874 Dr. J, W* Nicholson on a Structural 



as representing neon. Apparently the group (PiH) 3 has 

 considerable significance in atomic structure, according to 

 the present theory. 



Sodium. — The atomic weight of sodium is slightly greater 

 than 23, but not so great as 23*01, according to current 

 chemical opinion. The value 23'00<S is given by the group 

 4He + 7H. 



Magnesium, — This is an element, like beryllium, which 

 cannot be composed from the helium and hydrogen groups, 

 Its atomic weight is 24 32, a value given exactly by 

 2H + 5He + Pf, 



Lithium. — We have considered all the known elements 

 with atomic weights less than 25, with the exception of 

 lithium, and the addition of argon. Lithium is the element 

 which has presented the only difficulty, and it is possible 

 that this difficulty is only apparent. Until very recently, 

 the atomic weight of lithium was believed to be greater 

 than 7. A recent determination with carefully prepared 

 material, however, gave 6'94, at present the accepted value, 

 It is not unlikely that the actual value may be even smaller. 



The combination 3Nu-f 2H gives 6*90, and He + 3H gives 

 7*01, the older value. The first combination gives the best 

 result, and is used later. If it should be the case that the 

 second protyle is not hydrogen, but in a sense half of it, 

 so that all groupings -should be doubled, this difficulty is 

 removed on addition of the two groups. At present the 

 question must be left open, but there is some reason to 

 believe that the latter view is correct. 



The Inert Gases. 



After this preliminary sketch, we may proceed to a 

 detailed theory of a definite group of elements in the Periodic 

 System, and for this purpose we select the inert gases, in- 

 cluding the radioactive emanations. They are a very funda- 

 mental type of matter, and the groupings which are found 

 to be effective in representing them, from the point of view 

 of atomic weight, have an important place in the suggested 

 constitution of the other classes of elements. Too much 

 stress must not be laid, in many cases, on the particular 

 arrangements selected, which are purely speculative and 

 provisional, but it seems probable that they ma} T represent 

 something in the structure of the atom, from the constant 

 recurrence of those which are effective. It may be claimed 

 that they introduce a system into the Periodic Table which 

 does not appear to be fortuitous, at the same time enlarging 



