1917] The Complexity of the Chemical Elements 117 



AVEEKLY EYEXIXG MEETIXG, 

 Friday, May 18, 1917. 



Sir William Phipsox Beale, Bart., K.C. M.P., 

 Yice-Presideut, in the Chair. 



Professor Frederick Soddy, M.A. F.R.S. 



The Complexity of the Chemical Elements. 



The elements of the chemist are now known to be complex in three 

 different senses. In the first sense the complexity is one that 

 concerns the general nature of matter, and therefore of all the 

 elements in common to greater or less degree. It follows from the 

 relations between matter and electricity which have developed 

 gradually during the past century as the result of experiments made 

 and theories born within the four walls of this Institution. Associ- 

 ated initially with the names of Davy and Faraday, they have only 

 in these days come to full fruition as the result of the very brilliant 

 elucidation of the real nature of electricity by your distinguished 

 Professor of Physics, Sir Joseph Thomson. Such an advance, 

 developing slowly and fitfully, with long intervals of apparent 

 stagnation, needs to be reviewed from generation to generation, 

 disentangled from the undergrowth that obscures it, and its clear 

 conclusions driven home. This complexity of the chemical elements 

 is a consequence of the condition that neither free electricity nor 

 free matter can be studied alone, except in very special phenomena. 

 Our experimental knowledge of matter in quantity is necessarily 

 confined to the complex of matter and electricity which constitutes 

 the material world. This applies even to the " free " elements of 

 the chemist, which in reality are no more free then than they are in 

 their compounds. The difference is merely that, whereas in the 

 latter the elements are combined with other elements, in the so-called 

 free state they are combined with electricity. I shall touch l)ut 

 briefly on this first aspect, as in principle it is now fairly well under- 

 stood. But its consistent and detailed application to the study of 

 chemical character is still lacking. 



The second sense in which the elements, or some of them at least, 

 are known now to be complex has, in sharp contrast to the first, 

 developed suddenly and startlingly from the recognition in radio- 

 active changes, of different radio-elements, non-separable by chemical 



