of the Elements. 491 



with alkalies, forming vanadites. All four metals form teroxides, 

 which are undecomposable by heat alone. The teroxide of mo- 

 lybdenum is white or yellowish white, but when fused is of a 

 brownish yellow; that of vanadium is yellowish red; that of 

 tungsten, canary yellow, but occasionally white ; th^t of tan- 

 talum white when cold, yellow when hot. The teroxide of 

 molybdenum is volatile, fusible, and slightly soluble in water, 

 forming an acid solution ; that of vanadium is fixed, fusible, 

 and soluble in water, though to a still less extent. The ter- 

 oxides of tungsten and tantalum are fixed, infusible, and after 

 Ignition, insoluble. The hydrated teroxides of tungsten and 

 tantalum, when moistened with water, exert a faintly acid reaction 

 upon litmus paper, and are therefore somewhat soluble. Cor- 

 responding molybdates, vanadiates and tungstates are isomor- 

 phous ; tantalic is isomorphous with tungstic acid, tantalite with 

 wolfram. Molybdic and tungstic acids have the same atomic vo- 

 lume, namely 261 . The molybdates are colourless or yellow ; the 

 vanadiates more frequently yellow than colourless ; the tung- 

 states and tantalates colourless. The four acids are evidently 

 bibasic, and the salts with two atoms of fixed base are permanent 

 at a red heat. Intermediate between the binoxide and teroxide 

 of each of the first three metals, are several other oxides, remark- 

 able for the variety of their colours, — indeed the teroxides and 

 their salts are the least coloured compounds to which the mem- 

 bers of this group give origin. Each metal forms a tersulphide, 

 having the properties of a sulphur acid, and forming definite 

 sulphur salts, as does also the bisulphide of vanadium. The 

 terchlorides of the four metals are volatile, and present great 

 analogy both of composition and properties. Tantalum probably 

 presents a relation of parity with niobium and pelopium. This 

 group is associated with the ferric group by the isomorphism of 

 the chromates with the molybdates. Chromium, however, differs 

 from the members of this group in its most characteristic pro- 

 perty of forming sesquisalts, in its not forming bisalts, and in 

 the characters of its acid, more particularly as regards its solu- 

 bility in water and its destructibility by heat. 



The acids of this group present some analogy of properties 

 with the silicic, titanic, and stannic acids. Tantalates are gene- 

 rally found native in association with titanates. 



Moreover, tellurium and antimony, as representatives of the 

 second and third groups, are associated with this group by some 

 general resemblances. Certain sulphates are isomorphous with 

 corresponding molybdates.- 



2L2 



