118 Journal of the Mitchell Society [March 



be determined. In other words, the atomic number of any element can 

 be found in this way. 



Radioactivity has solved the constitution of the atom. Ruther- 

 ford's disintegration theory and his demonstration of the building 

 up of the helium atom have finally settled that problem. "We now 

 know that the atom is built up of positive and negative electricity — 

 according to Rutherford's conception, a positive nucleus of alpha par- 

 ticles surrounded by a field of negative electrons. The discussion of 

 this or other atomic models is apart from the object of this paper. 



The Periodic System represented the place occupied by an element 

 in the series as primarily a function of its mass, but in reality mass 

 is secondary and the electrical content is the chief factor. As already 

 stated there are two variables in the structure of each atom — mass and 

 electrical content. The former decides the position of the element in 

 the vertical columns of the Periodic Table and the latter decides the 

 position in the horizontal columns. In consequence of the influence 

 of the electrical content, Soddy reasons that a chemical element is not 

 necessarily homogeneous and its atomic weight may be, and possibly 

 is generally, a mean value rather than a natural constant. The fact 

 that some elements are known to be radio-active — that is, with some 

 of their atoms undergoing disintegration — that even such elements as 

 potassium and rubidium are sul)ject to a slow disintegration of their 

 atoms which involves the formation of atoms of lesser mass, brings 

 the thought near that possibly all elements are subject to the same 

 process of change except that the rate is too slow to admit of detection 

 by such instrumentalities as have hitherto been used. Quite recently 

 the statement has been made that by means of a new device it has been 

 found possible to detect and register the expulsion of one alpha par- 

 ticle from zinc in every nine and a half hours. So far as I know, this 

 has not been confirmed. But enough is definitely known to bring us 

 back to the worn atoms of Crookes. 



The addition of some thirty or forty new elements known as radio- 

 active elements but having valid claims to recognition as real elements 

 puts too severe a strain upon the Periodic Table as conceived and con- 

 structed. This is far in excess of the number of A^aeant places, espe- 

 cially when one reflects that the rare earths which have been shifted 

 from place to place are still dissatisfied with their accommodations. 

 Making use of the two variables named above, it was found that a few 

 of these radioactive elements — as, for instance, radium emanation. 



