1917] on The Complexity of the Chemical Elements 119 



hand and the spectra of X-rays on the other, and experiments on the 

 scattering of a-particles by matter, do give us for the first time a 

 definite conception as to what constitntes the difference between one 

 element and another. "We can say how gold would result from lead 

 or mercury, even though the control of the processes necessary to 

 effect the change still eludes us. The nuclear atom proposed by 

 Sir Ernest Rutherford, even though, admittedly, it is only a general 

 and incomplete beginning to a complete theory of atomic structure, 

 enormously simplifies the correlation of a large number of diverse 

 facts. This and what survives of the old electronic theory of matter, 

 in so far as it attempted to explain the Periodic Law, will therefore 

 be briefly referred to in conclusion. 



The Free Element a Compound of Matter and 

 Electricity. 



Although Davy and Faraday were the contemporaries of Dalton, 

 it must be remembered that it took chemists fifty years to put the 

 atomic theory on a definite and unassailable basis, so that neither of 

 these investigators had the benefit of the very clear view we hold 

 to-day. Davy was the originator of the first electro-chemical theory 

 of chemical combination, and Faraday's dictum, "the forces of 

 chemical affinity and electricity are one and the same," it is safe to 

 say, inspires all the modern attempts to reduce chemical character 

 to a science in the sense of something that can be measured quan- 

 titatively, as well as expressed qualitatively. Faraday's work on 

 the laws of electrolysis and the discovery that followed from it, when 

 the atomic theory came to be fully developed, that all monovalent 

 atoms or radicles carry the same charge, that divalent atoms carry 

 twice this charge and so on, can be regarded to-day as a simple 

 extension of the law of multiple proportions from compounds between 

 matter and matter to compounds between matter and electricity. 

 Long before the electric charge had been isolated, or the properties 

 of electricity divorced from matter discovered, the same law of 

 multiple proportions which led, without any possibility of escape, to 

 an atomic theory of matter, led, as Helmholtz pointed out in his 

 well-known Faraday lecture to the Chemical Society in this Theatre 

 in 1881, to an atomic theory of electricity. 



The work of Hittorf on the migration of ions, the bold and 

 upsetting conclusion of Arrhenius that in solution many of the 

 compounds hitherto regarded as most stable exist dissociated into 

 ions, the realisation that most of the reactions that take place 

 instantaneously, and are utilised for the identification of elements 

 in chemical analysis, are reactions of ions rather than of the element 

 in question, made very familiar to chemists the enormous difference 

 between the properties of the elements in the charged and in the 

 electrically neutral state. 



