VANADIUM. 615 



on cooling, large well formed crystals, AgO, CrO 3 + 2NH 3 , 



isomorphous with the analogous ammoniacal sulphate and 

 seleniate of silver. 



Chromate of magnesia forms, according to my own observa- 

 tions, yellow crystals which are very soluble, and contain 5 HO. 

 It does not form a double salt with chromate of potash, as 

 sulphate of magnesia does with sulphate of potash. It is re- 

 marked that the insoluble metallic chromates generally carry 

 down portions of the neutral precipitating salts, or of subsalts, 

 and their analysis is often unsatisfactory from that cause. 

 When the magnesian chromates are compared with the sul- 

 phates of the same family, the former are found to have their 

 water readily replaced by metallic oxides, but not by salts ; so 

 that subchromates with excess of oxide are numerous, while 

 few or no double chromates exist. 



Chlorochromic acid, Cr O 2 Cl, or 2Cr O 3 + Cr C1 3 . This is a 

 volatile liquid, obtained by distilling, in a glass retort, by a 

 gentle heat, 3 parts of bichromate of potash and 3j parts of 

 common salt, previously reduced to powder and mixed together, 

 with 5 parts by water measure, of oil of vitriol, discontinuing 

 the distillation when the vapours, from being a deep orange red, 

 become pale that change arising from watery vapour. The 

 compound is a heavy red liquid, decomposed by water. The 

 density of its vapour is 5.9 



Terfluoride of chromium, Cr F 3 , is obtained in the manner 

 already mentioned under the preparation of chromic acid. It is 

 a blood-red liquid. No corresponding terchloride of chromium 

 has been obtained in an isolated state. 



SECTION IV. 



VANADIUM. 

 Eg. 856.9 or 68.66; V. 



Vanadium, so named from Vanadis* a Scandinavian deity, 

 was discovered by Sefstroem in 1830, in the iron prepared from 

 the iron ore of Taberg, in Sweden, and procured afterwards in 

 larger quantity from the slag of that ore . It was found after- 

 wards by Mr. Johnston, in a new mineral discovered by him, 

 the vanadiate of lead from Wanlockhead. It is one of the 

 rarest of the elements. The metal itself has considerable re- 



