The Groundivork of the Universe, Sec. 65 



Professor Soddy, however, was not content merelj' Avith the 

 enunciation of this Law. He proceeded, as Mendeleef had done, 

 to predict certain results which must follow if his views wei e 

 correct ; and the fulfilment of his prediction has marked almost 

 as great a stride forward in our knowledge of the atom as that 

 which the Russian chemist made in connection with the relations 

 between the elements. 



The stable product which finally results fi-om the radioactive 

 disintegration of uranium is a material having all the chemical 

 properties of lead. The end-product of the thorium series is also 

 chemically indistinguishable from lead. Now, in order to attain 

 the stage of lead, as Professor Soddy pointed out, uranium has to 

 eject eight alpha-particles ; whilst thorium yields lead by the 

 ejection of six alpha-particles. Since each alpha-particle is a 

 helium atom with an atomic weight of four, it is evident that the 

 lead from uranium will have an atomic weight thirty-two units 

 lower than that of uranium ; whilst the lead from thorium will 

 have an atomic Aveight twenty-four units less than that of thorium 

 itself : — 



Atomic Weight Atomic A¥eight 



238-2 URANIUM THORIUM 232-4 



Loss of I 

 32 units eight atoms 

 of helium 



Loss of 



six atoms 



of helium - 24 units 



206-2 LEAD LEAD 208-4 



Chemically indistinguishable. 



The Atomic Weight of natural Lead is 207 -L 

 Basing himself upon these facts, Professor Soddy predicted that 

 although the lead obtained from uranium and that produced by 

 the disintegration of thorium were chemically identical Avith each 

 other, their atomic Aveights Avould be different : that of the 

 uranium derivative being 206-2 ; whilst that of lead from thorium 

 AA^ould be 208-4. This prediction has been tested with every 



