886 Dr. J. W. Nicholson on a Structural 



accuracy. They are accordingly passed over in the present 

 sketch, and we proceed to column 6. In this column elements 

 like vanadium and niobium will not be considered. They 

 are classed with nitrogen, to which they have little resem- 

 blance, except perhaps in the formation o£ salts similar to 

 the nitrates, and of oxychlorides. But phosphorus, arsenic, 

 antimony, and bismuth form a series whose properties 

 change continuously from non-metallic to metallic. Nitrogen 

 is also, in some respects, a starting-point of this series. The 

 suggested formulae are : — 



Nitrogen, H 4 . He 2 H 2 = 14*02 (14*01), 



Phosphorus, {He 2 (PfH) 3 }He 3 H = 31-05 (31-04), 



Arsenic, 3{He 2 (PfH) 3 }{Nu 2 (PfH) 3 }Pf 2 NuH = 74*96 (74-96), 



Antimony, 3{He 4 (PfH) 3 }2{He 2 (PfH) 3 }Nu 3 II = 120*22 (120-2), 



Bismuth, 8{He 2 (PfH) 3 }4{Nu 2 (PfH) 3 }Nu 2 (PfH) 2 = 208-08 (208). 



The formulae for phosphorus, arsenic, and antimony have 

 much in common, but that for bismuth is more reminiscent 

 of some of the preceding metals, though at the same time 

 not unlike the others of its group. The factor 3 in the inert 

 gas groupings appears for the first time in arsenic and 

 antimony, semi-metallic elements. It appears again in the 

 next group of elements. 



Oxygen, Sulphur, Selenium, Tellurium. — Of these four 

 elements of column 7 of the table, the last three form a 

 pronounced chemical series. Oxygen has little real relation 

 to the others, and certainly none to chromium, molybdenum, 

 and tungsten, which are its actual companions in the sub- 

 group. It is probable that it ought to have a column of its 

 own. But just in so far as nitrogen is, in some respects, 

 allied to phosphorus, so is oxygen to sulphur. It is very 

 easy, for example, to replace oxygen by sulphur in many 

 classes of organic compounds. The formula might therefore 

 be expected to show some relation to the other three. The 

 following may be suggested : — 



Oxygen, {Nu 2 (PfH) 3 }NuH = 16-00 (16-00), 



Sulphur, {IIe 4 (PfH) 3 }HeH 2 = 32*06 (32*07), 



Selenium, 3{Nu 4 (PfH) 3 }2{Nu 2 (PfH) 3 }NuH = 79-20 (79*20), 



Tellurium, 4{He 2 Nu 2 (PfH) 3 }2{He 2 (PfH) 3 }HeH 2 = 127*5 (127*5), 



There is a curious similarity between the formulae for 

 selenium and arsenic, and in fact between the last two sets 

 of formula?. In each case it is accompanied by a gradual 



