652 SCIENCE PROGRESS 



substances regarded as elements — whether metallic or non- 

 metallic — because they could not be resolved by any of the 

 means at the chemist's disposal, were interrelated in such a 

 way that there must be some genetic connexion between them. 

 Now that it has been shown that three accepted elements of high 

 atomic weight, Uranium, Thorium and Radium, are not simple 

 substances, the probability that the elements generally are com- 

 posite in their nature becomes very great indeed. 



Prof. Soddy would retain the term element even for Radium. 

 The question, " How can an element or the atom of an element 

 change?" has given rise, he says, to many arguments of 

 etymological rather than scientific importance. But science is 

 only compatible with correct etymology — it is the duty of 

 science to be correct in word as in deed. Prof. Soddy 

 attempts to wriggle out of the difficulty in an interesting 

 manner by arranging that : 



" You may, if you like, regard the Radium atom as a com- 

 pound of the atom of emanation and of the Helium atom which 

 result on its disintegration, as it certainly is such a compound 

 but you must make it quite clear that you do not mean a mere 

 chemical compound, which may at will be formed from and 

 decomposed into its constituents." 



At the risk of being ranked as " a more or less random 

 critic of younger workers in radioactivity," seeing no reason 

 why even the younger worker should be spared from criticism, 

 I venture to urge that the argument is illogical. 



There can be no question that, owing to the discoveries 

 under notice, the word element has now lost its significance 

 in chemistry and that the difficulty of defining it is consider- 

 able. We cannot base distinctions on degrees of stability, 

 as Prof. Soddy suggests should be done. But it is not easy to 

 find a substitute. Perhaps, in the future, we may come to 

 speak of chemical primaries, metallic or non-metallic. At one 

 time, the term atom meant the unit quantity of any substance, 

 simple or compound ; it was customary to speak of the atom 

 of water, for example. But when physical conceptions became 

 paramount and Avogadro's theorem was accepted by chemists 

 as their guiding principle, it became customary to apply the term 

 molecule only to the kinetic or acting unit and to reserve the 

 term atom for the ultimate elementary unit. Physicists, strangely 

 enough, have never followed chemists in thus giving a precise 



