114 Dr. Russell and Mr. Chadwick on the y Rays of 



Preparation of pure Polonium and of Radium I) and E. 



The method of separation of polonium which we employed 

 consisted of: a combination of ordinary chemical methods, 

 electrolysis, and volatilization. As it was possible by these 

 methods to prepare at the same time radium D and radium E 

 in the pure state, and as it was necessary to do this for 

 another research, a detailed account will now be given of 

 the separation of all of these bodies, though there is nothing 

 essentially new either in principle or in details in the methods 

 employed. 



Preliminary experiments were carried out on an old pre- 

 paration of radium (D+E + F) containing, as impurity, 

 lead sulphide. The object of these experiments was to 

 obtain each of these substances in the form of a thin film on 

 a metal as nearly as possible in quantitative amount, and 

 free from active and inactive impurities. When these ex- 

 periments were completed operations were carried out on 

 larger quantities. 



The largest source of polonium in the laboratory was the 

 accumulation of radium (D + E + F) in a preparation of 

 31 milligrammes of radium bromide which had been sealed up 

 and untouched for six or seven years. This material was 

 dissolved in hot water containing just enough HC1 to effect 

 solution. To this was added a solution containing 1 milli- 

 gramme lead chloride and the whole evaporated to about 

 10 c.cm. A plate of copper well polished on both sides 

 was rotated in this solution for about two hours. Prelimi- 

 nary experiments had shown that under these circumstances 

 about 95 per cent, of the polonium is deposited on the 

 copper. A fair proportion of radium E is also deposited 

 with it, but no radium D if lead be present. The copper 

 plate was then removed, carefully washed, and set aside. 



The radium solution was diluted, and heated, and a solu- 

 tion of H 2 S added to it in excess. This precipitated as 

 sulphides all the copper which had been previously dissolved 

 off the electrode and also the lead which had been previously 

 added. The precipitate contained the whole of the radium D, 

 and all the radium E and polonium not deposited on the copper. 

 It was dissolved in HN0 3 , the solution evaporated to dry- 

 ness, and the material redissolved in hot water containing a 

 little HOI. To obtain the radium D from this solution it 

 was treated as follows. Three milligrammes of aluminium in 

 the form of chloride were added to the solution, and then 

 ammonia in excess. This precipitates everything except the 

 copper. It is necessary to remove the copper at this stage 

 since the subsequent operation of separating radium D from 



