316 Prof. W. D. Harkins on the 



Second System of Classification of Isotopes. 



Before considering the relation between nuclear stability 

 and the isotopic number it is essential to outline a second 

 method for classifying isotopes. This has already been 

 suggested under the experimental correlations relating to 

 the oddness or evenness of the numbers representing positive 

 or negative nuclear electrons, and is given a definite form 

 in Table II. 



' Table IT. 



Classification of Isotopes according to Even and Odd 

 jSumber of Electrons. 



Abundance in Atomic Percentage. 

 Earth's Crust. Meteorites. 



Class I. N = even, P = eveu 86'9 93'2 



Class II. N = even, P = odd 11*2 20 



Class III. N = odd, P=odd 2-3 3-2 



Class IV. N=odd, Pleven O'O OO 



The Abundance of Atomic Species as Related to the 

 Isotopic and Class Numbers. 



It is important to consider the N/P, P plot given in fig. 1 

 (PI. XII.) as lying in a horizontal plane, while the abundance 

 of the atomic species may be imagined to be represented by 

 vertical coordinates. While such a three-dimensional plot 

 will not be presented as a single figure, it may be seen that 

 fig. 2 (PI. XII.), which gives the abundance of the atomic 

 species in the meteorites, represents these vertical coordinates 

 after they have been laid down in a horizontal plane. The 

 data from which this figure was constructed are collected in 

 Table III., while similar data for the earth's crust are given 

 in Table IV. and fig. 3 (PL XII.). 



The New Periodic System. — The plots represented in 

 figures 2 and 3 (PI. XII.) show that the abundance of the 

 atomic species of any isotopic number is a periodic function 

 of the atomic number. This periodicity is made much more 

 apparent by plotting the abundance of the element as a 

 function of the atomic number, since by doing this more 

 points on a single plot are made to represent actual data. 



