486 Prof. Odling on the Natural Ch'oupings 



even in moist air. The hydrates, and the ignited oxides of alu- 

 minium and zirconium, coiTespond closely in their properties. 



The isomorphism of alumina with the sesquioxides of the ferric 

 family is a point of considerable importance. At the same time, 

 in the characters of its regulus, and in its generation of but a 

 single series of uncoloured salts, aluminium presents a striking 

 dissimilarity to the members of the ferric group. It is observable 

 that the atomic weight of aluminium is sensibly one-half, and 

 the atomic weight of uranium sensibly double that of iron. 

 Moreover, the protosalts of uranium are of a green colour, like 

 those of iron. The atomic weight of aluminium, or 13'7, is iden- 

 tical with the mean difference of the atomic weights of the other 

 members of this group. 



Group X. Chromium, Manganese, Iron, Cobalt, Nickel, Copper. 

 That manganese and iron are associated by the strongest ana- 

 logies is generally admitted, and the parallelism of nickel and 

 cobalt is indisputable. Chromium serves to connect the ferric 

 with the molybdic family, but appears to be more ferric than 

 molybdic. I wish to show, in addition, that iron, nickel, and 

 copper form an extremely natural series. How the six metals 

 should be arranged with regard to one another, whether as a con- 

 vei'ging series, — 



Chromium, Iron, Manganese, 



Nickel, Cobalt, 



Copper ; 



or as two parallel series, — 



„ Chromium 



Iron Manganese 



Nickel Cobalt 

 Copper „ 



&c., I do not pretend to determine j I wish simply to show that 

 copper is undeniably a member of the ferric family, — that the 

 gradation, iron, nickel, and copper is as characteristic as that of 

 any admitted triad. 



The atomic weights occur in sequence, that of nickel being 

 the mean of the three : — 



89-25 -_ ^^ 

 — - — =29v5 mean, 

 o 



Mean difference =3 ? 

 The three metals have sensibly the same atomic heat, or 3"1, 

 3*2 3"0 respectively. They have the same primitive and saline 

 atomic volume, namely 44, which number likewise expresses the 



