16 MARINE PRODUCTS OF COMMERCE 



There are several grades of solar salt. The crude grade is commonly used for 

 salting fish and curing meat. This grade and the next, which is ground and sized, 

 are used for such industrial purposes as softening water, manufacturing chemicals, 

 freezing ice cream, curing hides, etc. Refined salt, which is about one-third of 

 the total amount, is made by dissolving and refining solar salt (Chapter 3). Then 

 it is sold for table and household use and food preparation, etc. 



Solar Salt 



Importance and I^ocation of Industry. Although the mining of rock salt and 

 the production of salt by the evaporation of brine with artificial heat now greatly 

 exceeds production by solar evaporation, the manufacture of salt from sea water 

 by this latter process is still an important industry in many warm countries where 

 the annual rainfall is light. In California a large proportion of the salt produced is 

 from the solar evaporation of sea water. This state ranked sixth among the salt- 

 producing states in 1948, producing 914,000 tons of salt by all methods. In 1948 

 a total of 746,303 tons of solar salt was produced in the United States. In Italy 

 the solar sea salt industry is the major salt industry of the country. Spain exports 

 large quantities of sea salt and Portugal has salt works at Aveiro, Figueria, Alcacer 

 do Sal, and Setubal. There are "salzgarten" at various places on the Adriatic Sea, 

 including Sabbioncello, Trieste, Pirano, and Copo d'Istra. France, Egypt, China, 

 Japan, India, Brazil, and many of the islands of the West Indies also possess im- 

 portant solar sea salt industries. 



The manufacture of salt from sea water can successfully compete with the pro- 

 duction of salt from rock salt only when the industry is located where a cheap 

 source of heat is available; about 90 per cent of the sea water must be evaporated 

 before any crystallization can take place. Solar heat is the only important method 

 of manufacturing salt from sea water; consequently, the product is called solar 

 salt. In some localities solar sea salt is called bay salt to distinguish it from solar, 

 artificial brine salt, which is also called solar salt. Inasmuch as rapid evaporation 

 of the water is necessary, the solar sea salt industry has thrived only along the 

 seacoast of countries having a dry climate or hot summers. 



Moreover, in order to establish a successful salt works a large acreage of level 

 land adjoining a bay or the ocean is required. The ground underlying the site 

 must be nearly impervious to water. Soils which are most satisfactory are clays 

 and marls. If the ground is "leaky", it must be puddled with clay before it can 

 be used. This is very important, as leaks in the bottom of salt ponds are very 

 difficult to stop and cause unnecessary dilution of the brine which reduces the 

 yield of salt. 



It is impractical, for obvious reasons, to discuss in a work of this nature all 

 the commercial methods of salt manufacture from sea water. There are five chief 

 types of processes in commercial use today: (1) The oriental leaching process. 

 (2) The oriental solar process, in which no attempt is made to separate impurities 

 from the salt. (3) The improved oriental solar process, in which sediment, cal- 

 cium carbonate, iron oxide, and calcium sulphate are separated by preliminary 

 evaporation of the sea water in concentration ponds. (4) The European solar 

 process, in which the sediment, iron sulfide, calcium carbonate, and calcium 

 sulfate are separated from the brine by preliminary evaporation of the sea water 

 and the greater proportion of the chlorides of calcium and magnesium are removed 



