14 LIFE: ITS NATURE AND ORIGIN 



with philosophic chagrin of his failure to insist on the significance of 

 his finding. 



All the evidence indicated that radioactive atoms are continu- 

 ously and spontaneously decomposing — giving off material par- 

 ticles and powerful radiations; but the precise origin of the matter 

 and the energy was still unknown. 



Soddy and the Periodic Table of the Elements 



Frederick Soddy (Nobel prize, 1921) investigated the chemical 

 properties of the substances released by successive radioactive 

 transformations, and observed a simple relation, in the Periodic 

 Table of the elements constructed by Mendeleef and Newlands, 

 between the position of the original and the final elements in- 

 volved in a radioactive disintegration series. Almost simultane- 

 ously Dr. A. S. Russell, Professor K. Fajans, and Dr. Soddy 

 announced the "displacement law": when a substance emits an 

 alpha particle (helium nucleus) it moves two places down in the 

 atomic table; but it moves one place up when it emits a beta 

 particle (electron). Later on, we shall see the importance of this 

 in the transformation of uranium 238 into neptunium and plu- 

 tonium. 



In 1906 Boltwood observed that his newly discovered radioactive 

 element ionium (atomic weight 230) was chemically so similar to 

 radium (atomic weight 226), that he was unable to separate their salts, 

 once they were mixed. On the basis of this and similar facts, Soddy 

 stated (1910): "These regularities may prove to be the beginning of 

 some embracing generalization, which will throw light not only on 

 radioactive processes, but on elements in general and the Periodic 

 Law . . . Chemical homogeneity is no longer a guarantee that any sup- 

 posed element is not a mixture of several different atomic weights, or 

 that any atomic weight is not merely a mean number." Professor 

 Theodore W. Richards of Harvard University (Nobel prize, 1914), in 

 making extremely accurate determinations of atomic weights, had 

 found marked differences in the atomic weights of lead from different 

 sources. Soddy further wrote: "The same algebraic sum of the posi- 

 tive and negative charges in the nucleus when the arithmetical sum is 

 different, gives what I call 'isotopes' or 'isotopic elements,' because 

 they occupy the same place in the Periodic Table. They are chemi- 

 cally identical, and save only as regards the relatively few physical 

 properties which depend upon atomic mass directly, physically iden- 

 tical also." 5a 



