[ 955 



OVTI. The Volatilization of Radium Emanation at Low 

 Temperatures. By R. W. Boyle, Ph.D., 1851 Exhibition 

 Science Scholar, McGill University *. 



Introduction. 



17^ ROM the researches o£ Rutherford f and o£ Gray and 

 Ramsay + we now have definite knowledge concerning 

 the condensation and volatilization of radium emanation at 

 temperatures higher than — 127° 0. These researches, 

 which have been carried out with quantities of emanation 

 as large as are available, have given definite values o£ the 

 vapour pressures corresponding to certain fixed temperatures. 



At the suggestion of Prof. Rutherford the writer has 

 recently been investigating the volatilization of this emana- 

 tion at temperatures from —180° U. upwards. It has been 

 necessary to adopt different experimental methods to suit the 

 widely different quantities of emanation employed. 



When extremely small quantities of emanation, say of the 

 order of the equilibrium amount from O001 mgm. of radium, 

 are condensed upon a surface, one can no longer speak of the 

 emanation being in a "•liquid" or in a "solid" state. For, 

 in these circumstances, the condensed "layer" must be of 

 less than molecular thickness §, and it would hardly be 

 expected that volatilization would proceed in full accordance 

 with the vapour-pressure laws as ordinarily understood. 



For experimenting under these conditions the method 

 devised by Rutherford and Soddy || in 1903 is best ap- 

 plicable. It will be recalled that the method was to condense 

 from a current of gas, acting as carrier, a very small quantity 

 of emanation upon the interior surface of a spiral tube, which 

 was immersed in a bath at very low temperature. After- 

 wards, while allowing the temperature of the bath to rise 

 slowly, a very slow gas current was sent through the spiral. 

 The emanation on volatilizing was swept out of the spiral 

 and through an ionization vessel, where it marked its presence 

 by causing an increase of ionization. 



The temperature of maximum volatilization was readily 



* Communicated bv Prof. E. Rutherford, F.R.S. 



+ Phil. Mag. [6] xvii. p. 723 (1909). 



X Proc. Chein. Soc. xxvi. p. 82 (1909) ; and later, Journ. Chem. Soc. 

 xcv. p. 1073 (1909). 



§ Based on the determination by Rutherford, later substantiated by 

 Gray and Ramsay and by Debierne, that the equilibrium amount of 

 emanation from 1 gm. of radium has a volume of 06 cub. mm. at 

 N.T.P. 



II Phil. Mag. [6] v. p. 561 (1903). 



3 R 2 



