THE HALOGENS 495 



mineral waters (those of Kreuznach and Staro-rossiisk) contain metallio 

 bromides and iodides, always in admixture with an excess of sodium 

 chloride. Those upper strata of the Stassfurt rock salt (Chapter X.) 

 which are a source of potassium salts also contain metallic bromides, 47 

 which collect in the mother liquors left after the crystallisation of the 

 potassium salts ; and this nOw forms the chief source (together with 

 certain American springs) of the bromine in common use. Bromine 

 may be easily liberated from a mixture of bromides and chlorides, 

 owing to the fact that chlorine displaces bromine from its compounds 

 with sodium, magnesium, calcium, &c. A colourless solution of 

 bromides and chlorides turns an orange colour after the passage of 

 chlorine, owing to the disengagement of bromine. 58 Bromine may be 

 extracted on a large scale by a similar method, but it is simpler to add 

 a small quantity of manganese peroxide and sulphuric acid to the 

 mother liquid direct. This sets free a portion of the chlorine, and this 

 chlorine liberates the bromine. 



Bromine is a dark brown liquid, giving brown fumes, and having a 

 poisonous suffocating smell, whence its name (from the Greek /?pfyto$, 

 signifying evil smelling). The vapour density of bromine shows that 

 its molecule is Br 2 . In the cold bromine freezes into brown-grey scales 

 like iodine. The melting point of pure bromine is 7-05. M The 

 density of liquid bromide at is 3-187, and at 15 about 3-0. The 

 boiling point of bromine is about 58'7 Bromine, like chlorine, is 

 soluble in water ; 1 part of bromine at 5 requires 27 parts of water, 

 and at 15 29 parts of water. The aqueous solution of bromine is of 



57 But there is no iodine in Stassfurt carnallite. 



8 The chlorine must not, however, be in large excess, as otherwise the bromine 

 would contain chlorine. Commercial bromine not unfrequently contains chlorine, as 

 bromine chloride ; this is more soluble in water than bromine, from which it may thus 

 be freed. To obtain pure bromine the commercial bromine is washed with waer, dried 

 by sulphuric acid, and distilled, the portion coming over at 58 being collected ; the 

 greater part is then converted into potassium bromide and dissolved, and the remainder 

 is added to the solution in order to separate iodine, which is removed by shaking with 

 carbon bisulphide. By heating the potassium bromide thus obtained with manganese 

 peroxide and sulphuric acid, bromine is obtained quite free from iodine, which, however, 

 is not present in certain kinds of commercial bromine (the Stassfurt, for instance). By 

 treatment with potash, the bromine is then converted into a mixture of potassium 

 bromide and bromate, and the mixture (which is in the proportion given in the equation) 

 is distilled with sulphuric acid, bromine being then evolved: 5KBr+KBr(>5 + 6H 2 SO4 

 = 6KHSO 4 + 8H 2 + 8Br 8 . After dissolving the bromine in a strong solution of calcium 

 bromide and precipitating with an excess of water, it loses all the chlorine it contained, 

 because chlorine forms calcium chloride with CaBr 2 . 



59 There has long existed a difference of opinion as to the melting point of pure 

 bromine. By some investigators (Begnault, Pierre) it was given as between 7 and - 8, 

 and by others (Balard, Liebig, Qnincke, Baumhauer) as between 20 and 25. There 

 is now no doubt, thanks more especially to the researches of Ramsay and Young (1885), 

 that pure bromine melts at about -7, This figure is not only established by direct ex- 



