of the Elements. 485 



We have no determination of the specific gravities or atomic 

 volumes of the metals, but the specific gravities of the oxides 

 occur in gradation,— 0^0 = 2-96, Y^O =4-82, and Th20 = 9-4. 

 The three elements are found allied in nature as constituents of 

 different varieties of gadolinite. The metals themselves have an 

 iron-grey colour, exhibit after burnishing a metallic lustre, are 

 infusible or difficultly fusible, are not oxidized by air or water at 

 ordinary temperatures, are combustible at a red heat, aud burn 

 in oxygen with great brilliancy. The three oxides are infusible, 

 and are scarcely soluble in acids after ignition. The three hy- 

 drates are insoluble in water, absorb carbonic acid from the air, 

 and decompose solutions of ammoniacal salts when boiled there- 

 with. The salts have for the most part an acid reaction, and are 

 decomposed at a red heat provided the acid be volatile. The 

 three chlorides are volatile and deliquescent. The hydrated 

 chlorides are decomposed by ignition, with evolution of chlor- 

 hydric acid. Each metal forms with potassium a double sul- 

 phate, in which the potassium and other metal occur in the pro- 

 portion of equivalent to equivalent. 



Grovp IX. Aluminium — Zirconium, Cerium, Uranium. 



No reliance whatever can be placed upon the existence of this 

 group. The atomic weights occur in sequence : — 



Zr = 33-6 139-6 ,. „ 



Ce = 46 -3-=46-omean. 



U = 60 



Sum 139'6 Mean difference = 14, or half 



that of Group VIII. 



These three elements are found associated in nature in similar 

 minerals. Eudyalite contains both cerium aud zirconium. In 

 eukolite from Norway we have a partial isomorphous replace- 

 ment of cerium for zirconium (Damour). Uranium and 

 cerium occur respectively together with yttrium in yttro-tan- 

 talite and yttro-cerite. All three metals are found associated 

 with tantaUc acid. Zirconium and cerium are each found in 

 combination with titanic acid. All three metals form sesqui- 

 oxides. Cerium and uranium also give rise to proto- and in- 

 termediate oxides. The sulphates of zirconium and cerium are 

 both precipitated by sulphate of potash. Zirconium probably 

 presents a relation of parity with norium and ilmenium, cerium 

 with lanthanium and didymium. Aluminium seems to be asso- 

 ciated more with this group than with any other. The charac- 

 ters of metallic zirconium correspond exactly with those accorded 

 to aluminium prior to the researches of Deville. Uranium, like 

 aluminium, is a white malleable metal, not readily oxidizable 



