838 Mr. G. N. Antonoff on Radium I) 



Method of Separation of the Long-period Products 

 from Radium. 



"Rutherford* effected a partial separation of radium E 

 from radium D by heating a platinum piate containing a 

 deposit of radium D, radium E, and radium F. Meyer and 

 v. Sehweidlerj separated the different constituents of radio- 

 lead by means of electrolysis or by depositing on different 

 metals. 



Various reagents were used with a view of separating the 

 radioactive products from each other and from radium. It 

 was found that by precipitation with barium sulphate, radium 

 and radium D could be separated from the radium E and 

 polonium in an old solution of radium. The following 

 method was adopted. A certain amount of an old solution 

 of radium was boiled down on a watch-glass to drive off the 

 emanation. The activity of the watch-glass was measured 

 when it had reached a minimum value and found to be 

 19"5 divs. per minute. This is the measure of the combined 

 activity of radium and polonium left on the glass. Equal 

 portions of the radium solution were taken. Barium salt in 

 varying quantities was added and precipitated as sulphate. 

 The activity remaining in the various portions of the solution 

 was found to be less and less with increasing quantities of 

 barium until a minimum value of 1*5 or 1*4 was reached, 

 after which the larger addition of barium in the remaining 

 portions was found to have no further effect. The experiment 

 was repeated on a larger scale. Where enough barium was 

 added the a-ray activity of the solution measured over some 

 months was found to decay according to an exponential law 

 with a period of about 134 days, which is about the period 

 of polonium. If insufficient barium was added to entrain 

 all the radium the activity of the remaining solution was 

 found to increase in the first few days. 



The fact that the quantity of polonium does not diminish 

 with increase of barium salt shows that there is no noticeable 

 entrainment of the polonium by barium sulphate. To test 

 this point more definitely two portions of an acid solution of 

 the active deposit of radium were taken. One portion was 

 evaporated to dryness on a watch-glass, the activity on which 

 was then found to be 21 divs. per minute. In the other 

 portion barium sulphate was precipitated, and, the precipitate 

 having been filtered off, the polonium was likewise evaporated 



* Phil. Mag. viii. p. 290 (1905). 

 t Loc. cit. 



