MANUFACTURE OF SALT FROM SEA-WATER 51 



This pond acts as a reservoir and sedimentation 

 compartment, where clay and other suspended mat- 

 ter settle. Here the preliminary evaporation takes 

 place. 



From this pond, the concentrated, clarified sea- 

 water is run out into a series of shallow reservoirs, 

 where the sun and wind effect further evaporation. 

 During this concentration, iron sulphide, calcium 

 carbonate, and calcium sulphate are precipitated 

 and settle to the bottom. The brine in these ponds 

 is usually pink in color because of the presence of 

 innumerable red bacteria and the so-called brine- 

 worms. 



As the concentration of the brine proceeds, it is 

 run from one reservoir to another until it reaches 

 saturation, when pure salt, sodium chloride, begins 

 to crystallize. At this stage of the process, the satu- 

 rated brine is allowed to run into crystallization 

 ponds, where the salt crystallizes as evaporation 

 proceeds. Here the brine remains until the impuri- 

 ties in the solution become so concentrated that they 

 begin to crystallize with the salt; at this point the 

 mother liquor, or bittern (from which the crystals 

 have been formed), is drawn off and either used in 

 the manufacture of magnesium and potassium salts 

 or discarded. 



The salt obtained by this process is of 93 to 97 

 per cent purity. The impurities are principally cal- 

 cium and magnesium salts, which absorb moisture 

 from the air. Accordingly this solar salt is hygro- 

 scopic and is of little use except for the curing of 

 fish and the salting of hides. 



