SALT FROM SEA WATER 17 



by withdrawing the mother liquor from the crystallizing ponds when these 

 salts begin to separate. (5) The Norwegian process, in which sea water is con- 

 centrated by freezing and salt is recovered by the evaporation of the concentrated 

 brine. 



In addition to the sea salt made by the five types of processes mentioned above, 

 a small amoimt is made in isolated places by the simple evaporation of sea water 

 in pans by means of artificial heat. Some salt is obtained annually from the evapo- 

 ration of sea water in natural lagoons which occur on some of the islands of the 

 West Indies and in Mexico, China, and elsewhere. 



In the oriental leaching process and oriental solar process no attempt is made 

 to separate the sodium chloride from the other salts; consequently, these salts 

 contain relatively large amounts of calcium, magnesium, and iron and are usually 

 dark in color. The salt prepared by the improved oriental process usually contains 

 less clay, calcium carbonate and sulfate, and iron oxide than that produced by 

 the ancient oriental process since these substances are removed in the concentra- 

 tion ponds where the brine undergoes a preliminary concentration previous to 

 its transfer to the crystallizing ponds. 



Since the European salt trade demands a white salt, more pains are taken to 

 separate the sand and clay from the salt. Moreover, the European salt-makers 

 attempt to separate the calcium and magnesium salts by preliminary evaporation 

 to a density of about 25° Be. (1.196 sp. gr.) before the brine is run into crystalliz- 

 ing ponds, and by removing the bittern or mother liquor when it begins to sepa- 

 rate salts other than sodium chloride. The Etiropean solar salt, however, is "wet" 

 because the separation of the calcium and magnesium chlorides is imperfect and 

 these salts impart hygroscopic properties. 



The process of manufacturing salt employed in California is a modification 

 of the European solar process. The California salt producers, having learned that 

 dry salt brings a higher price in America than wet salt, are careful to see that 

 their salt contains only traces of calcium and magnesium chlorides and sulfates. 

 This is accomplished by drawing off the bittern at a relatively low density. 

 Although they obtain a slightly smaller yield of salt, they produce nearly pure 

 sodium chloride. Table 6 gives analyses of solar sea salts manufactured in various 

 parts of the world. 



The various processes for the manufacture of salt are described in the following. 

 Since the California processes produce the purest salt and represent the best 

 commercial practice, these methods will be considered in greater detail than the 

 others. 



The Oriental Leaching Method. According to this ancient process, which is still 

 used by many Filipinos, level areas of land close to the sea are cleared of vegeta- 

 tion, the soil loosened and sprinkled four times daily with sea water from canals 

 which run through the salines. After about five days, during which a quantity 

 of salt has accumulated on the surface, the loose earth, together with the salt, is 

 scraped into leaching vats where it is leached with sea water until most of the 

 salt has been extracted and a brine containing 10 per cent or more of salt is 

 obtained. Then by means of bamboo piping the brine is drawn off through a dike 

 into a shallow cement, earthenware, or clay-lined well from which it is run into 

 crystallizing ponds floored with smooth broken pottery set in mortar to retard 

 seepage and prevent admixture of sand with the salt. When the brine has evapo- 



