Theory of the Chemical Elements. 887 



transition to the metallic state, selenium and tellurium 

 having metallic varieties. 



Fluorine , Chlorine, Bromine, Iodine. — Chlorine, bromine, 

 and iodine form a well-defined chemical series, but fluorine 

 is in some respects isolated, though quite fairly in accord 

 with the others. But it has many exceptional properties, 

 such as its extraordinary affinity for silicon. These elements 

 are accompanied in the column by manganese, which cannot 

 be regarded as related to them. The following may be 

 suggested : — 



Fluorine, Nu (PfH) 3 . H 2 (NuH) 2 = 19-02 (19'0), 

 Chlorine, 2{Nu 2 (PfH) 3 }rI 2 (PfH) 2 =35-47(35'46), 

 Bromine, 4{Nu 4 (PfH) 3 }H 2 Pf 2 (PfH) 2 = 79'93 (79*92), 

 Iodine, 4{He 4 (PfH) 3 }He 4 (PfH) 2 = 12692 (126-92). 



In the case of fluorine, the atomic weight is not known 

 to the second decimal, so that the alternative 



Fluorine, {Nu 2 (PfH) 3 }Pf Nu 2 = 18'98, 



is also worthy of consideration. These are the only two 

 alternatives. 



Chromium, Manganese, Iron, Nickel, Cobalt. — These metals 

 occupy paradoxical position* in the table. Chromium appears 

 as related to oxygen, and manganese to fluorine, while iron, 

 nickel, and cobalt appear as a triad after the eighth column. 

 It is significant that all appear consecutively in a row. 

 Chromium is further associated, with some chemical corre- 

 spondence, with molybdenum and tungsten. No analogue 

 of manganese has been discovered, and it is followed onlv 

 by vacant spaces. 



There is a considerable similarity amongst these metals, 

 for example in their capacity for forming salts such as the 

 bichromates, permanganates, and ferrates. Moreover, iron, 

 nickel, and cobalt are the magnetic metals. These con- 

 siderations point to some factor in their constitution which 

 has not occurred in the groups of elements already discussed, 

 and it is noteworthy that an application of the usual groupings 

 is not very successful. The best representations found are 

 as follows : — 



Chromium, 4He 2 {He 2 (PfH) 3 }H 2 = 52-00 (52-00), 

 Manganese, 6He 2 . Pf 3 = 54'938 (5493), 

 Iron, 6He 2 .He 2 = 55-84 (55-85), 

 Nickel, 4He,{He 2 (PfH) 3 }HePf 2 = 58-69 (58-68), 

 Cobalt, 4He 2 {He 2 (PfH) a }HHe 2 = 58-97 (58'97;. 

 3 N 2 



