202 



This action does take place, but the hydrogen bromide formed, 

 being less stable than HC1, is oxidized rapidly by the concen- 

 trated sulphuric acid, so that, although some of the gas escapes 

 oxidation, it is mixed with much free bromine and sulphur dioxide: 

 H 2 SO 4 + 2HBr -> S0 2 + 2H 2 + Br 2 . This action, indeed, en- 

 ables us to recognize a bromide, by the color of the bromine vapor 

 and the fuming of the hydrogen bromide produced. 



Properties of Hydrogen Bromide. The gas, like hydrogen 

 chloride, is colorless, and has an irritating effect when breathed. 

 It is extremely soluble in water, and fumes in moist air, giving a 

 fog of HBr dissolved in water. 



Chemically, hydrogen bromide is stable, though not so much so 

 as hydrogen chloride. Its aqueous solution is an active add. As 

 such, it gives double decomposition with bases and salts. Thus, 

 with a salt of silver, we get a cream-colored precipitate of in- 

 soluble silver bromide: 



AgNO 3 + HBr - AgBr j + HNO 3 . 



Chlorine-water, added to a solution of any bromide, displaces 

 the bromine, which may be recognized by its brown color (test for 

 a bromide) : 



C1 2 + 2Br- - 2C1- + Br 2 . 



A few drops of carbon disulphide, shaken with the mixture, will 

 settle to the bottom, carrying the brown bromine with it in a more 

 concentrated, easily recognizable form. 



Uses of Compounds of Bromine. Bromine is manu- 

 factured in large amounts in Germany and in the United States. 

 It is employed to make potassium bromide, and other bromides. 

 These are utilized in medicine, and to precipitate silver bromide 

 in the manufacture of photographic films and plates. 



