7o 



Mr. Henry Wilde on the 



I would also direct attention (i) to the common numeri- 

 cal difference of 4 between the halogens and the alkaline 

 metals in homologous positions, and (2) the common 

 difference of 8 between the oxygen series and the alkaline 

 earth metals in similar positions, (3) the natural arrangement 

 and extensions of Dumas' triads, in which the sum of the 

 atomic weights of the extremes is equal to double the 

 weights of the means. 



I 



+ Un — 



+ H2n — 



2 



Li = 7 



.. .. 7 * 







Gl = 8 

 .. .. g . 2 







3 



Na = 23 

 .. .. 2J 



F 



= 19 

 "i 9 



Mg = 24 

 •• "24 



O 



= 16 

 ■■id 



4 



K =39 

 .. .. 39 



CI 



= 35 

 "3SS 



Ca = 40 

 •• ■■ 40 



S 



= 32 

 '■32 



5 



Cu =62 

 " "63-3 







Zn =64 

 .. .. 6s 







6 



Rb=8 5 



Br 



= 81 

 -■So 



Sr =88 



Se 



= 80 

 ••79 



7 



Ag = 108 

 • • • • 108 







Cd =112 

 • • • • 112 







8 



Cs =131 

 .. .. j 32 



I 



= 127 



Ba = 136 

 .. .. I3? 



Te 



= 128 

 ■■128 



9 



x =154 







x = 160 







10 



x — 177 







x = 184 







11 



Hg = 200 

 *• •• 200 







Pb =208 

 • • • • 207 







* Accepted atomic weights. 



