602 Profs. B. B. Boltwood and E. Rutherford on 



sulphuric acid were evolved. To the residue, after cooling, 

 a small volume of dilute sulphuric acid was added and the 

 insoluble lead sulphate was filtered out on a small asbestos 

 filter. The lead sulphate was decomposed by warming: with 

 strong hydrochloric acid and potassium chlorate, sulphuric 

 acid was added to this solution and the operations just de- 

 scribed were repeated. The two filtrates from the lead 

 sulphate were combined, heated to boiling, and a slight 

 excess of ammonia was added. The small precipitate of 

 bismuth salt w as filtered from the solution, and was dissolved 

 in dilute hydrochloric acid. The volume of this solution 

 was accurately determined and a small definite fraction of 

 it was removed. To the main solution 5 grams of metallic 

 copper in the form of small clippings was added, the mixture 

 was warmed gently and was allowed to stand for several Lours 

 with frequent stirring. Under these conditions the polonium 

 present in the hydrochloric acid solution was completely 

 deposited in an adherent coating on the copper. The copper 

 was washed with water and dried. 



The copper with the polonium was introduced into a glass 

 tube similar in form but smaller than that used for the 

 radium salt (a, fig. 1). The air was removed from this tube 

 and a very small amount of pure oxygen was introduced. 

 The tube was then sealed. One hundred and twenty-eight 

 days later, the tube containing the polonium was attached 

 to the measuring apparatus, and the gases contained in it 

 were pumped out. During the pumping process the lower 

 end of the tube and the copper which it contained were 

 heated to bright redness, in order, if possible, to displace 

 any helium occluded in the metal. The helium contained in 

 the gaseous mixture was determined in the usual manner 

 and its volume was found to be O009 cubic millimetre. It 

 was readily identified by its spectrum. 



The small, definite fraction of the polonium solution which 

 had been removed before treating this solution with metallic 

 copper (see above), was diluted to about 10 cubic centimetres 

 with water slightly acidified with hydrochloric acid. This 

 solution was introduced into a glass vessel the bottom of 

 which consisted of a clean plate of metallic copper. Polo- 

 nium was deposited on this plate, and the number of 

 a particles expelled was kindly determined for us by. 

 Dr. Geiger. The number of a particles emitted per second. 

 was equal to 10*7 xlO 5 . The fraction of the solution re- 

 moved was equal to j\ T , The total number of a particles 

 emitted per second by the entire quantity of polonium was 

 therefore 14*0 x 10 7 . The number of a particles emitted per 



