334 Dr. A. W. Stewart on Atomic Structure 



substances are separable from one another by chemical 

 means*. On the above view, the " pseudo-isotopy " is due 

 to the influence of the " cometary " electrons upon the 

 atomic nucleus of which they form a temporary part at 

 certain points in their orbits. The removal of two positive 

 charges from the intermediate zone of bexavalent uranium 

 produces uranium-X^ which is actually isotonic with thorium 

 and has the atomic number 90 ; but the abstraction of two 

 charges from the " cometarv" orbits, although it has the 

 same effect upon the total residual charge, is only sufficient 

 to bring about a close resemblance between the product 

 (quadrivalent uranium) and thorium ; and is not enough to 

 produce total identity and a change in atomic numberf . 



Taken in conjunction with the experimental evidence, the 

 model suggests that those atoms which change their valency 

 should really be regarded as " pseudo-elements," since they 

 are capable of exhibiting two or more sets of distinct chemical 

 characteristics according to the number of electrons which 

 revolve in their "cometary" orbits. They are not " meta- 

 elements " of the type suggested by Grookest; for they have 

 definite atomic weights. They should rather he regarded as 

 a new type of isobares similar to hut not identical with 

 the radioactive isobaric elements like mesothorium-1 and 

 mesothorium-2. 



The dynamic conception of the model atom set forth above 

 suggests a possible solution of the problem of the atomic 

 weights of the elements, though at the present stage the 

 following suggestion must be treated with reserve. 



The fact that negative electrons exist apart from matter 

 as w r e know it, whilst positive electrons are never disso- 

 ciated from masses of at least atomic magnitude, suggests 

 that there is a close relation between mass and positive 

 electricity. Further, the connexion between the two factors 

 appears to be strengthened by the recognition that the atomic 

 weight of an element is approximately twice its atomic 



* Fleck, Trans. Chem. Soc. cv. p. 247 (1914). 



t Similar reasoning may he applied to other eases. For example, 

 Allen (Trans. Cbem. Soc. exiii. p. 389 (1918)) Las pointed out that the 

 " molecular number " of the ammonium group (NH 4 ) is 11, which is the 

 same as the atomic number of sodium: and he has drawn the conclusion 

 that this coincidence in value has some bearing upon the known resem- 

 blances between sodium and ammonium. In the model, the attachment 

 of four hydrogen atoms to the nitrogen atom would entail the intro- 

 duction of a corresponding number of electrical charges into the 

 "cometary" orbits: and to the effect of these upon the central nucleus, 

 may be ascribed the change in character of the nitrogen atom. 



+ Crookes, Trans. Cheni. Soc. liii. p. 487 (1888). 



