22 



M. J. A. Groshans on the 

 Triads. 



The name of Triads has been given to groups of elements 

 such as chlorine, bromine, and iodine, or phosphorus, arsenic, 

 and antimony ; and I shall retain the name, notwithstanding 

 the fact that each group contains at least four elements. Of 

 these four elements three are characteristic, while the fourth 

 may be regarded as & precursor, which, although participating 

 in the nature of the three principal elements, yet is distinct, 

 and possesses properties more or less different. 



The following table contains twenty elements arranged in 

 five triads. I have chosen those which appear to be complete, 

 and have added to the table the atomic weights and the 

 density-numbers with their differences. 



The density-numbers of the three principal elements in each 

 triad have a constant difference, which is in two of the groups 

 five units, in the other three six units. 















Table III. 





Triad* 

















No. 1. 



No. 2. 



No. 3. 



No. 4. 



No. 5. 



El. 



AW. 



B. 



A. 



EL 

 



AW. 



16 



B. 

 1 



A. 



El. AW. 



B. 



A. 



El. 



AW. 



B. 



A. 



El. 



AW. 



B. 

 5 



A. 



N 



14 



3 





F 



19 



4 





Na 



23 



4 





Me 



24 



















1 



















1 









2 



P 



31 



3 



5 



s 



32 



2 



6 



CI 



35-5 



4 



5 



K 



39 



5 



6 



Ca 



40 



7 



6 



As 



75 



8 



5 



Se 



79 



8 



6 



Br 



80 



9 



5 



Eb 



85 



11 



6 



Sr 



87*5 



13 



6 



Sb 



120 



13 





Te 



125 



14 





I 



127 



14 





Cs 



133 



17 





Ba 



137 



19 





El = element. AW = atomic weight. B =? density-number. 

 A = difference of density- numbers. 



The differences in the atomic weights of the three principal 

 elements all lie between 44 and 49*5. The equality of this 

 difference in the same triad is only approximate; and the 

 opinion, formerly held, of their exact equality has been ren- 

 dered untenable by the experiments of Stas and Marignac, as 

 ghown in Table IV. 



Table IV. 



I. 



II. 



III. 



IV. 



V. 



P 31 



44 



As 75 



45 

 Sb 120 



S 32 



47 

 Se 79 



46 

 Te 125 



CI 355 



44*5 

 Br 80 



47 

 I 127 



K 39 



46-2 

 Eb 852 



47 5 

 Cs 132-7 



Ca 40 



475 

 Sr 87-5 



49-5 

 Ba 137 



