Position of Helium, Argon, and Krypton in the Elements. 411 



on the right track. It also shows how many missing elements are 

 waiting for discovery, and it would not now be impossible to emulate 

 the brilliant feat of Mendeleef in the celebrated cases of Eka-silicon 

 and Eka-aluminium . Along the neutral line alone are places for many 

 more bodies, which will probably increase in density and atomic weight 

 until we come to inert bodies in the solid form. 



Four groups are seen under one another, each consisting of closely 

 allied elements which Professor Mendeleef has relegated to his 8th 

 family. They congregate round the atomic weight 57, manganese, 

 iron, nickel and cobalt; round the atomic weight 103, ruthenium, 

 rhodium, and palladium ; while lower down round atomic weight 195 

 are congregated osmium, iridium and platinum. These groups are 

 interperiodic because their atomic weights exclude them from the 

 small periods into which the other elements fall ; and because their 

 chemical relations with some members of the neighbouring groups 

 show that they are interperiodic in the sense of being formed in 

 transition stages. 



[Note, June 22nd, 1898. 



Since the above was written, Professor Ramsay and Mr. Travers 

 have discovered two other inert gases accompanying argon in the 

 atmosphere. These are called Neon and Metargon. From data sup- 

 plied me by Professor Ramsay, it is probable that neon has an atomic 

 weight of about 22, which would bring it into the neutral position 

 between fluorine and sodium. Metargon is said to have an atomic 

 weight of about 40 ; if so, it shares the third neutral position with 

 argon. 1 have marked the positions of these new elements on the 

 diagram.] 



VOL. LXIII. 2 I 



