the Active Deposit of Radium. 437 



apply formula (8) in order to evaluate D ; we find b given 

 as 4 cm. and I equal to 8 cm. 



Equation (10) of Section 5 becomes now 



D = -0266^; 



Q 



using Eckmann's experimental value for ^ given above we 

 W D = '0443. 



a *' 



Such an excellent agreement with the most probable value 

 obtained in the present investigation must be to some extent 

 fortuitous, but there can be little doubt as to the order of 

 magnitude of D. 



Summary. 



8. It is advisable to give here a brief synopsis of the 

 results obtained in the series of experiments dealing with the 

 active deposit of radium, including for the sake of con- 

 venience several results previously published. 



Suppose a quantity of radium emanation is mixed with a 

 dry dust-free gas; of the active deposit particles which are 

 produced a certain fraction are positively charged, the 

 remainder being neutral. This fraction depends upon the 

 nature of the gas, but not upon its pressure provided the 

 pressure be high enough to prevent any appreciable recoil on 

 to the walls of the vessel. The values of this fraction are 

 for air *, hydrogen, and carbon dioxide respectively, 8$"2, 

 88'2, and 78*0. When the emanation is mixed with ethyl 

 •ether, practically all the deposit particles are neutral. 



In a previous paper the view was put forward that the 

 distribution of charge among the deposit particles had its 

 origin in the motion of recoil of these particles when expelled 

 from the atoms of emanation. The recoil atom during its 

 motion produces a large number of ions, and in all proba- 

 bility is ionized itself so that it acquires a positive charge ; 

 however, it is always liable to lose its positive charge by 

 collision with an electron, and all the more readily in the 

 case of those gases or vapours such as carbon dioxide and 

 ether where the electrons do not quickly leave the columns f. 

 The general effect to be expected from such a process is that 

 when the deposit particles are brought to relative rest among 

 the gas molecules, there will be a definite fraction positively 

 charged, the remainder being neutral. 



* 1 1 is of interest to recall here that Lucian has found the number 

 049 for the traction of the deposit particles of actinium which are formed 

 with a positive charge in air. 



t Cf. Wellisch and Woodrow, Phil. Mag. [6] vol. xxvi. p. 511 (1913). 



