y. r >6 Dr. R. W. Boyle on the Volatilization of 



obtained by noting the temperature of the spiral when the 

 ionization attained its maximum value. 



Using this method with condensing spirals of copper tube, 

 Rutherford and Soddy* found that the volatilization of these 

 small quantities of emanation was rather sharply defined, 

 within a range of a few degrees about the temperature of 

 — It50° 0. More recently Mons. Laborde t applied the 

 same method, using condensing spirals of different materials, 

 and as a result claimed to have found marked differences in 

 the temperatures at which the emanation will volatilize from 

 the surfaces of different materials. Thus, from surfaces of 

 iron, tin, silver (a silver tube), and of copper, the volati- 

 lization is claimed to take place at —155 + 2° C. ; from the 

 surface of a silver deposit on glass, — 175 + 2° C. ; and from 

 the surface of glass itself, — 177 + 2° 0. It is remarkable 

 that there should be a difference of 20° C. between the 

 temperatures of maximum volatilization from the surface of 

 a silver tube and from the surface of a thick silver deposit 

 on glass; and it is noticeable that these temperature dif- 

 ferences were only found where glass spirals were concerned 

 in the experiments. 



These results had an important bearing upon the problem 

 of the writer's investigations, and in consequence some ex- 

 periments were performed to examine the effect of glass and 

 metal surfaces upon the temperatures in question. 



Method of Experiment. 



The arrangement of apparatuses represente 1 in fig. 1. The 

 condensing spiral DSD' was of tubing 0'35 cm. diameter, 

 and was immersed in sufficient pentane to cover the spiral in 

 a test-tube of 3 cm. diameter. Usually there were ten or 

 twelve turns in thp spiral. 



The test-tube was immersed, almost the whole of its length, 

 in a Dewar cylinder of 4 cm. diameter filled nearly to the 

 top with liquid air. The spiral and the electroscope KK' 

 were "short-circuited" by the tubes Zand F respectively, 

 so that a current of air could be used to sweep the conducting 

 tubes free from uncondensed emanation without disturbing the 

 condensed emanation in the spiral, and without unnecessarily 

 contaminating the electroscope. 



The operation of an experiment was as follows : — Emana- 

 tion, which had been mixed with air and stored in the 



* Loc. cit. 



t Le Radium, vi. p. 289 (1909). - 



