138 MR. H. WILDE ON THE 



are ouly three in number, and the atomic weight of 

 chromium = 52'2 establishes its position as the third 

 member of the series, and there is no other place for an 

 element with the chemical and physical properties of 

 chromium vacant in the table. For like reasons the 

 positions in the series of molybdenum and tungsten (the 

 analogues of chromium) are also determined. By assign- 

 ing to chromium the constitution 9 H6_, it forms a triad 

 with the missing elements ^ = 36, and <r=i8, which are, 

 within a unit, the atomic weights of fluorine and chlorine. 



In the arrangement of the elements which I have 

 classified as Hjn, little assistance is derived from known 

 analogies, when nitrogen and silicium are admitted in the 

 same series with the iron and platinum groups of metals ; 

 yet, it might be expected that elements so abundant, and 

 so widely diffused in nature as nitrogen, silicium, and 

 iron, would occupy important positions in any rational 

 classification of elementary species. We have seen that 

 the first three places in the preceding series Hw, H2w, 

 H^n, H5W, are all occupied by elements with atomic 

 weights which exclude nitrogen, silicium, and iron, while 

 the latter element is excluded from the series H4W, and 

 H6w, by chromium and titanium. The atomic weights of 

 N, Si, and Fe, besides being whole numbers, are exact 

 multiples of 7. N and Si are, consequently, excluded 

 from the vacant homologous positions in the series H4W, 

 H6w. 



Since the investigation of the properties of silicium by 

 Berzelius, who regarded silicic acid as a trioxide, much 

 discussion has arisen as to whether the atomic weight of 

 silicium be 21 or 28 ; or the formula for its oxide SiOj 

 or SiOj. Chemists are now generally agreed upon the 

 latter formula for silicic acid, and have accordingly 

 classified silicium with titanium, as the oxide SiO^, agrees 



