Law of Density-Numbers 



23 



The differences in the atomic weights between the precursors 

 and the first member of the triad proper varies from 16 to 17, 

 and the difference in density-numbers from to 2, as in 

 Table V. 



Table V. 



Atomic Weights. 



J. 



II. 



III. 



IV. 



Y. 



N 14 



17 

 P 31 



16 



16 

 S 32 



F 19 



165 

 CI 35-5 



Na 23 



16 

 K 39 



Mg 24 



16 

 Ca 40 





Density-numbers. 





N=3 







Pr-=3 



0=1 



1 

 S=2 



F=4 







Cl=4 



]N T a=4 



1 

 K =5 



Mg=5 



2 



0a=7 



Among the elements in Table L, besides those included in 

 the above triads, are to be found groups of two or more 

 elements which present the same properties as the triads. 



Thus there are three pairs with the difference 16. 



Table VI. 



Atomic 

 weight. 



Density- 

 number. 



Atomic 

 weight. 



Density- 

 number. 



Atomic 

 weight. 



Density- 

 number. 



Li 7 



16 



Na 23 



2 



2 

 4 



B 11 



16 



Al 27 



3 



1 

 4 



12 



16 



Si 28 



1 



3 

 4 



The difference of 16 in the atomic weights does not corre- 

 spond to a constant difference in the density-numbers \ but a 

 difference of 45 to 48 corresponds to 5 ; as is seen in Table VII. 



In the last pair (Ag, Tl) the differences are doubled. 







Table VII. 







Atomic 



weight. 



Density- 

 number. 



' Atomic 

 weight. 



Density- 

 number. 



1 



Atomic 

 weight. 



Density- 

 number. 



Cu 63o 



445 

 g 108 



11 



5 

 16 



Zn 65-5 



46-5 

 Cdll2 



11 

 5 



16 



Ag 108 



96 

 Tl 204 



16 



10 

 26 



