156 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 3 4 



Figure 1 shows the variation in pH of raw sea water as affected 

 by the addition of acid. Figure 2 shows the effect of variation of 

 pH on the percentage of total bromine that can be liberated from 

 the sea water by chlorine oxidation. Figure 3 indicates the effect 

 of variation of pH of sea water on the chemical equivalents of chlo- 

 rine required to liberate one equivalent of bromine. Figure 3 shows 

 that, at a pH of 3.5 or less, the theoretical mole of chlorine was 

 required per mole of bromine which was liberated. 



With the knowledge at hand of the definite proportion of acid 

 which would have to be added to sea water in order to promote a 

 highly efficient process, the next research problem which arose was 

 that of developing a means of immediately and continuously indi- 

 cating the progress of oxidation in the chlorination step, so that 

 the degree of liberation of bromine could be ascertained at any time. 



10 





3 4 



,// VALUE 



FIG. 3 



Err£CT or pH on chlorine required to liberate 



BROMINE IN SEA WATER 



With the use of the ocean as a source of bromine, such enormous 

 quantities of water were involved that, without some such control 

 method, together with a method of continuously recording acidity, 

 large losses of chlorine and acid would be sure to occur before the 

 operator would realize what was happening. A method was finally 

 developed which answered all requirements. 



The new method of oxidation control depended on the fact that for 

 every type of bromide-containing solution there is a characteristic 

 range of oxidation potential values. This range depends on the ini- 

 tial concentration of bromine ions and also upon the collective effect 

 of other ions present. It was found that, in acidified sea water, the 

 first traces of free bromine in a solution that was being tested caused 

 an immediate increase in oxidation potential. This rise was meas- 



