490 Prof. Odling on the Natural Groupings 



The members of this group are related, — 



1 . To the chloric group by the isomorphism of the perchlorates 

 and permanganates. 



2. To the sulphuric group by the isomorphism of the sulphates 

 with the manganates and chromates. 



3. To the silicic group by the isomorphism of hsematite and 

 ilmenite. 



4. To the calcic group by the isomorphism of the two sul- 

 phates, Ca2SO''.2H20, and Fe^SO*. 2W0 of Arragonite with 

 junckerite, &c. 



5. To the zincic group by a very general isomorphism, and by 

 the solubility of the prothydrates in ammonia. 



6. To the molybdic group by the isomorphism of the molyb- 

 dates and chromates. 



7. To the plumbic group by the analogy of the disalts of 

 copper to the disalts of mercury. 



8. To the aluminic group by the isomorphism of alumina and 

 ferric oxide. 



Group XI. — Molybdenum, Vanadium, Tungsten — Tantalum. 

 The members of this group are scarcely sufficiently well known 

 to warrant the propriety of their association being affirmed in an 

 absolute manner. Still with a very imperfect knowledge we are 

 able to point out many analogies, but scarcely any discrepancy 

 of importance. The sequence of atomic weights is very well 

 marked : — 



Mo = 46-0 206-5 ^^ ^ 



V = 68-5 —^ = ^^^• 



W = 92-0 



Sum 206-5 Mean difference = 24 ? 



The atomic weight of tantalum, or 184, is exactly double that of 

 tungsten. The four metals have, according to circumstances, a 

 white or grey colour ; they are lustrous, brittle, and fuse with great 

 difficulty, if at all. The specific gravity of molybdenum is be- 

 tween 7 and 8, that of tvingsten about 17"5. The specific gravities 

 of vanadium and tantalum are undetermined. Molybdenum 

 and tungsten have the same atomic volume, namely 69. Molyb- 

 denum forms an unstable protoxide and protosalts, vanadium a 

 protoxide but no protosalts ; tungsten and tantalum, as far as is 

 known, neither protoxides nor protosalts. All the metals of 

 this group form binoxides, and with the exception of tantalum, 

 bisulphides and bichlorides, &c. All four binoxides are of a 

 black or brown colour. Molybdenum and vanadium yield hy- 

 drated binoxides which are salifiable ; that of molybdenum is 

 even slightly soluble in water. The binoxide of vanadium unites 



