ELEMENTS, NEW AND CHEMICALLY NEW 127 



Again, the first-fruits of the discovery of radio- 

 activity were the recognition of the new elements 

 polonium, radium, and actinium by their unique 

 radioactive character in the first place. Then, in 

 the case of radium, its claim to the title of element 

 was confirmed, first by its exhibiting a unique 

 spectrum, then by its possession of unique chemical 

 character and atomic weight and by its occupying a 

 vacant place in the periodic table. The emanations, 

 next, as occupying a place in the family of argon 

 gases, were easily characterised, and for the radium 

 emanation unique spectrum was proved. Its origin 

 from radium by loss of one a-particle gives the atomic 

 weight as 222, which agrees with determinations 

 of its density and rate of diffusion. The chemical 

 characters of polonium and of actinium are different 

 from those of the elements they most closely resemble. 

 Polonium, or radium-7% by its close chemical analogy 

 to both bismuth and tellurium, was characterised as 

 an element of the sulphur family occupying the vacant 

 place contiguous to bismuth. Actinium, by its 

 resemblance in chemical character to the rare earths, 

 and especially to lanthanum, although capable of 

 being concentrated fractionally from that element, 

 was reasonably supposed to occupy the vacant place 

 in Group III, between radium and thorium. As will 

 later appear evident, both these elements in due 

 course may be expected to show unique spectra. 



Further progress in the elucidation of the chemical 

 character of successive products then underwent an 

 abrupt and, at first, very puzzling change of direction. 

 As member after member in the series was dis- 

 tinguished and characterised by its unique radio- 

 active character, by its disintegration in definite and 

 characteristic ways at definite and characteristic 

 rates, no further chemically new elements were 

 discovered. Unique radioactive character does not 



