608 CHROMIUM. 



ammonia, and forms a white saline mass, Ti C1 2 + 2NH 3 . 

 Metallic titanium is most easily obtained by heating this com- 

 pound to redness. Bichloride of titanium also absorbs phosphu- 

 retted hydrogen, and forms a dry brown powder. From this 

 compound when heated, a lemon yellow sublimate rises, which 

 Rose found to contain 3 atoms of bichloride of titanium, com- 

 bined with 1 atom of a compound of phosphuretted hydrogen 

 and hydrochloric acid, analogous to sal ammoniac, but which 

 could not be isolated. Bichloride of titanium forms double 

 salts with the alkaline chlorides, which are colourless and capa- 

 ble of crystallizing. 



A volatile bifluoride of titanium, Ti F 2 , was obtained, by Un- 

 verdorben, by distilling titanic acid in a platinum apparatus 

 with fluor spar in powder, and fuming sulphuric acid. 



A definite sulphate of titanic acid, TiO 2 + SO 3 , is obtained 

 by dissolving titanic acid in sulphuric acid, and evaporating to 

 dryness by a heat under redness. 



SECTION III. 



CHROMIUM. 

 Eg. 351.8 or 28.19; Cr. 



This metal, so remarkable for the variety and beauty of its 

 coloured preparations, was discovered by Vauquelin in 1797? 

 in the red mineral now known as chromate of lead. It has since 

 been found in other minerals, more particularly chrome iron 

 (FeO-f Cr 2 O 3 ), a mineral which many countries possess in con- 

 siderable quantity. It is from this ore that the compounds of 

 chromium, used in the arts, are actually derived. The metal 

 may be procured by the reduction of its oxide, in the usual way, 

 but with the same difficulty as manganese. Chromium is a 

 greyish white metal, of density 5.9, fusible with the greatest 

 difficulty, and not magnetic. It does not undergo oxidation in 

 the air; it dissolves in hydrofluoric acid with evolution of hy- 

 drogen. Chromium is also obtained as a brown powder, when 

 sesqui- chloride of chromium is heated in ammoniacal gas, 

 (Liebig). Chromium forms two compounds with oxygen, of 

 which the lower, or oxide of chromium, Cr 2 O 3 , is isomorphous 



