200 



Connecticut, contain some bromides, along with large quantities 

 of common salt. When the latter has been largely separated by 

 evaporation and crystallization, the bromides of sodium and 

 magnesium, which are more soluble, collect in the mother liquor. 



The bromine can be liberated at the positive electrode by elec- 

 trolysis. But usually a chemical process is employed. 



In one process, chlorine gas is dissolved in the liquor. This 

 displaces the bromine, and the latter can be distilled out by heat- 

 ing: 



2Br~ + C1 2 -> 2C1- + Br 2 . 



In another, process, oxidation of a bromide by pulverized 

 manganese dioxide and sulphuric acid is employed, and this 

 method can be used in the laboratory (Fig. 81, p. 308). 



The manganese dioxide is reduced to manganous sulphate 

 (compare p. 142), its oxygen combining with hydrogen from 

 H 2 SO 4 to form water. The sodium bromide used is converted 

 to sodium hydrogen sulphate (compare p. 126) and bromine is 

 liberated. 



Skeleton: NaBr -f Mn0 2 + H 2 S0 4 - Br 2 + NaHSO 4 + MnS0 4 + 



H 2 0. 



Balanced: 2NaBr + MnO 2 + 3H 2 SO 4 - Br 2 + 2NaHS0 4 +MnS0 4 



+ 2H 2 0. 



Physical Properties. Bromine is a liquid of a deep red- 

 brown color and the vapor, of the same color, has a suffocating 

 odor. It boils at 59. It is moderately soluble in water, giving 

 a 3.2 per cent solution (bromine- water), and is 



The density of the vapor gives it the formula 

 Br 2 . Great care must be used in handling bromine, as, when 

 spilt upon the skin, it kills the tissues and the sore is very liable 

 to become infected. 



Treatment of Burns. Burns made by bromine or strong 

 acids should be washed instantly with water and then with bi- 



