M. Wohler on the Bromide and Magnetic Oxide of Chromium. 457 



the crucible, and must therefore be afterwards washed out with 

 water. If any protochloride has been formed, which is the case 

 if the stream of chlorine has not been rapid enough, it will cause 

 the solution of a certain quantity of sesquichloride, which is 

 therefore lost. 



The same chemist* describes the preparation of the bromide 

 of chromium corresponding to the above chloride. The mixture 

 of charcoal and oxide in pellets is strongly heated and then 

 transferred to a hard glass tube, which is very strongly heated, 

 while a stream of bromine is passed through. Part of the bro- 

 mide sublimes beyond the mass of oxide ; another part remains 

 mixed with it, but may be easily separated. 



Sesquibromide of chromium, Cr- Br^, forms black crystalline 

 laminje of a semimetallic lustre, which are transparent with 

 olive-green colour, and iij a certain direction exhibit a feeble 

 dichroism towards red. On being pulverized, the crystals become 

 green. Heated in the air, the bromide is converted into oxide; 

 and in hydrogen it is reduced with the formation of a white pro- 

 tobromide. It is insoluble in water, and is more easily decom- 

 posed by alkalies than the chloride. In the preparation of ses- 

 quibi'omide, some protobromide is occasionally formed; and this 

 causes the solution of all the sesquibromide when the mass is 

 treated with water. Both the chloride and the bromide are 

 reduced, and deliquesce, when placed on metallic tin. 



The analysis of the bromide proved that it was free from oxy- 

 bromide. 



Wohler has observedf the formation of a magnetic oxide of 

 chromium. In the preparation of crystallized oxide of chromium, 

 by passing the vapour of oxychloride of chromium through a 

 heated tube, it was found, on removing the particles from the 

 glass, that parts of the oxide were decidedly magnetic. When 

 the oxide was prepared by decomposing the oxychloride at a 

 white heat, it was found to be quite destitute of magnetic pro- 

 perties ; but by effecting the decomposition of the oxychloride 

 at a temperature below redness, the oxide formed was strongly 

 magnetic. 



The magnetic oxide forms uncrystallized dark crusts, pale on 

 the inside, but lustrous on the side next the glass. It is attracted 

 by the magnet, and even shows feeble magnetic polarity. Pul- 

 verized, it forms a black powder, and in thin layers it is transpa- 

 rent with a brown colour. Heated in the air it becomes green, 

 and loses its magnetism. 



The oxide thus ])repared does not appear to be pure. If its 

 formula were Cr^ 0^, CrO, analogous to magnetic oxide of iron, 



* Liebig's Annalen, September 1859. t I'jiil- July 1859. 



