Polonium, Radium, and Radioactinium. 115 



radium E by depositing the latter on a plate of nickel does 

 not lead to satisfactory results when copper is present. The 

 aluminium is added to act as a nucleus for the small quantity 

 of lead hydroxide precipitated by the ammonia. The pre- 

 cipitate of lead and aluminium was then dissolved in the 

 minimum quantity o£ HC1 and evaporated to a volume of a 

 few cubic centimetres. A plate of polished nickel was 

 rotated in this solution for half an hour and then removed. 

 This removes from the radium D practically all the radium 

 E and polonium. 



A small quantity of nickel goes into solution. The solu- 

 tion is then treated with excess of ammonia. The nickel in 

 the solution is not precipitated by the ammonia, bat the lead 

 and the aluminium containing the radium D are precipitated 

 quantitatively. This precipitate was then filtered off and used 

 as source on the filter-paper. It is not advisable, nor is it 

 for any purpose necessary, to separate the lead and the 

 radium D from the aluminium. Two preparations of radium 

 D prepared in this way from two different quantities of old 

 radium were used by Rutherford and Richardson in their 

 work on the 7-rays of this substance*. 



The radium E grown from these radium D preparations is 

 separated as follows. The preparation is dissolved in the 

 minimum quantity of HC1, evaporated till the solution con- 

 tains a few c.cm. only, and a clean nickel plate varnished 

 on one side is rotated in it for half an hour. This removes 

 nearly all the radium E but no radium D whatever. The 

 radium E deposited on nickel acts as a convenient source 

 of that body. If it is necessary to have it deposited on 

 another metal, it is first deposited on nickel and then trans- 

 ferred to the other metal by volatilization. The details of 

 this operation are given below. To the solution from which 

 the radium E has been removed ammonia in excess is added. 

 The precipitated lead and aluminium containing the radium 

 D are filtered off from the nickel and used as a source on 

 the filter-paper. 



The large quantity of polonium on the copper plate was 

 freed from the radium E deposited with it by volatilization 

 in air. Preliminary experiments on the volatilization of 

 these bodies showed that in air at a temperature of 900° G. 

 polonium is completely volatilized in a short time, while at 

 this temperature little or no radium E is volatilized. This 

 fact was made use of in separating the polonium from the 

 radium E. To volatilize radium E in air it was found 



* E. Rutherford & II. Richardson, Phil. Mao-. Y0 ]. xxvi. p. 321 (1913). 



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