 

 cock R being closed, the radio-active emanation which is emitted by 

 the solution in A saturates the air above the solution. When the 

 emanation has accumulated in A for some days the reservoirs B and 

 C, whose inner walls are coated with zinc sulphide, are exhausted. 

 The cock R" is then closed and R opened, so that tlie air charged with 

 the emanation expands suddenly into the reservoirs B and C, which 

 immediately become luminous. 



Radium emanation comports itself as a gas from many points of 

 view. Thus it is shared in the same proportions as a gas would be by 

 two communicating reservoirs. It diffuses in air according to the law 

 of diffusion of gases, and has a coefficient of diffusion not far from that 

 of carbonic acid gas in air. *■ 



Messrs. Rutherford and Soddy discovered that the emanation has 

 the property of condensing at the temperature of liquid air.'' The 

 effects of such condensation may be shown with the apparatus pictured 

 in fig. 8. The cock R" being closed, and the emanation being diffused 

 throughout the apparatus, as at the conclusion of tlie experiment last 

 described, the reservoirs B and C (which are covered within with phos- 

 phorescent zinc sulphide) are luminous. On closing the cock R and 

 plunging the reservoir C in liquid air, at the end of a half hour, it is 

 seen that the reservoir B has lost its luminosit}', while the reservoir C 

 is still bright. Thus it is seen that the emanation has quitted the res- 

 ervoir B and become condensed in the cooled portion of the reservoir 

 C. However, the luminosity of C is not very intense, since the phos- 

 phorescence of sulphide of zinc is more feeble at the temperature of 

 liquid air than at ordinary temperatures; but 1^}^ closing the cock R', 

 which interrupts communication between the two reservoirs, and 

 again bringing C to the temperature of the surroundings, it becomes 

 again ))rilliantly illuminated, while B remains dark. Thus the ema- 

 nation which at fir.st filled the two reservoirs is now all contained in C. 



The preceding experiments tend to convince us that the emanation 

 is analogous to ordinar}' gases, but up to the present time the hypoth- 

 esis of the existence of such a gas rests wholly on the manifestations 



"Rutherford, Phil. Mag., 1900, 1901, 1902. Numerous articles— Dorn, Abh. 

 Naturfrshgesel. Halle, June, 1900; V. Curie, C. R. Nov. 17, 1902, Jan. 2B, 1903. 

 ^> Curie and Debierne, C. R., Dec. 2, 1901. 

 c Curie and Danne, C. R., 1903. 

 <^ Rutherford and Soddy, Phil. Mag., May, 1903. 



