488 PRINCIPLES OF CHEMISTRY 



as the salts of hypochlorous acid. The higher oxygen acids of iodine, 

 bromine, and chlorine are closely analogous to each other. Iodine was 

 discovered in 1811 by Courtois in kelp, and was soon investigated by 

 Clement, Gay-Lussac, and Davy. Bromine was discovered in 1826 by 

 Balard in the mother liquor of sea water. 



Bromine and iodine, like chlorine, occur in sea water in combina- 

 tion with metals. However, the amount of bromides, and especially 

 of iodides, in sea water is so small that their presence can only be 

 discovered by means of sensitive reactions. 56 In the extraction of salt 

 from sea water the bromides remain in the mother liquor, and can be 

 obtained therefrom ; this method is, however, rarely employed on a 

 large scale, as other and richer sources are known for the extraction of 

 this substance. Iodine and bromine also occur combined with silver, in 

 admixture with silver chloride, as a rare ore which is mainly found in 

 America. Certain mineral waters (those of Kreuznach and Schonebeck) 

 contain metallic 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, 57 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, <fec. A 

 colourless solution of bromides and chlorides turns an orange colour 

 after the passage of chlorine, owing to the disengagement of bromine. 5 * 

 Bromine may be extracted on a large scale by a similar method, but it 



56 One litre of sea water contains about 20 grams of chlorine, and about 0'07 grams- 

 of bromine. The Dead Sea contains about ten times as much. 



57 But there is no iodine in Stassfurt carnallite. 



58 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, which may thus be freed 

 from it. To obtain pure bromine the commercial bromine is washed with water, 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 re- 

 mainder 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 th<> proportion given in 

 the equation) is distilled with sulphuric acid, bromine being then evolved: 5KBr + KBrO5 



+ 6H<jSO4 = 6KHSO4 + 8H 2 O + 3Br 2 . 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 foi'ms calcium chloride with CaBr 2 . 



