778 The Production of Radium from Uranium. 



tellurium (Ber. d. I). Chem. Gesell. 1905, p. 591) fairly 

 conclusive evidence of a chemical nature is brought forward 

 that polonium (radio-tellurium) stands to tellurium in the 

 periodic table in a similar relation to that in which radium 

 stands to barium. It therefore immediately follows bismuth, 

 the atomic weight of which is 2085 (0 = 16), and the atomic 

 weight of polonium may be estimated with fair probability 

 as being in the neighbourhood of 212. Thus in the change 

 of the radium atom (225) into polonium, four a particles are 

 expelled and a reduction of atomic weight amounting to 

 about 13 units occurs, so that the view that the a. particle is 

 or becomes an atom of helium seems to be fairly well borne 

 out. In the change of the atom of uranium (238) into 

 radium a similar reduction of atomic weight of 13 units takes 

 place, and it may therefore be expected that about four a 

 particles are expelled in this case also. By analogy with 

 other disintegration series, it is to be expected that in 

 addition to the a-ray changes several rayless and /3-ray 

 changes occur also, and of the latter one. the change of 

 uranium into uranium X, is in fact known. The hypothesis 

 that there are several slow-period intermediate changes 

 between uranium and radium gains in definiteness by these 

 considerations. 



The results obtained in the investigations of the ratio in 

 which radium and uranium are contained in the natural 

 minerals, which have been recently published, bear out this 

 hypothesis in the strongest possible manner. Since the 

 drafting of the present paper Boltwood (Phil. Mag. [6] ix. 

 1905, p. 599) has published analyses of 22 minerals con- 

 taining very varying proportions of uranium, and finds in 

 each case the expected proportionality to exist between the 

 quantities of the two elements. McCoy (Ber. d. D. Chem. 

 Gesell. 1904, p. 2641) has examined the radioactivity of 

 several minerals containing uranium, and has shown that in 

 those in which thorium is not present the activity is pro- 

 portional to the quantity of uranium present. This supports 

 the view that radium, actinium, and polonium are all inter- 

 mediate products in the disintegration of uranium. An 

 interesting speculation arises as to the nature of the final 

 product in the disintegration series. After the change of 

 polonium, in which a rays only are expelled, no further changes 

 accompanied by the expulsion of radiant particles occur. If 

 the atomic weight of polonium is in fact 212, the expulsion 

 of one a particle from the atom would lower the atomic 

 weight further to about 208. Jf this change is in fact the 

 last of the series, the ultimate product must accumulate 



