374 PROCEEDINGS OF THE OHIO ACADEMY OF SCIENCE. 



the valence and atomic weights of the successive disintegration 

 products. 



Again suppose that the change consists in the expulsion of 

 I alpha particle and 2 beta particles. The loss of the alpha 

 particle would carry with it a change of valence of 2 and 'a 

 consequent shift of 2 places in the periodic arrangement of the 

 elements ; but the accompanying loss of 2 beta particles would 

 result in a change of valence of 2 also but in the opposite di- 

 rection to that caused by the loss of the alpha particle. The 

 product formed therefore would remain in the same position 

 in the periodic arrangement occupied by the parent element. 



From such considerations as these Soddy, Russell and Fajans 

 have been lead to conclude that two or more disintegrating ele- 

 ments with practically identical chemical properties I)ut differing 

 slightly in atomic weights may occupy the same position in the 

 periodic arrangement of the elements. It follows, therefore, that 

 some of the substances now regarded as elementary in character 

 may really consist of varying mixtures of closely related elements. 

 For example, lead obtained from a radioactive mineral may really 

 be a mixture of ordinary lead and one or more elementary sub- 

 stances with atomic weights differing slightly from the atomic 

 weight of lead, yet with properties so similar that it is impossible 

 to separate them by any known methods. This prediction was 

 fulfilled in a remarkable way when a year ago ( 1914) Richards 

 showed that the atomic weight of lead ol)tained from radioactive 

 minerals is less than the atomic weight of ordinary lead. — the 

 difference amounting in some determinations to as much as 0.75. 



It will be observed that in these changes we have an actual 

 transmutation of one element into another. It must be remem- 

 bered, however, that these transmutations are spontaneous, and 

 that up to the present time at least, no one has found a method 

 whereby such a change can be incited, or altered in velocity if 

 already in progress. 



It is often asked whether this disintegration of the atom, 

 attended as it is by a transmutation of one element into another, 

 is a property of all elements. The answer is that up to the 

 present time this property so far as known is confined to uranium 



