BKOMINE FROM SEA WATER STEWART 



155 



oxidized bromine products from which bromine could not have been 

 liberated easily again by chlorine. 



However, it was found that even in carefully neutralized sea 

 water, a satisfactory yield of bromine was not obtained. An ex- 

 planation of this appeared to be that in the exceptionally dilute 

 solution the liberated bromine hydrolyzed to form bromic and 

 hydrobromic acids according to the equation : 



3Br2 + 3H2O -> HBrOa + 5HBr 



This being the case, such reaction would have continued until a 

 sufficient concentration of hydrogen ions was obtained to suppress 

 the hydrolysis. 



In the production of bromine from Michigan brines, some hy- 

 drolysis and reabsorption of the halogen, with the attendant forma- 

 tion of acid, had been encountered. Because of the comparatively 

 smaller volume handled in the case of the natural brine, it was 



feasible to permit such acidification by hydrolysis to take place 

 and still to make a satisfactory recovery of the bromine. However, 

 in the case of the enormous quantity of liquid involved with sea 

 water as the source of bromine, such acidification by hydrolysis 

 would be uneconomical. Careful laboratory research, involving po- 

 tentiometric titration of natural sea water, showed that reabsorp- 

 tion of free bromine by hydrolysis ceased if the hydrogen-ion con- 

 centration were increased to a pH of 3 or 4 by the addition of acid 

 from an outside source. This indicated, therefore, that in order to 

 liberate bromine in sea water completely and efficiently, it would be 

 necessary first to add sufficient acid to give a pH of approximately 

 3.5. This would require the use of approximately 0.27 pound of 96 

 percent sulphuric acid per ton of sea water. In operation of the 

 tribromoaniline process, already mentioned, it had also been found 

 that it was desirable to add acid to the raw sea water before adding 

 the chlorine, but a greater proportion was employed. 



